| By Author | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Title | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Language |
|
Download this book: [ ASCII | HTML | PDF ] Look for this book on Amazon Tweet |
Title: Island Life - Or the Phenomena and Causes of Insular Faunas and Floras
Author: Wallace, Alfred Russel, 1823-1913
Language: English
As this book started as an ASCII text book there are no pictures available.
*** Start of this LibraryBlog Digital Book "Island Life - Or the Phenomena and Causes of Insular Faunas and Floras" ***
Transcriber's note: A few typographical errors have been corrected: they
are listed at the end of the text.
* * * * *
FRONTISPIECE
[Illustration]
ISLAND LIFE
OR
THE PHENOMENA AND CAUSES OF
INSULAR FAUNAS AND FLORAS
INCLUDING A REVISION AND ATTEMPTED SOLUTION OF
THE PROBLEM OF
GEOLOGICAL CLIMATES
BY
ALFRED RUSSEL WALLACE
AUTHOR OF "THE MALAY ARCHIPELAGO," "THE GEOGRAPHICAL DISTRIBUTION OF
ANIMALS,"
"DARWINISM," ETC.
_SECOND AND REVISED EDITION_
London
MACMILLAN AND CO.
AND NEW YORK
1895
_The Right of Translation and Reproduction is Reserved_
* * * * *
RICHARD CLAY AND SONS, LIMITED,
LONDON AND BUNGAY.
_First Edition printed 1880 (Med. 8vo).
Second Edition 1892 (Extra cr. 8vo). Reprinted 1895._
* * * * *
TO
SIR JOSEPH DALTON HOOKER,
K.C.S.I., C.B., F.R.S., ETC., ETC.
WHO, MORE THAN ANY OTHER WRITER,
HAS ADVANCED OUR KNOWLEDGE OF THE GEOGRAPHICAL
DISTRIBUTION OF PLANTS, AND ESPECIALLY
OF INSULAR FLORAS,
I Dedicate this Volume;
ON A KINDRED SUBJECT,
AS A TOKEN OF ADMIRATION AND REGARD.
* * * * *
{vi}
CORRECTIONS IN PRESENT ISSUE.
The first issue of this Edition being exhausted, the opportunity is taken
of making a few corrections, the most important of which are here stated:--
_Page_ 163. Statement modified as to supposed glaciation of South Africa.
_Pages_ 174 and 338. Many geologists now hold that there was no great
submergence during the glacial epoch. The passages referring to it have
therefore been re-written.
_Page_ 182. Colonel Fielden's explanation of the occurrence of large trees
on shores and in recent drift in high latitudes, is now added.
" 272. A species of Carex peculiar to Bermuda is now given.
" 356. _Geomalacus maculosus_, as a peculiar British species, is now
omitted.
Verbal alterations have also been made at pages 41, 105, 356, and 360.
* * * * *
{vii}
PREFACE TO THE SECOND EDITION
This edition has been carefully revised throughout, and owing to the great
increase to our knowledge of the Natural History of some of the islands
during the last twelve years considerable additions or alterations have
been required. The more important of these changes are the following:--
Chapter VII. The account of the migrations of animals and plants during and
since the Glacial Epoch, has been modified to accord with newer
information.
Chapters VIII and IX. The discussion of the causes of Glacial Epochs and
Mild Arctic Climates has been somewhat modified in view of the late Dr.
Croll's remarks, and the argument rendered clearer.
Chapter XIII. Several additions to the Fauna of the Galapagos have been
noted.
Chapter XV. Considerable additions have been made to this chapter embodying
the recent discoveries of birds and insects new to the Sandwich Islands,
while a much fuller account has been given of its highly peculiar and very
interesting flora.
Chapter XVI. Important additions and corrections have been made in the
lists of peculiar British animals and plants embodying the most recent
information.
Chapter XVII. Very large additions have been made to the mammalia and birds
of Borneo, and full lists of the peculiar species are given. {viii}
Chapter XVIII. A more accurate account is given of the birds of Japan.
Chapter XIX. The recent additions to the mammals and birds of Madagascar
are embodied in this chapter, and a fuller sketch is given of the rich and
peculiar flora of the island.
Chapter XXI. and XXII. Some important additions have been made to these
chapters owing to more accurate information as to the depth of the sea
around New Zealand, and to the discovery of abundant remains of fossil
plants of the tertiary and cretaceous periods both in New Zealand and
Australia.
In the body of the work I have in each case acknowledged the valuable
information given me by naturalists of eminence in their various
departments, and I return my best thanks to all who have so kindly assisted
me. I am however indebted in a special manner to one gentleman--Mr. Theo.
D. A. Cockerell, now Curator of the Museum of the Jamaica Institute--who
supplied me with a large amount of information by searching the most recent
works in the scientific libraries, by personal inquiries among naturalists,
and also by giving me the benefit of his own copious notes and
observations. Without his assistance it would have been difficult for me to
have made the present edition so full and complete as I hope it now is. In
a work of such wide range, and dealing with so large a body of facts some
errors will doubtless be detected, though, I trust few of importance.
PARKSTONE, DORSET, _December, 1891_.
* * * * *
{ix}
PREFACE TO THE FIRST EDITION
The present volume is the result of four years' additional thought and
research on the lines laid down in my _Geographical Distribution of
Animals_, and may be considered as a popular supplement to and completion
of that work.
It is, however, at the same time a complete work in itself: and, from the
mode of treatment adopted, it will, I hope, be well calculated to bring
before the intelligent reader the wide scope and varied interest of this
branch of natural history. Although some of the earlier chapters deal with
the same questions as my former volumes, they are here treated from a
different point of view; and as the discussion of them is more elementary
and at the same time tolerably full, it is hoped that they will prove both
instructive and interesting. The plan of my larger work required that
_genera_ only should be taken account of; in the present volume I often
discuss the distribution of _species_, and this will help to render the
work more intelligible to the unscientific reader.
The full statement of the scope and object of the present essay given in
the "Introductory" chapter, together with the "Summary" of the whole work
and the general view of the more important arguments given in the
"Conclusion," render it unnecessary for me to offer any further remarks on
these points. I may, however, state {x} generally that, so far as I am able
to judge, a real advance has here been made in the mode of treating
problems in Geographical Distribution, owing to the firm establishment of a
number of preliminary doctrines or "principles," which in many cases lead
to a far simpler and yet more complete solution of such problems than have
been hitherto possible. The most important of these doctrines are those
which establish and define--(1) The former wide extension of all groups now
discontinuous, as being a necessary result of "evolution"; (2) The
permanence of the great features of the distribution of land and water on
the earth's surface; and, (3) The nature and frequency of climatal changes
throughout geological time.
I have now only to thank the many friends and correspondents who have given
me information or advice. Besides those whose assistance is acknowledged in
the body of the work, I am especially indebted to four gentlemen who have
been kind enough to read over the proofs of chapters dealing with questions
on which they have special knowledge, giving me the benefit of valuable
emendations and suggestions. Mr. Edward R. Alston has looked over those
parts of the earlier chapters which relate to the mammals of Europe and the
North Temperate zone; Mr. S. B. J. Skertchley, of the Geological Survey,
has read the chapters which discuss the glacial epoch and other geological
questions; Professor A. Newton has looked over the passages referring to
the birds of the Madagascar group; while Sir Joseph D. Hooker has given me
the invaluable benefit of his remarks on my two chapters dealing with the
New Zealand flora.
CROYDON, _August, 1880_.
* * * * *
{xi}
CONTENTS
PART I
THE DISPERSAL OF ORGANISMS; ITS PHENOMENA, LAWS, AND CAUSES
CHAPTER I
INTRODUCTORY
Remarkable Contrasts in the Distribution of Animals--Britain and
Japan--Australia and New Zealand--Bali and Lombok--Florida and Bahama
Islands--Brazil and Africa--Borneo, Madagascar, and Celebes--Problems in
Distribution to be found in every Country--Can be Solved only by the
Combination of many distinct lines of inquiry, Biological and
Physical--Islands offer the best Subjects for the Study of
Distribution--Outline of the Subjects to be discussed in the Present
Volume.
_Pages_ 3-11
CHAPTER II
THE ELEMENTARY FACTS OF DISTRIBUTION.
Importance of Locality as an Essential Character of Species--Areas of
Distribution--Extent and Limitations of Specific Areas--Specific Range of
Birds--Generic Areas--Separate and Overlapping Areas--The Species of Tits
as illustrating Areas of Distribution--The Distribution of the Species of
Jays--Discontinuous Generic Areas--Peculiarities of Generic and Family
Distribution--General Features of Overlapping and Discontinuous
Areas--Restricted Areas of Families--The Distribution of Orders
_Pages_ 12-30
{xii}
CHAPTER III
CLASSIFICATION OF THE FACTS OF DISTRIBUTION.--ZOOLOGICAL REGIONS
The Geographical Divisions of the Globe do not Correspond to Zoological
Divisions--The Range of British Mammals as Indicating a Zoological
Region--Range of East Asian and North African Mammals--The Range of British
Birds--Range of East Asian Birds--The Limits of the Palæarctic
Region--Characteristic Features of the Palæarctic Region--Definition and
Characteristic Groups of the Ethiopian Region--Of the Oriental Region--Of
the Australian Region--Of the Nearctic Region--Of the Neotropical
Region--Comparison of Zoological Regions with the Geographical Divisions of
the Globe
_Pages_ 31-54
CHAPTER IV
EVOLUTION AS THE KEY TO DISTRIBUTION
Importance of the Doctrine of Evolution--The Origin of New
Species--Variation in Animals--The amount of Variation in North American
Birds--How New Species Arise from a Variable Species--Definition and Origin
of Genera--Cause of the Extinction of Species--The Rise and Decay of
Species and Genera--Discontinuous Specific Areas, why Rare--Discontinuity
of the Area of Parus Palustris--Discontinuity of Emberiza Schoeniclus--The
European and Japanese Jays--Supposed examples of Discontinuity among North
American Birds--Distribution and Antiquity of Families--Discontinuity a
Proof of Antiquity--Concluding remarks
_Pages_ 55-71
CHAPTER V
THE POWERS OF DISPERSAL OF ANIMALS AND PLANTS
Statement of the General Question of Dispersal--The Ocean as a Barrier to
the Dispersal of Mammals--The Dispersal of Birds--The Dispersal of
Reptiles--The Dispersal of Insects--The Dispersal of Land Mollusca--Great
Antiquity of Land-shells--Causes Favouring the Abundance of
Land-shells--The Dispersal of Plants--Special Adaptability of Seeds for
Dispersal--Birds as Agents in the Dispersal of Seeds--Ocean Currents as
Agents in Plant Dispersal--Dispersal along Mountain Chains--Antiquity of
Plants as Effecting their Distribution
_Pages_ 72-82
CHAPTER VI
GEOGRAPHICAL AND GEOLOGICAL CHANGES: THE PERMANENCE OF CONTINENTS
Changes of Land and Sea, their Nature and Extent--Shore-Deposits and
Stratified Rocks--The Movements of Continents--Supposed Oceanic {xiii}
Formations; the Origin of Chalk--Fresh-water and Shore-deposits as Proving
the Permanence of Continents--Oceanic Islands as Indications of the
Permanence of Continents and Oceans--General Stability of Continents with
Constant Change of Form--Effect of Continental Changes on the Distribution
of Animals--Changed Distribution Proved by the Extinct Animals of Different
Epochs--Summary of Evidence for the General Permanence of Continents and
Oceans.
_Pages_ 83-105
CHAPTER VII
CHANGES OF CLIMATE WHICH HAVE INFLUENCED THE DISPERSAL OF ORGANISMS: THE
GLACIAL EPOCH
Proofs of the Recent Occurrence of a Glacial Epoch--Moraines--Travelled
Blocks--Glacial Deposits of Scotland: the "Till"--Inferences from the
Glacial Phenomena of Scotland--Glacial Phenomena of North America--Effects
of the Glacial Epoch on Animal Life--Warm and Cold Periods--Palæontological
Evidence of Alternate Cold and Warm Periods--Evidence of Interglacial Warm
Periods on the Continent and in North America--Migrations and Extinctions
of Organisms Caused by the Glacial Epoch
_Pages_ 106-124
CHAPTER VIII
THE CAUSES OF GLACIAL EPOCHS
Various Suggested Causes--Astronomical Causes of Changes of
Climate--Difference of Temperature Caused by Varying Distances of the
Sun--Properties of Air and Water, Snow and Ice, in Relation to
Climate--Effects of Snow on Climate--High Land and Great Moisture Essential
to the Initiation of a Glacial Epoch--Perpetual Snow nowhere Exists on
Lowlands--Conditions Determining the Presence or Absence of Perpetual
Snow--Efficiency of Astronomical causes in Producing Glaciation--Action of
Meteorological Causes in Intensifying Glaciation--Summary of Causes of
Glaciation--Effect of Clouds and Fog in Cutting off the Sun's Heat--South
Temperate America as Illustrating the Influence of Astronomical Causes on
Climate--Geographical Changes how far a Cause of Glaciation--Land Acting as
a Barrier to Ocean-currents--The Theory of Interglacial Periods and their
Probable Character--Probable Effect of Winter in _aphelion_ on the Climate
of Britain--The Essential Principle of Climatal Change Restated--Probable
Date of the Last Glacial Epoch--Changes of the Sea-level Dependent on
Glaciation--The Planet Mars as Bearing on the Theory of Excentricity as a
Cause of Glacial Epochs
_Pages_ 125-168
{xiv}
CHAPTER IX
ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE ARCTIC REGIONS
Mr. Croll's Views on Ancient Glacial Epochs--Effects of Denudation in
Destroying the Evidence of Remote Glacial Epochs--Rise of Sea-level
Connected with Glacial Epochs a Cause of Further Denudation--What Evidence
of Early Glacial Epochs may be Expected--Evidences of Ice-action During the
Tertiary Period--The Weight of the Negative Evidence--Temperate Climates in
the Arctic Regions--The Miocene Arctic Flora--Mild Arctic Climates of the
Cretaceous Period--Stratigraphical Evidence of Long-continued Mild Arctic
Conditions--The Causes of Mild Arctic Climates--Geographical Conditions
Favouring Mild Northern Climates in Tertiary Times--The Indian Ocean as a
Source of Heat in Tertiary Times--Condition of North America During the
Tertiary Period--Effect of High Excentricity on Warm Polar
Climates--Evidences as to Climate in the Secondary and Palæozoic
Epochs--Warm Arctic Climates in Early Secondary and Palæozoic
Times--Conclusions as to the Climates of Secondary and Tertiary
Periods--General View of Geological Climates as Dependent on the Physical
Features of the Earth's Surface--Estimate of the Comparative Effects of
Geographical and Physical Causes in Producing Changes of Climate.
_Pages_ 169-209
CHAPTER X
THE EARTH'S AGE, AND THE RATE OF DEVELOPMENT OF ANIMALS AND PLANTS
Various Estimates of Geological Time--Denudation and Deposition of Strata
as a Measure of Time--How to Estimate the Thickness of the Sedimentary
Rocks--How to Estimate the Average Rate of Deposition of the Sedimentary
Rocks--The Rate of Geological Change Probably Greater in very Remote
Times--Value of the Preceding Estimate of Geological Time--Organic
Modification Dependent on Change of Conditions--Geographical Mutations as a
Motive Power in Bringing about Organic Changes--Climatal Revolutions as an
Agent in Producing Organic Changes--Present Condition of the Earth One of
Exceptional Stability as Regards Climate--Date of Last Glacial Epoch and
its Bearing on the Measurement of Geological Time--Concluding Remarks
_Pages_ 210-237
{xv}
PART II
INSULAR FAUNAS AND FLORAS
CHAPTER XI
THE CLASSIFICATION OF ISLANDS
Importance of Islands in the Study of the Distribution of
Organisms--Classification of Islands with Reference to
Distribution--Continental Islands--Oceanic Islands
_Pages_ 241-245
CHAPTER XII
OCEANIC ISLANDS:--THE AZORES AND BERMUDA
_The Azores, or Western Islands_
Position and Physical Features--Chief Zoological Features of the
Azores--Birds--Origin of the Azorean Bird-fauna--Insects of the
Azores--Land-shells of the Azores--The Flora of the Azores--The Dispersal
of Seeds--Birds as seed-carriers--Facilities for Dispersal of Azorean
Plants--Important Deduction from the Peculiarities of the Azorean Fauna and
Flora
_Pages_ 246-262
_Bermuda_
Position and Physical Features--The Red Clay of Bermuda--Zoology of
Bermuda--Birds of Bermuda--Comparison of the Bird-faunas of Bermuda and the
Azores--Insects of Bermuda--Land Mollusca--Flora of Bermuda--Concluding
Remarks on the Azores and Bermuda
_Pages_ 263-274
CHAPTER XIII
THE GALAPAGOS ISLANDS
Position and Physical Features--Absence of Indigenous Mammalia and
Amphibia--Reptiles--Birds--Insects and Land-shells--The Keeling Islands as
Illustrating the Manner in which Oceanic Islands are Peopled--Flora of the
Galapagos--Origin of the Flora of the Galapagos--Concluding remarks
_Pages_ 273-291
CHAPTER XIV
ST. HELENA
Position and Physical Features of St. Helena--Change Effected by European
Occupation--The Insects of St. Helena--Coleoptera--Peculiarities and Origin
of the Coleoptera of St. Helena--Land-shells of St. Helena--Absence of
Fresh-water Organisms--Native Vegetation of St. Helena--The Relations of
the St. Helena Compositæ--Concluding Remarks on St. Helena
_Pages_ 292-309
{xvi}
CHAPTER XV
THE SANDWICH ISLANDS
Position and Physical Features--Zoology of the Sandwich
Islands--Birds--Reptiles--Land-shells--Insects--Vegetation of the Sandwich
Islands--Peculiar Features of the Hawaiian Flora--Antiquity of the Hawaiian
Fauna and Flora--Concluding Observations on the Fauna and Flora of the
Sandwich Islands--General Remarks on Oceanic Islands
_Pages_ 310-330
CHAPTER XVI
CONTINENTAL ISLANDS OF RECENT ORIGIN: GREAT BRITAIN
Characteristic Features of Recent Continental Islands--Recent Physical
Changes of the British Isles--Proofs of Former Elevation--Submerged
Forests--Buried River Channels--Time of Last Union with the Continent--Why
Britain is Poor in Species--Peculiar British Birds---Fresh-water
Fishes--Cause of Great Speciality in Fishes--Peculiar British
Insects--Lepidoptera Confined to the British Isles--Peculiarities of the
Isle of Man Lepidoptera--Coleoptera Confined to the British
Isles--Trichoptera Peculiar to the British Isles--Land and Fresh-water
Shells--Peculiarities of the British Flora--Peculiarities of the Irish
Flora--Peculiar British Mosses and Hepaticæ--Concluding Remarks on the
Peculiarities of the British Fauna and Flora
_Pages_ 331-372
CHAPTER XVII
BORNEO AND JAVA
Position and Physical Features of Borneo--Zoological Features of Borneo:
Mammalia--Birds--The Affinities of the Borneo Fauna--Java, its Position and
Physical Features--General Character of the Fauna of Java--Differences
Between the Fauna of Java and that of the other Malay Islands--Special
Relations of the Javan Fauna to that of the Asiatic Continent--Past
Geographical Changes of Java and Borneo--The Philippine Islands--Concluding
Remarks on the Malay Islands
_Pages_ 373-390
CHAPTER XVIII
JAPAN AND FORMOSA
Japan, its Position and Physical Features--Zoological Features of
Japan--Mammalia--Birds--Birds Common to Great Britain and Japan--Birds
Peculiar to Japan--Japan Birds Recurring in Distant
Areas--Formosa--Physical Features of Formosa--Animal Life of
Formosa--Mammalia--Land Birds Peculiar to Formosa--Formosan Birds Recurring
in India or Malaya--Comparison of Faunas of Hainan, Formosa, and
Japan--General Remarks on Recent Continental Islands
_Pages_ 391-410
{xvii}
CHAPTER XIX
ANCIENT CONTINENTAL ISLANDS: THE MADAGASCAR GROUP
Remarks on Ancient Continental Islands--Physical Features of
Madagascar--Biological Features of Madagascar--Mammalia--Reptiles--Relation
of Madagascar to Africa--Early History of Africa and Madagascar--Anomalies
of Distribution and how to Explain Them--The Birds of Madagascar as
Indicating a Supposed Lemurian Continent--Submerged Islands Between
Madagascar and India--Concluding Remarks on "Lemuria"--The Mascarene
Islands--The Comoro Islands--The Seychelles Archipelago--Birds of the
Seychelles--Reptiles and Amphibia--Fresh-water Fishes--Land
Shells--Mauritius, Bourbon, and Rodriguez--Birds--Extinct Birds and their
Probable Origin--Reptiles--Flora of Madagascar and the Mascarene
Islands--Curious Relations of Mascarene Plants--Endemic Genera of Mauritius
and Seychelles--Fragmentary Character of the Mascarene Flora--Flora of
Madagascar Allied to that of South Africa--Preponderance of Ferns in the
Mascarene Flora--Concluding Remarks on the Madagascar Group
_Pages_ 411-449
CHAPTER XX
ANOMALOUS ISLANDS: CELEBES
Anomalous Relations of Celebes--Physical Features of the Island--Zoological
Character of the Islands Around Celebes--The Malayan and Australian
Banks--Zoology of Celebes: Mammalia--Probable Derivation of the Mammals of
Celebes--Birds of Celebes--Bird-types Peculiar to Celebes--Celebes not
Strictly a Continental Island--Peculiarities of the Insects of
Celebes--Himalayan Types of Birds and Butterflies in Celebes--Peculiarities
of Shape and Colour of Celebesian Butterflies--Concluding Remarks--Appendix
on the Birds of Celebes
_Pages_ 450-470
CHAPTER XXI
ANOMALOUS ISLANDS: NEW ZEALAND
Position and Physical Features of New Zealand--Zoological Character of New
Zealand--Mammalia--Wingless Birds Living and Extinct--Recent Existence of
the Moa--Past Changes of New Zealand deduced from its Wingless Birds--Birds
and Reptiles of New Zealand--Conclusions from the Peculiarities of the New
Zealand Fauna
_Pages_ 471-486
{xviii}
CHAPTER XXII
THE FLORA OF NEW ZEALAND: ITS AFFINITIES AND PROBABLE ORIGIN
Relations of the New Zealand Flora to that of Australia--General Features
of the Australian Flora--The Floras of South-eastern and South-western
Australia--Geological Explanation of the Differences of these Two
Floras--The Origin of the Australian Element in the New Zealand
Flora--Tropical Character of the New Zealand Flora Explained--Species
Common to New Zealand and Australia mostly Temperate Forms--Why Easily
Dispersed Plants have often Restricted Ranges--Summary and Conclusion on
the New Zealand Flora
_Pages_ 487-508
CHAPTER XXIII
ON THE ARCTIC ELEMENT IN SOUTH TEMPERATE FLORAS
European Species and Genera of Plants in the Southern
Hemisphere--Aggressive Power of the Scandinavian Flora--Means by which
Plants have Migrated from North to South--Newly Moved Soil as Affording
Temporary Stations to Migrating Plants--Elevation and Depression of the
Snow-line as Aiding the Migration of Plants--Changes of Climate Favourable
to Migration--The Migration from North to South has been Long going
on--Geological Changes as Aiding Migration--Proofs of Migration by way of
the Andes--Proofs of Migration by way of the Himalayas and Southern
Asia--Proofs of Migration by way of the African Highlands--Supposed
Connection of South Africa and Australia--The Endemic Genera of Plants in
New Zealand--The Absence of Southern Types from the Northern
Hemisphere--Concluding Remarks on the New Zealand and South Temperate
Floras
_Pages_ 509-530
CHAPTER XXIV
SUMMARY AND CONCLUSION
The Present Volume is the Development and Application of a
Theory--Statement of the Biological and Physical Causes of
Dispersal--Investigation of the Facts of Dispersal--Of the Means of
Dispersal--Of Geographical Changes Affecting Dispersal--Of Climatal Changes
Affecting Dispersal--The Glacial Epoch and its Causes--Alleged Ancient
Glacial Epochs--Warm Polar Climates and their Causes--Conclusions as to
Geological Climates--How Far Different from those of Mr. Croll--Supposed
Limitations of Geological Time--Time Amply Sufficient both for Geological
and Biological Development--Insular Faunas and Floras--The North Atlantic
Islands--The Galapagos--St. Helena and the Sandwich Islands--Great Britain
as a Recent Continental Island--Borneo and Java--Japan and
Formosa--Madagascar as an Ancient Continental Island--Celebes and New
Zealand as Anomalous Islands--The Flora of New Zealand and its Origin--The
European Element in the South Temperate Floras--Concluding Remarks
_Pages_ 531-545
* * * * *
{xix}
MAPS AND ILLUSTRATIONS
PAGE
1. MAP SHOWING THE DISTRIBUTION OF THE TRUE JAYS _Frontispiece._
2. MAP SHOWING THE ZOOLOGICAL REGIONS _To face_ 31
3. MAP SHOWING THE DISTRIBUTION OF _PARUS PALUSTRIS_ _To face_ 66
4. A GLACIER WITH MORAINES (From Sir C. Lyell's _Principles
of Geology_) 109
5. MAP OF THE ANCIENT RHONE GLACIER (From Sir C. Lyell's
_Antiquity of Man_) 110
6. DIAGRAM SHOWING THE EFFECTS OF EXCENTRICITY AND PRECESSION
ON CLIMATE 127
7. DIAGRAM OF EXCENTRICITY AND PRECESSION 129
8. MAP SHOWING THE EXTENT OF THE NORTH AND SOUTH POLAR ICE 138
9. DIAGRAM SHOWING CHANGES OF EXCENTRICITY DURING THREE MILLION
YEARS 171
10. OUTLINE MAP OF THE AZORES 248
11. MAP OF BERMUDA AND THE AMERICAN COAST 263
12. SECTION OF BERMUDA AND ADJACENT SEA-BOTTOM 264
{xx}
13. MAP OF THE GALAPAGOS AND ADJACENT COASTS OF SOUTH AMERICA 276
14. MAP OF THE GALAPAGOS 277
15. MAP OF THE SOUTH ATLANTIC, SHOWING POSITION OF ST. HELENA 293
16. MAP OF THE SANDWICH ISLANDS 311
17. MAP OF THE NORTH PACIFIC, WITH ITS SUBMERGED BANKS 312
18. MAP SHOWING THE BANK CONNECTING BRITAIN WITH THE CONTINENT 333
19. MAP OF BORNEO AND JAVA, SHOWING THE GREAT SUBMARINE BANK OF
SOUTH-EASTERN ASIA 373
20. MAP OF JAPAN AND FORMOSA 392
21. PHYSICAL SKETCH MAP OF MADAGASCAR (From _Nature_) 413
22. MAP OF MADAGASCAR GROUP, SHOWING DEPTHS OF SEA 415
23. MAP OF THE INDIAN OCEAN 424
24. MAP OF CELEBES AND THE SURROUNDING ISLANDS 451
25. MAP SHOWING DEPTHS OF SEA AROUND AUSTRALIA AND NEW ZEALAND 471
26. MAP SHOWING THE PROBABLE CONDITION OF AUSTRALIA DURING THE
CRETACEOUS EPOCH 496
* * * * *
ISLAND LIFE
PART I
_THE DISPERSAL OF ORGANISMS_
_ITS PHENOMENA, LAWS, AND CAUSES_
{3}
CHAPTER I
INTRODUCTORY
Remarkable Contrasts in distribution of Animals--Britain and
Japan--Australia and New Zealand--Bali and Lombok--Florida and Bahama
Islands--Brazil and Africa--Borneo, Madagascar, and Celebes--Problems
in distribution to be found in every country--Can be solved only by the
combination of many distinct lines of inquiry, biological and
physical--Islands offer the best subjects for the study of
distribution--Outline of the subjects to be discussed in the present
volume.
When an Englishman travels by the nearest sea-route from Great Britain to
Northern Japan he passes by countries very unlike his own, both in aspect
and natural productions. The sunny isles of the Mediterranean, the sands
and date-palms of Egypt, the arid rocks of Aden, the cocoa groves of
Ceylon, the tiger-haunted jungles of Malacca and Singapore, the fertile
plains and volcanic peaks of Luzon, the forest-clad mountains of Formosa,
and the bare hills of China, pass successively in review; till after a
circuitous voyage of thirteen thousand miles he finds himself at Hakodadi
in Japan. He is now separated from his starting-point by the whole width of
Europe and Northern Asia, by an almost endless succession of plains and
mountains, arid deserts or icy plateaux, yet when he visits the interior of
the country he sees so many familiar natural objects that he can hardly
help fancying he is close to his home. He finds the woods and fields
tenanted by tits, hedge-sparrows, wrens, wagtails, larks, redbreasts, {4}
thrushes, buntings, and house-sparrows, some absolutely identical with our
own feathered friends, others so closely resembling them that it requires a
practised ornithologist to tell the difference. If he is fond of insects he
notices many butterflies and a host of beetles which, though on close
examination they are found to be distinct from ours, are yet of the same
general aspect, and seem just what might be expected in any part of Europe.
There are also of course many birds and insects which are quite new and
peculiar, but these are by no means so numerous or conspicuous as to remove
the general impression of a wonderful resemblance between the productions
of such remote islands as Britain and Yesso.
Now let an inhabitant of Australia sail to New Zealand, a distance of less
than thirteen hundred miles, and he will find himself in a country whose
productions are totally unlike those of his own. Kangaroos and wombats
there are none, the birds are almost all entirely new, insects are very
scarce and quite unlike the handsome or strange Australian forms, while
even the vegetation is all changed, and no gum-tree, or wattle, or
grass-tree meets the traveller's eye.
But there are some more striking cases even than this, of the diversity of
the productions of countries not far apart. In the Malay Archipelago there
are two islands, named Bali and Lombok, each about as large as Corsica, and
separated by a strait only fifteen miles wide at its narrowest part. Yet
these islands differ far more from each other in their birds and quadrupeds
than do England and Japan. The birds of the one are extremely _unlike_
those of the other, the difference being such as to strike even the most
ordinary observer. Bali has red and green woodpeckers, barbets,
weaver-birds, and black-and-white magpie-robins, none of which are found in
Lombok, where, however, we find screaming cockatoos and friar-birds, and
the strange mound-building megapodes, which are all equally unknown in
Bali. Many of the kingfishers, crow-shrikes, and other birds, though of the
same general form, are of very distinct species; and though a considerable
number of birds are the same in both islands the difference {5} is none the
less remarkable--as proving that mere distance is one of the least
important of the causes which have determined the likeness or unlikeness in
the animals of different countries.
In the western hemisphere we find equally striking examples. The Eastern
United States possess very peculiar and interesting plants and animals, the
vegetation becoming more luxuriant as we go south but not altering in
essential character, so that when we reach Alabama or Florida we still find
ourselves in the midst of pines, oaks, sumachs, magnolias, vines, and other
characteristic forms of the temperate flora; while the birds, insects, and
land-shells are of the same general character with those found further
north.[1] But if we now cross over the narrow strait, about fifty miles
wide, which separates Florida from the Bahama Islands, we find ourselves in
a totally different country, surrounded by a vegetation which is
essentially tropical and generally identical with that of Cuba. The change
is most striking, because there is little difference of climate, of soil,
or apparently of position, to account for it; and when we find that the
birds, the insects, and especially the land-shells of the Bahamas are
almost all West Indian, while the North American types of plants and
animals have almost all completely disappeared, we shall be convinced that
such differences and resemblances cannot be due to existing conditions, but
must depend upon laws and causes to which mere proximity of position offers
no clue.
Hardly less uncertain and irregular are the effects of climate. Hot
countries usually differ widely from cold ones in all their organic forms;
but the difference is by no means constant, nor does it bear any proportion
to difference of temperature. Between frigid Canada and sub-tropical
Florida there are less marked differences in the animal productions than
between Florida and Cuba or Yucatan, so much more alike in climate and so
much nearer together. So the differences between the birds and quadrupeds
of temperate Tasmania and tropical North {6} Australia are slight and
unimportant as compared with the enormous differences we find when we pass
from the latter country to equally tropical Java. If we compare
corresponding portions of different continents, we find no indication that
the almost perfect similarity of climate and general conditions has any
tendency to produce similarity in the animal world. The equatorial parts of
Brazil and of the West Coast of Africa are almost identical in climate and
in luxuriance of vegetation, but their animal life is totally diverse. In
the former we have tapirs, sloths, and prehensile-tailed monkeys; in the
latter elephants, antelopes, and man-like apes; while among birds, the
toucans, chatterers, and humming-birds of Brazil are replaced by the
plantain-eaters, bee-eaters, and sun-birds of Africa. Parts of
South-temperate America, South Africa, and South Australia, correspond
closely in climate; yet the birds and quadrupeds of these three districts
are as completely unlike each other as those of any parts of the world that
can be named.
If we visit the great islands of the globe, we find that they present
similar anomalies in their animal productions, for while some exactly
resemble the nearest continents others are widely different. Thus the
quadrupeds, birds and insects of Borneo correspond very closely to those of
the Asiatic continent, while those of Madagascar are extremely unlike
African forms, although the distance from the continent is less in the
latter case than in the former. And if we compare the three great islands
Sumatra, Borneo, and Celebes--lying as it were side by side in the same
ocean--we find that the two former, although furthest apart, have almost
identical productions, while the two latter, though closer together, are
more unlike than Britain and Japan situated in different oceans and
separated by the largest of the great continents.
These examples will illustrate the kind of questions it is the object of
the present work to deal with. Every continent, every country, and every
island on the globe, offers similar problems of greater or less complexity
and interest, and the time has now arrived when their solution can be
attempted with some prospect of success. Many {7} years study of this class
of subjects has convinced me that there is no short and easy method of
dealing with them; because they are, in their very nature, the visible
outcome and residual product of the whole past history of the earth. If we
take the organic productions of a small island, or of any very limited
tract of country, such as a moderate-sized country parish, we have, in
their relations and affinities--in the fact that they are _there_ and
others are _not_ there, a problem which involves all the migrations of
these species and their ancestral forms--all the vicissitudes of climate
and all the changes of sea and land which have affected those
migrations--the whole series of actions and reactions which have determined
the preservation of some forms and the extinction of others,--in fact the
whole history of the earth, inorganic and organic, throughout a large
portion of geological time.
We shall perhaps better exhibit the scope and complexity of the subject,
and show that any intelligent study of it was almost impossible till quite
recently, if we concisely enumerate the great mass of facts and the number
of scientific theories or principles which are necessary for its
elucidation.
We require then in the first place an adequate knowledge of the fauna and
flora of the whole world, and even a detailed knowledge of many parts of
it, including the islands of more special interest and their adjacent
continents. This kind of knowledge is of very slow growth, and is still
very imperfect;[2] and in many cases it can {8} never now be obtained owing
to the reckless destruction of forests and with them of countless species
of plants and animals. In the next place we require a true and natural
classification of animals and plants, so that we may know their real
affinities; and it is only now that this is being generally arrived at. We
further have to make use of the theory of "descent with modification" as
the only possible key to the interpretation of the facts of distribution,
and this theory has only been generally accepted within the last twenty
years. It is evident that, so long as the belief in "special creations" of
each species prevailed, no explanation of the complex facts of distribution
_could_ be arrived at or even conceived; for if each species was created
where it is now found no further inquiry can take us beyond that fact, and
there is an end of the whole matter. Another important factor in our
interpretation of the phenomena of distribution, is a knowledge of the
extinct forms that have inhabited each country during the tertiary and
secondary periods of geology. New facts of this kind are daily coming to
light, but except as regards Europe, North America, and parts of India,
they are extremely scanty; and even in the best-known countries the record
itself is often very defective and fragmentary. Yet we have already
obtained remarkable evidence of the migrations of many animals and plants
in past ages, throwing an often unexpected light on the actual distribution
of many groups.[3] By this means alone can we obtain positive evidence of
the past migrations of organisms; and when, as too frequently is the case,
this is altogether wanting, we {9} have to trust to collateral evidence and
more or less probable hypothetical explanations. Hardly less valuable is
the evidence of stratigraphical geology; for this often shows us what parts
of a country have been submerged at certain epochs, and thus enables us to
prove that certain areas have been long isolated and the fauna and flora
allowed time for special development. Here, too, our knowledge is
exceedingly imperfect, though the blanks upon the geological map of the
world are yearly diminishing in extent. Lastly, as a most valuable
supplement to geology, we require to know approximately, the depth and
contour of the ocean-bed, since this affords an important clue to the
former existence of now-submerged lands, uniting islands to continents, or
affording intermediate stations which have aided the migrations of many
organisms. This kind of information has only been partially obtained during
the last few years; and it will be seen in the latter part of this volume,
that some of the most recent deep-sea soundings have afforded a basis for
an explanation of one of the most difficult and interesting questions in
geographical biology--the origin of the fauna and flora of New Zealand.
Such are the various classes of evidence that bear directly on the question
of the distribution of organisms; but there are others of even a more
fundamental character, and the importance of which is only now beginning to
be recognised by students of nature. These are, firstly, the wonderful
alterations of climate which have occurred in the temperate and polar
zones, as proved by the evidences of glaciation in the one and of luxuriant
vegetation in the other; and, secondly, the theory of the permanence of
existing continents and oceans. If glacial epochs in temperate lands and
mild climates near the poles have, as now believed by men of eminence,
occurred several times over in the past history of the earth, the effects
of such great and repeated changes, both on the migration, modification,
and extinction, of species, must have been of overwhelming importance--of
more importance perhaps than even the geological changes of sea and land.
It is therefore necessary to consider the evidence for these climatal
changes; {10} and then, by a critical examination of their possible causes,
to ascertain whether they were isolated phenomena, were due to recurrent
cosmical actions, or were the result of a great system of terrestrial
development. The latter is the conclusion we arrive at; and this conclusion
brings with it the conviction, that in the theory which accounts for both
glacial epochs and warm polar climates, we have the key to explain and
harmonize many of the most anomalous biological and geological phenomena,
and one which is especially valuable for the light it throws on the
dispersal and existing distribution of organisms. The other important
theory, or rather corollary from the preceding theory--that of the
permanence of oceans and the general stability of continents throughout all
geological time, is as yet very imperfectly understood, and seems, in fact,
to many persons in the nature of a paradox. The evidence for it, however,
appears to me to be conclusive; and it is certainly the most fundamental
question in regard to the subject we have to deal with: since, if we once
admit that continents and oceans may have changed places over and over
again (as many writers maintain), we lose all power of reasoning on the
migrations of ancestral forms of life, and are at the mercy of every wild
theorist who chooses to imagine the former existence of a now-submerged
continent to explain the existing distribution of a group of frogs or a
genus of beetles.
As already shown by the illustrative examples adduced in this chapter, some
of the most remarkable and interesting facts in the distribution and
affinities of organic forms are presented by islands in relation to each
other and to the surrounding continents. The study of the productions of
the Galapagos--so peculiar, and yet so decidedly related to the American
continent--appears to have had a powerful influence in determining the
direction of Mr. Darwin's researches into the origin of species; and every
naturalist who studies them has always been struck by the unexpected
relations or singular anomalies which are so often found to characterize
the fauna and flora of islands. Yet their full importance in connection
with the history of the earth and its inhabitants has hardly yet {11} been
recognised; and it is in order to direct the attention of naturalists to
this most promising field of research, that I restrict myself in this
volume to an elucidation of some of the problems they present to us. By far
the larger part of the islands of the globe are but portions of continents
undergoing some of the various changes to which they are ever subject; and
the correlative proposition, that every portion of our continents has again
and again passed through insular conditions, has not been sufficiently
considered, but is, I believe, the statement of a great and most suggestive
truth, and one which lies at the foundation of all accurate conception of
the physical and organic changes which have resulted in the present state
of the earth.
The indications now given of the scope and purpose of the present volume
renders it evident that, before we can proceed to the discussion of the
remarkable phenomena presented by insular faunas and floras, and the
complex causes which have produced them, we must go through a series of
preliminary studies, adapted to give us a command of the more important
facts and principles on which the solution of such problems depends. The
succeeding eight chapters will therefore be devoted to the explanation of
the mode of distribution, variation, modification, and dispersal, of
species and groups, illustrated by facts and examples; of the true nature
of geological change as affecting continents and islands; of changes of
climate, their nature, causes, and effects; of the duration of geological
time and the rate of organic development.
* * * * *
{12}
CHAPTER II
THE ELEMENTARY FACTS OF DISTRIBUTION
Importance of Locality as an essential character of Species--Areas of
Distribution--Extent and Limitations of Specific Areas--Specific range
of Birds--Generic Areas--Separate and overlapping areas--The species of
Tits as illustrating Areas of Distribution--The distribution of the
species of Jays--Discontinuous generic areas--Peculiarities of generic
and family distribution--General features of overlapping and
discontinuous areas--Restricted areas of Families--The distribution of
Orders.
So long as it was believed that the several species of animals and plants
were "special creations," and had been formed expressly to inhabit the
countries in which they are now found, their habitat was an ultimate fact
which required no explanation. It was assumed that every animal was
_exactly_ adapted to the climate and surroundings amid which it lived, and
that the only, or, at all events, the chief reason why it did not inhabit
another country was, that the climate or general conditions of that country
were not suitable to it, but in what the unsuitability consisted we could
rarely hope to discover. Hence the exact locality of any species was not
thought of much importance from a scientific point of view, and the idea
that anything could be learnt by a comparative study of different floras
and faunas never entered the minds of the older naturalists.
But so soon as the theory of evolution came to be generally adopted, and it
was seen that each animal could only have come into existence in some area
where ancestral {13} forms closely allied to it already lived, a real and
important relation was established between an animal and its native
country, and a new set of problems at once sprang into existence. From the
old point of view the _diversities_ of animal life in the separate
continents, even where physical conditions were almost identical, was the
fact that excited astonishment; but seen by the light of the evolution
theory, it is the _resemblances_ rather than the diversities in these
distant continents and islands that are most difficult to explain. It thus
comes to be admitted that a knowledge of the exact area occupied by a
species or a group is a real portion of its natural history, of as much
importance as its habits, its structure, or its affinities; and that we can
never arrive at any trustworthy conclusions as to how the present state of
the organic world was brought about, until we have ascertained with some
accuracy the general laws of the distribution of living things over the
earth's surface.
_Areas of Distribution._--Every species of animal has a certain area of
distribution to which, as a rule, it is permanently confined, although, no
doubt, the limits of its range fluctuate somewhat from year to year, and in
some exceptional cases may be considerably altered in a few years or
centuries. Each species is moreover usually limited to one continuous area,
over the whole of which it is more or less frequently to be met with, but
there are many apparent and some real exceptions to this rule. Some animals
are so adapted to certain kinds of country--as to forests or marshes,
mountains or deserts--that they cannot, permanently, live elsewhere. These
may be found scattered over a wide area in suitable spots only, but can
hardly on that account be said to have several distinct areas of
distribution. As an example we may name the chamois, which lives only on
high mountains, but is found in the Pyrenees, the Alps, the Carpathians, in
some of the Greek mountains and the Caucasus. The variable hare is another
and more remarkable case, being found all over Northern Europe and Asia
beyond lat. 55°, and also in Scotland and Ireland. In central Europe it is
unknown till we come to the Alps, the Pyrenees, and the Caucasus, where it
again appears. This is one of the best cases known of the {14}
discontinuous distribution of a _species_, there being a gap of about a
thousand miles between its southern limits in Russia, and its reappearance
in the Alps. There are of course numerous instances in which species occur
in two or more islands, or in an island and continent, and are thus
rendered discontinuous by the sea, but these involve questions of changes
in sea and land which we shall have to consider further on. Other cases are
believed to exist of still wider separation of a species, as with the marsh
titmice and the reed buntings of Europe and Japan, where similar forms are
found in the extreme localities, while distinct varieties or sub-species,
inhabit the intervening districts.
_Extent and Limitations of Specific Areas._--Leaving for the present these
cases of want of continuity in a species, we find the most wide difference
between the extent of country occupied, varying in fact from a few square
miles to almost the entire land surface of the globe. Among the mammalia,
however, the same species seldom inhabits both the old and new worlds,
unless they are strictly arctic animals, as the reindeer, the elk, the
arctic fox, the glutton, the ermine, and some others. The common wolf of
Europe and Northern Asia is thought by many naturalists to be identical
with the variously coloured wolves of North America extending from the
Arctic Ocean to Mexico, in which case this will have perhaps the widest
range of any species of mammal. Little doubt exists as to the identity of
the brown bears and the beavers of Europe and North America; but all these
species range up to the arctic circle, and there is no example of a mammal
universally admitted to be identical yet confined to the temperate zones of
the two hemispheres. Among the undisputed species of mammalia the leopard
has an enormous range, extending all over Africa and South Asia to Borneo
and the east of China, and thus having probably the widest range of any
known mammal. The winged mammalia have not usually very wide ranges, there
being only one bat common to the Old and New Worlds. This is a British
species, _Vesperugo serotinus_, which is found over the larger part of
North America, Europe and Asia, as far {15} as Pekin, and even extends into
tropical Africa, thus rivalling the leopard and the wolf in the extent of
country it occupies.
Of very restricted ranges there are many examples, but some of these are
subject to doubts as to the distinctness of the species or as to its
geographical limits being really known. In Europe we have a distinct
species of ibex (_Capra Pyrenaica_) confined to the Pyrenean mountains,
while the true marmot is restricted to the Alpine range. More remarkable is
the Pyrenean water-mole (_Mygale Pyrenaica_), a curious small insectivorous
animal found only in a few places in the northern valleys of the Pyrenees.
In islands there are many cases of undoubted restriction of species to a
small area, but these involve a different question from the range of
species on continents where there is no _apparent_ obstacle to their wider
extension.
_Specific range of Birds._--Among birds we find instances of much wider
range of species, which is only what might be expected considering their
powers of flight; but, what is very curious, we also find more striking
(though perhaps not more frequent) examples of extreme limitation of range
among birds than among mammals. Of the former phenomenon perhaps the most
remarkable case is that afforded by the osprey or fishing-hawk, which
ranges over the greater portion of all the continents, as far as Brazil,
South Africa, the Malay Islands, and Tasmania. The barn owl (_Strix
flammea_) has nearly as wide a range, but in this case there is more
diversity of opinion as to the specific difference of many of the forms
inhabiting remote countries, some of which seem undoubtedly to be distinct.
Among passerine birds the raven has probably the widest range, extending
from the arctic regions to Texas and New Mexico in America, and to North
India and Lake Baikal in Asia; while the little northern willow-wren
(_Phylloscopus borealis_) ranges from arctic Norway across Asia to Alaska,
and southward to Ceylon, China, Borneo, and Timor.
Of very restricted continental ranges the best examples in Europe are, the
little blue magpie (_Cyanopica cooki_) confined to the central portions of
the Spanish peninsula; and the Italian sparrow found only in Italy and
Corsica. {16} In Asia, Palestine affords some examples of birds of very
restricted range--a beautiful sun-bird (_Nectarinea osea_) a peculiar
starling (_Amydrus tristramii_) and some others, being almost or quite
confined to the warmer portions of the valley of the Jordan. In the
Himalayas there are numbers of birds which have very restricted ranges, but
those of the Neilgherries are perhaps better known, several species of
laughing thrushes and some other birds being found only on the summits of
these mountains. The most wonderfully restricted ranges are, however, to be
found among the humming-birds of tropical America. The great volcanic peaks
of Chimborazo and Pichincha have each a peculiar species of humming-bird
confined to a belt just below the limits of perpetual snow, while the
extinct volcano of Chiriqui in Veragua has a species confined to its wooded
crater. One of the most strange and beautiful of the humming-birds
(_Loddigesia mirabilis_) was obtained once only, more than forty years ago,
near Chachapoyas in the Andes of northern Peru; and though Mr. Gould sent
many drawings of the bird to people visiting the district and for many
years offered a high reward for a specimen, no other has ever been seen![4]
The above details will sufficiently explain what is meant by the "specific
area" or range of a species. The very wide and very narrow ranges are
exceptional, the great majority of species both of mammals and birds
ranging over moderately wide areas, which present no striking contrasts in
climate and physical conditions. Thus a large proportion of European birds
range over the whole continent in an east and west direction, but
considerable numbers are restricted either to the northern or the southern
half. In Africa some species range over all the continent south of the
desert, while large numbers are restricted to the equatorial forests, or to
the upland plains. In North America, if we exclude the tropical and the
arctic portions, a considerable number of species range over all the
temperate parts of the continent, while still {17} more are restricted to
the east, the centre, or the west, respectively.
_Generic Areas._--Having thus obtained a tolerably clear idea of the main
facts as to the distribution of isolated species, let us now consider those
collections of closely-allied species termed genera. What a genus is will
be sufficiently understood by a few illustrations. All the different kinds
of dogs, jackals, and wolves belong to the dog genus, Canis; the tiger,
lion, leopard, jaguar, and the wild cats, to the cat genus, Felis; the
blackbird, song-thrush, missel-thrush, fieldfare, and many others to the
thrush genus, Turdus; the crow, rook, raven, and jackdaw, to the crow
genus, Corvus; but the magpie belongs to another, though closely-allied
genus, Pica, distinguished by the different form and proportions of its
wings and tail from all the species of the crow genus. The number of
species in a genus varies greatly, from one up to several hundreds. The
giraffe, the glutton, the walrus, the bearded reedling, the secretary-bird,
and many others, have no close allies, and each forms a genus by itself.
The beaver genus, Castor, and the camel genus, Camelus, each consist of two
species. On the other hand, the deer genus, Cervus has forty species; the
mouse and rat genus, Mus more than a hundred species; and there is about
the same number of the thrush genus; while among the lower classes of
animals genera are often very extensive, the fine genus Papilio, or
swallow-tailed butterflies, containing more than four hundred species; and
Cicindela, which includes our native tiger beetles, has about the same
number. Many genera of shells are very extensive, and one of them--the
genus Helix, including the commonest snails, and ranging all over the
world--is probably the most extensive in the animal kingdom, numbering
about two thousand described species.[5]
_Separate and Overlapping Areas._--The species of a genus are distributed
in two ways. Either they occupy distinct areas which do not touch each
other and are sometimes widely separated, or they touch and occasionally
overlap {18} each other, each species occupying an area of its own which
rarely coincides exactly with that of any other species of the same genus.
In some cases, when a river, a mountain-chain, or a change of conditions as
from pasture to desert or forest, determines the range of species, the
areas of two species of the same genus may just meet, one beginning where
the other ends; but this is comparatively rare. It occurs, however, in the
Amazon valley, where several species of monkeys, birds, and insects come up
to the south bank of the river but do not pass it, while allied species
come to the north bank, which in like manner forms their boundary. As
examples we may mention that one of the Saki monkeys (_Pithecia monachus?_)
comes up to the south bank of the Upper Amazon, while immediately we cross
over to the north bank we find another species (_Pithecia rufibarbata?_).
Among birds we have the green jacamar (_Galbula viridis_), abundant on the
north bank of the Lower Amazon, while on the south bank we have two allied
species (_Galbula rufoviridis_ and _G. cyaneicollis_); and among insects we
have at Santarem on the south bank of the Amazon, the beautiful blue
butterfly, _Callithea sapphira_, while almost opposite to it, at
Monte-alegre, an allied species, _Callithea Leprieuri_ is alone found.
Perhaps the most interesting and best known case of a series of allied
species, whose ranges are separate but conterminous, is that of the
beautiful South American wading birds, called trumpeters, and forming the
genus Psophia. There are five species, all found in the Amazon valley, but
each limited to a well-marked district bounded by great rivers. On the
north bank of the Amazon there are two species, one in its lower valley
extending up to the Rio Negro; and the other in the central part of the
valley beyond that river; while to the south of the Amazon there are three,
one above the Madeira, one below it, and a third near Para, probably
separated from the last by the Tocantins river.
Overlapping areas among the species of a genus is a more common phenomenon,
and is almost universal where these species are numerous in the same
continent. It is, however, exceedingly irregular, so that we often find one
{19} species extending over a considerable portion of the area occupied by
the genus and including the entire areas of some of the other species. So
little has been done to work out accurately the limits of species that it
is very difficult to give examples. One of the best is to be found in the
genus _Dendroeca_, a group of American wood-warblers. These little birds
all migrate in the winter into the tropical regions, but in the summer they
come north, each having its particular range. Thus, _D. dominica_ comes as
far as the middle Eastern States, _D. coerulea_ keeps west of the
Alleghanies, _D. discolor_ comes to Michigan and New England; four other
species go farther north in Canada, while several extend to the borders of
the Arctic zone.
_The Species of Tits as Illustrating Areas of Distribution._--In our own
hemisphere the overlapping of allied species may be well illustrated by the
various kinds of titmice, constituting the genus Parus, several of which
are among our best known English birds. The great titmouse (_Parus major_)
has the widest range of all, extending from the Arctic circle to Algeria,
Palestine, and Persia, and from Ireland right across Siberia to the Ochotsk
sea, probably following the great northern forest belt. It does not extend
into China and Japan, where distinct species are found. Next in extent of
range is the coal tit (_Parus ater_) which inhabits all Europe from the
Mediterranean to about 64° N. latitude, in Asia Minor to the Lebanon and
Caucasus, and across Siberia to Amoorland and Japan. The marsh tit (_Parus
palustris_) inhabits temperate and south Europe from 61° N. latitude in
Norway to Poland and South-west Russia, and in the south from Spain to Asia
Minor. Closely allied to this--of which it is probably only a variety or
sub-species--is the northern marsh tit (_Parus borealis_), which overlaps
the last in Norway and Sweden, and also in South Russia and the Alps, but
extends further north into Lapland and North Russia, and thence probably in
a south-easterly direction across Central Asia to North China. Yet another
closely-allied species (_Parus camtschatkensis_) ranges from North-eastern
Russia across Northern Siberia to Lake Baikal and to Hakodadi in Japan,
thus overlapping _Parus borealis_ in the {20} western portion of its area.
Our little favourite, the blue tit (_Parus coeruleus_) ranges over all
Europe from the Arctic circle to the Mediterranean, and on to Asia Minor
and Persia, but does not seem to pass beyond the Ural mountains. Its lovely
eastern ally the azure tit (_Parus cyaneus_) overlaps the range of _P.
coeruleus_ in Western Europe as far as St. Petersburg and Austria, rarely
straggling to Denmark, while it stretches all across Central Asia between
the latitudes 35° and 56° N. as far as the Amoor valley. Besides these
wide-ranging species there are several others which are more restricted.
_Parus teneriffæ_, a beautiful dark blue form of our blue tit, inhabits
North-west Africa and the Canaries; _Parus ledouci_, closely allied to our
coal tit, is found only in Algeria; _Parus lugubris_, allied to the marsh
tit, is confined to South-east Europe and Asia Minor, from Hungary and
South Russia to Palestine; and _Parus cinctus_, another allied form, is
confined to the extreme north in Lapland, Finland, and perhaps Northern
Russia and Siberia. Another beautiful little bird, the crested titmouse
(_Parus cristatus_) is sometimes placed in a separate genus. It inhabits
nearly all Central and South Europe, wherever there are pine forests, from
64° N. latitude to Austria and North Italy, and in the west to Spain and
Gibraltar, while in the east it does not pass the Urals and the Caucasus
range. Its nearest allies are in the high Himalayas.
These are all the European tits, but there are many others inhabiting Asia,
Africa, and North America; so that the genus Parus has a very wide range,
in Asia to Ceylon and the Malay Islands, in Africa to the Cape, and in
North America to the highlands of Mexico.
_The Distribution of the Species of Jays._--Owing to the very wide range of
several of the tits, the uncertainty of the specific distinction of others,
and the difficulty in many cases of ascertaining their actual distribution,
it has not been found practicable to illustrate this genus by means of a
map. For this purpose we have chosen the genus Garrulus or the jays, in
which the species are less numerous, the specific areas less extensive, and
the species generally better defined; while being large and handsome {21}
birds they are sure to have been collected, or at least noticed, wherever
they occur. There are, so far as yet known, twelve species of true jays,
occupying an area extending from Western Europe to Eastern Asia and Japan,
and nowhere passing the Arctic circle to the north, or the tropic of Cancer
to the south, so that they constitute one of the most typical of the
Palæarctic[6] genera. The following are the species, beginning with the
most westerly and proceeding towards the east. The numbers prefixed to each
species correspond to those on the coloured map which forms the
frontispiece to this volume.
1. _Garrulus glandarius._--The common jay, inhabits the British Isles and
all Europe except the extreme north, extending also into North Africa,
where it has been observed in many parts of Algeria. It occurs near
Constantinople, but apparently not in Asia Minor; and in Russia, up to, but
not beyond, the Urals. The jays being woodland birds are not found in open
plains or barren uplands, and their distribution is hence by no means
uniform within the area they actually occupy.
2. _Garrulus cervicalis._--The Algerian jay, is a very distinct species
inhabiting a limited area in North Africa, and found in some places along
with the common species.
3. _Garrulus krynicki._--The black-headed jay, is closely allied to the
common species, but quite distinct, inhabiting a comparatively small area
in South-eastern Europe, and Western Asia.
4. _Garrulus atricapillus._--The Syrian jay, is very closely allied to the
last, and inhabits an adjoining area in Syria, Palestine, and Southern
Persia.
5. _Garrulus hyrcanus._--The Persian jay, is a small species allied to our
jay and only known from the Elburz Mountains in the north of Persia.
6. _Garrulus brandti._--Brandt's jay, is a very distinct species, having an
extensive range across Asia from the Ural Mountains to North China,
Mandchuria, and the northern island of Japan, and also crossing the Urals
into {22} Russia where it has been found as far west as Kazan in districts
where the common jay also occurs.
7. _Garrulus lanceolatus._--The black-throated jay, is a very distinct form
known only from the North-western Himalayas and Nepal, common about Simla,
and extending into Cashmere beyond the range of the next species.
8. _Garrulus bispecularis._--The Himalayan jay is also very distinct,
having the head coloured like the back, and not striped as in all the
western species. It inhabits the Himalayas east of Cashmere, but is more
abundant in the western than the eastern division, though according to the
Abbé David it reaches Moupin in East Thibet.
9. _Garrulus sinensis._--The Chinese jay, is very closely allied to the
Himalayan, of which it is sometimes classed as a sub-species. It seems to
be found in all the southern mountains of China, from Foochow on the east
to Sze-chuen and East Thibet on the west, as it is recorded from Moupin by
the Abbé David as well as the Himalayan bird--a tolerable proof that it is
a distinct form.
10. _Garrulus taivanus._--The Formosan jay is a very close ally of the
preceding, confined to the island of Formosa.
11. _Garrulus japonicus._--The Japanese jay is nearly allied to our common
British species, being somewhat smaller and less brightly coloured, and
with black orbits; yet these are the most widely separated species of the
genus. According to Mr. Seebohm this species is equally allied to the
Chinese and Siberian jays.
In the accompanying map (see frontispiece) we have laid down the
distribution of each species so far as it can be ascertained from the works
of Sharpe and Dresser for Europe, Jerdon for India, Swinhoe for China, and
Mr. Seebohm's recent work for Japan. There is, however, much uncertainty in
many places, and gaps have to be filled up conjecturally, while such a
large part of Asia is still very imperfectly explored, that considerable
modifications may have to be made when the country becomes more accurately
known. But though details may be modified we can hardly suppose that the
great features of the several specific areas, or their relations to each
other {23} will be much affected; and these are what we have chiefly to
consider as bearing on the questions here discussed.
The first thing that strikes us on looking at the map, is, the small amount
of overlapping of the several areas, and the isolation of many of the
species; while the next most striking feature is the manner in which the
Asiatic species almost surround a vast area in which no jays are found. The
only species with large areas, are the European _G. glandarius_ and the
Asiatic _G. Brandti_. The former has three species overlapping it--in
Algeria, in South-eastern and North-eastern Europe respectively. The Syrian
jay (No. 4), is not known to occur anywhere with the black-headed jay (No.
3), and perhaps the two areas do not meet. The Persian jay (No. 5), is
quite isolated. The Himalayan and Chinese jays (Nos. 7, 8, and 9) form a
group which are isolated from the rest of the genus; while the Japanese jay
(No. 11), is also completely isolated as regards the European jays to which
it is nearly allied. These peculiarities of distribution are no doubt in
part dependent on the habits of the jays, which live only in well-wooded
districts, among deciduous trees, and are essentially non-migratory in
their habits, though sometimes moving southwards in winter. This will
explain their absence from the vast desert area of Central Asia, but it
will not account for the gap between the North and South Chinese species,
nor for the absence of jays from the wooded hills of Turkestan, where Mr.
N. A. Severtzoff collected assiduously, obtaining 384 species of birds but
no jay. These peculiarities, and the fact that jays are never very abundant
anywhere, seem to indicate that the genus is now a decaying one, and that
it has at no very distant epoch occupied a larger and more continuous area,
such as that of the genus Parus at the present day.
_Discontinuous generic Areas._--It is not very easy to find good examples
of genera whose species occupy two or more quite disconnected areas, for
though such cases may not be rare, we are seldom in a position to mark out
the limits of the several species with sufficient accuracy. The best and
most remarkable case among European birds is {24} that of the blue magpies,
forming the genus Cyanopica. One species (_C. cooki_) is confined (as
already stated) to the wooded and mountainous districts of Spain and
Portugal, while the only other species of the genus (_C. cyanus_) is found
far away in North-eastern Asia and Japan, so that the two species are
separated by about 5,000 miles of continuous land. Another case is that of
the curious little water-moles forming the genus Mygale, one species _M.
muscovitica_, being found only on the banks of the Volga and Don in
South-eastern Russia, while the other, _M. pyrenaica_, is confined to
streams on the northern side of the Pyrenees. In tropical America there are
four different kinds of bell-birds belonging to the genus Chasmorhynchus,
each of which appears to inhabit a restricted area completely separated
from the others. The most northerly is _C. tricarunculatus_ of Costa Rica
and Veragua, a brown bird with a white head and three long caruncles
growing upwards at the base of the beak. Next comes _C. variegatus_, in
Venezuela, a white bird with a brown head and numerous caruncles on the
throat, perhaps conterminous with the last; in Guiana, extending to near
the mouth of the Rio Negro, we have _C. niveus_, the bell-bird described by
Waterton, which is pure white, with a single long fleshy caruncle at the
base of the beak; the last species, _C. nudicollis_, inhabits South-east
Brazil, and is also white, but with black stripes over the eyes, and with a
naked throat. These birds are about the size of thrushes, and are all
remarkable for their loud, ringing notes, like a bell or a blow on an
anvil, as well as for their peculiar colours. They are therefore known to
the native Indians wherever they exist, and we may be the more sure that
they do not spread over the intervening areas where they have never been
found, and where the natives know nothing of them.
A good example of isolated species of a group nearer home, is afforded by
the snow-partridges of the genus Tetraogallus. One species inhabits the
Caucasus range and nowhere else, keeping to the higher slopes from 6,000 to
11,000 feet above the sea, and accompanying the ibex in its wanderings, as
both feed on the same plants. Another {25} has a wider range in Asia Minor
and Persia, from the Taurus mountains to the South-east corner of the
Caspian Sea; a third species inhabits the Western Himalayas, between the
forests and perpetual snow, extending eastwards to Nepal; while a fourth is
found on the north side of the mountains in Thibet, and the ranges of these
two perhaps overlap; the last species inhabit the Altai mountains, and like
the two first appears to be completely separated from all its allies.
There are some few still more extraordinary cases in which the species of
one genus are separated in remote continents or islands. The most striking
of these is that of the tapirs, forming the genus Tapirus, of which there
are two or three species in South America, and one very distinct species in
Malacca and Borneo, separated by nearly half the circumference of the
globe. Another example among quadrupeds is a peculiar genus of moles named
Urotrichus, of which one species inhabits Japan and the other British
Columbia. The cuckoo-like honey-guides, forming the genus Indicator, are
tolerably abundant in tropical Africa, but there are two outlying species,
one in the Eastern Himalaya mountains, the other in Borneo, both very rare,
and recently an allied species has been found in the Malay peninsula. The
beautiful blue and green thrush-tits forming the genus Cochoa, have two
species in the Eastern Himalayas and Eastern China, while the third is
confined to Java; the curious genus Eupetes, supposed to be allied to the
dippers, has one species in Sumatra and Malacca, while four other species
are found two thousand miles distant in New Guinea; lastly, the lovely
ground-thrushes of the genus Pitta, range from Hindostan to Australia,
while a single species, far removed from all its near allies, inhabits West
Africa.
_Peculiarities of Generic, and Family Distribution._--The examples now
given sufficiently illustrate the mode in which the several species of a
genus are distributed. We have next to consider genera as the component
parts of families, and families of orders, from the same point of view.
{26}
All the phenomena presented by the species of a genus are reproduced by the
genera of a family, and often in a more marked degree. Owing, however, to
the extreme restriction of genera by modern naturalists, there are not many
among the higher animals that have a world-wide distribution. Among the
mammalia there is no such thing as a truly cosmopolitan genus. This is
owing to the absence of all the higher orders except the mice from
Australia, while the genus Mus, which occurs there, is represented by a
distinct group, Hesperomys, in America. If, however, we consider the
Australian dingo as a native animal we might class the genus Canis as
cosmopolite, but the wild dogs of South America are now formed into
separate genera by some naturalists. Many genera, however, range over three
or more continents, as Felis (the cat genus) absent only from Australia;
Ursus (the bear genus) absent from Australia and tropical Africa; Cervus
(the deer genus) with nearly the same range; and Sciurus (the squirrel
genus) found in all the continents but Australia. Among birds Turdus, the
thrush, and Hirundo, the swallow genus, are the only perching birds which
are truly cosmopolites; but there are many genera of hawks, owls, wading
and swimming birds, which have a world-wide range.
As a great many genera consist of single species there is no lack of cases
of great restriction, such as the curious lemur called the "potto," which
is found only at Sierra Leone, and forms the genus Perodicticus; the true
chinchillas found only in the Andes of Peru and Chili south of 9° S. lat.
and between 8,000 and 12,000 feet elevation; several genera of finches each
confined to limited portions of the higher Himalayas, the blood-pheasants
(Ithaginis) found only above 10,000 feet from Nepal to East Thibet; the
bald-headed starling of the Philippine islands, the lyre-birds of East
Australia, and a host of others.
It is among the different genera of the same family that we meet with the
most striking examples of discontinuity, although these genera are often as
unmistakably allied as are the species of a genus; and it is these cases
that furnish the most interesting problems to the student of distribution.
{27} We must therefore consider them somewhat more fully.
Among mammalia the most remarkable of these divided families is that of the
camels, of which one genus Camelus, the true camels, comprising the camel
and dromedary, is confined to Asia, while the other Auchenia, comprising
the llamas and alpacas, is found only in the high Andes and in the plains
of temperate South America. Not only are these two genera separated by the
Atlantic and by the greater part of the land of two continents, but one is
confined to the Northern and the other to the Southern hemisphere. The next
case, though not so well known, is equally remarkable; it is that of the
Centetidæ, a family of small insectivorous animals, which are wholly
confined to Madagascar and the large West Indian islands Cuba and Hayti,
the former containing five genera and the latter a single genus with a
species in each island. Here again we have the whole continent of Africa as
well as the Atlantic ocean separating allied genera. Two families (or
subfamilies) of rat-like animals, Octodontidæ and Echimyidæ, are also
divided by the Atlantic. Both are mainly South American, but the former has
two genera in North and East Africa, and the latter also two in South and
West Africa. Two other families of mammalia, though confined to the Eastern
hemisphere, are yet markedly discontinuous. The Tragulidæ are small
deer-like animals, known as chevrotains or mouse-deer, abundant in India
and the larger Malay islands and forming the genus Tragulus; while another
genus, Hyomoschus, is confined to West Africa. The other family is the
Simiidæ or anthropoid apes, in which we have the gorilla and chimpanzee
confined to West and Central Africa, while the allied orangs are found only
in the islands of Sumatra and Borneo, the two groups being separated by a
greater space than the Echimyidæ and other rodents of Africa and South
America.
Among birds and reptiles we have several families, which, from being found
only within the tropics of Asia, Africa, and America, have been termed
tropicopolitan groups. The Megalæmidæ or barbets are gaily coloured {28}
fruit-eating birds, almost equally abundant in tropical Asia and Africa,
but less plentiful in America, where they probably suffer from the
competition of the larger sized toucans. The genera of each country are
distinct, but all are closely allied, the family being a very natural one.
The trogons form a family of very gorgeously coloured and remarkable
insect-eating birds very abundant in tropical America, less so in Asia, and
with a single genus of two species in Africa.
Among reptiles we have two families of snakes--the Dendrophidæ or
tree-snakes, and the Dryiophidæ or green whip-snakes--which are also found
in the three tropical regions of Asia, Africa, and America, but in these
cases even some of the genera are common to Asia and Africa, or to Africa
and America. The lizards forming the family Amphisbænidæ are divided
between tropical Africa and America, a few species only occurring in the
southern portion of the adjacent temperate regions; while even the
peculiarly American family of the iguanas is represented by two genera in
Madagascar, and one in the Fiji and Friendly Islands. Passing on to the
Amphibians the worm-like Cæciliadæ are tropicopolitan, as are also the
toads of the family Engystomatidæ. Insects also furnish some analogous
cases, three genera of Cicindelidæ, (Pogonostoma, Ctenostoma, and
Peridexia) showing a decided connection between this family in South
America and Madagascar; while the beautiful family of diurnal moths,
Uraniidæ, is confined to the same two countries. A somewhat similar but
better known illustration is afforded by the two genera of ostriches, one
confined to Africa and Arabia, the other to the plains of temperate South
America.
_General features of Overlapping and Discontinuous Areas._--These numerous
examples of discontinuous genera and families form an important section of
the facts of animal dispersal which any true theory must satisfactorily
account for. In greater or less prominence they are to be found all over
the world, and in every group of animals, and they grade imperceptibly into
those cases of conterminous and overlapping areas which we have seen to
{29} prevail in most extensive groups of species, and which are perhaps
even more common in those large families which consist of many closely
allied genera. A sufficient proof of the overlapping of generic areas is
the occurrence of a number of genera of the same family together. Thus in
France or Italy about twenty genera of warblers (Sylviadæ) are found, and
as each of the thirty-three genera of this family inhabiting temperate
Europe and Asia has a different area, a great number must here overlap. So,
in most parts of Africa, at least ten or twelve genera of antelopes may be
found, and in South America a large proportion of the genera of monkeys of
the family Cebidæ occur in many districts; and still more is this the case
with the larger bird families, such as the tanagers, the tyrant shrikes, or
the tree-creepers, so that there is in all these extensive families no
genus whose area does not overlap that of many others. Then among the
moderately extensive families we find a few instances of one or two genera
isolated from the rest, as the spectacled bear, Tremarctos, found only in
Chili, while the remainder of the family extends from Europe and Asia over
North America to the Mountains of Mexico, but no further south; the Bovidæ,
or hollow-horned ruminants, which have a few isolated genera in the Rocky
Mountains and the islands of Sumatra and Celebes; and from these we pass on
to the cases of wide separation already given.
_Restricted Areas of Families._--As families sometimes consist of single
genera and even single species, they often present examples of very
restricted range; but what is perhaps more interesting are those cases in
which a family contains numerous species and sometimes even several genera,
and yet is confined to a narrow area. Such are the golden moles
(Chrysochloridæ) consisting of two genera and three species, confined to
extratropical South Africa; the hill-tits (Liotrichidæ), a family of
numerous genera and species mainly confined to the Himalayas, but with a
few straggling species in the Malay countries and the mountains of China;
the Pteroptochidæ, large wren-like birds, consisting of eight genera and
nineteen species, almost entirely confined to temperate South America and
{30} the Andes; and the birds-of-paradise, consisting of nineteen or twenty
genera and about thirty-five species, almost all inhabitants of New Guinea
and the immediately surrounding islands, while a few, doubtfully belonging
to the family, extend to East Australia. Among reptiles the most striking
case of restriction is that of the rough-tailed burrowing snakes
(Uropeltidæ), the five genera and eighteen species being strictly confined
to Ceylon and the southern parts of the Indian Peninsula.
_The Distribution of Orders._--When we pass to the larger groups, termed
orders, comprising several families, we find comparatively few cases of
restriction and many of worldwide distribution; and the families of which
they are composed are strictly comparable to the genera of which families
are composed, inasmuch as they present examples of overlapping, or
conterminous, or isolated areas, though the latter are comparatively rare.
Among mammalia the Insectivora offer the best example of an order, several
of whose families inhabit areas more or less isolated from the rest; while
the Marsupialia have six families in Australia, and one, the opossums, far
off in America.
Perhaps, more important is the limitation of some entire orders to certain
well-defined portions of the globe. Thus the Proboscidea, comprising the
single family and genus of the elephants, and the Hyracoidea, that of the
Hyrax or Syrian coney, are confined to parts of Africa and Asia; the
Marsupials to Australia and America; and the Monotremata, the lowest of all
mammals--comprising the duck-billed Platypus and the spiny Echidna, to
Australia and New Guinea. Among birds the Struthiones or ostrich tribe are
almost confined to the three Southern continents, South America, Africa and
Australia; and among Amphibia the tailed Batrachia--the newts and
salamanders--are similarly restricted to the northern hemisphere.
These various facts will receive their explanation in a future chapter.
* * * * *
[Illustration]
{31}
CHAPTER III
CLASSIFICATION OF THE FACTS OF DISTRIBUTION.--ZOOLOGICAL REGIONS
The Geographical Divisions of the Globe do not correspond to Zoological
divisions--The range of British Mammals as indicating a Zoological
Region--Range of East Asian and North African Mammals--The Range of
British Birds--Range of East Asian Birds--The limits of the Palæarctic
Region--Characteristic features of the Palæarctic Region--Definition
and characteristic groups of the Ethiopian Region--Of the Oriental
Region--Of the Australian Region--Of the Nearctic Region--Of the
Neotropical Region--Comparison of Zoological Regions with the
Geographical Divisions of the Globe.
Having now obtained some notion of how animals are dispersed over the
earth's surface, whether as single species or as collected in those groups
termed genera, families, and orders, it will be well, before proceeding
further, to understand something of the classification of the facts we have
been considering, and some of the simpler conclusions these facts lead to.
We have hitherto described the distribution of species and groups of
animals by means of the great geographical divisions of the globe in common
use; but it will have been observed that in hardly any case do these define
the limits of anything beyond species, and very seldom, or perhaps never,
even those accurately. Thus the term "Europe" will not give, with any
approach to accuracy, the range of any one genus of mammals or birds, and
{32} perhaps not that of half-a-dozen species. Either they range into
Siberia, or Asia Minor, or Palestine, or North Africa; and this seems to be
always the case when their area of distribution occupies a large portion of
Europe. There are, indeed, a few species limited to Central or Western or
Southern Europe, and these are almost the only cases in which we can use
the word for zoological purposes without having to add to it some portion
of another continent. Still less useful is the term Asia for this purpose,
since there is probably no single animal or group confined to Asia which is
not also more or less nearly confined to the tropical or the temperate
portion of it. The only exception is perhaps the tiger, which may really be
called an Asiatic animal, as it occupies nearly two-thirds of the
continent; but this is an unique example, while the cases in which Asiatic
animals and groups are strictly limited to a portion of Asia, or extend
also into Europe or into Africa or to the Malay Islands, are exceedingly
numerous. So, in Africa, very few groups of animals range over the whole of
it without going beyond either into Europe or Asia Minor or Arabia, while
those which are purely African are generally confined to the portion south
of the tropic of Cancer. Australia and America are terms which better serve
the purpose of the zoologist. The former defines the limit of many
important groups of animals; and the same may be said of the latter, but
the division into North and South America introduces difficulties, for
almost all the groups especially characteristic of South America are found
also beyond the isthmus of Panama, in what is geographically part of the
northern continent.
It being thus clear that the old and popular divisions of the globe are
very inconvenient when used to describe the range of animals, we are
naturally led to ask whether any other division can be made which will be
more useful, and will serve to group together a considerable number of the
facts we have to deal with. Such a division was made by Mr. P. L. Sclater
more than twenty years ago, and it has, with some slight modifications,
come into pretty general use in this country, and to some extent also {33}
abroad; we shall therefore proceed to explain its nature and the principles
on which it is established, as it will have to be often referred to in
future chapters of this work, and will take the place of the old
geographical divisions whose inconvenience has already been pointed out.
The primary zoological divisions of the globe are called "regions," and we
will begin by ascertaining the limits of the region of which our own
country forms a part.
_The Range of British Mammals as indicating a Zoological Region._--We will
first take our commonest wild mammalia and see how far they extend, and
especially whether they are confined to Europe or range over parts of other
continents:
1. Wild Cat | Europe | N. Africa | Siberia, Afghanistan.
2. Fox | Europe | N. Africa | Central Asia to Amoor.
3. Weasel | Europe | N. Africa | Central Asia to Amoor.
4. Otter | Europe | N. Africa | Siberia.
5. Badger | Europe | N. Africa | Central Asia to Amoor.
6. Stag | Europe | N. Africa | Central Asia to Amoor.
7. Hedgehog | Europe | -- | Central Asia to Amoor.
8. Mole | Europe | -- | Central Asia.
9. Squirrel | Europe | -- | Central Asia to Amoor.
10. Dormouse | Europe | -- | --
11. Water-rat | Europe | -- | Central Asia to Amoor.
12. Hare | Europe | -- | W. Siberia, Persia.
13. Rabbit | Europe | N. Africa | --
We thus see that out of thirteen of our commonest quadrupeds only one is
confined to Europe, while seven are found also in Northern Africa, and
eleven range into Siberia, most of them stretching quite across Asia to the
valley of the Amoor on the extreme eastern side of that continent. Two of
the above-named British species, the fox and weasel, are also inhabitants
of the New World, being as common in the northern parts of North America as
they are with us; but with these exceptions the entire range of our
commoner species is given, and they clearly show that all Northern Asia and
Northern Africa must be added to Europe in order to form the region which
they collectively inhabit. If now we go into Central Europe and take, for
example, the quadrupeds of Germany, we shall find that these too, although
much more numerous, are confined to the same limits, except that some of
the {34} more arctic kinds, as already stated, extend into the colder
regions of North America.
_Range of East Asian and North African Mammals._--Let us now pass to the
other side of the great northern continent, and examine the list of the
quadrupeds of Amoorland, in the same latitude as Germany. We find that
there are forty-four terrestrial species (omitting the bats, the seals, and
other marine animals), and of these no less than twenty-six are identical
with European species, and twelve or thirteen more are closely allied
representatives, leaving only five or six which are peculiarly Asiatic. We
can hardly have a more convincing proof of the essential oneness of the
mammalia of Europe and Northern Asia.
In Northern Africa we do not find so many European species (though even
here they are very numerous) because a considerable number of West Asiatic
and desert forms occur. Having, however, shown that Europe and Western Asia
have almost identical animals, we may treat all these as really European,
and we shall then be able to compare the quadrupeds of North Africa with
those of Europe and West Asia. Taking those of Algeria as the best known,
we find that there are thirty-three species identical with those of Europe
and West Asia, while twenty-four more, though distinct, are closely allied,
belonging to the same genera; thus making a total of fifty-seven of
European type. On the other hand, we have seven species which are either
identical with species of tropical Africa or allied to them, and six more
which are especially characteristic of the African and Asiatic deserts
which form a kind of neutral zone between the temperate and tropical
regions. If now we consider that Algeria and the adjacent countries
bordering the Mediterranean form part of Africa, while they are separated
from Europe by a wide sea and are only connected with Asia by a narrow
isthmus, we cannot but feel surprised at the wonderful preponderance of the
European and West Asiatic elements in the mammalia which inhabit the
district.
_The Range of British Birds._--As it is very important that no doubt should
exist as to the limits of the zoological {35} region of which Europe forms
a part, we will now examine the birds, in order to see how far they agree
in their distribution with the mammalia. Of late years great attention has
been paid to the distribution of European and Asiatic birds, many
ornithologists having travelled in North Africa, in Palestine, in Asia
Minor, in Persia, in Siberia, in Mongolia, and in China; so that we are now
able to determine the exact ranges of many species in a manner that would
have been impossible a few years ago. These ranges are given for all
British species in the new edition of Yarrell's _History of British Birds_
edited by Professor Newton, while those of all European birds are given in
still more detail in Mr. Dresser's beautiful work on the birds of Europe.
In order to confine our examination within reasonable limits, and at the
same time give it the interest attaching to familiar objects, we will take
the whole series of British Passeres or perching birds given in Professor
Newton's work (118 in number) and arrange them in series according to the
extent of their range. These include not only the permanent residents and
regular migrants to our country, but also those which occasionally straggle
here, so that it really comprises a large proportion of all European birds.
I. BRITISH BIRDS WHICH EXTEND TO NORTH AFRICA AND CENTRAL OR NORTH-EAST
ASIA.
1. _Lanius collurio_ Red backed Shrike (also all Africa).
2. _Oriolus Galbula_ Golden Oriole (also all Africa).
3. _Turdus musicus_ Song-Thrush.
4. ,, _iliacus_ Red-wing.
5. ,, _pilaris_ Fieldfare.
6. _Monticola saxatilis_ Blue rock Thrush.
7. _Ruticilla suecica_ Bluethroat (also India in winter).
8. _Saxicola rubicola_ Stonechat (also India in winter).
9. ,, _oenanthe_ Wheatear (also N. America).
10. _Acrocephalus arundinaceus_ Great Reed-Warbler.
11. _Sylvia curruca_ Lesser Whitethroat.
12. _Parus major_ Great Titmouse.
13. _Motacilla sulphurea_ Grey Wagtail (also China and Malaya).
14. ,, _raii_ Yellow Wagtail.
15. _Anthus trivialis_ Tree Pipit.
16. ,, _spiloletta_ Water Pipit.
17. ,, _campestris_ Tawny Pipit.
18. _Alauda arvensis_ Skylark.
19. ,, _cristata_ Crested Lark.
{36}
20. _Emberiza schoeniclus_ Reed Bunting.
21. ,, _citrinella_ Yellow-hammer.
22. _Fringilla montifringilla_ Brambling.
23. _Passer montanus_ Tree Sparrow (also S. Asia).
24. ,, _domesticus_ House Sparrow.
25. _Coccothraustes vulgaris_ Hawfinch.
26. _Carduelis spinus_ Siskin (also China).
27. _Loxia curvirostra_ Crossbill.
28. _Sturnus vulgaris_ Starling.
29. _Pyrrhocorax graculus_ Chough.
30. _Corvus corone_ Crow.
31. _Hirundo rustica_ Swallow (all Africa and Asia).
32. _Cotyle riparia_ Sand Martin (also India and N. America).
II. BRITISH BIRDS WHICH RANGE TO CENTRAL OR NORTH-EAST ASIA.
1. _Lanius excubitor_ Great Grey Shrike.
2. _Turdus varius_ White's Thrush (also to Japan).
3. ,, _atrigularis_ Black-throated Thrush.
4. _Acrocephalus nævius_ Grasshopper Warbler.
5. _Phylloscopus superciliosus_ Yellow-browed Warbler.
6. _Certhia familiaris_ Tree-creeper.
7. _Parus coeruleus_ Blue Titmouse.
8. ,, _ater_ Coal Titmouse.
9. ,, _palustris_ Marsh Titmouse.
10. _Acredula caudata_ Long-tailed Titmouse.
11. _Ampelis garrulus_ Wax-wing.
12. _Anthus richardi_ Richard's Pipit.
13. _Alauda alpestris_ Shore Lark (also N. America).
14. _Plectrophanes nivalis_ Snow-Bunting (also N. America).
15. ,, _lapponicus_ Lapland Bunting.
16. _Emberiza rustica_ Rustic Bunting (also China).
17. ,, _pusilla_ Little Bunting.
18. _Linota linaria_ Mealy Redpole (also N. America).
19. _Pyrrhula erythrina_ Scarlet Grosbeak (also N. India, China).
20. ,, _enucleator_ Pine Grosbeak (also N. America).
21. _Loxia bifasciata_ Two-barred Crossbill.
22. _Pastor roseus_ Rose-coloured Starling (also India).
23. _Corvus corax_ Raven (also N. America).
24. _Pica rustica_ Magpie.
25. _Nucifraga caryocatactes_ Nutcracker.
III. BRITISH BIRDS RANGING INTO N. AFRICA AND W. ASIA.
1. _Lanius minor_ Lesser Grey Shrike.
2. ,, _auriculatus_ Woodchat (also Tropical Africa).
3. _Muscicapa grisola_ Spotted Flycatcher (also E. and S.
Africa).
4. ,, _atricapilla_ Pied Flycatcher (also Central Africa).
5. Turdus _viscivorus_ Mistletoe-Thrush (N. India in winter).
6. ,, _merula_ Blackbird.
7. ,, _torquatus_ Ring Ouzel.
8. _Accentor modularis_ Hedge Sparrow.
9. _Erithacus rubecula_ Redbreast.
10. _Daulias luscinia_ Nightingale.
{37}
11. _Ruticilla phænicurus_ Redstart.
12. ,, _tithys_ Black Redstart.
13. _Saxicola rubetra_ Whinchat.
14. _Aëdon galactodes_ Rufous Warbler.
15. _Acrocephalus streperus_ Reed Warbler.
16. ,, _schænobenus_ Sedge Warbler.
17. _Melizophilus undatus_ Dartford Warbler.
18. _Sylvia rufa_ Greater Whitethroat.
19. ,, _salicaria_ Garden Warbler.
20. ,, _atricapilla_ Blackcap.
21. ,, _orphea_ Orphean Warbler.
22. _Phylloscopus sibilatrix_ Wood Wren.
23. ,, _trochilus_ Willow Wren.
24. ,, _collybita_ Chiffchaff.
25. _Regulus cristatus_ Golden-crested Wren.
26. ,, _ignicapillus_ Fire-crested Wren.
27. _Troglodytes parvulus_ Wren.
28. _Sitta cæsia_ Nuthatch.
29. _Motacilla alba_ White Wagtail (also W. Africa).
30. ,, _flava_ Blue-headed Wagtail.
31. _Anthus pratensis_ Meadow-Pipit.
32. _Alauda arborea_ Woodlark.
33. _Calandrella brachydactyla_ Short-toed Lark.
34. _Emberiza miliaria_ Common Bunting.
35. ,, _cirlus_ Cirl Bunting.
36. ,, _hortulana_ Ortolan.
37. _Fringilla coelebs_ Chaffinch.
38. _Coccothraustes chloris_ Greenfinch.
39. _Serinus hortulanus_ Serin.
40. _Carduelis elegans_ Goldfinch.
41. _Linota cannabina_ Linnet.
42. _Corvus monedula_ Jackdaw.
43. _Chelidon urbica_ House-Martin.
IV. BRITISH BIRDS RANGING TO NORTH AFRICA.
1. _Hypolais icterina_ Icterine Warbler.
2. _Acrocephalus aquaticus_ Aquatic Warbler.
3. ,, _luscinioides_ Savi's Warbler.
4. _Motacilla lugubris_ Pied Wagtail.
5. _Pyrrhula europæa_ Bullfinch.
6. _Garrulus glandarius_ Jay.
V. BRITISH BIRDS RANGING TO WEST ASIA ONLY.
1. _Accentor collaris_ Alpine Accentor.
2. _Muscicapa parva_ Red-breasted Flycatcher (to N. W.
India).
3. _Panurus biarmicus_ Bearded Titmouse.
4. _Melanocorypha sibirica_ White-winged Lark.
5. _Euspiza melanocephala_ Black-headed Bunting.
6. _Linota flavirostris_ Twite.
7. _Corvus frugilegus_ Rook.
VI. BRITISH BIRDS CONFINED TO EUROPE.
1. _Cinclus aquaticus_ Dipper (closely allied races inhabit
other parts of the Palæarctic Region).
2. _Parus cristatus_ Crested Titmouse.
{38}
3. _Anthus obscurus_ Rock Pipit.
4. _Linota rufescens_ Lesser Redpoll (closely allied races in
N. Asia and N. America).
5. _Loxia pityopsittacus_ Parrot Crossbill (a closely allied form
in N. Asia).
We find, that out of a total of 118 British Passeres there are:
32 species which range to North Africa and Central or East Asia.
25 species which range to Central or East Asia, but not to North
Africa.
43 species which range to North Africa and Western Asia.
6 species which range to North Africa, but not at all into Asia.
7 species which range to West Asia, but not to North Africa.
5 species which do not range out of Europe.
These figures agree essentially with those furnished by the mammalia, and
complete the demonstration that all the temperate portions of Asia and
North Africa must be added to Europe to form a natural zoological division
of the earth. We must also note how comparatively few of these overpass the
limits thus indicated; only seven species extending their range
occasionally into tropical or South Africa, eight into some parts of
tropical Asia, and six into arctic or temperate North America.
_Range of East Asian Birds._--To complete the evidence we only require to
know that the East Asiatic birds are as much like those of Europe, as we
have already shown to be the case when we take the point of departure from
our end of the continent. This does not follow necessarily, because it is
possible that a totally distinct North Asiatic fauna might there prevail;
and, although our birds go eastward to the remotest parts of Asia, their
birds might not come westward to Europe. The birds of Eastern Siberia have
been carefully studied by Russian naturalists and afford us the means of
making the required comparison. There are 151 species belonging to the
orders Passeres and Picariæ (the perching and climbing birds), and of these
no less than 77, or more than half, are absolutely identical {39} with
European species; 63 are peculiar to North Asia, but all except five or six
of these are allied to European forms; the remaining 11 species are
migrants from South-eastern Asia. The resemblance is therefore equally
close whichever extremity of the Euro-Asiatic continent we take as our
starting point, and is equally remarkable in birds as in mammalia. We have
now only to determine the limits of this, our first zoological region,
which has been termed the "Palæarctic" by Mr. Sclater, meaning the
"northern old-world" region--a name now well known to naturalists.
_The Limits of the Palæarctic Region._--The boundaries of this region, as
nearly as they can be ascertained, are shown on our general map at the
beginning of this chapter, but it will be evident on consideration, that,
except in a few places, its limits can only be approximately defined. On
the north, east, and west it extends to the ocean, and includes a number of
islands whose peculiarities will be pointed out in a subsequent chapter; so
that the southern boundary alone remains, but as this runs across the
entire continent from the Atlantic to the Pacific ocean, often traversing
little-known regions, we may perhaps never be able to determine it
accurately, even if it admits of such determination. In drawing the
boundary line across Africa we meet with our first difficulty. The
Euro-Asiatic animals undoubtedly extend to the northern borders of the
Sahara, while those of tropical Africa come up to its southern margin, the
desert itself forming a kind of sandy ocean between them. Some of the
species on either side penetrate and even cross the desert, but it is
impossible to balance these with any accuracy, and it has therefore been
thought best, as a mere matter of convenience, to consider the geographical
line of the tropic of Cancer to form the boundary. We are thus enabled to
define the Palæarctic region as including all north temperate Africa; and,
a similar intermingling of animal types occurring in Arabia, the same
boundary line is continued to the southern shore of the Persian Gulf.
Persia and Afghanistan undoubtedly belong to the Palæarctic region, and
Baluchistan should probably go with these. The boundary in the
north-western part of India is again difficult to determine, but it {40}
cannot be far one way or the other from the river Indus as far up as
Attock, opposite the mouth of the Cabool river. Here it will bend to the
south-east, passing a little south of Cashmeer, and along the southern
slopes of the Himalayas into East Thibet and China, at heights varying from
9,000 to 11,000 feet according to soil, aspect, and shelter. It may,
perhaps, be defined as extending to the upper belt of forests as far as
coniferous trees prevail; but the temperate and tropical faunas are here so
intermingled that to draw any exact parting line is impossible. The two
faunas are, however, very distinct. In and above the pine woods there are
abundance of warblers of northern genera, with wrens, numerous titmice, and
a great variety of buntings, grosbeaks, bullfinches and rosefinches, all
more or less nearly allied to the birds of Europe and Northern Asia; while
a little lower down we meet with a host of peculiar birds allied to those
of tropical Asia and the Malay Islands, but often of distinct genera. There
can be no doubt, therefore, of the existence here of a pretty sharp line of
demarkation between the temperate and tropical faunas, though this line
will be so irregular, owing to the complex system of valleys and ridges,
that in our present ignorance of much of the country it cannot be marked in
detail on any map.
Further east in China it is still more difficult to determine the limits of
the region, owing to the great intermixture of migrating birds; tropical
forms passing northwards in summer as far as the Amoor river, while the
northern forms visit every part of China in winter. From what we know,
however, of the distribution of some of the more typical northern and
southern species, we are able to fix the limits of the Palæarctic region a
little south of Shanghai on the east coast. Several tropical genera come as
far north as Ningpo or even Shanghai, but rarely beyond; while in Formosa
and Amoy tropical forms predominate. Such decidedly northern forms as
bullfinches and hawfinches are found at Shanghai; hence we may commence the
boundary line on the coast between Shanghai and Ningpo, but inland it
probably bends a little southward, and then northward to the mountains and
valleys of West {41} China and East Thibet in about 32° N. latitude; where,
at Moupin, a French missionary, Père David, made extensive collections
showing this district to be at the junction of the tropical and temperate
faunas. Japan, as a whole, is decidedly Palæarctic, although its extreme
southern portion, owing to its mild insular climate and evergreen
vegetation, gives shelter to a number of tropical forms.
_Characteristic Features of the Palæarctic Region._--Having thus
demonstrated the unity of the Palæarctic region by tracing out the
distribution of a large proportion of its mammalia and birds, it only
remains to show how far it is characterised by peculiar groups such as
genera and families, and to say a few words on the lower forms of life
which prevail in it.
Taking first the mammalia, we find this region distinguished by possessing
two peculiar genera of Talpidæ or moles, the family being confined to the
Palæarctic and Nearctic regions. The true hedgehogs (Erinaceus) are also
characteristic, being only found elsewhere in South Africa and in the
northern part of the Oriental region. Among Carnivora, the racoon-dog
(Nyctereutes) of North-eastern Asia, and the true badgers of the genus
Meles are peculiar, most other parts of the world possessing distinct
genera of badgers. It has six peculiar genera, or subgenera, of deer; seven
peculiar genera of Bovidæ, chiefly antelopes; while the entire group of
goats and sheep, comprising twenty-two species, is almost confined to it,
one species only occurring in the Rocky mountains of North America and
another in the Nilgiris of Southern India. Among the rodents there are nine
genera with twenty-seven species wholly confined to it, while several
others, as the hamsters, the dormice, and the pikas, have only a few
species elsewhere.
In birds there are a large number of peculiar genera of which we need
mention only a few of the more important, as the grass-hopper warblers
(Locustella) with seven species, the Accentors with twelve species, and
about a dozen other genera of warblers, including the robins; the bearded
titmouse and several allied genera; the long-tailed titmice forming the
genus Acredula; the magpies, choughs, and nut-crackers; a host of finches,
among which the bullfinches (Pyrrhula) and the buntings (Emberiza) are the
{42} most important. The true pheasants (Phasianus) are wholly Palæarctic,
except one species in Formosa, as are several genera of wading birds.
Though the reptiles of cold countries are few as compared with those of the
tropics, the Palæarctic region in its warmer portions has a considerable
number, and among these are many which are peculiar to it. Such are four
genera of snakes, seven of lizards, five of frogs and toads, and twelve of
newts and salamanders; while of fresh-water fishes there are about twenty
peculiar genera.[7] Among insects we may mention the elegant Apollo
butterflies of the Alps as forming a peculiar genus (Parnassius), only
found elsewhere in the Rocky Mountains of North America, while the
beautiful genus Thais of the south of Europe and Sericinus of North China
are equally remarkable. Among other insects we can only now refer to the
great family of Carabidæ, or predaceous ground-beetles, which are immensely
numerous in this region, there being about fifty peculiar genera; while the
large and handsome genus Carabus, with its allies Procerus and Procrustes,
containing nearly 300 species, is almost wholly confined to this region,
and would alone serve to distinguish it zoologically from all other parts
of the globe.
{43}
Having given so full an exposition of the facts which determine the extent
and boundaries of the Palæarctic region, there is less need of entering
into much detail as regards the other regions of the Eastern Hemisphere;
their boundaries being easily defined, while their forms of animal life are
well marked and strongly contrasted.
_Definition and Characteristic Groups of the Ethiopian Region._--The
Ethiopian region consists of all tropical and south Africa, to which are
appended the large island of Madagascar and the Mascarene Islands to the
east and north of it, though these differ materially from the continent,
and will have to be discussed in a separate chapter. For the present, then,
we will take Africa south of the tropic of Cancer, and consider how far its
animals are distinct from those of the Palæarctic region.
Taking first the mammalia, we find the following remarkable animals at once
separating it from the Palæarctic and every other region. The gorilla and
chimpanzee, the baboons, numerous lemurs, the spotted hyæna, the aard-wolf
and hyæna-dog, zebras, the hippopotamus, giraffe, and more than seventy
peculiar antelopes. Here we have a wonderful collection of large and
peculiar quadrupeds, but the Ethiopian region is also characterised by the
absence of others which are not only abundant in the Palæarctic region but
in many tropical regions as well. The most remarkable of these deficiencies
are the bears the deer and the wild oxen, all of which abound in the
tropical parts of Asia while bears and deer extend into both North and
South America. Besides the large and conspicuous animals mentioned above,
Africa possesses a number of completely isolated groups; such are the
potamogale, a curious otter-like water-shrew, discovered by Du Chaillu in
West Africa, so distinct as to constitute a new family, Potamogalidæ; the
goldenmoles, also forming a peculiar family, Chrysochloridæ; as do the
elephant-shrews, Macroscelididæ; the singular aard-varks, or earth-pigs,
forming a peculiar family of Edentata called Orycteropodidæ; while there
are numerous peculiar genera of monkeys, swine, civets, and rodents.
Among birds the most conspicuous and remarkable are, the great-billed
vulture-crows (Corvultur), the long-tailed {44} whydah finches (Vidua), the
curious ox-peckers (Buphaga), the splendid metallic starlings
(Lamprocolius), the handsome plantain-eaters (Musophaga), the
ground-hornbills (Bucorvus), the numerous guinea-fowls belonging to four
distinct genera, the serpent-eating secretary-bird (Serpentarius), the huge
boat-billed heron (Balæniceps), and the true ostriches. There are also
three quite peculiar African families, the Musophagidæ or plantain-eaters,
including the elegant crested touracos; the curious little finch-like
colies (Coliidæ), and the Irrisoridæ, insect-eating birds allied to the
hoopoes but with glossy metallic plumage and arboreal habits.
In reptiles, fishes, insects, and land-shells, Africa is very rich, and
possesses an immense number of peculiar forms. These are not sufficiently
familiar to require notice in a work of this character, but we may mention
a few as mere illustrations: the puff-adders, the most hideous of poisonous
snakes; the chameleons, the most remarkable of lizards; the
goliath-beetles, the largest and handsomest of the Cetoniidæ; and some of
the Achatinæ, which are the largest of all known land-shells.
_Definition and Characteristic Groups of the Oriental Region._--The
Oriental region comprises all Asia south of the Palæarctic limits, and
along with this the Malay Islands as far as the Philippines, Borneo, and
Java. It was called the Indian region by Mr. Sclater, but this term has
been objected to because the Indo-Chinese and Malayan districts are the
richest and most characteristic, while the peninsula of India is the
poorest portion of it. The name "Oriental" has therefore been adopted in my
work on _The Geographical Distribution of Animals_ as preferable to either
Malayan or Indo-Australian, both of which have been proposed, but are
objectionable, as being already in use in a different sense.
The great features of the mammals of the Oriental region are, the
long-armed apes, the orang-utans, the tiger, the sun-bears and honey-bears,
the tapir, the chevrotains or mouse-deer, and the Indian elephant. Its most
conspicuous birds are the immense number and variety of babbling-thrushes
(Timaliidæ), its beautiful little hill-tits (Liotrichidæ), its green
bulbuls (Phyllornithidæ), its many varieties {45} of the crow-family, its
beautiful gapers and pittas adorned with the most delicate colours, its
great variety of hornbills, and its magnificent Phasianidæ, comprising the
peacocks, argus-pheasants, fire-backed pheasants, and jungle-fowl. Many of
these are, it is true, absent from the peninsula of Hindostan, but
sufficient remain there to ally it with the other parts of the region.
Among the remarkable but less conspicuous forms of mammalia which are
peculiar to this region are, monkeys of the genus Presbyter, extending to
every part of it; lemurs of three peculiar genera--Nycticebus and Loris
(slow lemurs) and Tarsius (spectre lemurs); the flying lemur
(Galeopithecus), now classed as a peculiar family of Insectivora and found
only in the Malay Islands; the family of the Tupaias, or squirrel-shrews,
curious little arboreal Insectivora somewhat resembling squirrels; no less
than twelve peculiar genera of the civet family, three peculiar antelopes,
five species of rhinoceros, and the round-tailed flying squirrels forming
the genus Pteromys.
Of the peculiar groups of birds we can only mention a few. The curious
little tailor-birds of the genus Orthotomus are found over the whole region
and almost alone serve to characterise it, as do the fine
laughing-thrushes, forming the genus Garrulax; while the beautiful
grass-green fruit-thrushes (Phyllornis), and the brilliant little minivets
(Pericrocotus), are almost equally universal. Woodpeckers are abundant,
belonging to a dozen peculiar genera; while gaudy barbets and strange forms
of cuckoos and hornbills are also to be met with everywhere. Among game
birds, the only genus that is universally distributed, and which may be
said to characterise the region, is Gallus, comprising the true
jungle-fowl, one of which, Gallus bankiva, is found from the Himalayas and
Central India to Malacca, Java, and even eastward to Timor, and is the
undoubted origin of almost all our domestic poultry. Southern India and
Ceylon each possesses distinct species of jungle-fowl, and a third very
handsome green bird (Gallus æneus inhabits Java.)
Reptiles are as abundant as in Africa, but they present no well-known
groups which can be considered as specially characteristic. Among insects
we may notice the {46} magnificent golden and green Papilionidæ of various
genera as being unequalled in the world; while the great Atlas moth is
probably the most gigantic of Lepidoptera, being sometimes ten inches
across the wings, which are also very broad. Among the beetles the strange
flat-bodied Malayan mormolyce is the largest of all the Carabidæ, while the
catoxantha is equally a giant among the Buprestidæ. On the whole, the
insects of this region probably surpass those of any other part of the
world, except South America, in size, variety, and beauty.
_Definition and Characteristic Groups of the Australian Region._--The
Australian region is so well marked off from the Oriental, as well as from
all other parts of the world, by zoological peculiarities, that we need not
take up much time in describing it, especially as some of its component
islands will come under review at a subsequent stage of our work. Its most
important portions are Australia and New Guinea, but it also includes all
the Malayan and Pacific Islands to the east of Borneo, Java, and Bali, the
Oriental region terminating with the submarine bank on which those islands
are situated. The island of Celebes is included in this region from a
balance of considerations, but it almost equally well belongs to the
Oriental, and must be left out of the account in our general sketch of the
zoological features of the Australian region.
The great feature of the Australian region is the almost total absence of
all the forms of terrestrial mammalia which abound in the rest of the
world, their place being supplied by a great variety of Marsupials. In
Australia and New Guinea there are no Insectivora, Carnivora, nor Ungulata,
while even the rodents are only represented by a few small rats and mice.
In the remoter Pacific Islands mammals are altogether absent (except
perhaps in New Zealand), but in the Moluccas and other islands bordering on
the Oriental region the higher mammals are represented by a few deer,
civets, and pigs, though it is doubtful whether the two former may not have
been introduced by man, as was almost certainly the case with the
semi-domesticated dingo of Australia.[8] These peculiarities in the
mammalia {47} are so great that every naturalist agrees that Australia must
be made a separate region, the only difference of opinion being as to its
extent, some thinking that New Zealand should form another separate region;
but this question need not now delay us.
In birds Australia is by no means so isolated from the rest of the world,
as it contains great numbers of warblers, thrushes, flycatchers, shrikes,
crows, and other familiar types of the Eastern Hemisphere; yet a
considerable number of the most characteristic Oriental families are
absent. Thus there are no vultures, woodpeckers, pheasants, bulbuls, or
barbets in the Australian region; and the absence of these is almost as
marked a feature as that of cats, deer, or monkeys, among mammalia. The
most conspicuous and characteristic birds of the Australian region are, the
piping crows; the honey-suckers (Meliphagidæ), a family quite peculiar to
the region; the lyre-birds; the great terrestrial kingfishers (Dacelo); the
great goat-suckers called more-porks in Australia and forming the genus
Podargus; the wonderful abundance of parrots, including such remarkable
forms as the white and black cockatoos, and the gorgeously coloured
brush-tongued lories; the almost equal abundance of fine pigeons more gaily
coloured than any others on the globe; the strange brush-turkeys and
mound-builders, the only birds that {48} never sit upon their eggs, but
allow them to be hatched, reptile-like, by the heat of the sand or of
fermenting vegetable matter; and lastly, the emus and cassowaries, in which
the wings are far more rudimentary than in the ostriches of Africa and
South America. New Guinea and the surrounding islands are remarkable for
their tree-kangaroos, their birds-of-paradise, their raquet-tailed
kingfishers, their great crown-pigeons, their crimson lories, and many
other remarkable birds. This brief outline being sufficient to show the
distinctness and isolation of the Australian region, we will now pass to
the consideration of the Western Hemisphere.
_Definition and Characteristic Groups of the Nearctic Region._--The
Nearctic region comprises all temperate and arctic North America, including
Greenland, the only doubt being as to its southern boundary, many northern
types penetrating into the tropical zone by means of the highlands and
volcanic peaks of Mexico and Guatemala, while a few which are
characteristic of the tropics extend northward into Texas and California.
There is, however, considerable evidence showing that on the east coast the
Rio Grande del Norte, and on the west a point nearly opposite Cape St.
Lucas, form the most natural boundary; but instead of being drawn straight
across, the line bends to the south-east as soon as it rises on the flanks
of the table-land, forming a deep loop which extends some distance beyond
the city of Mexico, and perhaps ought to be continued along the higher
ridges of Guatemala.
The Nearctic region is so similar to the Palæarctic in position and
climate, and the two so closely approach each other at Behring Straits,
that we cannot wonder at there being a certain amount of similarity between
them--a similarity which some naturalists have so far over-estimated as to
think that the two regions ought to be united. Let us therefore carefully
examine the special zoological features of this region, and see how far it
resembles, and how far differs from, the Palæarctic.
At first sight the mammalia of North America do not seem to differ much
from those of Europe or Northern Asia. There are cats, lynxes, wolves and
foxes, weasels, bears, elk and deer, voles, beavers, squirrels, marmots,
and {49} hares, all very similar to those of the Eastern Hemisphere, and
several hardly distinguishable. Even the bison or "buffalo" of the
prairies, once so abundant and characteristic, is a close ally of the now
almost extinct "aurochs" of Lithuania. Here, then, we undoubtedly find a
very close resemblance between the two regions, and if this were all, we
should have great difficulty in separating them. But along with these, we
find another set of mammals, not quite so conspicuous but nevertheless very
important. We have first, three peculiar genera of moles, one of which, the
star-nosed mole, is a most extraordinary creature, quite unlike anything
else. Then there are three genera of the weasel family, including the
well-known skunk (Mephitis), all quite different from Eastern forms. Then
we come to a peculiar family of carnivora, the racoons, very distinct from
anything in Europe or Asia; and in the Rocky Mountains we find the
prong-horn antelope (Antilocapra) and the mountain goat of the trappers
(Aplocerus), both peculiar genera. Coming to the rodents we find that the
mice of America differ in some dental peculiarities from those of the rest
of the world, and thus form several distinct genera; the jumping mouse
(Xapus) is a peculiar form of the jerboa family, and then we come to the
pouched rats (Geomyidæ), a very curious family consisting of four genera
and nineteen species, peculiar to North America, though not confined to the
Nearctic region. The prairie dogs (Cynomys), the tree porcupine
(Erethizon), the curious sewellel (Haploodon), and the opossum (Didelphys)
complete the list of peculiar mammalia which distinguish the northern
region of the new world from that of the old. We must add to these
peculiarities some remarkable deficiencies. The Nearctic region has no
hedgehogs, nor wild pigs, nor dormice, and only one wild sheep in the Rocky
Mountains as against twenty species of sheep and goats in the Palæarctic
region.
In birds also the similarities to our own familiar songsters first strike
us, though the differences are perhaps really greater than in the
quadrupeds. We see thrushes and wrens, tits and finches, and what seem to
be warblers and flycatchers and starlings in abundance; but a closer
examination shows the ornithologist that what he took for the {50} latter
are really quite distinct, and that there is not a single true flycatcher
of the family Muscicapidæ, or a single starling of the family Sturnidæ in
the whole continent, while there are very few true warblers (Sylviidæ),
their place being taken by the quite distinct families Mniotiltidæ or
wood-warblers, and Vireonidæ or greenlets. In like manner the flycatchers
of America belong to the totally distinct family of tyrant-birds,
Tyrannidæ, and those that look like starlings to the hang-nests, Icteridæ;
and these four peculiar families comprise about a hundred and twenty
species, and give a special character to the ornithology of the country.
Add to these such peculiar birds as the mocking thrushes (Mimus), the blue
jays (Cyanocitta), the tanagers, the peculiar genera of cuckoos (Coccygus
and Crotophaga), the humming-birds, the wild turkeys (Meleagris), and the
turkey-buzzards (Cathartes), and we see that if there is any doubt as to
the mammals of North America being sufficiently distinct to justify the
creation of a separate region, the evidence of the birds would alone settle
the question.
The reptiles, and some others of the lower animals, add still more to this
weight of evidence. The true rattlesnakes are highly characteristic, and
among the lizards are several genera of the peculiar American family, the
Iguanidæ. Nowhere in the world are the tailed batrachians so largely
developed as in this region, the Sirens and the Amphiumidæ forming two
peculiar families, while there are nine peculiar genera of salamanders, and
two others allied respectively to the Proteus of Europe and the Sieboldia
or giant salamander of Japan. There are seven peculiar families and about
thirty peculiar genera of fresh-water fishes; while the fresh-water
molluscs are more numerous than in any other region, more than thirteen
hundred species and varieties having been described.
Combining the evidence derived from all these classes of animals, we find
the Nearctic region to be exceedingly well characterised, and to be amply
distinct from the Palæarctic. The few species that are common to the two
are almost all arctic, or, at least, northern types, and may be compared
with those desert forms which occupy the debatable ground between the
Palæarctic, Ethiopian, and Oriental regions. {51} If, however, we compare
the number of species, which are common to the Nearctic and Palæarctic
regions with the number common to the western and eastern extremities of
the latter region, we shall find a wonderful difference between the two
cases; and if we further call to mind the number of important groups
characteristic of the one region but absent from the other, we shall be
obliged to admit that the relation that undoubtedly exists between the
faunas of North America and Europe is of a very distinct nature from that
which connects together Western Europe and North-eastern Asia in the bonds
of zoological unity.
_Definition and Characteristic Groups of the Neotropical Region._--The
Neotropical region requires very little definition, since it comprises the
whole of America south of the Nearctic region, with the addition of the
Antilles or West Indian Islands. Its zoological peculiarities are almost as
marked as those of Australia, which, however, it far exceeds in the extreme
richness and variety of all its forms of life. To show how distinct it is
from all the other regions of the globe, we need only enumerate some of the
best known and more conspicuous of the animal forms which are peculiar to
it. Such are, among mammalia--the prehensile-tailed monkeys and the
marmosets, the blood-sucking bats, the coati-mundis, the peccaries, the
llamas and alpacas, the chinchillas, the agoutis, the sloths, the
armadillos, and the ant-eaters; a series of types more varied, and more
distinct from those of the rest of the world than any other continent can
boast of. Among birds we have the charming sugar-birds, forming the family
Coerebidæ; the immense and wonderfully varied group of tanagers; the
exquisite little manakins, and the gorgeously-coloured chatterers; the host
of tree-creepers of the family Dendrocolaptidæ; the wonderful toucans; the
puff-birds, jacamars, todies and motmots; the marvellous assemblage of four
hundred distinct kinds of humming-birds; the gorgeous macaws; the
curassows, the trumpeters, and the sun-bitterns. Here again there is no
other continent or region that can produce such an assemblage of remarkable
and perfectly distinct groups of birds; and no less wonderful is its
richness in species, since these fully equal, if they do not surpass, those
of the {52} two great tropical regions of the Eastern Hemisphere (the
Ethiopian and the Oriental) combined.
As an additional indication of the distinctness and isolation of the
Neotropical region from all others, and especially from the whole Eastern
Hemisphere, we must say something of the otherwise widely distributed
groups which are absent. Among mammalia we have first the order
Insectivora, entirely absent from South America, though a few species are
found in Central America and the West Indies; the Viverridæ or civet family
is wholly wanting, as are every form of sheep, oxen, or antelopes; while
the swine, the elephants, and the rhinoceroses of the old world are
represented by the diminutive peccaries and tapirs.
Among birds we have to notice the absence of tits, true flycatchers,
shrikes, sunbirds, starlings, larks (except a solitary species in the
Andes), rollers, bee-eaters, and pheasants, while warblers are very scarce,
and the almost cosmopolitan wagtails are represented by a single species of
pipit.
We must also notice the preponderance of low or archaic types among the
animals of South America. Edentates, marsupials, and rodents form the
majority of the terrestrial mammalia; while such higher groups as the
carnivora and hoofed animals are exceedingly deficient. Among birds a low
type of Passeres, characterised by the absence of the singing muscles, is
excessively prevalent, the enormous groups of the ant-thrushes, tyrants,
tree-creepers, manakins, and chatterers belonging to it. The Picariæ (a
lower group) also prevail to a far greater extent than in any other
regions, both in variety of forms and number of species; and the chief
representatives of the gallinaceous birds--the curassows and tinamous, are
believed to be allied, the former to the brush-turkeys of Australia, the
latter (very remotely) to the ostriches, two of the least developed types
of birds.
Whether, therefore, we consider its richness in peculiar forms of animal
life, its enormous variety of species, its numerous deficiencies as
compared with other parts of the world, or the prevalence of a low type of
organisation among its higher animals, the Neotropical region stands out as
undoubtedly the most remarkable of the great zoological divisions of the
earth.
In reptiles, amphibia, fresh-water fishes, and insects, {53} this region is
equally peculiar, but we need not refer to these here, our only object now
being to establish by a sufficient number of well-known and easily
remembered examples, the distinctness of each region from all others, and
its unity as a whole. The former has now been sufficiently demonstrated,
but it may be well to say a few words as to the latter point.
The only outlying portions of the region about which there can be any doubt
are--Central America, or that part of the region north of the Isthmus of
Panama, the Antilles or West Indian Islands, and the temperate portion of
South America including Chili and Patagonia.
In Central America, and especially in Mexico, we have an intermixture of
South American and North American animals, but the former undoubtedly
predominate, and a large proportion of the peculiar Neotropical groups
extend as far as Costa Rica. Even in Guatemala and Mexico we have howling
and spider-monkeys, coati-mundis, tapirs, and armadillos; while chatterers,
manakins, ant-thrushes, and other peculiarly Neotropical groups of birds
are abundant. There is therefore no doubt as to Mexico forming part of this
region, although it is comparatively poor, and exhibits the intermingling
of temperate and tropical forms.
The West Indies are less clearly Neotropical, their poverty in mammals as
well as in most other groups being extreme, while great numbers of North
American birds migrate there in winter. The resident birds, however,
comprise trogons, sugar-birds, chatterers, with many humming-birds and
parrots, representing eighteen peculiar Neotropical genera; a fact which
decides the region to which the islands belong.
South temperate America is also very poor as compared with the tropical
parts of the region, and its insects contain a considerable proportion of
north temperate forms. But it contains armadillos, cavies and opossums; and
its birds all belong to American groups, though, owing to the inferior
climate and deficiency of forests, a number of the families of birds
peculiar to tropical America are wanting. Thus there are no manakins,
chatterers, toucans, trogons, or motmots; but there are abundance of
hang-nests, tyrant-birds, ant-thrushes, tree-creepers, and a fair {54}
proportion of humming-birds, tanagers and parrots. The zoology is therefore
thoroughly Neotropical, although somewhat poor; and it has a number of
peculiar forms of strictly Neotropical types--as the chinchillas, alpacas,
&c., which are not found in the tropical regions except in the high Andes.
_Comparison of Zoological Regions with the Geographical Divisions of the
Globe._--Having now completed our survey of the great zoological regions of
the globe, we find that they do not differ so much from the old
geographical divisions as our first example might have led us to suppose.
Europe, Asia, Africa, Australia, North America, and South America, really
correspond, each to a zoological region, but their boundaries require to be
modified more or less considerably; and if we remember this, and keep their
extensions or limitations always in our mind, we may use the terms "South
American" or "North American," as being equivalent to Neotropical and
Nearctic, without much inconvenience, while "African" and "Australian"
equally well serve to express the zoological type of the Ethiopian and
Australian regions. Europe and Asia require more important modifications.
The European fauna does indeed well represent the Palæarctic in all its
main features, and if instead of Asia we say tropical Asia we have the
Oriental region very fairly defined; so that the relation of the
geographical with the zoological primary divisions of the earth is
sufficiently clear. In order to make these relations visible to the eye and
more easily remembered, we will put them into a tabular form:
Regions. Geographical Equivalent.
Palæarctic EUROPE, with north temperate Africa and Asia.
Ethiopian AFRICA (south of the Sahara) with Madagascar.
Oriental TROPICAL ASIA, to Philippines and Java.
Australian AUSTRALIA, with Pacific Islands, Moluccas, &c.
Nearctic NORTH AMERICA, to North Mexico.
Neotropical SOUTH AMERICA, with tropical N. America and W. Indies.
The following arrangement of the regions will indicate their geographical
position, and to a considerable extent their relation to each other.
N E A R C T I C--P A L Æ A R C T I C
| | |
| | ORIENTAL
| ETHIOPIAN |
NEO- |
TROPICAL AUSTRALIAN
May 4th. Diameter of spot 31° 24'
June 4th. ,, ,, 28° 0'
,, 17th. ,, ,, 22° 54'
July 4th. ,, ,, 18° 24'
,, 12th. ,, ,, 15° 20'
,, 20th. ,, ,, 18° 0'
We thus see that Mars has two permanent snow-caps, of nearly equal size in
winter but diminishing very unequally {55} in summer, when the southern cap
is reduced to nearly one third the size of the northern; and this fact is
held by Mr. Carpenter, as it was by the late Mr. Belt, to be opposed to the
view of the hemisphere which has winter in _aphelion_ (as the southern now
has both in the Earth and Mars), having been alone glaciated during periods
of high excentricity.[9]
Before, however, we can draw any conclusion from the case of Mars, we must
carefully scrutinise the facts, and the conditions they imply. In the first
place, there is evidently this radical difference between the state of Mars
now and of the Earth during a glacial period--that Mars has no great
ice-sheets spreading over its temperate zone, as the Earth undoubtedly had.
This we know from the fact of the _rapid_ disappearance of the white
patches over a belt three degrees wide in a fortnight (equal to a width of
about 100 miles of our measure), and in the northern hemisphere of eight
degrees wide (about 280 miles) between May 4th and July 12th. Even with our
much more powerful sun, which gives us more than twice as much heat as Mars
receives, no such diminution of an ice-sheet, or of glaciers of even
moderate thickness, could possibly occur; but the phenomenon is on the
contrary exactly analogous to what actually takes place on the plains of
Siberia in summer. These, as I am informed by Mr. Seebohm, are covered with
snow during winter and spring to a depth of six or eight feet, which
diminishes very little even under the hot suns of May, till warm winds
combine with the sun in June, when in about a fortnight the whole of it
disappears, and a little later the whole of northern Asia is free from its
winter covering. As, however, the sun of Mars is so much less powerful than
ours, we may be {56} sure that the snow (if it is real snow) is much less
thick--a mere surface-coating in fact, such as occurs in parts of Russia
where the precipitation is less, and the snow accordingly does not exceed
two or three feet in thickness.
We now see the reason why the _southern_ pole of Mars parts with its white
covering so much more quickly and to so much greater an extent than the
_northern_, for the south pole during summer is nearest the sun, and, owing
to the great excentricity of Mars, would have about one-third more heat
than during the summer of the northern hemisphere; and this greater heat
would cause the winds from the equator to be both warmer and more powerful,
and able to produce the same effects on the scanty Martian snows as they
produce on our northern snow-plains. The reason why both poles of Mars are
almost equally snow-covered in winter is not difficult to understand. Owing
to the greater obliquity of the ecliptic, and the much greater length of
the year, the polar regions will be subject to winter darkness fully twice
as long as with us, and the fact that one pole is nearer the sun during
this period than the other at a corresponding period, will therefore make
no perceptible difference. It is also probable that the two poles of Mars
are approximately alike as regards their geographical features, and that
neither of them is surrounded by very high land on which ice may
accumulate. With us at the present time, on the other hand, geographical
conditions completely mask and even reverse the influence of excentricity,
and that of winter in _perihelion_ in the northern, and summer in
_perihelion_ in the southern, hemisphere. In the north we have a
preponderance of sea within the Arctic circle, and of lowlands in the
temperate zone. In the south exactly opposite conditions prevail, for there
we have a preponderance of land (and much of it high land) within the
Antarctic circle, and of sea in the temperate zone. Ice, therefore,
accumulates in the south, while a thin coating of snow, easily melted in
summer, is the prevalent feature in the north; and these contrasts react
upon climate to such an extent, that in the southern ocean, islands in the
latitude of Ireland have glaciers descending to the level of the sea, and
constant snowstorms {57} in the height of summer, although the sun is then
actually nearer the earth than it is during our northern summer!
It is evident, therefore, that the phenomena presented by the varying polar
snows of Mars are in no way opposed to that modification of Dr. Croll's
theory of the conditions which brought about the glacial epochs of our
northern hemisphere, which is here advocated; but are perfectly explicable
on the same general principles, if we keep in mind the distinction between
an ice-sheet--which a summer's sun cannot materially diminish, but may even
increase by bringing vapour to be condensed into snow--and a thin snowy
covering which may be annually melted and annually renewed, with great
rapidity and over large areas. Except within the small circles of perpetual
polar snow there can at the present time be no ice-sheets in Mars; and the
reason why this permanent snowy area is more extensive around the northern
than around the southern pole may be partly due to higher land at the
north, but is perhaps sufficiently explained by the diminished power of the
summer sun, owing to its greatly increased distance at that season in the
northern hemisphere, so that it is not able to melt so much of the snow
which has accumulated during the long night of winter.
* * * * *
{58}
CHAPTER IX
ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE ARCTIC REGIONS
Dr. Croll's Views on Ancient Glacial Epochs--Effects of Denudation in
Destroying the Evidence of Remote Glacial Epochs--Rise of Sea-level
Connected with Glacial Epochs a Cause of Further Denudation--What
Evidence of Early Glacial Epochs may be Expected--Evidences of
Ice-action During the Tertiary Period--The Weight of the Negative
Evidence--Temperate Climates in the Arctic Regions--The Miocene Arctic
Flora--Mild Arctic Climates of the Cretaceous Period--Stratigraphical
Evidence of Long-continued Mild Arctic Conditions--The Causes of Mild
Arctic Climates--Geographical Conditions Favouring Mild Northern
Climates in Tertiary Times--The Indian Ocean as a Source of Heat in
Tertiary Times--Condition of North America During the Tertiary
Period--Effect of High Excentricity on Warm Polar Climates--Evidences
as to Climate in the Secondary and Palæozoic Epochs--Warm Arctic
Climates in Early Secondary and Palæozoic Times--Conclusions as to the
Climates of Secondary and Tertiary Periods--General View of Geological
Climates as Dependent on the Physical Features of the Earth's
Surface--Estimate of the Comparative Effects of Geographical and
Physical Causes in Producing Changes of Climate.
If we adopt the view set forth in the preceding chapter as to the character
of the glacial epoch and of the accompanying alternations of climate, it
must have been a very important agent in producing changes in the
distribution of animal and vegetable life. The intervening mild periods,
which almost certainly occurred during its earlier and later phases, may
have been sometimes more equable than even our present insular climate, and
severe frosts were probably then unknown. During the four or five {59}
thousand years that each specially mild period may have lasted, some
portions of the north temperate zone, which had been buried in snow or ice,
would become again clothed with vegetation and stocked with animal life,
both of which, as the cold again came on, would be driven southward, or
perhaps partially exterminated. Forms usually separated would thus be
crowded together, and a struggle for existence would follow, which must
have led to the modification or the extinction of many species. When the
survivors in the struggle had reached a state of equilibrium, a fresh field
would be opened to them by the later ameliorations of climate; the more
successful of the survivors would spread and multiply; and after this had
gone on for thousands of generations, another change of climate, another
southward migration, another struggle of northern and southern forms would
take place.
But if the last glacial epoch has coincided with, and has been to a
considerable extent caused by, a high excentricity of the earth's orbit, we
are naturally led to expect that earlier glacial epochs would have occurred
whenever the excentricity was unusually large. Dr. Croll has published
tables showing the varying amounts of excentricity for three million years
back; and from these it appears that there have been many periods of high
excentricity, which has often been far greater than at the time of the last
glacial epoch.[10] The accompanying diagram has been drawn from these
tables, and it will be seen that the highest excentricity occurred 850,000
years ago, at which time the difference between the sun's distance at
_aphelion_ and _perihelion_ was thirteen and a half millions of miles,
whereas during the last glacial period the maximum difference was ten and a
half million miles.
[Illustration: DIAGRAM SHOWING THE CHANGES OF EXCENTRICITY DURING THE LAST
THREE MILLION YEARS.]
Now, judging by the amount of organic and physical change that occurred
during and since the glacial epoch, and that which has occurred since the
Miocene period, it is considered probable that this maximum of excentricity
coincided with some part of the latter period; and Dr. Croll maintains that
a glacial epoch must then have {60} occurred surpassing in severity that of
which we have such convincing proofs, and consisting like it of
alternations of cold and warm phases every 10,500 years. The diagram also
shows us another long-continued period of high excentricity from 1,750,000
to 1,950,000 years ago, and yet another almost equal to the maximum
2,500,000 years back. These may perhaps have occurred during the Eocene and
Cretaceous epochs respectively, or all may have been included within the
limits of the Tertiary period. As two of these high excentricities greatly
exceed that which caused our glacial epoch, while the third is almost equal
to it and of longer duration, they seem to afford us the means of testing
rival theories of the causes of glaciation. If, as Dr. Croll argues, high
excentricity is the great and dominating agency in bringing on glacial
epochs, geographical changes being subordinate, then there must have been
glacial epochs of great severity at all these three periods; while if he is
also correct in supposing that the alternate phases of precession would
inevitably produce glaciation in one hemisphere, and a proportionately mild
and equable climate in the opposite hemisphere, then we should have to look
for evidence of exceptionally warm and exceptionally cold periods,
occurring {61} alternately and with several repetitions, within a space of
time which, geologically speaking, is very short indeed.
Let us then inquire first into the character of the evidence we should
expect to find of such changes of climate, if they have occurred; we shall
then be in a better position to estimate at its proper value the evidence
that actually exists, and, after giving it due weight, to arrive at some
conclusion as to the theory that best explains and harmonises it.
_Effects of Denudation in Destroying the Evidence of Remote Glacial
Epochs._--It may be supposed, that if earlier glacial epochs than the last
did really occur, we ought to meet with some evidence of the fact
corresponding to that which has satisfied us of the extensive recent
glaciation of the northern hemisphere; but Dr. Croll and other writers have
ably argued that no such evidence is likely to be found. It is now
generally admitted that sub-aërial denudation is a much more powerful agent
in lowering and modifying the surface of a country than was formerly
supposed. It has in fact been proved to be so powerful that the difficulty
now felt is, not to account for the denudation which can be proved to have
occurred, but to explain the apparent persistence of superficial features
which ought long ago to have been destroyed.
A proof of the lowering and eating away of the land-surface which every one
can understand, is to be found in the quantity of solid matter carried down
to the sea and to low grounds by rivers. This is capable of pretty accurate
measurement, and it has been carefully measured for several rivers, large
and small, in different parts of the world. The details of these
measurements will be given in a future chapter, and it is only necessary
here to state that the average of them all gives us this result--that one
foot must, on an average, be taken off the entire surface of the land each
3,000 years in order to produce the amount of sediment and matter in
solution which is actually carried into the sea. To give an idea of the
limits of variation in different rivers it may be mentioned that the
Mississippi is one which denudes its valley at a slow rate, taking 6,000
{62} years to remove one foot; while the Po is the most rapid, taking only
729 years to do the same work in its valley. The cause of this difference
is very easy to understand. A large part of the area of the Mississippi
basin consists of the almost rainless prairie and desert regions of the
west, while its sources are in comparatively arid mountains with scanty
snow-fields, or in a low forest-clad plateau. The Po, on the other hand, is
wholly in a district of abundant rainfall, while its sources are spread
over a great amphitheatre of snowy Alps nearly 400 miles in extent, where
the denuding forces are at a maximum. As Scotland is a mountain region of
rather abundant rainfall, the denuding power of its rains and rivers is
probably rather above than under the average, but to avoid any possible
exaggeration we will take it at a foot in 4,000 years.
Now if the end of the glacial epoch be taken to coincide with the
termination of the last period of high excentricity, which occurred about
80,000 years ago (and no geologist will consider this too long for the
changes which have since taken place), it follows that the entire surface
of Scotland must have been since lowered an average amount of twenty feet.
But over large areas of alluvial plains, and wherever the rivers have
spread during floods, the ground will have been raised instead of lowered;
and on all nearly level ground and gentle slopes there will have been
comparatively little denudation; so that proportionally much more must have
been taken away from mountain sides and from the bottoms of valleys having
a considerable downward slope. One of the very highest authorities on the
subject of denudation, Mr. Archibald Geikie, estimates the area of these
more rapidly denuded portions as only one-tenth of the comparatively level
grounds, and he further estimates that the former will be denuded about ten
times as fast as the latter. It follows that the valleys will be deepened
and widened on the average about five feet in the 4,000 years instead of
one foot; and thus many valleys must have been deepened and widened 100
feet, and some even more, since the glacial epoch, while the more level
portions of the country will have been lowered on the average only about
two feet. {63}
Now Dr. Croll gives us the following account of the present aspect of the
surface of a large part of the country:--
"Go where one will in the lowlands of Scotland and he shall hardly find a
single acre whose upper surface bears the marks of being formed by the
denuding agents now in operation. He will observe everywhere mounds and
hollows which cannot be accounted for by the present agencies at work....
In regard to the general surface of the country the present agencies may be
said to be just beginning to carve a new line of features out of the old
glacially-formed surface. But so little progress has yet been made, that
the kames, gravel-mounds, knolls of boulder clay, &c., still retain in most
cases their original form."[11]
The facts here seem a little inconsistent, and we must suppose that Dr.
Croll has somewhat exaggerated the universality and complete preservation
of the glaciated surface. The amount of average denudation, however, is not
a matter of opinion but of measurement; and its consequences can in no way
be evaded. They are, moreover, strictly proportionate to the time elapsed;
and if so much of the old surface of the country has certainly been
remodelled or carried into the sea since the last glacial epoch, it becomes
evident that any surface-phenomena produced by still earlier glacial epochs
_must_ have long since entirely disappeared.
_Rise of the Sea-level Connected with Glacial Epochs, a Cause of Further
Denudation._--There is also another powerful agent that must have assisted
in the destruction of any such surface deposits or markings. During the
last glacial epoch itself there were several minor oscillations of the
land, without counting the great submergence of over 1,300 feet, supposed
to be indicated by patches of shelly clays and gravels in Wales and
Ireland, and also in a few localities in England and Scotland, since these
are otherwise explained by many geologists. Other subsidences have no doubt
occurred in the same areas during the Tertiary epoch, and some writers
connect these subsidences with the glacial {64} period itself, the unequal
amount of ice at the two poles causing the centre of gravity of the earth
to be displaced when, of course, the surface of the ocean will conform to
it and appear to rise in the one hemisphere and sink in the other. If this
is the case, subsidences of the land are natural concomitants of a glacial
period, and will powerfully aid in removing all evidence of its occurrence.
We have seen reason to believe, however, that during the height of the
glacial epoch the extreme cold persisted through the successive phases of
precession, and if so, both polar areas would probably be glaciated at
once. This would cause the abstraction of a large quantity of water from
the ocean, and a proportionate elevation of the land, which would react on
the accumulation of snow and ice, and thus add another to that wonderful
series of physical agents which act and react on each other so as to
intensify glacial epochs.
But whether or not these causes would produce any important fluctuations of
the sea-level is of comparatively little importance to our present inquiry,
because the wide extent of marine Tertiary deposits in the northern
hemisphere and their occurrence at considerable elevations above the
present sea-level, afford the most conclusive proofs that great changes of
sea and land have occurred throughout the entire Tertiary period; and these
repeated submergences and emergences of the land combined with sub-aërial
and marine denudation, would undoubtedly destroy all those superficial
evidences of ice-action on which we mainly depend for proofs of the
occurrence of the last glacial epoch.
_What Evidence of Early Glacial Epochs may be Expected._--Although we may
admit the force of the preceding argument as to the extreme improbability
of our finding any clear evidence of the superficial action of ice during
remote glacial epochs, there is nevertheless one kind of evidence that we
ought to find, because it is both wide-spread and practically
indestructible.
One of the most constant of all the phenomena of a glaciated country is the
abundance of icebergs produced by the breaking off of the ends of glaciers
which terminate {65} in arms of the sea, or of the terminal face of the
ice-sheet which passes beyond the land into the ocean. In both these cases
abundance of rocks and _débris_, such as form the terminal moraines of
glaciers on land, are carried out to sea and deposited over the sea-bottom
of the area occupied by icebergs. In the case of an ice-sheet it is almost
certain that much of the ground-moraine, consisting of mud and imbedded
stones, similar to that which forms the "till" when deposited on land, will
be carried out to sea with the ice and form a deposit of marine "till" near
the shore.
It has indeed been objected that when an ice-sheet covered an entire
country there would be no moraines, and that rocks or _débris_ are very
rarely seen on icebergs. But during every glacial epoch there will be a
southern limit to the glaciated area, and everywhere near this limit the
mountain-tops will rise far above the ice and deposit on it great masses of
_débris_; and as the ice-sheet spreads, and again as it passes away, this
moraine-forming area will successively occupy the whole country. But even
such an ice-clad country as Greenland is now known to have protruding peaks
and rocky masses which give rise to moraines on its surface;[12] and, as
rocks from Cumberland and Ireland were carried by the ice-sheet to the Isle
of Man, there must have been a very long period during which the ice-sheets
of Britain and Ireland terminated in the ocean and sent off abundance of
rock-laden bergs into the surrounding seas; and the same thing must have
occurred along all the coasts of Northern Europe and Eastern America.
We cannot therefore doubt that throughout the greater part of the duration
of a glacial epoch the seas adjacent to the glaciated countries would
receive continual deposits of large rocks, rock-fragments, and gravel,
similar to the material of modern and ancient moraines, and analogous to
the drift and the numerous travelled blocks which the ice has undoubtedly
scattered broadcast over every glaciated country; and these rocks and
boulders would be imbedded in whatever deposits were then forming, either
from the matter carried down by rivers or from the mud ground off {66} the
rocks and carried out to sea by the glaciers themselves. Moreover, as
icebergs float far beyond the limits of the countries which gave them
birth, these ice-borne materials would be largely imbedded in deposits
forming from the denudation of countries which had never been glaciated, or
from which the ice had already disappeared.
But if every period of high excentricity produced a glacial epoch of
greater or less extent and severity, then, on account of the frequent
occurrence of a high phase of excentricity during the three million years
for which we have the tables, these boulder and rock-strewn deposits would
be both numerous and extensive. Four hundred thousand years ago the
excentricity was almost exactly the same as it is now, and it continually
increased from that time up to the glacial epoch. Now if we take double the
present excentricity as being sufficient to produce some glaciation in the
temperate zone, we find (by drawing out the diagram at p. 171 on a larger
scale) that during 1,150,000 years out of the 2,400,000 years immediately
preceding the last glacial epoch, the excentricity reached or exceeded this
amount, consisting of sixteen separate epochs, divided from each other by
periods varying from 30,000 to 200,000 years. But if the last glacial epoch
was at its maximum 200,000 years ago, a space of three million years will
certainly include much, if not all, of the Tertiary period; and even if it
does not, we have no reason to suppose that the character of the
excentricity would suddenly change beyond the three million years.
It follows, therefore, that if periods of high excentricity, like that
which appears to have been synchronous with our last glacial epoch and is
generally admitted to have been one of its efficient causes, always
produced glacial epochs (with or without alternating warm periods), then
the whole of the Tertiary deposits in the north temperate and Arctic zones
should exhibit frequent alternations of boulder and rock-bearing beds, or
coarse rock-strewn gravels analogous to our existing glacial drift, and
with some corresponding change of organic remains. Let us then see what
evidence can be adduced of the existence of such deposits, and whether it
is adequate to support the {67} theory of repeated glacial epochs during
the Tertiary period.
_Evidences of Ice-action during the Tertiary Period._--The Tertiary fossils
both of Europe and North America indicate throughout warm or temperate
climates, except those of the more recent Pliocene deposits which merge
into the earlier glacial beds. The Miocene deposits of Central and Southern
Europe, for example, contain marine shells of some genera now only found
farther south, while the fossil plants often resemble those of Madeira and
the southern states of North America. Large reptiles, too, abounded, and
man-like apes lived in the south of France and in Germany. Yet in Northern
Italy, near Turin, there are beds of sandstone and conglomerate full of
characteristic Miocene shells, but containing in an intercalated deposit
angular blocks of serpentine and greenstone often of enormous size, one
being fourteen feet long, and another twenty-six feet. Some of the blocks
were observed by Sir Charles Lyell to be faintly striated and partly
polished on one side, and they are scattered through the beds for a
thickness of nearly 150 feet. It is interesting that the particular bed in
which the blocks occur yields no organic remains, though these are
plentiful both in the underlying and overlying beds, as if the cold of the
icebergs, combined with the turbidity produced by the glacial mud, had
driven away the organisms adapted to live only in a comparatively warm sea.
Rock similar in kind to these erratics occurs about twenty miles distant in
the Alps.
The Eocene period is even more characteristically tropical in its flora and
fauna, since palms and Cycadaceæ, turtles, snakes, and crocodiles then
inhabited England. Yet on the north side of the Alps, extending from
Switzerland to Vienna, and also south of the Alps near Genoa, there is a
deposit of finely-stratified sandstone several thousand feet in thickness,
quite destitute of organic remains, but containing in several places in
Switzerland enormous blocks either angular or partly rounded, and composed
of oolitic limestone or of granite. Near the Lake of Thun some of the
granite blocks found in this deposit are of enormous size, one of them
being 105 feet long, ninety feet wide, {68} and forty-five feet thick! The
granite is red, and of a peculiar kind which cannot be matched anywhere in
the Alps, or indeed elsewhere. Similar erratics have also been found in
beds of the same age in the Carpathians and in the Apennines, indicating
probably an extensive inland European sea into which glaciers descended
from the surrounding mountains, depositing these erratics, and cooling the
water so as to destroy the mollusca and other organisms which had
previously inhabited it. It is to be observed that wherever these erratics
occur they are always in the vicinity of great mountain ranges; and
although these can be proved to have been in great part elevated during the
Tertiary period, we must also remember that they must have been since very
much lowered by denudation, of the amount of which, the enormously thick
Eocene and Miocene beds now forming portions of them is in some degree a
measure as well as a proof. It is not therefore at all improbable that
during some part of the Tertiary period these mountains may have been far
higher than they are now, and this we know might be sufficient for the
production of glaciers descending to the sea-level, even were the climate
of the lowlands somewhat warmer than at present.[13]
_The Weight of the Negative Evidence._--But when we proceed to examine the
Tertiary deposits of other parts of {69} Europe, and especially of our own
country, for evidence of this kind, not only is such evidence completely
wanting, but the facts are of so definite a character as to satisfy most
geologists that it can never have existed; and the same maybe said of
temperate North America and of the Arctic regions generally.
In his carefully written paper on "The Climate Controversy" the late Mr.
Searles V. Wood, Jun., remarks on this point as follows: "Now the Eocene
formation is complete in England, and is exposed in continuous section
along the north coast of the Isle of Wight from its base to its junction
with the Oligocene (or Lower Miocene according to some), and along the
northern coast of Kent from its base to the Lower Bagshot Sand. It has been
intersected by railway and other cuttings in all directions and at all
horizons, and pierced by wells innumerable; while from its strata in
England, France, and Belgium, the most extensive collections of organic
remains have been made of any formation yet explored, and from nearly all
its horizons, for at one place or another in these three countries nearly
every horizon may be said to have yielded fossils of some kind. These
fossils, however, whether they be the remains of a flora such as that of
Sheppey, or of a vertebrate fauna containing the crocodile and alligator,
such as is yielded by beds indicative of terrestrial conditions, or of a
molluscan assemblage such as is present in marine or fluvio-marine beds of
the formation, are of unmistakably tropical or sub-tropical character
throughout; and no trace whatever has appeared of the intercalation of a
glacial period, much less of successive intercalations indicative of more
than one period of 10,500 years' glaciation. Nor can it be urged that the
glacial epochs of the Eocene in England were intervals of dry land, and so
have left no evidence of their existence behind them, because a large part
of the continuous sequence of Eocene deposits in this country consists of
alternations of fluviatile, fluvio-marine, and purely marine strata; so
that it seems impossible that during the accumulation of the Eocene
formation in England a glacial period could have occurred without its
evidences being {70} abundantly apparent. The Oligocene of Northern Germany
and Belgium, and the Miocene of those countries and of France, have also
afforded a rich molluscan fauna, which, like that of the Eocene, has as yet
presented no indication of the intrusion of anything to interfere with its
uniformly sub-tropical character."[14]
This is sufficiently striking; but when we consider that this enormous
series of deposits, many thousand feet in thickness, consists wholly of
alternations of clays, sands, marls, shales, or limestones, with a few beds
of pebbles or conglomerate, not one of the whole series containing
irregular blocks of foreign material, boulders or gravel, such as we have
seen to be the essential characteristic of a glacial epoch; and when we
find that this same general character pervades all the extensive Tertiary
deposits of temperate North America, we shall, I think, be forced to the
conclusion that no general glacial epochs could have occurred during their
formation. It must be remembered that the "imperfection of the geological
record" will not help us here, because the series of Tertiary deposits is
unusually complete, and we must suppose some destructive agency to have
selected all the intercalated glacial beds and to have so completely made
away with them that not a fragment remains, while preserving all or almost
all the _interglacial_ beds; and to have acted thus capriciously, not in
one limited area only, but over the whole northern hemisphere, with the
local exceptions on the flanks of great mountain ranges already referred
to.
_Temperate Climates in the Arctic Regions._--As we have just seen, the
geological evidence of the persistence of sub-tropical or warm climates in
the north temperate zone during the greater part of the Tertiary period is
almost irresistible, and we have now to consider the still more
extraordinary series of observations which demonstrate that this
amelioration of climate extended into the Arctic zone, and into countries
now almost wholly buried in snow and ice. These warm Arctic climates have
been explained by Dr. Croll as due to periods of high excentricity with
winter in _perihelion_, a theory which implies alternating {71} epochs of
glaciation far exceeding what now prevails; and it is therefore necessary
to examine the evidence pretty closely in order to see if this view is more
tenable in the case of the north polar regions than we have found it to be
in that of the north temperate zone.
The most recent of these milder climates is perhaps indicated by the
abundant remains of large mammalia--such as the mammoth, woolly rhinoceros,
bison and horse, in the icy alluvial plains of Northern Siberia, and
especially in the Liakhov Islands in the same latitude as the North Cape of
Asia. These remains occur not in one or two spots only, as if collected by
eddies at the mouth of a river, but along the whole borders of the Arctic
Ocean; and it is generally admitted that the animals must have lived upon
the adjacent plains, and that a considerably milder climate than now
prevails could alone have enabled them to do so. How long ago this occurred
we do not know, but one of the last intercalated mild periods of the
glacial epoch itself seems to offer all the necessary conditions. Again,
Sir Edward Belcher discovered on the dreary shores of Wellington Channel in
75½° N. Lat. the trunk and root of a fir tree which had evidently grown
where it was found. It appeared to belong to the species _Abies alba_, or
white fir, which now reaches 68° N. Lat. and is the most northerly conifer
known. Similar trees, one four feet in circumference and thirty feet long,
were found by Lieut. Mecham in Prince Patrick's Island in Lat. 76° 12' N.,
and other Arctic explorers have found remains of trees in high
latitudes.[15]
Similar indications of a recent milder climate are found in Spitzbergen.
Professor Nordenskjöld says: "At various places on Spitzbergen, at the
bottom of Lomme Bay, at Cape Thordsen, in Blomstrand's strata in Advent
Bay, there are found large and well-developed shells of a bivalve, _Mytilus
edulis_, which is not now found living on the coast of Spitzbergen, though
on the west coast of Scandinavia it everywhere covers the rocks near the
sea-shore. These shells occur most plentifully in the bed of a river which
runs through Reindeer Valley at Cape Thordsen. They {72} are probably
washed out of a thin bed of sand at a height of about twenty or thirty feet
above the present sea-level, which is intersected by the river. The
geological age of this bed cannot be very great, and it has clearly been
formed since the present basin of the Ice Sound, or at least the greater
part of it, has been hollowed out by glacial action."[16]
_The Miocene Arctic Flora._--One of the most startling and important of the
scientific discoveries of the last forty years has been that of the relics
of a luxuriant Miocene flora in various parts of the Arctic regions. It is
a discovery that was totally unexpected, and is even now considered by many
men of science to be completely unintelligible; but it is so thoroughly
established, and it has such a direct and important bearing on the subjects
we are discussing in the present volume, that it is necessary to lay a
tolerably complete outline of the facts before our readers.
The Miocene flora of temperate Europe was very like that of Eastern Asia,
Japan, and the warmer part of Eastern North America of the present day. It
is very richly represented in Switzerland by well preserved fossil remains,
and after a close comparison with the flora of other countries Professor
Heer concludes that the Swiss Lower Miocene flora indicates a climate
corresponding to that of Louisiana, North Africa, and South China, while
the Upper Miocene climate of the same country would correspond to that of
the south of Spain, Southern Japan, and Georgia (U.S. of America). Of this
latter flora, found chiefly at Oeninghen in the northern extremity of
Switzerland, 465 species are known, of which 166 species are trees or
shrubs, half of them being evergreens. They comprise sequoias like the
Californian giant trees, camphor-trees, cinnamons, sassafras, bignonias,
cassias, gleditschias, tulip-trees, and many other American genera,
together with maples, ashes, planes, oaks, poplars, and other familiar
European trees represented by a variety of extinct species. If we now go to
the west coast of Greenland in 70° N. Lat. we find abundant remains of a
flora of the same general {73} type as that of Oeninghen but of a more
northern character. We have a sequoia identical with one of the species
found at Oeninghen, a chestnut, salisburia, liquidambar, sassafras, and
even a magnolia. We have also seven species of oaks, two planes, two vines,
three beeches, four poplars, two willows, a walnut, a plum, and several
shrubs supposed to be evergreens; altogether 137 species, mostly well and
abundantly preserved!
But even further north, in Spitzbergen, in 78° and 79° N. Lat. and one of
the most barren and inhospitable regions on the globe, an almost equally
rich fossil flora has been discovered including several of the Greenland
species, and others peculiar, but mostly of the same genera. There seem to
be no evergreens here except coniferæ, one of which is identical with the
swamp-cypress (_Taxodium distichum_) now found living in the Southern
United States! There are also eleven pines, two Libocedrus, two sequoias,
with oaks, poplars, birches, planes, limes, a hazel, an ash, and a walnut;
also water-lilies, pond-weeds, and an iris--altogether about a hundred
species of flowering plants. Even in Grinnell Land, within 8¼ degrees of
the pole, a similar flora existed, twenty-five species of fossil plants
having been collected by the last Arctic expedition, of which eighteen were
identical with the species from other Arctic localities. This flora
comprised poplars, birches, hazels, elms, viburnums, and eight species of
conifers including the swamp cypress and the Norway spruce (_Pinus abies_)
which last does not now extend beyond 69½° N.
Fossil plants closely resembling those just mentioned have been found at
many other Arctic localities, especially in Iceland, on the Mackenzie River
in 65° N. Lat. and in Alaska. As an intermediate station we have, in the
neighbourhood of Dantzic in Lat. 55° N., a similar flora, with the
swamp-cypress, sequoias, oaks, poplars, and some cinnamons, laurels, and
figs. A little further south, near Breslau, north of the Carpathians, a
rich flora has been found allied to that of Oeninghen, but wanting in some
of the more tropical forms. Again, in the Isle of Mull in Scotland, in
about 56½° N. Lat., a plant-bed has been discovered {74} containing a
hazel, a plane, and a sequoia, apparently identical with a Swiss Miocene
species.
We thus find one well-marked type of vegetation spread from Switzerland and
Vienna to North Germany, Scotland, Iceland, Greenland, Alaska, and
Spitzbergen, some few of the species even ranging over the extremes of
latitude between Oeninghen and Spitzbergen, but the great majority being
distinct, and exhibiting decided indications of a decrease of temperature
according to latitude, though much less in amount than now exists. Some
writers have thought that the great similarity of the floras of Greenland
and Oeninghen is a proof that they were not contemporaneous, but
successive; and that of Greenland has been supposed to be as old as the
Eocene. But the arguments yet adduced do not seem to prove such a
difference of age, because there is only that amount of specific and
generic diversity between the two which might be produced by distance and
difference of temperature, under the exceptionally equable climate of the
period. We have even now examples of an equally wide range of well-marked
types; as in temperate South America, where many of the genera and some of
the species range from the Straits of Magellan to Valparaiso--places
differing as much in latitude as Switzerland and West Greenland; and the
same may be said of North Australia and Tasmania, where, at a greater
latitudinal distance apart, closely allied forms of Eucalyptus, Acacia,
Casuarina, Stylidium, Goodenia, and many other genera would certainly form
a prominent feature in any fossil flora now being preserved.
_Mild Arctic Climates of the Cretaceous Period._--In the Upper Cretaceous
deposits of Greenland (in a locality not far from those of the Miocene age
last described) another remarkable flora has been discovered, agreeing
generally with that of Europe and North America of the same geological age.
Sixty-five species of plants have been identified, of which there are
fifteen ferns, two cycads, eleven coniferæ, three monocotyledons, and
thirty-four dicotyledons. One of the ferns is a tree-fern with thick stems,
which has also been found in the Upper Greensand of England. Among the
conifers the giant sequoias are found, and among {75} the dicotyledons the
genera Populus, Myrica, Ficus, Sassafras, Andromeda, Diospyros, Myrsine,
Panax, as well as magnolias, myrtles, and leguminosæ. Several of these
groups occur also in the much richer deposits of the same age in North
America and Central Europe; but all of them evidently afford such
fragmentary records of the actual flora of the period, that it is
impossible to say that any genus found in one locality was absent from the
other merely because it has not yet been found there. On the whole, there
seems to be less difference between the floras of Arctic and temperate
latitudes in Upper Cretaceous than in Miocene times.
In the same locality in Greenland (70° 33' N. Lat. and 52° W. Long.), and
also in Spitzbergen, a more ancient flora, of Lower Cretaceous age, has
been found; but it differs widely from the other in the great abundance of
cycads and conifers and the scarcity of exogens, which latter are
represented by a single poplar. Of the thirty-eight ferns, fifteen belong
to the genus Gleichenia now almost entirely tropical. There are four genera
of cycads, and three extinct genera of conifers, besides Glyptostrobus and
Torreya now found only in China and California, six species of true pines,
and five of the genus Sequoia, one of which occurs also in Spitzbergen. The
European deposits of the same age closely agree with these in their general
character, conifers, cycads, and ferns forming the mass of the vegetation,
while exogens are entirely absent, the above-named Greenland poplar being
the oldest known dicotyledonous plant.[17]
If we take these facts as really representing the flora of the period, we
shall be forced to conclude that, measured by the change effected in its
plants, the lapse of time between the Lower and Upper Cretaceous deposits
was far greater than between the Upper Cretaceous and the Miocene--a
conclusion quite opposed to the indications afforded by the mollusca and
the higher animals of the two periods. It seems probable, therefore, that
these Lower Cretaceous plants represent local peculiarities of {76}
vegetation such as now sometimes occur in tropical countries. On sandy or
coralline islands in the Malay Archipelago there will often be found a
vegetation consisting almost wholly of cycads, pandani, and palms, while a
few miles off, on moderately elevated land, not a single specimen of either
of these families may be seen, but a dense forest of dicotyledonous trees
covering the whole country. A lowland vegetation, such as that above
described, might be destroyed and its remains preserved by a slight
depression, allowing it to be covered up by the detritus of some adjacent
river, while not only would the subsidence of high land be a less frequent
occurrence, but when it did occur the steep banks would be undermined by
the waves, and the trees falling down would be floated away, and would
either be cast on some distant shore or slowly decay on the surface or in
the depths of the ocean.
From the remarkable series of facts now briefly summarized, we learn, that
whenever plant-remains have been discovered within the Arctic regions,
either in Tertiary or Cretaceous deposits, they show that the climate was
one capable of supporting a rich vegetation of trees, shrubs, and
herbaceous plants, similar in general character to that which prevailed in
the temperate zone at the same periods, but showing the influence of a less
congenial climate. These deposits belong to at least four distinct
geological horizons, and have been found widely scattered within the Arctic
circle, yet nowhere has any proof been obtained of intercalated cold
periods, such as would be indicated by the remains of a stunted vegetation,
or a molluscan fauna similar to that which now prevails there.
_Stratigraphical Evidence of Long-Continued Mild Arctic Conditions._--Let
us now turn to the stratigraphical evidence, which, as we have already
shown, offers a crucial test of the occurrence or non-occurrence of
glaciation during any extensive geological period; and here we have the
testimony of perhaps the greatest living authority on Arctic
geology--Professor Nordenskjöld. In his lecture on "The Former Climate of
the Polar Regions," he says: "The character of the coasts in the Arctic
regions is especially favourable to geological investigations. While the
valleys are for the {77} most part filled with ice, the sides of the
mountains in summer, even in the 80th degree of latitude, and to a height
of 1,000 or 1,500 feet above the level of the sea, are almost wholly free
from snow. Nor are the rocks covered with any amount of vegetation worth
mentioning; and, moreover, the sides of the mountains on the shore itself
frequently present perpendicular sections, which everywhere expose their
bare surfaces to the investigator. The knowledge of a mountain's geognostic
character, at which one, in the more southerly countries, can only arrive
after long and laborious researches, removal of soil and the like, is here
gained almost at the first glance; and as we have never seen in Spitzbergen
nor in Greenland, in these sections often many miles in length, and
including one may say all formations from the Silurian to the Tertiary, any
boulders even as large as a child's head, there is not the smallest
probability that strata of any considerable extent, containing boulders,
are to be found in the polar tracts previous to the middle of the Tertiary
period. Since, then, both an examination of the geognostic condition, and
an investigation of the fossil flora and fauna of the polar lands, show no
signs of a glacial era having existed in those parts before the termination
of the Miocene period, we are fully justified in rejecting, on the evidence
of actual observation, the hypotheses founded on purely theoretical
speculations, which assume the many times repeated alternation of warm and
glacial climates between the present time and the earliest geological
ages."[18] And again, in his _Sketch of the Geology of Spitzbergen_, after
describing the various formations down to the Miocene, he says: "All the
fossils found in the foregoing strata show that Spitzbergen, during former
geological ages, enjoyed a magnificent climate, which indeed was somewhat
colder during the Miocene period, but was still favourable for an
extraordinarily abundant vegetation, much more luxuriant than that which
now occurs even in the southern part of Scandinavia: and I have in those
strata sought in vain for any sign, that, as some geologists have of late
endeavoured to render probable, these favourable climatic conditions have
been broken off {78} by intervals of ancient glacial periods. The profiles
I have had the opportunity to examine during my various Spitzbergen
expeditions would certainly, if laid down on a line, occupy an extent of _a
thousand English miles_; and if any former glacial period had existed in
this region, there ought to have been some trace to be observed of erratic
blocks, or other formations which distinguish glacial action. But this has
not been the case. In the strata, whose length I have reckoned alone, I
have not found a single fragment of a foreign rock so large as a child's
head."[19]
Now it is quite impossible to ignore or evade the force of this testimony
as to the continuous warm climates of the north temperate and polar zones
throughout Tertiary times. The evidence extends over a vast area, both in
space and time, it is derived from the work of the most competent living
geologists, and it is absolutely consistent in its general tendency. We
have in the Lower Cretaceous period an almost tropical climate in France
and England, a somewhat lower temperature in the United States, and a mild
insular climate in the Arctic regions. In each successive period the
climate becomes somewhat less tropical; but down to the Upper Miocene it
remains warm temperate in Central Europe, and cold temperate within the
polar area, with not a trace of any intervening periods of Arctic cold. It
then gradually cools down and merges through the Pliocene into the glacial
epoch in Europe, while in the Arctic zone there is a break in the record
between the Miocene and the recent glacial deposits.[20]
{79}
Accepting this as a substantially correct account of the general climatic
aspect of the Tertiary period in the northern hemisphere, let us see
whether the principles we have already laid down will enable us to give a
satisfactory explanation of its causes.
_The Causes of mild Arctic Climates._--In his remarkable series of papers
on "Ocean Currents," the late Dr. James Croll has proved, with a wealth of
argument and illustration whose cogency is irresistible, that the very
habitability of our globe is due to the equalizing climatic effects of the
waters of the ocean; and that it is to the same cause that we owe, either
directly or indirectly, almost all the chief diversities of climate between
places situated in the same latitude. Owing to the peculiar distribution of
land and sea upon the globe, more than its fair proportion of the warm
equatorial waters is directed towards the western shores of Europe, the
result being that the British Isles, Norway, and Spitzbergen, have all a
milder climate than any other parts of the globe in corresponding
latitudes. A very small portion of the Arctic regions, however, obtains
this benefit, and it thus remains, generally speaking, a land of snow and
ice, with too short a summer to nourish more than a very scanty and
fugitive vegetation. The only other opening than that between Iceland and
Britain by which warm water penetrates within the Arctic circle, is through
Behring's Straits; but this is both shallow and limited in width, and the
consequence is that the larger part of the warm currents of the Pacific
turns back along the shores of the Aleutian Islands and North-west America,
while a very small quantity enters the icy ocean.
But if there were other and wider openings into the Arctic Ocean, a vast
quantity of the heated water which is now turned backward would enter it,
and would produce an amelioration of the climate of which we can hardly
form a conception. A great amelioration of climate would also be caused by
the breaking up or the lowering of such {80} Arctic highlands as now favour
the accumulation of ice; while the interpenetration of the sea into any
part of the great continents in the tropical or temperate zones would again
tend to raise the winter temperature, and render any long continuance of
snow in their vicinity almost impossible.
Now geologists have proved, quite independently of any such questions as we
are here discussing, that changes of the very kinds above referred to have
occurred during the Tertiary period; and that there has been, speaking
broadly, a steady change from a comparatively fragmentary and insular
condition of the great north temperate lands in early Tertiary times, to
that more compact and continental condition which now prevails. It is, no
doubt, difficult and often impossible to determine how long any particular
geographical condition lasted, or whether the changes in one country were
exactly coincident with those in another; but it will be sufficient for our
purpose briefly to indicate those more important changes of land and sea
during the Tertiary period, which must have produced a decided effect on
the climate of the northern hemisphere.
_Geographical Changes Favouring Mild Northern Climates in Tertiary
Times._--The distribution of the Eocene and Miocene formations shows, that
during a considerable portion of the Tertiary period, an inland sea, more
or less occupied by an archipelago of islands, extended across Central
Europe between the Baltic and the Black and Caspian Seas, and thence by
narrower channels south-eastward to the valley of the Euphrates and the
Persian Gulf, thus opening a communication between the North Atlantic and
the Indian Oceans. From the Caspian also a wide arm of the sea extended
during some part of the Tertiary epoch northwards to the Arctic Ocean, and
there is nothing to show that this sea may not have been in existence
during the whole Tertiary period. Another channel probably existed over
Egypt[21] into the eastern {81} basin of the Mediterranean and the Black
Sea; while it is probable that there was a communication between the Baltic
and the White Sea, leaving Scandinavia as an extensive island. Turning to
India, we find that an arm of the sea of great width and depth extended
from the Bay of Bengal to the mouths of the Indus; while the enormous
depression indicated by the presence of marine fossils of Eocene age at a
height of 10,500 feet in Western Tibet, renders it not improbable that a
more direct channel across Afghanistan may have opened a communication
between the West Asiatic and Polar seas.
It may be said that the changes here indicated are not warranted by an
actual knowledge of continuous Tertiary deposits over the situations of the
alleged marine channels; but it is no less certain that the seas in which
any particular strata were deposited were _always_ more extensive than the
fragments of those strata now existing, and _often_ immensely more
extensive. The Eocene deposits of Europe, for example, have certainly
undergone enormous denudation both marine and subaërial, and may have once
covered areas where we now find older deposits (as the chalk once covered
the weald), while a portion of them may lie concealed under Miocene,
Pliocene, or recent beds. We find them widely scattered over Europe and
Asia, and often elevated into lofty mountain ranges; and we should
certainly err far more seriously in confining the Eocene seas to the exact
areas where we now find Eocene rocks, than in liberally extending them, so
as to connect the several detached portions of the formation whenever there
is no valid argument against our doing so. Considering then, that some one
or more of the sea-communications here indicated almost certainly existed
during Eocene and Miocene times, let us endeavour to estimate the probable
effect such communications would have upon the climate of the northern
hemisphere.
_The Indian Ocean as a Source of Heat in Tertiary Times._--If we compare
the Indian Ocean with the South Atlantic we shall see that the position and
outline of the former are very favourable for the accumulation of a large
body of warm water moving northwards. Its southern {82} opening between
South Africa and Australia is very wide, and the tendency of the
trade-winds would be to concentrate the currents towards its north-western
extremity, just where the two great channels above described formed an
outlet to the northern seas. As will be shown in our nineteenth chapter,
there was probably, during the earlier portion of the Tertiary period at
least, several large islands in the space between Madagascar and South
India; but these had wide and deep channels between them, and their
existence may have been favourable to the conveyance of heated water
northward, by concentrating the currents, and thus producing massive bodies
of moving water analogous to the Gulf Stream of the Atlantic.[22] Less heat
would thus be lost by evaporation and radiation in the tropical zone, and
an impulse would be acquired which would carry the warm water into the
north polar area. About the same period Australia was probably divided into
two islands, separated by a wide channel in a north and south direction
(see Chapter XXII.), and through this another current would almost
certainly set northwards, and be directed to the north-west by the southern
extension of Malayan Asia. The more insular condition at this period of
Australia, India, and North Africa, with the depression and probable
fertility of the Central Asiatic plateau, would lead to the Indian Ocean
being traversed by regular trade-winds instead of by variable monsoons, and
thus the constant _vis a tergo_, which is so efficient in the Atlantic,
would keep up a steady and powerful current towards the northern parts of
the Indian Ocean, and thence through the midst of the European archipelago
to the northern seas.
Now it is quite certain that such a condition as we have here sketched out
would produce a wonderful effect on the climate of Central Europe and
Western and Northern Asia. Owing to the warm currents being concentrated in
inland seas instead of being dispersed over a wide ocean like the {83}
North Atlantic, much more heat would be conveyed into the Arctic Ocean, and
this would altogether prevent the formation of ice on the northern shores
of Asia, which continent did not then extend nearly so far north and was
probably deeply inter-penetrated by the sea. This open ocean to the north,
and the warm currents along all the northern lands, would so equalise
temperature, that even the northern parts of Europe might then have enjoyed
a climate fully equal to that of the warmer parts of New Zealand at the
present day, and might have well supported the luxuriant vegetation of the
Miocene period, even without any help from similar changes in the western
hemisphere.[23]
_Condition of North America during the Tertiary Period._--But changes of a
somewhat similar character have also taken place in America and the
Pacific. An enormous area west of the Mississippi, extending over much of
the Rocky Mountains, consists of marine Cretaceous beds 10,000 feet thick,
indicating great and long-continued subsidence, and an insular condition of
Western America with a sea probably extending northwards to the Arctic
Ocean. As marine Tertiary deposits are found conformably overlying these
Cretaceous strata, Professor Dana is of opinion that the great elevation of
this part of America did not begin till early Tertiary times. Other
Tertiary beds in California, Alaska, Kamschatka, the Mackenzie River, the
Parry Islands, and Greenland, indicate partial submergence {84} of all
these lands with the possible influx of warm water from the Pacific; and
the considerable elevation of some of the Miocene beds in Greenland and
Spitzbergen renders it probable that these countries were then much less
elevated, in which case only their higher summits would be covered with
perpetual snow, and no glaciers would descend to the sea.
In the Pacific there was probably an elevation of land counterbalancing, to
some extent, the great depression of so much of the northern continents.
Our map in Chapter XV. shows the islands that would be produced by an
elevation of the great shoals under a thousand fathoms deep, and it is seen
that these all trend in a south-east and north-west direction, and would
thus facilitate the production of definite currents impelled by the
south-east trades towards the north-west Pacific, where they would gain
access to the polar seas through Behring's Straits, which were, perhaps,
sometimes both wider and deeper than at present.
_Effect of these Changes on the Climate of the Arctic Regions._--These
various changes of sea and land, all tending towards a transference of heat
from the equator to the north temperate zone, were not improbably still
further augmented by the existence of a great inland South American sea
occupying what are now the extensive valleys of the Amazon and Orinoco, and
forming an additional reservoir of super-heated water to add to the supply
poured into the North Atlantic.
It is not of course supposed that all the modifications here indicated
co-existed at the same time. We have good reason to believe, from the known
distribution of animals in the Tertiary period, that land-communications
have at times existed between Europe or Asia and North America, either by
way of Behring's Straits, or by Iceland, Greenland, and Labrador. But the
same evidence shows that these land-communications were the exception
rather than the rule, and that they occurred only at long intervals and for
short periods, so as at no time to bring about anything like a complete
interchange of the productions of the two continents.[24] We may therefore
admit that the {85} communication between the tropical and Arctic oceans
was occasionally interrupted in one or other direction; but if we look at a
globe instead of a Mercator's chart of the world, we shall see that the
disproportion between the extent of the polar and tropical seas is so
enormous that a single wide opening, with an adequate impulse to carry in a
considerable stream of warm water, would be amply sufficient for the
complete abolition of polar snow and ice, when aided by the absence of any
great areas of high land within the polar circle, such high land being, as
we have seen, essential to the production of perpetual snow even at the
present time.
Those who wish to understand the effect of oceanic currents in conveying
heat to the north temperate and polar regions, should study the papers of
Dr. Croll already referred to. But the same thing is equally well shown by
the facts of the actual distribution of heat due to the Gulf Stream. The
difference between the mean annual temperatures of the opposite coasts of
Europe and America is well known and has been already quoted, but the
difference of their mean _winter_ temperature is still more striking, and
it is this which concerns us as more especially affecting the distribution
of vegetable and animal life. Our mean winter temperature in the west of
England is the same as that of the Southern United States, as well as that
of Shanghai in China, both about twenty degrees of latitude further south;
and as we go northward the difference increases, so that the winter climate
of Nova Scotia in Lat. 45° is found within the Arctic circle on the coast
of Norway; and if the latter country did not consist almost wholly of
precipitous snow-clad mountains, it would be capable of supporting most of
the vegetable products of the American coast in the latitude of
Bordeaux.[25]
{86}
With these astounding facts before us, due wholly to the transference of a
portion of the warm currents of the Atlantic to the shores of Europe, even
with all the disadvantages of an icy sea to the north-east and ice-covered
Greenland to the north-west, how can we doubt the enormously greater effect
of such a condition of things as has been shown to have existed during the
Tertiary epoch? Instead of _one_ great stream of warm water spreading
widely over the North Atlantic and thus losing the greater part of its
store of heat _before_ it reaches the Arctic seas, we should have _several_
streams conveying the heat of far more extensive tropical oceans by
comparatively narrow inland channels, thus being able to transfer a large
proportion of their heat _into_ the northern and Arctic seas. The heat that
they gave out during the passage, instead of being widely dispersed by
winds and much of it lost in the higher atmosphere, would directly
ameliorate the climate of the continents they passed through, and prevent
all accumulation of snow except on the loftiest mountains. The formation of
ice in the Arctic seas would then be impossible; and the mild winter
climate of the latitude of North {87} Carolina, which by the Gulf Stream is
transferred 20° northwards to our islands, might certainly, under the
favourable conditions which prevailed during the Cretaceous, Eocene, and
Miocene periods, have been carried another 20° north to Greenland and
Spitzbergen; and this would bring about exactly the climate indicated by
the fossil Arctic vegetation. For it must be remembered that the Arctic
summers are, even now, really hotter than ours, and if the winter's cold
were abolished and all ice-accumulation prevented, the high northern lands
would be able to support a far more luxuriant summer vegetation than is
possible in our unequal and cloudy climate.[26]
_Effect of High Excentricity on the Warm Polar Climates._--If the
explanation of the cause of the glacial epoch given in the last chapter is
a correct one, it will, I believe, follow that changes in the amount of
excentricity will produce no important alteration of the climates of the
temperate and Arctic zones so long as favourable geographical conditions,
such as have been now sketched out, render the accumulation of ice
impossible. The effect of a high excentricity in producing a glacial epoch
was shown to be due to the capacity of snow and ice for storing up cold,
and its singular power (when in large masses) of preserving itself unmelted
under a hot sun by itself causing the interposition of a protective
covering of cloud and vapour. But mobile currents of water have no such
power of {88} accumulating and storing up heat or cold from one year to
another, though they do in a pre-eminent degree possess the power of
equalising the temperature of winter and summer and of conveying the
superabundant heat of the tropics to ameliorate the rigour of the Arctic
winters. However great was the difference between the amount of heat
received from the sun in winter and summer in the Arctic zone during a
period of high excentricity and winter in _aphelion_, the inequality would
be greatly diminished by the free ingress of warm currents to the polar
area; and if this was sufficient to prevent any accumulation of ice, the
summers would be warmed to the full extent of the powers of the sun during
the long polar day, which is such as to give the pole at midsummer actually
more heat during the twenty-four hours than the equator receives during its
day of twelve hours. The only difference, then, that would be directly
produced by the changes of excentricity and precession would be, that the
summers would be at one period almost tropical, at the other of a more mild
and uniform temperate character; while the winters would be at one time
somewhat longer and colder, but never, probably, more severe than they are
now in the west of Scotland.
But though high excentricity would not directly modify the mild climates
produced by the state of the northern hemisphere which prevailed during
Cretaceous, Eocene, and Miocene times, it might indirectly affect it by
increasing the mass of Antarctic ice, and thus increasing the force of the
trade-winds and the resulting northward-flowing warm currents. Now there
are many peculiarities in the distribution of plants and of some groups of
animals in the southern hemisphere, which render it almost certain that
there has sometimes been a greater extension of the Antarctic lands during
Tertiary times; and it is therefore not improbable that a more or less
glaciated condition may have been a long persistent feature of the southern
hemisphere, due to the peculiar distribution of land and sea which favours
the production of ice-fields and glaciers. And as we have seen that during
the last three million years the excentricity has been almost always much
higher than {89} it is now, we should expect that the quantity of ice in
the southern hemisphere will usually have been greater, and will thus have
tended to increase the force of those oceanic currents which produce the
mild climates of the northern hemisphere.
_Evidences of Climate in the Secondary and Palæozoic Epochs._--We have
already seen, that so far back as the Cretaceous period there is the most
conclusive evidence of the prevalence of a very mild climate not only in
temperate but also in Arctic lands, while there is no proof whatever, or
even any clear indication, of early glacial epochs at all comparable in
extent and severity with that which has so recently occurred; and we have
seen reason to connect this state of things with a distribution of land and
sea highly favourable to the transference of warm water from equatorial to
polar latitudes. So far as we can judge by the plant-remains of our own
country, the climate appears to have been almost tropical in the Lower
Eocene period; and as we go further back we find no clear indications of a
higher, but often of a lower temperature, though always warmer or more
equable than our present climate. The abundant corals and reptiles of the
Oolite and Lias indicate equally tropical conditions; but further back, in
the Trias, the flora and fauna, in the British area, become poorer, and
there is nothing incompatible with a climate no warmer than that of the
Upper Miocene. This poverty is still more marked in the Permian formation,
and it is here that some indications of ice-action are found in the Lower
Permian conglomerates of the west of England. These beds contain abundant
fragments of various rocks, often angular and sometimes weighing half a
ton, while others are partially rounded, and have polished and striated
surfaces, just like the stones of the "till." They lie confusedly bedded in
a red unstratified marl, and some of them can be traced to the Welsh hills
from twenty to fifty miles distant. This remarkable formation was first
pointed out as proving a remote glacial period, by Professor Ramsay; and
Sir Charles Lyell agreed that this is the only possible explanation that,
with our present knowledge, we can give of them.
Permian breccias are also found in Ireland, containing {90} blocks of
Silurian and Old Red sandstone rocks which Professor Hull believes could
only have been carried by floating ice. Similar breccias occur in the south
of Scotland, and these are stated to be "overlain by a deposit of glacial
age, so similar to the breccia below as to be with difficulty distinguished
from it."[27]
These numerous physical indications of ice-action over a considerable area
during the same geological period, coinciding with just such a poverty of
organic remains as might be produced by a very cold climate, are very
important, and seem clearly to indicate that at this remote period
geographical conditions were such as to bring about a glacial epoch, or
perhaps only local glaciation, in our part of the world.
Boulder-beds also occur in the Carboniferous formation, both in Scotland,
on the continent of Europe, and in North America; and Professor Dawson
considers that he has detected true glacial deposits of the same age in
Nova Scotia. Boulder-beds also occur in the Silurian rocks of Scotland and
North America, and according to Professor Dawson, even in the Huronian,
older than our Cambrian. None of these indications are however so
satisfactory as those of Permian age, where we have the very kind of
evidence we looked for in vain throughout the whole of the Tertiary and
Secondary periods. Its presence in several localities in such ancient rocks
as the Permian is not only most important as indicating a glacial epoch of
some kind in Palæozoic times, but confirms us in the validity of our
conclusion, that the _total_ absence of any such evidence throughout the
Tertiary and Secondary epochs demonstrates the absence of recurring glacial
epochs in the northern hemisphere, notwithstanding the frequent recurrence
of periods of high excentricity.
_Warm Arctic Climates in Early Secondary and Palæozoic Times._--The
evidence we have already adduced of the mild climates prevailing in the
Arctic regions throughout the Miocene, Eocene, and Cretaceous periods is
supplemented by a considerable body of facts relating to still earlier
epochs.
{91}
In the Jurassic period, for example, we have proofs of a mild Arctic
climate, in the abundant plant-remains of East Siberia and Amurland, with
less productive deposits in Spitzbergen, and at Ando in Norway just within
the Arctic circle. But even more remarkable are the marine remains found in
many places in high northern latitudes, among which we may especially
mention the numerous ammonites and the vertebræ of huge reptiles of the
genera Ichthyosaurus and Teleosaurus found in the Jurassic deposits of the
Parry Islands in 77° N. Lat.
In the still earlier Triassic age, nautili and ammonites inhabited the seas
of Spitzbergen, where their fossil remains are now found.
In the Carboniferous formation we again meet with plant-remains and beds of
true coal in the Arctic regions. Lepidodendrons and Calamites, together
with large spreading ferns, are found at Spitzbergen, and at Bear Island in
the extreme north of Eastern Siberia; while marine deposits of the same age
contain abundance of large stony corals.
Lastly, the ancient Silurian limestones, which are widely spread in the
high Arctic regions, contain abundance of corals and cephalopodous mollusca
resembling those from the same deposits in more temperate lands.
_Conclusions as to the Climates of Tertiary and Secondary Periods._--If now
we look at the whole series of geological facts as to the animal and
vegetable productions of the Arctic regions in past ages, it is certainly
difficult to avoid the conclusion that they indicate a climate of a
uniformly temperate or warm character. Whether in Miocene, Upper or Lower
Cretaceous, Jurassic, Triassic, Carboniferous or Silurian times, and in all
the numerous localities extending over more than half the polar regions, we
find one uniform climatic aspect in the fossils. This is quite inconsistent
with the theory of alternate cold and mild epochs during phases of high
excentricity, and persistent cold epochs when the excentricity was as low
as it is now or lower, for that would imply that the duration of cold
conditions was _greater_ than that of warm. Why then should the fauna and
flora of the cold epochs _never_ be {92} preserved? Mollusca and many other
forms of life are abundant in the Arctic seas, and there is often a
luxuriant dwarf woody vegetation on the land, yet in no one case has a
single example of such a fauna or flora been discovered of a date anterior
to the last glacial epoch. And this argument is very much strengthened when
we remember that an exactly analogous series of facts is found over all the
temperate zones. Everywhere we have abundant floras and faunas indicating
warmer conditions than such as now prevail, but never in a single instance
one which as clearly indicates colder conditions. The fact that drift with
Arctic shells was deposited during the last glacial epoch, as well as
gravels and crag with the remains of arctic animals and plants, shows us
that there is nothing to prevent such deposits being formed in cold as well
as in warm periods; and it is quite impossible to believe that in every
place and at all epochs all records of the former have been destroyed,
while in a considerable number of instances those of the latter have been
preserved. When to this uniform testimony of the palæontological evidence
we add the equally uniform absence of any indication of those ice-borne
rocks, boulders, and drift, which are the constant and necessary
accompaniment of every period of glaciation, and which must inevitably
pervade all the marine deposits formed over a wide area so long as the
state of glaciation continues, we are driven to the conclusion that the
last glacial epoch of the northern hemisphere was exceptional, and was not
preceded by numerous similar glacial epochs throughout Tertiary and
Secondary time.
But although glacial epochs (with the one or two exceptions already
referred to) were certainly absent, considerable changes of climate may
have frequently occurred, and these would lead to important changes in the
organic world. We can hardly doubt that some such change occurred between
the Lower and Upper Cretaceous periods, the floras of which exhibit such an
extraordinary contrast in general character. We have also the testimony of
Mr. J. S. Gardner, who has long worked at the fossil floras of the Tertiary
deposits, and who states, that {93} there is strong negative and some
positive evidence of alternating warmer and colder conditions, not glacial,
contained not only in English Eocene, but all Tertiary beds throughout the
world.[28] In the case of marine faunas it is more difficult to judge, but
the numerous changes in the fossil remains from bed to bed only a few feet
and sometimes a few inches apart, may be sometimes due to change of
climate; and when it is recognised that such changes have probably occurred
at all geological epochs and their effects are systematically searched for,
many peculiarities in the distribution of organisms through the different
members of one deposit may be traced to this cause.
_General View of Geological Climates as dependent on the Physical Features
of the Earth's Surface._--In the preceding chapters I have earnestly
endeavoured to arrive at an explanation of geological climates in the
temperate and Arctic zones, which should be in harmony with the great body
of geological facts now available for their elucidation. If my conclusions
as here set forth diverge considerably from those of Dr. Croll, it is not
from any want of appreciation of his facts and arguments, since for many
years I have upheld and enforced his views to the best of my ability. But a
careful re-examination of the whole question has now convinced me that an
error has been made in estimating the comparative effect of geographical
and astronomical causes on changes of climate, and that, while the latter
have undoubtedly played an important part in bringing about the glacial
epoch, it is to the former that the mild climates of the Arctic regions are
almost entirely due. If I have now succeeded in approaching to a true
solution of this difficult problem, I owe it mainly to the study of Dr.
Croll's writings, since my theory is entirely based on the facts and
principles so clearly set forth in his admirable papers on "Ocean Currents
in relation to the Distribution of Heat over the Globe." The main features
of this theory as distinct from that of Dr. Croll I will now endeavour to
summarise.
Looking at the subject broadly, we see that the climatic {94} condition of
the northern hemisphere is the result of the peculiar distribution of land
and water upon the globe; and the general permanence of the position of the
continental and oceanic areas--which we have shown to be proved by so many
distinct lines of evidence--is also implied by the general stability of
climate throughout long geological periods. The land surface of our earth
appears to have always consisted of three great masses in the north
temperate zone, narrowing southward, and terminating in three comparatively
narrow extremities represented by Southern America, South Africa, and
Australia. Towards the north these masses have approached each other, and
have sometimes become united; leaving beyond them a considerable area of
open polar sea. Towards the south they have never been much further
prolonged than at present, but far beyond their extremities an extensive
mass of land has occupied the south polar area.
This arrangement is such as would cause the northern hemisphere to be
always (as it is now) warmer than the southern, and this would lead to the
preponderance of northward winds and ocean currents, and would bring about
the concentration of the latter in three great streams carrying warmth to
the north-polar regions. These streams would, as Dr. Croll has so well
shown, be greatly increased in power by the glaciation of the south polar
land; and whenever any considerable portion of this land was elevated, such
a condition of glaciation would certainly be brought about, and would be
heightened whenever a high degree of excentricity prevailed.
It is now the general opinion of geologists that the great continents have
undergone a process of development from earlier to later times. Professor
Dana appears to have been the first who taught it explicitly in the case of
the North American continent, and he has continued the development of his
views from 1856, when he discussed the subject in the _American Journal_,
to the later editions of his _Manual of Geology_ in which the same views
are extended to all the great continents. He says:--
"The North American continent, which since early {95} time had been
gradually expanding in each direction from the northern Azoic, eastward,
westward, and southward, and which, after the Palæozoic, was finished in
its rocky foundation, excepting on the borders of the Atlantic and Pacific
and the area of the Rocky Mountains, had reached its full expansion at the
close of the Tertiary period. The progress from the first was uniform and
systematic: the land was at all times simple in outline; and its
enlargement took place with almost the regularity of an exogenous
plant."[29]
A similar development undoubtedly took place in the European area, which
was apparently never so compact and so little interpenetrated by the sea as
it is now, while Europe and Asia have only become united into one unbroken
mass since late Tertiary times.
If, however, the greater continents have become more compact and massive
from age to age, and have received their chief extensions northward at a
comparatively recent period, while the Antarctic lands had a corresponding
but somewhat earlier development, we have all the conditions requisite to
explain the persistence, with slight fluctuations, of warm climates far
into the north-polar area throughout Palæozoic, Mesozoic, and Tertiary
times. At length, during the latter part of the Tertiary epoch, a
considerable elevation took place, closing up several of the water passages
to the north, and raising up extensive areas in the Arctic regions to
become the receptacle of snow and ice-fields. This elevation is indicated
by the abundance of Miocene and the absence of Pliocene deposits in the
Arctic zone and the considerable altitude of many Miocene rocks in Europe
and North America; and the occurrence at this time of a long-continued
period of high excentricity necessarily brought on the glacial epoch in the
manner already described in our last chapter. A depression seems to have
occurred during the glacial period itself in North America as in Britain,
but this may have been due partly to the weight of the ice and partly to a
rise of the ocean {96} level caused by the earth's centre of gravity being
shifted towards the north.
We thus see that the last glacial epoch was the climax of a great process
of continental development which had been going on throughout long
geological ages; and that it was the direct consequence of the north
temperate and polar land having attained a great extension and a
considerable altitude just at the time when a phase of very high
excentricity was coming on. Throughout earlier Tertiary and Secondary times
an equally high excentricity often occurred, but it never produced a
glacial epoch, because the north temperate and polar areas had less high
land, and were more freely open to the influx of warm oceanic currents. But
wherever great plateaux with lofty mountains occurred in the temperate zone
a considerable _local_ glaciation might be produced, which would be
specially intense during periods of high excentricity; and it is to such
causes we must impute the indications of ice-action in the vicinity of the
Alps during the Tertiary period. The Permian glaciation appears to have
been more extensive, and it is quite possible that at this remote epoch a
sufficient mass of high land existed in our area and northwards towards the
pole, to have brought on a true glacial period comparable with that which
has so recently passed away.
_Estimate of the comparative effects of Geographical and Astronomical
Causes in producing Changes of Climate._--It appears then, that while
geographical and physical causes alone, by their influence on ocean
currents, have been the main agents in producing the mild climates which
for such long periods prevailed in the Arctic regions, the concurrence of
astronomical causes--high excentricity with winter in _aphelion_--was
necessary to the production of the great glacial epoch. If we reject this
latter agency, we shall be obliged to imagine a concurrence of geographical
changes at a very recent period of which we have no evidence. We must
suppose, for example, that a large part of the British Isles--Scotland,
Ireland, and Wales at all events--were simultaneously elevated so as to
bring extensive areas above the line of perpetual snow; that {97} about the
same time Scandinavia, the Alps, and the Pyrenees received a similar
increase of altitude; and that, almost simultaneously, Eastern North
America, the Sierra Nevada of California, the Caucasus, Lebanon, the
southern mountains of Spain, the Atlas range, and the Himalayas, were each
some thousands of feet higher than they are now; for all these mountains
present us with indications of a recent extension of their glaciers, in
superficial phenomena so similar to those which occur in our own country
and in Western Europe, that we cannot suppose them to belong to a different
epoch. Such a supposition is rendered more difficult by the general
concurrence of scientific testimony to a partial submergence during the
glacial epoch, not only in all parts of Britain, but in North America,
Scandinavia, and, as shown by the wide extension of the drift, in Northern
Europe; and when to this we add the difficulty of understanding how any
probable addition to the altitude of our islands could have brought about
the extreme amount of glaciation which they certainly underwent, and when,
further, we know that a phase of very high excentricity did occur at a
period which is generally admitted to agree well with physical evidence of
the time elapsed since the cold passed away, there seems no sufficient
reason why such an agency should be ignored.
No doubt a prejudice has been excited against it in the minds of many
geologists, by its being thought to lead _necessarily_ to frequently
recurring glacial epochs throughout all geological time. But I have here
endeavoured to show that this is _not_ a necessary consequence of the
theory, because a concurrence of favourable geographical conditions is
essential to the initiation of a glaciation, which when once initiated has
a tendency to maintain itself throughout the varying phases of precession
occurring during a period of high excentricity. When, however, geographical
conditions favour warm Arctic climates--as it has been shown they have done
throughout the larger portion of geological time--then changes of
excentricity, to however great an extent, have no tendency to bring about a
state of glaciation, because warm oceanic currents have a {98}
preponderating influence, and without very large areas of high northern
land to act as condensers, no perpetual snow is possible, and hence the
initial process of glaciation does not occur.
The theory as now set forth should commend itself to geologists, since it
shows the direct dependence of climate on physical processes, which are
guided and modified by those changes in the earth's surface which geology
alone can trace out. It is in perfect accord with the most recent teachings
of the science as to the gradual and progressive development of the earth's
crust from the rudimentary formations of the Azoic age, and it lends
support to the view that no inportant[**important] departure from the great
lines of elevation and depression originally marked out on the earth's
surface has ever taken place.
It also shows us how important an agent in the production of a habitable
globe with comparatively small extremes of climates over its whole area, is
the great disproportion between the extent of the land and the water
surfaces. For if these proportions had been reversed, large areas of land
would necessarily have been removed from the beneficial influence of
aqueous currents or moisture-laden winds; and slight geological changes
might easily have led to half the land surface becoming covered with
perpetual snow and ice, or being exposed to extremes of summer heat and
winter cold, of which our water-permeated globe at present affords no
example. We thus see that what are usually regarded as geographical
anomalies--the disproportion of land and water, the gathering of the land
mainly into one hemisphere, and the singular arrangement of the land in
three great southward-pointing masses--are really facts of the greatest
significance and importance, since it is to these very anomalies that the
universal spread of vegetation and the adaptability of so large a portion
of the earth's surface for human habitation is directly due.
* * * * *
{99}
CHAPTER X
THE EARTH'S AGE, AND THE RATE OF DEVELOPMENT OF ANIMALS AND PLANTS
Various Estimates of Geological Time--Denudation and Deposition of
Strata as a Measure of Time--How to Estimate the Thickness of the
Sedimentary Rocks--How to Estimate the Average Rate of Deposition of
the Sedimentary Rocks--The Rate of Geological Change Probably greater
in very Remote Times--Value of the Preceding Estimate of Geological
Time--Organic Modification Dependent on Change of
Conditions--Geographical Mutations as a Motive Power in bringing about
Organic Changes--Climatal Revolutions as an Agent in Producing Organic
Changes--Present Condition of the Earth one of Exceptional Stability as
Regards Climate--Date of last Glacial Epoch and its Bearing on the
Measurement of Geological Time--Concluding Remarks.
The subjects discussed in the last three chapters introduce us to a
difficulty which has hitherto been considered a very formidable one--that
the maximum age of the habitable earth, as deduced from physical
considerations, does not afford sufficient time either for the geological
or the organic changes of which we have evidence. Geologists continually
dwell on the slowness of the processes of upheaval and subsidence, of
denudation of the earth's surface, and of the formation of new strata;
while on the theory of development, as expounded by Mr. Darwin, the
variation and modification of organic forms is also a very slow process,
and has usually been considered to require an {100} even longer series of
ages than might satisfy the requirements of physical geology alone.
As an indication of the periods usually contemplated by geologists, we may
refer to Sir Charles Lyell's calculation in the tenth edition of his
_Principles of Geology_ (omitted in later editions), by which he arrived at
240 millions of years as having probably elapsed since the Cambrian
period--a very moderate estimate in the opinion of most geologists. This
calculation was founded on the rate of modification of the species of
mollusca; but much more recently Professor Haughton has arrived at nearly
similar figures from a consideration of the rate of formation of rocks and
their known maximum thickness, whence he deduces a maximum of 200 millions
of years for the whole duration of geological time, as indicated by the
series of stratified formations.[30] But in the opinion of all our first
naturalists and geologists, the period occupied in the formation of the
known stratified rocks only represents a portion, and perhaps a small
portion, of geological time. In the sixth edition of the _Origin of
Species_ (p. 286), Mr. Darwin says: "Consequently, if the theory be true,
it is indisputable that before the lowest Cambrian stratum was deposited
long periods elapsed, as long as, or probably far longer than, the whole
interval from the Cambrian age to the present day; and that during these
vast periods the world swarmed with living creatures." Professor Huxley, in
his anniversary address to the Geological Society in 1870, adduced a number
of special cases showing that, on the theory of development, almost all the
higher forms of life must have existed during the Palæozoic period. Thus,
from the fact that almost the whole of the Tertiary period has been
required to convert the ancestral Orohippus into the true horse, he
believes that, in order to have time for the much greater change of the
ancestral Ungulata into the two great odd-toed and even-toed divisions (of
which change there is no trace even among the earliest Eocene mammals), we
should require a large portion, if not the whole, of the Mesozoic or
Secondary period. Another case is furnished by the bats and whales, both of
which strange modifications of the {101} mammalian type occur perfectly
developed in the Eocene formation. What countless ages back must we then go
for the origin of these groups, the whales from some ancestral carnivorous
animal, and the bats from the insectivora! And even then we have to seek
for the common origin of carnivora, insectivora, ungulata, and marsupials
at a far earlier period; so that, on the lowest estimate, we must place the
origin of the mammalia very far back in Palæozoic times. Similar evidence
is afforded by reptiles, of which Professor Huxley says: "If the very small
differences which are observable between the crocodiles of the older
Secondary formations and those of the present day furnish any sort of an
approximation towards an estimate of the average rate of change among
reptiles, it is almost appalling to reflect how far back in Palæozoic times
we must go before we can hope to arrive at that common stock from which the
crocodiles, lizards, _Ornithoscelida_, and _Plesiosauria_, which had
attained so great a development in the Triassic epoch, must have been
derived." Professor Ramsay has expressed similar views, derived from a
general study of the whole series of geological formations and their
contained fossils. He says, speaking of the abundant, varied, and
well-developed fauna of the Cambrian period: "In this earliest known
_varied_ life we find no evidence of its having lived near the beginning of
the zoological series. In a broad sense, compared with what must have gone
before, both biologically and physically, all the phenomena connected with
this old period seem, to my mind, to be of quite a recent description; and
the climates of seas and lands were of the very same kind as those the
world enjoys at the present day."[31]
These opinions, and the facts on which they are founded, are so weighty,
that we can hardly doubt that, if the time since the Cambrian epoch is
correctly estimated at 200 millions of years, the date of the commencement
of life on the earth cannot be much less than 500 millions; while it may
not improbably have been longer, because the reaction of {102} the organism
under changes of the environment is believed to have been less active in
low and simple, than in high and complex forms of life, and thus the
processes of organic development may for countless ages have been
excessively slow.
But according to the physicists, no such periods as are here contemplated
can be granted. From a consideration of the possible sources of the heat of
the sun, as well as from calculations of the period during which the earth
can have been cooling to bring about the present rate of increase of
temperature as we descend beneath the surface, Sir William Thomson
concludes that the crust of the earth cannot have been solidified much
longer than 100 million years (the maximum possible being 400 millions),
and this conclusion is held by Dr. Croll and other men of eminence to be
almost indisputable.[32] It will therefore be well to consider on what data
the calculations of geologists have been founded, and how far the views
here set forth, as to frequent changes of climate throughout all geological
time, may affect the rate of biological change.
_Denudation and Deposition of Strata as a Measure of Time._--The materials
of all the stratified rocks of the globe have been obtained from the dry
land. Every point of the surface is exposed to the destructive influences
of sun and wind, frost, snow, and rain, which break up and wear away the
hardest rocks as well as the softer deposits, and by means of rivers convey
the worn material to the sea. The existence of a considerable depth of soil
over the greater part of the earth's surface; of vast heaps of rocky
_débris_ at the foot of every inland cliff; of enormous deposits of gravel,
sand, and loam; as well as the shingle, pebbles, sand or mud, of every
sea-shore, alike attest the universality of this destructive agency. It is
no less clearly shown by the way in which almost every drop of running
water--whether in gutter, brooklet, stream or large river--becomes
discoloured after each heavy rainfall, since the matter which causes this
discolouration must be derived from the surface {103} of the country, must
always pass from a higher to a lower level, and must ultimately reach the
sea, unless it is first deposited in some lake, or by the overflowing of a
river goes to form an alluvial plain. The universality of this subaërial
denudation, both as regards space and time, renders it certain that its
cumulative effects must be very great; but no attempt seems to have been
made to determine the magnitude of these effects till Mr. Alfred Tylor, in
1853,[33] pointed out that by measuring the quantity of solid matter
brought down by rivers (which can be done with considerable accuracy), we
may obtain the amount of lowering of the land-area, and also the rise of
the ocean level, owing to the quantity of matter deposited on its floor. A
few years later Dr. Croll applied the same method in more detail to an
estimate of the amount by which the land is lowered in a given period; and
the validity of this method has been upheld by Sir A. Geikie, Sir Charles
Lyell, and all our best geologists, as affording a means of actually
determining with some approach to accuracy, the time occupied by one
important phase of geological change.
The quantity of matter carried away from the land by a river is greater
than at first sight appears, and is more likely to be under- than
over-estimated. By taking samples of water near the mouth of a river (but
above the influence of the tide) at a sufficient number of points in its
channel and at different depths, and repeating this daily or at other short
intervals throughout the year, it is easy to determine the quantity of
solid matter held in suspension and solution; and if corresponding
observations determine the quantity of water that is discharged, the total
amount of solid matter brought down annually may be calculated. But besides
this, a considerable quantity of sand or even gravel is carried along the
bottom or bed of the river, and this has rarely been estimated, so that the
figures hitherto obtained are usually under the real quantities. There is
also another source of error caused by the quantity of matter the river may
deposit in lakes or in flooded lands during its course, for this adds to
the amount of denudation performed by the river, although {104} the matter
so deposited does not come down to the sea. After a careful examination of
all the best records, Sir A. Geikie arrives at the following results, as to
the quantity of matter removed by seven rivers from their basins, estimated
by the number of years required to lower the whole surface an average of
one foot:
The Mississippi removes one foot in 6,000 years.
,, Ganges ,, ,, 2,358 ,,
,, Hoang Ho ,, ,, 1,464 ,,
,, Rhone ,, ,, 1,528 ,,
,, Danube ,, ,, 6,846 ,,
,, Po ,, ,, 729 ,,
,, Nith ,, ,, 4,723 ,,
Here we see an intelligible relation between the character of the river
basin and the amount of denudation. The Mississippi has a large portion of
its basin in an arid country, and its sources are either in forest-clad
plateaux or in mountains free from glaciers and with a scanty rainfall. The
Danube flows through Eastern Europe where the rainfall is considerably less
than in the west, while comparatively few of its tributaries rise among the
loftiest Alps. The proportionate amounts of denudation being then what we
might expect, and as all are probably under rather than over the truth, we
may safely take the average of them all as representing an amount of
denudation which, if not true for the whole land surface of the globe, will
certainly be so for a very considerable proportion of it. This average is
almost exactly one foot in three thousand years.[34] The mean altitude of
the several {105} continents has been recently estimated by Mr. John
Murray,[35] to be as follows: Europe 939 feet, Asia 3,189 feet, Africa 2020
feet, North America 1,888 feet, and South America 2,078 feet. At the rate
of denudation above given, it results that, were no other forces at work,
Europe would be planed down to the sea-level in about two million eight
hundred thousand years; while if we take a somewhat slower rate for North
America, that continent might last about four or five million years.[36]
This also implies that the mean height of these continents would have been
about double what it is now three million and five million years ago
respectively: and as we have no reason to suppose this to have been the
case, we are led to infer the constant action of that upheaving force which
the presence of sedimentary formations even on the highest mountains also
demonstrates.
We have already discussed the unequal rate of denudation on hills, valleys,
and lowlands, in connection with the evidence of remote glacial epochs (p.
173); what we have now to consider is, what becomes of all this denuded
matter, and how far the known rate of denudation affords us a measure of
the rate of deposition, and thus gives us some indication of the lapse of
geological time from a comparison of this rate with the observed thickness
of stratified rocks on the earth's surface.
{106}
_How to Estimate the Thickness of the Sedimentary Rocks._--The sedimentary
rocks of which the earth's crust is mainly composed consist, according to
Sir Charles Lyell's classification, of fourteen great formations, of which
the most ancient is the Laurentian, and the most recent the Post-Tertiary
or Pleistocene; with thirty important subdivisions, each of which again
consists of a more or less considerable number of distinct beds or strata.
Thus, the Silurian formation is divided into Upper and Lower Silurian, each
characterized by a distinct set of fossil remains, and the Upper Silurian
again consists of a large number of separate beds, such as the Wenlock
Limestone, the Upper Llandovery Sandstone the Lower Llandovery Slates, &c.,
each usually characterised by a difference of mineral composition or
mechanical structure, as well as by some peculiar fossils. These beds and
formations vary greatly in extent, both above and beneath the surface, and
are also of very various thicknesses in different localities. A thick bed
or series of beds often thins out in a given direction, and sometimes
disappears altogether, so that two beds which were respectively above and
beneath it may come into contact. As an example of this thinning out,
American geologists adduce the Palæozoic formations of the Appalachian
Mountains, which have a total thickness of 42,000 feet, but as they are
traced westward thin out till they become only 4,000 feet in total
thickness. In like manner the Carboniferous grits and shales are 18,000
feet thick in Yorkshire and Lancashire, but they thin out southwards, so
that in Leicestershire they are only 3,000 feet thick; and similar
phenomena occur in all strata and in every part of the world. It must be
observed that this thinning out has nothing to do with denudation (which
acts upon the surface of a country so as to produce great irregularities of
contour), but is a regular attenuation of the layers of rock, due to a
deficiency of sediment in certain directions at the original formation of
the deposit. Owing to this thinning out of stratified rocks, they are on
the whole of far less extent than is usually supposed. When we see a
geological map showing successive formations following each other in long
irregular belts across the country (as is well {107} seen in the case of
the Secondary rocks of England), and a corresponding section showing each
bed dipping beneath its predecessor, we are apt to imagine that beneath the
uppermost bed we should find all the others following in succession like
the coats of an onion. But this is far from being the case, and a
remarkable proof of the narrow limitation of these formations has been
recently obtained by a boring at Ware through the Chalk and Gault Clay,
which latter immediately rests on the Upper Silurian Wenlock Limestone full
of characteristic fossils, at a depth of only 800 feet. Here we have an
enormous gap, showing that none of earlier Secondary or late Palæozoic
formations extend to this part of England, unless indeed they had been all
once elevated and entirely swept away by denudation.[37]
But if we consider how such deposits are now forming, we shall find that
the thinning out of the beds of each formation, and their restriction to
irregular bands and patches, is exactly what we should expect. The enormous
quantity of sediment continually poured into the sea by rivers, gradually
subsides to the bottom as soon as the motion of the water is checked. All
the heavier material must be deposited near the shore or in those areas
over which it is first spread by the tides or currents of the ocean; while
only the very fine mud and clay is carried out to considerable distances.
Thus all stratified deposits {108} will form most quickly near the shores,
and will thin out rapidly at greater distances, little or none being formed
in the depths of the great oceans. This important fact was demonstrated by
the specimens of sea-bottom examined during the voyage of the _Challenger_,
all the "shore deposits" being usually confined within a distance of 100 or
150 miles from the coast; while the "deep-sea deposits" are either purely
organic, being formed of the calcareous or siliceous skeletons of
globigerinæ, radiolarians, and diatomaceæ, or are clays formed of
undissolved portions of these, together with the disintegrated or dissolved
materials of pumice and volcanic dust, which being very light are carried
by wind or by water over the widest oceans.
From the preceding considerations we shall be better able to appreciate the
calculations as to the thickness of stratified deposits made by geologists.
Professor Ramsay has calculated that the sedimentary rocks of Britain alone
have a total _maximum_ thickness of 72,600 feet; while Professor Haughton,
from a survey of the whole world, estimates the _maximum_ thickness of the
known stratified rocks at 177,200 feet. Now these _maximum_ thicknesses of
each deposit will have been produced only where the conditions were
exceptionally favourable, either in deep water near the mouths of great
rivers, or in inland seas, or in places to which the drainage of extensive
countries was conveyed by ocean currents; and this great thickness will
necessarily be accompanied by a corresponding thinness, or complete absence
of deposit, elsewhere. How far the series of rocks found in any extensive
area, as Europe or North America, represents the whole series of deposits
which have been made there we cannot tell; but there is no reason to think
that it is a very inadequate representation of their _maximum_ thickness,
though it undoubtedly is of their _extent_ and _bulk_. When we see in how
many distinct localities patches of the same formation occur, it seems
improbable that the whole of the deposits formed during any one period
should have been destroyed, even in such an area as Europe, while it is
still more improbable that they should be so destroyed over the whole
world; and {109} if any considerable portion of them is left, that portion
may give a fair idea of their average, or even of their maximum, thickness.
In his admirable paper on "The Mean Thickness of the Sedimentary
Rocks,"[38] Dr. James Croll has dwelt on the extent of denudation in
diminishing the mean thickness of the rocks that have been formed,
remarking, "Whatever the present mean thickness of all the sedimentary
rocks of our globe may be, it must be small in comparison to the mean
thickness of all the sedimentary rocks which have been formed. This is
obvious from the fact that the sedimentary rocks of one age are partly
formed from the destruction of the sedimentary rocks of former ages. From
the Laurentian age down to the present day the stratified rocks have been
undergoing constant denudation." This is perfectly true, and yet the mean
thickness of that portion of the sedimentary rocks which remains may not be
very different from that of the entire mass, because denudation acts only
on those rocks which are exposed on the surface of a country, and most
largely on those that are upheaved; while, except in the rare case of an
extensive formation being _quite horizontal_, and wholly exposed to the sea
or to the atmosphere, denudation can have no tendency to diminish the
thickness of any entire deposit.[39] Unless, therefore, a formation is
completely destroyed by denudation in every part of the world (a thing very
improbable), we may have in existing rocks a not very inadequate
representation of the _mean thickness_ of all that have been formed, and
even of the _maximum_ thickness of the larger portion. This will be the
more likely because it is almost certain that many rocks contemporaneously
formed are counted by geologists as distinct formations, whenever they
differ in lithological character or in organic remains. But we know that
limestones, sandstones, and shales, are always forming at the same time;
{110} while a great difference in organic remains may arise from
comparatively slight changes of geographical features, or from difference
in the depth or purity of the water in which the animals lived.[40]
_How to Estimate the Average Rate of Deposition of the Sedimentary
Rocks._--But if we take the estimate of Professor Haughton (177,200 feet),
which, as we have seen, is probably excessive, for the maximum thickness of
the sedimentary rocks of the globe of all known geological ages, can we
arrive at any estimate of the rate at which they were formed? Dr. Croll has
attempted to make such an estimate, but he has taken for his basis the
_mean_ thickness of the rocks, which we have no means whatever of arriving
at, and which he guesses, allowing for denudation, to be equal to the
_maximum_ thickness as measured by geologists. The land-area of the globe
is, according to Dr. Croll, 57,000,000[41] square miles, and he gives the
coast-line as 116,000 miles. This, however, is, for our purpose, rather too
much, as it allows for bays, inlets, and the smaller islands. An
approximate measurement on a globe shows that 100,000 miles will be nearer
the mark, and this has the advantage of being an easily remembered even
number. The distance from the coast, to which shore-deposits usually
extend, may be reckoned at about 100 or 150 miles, but by far the larger
portion of the matter brought down from the land will be deposited
comparatively close to the shore; that is, within twenty or thirty miles.
If we suppose the portion deposited beyond thirty miles to be added to the
deposits within that distance, and the whole reduced to a uniform thickness
in a direction at right angles to the coast, we should probably include all
areas where deposits of the maximum thickness {111} are forming at the
present time, along with a large but unknown proportion of surface where
the deposits were far below the maximum thickness. This follows, if we
consider that deposit must go on very unequally along different parts of a
coast, owing to the distance from each other of the mouths of great rivers
and the limitations of ocean currents; and because, compared with the areas
over which a thick deposit is forming annually, those where there is little
or none are probably at least twice as extensive. If, therefore, we take a
width of thirty miles along the whole coast-line of the globe as
representing the area over which deposits are forming, corresponding to the
maximum thickness as measured by geologists, we shall certainly over rather
than under-estimate the possible rate of deposit.[42]
Now a coast line of 100,000 miles with a width of 30 gives an area of
3,000,000 square miles, on which the denuded matter of the whole land-area
of 57,000,000 square {112} miles is deposited. As these two areas are as 1
to 19, it follows that deposition, as measured by _maximum_ thickness, goes
on at least nineteen times as fast as denudation--probably very much
faster. But the mean rate of denudation over the whole earth is about one
foot in three thousand years; therefore the rate of maximum deposition will
be at least 19 feet in the same time; and as the total maximum thickness of
all the stratified rocks of the globe is, according to Professor Haughton,
177,200 feet, the time required to produce this thickness of rock, at the
present rate of denudation and deposition, is only 28,000,000 years.[43]
_The Rate of Geological Change Probably Greater in very Remote Times._--The
opinion that denudation and deposition went on more rapidly in earlier
times owing to the frequent occurrence of vast convulsions and cataclysms
was strenuously opposed by Sir Charles Lyell, who so well showed that
causes of the very same nature as those now in action were sufficient to
account for all the phenomena presented by the rocks throughout the whole
series of geological formations. But while upholding the soundness of the
views of the "uniformitarians" as opposed to the "convulsionists," we must
yet admit that there is reason for believing in a gradually increasing
intensity of all telluric action as we go back into past time. This subject
has been well treated by Mr. W. J. Sollas,[44] who shows that, if, as all
physicists maintain, the sun gave out perceptibly more heat in past ages
than now, this alone would cause an increase in almost all the forces that
have brought about geological phenomena. With greater heat there would be a
more extensive aqueous atmosphere, and, perhaps, a greater difference
between equatorial and polar temperatures; hence more violent winds,
heavier rains and snows, {113} and more powerful oceanic currents, all
producing more rapid denudation. At the same time, the internal heat of the
earth being greater, it would be cooling more rapidly, and thus the forces
of contraction--which cause the upheaving of mountains, the eruption of
volcanoes, and the subsidence of extensive areas--would be more powerful
and would still further aid the process of denudation. Yet again, the
earth's rotation was certainly more rapid in very remote times, and this
would cause more impetuous tides and still further add to the denuding
power of the ocean. It thus appears that, as we go back into the past,
_all_ the forces tending to the continued destruction and renewal of the
earth's surface would be in more powerful action, and must therefore tend
to reduce the time required for the deposition and upheaval of the various
geological formations. It may be true, as many geologists assert, that the
changes here indicated are so slow that they would produce comparatively
little effect within the time occupied by the known sedimentary rocks, yet,
whatever effect they did produce would certainly be in the direction here
indicated, and as several causes are acting together, their combined
effects may have been by no means unimportant. It must also be remembered
that such an increase of the primary forces on which all geologic change
depends would act with great effect in still further intensifying those
alternations of cold and warm periods in each hemisphere, or, more
frequently, of excessive and equable seasons, which have been shown to be
the result of astronomical, combined with geographical, revolutions; and
this would again increase the rapidity of denudation and deposition, and
thus still further reduce the time required for the production of the known
sedimentary rocks. It is evident therefore that these various
considerations all combine to prove that, in supposing that the rate of
denudation has been on the average only what it is now, we are almost
certainly over-estimating the _time_ required to have produced the whole
series of formations from the Cambrian upwards.
_Value of the Preceding Estimate of Geological Time._--It is not of course
supposed that the calculation here given {114} makes any approach to
accuracy, but it is believed that it does indicate the _order_ of magnitude
of the time required. We have a certain number of data, which are not
guessed but the result of actual measurement; such are, the amount of solid
matter carried down by rivers, the width of the belt within which this
matter is mainly deposited, and the maximum thickness of the known
stratified rocks.[45] A considerable but unknown amount of denudation is
effected by the waves of the ocean eating away coast lines. This was once
thought to be of more importance than sub-aërial denudation, but it is now
believed to be comparatively slow in its action.[46] Whatever it may be,
however, it adds to the rate of formation of new strata, and its omission
from the calculation is again on the side of making the lapse of time
greater rather than less than the true amount. Even if a considerable
modification should be needed in some of the assumptions it has been
necessary to make, the result must still show that, so far as the time
required for the formation of the known stratified rocks, the hundred
million years allowed by physicists is not only ample, but will permit of
even more than an equal period anterior to the lowest Cambrian rocks, as
demanded by Mr. Darwin--a demand supported and enforced by the arguments,
taken from independent standpoints, of Professor Huxley and Professor
Ramsay.
_Organic Modification Dependent on Change of Conditions._--Having {115}
thus shown that the physical changes of the earth's surface may have gone
on much more rapidly and occupied much less time than has generally been
supposed, we have now to inquire whether there are any considerations which
lead to the conclusion that organic changes may have gone on with
corresponding rapidity.
There is no part of the theory of natural selection which is more clear and
satisfactory than that which connects changes of specific forms with
changes of external conditions or environment. If the external world
remains for a moderate period unchanged, the organic world soon reaches a
state of equilibrium through the struggle for existence; each species
occupies its place in nature, and there is then no inherent tendency to
change. But almost any change whatever in the external world disturbs this
equilibrium, and may set in motion a whole series of organic revolutions
before it is restored. A change of climate in any direction will be sure to
injure some and benefit other species. The one will consequently diminish,
the other increase in number; and the former may even become extinct. But
the extinction of a species will certainly affect other species which it
either preyed upon, or competed with, or served for food; while the
increase of any one animal may soon lead to the extinction of some other to
which it was inimical. These changes will in their turn bring other
changes; and before an equilibrium is again established, the proportions,
ranges, and numbers, of the species inhabiting the country may be
materially altered. The complex manner in which animals are related to each
other is well exhibited by the importance of insects, which in many parts
of the world limit the numbers or determine the very existence of some of
the higher animals. Mr. Darwin says:--"Perhaps Paraguay offers the most
curious instance of this; for here neither cattle, nor horses, nor dogs
have ever run wild, though they swarm southward and northward in a wild
state; and Azara and Rengger have shown that this is caused by the greater
number in Paraguay of a certain fly, which lays its eggs in the navels of
these animals when first born. The increase of these flies, numerous as
they are, must be {116} habitually checked by some means, probably by other
parasitic insects. Hence, if certain insectivorous birds were to decrease
in Paraguay, the parasitic insects would probably increase; and this would
lessen the number of navel-frequenting flies--then cattle and horses would
run wild; and this would certainly alter (as indeed I have observed in
parts of South America) the vegetation: this again would largely affect the
insects, and this, as we have seen in Staffordshire, the insectivorous
birds, and so onwards in ever increasing circles of complexity."
Geographical changes would be still more important, and it is almost
impossible to exaggerate the modifications of the organic world that might
result from them. A subsidence of land separating a large island from a
continent would affect the animals and plants in a variety of ways. It
would at once modify the climate, and so produce a series of changes from
this cause alone; but more important would be its effect by isolating small
groups of individuals of many species and thus altering their relations to
the rest of the organic world. Many of these would at once be exterminated,
while others, being relieved from competition, might flourish and become
modified into new species. Even more striking would be the effects when two
continents, or any two land areas which had been long separated, were
united by an upheaval of the strait which divided them. Numbers of animals
would now be brought into competition for the first time. New enemies and
new competitors would appear in every part of the country; and a struggle
would commence which, after many fluctuations, would certainly result in
the extinction of some species, the modification of others, and a
considerable alteration in the proportionate numbers and the geographical
distribution of almost all.
Any other changes which led to the intermingling of species whose ranges
were usually separate would produce corresponding results. Thus, increased
severity of winter or summer temperature, causing southward migrations and
the crowding together of the productions of distinct regions, must
inevitably produce a struggle for existence, which would lead to many
changes both in the characters and {117} the distribution of animals. Slow
elevations of the land would produce another set of changes, by affording
an extended area in which the more dominant species might increase their
numbers; and by a greater range and variety of alpine climates and mountain
stations, affording room for the development of new forms of life.
_Geographical Mutations as a Motive Power in Bringing about Organic
Changes._--Now, if we consider the various geographical changes which, as
we have seen, there is good reason to believe have ever been going on in
the world, we shall find that the motive power to initiate and urge on
organic changes has never been wanting. In the first place, every
continent, though permanent in a general sense, has been ever subject to
innumerable physical and geographical modifications. At one time the total
area has increased, and at another has diminished; great plateaus have
gradually risen up, and have been eaten out by denudation into mountain and
valley; volcanoes have burst forth, and, after accumulating vast masses of
eruptive matter, have sunk down beneath the ocean, to be covered up with
sedimentary rocks, and at a subsequent period again raised above the
surface; and the _loci_ of all these grand revolutions of the earth's
surface have changed their position age after age, so that each portion of
every continent has again and again been sunk under the ocean waves, formed
the bed of some inland sea, or risen high into plateaus and mountain
ranges. How great must have been the effects of such changes on every form
of organic life! And it is to such as these we may perhaps trace those
great changes of the animal world which have seemed to revolutionise it,
and have led us to class one geological period as the age of reptiles,
another as the age of fishes, and a third as the age of mammals.
But such changes as these must necessarily have led to repeated unions and
separations of the land masses of the globe, joining together continents
which were before divided, and breaking up others into great islands or
extensive archipelagoes. Such alterations of the means of transit would
probably affect the organic world even more profoundly than the changes of
area, of altitude, or {118} of climate, since they afforded the means, at
long intervals, of bringing the most diverse forms into competition, and of
spreading all the great animal and vegetable types widely over the globe.
But the isolation of considerable masses of land for long periods also
afforded the means of preservation to many of the lower types, which thus
had time to become modified into a variety of distinct forms, some of which
became so well adapted to special modes of life that they have continued to
exist to the present day, thus affording us examples of the life of early
ages which would probably long since have become extinct had they been
always subject to the competition of the more highly organised animals. As
examples of such excessively archaic forms, we may mention the mud-fishes
and the ganoids, confined to limited fresh-water areas; the frogs and
toads, which still maintain themselves vigorously in competition with
higher forms; and among mammals the Ornithorhynchus and Echidna of
Australia; the whole order of Marsupials--which, out of Australia, where
they are quite free from competition, only exist abundantly in South
America, which was certainly long isolated from the northern continents;
the Insectivora, which, though widely scattered, are generally nocturnal or
subterranean in their habits; and the Lemurs, which are most abundant in
Madagascar, where they have long been isolated, and almost removed from the
competition of higher forms.
_Climatal Revolutions as an Agent in Producing Organic Changes._--The
geographical and geological changes we have been considering are probably
those which have been most effective in bringing about the great features
of the distribution of animals, as well as the larger movements in the
development of organised beings; but it is to the alternations of warm and
cold, or of uniform and excessive climates--of almost perpetual spring in
arctic as well as in temperate lands, with occasional phases of cold
culminating at remote intervals in glacial epochs,--that we must impute
some of the more remarkable changes both in the specific characters and in
the distribution of organisms.[47] {119} Although the geological evidence
is opposed to the belief in early glacial epochs except at very remote and
distant intervals, there is nothing which contradicts the occurrence of
repeated changes of climate, which, though too small in amount to produce
any well-marked physical or organic change, would yet be amply sufficient
to keep the organic world in a constant state of movement, and which, by
subjecting the whole flora and fauna of a country at comparatively short
intervals to decided changes of physical conditions, would supply that
stimulus and motive power which, as we have seen, is all that is necessary
to keep the processes of "natural selection" in constant operation.
The frequent recurrence of periods of high and of low excentricity must
certainly have produced changes of climate of considerable importance to
the life of animals and plants. During periods of high excentricity with
summer in _perihelion_, that season would be certainly very much hotter,
while the winters would be longer and colder than at present; and although
geographical conditions might prevent any permanent increase of snow and
ice even in the extreme north, yet we cannot doubt that the whole northern
hemisphere would then have a very different climate than when the changing
phase of precession brought a very cool summer and a very mild winter--a
perpetual spring, in fact. Now, such a change of climate would certainly be
calculated to bring about a considerable change of _species_, both by
modification and migration, without any such decided change of _type_
either in the vegetation or the animals that we could say from their fossil
remains that any change of climate had taken place. Let us suppose, for
instance, that the climate of England and that of Canada were to be
mutually exchanged, and that the change took five or six thousand years to
bring about, it cannot be doubted that considerable modifications in the
fauna and flora of both countries would be the result, although it is
impossible to predict {120} what the precise changes would be. We can
safely say, however, that some species would stand the change better than
others, while it is highly probable that some would be actually benefited
by it, and that others would be injured. But the benefited would certainly
increase, and the injured decrease, in consequence, and thus a series of
changes would be initiated that might lead to most important results.
Again, we are sure that some species would become modified in adaptation to
the change of climate more readily than others, and these modified species
would therefore increase at the expense of others not so readily modified;
and hence would arise on the one hand extinction of species, and on the
other the production of new forms.
But this is the very least amount of change of climate that would certainly
occur every 10,500 years when there was a high excentricity, for it is
impossible to doubt that a varying distance of the sun in summer from 86 to
99 millions of miles (which is what occurred during--as supposed--the
Miocene period, 850,000 years ago) would produce an important difference in
the summer temperature and in the actinic influence of sunshine on
vegetation. For the intensity of the sun's rays would vary as the square of
the distance, or nearly as 74 to 98, so that the earth would be actually
receiving one-fourth less sun-heat during summer at one time than at the
other. An equally high excentricity occurred 2,500,000 years back, and no
doubt was often reached during still earlier epochs, while a lower but
still very high excentricity has frequently prevailed, and is probably near
its average value. Changes of climate, therefore, every 10,500 years, of
the character above indicated and of varying intensity, have been the rule
rather than the exception in past time; and these changes must have been
variously modified by changing geographical conditions so as to produce
climatic alterations in different directions, giving to the ancient lands
either dry or wet seasons, storms or calms, equable or excessive
temperatures, in a variety of combinations of which the earth perhaps
affords no example under the present low phase of {121} excentricity and
consequent slight inequality of sun-heat.
_Present Condition of the Earth One of Exceptional Stability as Regards
Climate._--It will be seen, by a reference to the diagram at page 171, that
during the last three million years the excentricity has been _less_ than
it is now on eight occasions, for short periods only, making up a total of
about 280,000 years; while it has been _more_ than it is now for many long
periods, of from 300,000 to 700,000 years each, making a total of 2,720,000
years; or nearly as 10 to 1. For nearly half the entire period, or
1,400,000 years, the excentricity has been nearly double what it is now,
and this is not far from its mean condition. We have no reason for
supposing that this long period of three million years, for which we have
tables, was in any way exceptional as regards the degree or variation of
excentricity; but, on the contrary, we may pretty safely assume that its
variations during this time fairly represent its average state of increase
and decrease during all known geological time. But when the glacial epoch
ended, 72,000 years ago, the excentricity was about double its present
amount; it then rapidly decreased till, at 60,000 years back, it was very
little greater than it is now, and since then it has been uniformly small.
It follows that, for about 60,000 years before our time, the mutations of
climate every 10,500 years have been comparatively unimportant, and that
the temperate zones have enjoyed _an exceptional stability of climate_.
During this time those powerful causes of organic change which depend on
considerable changes of climate and the consequent modifications,
migrations, and extinctions of species, will not have been at work; the
slight changes that did occur would probably be so slow and so little
marked that the various species would be able to adapt themselves to them
without much disturbance; and the result would be _an epoch of exceptional
stability of species_.
But it is from this very period of _exceptional stability_ that we obtain
our only _scale_ for measuring the rate of organic change. It includes not
only the historical period, {122} but that of the Swiss Lake dwellings, the
Danish shell-mounds, our peat-bogs, our sunken forests, and many of our
superficial alluvial deposits--the whole in fact, of the iron, bronze, and
neolithic ages. Even some portion of the palæolithic age, and of the more
recent gravels and cave-earths may come into the same general period if
they were formed when the glacial epoch was passing away. Now throughout
all these ages we find no indication of change of species, and but little,
comparatively, of migration. We thus get an erroneous idea of _the
permanence and stability of specific forms_, due to the period immediately
antecedent to our own being a _period of exceptional permanence and
stability_ as regards climatic and geographical conditions.[48]
_Date of Last Glacial Epoch and its Bearing on the Measurement of
Geological Time._--Directly we go back from this stable period we come upon
changes both in the forms and in the distribution of species; and when we
pass beyond the last glacial epoch into the Pliocene period we find
ourselves in a comparatively new world, surrounded by a considerable number
of species altogether different from any which now exist, together with
many others which, though still living, now inhabit distant regions. It
seems not improbable that what is termed the Pliocene period, was really
the coming on of the glacial epoch, and this is the opinion of Professor
Jules Marcou.[49] According to our views, a considerable amount of
geographical change must have occurred at the change from the Miocene to
the Pliocene, favouring the refrigeration of the northern hemisphere, and
leading, in the way already pointed out, to the glacial epoch whenever a
high degree of excentricity {123} prevailed. As many reasons combine to
make us fix the height of the glacial epoch at the period of high
excentricity which occurred 200,000 years back, and as the Pliocene period
was probably not of long duration, we must suppose the next great phase of
very high excentricity (850,000 years ago) to fall within the Miocene
epoch. Dr. Croll believes that this must have produced a glacial period,
but we have shown strong reasons for believing that, in concurrence with
favourable geographical conditions, it led to uninterrupted warm climates
in the temperate and northern zones. This, however, did not prevent the
occurrence of local glaciation wherever other conditions led to its
initiation, and the most powerful of such conditions is a great extent of
high land. Now we know that the Alps acquired a considerable part of their
elevation during the latter part of the Miocene period, since Miocene rocks
occur at an elevation of over 6,000 feet, while Eocene beds occur at nearly
10,000 feet. But since that time there has been a vast amount of
denudation, so that these rocks may have been at first raised much higher
than we now find them, and thus a considerable portion of the Alps may have
been more elevated than they are now. This would certainly lead to an
enormous accumulation of snow, which would be increased when the
excentricity reached a maximum, as already fully explained, and may then
have caused glaciers to descend into the adjacent sea, carrying those
enormous masses of rock which are buried in the Upper Miocene of the
Superga in Northern Italy. An earlier epoch of great altitude in the Alps
coinciding with the very high excentricity 2,500,000 years ago, may have
caused the local glaciation of the Middle Eocene period when the enormous
erratics of the Flysch conglomerate were deposited in the inland seas of
Northern Switzerland, the Carpathians, and the Apennines. This is quite in
harmony with the indications of an uninterrupted warm climate and rich
vegetation during the very same period in the adjacent low countries, just
as we find at the present day in New Zealand a delightful climate and a
rich vegetation of Metrosideros, {124} fuchsias and tree-ferns on the very
borders of huge glaciers, descending to within 700 feet of the sea-level.
It is not pretended that these estimates of geological time have any more
value than probable guesses; but it is certainly a curious coincidence that
two remarkable periods of high excentricity should have occurred, at such
periods and at such intervals apart, as very well accord with the
comparative remoteness of the two deposits in which undoubted signs of
ice-action have been found, and that both these are localised in the
vicinity of mountains which are known to have acquired a considerable
elevation at about the same period of time.
In the tenth edition of the _Principles of Geology_, Sir Charles Lyell,
taking the amount of change in the species of mollusca as a guide,
estimated the time elapsed since the commencement of the Miocene as
one-third that of the whole Tertiary epoch, and the latter at one-fourth
that of geological time since the Cambrian period. Professor Dana, on the
other hand, estimates the Tertiary as only one-fifteenth of the Mesozoic
and Palæozoic combined. On the estimate above given, founded on the dates
of phases of high excentricity, we shall arrive at about four million years
for the Tertiary epoch, and sixteen million years for the time elapsed
since the Cambrian, according to Lyell, or sixty millions according to
Dana. The estimate arrived at from the rate of denudation and deposition
(twenty-eight million years) is nearly midway between these, and it is, at
all events, satisfactory that the various measures result in figures of the
same order of magnitude, which is all one can expect when discussing so
difficult and exceedingly speculative a subject.
The only value of such estimates is to define our notions of geological
time, and to show that the enormous periods, of hundreds of millions of
years, which have sometimes been indicated by geologists, are neither
necessary nor warranted by the facts at our command; while the present
result places us more in harmony with the calculations of physicists, by
leaving a very wide margin between geological time as defined by the
fossiliferous rocks, and that {125} far more extensive period which
includes all possibility of life upon the earth.
_Concluding Remarks._--In the present chapter I have endeavoured to show
that, combining the measured rate of denudation with the estimated
thickness and probable extent of the known series of sedimentary rocks, we
may arrive at a rude estimate of the time occupied in the formation of
those rocks. From another point of departure--that of the probable date of
the Miocene period, as determined by the epoch of high excentricity
supposed to have aided in the production of the Alpine glaciation during
that period, and taking the estimate of geologists as to the proportionate
amount of change in the animal world since that epoch--we obtain another
estimate of the duration of geological time, which, though founded on far
less secure data, agrees pretty nearly with the former estimate. The time
thus arrived at is immensely less than the usual estimates of geologists,
and is so far within the limits of the duration of the earth as calculated
by Sir William Thomson, as to allow for the development of the lower
organisms an amount of time anterior to the Cambrian period several times
greater than has elapsed between that period and the present day. I have
further shown that, in the continued mutations of climate produced by high
excentricity and opposite phases of precession, even though these did not
lead to glacial epochs, we have a motive power well calculated to produce
far more rapid organic changes than have hitherto been thought possible;
while in the enormous amount of specific variation (as demonstrated in an
earlier chapter), we have ample material for that power to act upon, so as
to keep the organic world in a state of rapid change and development
proportioned to the comparatively rapid changes in the earth's surface.
We have now finished the series of preliminary studies of the biological
conditions and physical changes which have affected the modification and
dispersal of organisms, and have thus brought about their actual
distribution on {126} the surface of the earth. These studies will, it is
believed, place us in a condition to solve most of the problems presented
by the distribution of animals and plants, whenever the necessary facts,
both as to their distribution and their affinities, are sufficiently well
known; and we now proceed to apply the principles we have established to
the interpretation of the phenomena presented by some of the more important
and best known of the islands of our globe, limiting ourselves to these for
reasons which have been already sufficiently explained in our preface.
* * * * *
PART II
_INSULAR FAUNAS AND FLORAS_
{241}
CHAPTER XI
THE CLASSIFICATION OF ISLANDS
Importance of Islands in the Study of the Distribution of
Organisms--Classification of Islands with Reference to
Distribution--Continental Islands--Oceanic Islands.
In the preceding chapters, forming the first part of our work, we have
discussed, more or less fully, the general features presented by animal
distribution, as well as the various physical and biological changes which
have been the most important agents in bringing about the present condition
of the organic world.
We now proceed to apply these principles to the solution of the numerous
problems presented by the distribution of animals; and in order to limit
the field of our inquiry, and at the same time to deal only with such facts
as may be rendered intelligible and interesting to those readers who have
not much acquaintance with the details of natural history, we propose to
consider only such phenomena as are presented by the islands of the globe.
_Importance of Islands in the Study of the Distribution of
Organisms._--Islands possess many advantages for the study of the laws and
phenomena of distribution. As compared with continents they have a
restricted area and definite boundaries, and in most cases their
geographical and biological limits coincide. The number of species and of
genera they contain is always much smaller than in the {242} case of
continents, and their peculiar species and groups are usually well defined
and strictly limited in range. Again, their relations with other lands are
often direct and simple, and even when more complex are far easier to
comprehend than those of continents; and they exhibit besides certain
influences on the forms of life and certain peculiarities in their
distribution which continents do not present, and whose study offers many
points of interest.
In islands we have the facts of distribution presented to us, sometimes in
their simplest forms, in other cases becoming gradually more and more
complex; and we are therefore able to proceed step by step in the solution
of the problems they present. But as in studying these problems we have
necessarily to take into account the relations of the insular and
continental faunas, we also get some knowledge of the latter, and acquire
besides so much command over the general principles which underlie all
problems of distribution, that it is not too much to say that when we have
mastered the difficulties presented by the peculiarities of island life we
shall find it comparatively easy to deal with the more complex and less
clearly defined problems of continental distribution.
_Classification of Islands with Reference to Distribution._--Islands have
had two distinct modes of origin--they have either been separated from
continents of which they are but detached fragments, or they have
originated in the ocean and have never formed part of a continent or any
large mass of land. This difference of origin is fundamental, and leads to
a most important difference in their animal inhabitants; and we may
therefore first distinguish the two classes--oceanic and continental
islands.
Mr. Darwin appears to have been the first writer who called attention to
the number and importance, both from a geological and biological point of
view, of oceanic islands. He showed that with very few exceptions all the
remoter islands of the great oceans were of volcanic or coralline
formation, and that none of them contained indigenous mammalia or amphibia.
He also showed the connection of these two phenomena, and maintained that
none of the islands so characterised had ever formed {243} part of a
continent. This was quite opposed to the opinions of the scientific men of
the day, who almost all held the idea of continental extensions, and of
oceanic islands being their fragments, and it was long before Mr. Darwin's
views obtained general acceptance. Even now the belief still lingers; and
we continually hear of old Atlantic or Pacific continents, of "Atlantis" or
"Lemuria," of which hypothetical lands many existing islands, although
wholly volcanic, are thought to be the remnants. We have already seen that
Darwin connected the peculiar geological structure of oceanic islands with
the permanence of the great oceans which contain them, and we have shown
that several distinct lines of evidence all point to the same conclusion.
We may therefore define oceanic islands, as follows:--Islands of volcanic
or coralline formation, usually far from continents and always separated
from them by very deep sea, entirely without indigenous land mammalia or
amphibia, but with a fair number of birds and insects, and usually with
some reptiles. This definition will exclude only two islands which have
been sometimes classed as oceanic--New Zealand and the Seychelles.
Rodriguez, which was once thought to be another exception, has been shown
by the explorations during the Transit of Venus Expedition to be
essentially volcanic, with some upraised coralline limestone.
_Continental Islands._--Continental islands are always more varied in their
geological formation, containing both ancient and recent stratified rocks.
They are rarely very remote from a continent, and they always contain some
land mammals and amphibia, as well as representatives of the other classes
and orders in considerable variety. They may, however, be divided into two
well-marked groups--ancient and recent continental islands--the characters
of which may be easily defined.
Recent continental islands are always situated on submerged banks
connecting them with a continent, and the depth of the intervening sea
rarely exceeds 100 fathoms. They resemble the continent in their geological
structure, while their animal and vegetable productions are either almost
identical with those of the continent, or if {244} otherwise, the
difference consists in the presence of closely allied species of the same
types, with occasionally a very few peculiar genera. They possess in fact
all the characteristics of a portion of the continent, separated from it at
a recent geological period.
Ancient continental islands differ greatly from the preceding in many
respects. They are not united to the adjacent continent by a shallow bank,
but are usually separated from it by a depth of sea of several hundreds to
more than a thousand fathoms. In geological structure they agree generally
with the more recent islands; like them they possess mammalia and amphibia,
usually in considerable abundance, as well as all other classes of animals;
but these are highly peculiar, almost all being distinct species, and many
forming distinct and peculiar genera or families. They are also well
characterised by the fragmentary nature of their fauna, many of the most
characteristic continental orders or families being quite unrepresented,
while some of their animals are allied, not to such forms as inhabit the
adjacent continent, but to others found only in remote parts of the world.
This very remarkable set of characters marks off the islands which exhibit
them as a distinct class, which often present the greatest anomalies and
most difficult problems to the student of distribution.
_Oceanic Islands._--The total absence of warm-blooded terrestrial animals
in an island otherwise well suited to maintain them, is held to prove that
such island is no mere fragment of any existing or submerged continent, but
one that has been actually produced in mid-ocean. It is true that if a
continental island were to be completely submerged for a single day and
then again elevated, its higher terrestrial animals would be all destroyed,
and if it were situated at a considerable distance from land it would be
reduced to the same zoological condition as an oceanic island. But such a
complete submergence and re-elevation appears never to have taken place,
for there is no single island on the globe which has the physical and
geological features of a continental, combined with the zoological features
of an oceanic island. It is true that some of the coral-islands may be
formed upon submerged lands {245} of a continental character, but we have
no proof of this; and even if it were so, the existing islands are to all
intents and purposes oceanic.
We will now pass on to a consideration of some of the more interesting
examples of these three classes, beginning with oceanic islands.
All the animals which now inhabit such oceanic islands must either
themselves have reached them by crossing the ocean, or be the descendants
of ancestors who did so. Let us then see what are, in fact, the animal and
vegetable inhabitants of these islands, and how far their presence can be
accounted for. We will begin with the Azores, or Western Islands, because
they have been thoroughly well explored by naturalists, and in their
peculiarities afford us an important clue to some of the most efficient
means of distribution among several classes of animals.
* * * * *
{246}
CHAPTER XII
OCEANIC ISLANDS:--THE AZORES AND BERMUDA
THE AZORES, OR WESTERN ISLANDS
Position and Physical Features--Chief Zoological Features of the
Azores--Birds--Origin of the Azorean Bird Fauna--Insects of the
Azores--Land-Shells of the Azores--The Flora of the Azores--The
Dispersal of Seeds--Birds as Seed-Carriers--Facilities for Dispersal of
Azorean Plants--Important Deduction from the Peculiarities of the
Azorean Fauna and Flora.
BERMUDA
Position and Physical Features--The Red Clay of Bermuda--Zoology of
Bermuda--Birds of Bermuda--Comparison of the Bird Faunas of Bermuda and
the Azores--Insects of Bermuda--Land Mollusca--Flora of
Bermuda--Concluding Remarks on the Azores and Bermuda.
We will commence our investigation into the phenomena presented by oceanic
islands, with two groups of the North Atlantic, in which the facts are of a
comparatively simple nature and such as to afford us a valuable clue to a
solution of the more difficult problems we shall have to deal with further
on. The Azores and Bermuda offer great contrasts in physical features, but
striking similarities in geographical position. The one is volcanic, the
other coralline; but both are surrounded by a wide expanse of ocean of
enormous depth, the one being about as far from Europe as the other is from
America. Both are situated in the {247} temperate zone, and they differ
less than six degrees in latitude, yet the vegetation of the one is wholly
temperate, while that of the other is almost tropical. The productions of
the one are related to Europe, as those of the other are to America, but
they present instructive differences; and both afford evidence of the
highest value as to the means of dispersal of various groups of organisms
across a wide expanse of ocean.
THE AZORES, OR WESTERN ISLANDS.
These islands, nine in number, form a widely scattered group, situated
between 37° and 39° 40' N. Lat. and stretching in a south-east and
north-west direction over a distance of nearly 400 miles. The largest of
the islands, San Miguel, is about forty miles long, and is one of the
nearest to Europe, being rather under 900 miles from the coast of Portugal,
from which it is separated by an ocean 2,500 fathoms deep. The depth
between the islands does not seem to be known, but the 1,000 fathom line
encloses the whole group pretty closely, while a depth of about 1,800
fathoms is reached within 300 miles in all directions. These great depths
render it in the highest degree improbable that the Azores have ever been
united with the European continent; while their being wholly volcanic is
equally opposed to the view of their having formed part of an extensive
Atlantis including Madeira and the Canaries. The only exception to their
volcanic structure is the occurrence in one small island only (Santa Maria)
of some marine deposits of Upper Miocene age--a fact which proves some
alterations of level, and perhaps a greater extension of this island at
some former period, but in no way indicates a former union of the islands,
or any greater extension of the whole group. It proves, however, that the
group is of considerable antiquity, since it must date back to Miocene
times; and this fact may be of importance in considering the origin and
peculiar features of the fauna and flora. It thus appears that in all
physical features the Azores correspond strictly with our physical
definition of "oceanic islands," while their great distance {248} from any
other land, and the depth of the ocean around them, make them typical
examples of the class. We should therefore expect them to be equally
typical in their fauna and flora; and this is the case as regards the most
important characteristics, although in some points of detail they present
exceptional phenomena.
[Illustration: OUTLINE MAP OF THE AZORES.]
NOTE.--
The light tint shows where the sea is less than 1,000 fathoms deep.
The dark tint " " " more than 1,000 fathoms deep.
The figures show depths in fathoms.
_Chief Zoological Features of the Azores._[50]--The great feature of
oceanic islands--the absence of all indigenous land-mammalia and
amphibia--is well shown in this {249} group; and it is even carried
further, so as to include all terrestrial vertebrata, there being no snake,
lizard, frog, or fresh-water fish, although the islands are sufficiently
extensive, possess a mild and equable climate, and are in every way adapted
to support all these groups. On the other hand, flying creatures, as birds
and insects, are abundant; and there is also one flying mammal--a small
European bat. It is true that rabbits, weasels, rats and mice, and a small
lizard peculiar to Madeira and Teneriffe, are now found wild in the Azores,
but there is good reason to believe that these have all been introduced by
human agency. The same may be said of the gold-fish and eels now found in
some of the lakes, there being not a single fresh-water fish which is truly
indigenous to the islands. When we consider that the nearest part of the
group is about 900 miles from Portugal, and more than 550 miles from
Madeira, it is not surprising that none of these terrestrial animals can
have passed over such a wide expanse of ocean unassisted by man.
Let us now see what animals are believed to have reached the group by
natural means, and thus constitute its indigenous fauna. These consist of
birds, insects, and land-shells, each of which must be considered
separately.
_Birds._--Fifty-three species of birds have been observed at the Azores,
but the larger proportion (thirty-one) are either aquatic or waders--birds
of great powers of flight, whose presence in the remotest islands is by no
means remarkable. Of these two groups twenty are residents, breeding in the
islands, while eleven are stragglers only visiting the islands
occasionally, and all are common European species. The land-birds,
twenty-two in number, are more interesting, four only being stragglers,
while eighteen are permanent residents. The following is a list of these
resident land-birds:--
1. Common Buzzard (_Buteo vulgaris_)
2. Long-eared Owl (_Asio otus_)
3. Barn Owl (_Strix flammea_)
4. Blackbird (_Turdus merula_)
5. Robin (_Erythacus rubecula_)
6. Blackcap (_Sylvia atricapilla_)
{250}
7. Gold-crest (_Regulus cristatus_)
8. Wheatear (_Saxicola oenanthe_)
9. Grey Wagtail (_Motacilla sulphurea_)
10. Atlantic Chaffinch (_Fringilla tintillon_)
11. Azorean Bullfinch (_Pyrrhula murina_)
12. Canary (_Serinus canarius_)
13. Common Starling (_Sturnus vulgaris_)
14. Lesser Spotted Woodpecker (_Dryobates minor_)
15. Wood-pigeon (_Columba palumbus_)
16. Rock Dove (_Columba livia_)
17. Red-legged Partridge (_Caccabis rufa_)
18. Common Quail (_Coturnix communis_)
All the above-named birds are common in Europe and North Africa except
three--the Atlantic chaffinch and the canary which inhabit Madeira and the
Canary Islands, and the Azorean bullfinch, which is peculiar to the islands
we are considering.
_Origin of the Azorean Bird-fauna._--The questions we have now before us
are--how did these eighteen species of birds first reach the Azores, and
how are we to explain the presence of a single peculiar species while all
the rest are identical with European birds? In order to answer them, let us
first see what stragglers now actually visit the Azores from the nearest
continents. The four species given in Mr. Godman's list are the kestrel,
the oriole, the snow-bunting, and the hoopoe; but he also tells us that
there are certainly others, and adds: "Scarcely a storm occurs in spring or
autumn without bringing one or more species foreign to the islands; and I
have frequently been told that swallows, larks, grebes, and other species
not referred to here, are not uncommonly seen at those seasons of the
year."
We have, therefore, every reason to believe that the birds which are now
residents originated as stragglers, which occasionally found a haven in
these remote islands when driven out to sea by storms. Some of them, no
doubt, still often arrive from the continent, but these cannot easily be
distinguished as new arrivals among those which are permanent inhabitants.
Many facts mentioned by Mr. Godman show that this is the case. A barn-owl,
much exhausted, flew on board a whaling-ship when 500 miles S.W. of the
Azores; and even if it had come from {251} Madeira it must have travelled
quite as far as from Portugal to the islands. Mr. Godman also shot a single
specimen of the wheatear in Flores after a strong gale of wind, and as no
one on the island knew the bird, it was almost certainly a recent arrival.
Subsequently a few were found breeding in the old crater of Corvo, a small
adjacent island; and as the species is not found in any other island of the
group, we may infer that this bird is a recent immigrant in process of
establishing itself.
Another fact which is almost conclusive in favour of the bird-population
having arrived as stragglers is, that they are most abundant in the islands
nearest to Europe and Africa. The Azores consist of three divisions--an
eastern, consisting of two islands, St. Michael's and St. Mary's; a central
of five, Terceira, Graciosa, St. George's, Pico, and Fayal; and a western
of two, Flores and Corvo. Now had the whole group once been united to the
continent, or even formed parts of one extensive Atlantic island, we should
certainly expect the central group, which is more compact and has a much
larger area than all the rest, to have the greatest number and variety of
birds. But the fact that birds are most numerous in the eastern group, and
diminish as we go westward, is entirely opposed to this theory, while it is
strictly in accordance with the view that they are all stragglers from
Europe, Africa, or the other Atlantic islands. Omitting oceanic wanderers,
and including all birds which have probably arrived involuntarily, the
numbers are found to be forty species in the eastern group, thirty-six in
the central, and twenty-nine in the western.
To account for the presence of one peculiar species--the bullfinch (which,
however, does not differ from the common European bullfinch more than do
some of the varieties of North American birds from their type-species) is
not difficult; the wonder rather being that there are not more peculiar
forms. In our third chapter we have seen how great is the amount of
individual variation in birds, and how readily local varieties become
established wherever the physical conditions are sufficiently distinct. Now
we can hardly have a greater difference of conditions {252} than between
the continent of Europe or North Africa, and a group of rocky islands in
mid-Atlantic, situated in the full course of the Gulf Stream and with an
excessively mild though stormy climate. We have every reason to believe
that special modifications would soon become established in any animals
completely isolated under such conditions. But they are not, as a rule,
thus completely isolated, because, as we have seen, stragglers arrive at
short intervals; and these, mixing with the residents, keep up the purity
of the breed. It follows, that only those species which reach the Azores at
very remote intervals will be likely to acquire well-marked distinctive
characters; and this appears to have happened with the bullfinch alone, a
bird which does not migrate, and is therefore less likely to be blown out
to sea, more especially as it inhabits woody districts. A few other Azorean
birds, however, exhibit slight differences from their European allies.
There is another reason for the very slight amount of peculiarity presented
by the fauna of the Azores as compared with many other oceanic islands,
dependent on its comparatively recent origin. The islands themselves may be
of considerable antiquity, since a few small deposits, believed to be of
Miocene age, have been found on them, but there can be little doubt that
their present fauna, at all events as concerns the birds, had its origin
since the date of the last glacial epoch. Even now icebergs reach the
latitude of the Azores but a little to the west of them; and when we
consider the proofs of extensive ice-action in North America and Europe, we
can hardly doubt that these islands were at that time surrounded with
pack-ice, while their own mountains, reaching 7,600 feet high in Pico,
would almost certainly have been covered with perpetual snow and have sent
down glaciers to the sea. They might then have had a climate almost as bad
as that now endured by the Prince Edward Islands in the southern
hemisphere, nearly ten degrees farther from the equator, where there are no
land-birds whatever, although the distance from Africa is not much greater
than that of the Azores from Europe, while the vegetation is limited to a
few alpine plants and mosses. This recent origin of the {253} birds
accounts in a great measure for their identity with those of Europe,
because, whatever change has occurred must have been effected in the
islands themselves, and in a time limited to that which has elapsed since
the glacial epoch passed away.
_Insects of the Azores._--Having thus found no difficulty in accounting for
the peculiarities presented by the birds of these islands, we have only to
see how far the same general principles will apply to the insects and
land-shells. The butterflies, moths, and hymenoptera, are few in number,
and almost all seem to be common European species, whose presence is
explained by the same causes as those which have introduced the birds.
Beetles, however, are more numerous, and have been better studied, and
these present some features of interest. The total number of species yet
known is 212, of which 175 are European; but out of these 101 are believed
to have been introduced by human agency, leaving seventy-four really
indigenous. Twenty-three of these indigenous species are not found in any
of the other Atlantic islands, showing that they have been introduced
directly from Europe by causes which have acted more powerfully here than
farther south. Besides these there are thirty-six species not found in
Europe, of which nineteen are natives of Madeira or the Canaries, three are
American, and fourteen are altogether peculiar to the Azores. These latter
are mostly allied to species found in Europe or in the other Atlantic
islands, while one is allied to an American species, and two are so
distinct as to constitute new genera. The following list of these peculiar
species will be interesting:--
CARABIDÆ.
_Anchomenus aptinoides_ Allied to a species from the Canaries.
_Bembidium hesperus_ Allied to the European _B. lætum_.
DYTISCIDÆ.
_Agabus godmanni_ Allied to the European _A. dispar_.
COLYDIIDÆ.
_Tarphius wollastoni_ A genus almost peculiar to the Atlantic
islands.
{254}
ELATERIDÆ.
_Heteroderes azoricus_ Allied to a Brazilian species.
_Elastrus dolosus_ Belongs to a peculiar Madagascar genus!
MELYRIDÆ.
_Attalus miniaticollis_ Allied to a Canarian species.
RHYNCOPHORA.
_Phlæophagus variabilis_ Allied to European and Atlantic species.
_Acalles droueti_ A Mediterranean and Atlantic genus.
_Laparocerus azoricus_ Allied to Madeiran species.
_Asynonychun godmansi_ A peculiar genus, allied to _Brachyderes_, of
the south of Europe.
_Neocnemis occidentalis_ A peculiar genus, allied to the European
genus _Strophosomus_.
HETEROMERA.
_Helops azoricus_ Allied to _H. vulcanus_ of Madeira.
STAPHYLINIDÆ.
_Xenomma melanocephala_ Allied to _X. filiforme_ from the Canaries.
This greater amount of speciality in the beetles than in the birds may be
due to two causes. In the first place many of these small insects have no
doubt survived the glacial epoch, and may, in that case, represent very
ancient forms which have become extinct in their native country; and in the
second place, insects have many more chances of reaching remote islands
than birds, for not only may they be carried by gales of wind, but
sometimes, in the egg or larva state or even as perfect insects, they may
be drifted safely for weeks over the ocean, buried in the light stems of
plants or in the solid wood of trees in which many of them undergo their
transformations. Thus we may explain the presence of three common South
American species (two elaters and a longicorn), all wood-eaters, and
therefore liable to be occasionally brought in floating timber by the Gulf
Stream. But insects are also immensely more numerous in species than are
land-birds, and their transmission would be in most cases quite
involuntary, and not dependent on their own powers of flight as with birds;
and thus the chances against the same species being frequently carried to
the same island would be considerable. If we add to this the dependence of
so {255} many insects on local conditions of climate and vegetation, and
their liability to be destroyed by insectivorous birds, we shall see that,
although there may be a greater probability of insects as a whole reaching
the islands, the chance against any particular species arriving there, or
against the same species arriving frequently, is much greater than in the
case of birds. The result is, that (as compared with Britain for example)
the birds are, proportionately, much more numerous than the beetles, while
the peculiar species of beetles are much more numerous than among birds,
both facts being quite in accordance with what we know of the habits of the
two groups. We may also remark, that the small size and obscure characters
of many of the beetles renders it probable that species now supposed to be
peculiar, really inhabit some parts of Europe or North Africa.
It is interesting to note that the two families which are pre-eminently
wood, root, or seed eaters, are those which present the greatest amount of
speciality. The two Elateridæ alone exhibit remote affinities, the one with
a Brazilian the other with a Madagascar group; while the only peculiar
genera belong to the Rhyncophora, but are allied to European forms. These
last almost certainly form a portion of the more ancient fauna of the
islands which migrated to them in pre-glacial times, while the Brazilian
elater appears to be the solitary example of a living insect brought by the
Gulf Stream to these remote shores. The elater, having its nearest living
ally in Madagascar (_Elastrus dolosus_), cannot be held to indicate any
independent communication between these distant islands; but is more
probably a relic of a once more widespread type which has only been able to
maintain itself in these localities. Mr. Crotch states that there are some
_species_ of beetles common to Madagascar and the Canary Islands, while
there are several _genera_, common to Madagascar and South America, and
some to Madagascar and Australia. The clue to these apparent anomalies is
found in other genera being common to Madagascar, Africa, and South
America, while others are Asiatic or Australian. Madagascar, in fact, has
insect relations with every part of {256} the globe, and the only rational
explanation of such facts is, that they are indications of very ancient and
once widespread groups, maintaining themselves only in a few widely
separated portions of what was at one time or another the area of their
distribution.
_Land-shells of the Azores._--Like the insects and birds, the land-shells
of these islands have a generally European aspect, but with a larger
proportion of peculiar species. This was to be expected, because the means
by which molluscs are carried over the sea are far less numerous and varied
than in the case of insects;[51] and we may therefore conclude that their
introduction is a very rare event, and that a species once arrived remains
for long periods undisturbed by new arrivals, and is therefore more likely
to become modified by the new conditions, and then fixed as a distinct
type. Out of the sixty-nine known species, thirty-seven are common to
Europe or the other Atlantic islands, while thirty-two are peculiar, though
almost all are distinctly allied to European types. The majority of these
shells, especially the peculiar forms, are very small, and many of them may
date back to beyond the glacial epoch. The eggs of these would be
exceedingly minute, and might occasionally be carried on leaves or other
materials during gales of exceptional violence and duration, while others
might be conveyed with the earth that often sticks to the feet of birds.
There are also, probably, other unknown means of conveyance; but however
this may be, the general character of the land-molluscs is such as to
confirm the conclusions we have arrived at from a study of the birds and
insects,--that these islands have never been connected with a continent,
and have been peopled with living things by such forms only as in some way
or other have been able to reach them across many hundred miles of ocean.
_The Flora of the Azores._--The flowering-plants of the Azores have been
studied by one of our first botanists, Mr. H. C. Watson, who has himself
visited the islands and made extensive collections; and he has given a
complete catalogue of the species in Mr. Godman's volume. As our {257}
object in the present work is to trace the past history of the more
important islands by means of the forms of life that inhabit them, and as
for this purpose plants are sometimes of more value than any class of
animals, it will be well to take advantage of the valuable materials here
available, in order to ascertain how far the evidence derived from the two
organic kingdoms agrees in character; and also to obtain some general
results which may be of service in our discussion of more difficult and
more complex problems.
There are in the Azores 480 known species of flowering-plants and ferns, of
which no less than 440 are found also in Europe, Madeira, or the Canary
Islands; while forty are peculiar to the Azores, but are more or less
closely allied to European species. As botanists are no less prone than
zoologists to invoke former land-connections and continental extensions to
account for the wide dispersal of objects of their study, it will be well
to examine somewhat closely what these facts really imply.
_The Dispersal of Seeds._--The seeds of plants are liable to be dispersed
by a greater variety of agents than any other organisms, while their
tenacity of life, under varying conditions of heat and cold, drought and
moisture, is also exceptionally great. They have also an advantage, in that
the great majority of flowering plants have the sexes united in the same
individual, so that a single seed in a state fit to germinate may easily
stock a whole island. The dispersal of seeds has been studied by Sir Joseph
Hooker, Mr. Darwin, and many other writers, who have made it sufficiently
clear that they are in many cases liable to be carried enormous distances.
An immense number are specially adapted to be carried by the wind, through
the possession of down or hairs, or membranous wings or processes; while
others are so minute, and produced in such profusion, that it is difficult
to place a limit to the distance they might be carried by gales of wind or
hurricanes. Another class of somewhat heavier seeds or dry fruits are
capable of being exposed for a long time to sea-water without injury. Mr.
Darwin made many experiments on this point, and he found that many seeds,
especially of Atriplex, {258} Beta, oats, Capsicum, and the potato, grew
after 100 days' immersion, while a large number survived fifty days. But he
also found that most of them sink after a few days' immersion, and this
would certainly prevent them being floated to very great distances. It is
very possible, however, that dried branches or flower-heads containing
seeds would float longer, while it is quite certain that many tropical
seeds do float for enormous distances, as witness the double cocoa-nuts
which cross the Indian ocean from the Seychelle Islands to the coast of
Sumatra, and the West Indian beans which frequently reach the west coast of
Scotland. There is therefore ample evidence of the possibility of seeds
being conveyed across the sea for great distances by winds and surface
currents.[52]
_Birds as Seed-carriers._--The great variety of fruits that are eaten by
birds afford a means of plant-dispersal in the fact that seeds often pass
through the bodies of birds in a state well-fitted for germination; and
such seeds may occasionally be carried long distances by this means. Of the
twenty-two land-birds found in the Azores, half are, more or less,
fruit-eaters, and these may have been the means of introducing many plants
into the islands.
Birds also frequently have small portions of earth on their feet; and Mr.
Darwin has shown by actual experiment that almost all such earth contains
seeds. Thus in {259} nine grains of earth on the leg of a woodcock a seed
of the toad-rush was found which germinated; while a wounded red-legged
partridge had a ball of earth weighing six and a half ounces adhering to
its leg, and from this earth Mr. Darwin raised no less than eighty-two
separate plants of about five distinct species. Still more remarkable was
the experiment with six and three-quarter ounces of mud from the edge of a
little pond, which, carefully treated under glass, produced 537 distinct
plants! This is equal to a seed for every six grains of mud, and when we
consider how many birds frequent the edges of ponds in search of food, or
come there to drink, it is evident that great numbers of seeds may be
dispersed by this means.
Many seeds have hispid awns, hooks, or prickles which readily attach them
to the feathers of birds, and a great number of aquatic birds nest inland
on the ground; and as these are pre-eminently wanderers, they must often
aid in the dispersal of such plants.[53]
{260}
_Facilities for Dispersal of Azorean Plants._--Now in the course of very
long periods of time the various causes here enumerated would be sufficient
to stock the remotest islands with vegetation, and a considerable part of
the Azorean flora appears well adapted to be so conveyed. Of the 439
flowering-plants in Mr. Watson's list, I find that about forty-five belong
to genera that have either pappus or winged seeds; sixty-five to such as
have very minute seeds; thirty have fleshy fruits such as are greedily
eaten by birds; several have hispid seeds; and eighty-four are glumaceous
plants, which are all probably well-adapted for being carried partly by
winds and partly by currents, as well as by some of the other causes
mentioned. On the other hand we have a very suggestive fact in the absence
from the Azores of most of the trees and shrubs with large and heavy
fruits, however common they may be in Europe. Such are oaks, chestnuts,
hazels, apples, beeches, alders, and firs; while the only trees or large
shrubs are the Portugal laurel, myrtle, laurestinus, elder, _Laurus
canariensis_, _Myrica faya_, and a doubtfully peculiar juniper--all small
berry-bearers, and therefore likely to have been conveyed by one or other
of the modes suggested above.
There can be little doubt that the truly indigenous flora of the islands is
far more scanty than the number of plants recorded would imply, because a
large but unknown proportion of the species are certainly importations,
voluntary or involuntary, by man. As, however, the general character of the
whole flora is that of the south-western peninsula of Europe, and as most
of the introduced plants have come from the same country, it is almost
impossible now to separate them, and Mr. Watson has not attempted to do so.
The whole flora contains representatives of eighty natural orders and 250
genera: and even if we suppose that one-half the species only are truly
indigenous, {261} there will still remain a wonderfully rich and varied
flora to have been carried, by the various natural means above indicated,
over 900 miles of ocean, more especially as the large proportion of species
identical with those of Europe shows that their introduction has been
comparatively recent, and that it is, probably (as in the case of the
birds) still going on. We may therefore feel sure that we have here by no
means reached the limit of distance to which plants can be conveyed by
natural means across the ocean; and this conclusion will be of great value
to us in investigating other cases where the evidence at our command is
less complete, and the indications of origin more obscure or conflicting.
Of the forty species which are considered to be peculiar to the islands,
all are allied to European plants except six, whose nearest affinities are
in the Canaries or Madeira. Two of the Compositæ are considered to be
distinct genera, but in this order generic divisions rest on slight
technical distinctions; and the _Campanula vidalii_ is very distinct from
any other known species. With these exceptions, most of the peculiar
Azorean species are closely allied to European plants, and are in several
cases little more than varieties of them. While therefore we may believe
that the larger part of the existing flora reached the islands since the
glacial epoch, a portion of it may be more ancient, as there is no doubt
that a majority of the species could withstand some lowering of
temperature; while in such a warm latitude and surrounded with sea, there
would always be many sunny and sheltered spots in which even tender plants
might flourish.
_Important Deduction from the Peculiarities of the Azorean Fauna and
Flora._--There is one conclusion to be drawn from the almost wholly
European character of the Azorean fauna and flora which deserves special
attention, namely, that the peopling of remote islands is not due so much
to ordinary or normal, as to extraordinary and exceptional causes. These
islands lie in the course of the south-westerly return trades and also of
the Gulf Stream, and we should therefore naturally expect that American
birds, insects, and plants would preponderate if they were {262} conveyed
by the regular winds and currents, which are both such as to prevent
European species from reaching the islands. But the violent storms to which
the Azores are liable blow from all points of the compass; and it is
evidently to these, combined with the greater proximity and more favourable
situation of the coasts of Europe and North Africa, that the presence of a
fauna and flora so decidedly European is to be traced.
The other North Atlantic Islands--Madeira, the Canaries, and the Cape de
Verdes--present analogous phenomena to those of the Azores, but with some
peculiarities dependent on their more southern position, their richer
vegetation, and perhaps their greater antiquity. These have been
sufficiently discussed in my _Geographical Distribution of Animals_ (Vol.
I. pp. 208-215); and as we are now dealing with what may be termed typical
examples of oceanic islands, for the purpose of illustrating the laws, and
solving the problems presented by the dispersal of animals, we will pass on
to other cases which have been less fully discussed in that work.
BERMUDA.
The Bermudas are a small group of low islands formed of coral, and blown
coral-sand consolidated into rock. They are situated in 32° N. Lat., about
700 miles from North Carolina, and somewhat farther from the Bahama
Islands, and are thus rather more favourably placed for receiving
immigrants from America and its islands than the Azores are with respect to
Europe. There are about 100 islands and islets in all, but their total area
does not exceed fifty square miles. They are surrounded by reefs, some at a
distance of thirty miles from the main group; and the discovery of a layer
of earth with remains of cedar-trees forty-eight feet below the present
high-water mark shows that the islands have once been more extensive and
probably included the whole area now occupied by shoals and reefs.[54]
Immediately beyond these reefs, {263} however, extends a very deep ocean,
while about 450 miles distant in a south-east direction, the deepest part
of the North Atlantic is reached, where soundings of 3,825 and 3,875
fathoms have been obtained. It is clear therefore that these islands are
typically oceanic.
[Illustration: MAP OF BERMUDA AND THE AMERICAN COAST.]
NOTE.--The light tint indicates sea less than 1,000 fathoms deep.
The dark tint ,, ,, more than 1,000 fathoms deep.
The figures show the depth in fathoms.
Soundings were taken by the _Challenger_ in four {264} different directions
around Bermuda, and always showed a rapid deepening of the sea to about
2,500 fathoms. This was so remarkable, that in his reports to the
Admiralty, Captain Nares spoke of Bermuda as "a solitary peak rising
abruptly from a base only 120 miles in diameter;" and in another place as
"an isolated peak rising abruptly from a very small base." These
expressions show that Bermuda is looked upon as a typical example of an
"oceanic peak"; and on examining the series of official reports of the
_Challenger_ soundings, I can find no similar case, although some coasts,
both of continents and islands, descend more abruptly. In order to show,
therefore, what is the real character of this peak, I have drawn a section
of it on a true scale from the soundings taken in a north and south
direction where the descent is steepest. It will be seen that the slope is
on both sides very easy, being 1 in 16 on the south, and 1 in 19 on the
north. The portion nearest the islands will slope more rapidly, perhaps
reaching in places 1 in 10; but even this is not steeper than many country
roads in hilly countries, while the remainder would be a hardly perceptible
slope. Although generally very low, some parts of these islands rise to 250
feet above the sea-level, consisting of various kinds of limestone rock,
sometimes soft and friable, but often very hard and even crystalline. It
consists of beds which sometimes dip as much as 30°, and which also show
great contortions, so that at first sight the islands appear to exhibit on
a small scale the phenomena of a disturbed Palæozoic district. It has
however long been known that these rocks are all due to the wind, {265}
which blows up the fine calcareous sand, the product of the disintegration
of coral, shells, serpulæ, and other organisms, forming sand-hills forty
and fifty feet high, which move gradually along, overwhelming the lower
tracts of land behind them. These are consolidated by the percolation of
rain-water, which dissolves some of the lime from the more porous tracts
and deposits it lower down, filling every fissure with stalagmite.
[Illustration: SECTION OF BERMUDA AND ADJACENT SEA BOTTOM.
The figures show the depth in fathoms at fifty-five miles north and
forty-six miles south of the islands respectively.]
_The Red Clay of Bermuda._--Besides the calcareous rocks there is found in
many parts of the islands a layer of red earth or clay, containing about
thirty per cent. of oxide of iron. This very closely resembles, both in
colour and chemical composition, the red clay of the ocean floor, found
widely spread in the Atlantic at depths of from 2,300 to 3,150 fathoms, and
occurring abundantly all round Bermuda. It appears, therefore, at first
sight, as if the ocean bed itself has been here raised to the surface, and
a portion of its covering of red clay preserved; and this is the view
adopted by Mr. Jones in his paper on the "Botany of Bermuda." He says,
after giving the analysis: "This analysis tends to convince us that the
deep chocolate-coloured red clay of the islands found in the lower levels,
and from high-water mark some distance into the sea, originally came from
the ocean floor, and that when by volcanic agency the Bermuda column was
raised from the depths of the sea, its summit, most probably broken in
outline, appeared above the surface covered with this red mud, which in the
course of ages has but slightly changed its composition, and yet possesses
sufficient evidence to prove its identity with that now lying contiguous to
the base of the Bermuda column." But in his _Guide to Bermuda_ Mr. Jones
tells us that this same red earth has been found, two feet thick, under
coral rock at a depth of forty-two feet below low-water mark, and that it
"rested on a bed of compact calcareous sandstone." Now it is quite certain
that this "calcareous sandstone" was never formed at the bottom of the deep
ocean 700 miles from land; and the occurrence of the red earth at different
levels upon coralline sand rock is therefore more probably due to some
process of decomposition of the rock itself, {266} or of the minute
organisms which abound in the blown sand.[55]
_Zoology of Bermuda._--As might be expected from their extreme isolation,
these islands possess no indigenous terrestrial mammalia, frogs, or
snakes.[56] There is however one lizard, which Professor Cope considers to
be distinct from any American species, and which he has named _Plestiodon
(Eumeces) longirostris_. It is said to be most nearly allied to _Eumeces
quinquelineatus_ of the south-eastern States, from which it differs in
having nearly ten more rows of scales, the tail thicker, and the muzzle
longer. In colour it is ashy brown above, greenish blue beneath, with a
white line black-margined on the sides, and it seems to be tolerably
abundant in the islands. This lizard is especially interesting as being the
only vertebrate animal which exhibits any peculiarity.
_Birds._--Notwithstanding its small size, low altitude and {267} remote
position, a great number of birds visit Bermuda annually, some in large
numbers, others only as accidental stragglers. Altogether, over 180 species
have been recorded, rather more than half being wading and swimming birds,
whose presence is not so much to be wondered at as they are great
wanderers; while about eighty-five are land birds, many of which would
hardly be supposed capable of flying so great a distance. Of the 180
species, however, about thirty have only been seen once, and a great many
more are very rare; but about twenty species of land birds are recorded as
tolerably frequent visitors, and nearly half these appear to come every
year.
There are only eleven species which are permanent residents on the
island--eight land, and three water birds, and of these one has been almost
certainly introduced. These resident birds are as follows:--
1. _Galeoscoptes carolinensis._ (The Cat bird.) Migrates along the east
coast of the United States.
2. _Sialia sialis._ (The Blue bird.) Migrates along the east coast.
3. _Vireo novæboracensis._ (The White-eyed green Tit.) Migrates along
the east coast.
4. _Passer domesticus._ (The English Sparrow.) ? Introduced.
5. _Corvus americanus._ (The American Crow.) Common over all North
America.
6. _Cardinalis virginianus._ (The Cardinal bird.) Migrates from
Carolina southward.
7. _Chamoepelia passerina._ (The ground Dove.) Louisiana, W. Indies,
and Mexico.
8. _Ortyx virginianus._ (The American Quail.) New England to Florida.
9. _Ardea herodias._ (The Great Blue Heron.) All North America.
10. _Gailinula galeata._ (The Florida Gallinule.) Temperate and
tropical North America.
11. _Phäeton flavirostris._ (The Tropic Bird.)
It will be seen that these are all very common North American birds, and
most of them are constant visitors from the mainland, so that however long
they may have inhabited the islands there has been no chance for them to
have acquired any distinctive characters owing to the want of isolation.
Among the most regular visitants which are not resident, are the common N.
American kingfisher (_Ceryle alcyon_), {268} the night-hawk (_Chordeiles
virginianus_), the wood wagtail (_Siurus novæboracensis_), the snow-bunting
(_Plectrophanes nivalis_), and the wide-ranging rice-bird (_Dolichonyx
oryzivora_), all very common and widespread in North America.
_Comparison of the Bird-faunas of Bermuda and the Azores._--The bird-fauna
of Bermuda thus differs from that of the Azores, in the much smaller number
of resident species, and the presence of several regular migrants. This is
due, first, to the small area and little varied surface of these islands,
as well as to their limited flora and small supply of insects not affording
conditions suitable for the residence of many species all the year round;
and, secondly, to the peculiarity of the climate of North America, which
causes a much larger number of its birds to be migratory than in Europe.
The Northern United States and Canada, with a sunny climate, luxuriant
vegetation, and abundant insect-life during the summer, supply food and
shelter to an immense number of insectivorous and frugivorous birds; so
that during the breeding season Canada is actually richer in bird-life than
Florida. But as the severe winter comes on all these are obliged to migrate
southward, some to Carolina, Georgia, and Florida, others as far as the
West Indies, Mexico, or even to Guatemala and South America.
Every spring and autumn, therefore a vast multitude of birds, belonging to
more than a hundred distinct species, migrate northward or southward in
Eastern America. A large proportion of these pass along the Atlantic coast,
and it has been observed that many of them fly some distance out to sea,
passing straight across bays from headland to headland by the shortest
route.
Now as the time of these migrations is the season of storms, especially the
autumnal one, which nearly coincides with the hurricanes of the West Indies
and the northerly gales of the coast of America, the migrating birds are
very liable to be carried out to sea. Sometimes they may, as Mr. Jones
suggests, be carried up by local whirlwinds to a great height, where
meeting with a westerly or north-westerly gale, they are rapidly driven
sea-ward. The great majority no doubt perish, but some reach the Bermudas
{269} and form one of its most striking autumnal features. In October, Mr.
Jones tells us, the sportsman enjoys more shooting than at any other time.
The violent revolving gales, which occur almost weekly, bring numbers of
birds of many species from the American continent, the different members of
the duck tribe forming no inconsiderable portion of the whole; while the
Canada goose, and even the ponderous American swan, have been seen amidst
the migratory host. With these come also such delicate birds as the
American robin (_Turdus migratorius_), the yellow-rumped warbler
(_Dendroeca coronata_), the pine warbler (_Dendroeca pinus_), the wood
wagtail (_Siurus novæboracensis_), the summer red bird (_Pyranga æstiva_),
the snow-bunting (_Plectrophanes nivalis_), the red-poll (_Ægiothus
linarius_), the king bird (_Tyrannus carolinensis_), and many others. It is
no doubt in consequence of this repeated immigration that none of the
Bermuda birds have acquired any special peculiarity constituting even a
distinct variety; for the few species that are resident and breed in the
islands are continually crossed by individual immigrants of the same
species from the mainland.
Four European birds also have occurred in Bermuda;--the wheatear (_Saxicola
oenanthe_), which visits Iceland and Lapland and sometimes the northern
United States; the skylark (_Alauda arvensis_), but this was probably an
imported bird or an escape from some ship; the land-rail (_Crex
pratensis_), which also wanders to Greenland and the United States; and the
common snipe (_Scolopax gallinago_), which occurs not unfrequently in
Greenland but has not yet been noticed in North America. It is however so
like the American snipe (_S. wilsoni_), that a straggler might easily be
overlooked.
Two small bats of N. American species also occasionally reach the island,
while two others from the West Indies have more rarely occurred, and these
are the only wild mammalia except rats and mice.
_Insects of Bermuda._--Insects appear to be very scarce; but it is evident
from the lists given by Mr. Jones, and more recently by Professor Heilprin,
that only the more conspicuous species have been yet collected. These {270}
comprise nineteen beetles, eleven bees and wasps, twenty-six butterflies
and moths, nine flies, and the same number of Hemiptera, Orthoptera, and
Neuroptera respectively. All appear to be common North American or West
Indian species; but until some competent entomological collector visits the
islands it is impossible to say whether there are or are not any peculiar
species.[57]
_Land Mollusca._--The land-shells of the Bermudas are somewhat more
interesting, as they appear to be the only group of animals except reptiles
in which there are any peculiar species. The following list was kindly
furnished me by Mr. Thomas Bland of New York, who has made a special study
of the terrestrial molluscs of the West Indian Islands, from which those of
the Bermudas have undoubtedly been derived. The nomenclature has been
corrected in accordance with the list given in Professor Heilprin's work on
the islands. The species which are peculiar to the islands are indicated by
italics.
LIST OF THE LAND-SHELLS OF BERMUDA.
1. Succinea fulgens. (Lea.) Also in Cuba.
2. ,, Bermudensis. (Pfeiffer.) ,, Barbadoes (?)
3. ,, margarita. (Pfr.) ,, Haiti.
4. _Poecilozonites Bermudensis._ (Pfr.) A peculiar form, which, according
to Mr. Binney, "cannot be
placed in any recognised genus."
A larger sub-fossil variety also
occurs, named _H. Nelsoni_, by
Mr. Bland, and which appears
sufficiently distinct to be
classed as another species.
5. ,, _circumfirmatas_ (Redfield.)
6. ,, _discrepans._ (Pfr.)
7. ,, _Reinianus._ (Pfr.)
8. Patula (Thysanophora) hypolepta (Shuttleworth.)
9. ,, vortex. (Pfr.) Southern Florida and West Indies.
10. Helix microdonta. (Desh.) Bahama Islands, Florida, Texas.
11. ,, appressa. (Say.) Virginia and adjacent states;
perhaps introduced into Bermuda.
{271}
12. ,, pulchella. (Müll.) Europe; very close to _H.
minuta_ (Say) of the United
States. Introduced into Bermuda
(?)
13. ,, ventricosa. (Drap.) Azores, Canary Islands, and South
Europe.
14. Bulimulus nitidulus. (Pfr.) Cuba, Haiti, &c.
15. Stenogyra octona. (Ch.) West Indies and South America.
16. Stenogyra decollata (Linn.) A South European species.
Introduced.
17. Coecilianella acicula. (Müll.) Florida, New Jersey, and Europe.
18. Pupa pellucida. (Pfr.) West Indies, and Yucatan.
19. ,, Barbadensis. (Pfr.) Barbadoes (?)
20. ,, Jamaicensis. (C. B. Ad.) Jamaica.
21. Helicina convexa. (Pfr.) Barbuda.[58]
Mr. Bland indicates only four species as certainly peculiar to Bermuda, and
another sub-fossil species; while one or two of the remainder are indicated
as doubtfully identical with those of other countries. We have thus about
one-fifth of the land-shells peculiar, while almost all the other
productions of the islands are identical with those of the adjacent
continent and islands. This corresponds, however, with what occurs
generally in islands at some distance from continents. In the Azores only
one land-bird is peculiar out of eighteen resident species; the beetles
show about one-eighth of the probably non-introduced species as peculiar;
the plants about one-twentieth; while the land-shells have about half the
species peculiar. This difference is well explained by the much greater
difficulty of transmission over wide seas, in the case of land-shells, than
of any other terrestrial organisms. It thus happens that when a species has
once been conveyed it may remain isolated for unknown ages, and has time to
become modified by local conditions unchecked by the introduction of other
individuals of the original type.
_Flora of Bermuda._--Unfortunately no good account of the plants of these
islands has yet been published. Mr. {272} Jones, in his paper "On the
Vegetation of the Bermudas" gives a list of no less than 480 species of
flowering plants; but this number includes all the culinary plants,
fruit-trees, and garden flowers, as well as all the ornamental trees and
shrubs from various parts of the world which have been introduced, mixed up
with the European and American weeds that have come with agricultural or
garden seeds, and the really indigenous plants, in one undistinguished
series. It appears too, that the late Governor, Major-General Lefroy, "has
sown and distributed throughout the islands packets of seeds from Kew,
representing no less than 600 species, principally of trees and shrubs
suited to sandy coast soils"--so that it will be more than ever difficult
in future years to distinguish the indigenous from the introduced
vegetation.
From the researches of Dr. Rein and Mr. Moseley there appear to be about
250 flowering plants in a wild state, and of these Mr. Moseley thinks less
than half are indigenous. The majority are tropical and West Indian, while
others are common to the Southern States of North America; the former class
having been largely brought by means of the Gulf Stream, the latter by the
agency of birds or by winds. Mr. Jones tells us that the currents bring
numberless objects animate and inanimate from the Carribean Sea, including
the seeds of trees, shrubs, and other plants, which are continually cast
ashore and sometimes vegetate. The soap-berry tree (_Sapindus saponaria_)
has been actually observed to originate in this way.
The only _species_ of flowering plant peculiar to Bermuda is _Carex
Bermudiana_ (Hemsley), which is said to be allied to a species found only
in St. Helena; but there are some local forms of continental species, among
which are _Sisyrinchium Bermudianum_ and a variety of _Rhus toxicodendron_.
There are, however, two ferns--an Adiantum and a Nephrodium, which are
unknown from any other locality. The juniper, which is so conspicuous a
feature of the islands, is said to be a West Indian species (_Juniperus
barbadensis_) found in Jamaica and the Bahamas, not the North American red
{273} cedar; but there seems to be still some doubt about this common
plant.
Mr. Moseley, who visited Bermuda in the _Challenger_, has well explained
the probable origin of the vegetation. The large number of West Indian
plants is no doubt due to the Gulf Stream and constant surface drift of
warm water in this direction, while others have been brought by the annual
cyclones which sweep over the intervening ocean. The great number of
American migratory birds, including large flocks of the American golden
plover, with ducks and other aquatic species, no doubt occasionally bring
seeds, either in the mud attached to their feet or in their stomachs.[59]
As these causes are either constantly in action or recur annually, it is
not surprising that almost all the species should be unchanged owing to the
frequent intercrossing of freshly-arrived specimens. If a competent
botanist were thoroughly to explore Bermuda, eliminate the species
introduced by human agency, and investigate the source from whence the
others were derived and the mode by which they had reached so remote an
island, we should obtain important information as to the dispersal of
plants, which might afford us a clue to the solution of many difficult
problems in their geographical distribution.
_Concluding Remarks._--The two groups of islands we have now been
considering furnish us with some most instructive facts as to the power of
many groups of organisms to pass over from 700 to 900 miles of open sea.
There is no doubt whatever that all the indigenous species have thus
reached these islands, and in many cases the process may be seen going on
from year to year. We find that, as regards birds, migratory habits and the
liability to be caught by violent storms are the conditions which determine
the island-population. In both islands the land-birds are almost
exclusively migrants; and in both, the non-migratory groups--wrens, tits,
creepers, and nuthatches--are absent; while the number of annual visitors
is greater in proportion as the migratory habits and prevalence of storms
afford more efficient means for their introduction. {274}
We find also, that these great distances do not prevent the immigration of
some insects of most of the orders, and especially of a considerable number
and variety of beetles; while even land-shells are fairly represented in
both islands, the large proportion of peculiar species clearly indicating
that, as we might expect, individuals of this group of organisms arrive
only at long and irregular intervals.
Plants are represented by a considerable variety of orders and genera, most
of which show some special adaptation for dispersal by wind or water, or
through the medium of birds; and there is no reason to doubt that besides
the species that have actually established themselves, many others must
have reached the islands, but were either not suited to the climate and
other physical conditions, or did not find the insects necessary to their
fertilisation, and were therefore unable to maintain themselves.
If now we consider the extreme remoteness and isolation of these islands,
their small area and comparatively recent origin, and that, notwithstanding
all these disadvantages, they have acquired a very considerable and varied
flora and fauna, we shall, I think, be convinced, that with a larger area
and greater antiquity, mere separation from a continent by many hundred
miles of sea would not prevent a country from acquiring a very luxuriant
and varied flora, and a fauna also rich and peculiar as regards all classes
except terrestrial mammals, amphibia, and some groups of reptiles. This
conclusion will be of great importance in those cases where the evidence as
to the exact origin of the fauna and flora of an island is less clear and
satisfactory than in the case of the Azores and Bermuda.
* * * * *
{275}
CHAPTER XIII
THE GALAPAGOS ISLANDS
Position and Physical Features--Absence of Indigenous Mammalia and
Amphibia--Reptiles--Birds--Insects and Land-Shells--The Keeling Islands
as Illustrating the Manner in which Oceanic Islands are Peopled--Flora
of the Galapagos--Origin of the Flora of the Galapagos--Concluding
Remarks.
The Galapagos differ in many important respects from the islands we have
examined in our last chapter, and the differences are such as to have
affected the whole character of their animal inhabitants. Like the Azores,
they are volcanic, but they are much more extensive, the islands being both
larger and more numerous; while volcanic action has been so recent that a
large portion of their surface consists of barren lava-fields. They are
considerably less distant from a continent than either the Azores or
Bermuda, being about 600 miles from the west coast of South America and a
little more than 700 from Veragua, with the small Cocos Islands
intervening; and they are situated on the equator instead of being in the
north temperate zone. They stand upon a deeply submerged bank, the 1,000
fathom line encircling all the more important islands at a few miles
distance, whence there appears to be a comparatively steep descent all
round to the average depth of that portion of the Pacific, between 2,000
and 3,000 fathoms. {276}
[Illustration: MAP OF THE GALAPAGOS AND ADJACENT COASTS OF SOUTH AMERICA.]
The light tint shows where the sea is less than 1,000 fathoms deep.
The figures show the depth in fathoms.
The whole group occupies a space of about 300 by 200 miles. It consists of
five large and twelve small islands; the largest (Albemarle Island) being
about eighty miles long and of very irregular shape, while the four next in
importance--Chatham, Indefatigable, James, and Narborough Islands, are each
about twenty-five or thirty miles {277} long, and of a rounded or elongate
form. The whole are entirely volcanic, and in the western islands there are
numerous active volcanoes. Unlike the other groups of islands we have been
considering, these are situated in a comparatively calm sea, where storms
are of rare occurrence and even strong winds almost unknown. They are
traversed by ocean currents which are strong and constant, flowing towards
the north-west from the coast of Peru; {278} and these physical conditions
have had a powerful influence on the animal and vegetable forms by which
the islands are now inhabited. The Galapagos have also, during three
centuries, been frequently visited by Europeans, and were long a favourite
resort of buccaneers and traders, who found an ample supply of food in the
large tortoises which abound there; and to these visits we may perhaps
trace the introduction of some animals whose presence it is otherwise
difficult to account for. The vegetation is generally scanty, but still
amply sufficient for the support of a considerable amount of animal life,
as shown by the cattle, horses, asses, goats, pigs, dogs, and cats, which
now run wild in some of the islands.
[Illustration: MAP OF THE GALAPAGOS.]
The light tint shows a depth of less than 1,000 fathoms.
The figures show the depth in fathoms.
_Absence of Indigenous Mammalia and Amphibia._--As in all other oceanic
islands, we find here no truly indigenous mammalia, for though there is a
mouse of the American genus Hesperomys, which differs somewhat from any
known species, we can hardly consider this to be indigenous; first, because
these creatures have been little studied in South America, and there may
yet be many undescribed species, and in the second place because even had
it been introduced by some European or native vessel, there is ample time
in two or three hundred years for the very different conditions to have
established a marked diversity in the characters of the species. This is
the more probable because there is also a true rat of the Old World genus
Mus, which is said to differ slightly from any known species; and as this
genus is not a native of the American continents we are sure that it must
have been recently introduced into the Galapagos. There can be little doubt
therefore that the islands are completely destitute of truly indigenous
mammalia; and frogs and toads, the only tropical representatives of the
Amphibia, are equally unknown.
_Reptiles._--Reptiles, however, which at first sight appear as unsuited as
mammals to pass over a wide expanse of ocean, abound in the Galapagos,
though the species are not very numerous. They consist of land-tortoises,
lizards and snakes. The tortoises consist of two peculiar species, _Testudo
microphyes_, found in most of the islands, and _T. {279} abingdonii_
recently discovered on Abingdon Island, as well as one extinct species, _T.
ephippium_, found on Indefatigable Island. These are all of very large
size, like the gigantic tortoises of the Mascarene Islands, from which,
however, they differ in structural characters; and Dr. Günther believes
that they have been originally derived from the American continent.[60]
Considering the well known tenacity of life of these animals, and the large
number of allied forms which have aquatic or sub-aquatic habits, it is not
a very extravagant supposition that some ancestral form, carried out to sea
by a flood, was once or twice safely drifted as far as the Galapagos, and
thus originated the races which now inhabit them.
The lizards are five in number; a peculiar species of gecko,
_Phyllodactylus galapagensis_, and four species of the American family
Iguanidæ. Two of these are distinct species of the genus Tropidurus, the
other two being large, and so very distinct as to be classed in peculiar
genera. One of these is aquatic and found in all the islands, swimming in
the sea at some distance from the shore and feeding on seaweed; the other
is terrestrial, and is confined to the four central islands. These last
were originally described as _Amblyrhynchus cristatus_ by Mr. Bell, and _A.
subcristatus_ by Gray; they were afterwards placed in two other genera
Trachycephalus and Oreocephalus (_see_ Brit. Mus. Catalogue of Lizards),
while in a recent paper by Dr. Steindachner, the marine species is again
classed as Amblyrhynchus, while the terrestrial form is placed in another
genus Conolophus, both genera being peculiar to the Galapagos.
How these lizards reached the islands we cannot tell. The fact that they
all belong to American genera or families indicates their derivation from
that continent, while their being all distinct species is a proof that
their arrival took place at a remote epoch, under conditions perhaps
somewhat different from any which now prevail. It is certain that animals
of this order have some means of crossing the sea not possessed by any
other land vertebrates, {280} since they are found in a considerable number
of islands which possess no mammals nor any other land reptiles; but what
those means are has not yet been positively ascertained.
It is unusual for oceanic islands to possess snakes, and it is therefore
somewhat of an anomaly that two species are found in the Galapagos. Both
are closely allied to South American forms, and one is hardly different
from a Chilian snake, so that they indicate a more recent origin than in
the case of the lizards. Snakes it is known can survive a long time at sea,
since a living boa-constrictor once reached the island of St. Vincent from
the coast of South America, a distance of two hundred miles by the shortest
route. Snakes often frequent trees, and might thus be conveyed long
distances if carried out to sea on a tree uprooted by a flood such as often
occurs in tropical climates and especially during earthquakes. To some such
accident we may perhaps attribute the presence of these creatures in the
Galapagos, and that it is a very rare one is indicated by the fact that
only two species have as yet succeeded in obtaining a footing there.
_Birds._--We now come to the birds, whose presence here may not seem so
remarkable, but which yet present features of interest not exceeded by any
other group. About seventy species of birds have now been obtained on these
islands, and of these forty-one are peculiar to them. But all the species
found elsewhere, except one, belong to the aquatic tribes or the waders
which are pre-eminently wanderers, yet even of these eight are peculiar.
The true land-birds are forty-two in number, and all but one are entirely
confined to the Galapagos; while three-fourths of them present such
peculiarities that they are classed in distinct genera. All are allied to
birds inhabiting tropical America, some very closely; while one--the common
American rice-bird which ranges over the whole northern and part of the
southern continents--is the only land-bird identical with those of the
mainland. The following is a list of these land-birds taken from Mr.
Salvin's memoir in the _Transactions of the Zoological Society_ for the
year 1876, to which are added nine species collected in 1888 and {281}
described by Mr. Ridgway in the _Proceedings of the U.S. National Museum_
(XII. p. 101) and some additional species obtained in 1889.
TURDIDÆ.
1. Nesomimus trifasciatus } This and the two allied species
2. ,, melanotus } are related to a Peruvian bird
3. ,, parvulus } _Mimus longicaudus_.
4. ,, macdonaldi (Ridg.)
5. ,, personatus (Ridg.)
MNIOTILTIDÆ.
6. Dendroeca aureola { Closely allied to the wide-ranging
{ _D. æstiva_.
HIRUNDINIDÆ.
7. Progne concolor { Allied to _P. purpurea_ of North
{ and South America.
COEREBIDÆ.
8. Certhidea olivacea } A peculiar genus allied to the
9. ,, fusca } Andean genus Conirostrum.
10. ,, cinerascens }
FRINGILLIDÆ.
11. Geospiza magnirostris
12. ,, strenua
13. ,, dubia A distinct genus, but allied to the
14. ,, fortis South American genus Guiraca.
15. ,, nebulosa
16. ,, fuliginosa
17. ,, parvula
18. ,, dentirostris
19. ,, conirostris (Ridg.)
20. ,, media (Ridg.)
21. ,, difficilis (Sharpe)
22. Cactornis scandens
23. ,, assimilis
24. ,, abingdoni
25. ,, pallida A genus allied to the last.
26. ,, brevirostris (Ridg.)
27. ,, hypoleuca (Ridg.) A very peculiar genus allied to
28. Camarhynchus psittaculus Neorhynchus of the west coast
29. ,, crassirostris of Peru.
30. ,, variegatus
31. ,, prosthemelas
32. ,, habeli
33. ,, townsendi (Ridg.)
34. ,, pauper (Ridg.)
{282}
ICTERIDÆ.
35. Dolichonyx oryzivorus Ranges from Canada to Paraguay.
TYRANNIDÆ.
36. Pyrocephalus nanus
37. P. minimus (Ridg.) Allied to _P. rubincus_ of Ecuador.
38. Myiarchus magnirostris Allied to West Indian species.
COLUMBIDÆ.
39. Zenaida galapagensis { A peculiar species of a S.
{ American genus.
FALCONIDÆ.
40. Buteo galapagensis A buzzard of peculiar coloration.
STRIGIDÆ.
41. Asio galapagensis } Hardly distinct from the widespread
} _A. brachyotus._
42. Strix punctatissima Allied to _S. flammea_ but quite
distinct.
We have here every gradation of difference from perfect identity with the
continental species to genera so distinct that it is difficult to determine
with what forms they are most nearly allied; and it is interesting to note
that this diversity bears a distinct relation to the probabilities of, and
facilities for, migration to the islands. The excessively abundant
rice-bird, which breeds in Canada and swarms over the whole United States,
migrating to the West Indies and South America, visiting the distant
Bermudas almost every year, and extending its range as far as Paraguay, is
the only species of land-bird which remains completely unchanged in the
Galapagos; and we may therefore conclude that some stragglers of the
migrating host reach the islands sufficiently often to keep up the purity
of the breed. Next, we have the almost cosmopolite short-eared owl (_Asio
brachyotus_), which ranges from China to Ireland, and from Greenland to the
Straits of Magellan, and of this the Galapagos bird is probably only one of
the numerous varieties. The little wood warbler (_Dendroeca aureola_) is
closely allied to a species which {283} ranges over the whole of North
America and as far south as New Grenada. It has also been occasionally met
with in Bermuda, an indication that it has considerable powers of flight
and endurance. The more distinct _species_--as the tyrant fly-catchers
(Pyrocephalus and Myiarchus), the ground-dove (Zenaida), and the buzzard
(Buteo), are all allied to non-migratory species peculiar to tropical
America, and of a more restricted range; while the distinct _genera_ are
allied to South American groups of thrushes, finches, and sugar-birds which
have usually restricted ranges, and whose habits are such as not to render
them likely to be carried out to sea. The remote ancestral forms of these
birds which, owing to some exceptional causes, reached the Galapagos, have
thus remained uninfluenced by later migrations, and have, in consequence,
been developed into a variety of distinct types adapted to the peculiar
conditions of existence under which they have been placed. Sometimes the
different species thus formed are confined to one or two of the islands
only, as the three species of Certhidea, which are divided between the
islands but do not appear ever to occur together. _Nesomimus parvulus_ is
confined to Albemarle Island, and _N. trifasciatus_ to Charles Island;
_Cactornis pallida_ to Indefatigable Island, _C. brevirostris_ to Chatham
Island, and _C. abingdoni_ to Abingdon Island.
Now all these phenomena are strictly consistent with the theory of the
peopling of the islands by accidental migrations, if we only allow them to
have existed for a sufficiently long period; and the fact that volcanic
action has ceased on many of the islands, as well as their great extent,
would certainly indicate a considerable antiquity.
The great difference presented by the birds of these islands as compared
with those of the equally remote Azores and Bermudas, is sufficiently
explained by the difference of climatal conditions. At the Galapagos there
are none of those periodic storms, gales, and hurricanes which prevail in
the North Atlantic, and which every year carry some straggling birds of
Europe or North America to the former islands; while, at the same time, the
majority of the tropical American birds are {284} nonmigratory, and thus
afford none of the opportunities presented by the countless hosts of
migrants which pass annually northward and southward along the European,
and especially along the North American coasts. It is strictly in
accordance with these different conditions that we find in one case an
almost perfect identity with, and in the other an almost equally complete
diversity from, the continental species of birds.
_Insects and Land-shells._--The other groups of land-animals add little of
importance to the facts already referred to. The insects are very scanty;
the most plentiful group, the beetles, only furnishing about forty species
belonging to thirty-two genera and nineteen families. The species are
almost all peculiar, as are some of the genera. They are mostly small and
obscure insects, allied either to American or to world-wide groups. The
Carabidæ and the Heteromera are the most abundant groups, the former
furnishing six and the latter nine species.[61]
{285}
The land-shells are not abundant--about twenty in all, most of them
peculiar species, but not otherwise remarkable. The observation of Captain
Collnet, quoted by Mr. Darwin in his _Journal_, that drift-wood, bamboos,
canes, and the nuts of a palm, are often washed on the south-eastern shores
of the islands, furnishes an excellent clue to the manner in which many of
the insects and land-shells may have reached the Galapagos. Whirlwinds also
have been known to carry quantities of leaves and other vegetable _débris_
to great heights in the air, and these might be then carried away by strong
upper currents and dropped at great distances, and with them small insects
and mollusca, or their eggs. We must also remember that volcanic islands
are subject to subsidence as well as elevation; and it is quite possible
that during the long period the Galapagos have existed some islands may
have intervened between them and the coast, and have served as
stepping-stones by which the passage to them of various organisms would be
greatly facilitated. Sunken banks, the relics of such islands, are known to
exist in many parts of the ocean, and countless others, no doubt, remain
undiscovered.
_The Keeling Islands as Illustrating the Manner in which Oceanic Islands
are Peopled._--That such causes as have been here adduced are those by
which oceanic islands have been peopled, is further shown by the condition
of equally remote islands which we know are of comparatively recent origin.
Such are the Keeling or Cocos Islands in the Indian Ocean, situated about
the same distance from Sumatra as the Galapagos from South America, but
mere coral reefs, supporting abundance of cocoa-nut palms as their chief
vegetation. These islands were visited by Mr. {286} Darwin, and their
natural history carefully examined. The only mammals are rats, brought by a
wrecked vessel and said by Mr. Waterhouse to be common English rats, "but
smaller and more brightly coloured;" so that we have here an illustration
of how soon a difference of race is established under a constant and
uniform difference of conditions. There are no true land-birds, but there
are snipes and rails, both apparently common Malayan species. Reptiles are
represented by one small lizard, but no account of this is given in the
_Zoology of the Voyage of the Beagle_, and we may therefore conclude that
it was an introduced species. Of insects, careful collecting only produced
thirteen species belonging to eight distinct orders. The only beetle was a
small Elater, the Orthoptera were a Gryllus and a Blatta; and there were
two flies, two ants, and two small moths, one a Diopæa which swarms
everywhere in the eastern tropics in grassy places. All these insects were
no doubt brought either by winds, by floating timber (which reaches the
islands abundantly), or by clinging to the feathers of aquatic or wading
birds; and we only require more time to introduce a greater variety of
species, and a better soil and more varied vegetation, to enable them to
live and multiply, in order to give these islands a fauna and flora equal
to that of the Bermudas. Of wild plants there were only twenty species,
belonging to nineteen genera and to no less than sixteen natural families,
while all were common tropical shore plants.[62] These islands are thus
evidently stocked by waifs and strays brought by the winds and waves; but
their scanty vegetation is mainly due to unfavourable conditions--the
barren coral rock and sand, of which they are wholly composed, together
with exposure to sea-air, being suitable to a very limited number of
species which soon monopolise the surface. With more variety of soil and
aspect a greater variety of plants would establish themselves, and these
would favour the preservation and increase of more insects, birds, and
{287} other animals, as we find to be the case in many small and remote
islands.[63]
_Flora of the Galapagos._--The plants of these islands are so much more
numerous than the known animals, even including the insects, they have been
so carefully studied by eminent botanists, and their relations throw so
much light on the past history of the group, that no apology is needed for
giving a brief outline of the peculiarities and affinities of the flora.
The statements we shall make on this subject will be taken from the Memoir
of Sir Joseph Hooker in the _Linnæan Transactions_ for 1851, founded on Mr.
Darwin's collections, and a later paper by N. J. Andersson in the _Linnæa_
of 1861, embodying more recent discoveries. {288}
The total number of flowering plants known at the latter date was 332, of
which 174 were peculiar to the islands, while 158 were common to other
countries.[64] Of these latter about twenty have been introduced by man,
while the remainder are all natives of some part of America, though about a
third part are species of wide range extending into both hemispheres. Of
those confined to America, forty-two are found in both the northern and
southern continents, twenty-one are confined to South America, while twenty
are found only in North America, the West Indies, or Mexico. This equality
of North American and South American species in the Galapagos is a fact of
great significance in connection with the observation of Sir Joseph Hooker
that the _peculiar_ species are allied to the plants of temperate America
or to those of the high Andes, while the non-peculiar species are mostly
such as inhabit the hotter regions of the tropics near the level of the
sea. He also observes that the seeds of this latter class of Galapagos
plants often have special means of transport, or belong to groups whose
seeds are known to stand long voyages and to possess great vitality. Mr.
Bentham also, in his elaborate account of the Compositæ,[65] remarks on the
decided Central American or Mexican affinities of the Galapagos species, so
that we may consider this to be a thoroughly well-established fact.
The most prevalent families of plants in the Galapagos are the Compositæ
(40 sp.), Gramineæ (32 sp.), Leguminosæ (30 sp.), and Euphorbiaceæ (29
sp.). Of the Compositæ most of the species, except such as are common weeds
or shore plants, are peculiar, but there are only two peculiar genera,
allied to Mexican forms and not very distinct; while the genus Lipochæta,
represented here by a single species, is only found elsewhere in the
Sandwich Islands though it has American affinities.
_Origin of the Galapagos Flora._--These facts are explained by the past
history of the American continent, its {289} separation at various epochs
by arms of the sea uniting the two oceans across what is now Central
America (the last separation being of recent date, as shown by the
considerable number of identical species of fishes on both sides of the
isthmus), and the influence of the glacial epoch in driving the temperate
American flora southward along the mountain plateaus.[66] At the time when
the two oceans were united a portion of the Gulf Stream may have been
diverted into the Pacific, giving rise to a current, some part of which
would almost certainly have reached the Galapagos, and this may have helped
to bring about that singular assemblage of West Indian and Mexican plants
now found there. And as we now believe that the duration of the last
glacial epoch in its successive phases was much longer than the time which
has elapsed since it finally passed away, while throughout the Miocene
epoch the snow-line would often be lowered during periods of high
excentricity, we are enabled to comprehend the nature of the causes which
may have led to the islands being stocked with those north tropical or
mountain types which are so characteristic a feature of that portion of the
Galapagos flora which consists of peculiar species.
On the whole, the flora agrees with the fauna in indicating a moderately
remote origin, great isolation, and changes of conditions affording
facilities for the introduction of organisms from various parts of the
American coast, and even from the West Indian Islands and Gulf of Mexico.
As in the case of the birds, the several islands differ considerably in
their native plants, many species being limited to one or two islands only,
while others extend to several. This is, of course, what might be expected
on any theory of their origin; because, even if the whole of the islands
had once been united and afterwards separated, long continued isolation
would often lead to the differentiation of species, while the varied
conditions to be found upon islands differing in size and altitude as well
as in luxuriance of vegetation, would often lead to the extinction of a
species on one island and its preservation on another. If the several
islands had been equally well {290} explored, it might be interesting to
see whether, as in the case of the Azores, the number of species diminished
in those more remote from the coast; but unfortunately our knowledge of the
productions of the various islands of the group is exceedingly unequal,
and, except in those cases in which representative species inhabit distinct
islands, we have no certainty on the subject. All the more interesting
problems in geographical distribution, however, arise from the relation of
the fauna and flora of the group as a whole to those of the surrounding
continents, and we shall therefore for the most part confine ourselves to
this aspect of the question in our discussion of the phenomena presented by
oceanic or continental islands.
_Concluding Remarks._--The Galapagos offer an instructive contrast with the
Azores, showing how a difference of conditions that might be thought
unimportant may yet produce very striking results in the forms of life.
Although the Galapagos are much nearer a continent than the Azores, the
number of species of plants common to the continent is much less in the
former case than in the latter, and this is still more prominent a
characteristic of the insect and the bird faunas. This difference has been
shown to depend, almost entirely, on the one archipelago being situated in
a stormy, the other in a calm portion of the ocean; and it demonstrates the
preponderating importance of the atmosphere as an agent in the dispersal of
birds, insects, and plants. Yet ocean-currents and surface-drifts are
undoubtedly efficient carriers of plants, and, with plants, of insects and
shells, especially in the tropics; and it is probably to this agency that
we may impute the recent introduction of a number of common Peruvian and
Chilian littoral species, and also of several West Indian types at a more
remote period when the Isthmus of Panama was submerged.
In the case of these islands we see the importance of taking account of
past conditions of sea and land and past changes of climate, in order to
explain the relations of the peculiar or endemic species of their fauna and
flora; and we may even see an indication of the effects of climatal changes
in the northern hemisphere, in the north {291} temperate or alpine
affinities of many of the plants, and even of some of the birds. The
relation between the migratory habits of the birds and the amount of
difference from continental types is strikingly accordant with the fact
that it is almost exclusively migratory birds that annually reach the
Azores and Bermuda; while the corresponding fact that the seeds of those
plants, which are common to the Galapagos and the adjacent continent, have
all--as Sir Joseph Hooker states--some special means of dispersal, is
equally intelligible. The reason why the Galapagos possess four times as
many peculiar species of plants as the Azores is clearly a result of the
less constant introduction of seeds, owing to the absence of storms; the
greater antiquity of the group, allowing more time for specific change; and
the influence of cold epochs and of alterations of sea and land, in
bringing somewhat different sets of plants at different times within the
influence of such modified winds and currents as might convey them to the
islands.
On the whole, then, we have no difficulty in explaining the probable origin
of the flora and fauna of the Galapagos, by means of the illustrative facts
and general principles already adduced.
* * * * *
{292}
CHAPTER XIV
ST. HELENA
Position and Physical Features of St. Helena--Change Effected by
European Occupation--The Insects of St.
Helena--Coleoptera--Peculiarities and Origin of the Coleoptera of St.
Helena--Land-shells of St. Helena--Absence of Fresh-water
Organisms--Native Vegetation of St. Helena--The Relations of the St.
Helena Compositæ--Concluding Remarks on St. Helena.
In order to illustrate as completely as possible the peculiar phenomena of
oceanic islands, we will next examine the organic productions of St. Helena
and of the Sandwich Islands, since these combine in a higher degree than
any other spots upon the globe, extreme isolation from all more extensive
lands, with a tolerably rich fauna and flora whose peculiarities are of
surpassing interest. Both, too, have received considerable attention from
naturalists; and though much still remains to be done in the latter group,
our knowledge is sufficient to enable us to arrive at many interesting
results.
{293} [Illustration: MAP OF THE SOUTH ATLANTIC OCEAN SHOWING THE POSITION
OF ST. HELENA.]
The light tint shows depths of less than 1,000 fathoms.
The figures show depths of the sea in fathoms.
_Position and Physical Features of St. Helena._--This island is situated
nearly in the middle of the South Atlantic Ocean, being more than 1,100
miles from the coast of Africa, and 1,800 from South America. It is about
ten miles long by eight wide, and is wholly volcanic, consisting of ancient
basalts, lavas, and other volcanic products. It is very mountainous and
rugged, bounded for {294} the most part by enormous precipices, and rising
to a height of 2,700 feet above the sea-level. An ancient crater, about
four miles across, is open on the south side, and its northern rim forms
the highest and central ridge of the island. Many other hills and peaks,
however, are more than two thousand feet high, and a considerable portion
of the surface consists of a rugged plateau, having an elevation of about
fifteen hundred to two thousand feet. Everything indicates that St. Helena
is an isolated volcanic mass built up from the depths of the ocean. Mr.
Wollaston remarks: "There are the strongest reasons for believing that the
area of St. Helena was never _very_ much larger than it is at present--the
comparatively shallow sea-soundings within about a mile and a half from the
shore revealing an abruptly defined ledge, _beyond_ which no bottom is
reached at a depth of 250 fathoms; so that the original basaltic mass,
which was gradually piled up by means of successive eruptions from beneath
the ocean, would appear to have its limit definitely marked out by this
suddenly-terminating submarine cliff--the space between it and the existing
coast-line being reasonably referred to that slow process of disintegration
by which the island has been reduced, through the eroding action of the
elements, to its present dimensions." If we add to this that between the
island and the coast of Africa, in a south-easterly direction, is a
profound oceanic gulf known to reach a depth of 2,860 fathoms, or 17,160
feet, while an equally deep, or perhaps deeper, ocean, extends to the west
and south-west, we shall be satisfied that St. Helena is a true oceanic
island, and that it owes none of its peculiarities to a former union with
any continent or other distant land.
_Change Effected by European Occupation._--When first discovered, in the
year 1501, St. Helena was densely covered with a luxuriant forest
vegetation, the trees overhanging the seaward precipices and covering every
part of the surface with an evergreen mantle. This indigenous vegetation
has been almost wholly destroyed; and although an immense number of foreign
plants have been introduced, and have more or less completely established
themselves, {295} yet the general aspect of the island is now so barren and
forbidding that some persons find it difficult to believe that it was once
all green and fertile. The cause of the change is, however, very easily
explained. The rich soil formed by decomposed volcanic rock and vegetable
deposits could only be retained on the steep slopes so long as it was
protected by the vegetation to which it in great part owed its origin. When
this was destroyed, the heavy tropical rains soon washed away the soil, and
has left a vast expanse of bare rock or sterile clay. This irreparable
destruction was caused in the first place by goats, which were introduced
by the Portuguese in 1513, and increased so rapidly that in 1588, they
existed in thousands. These animals are the greatest of all foes to trees,
because they eat off the young seedlings, and thus prevent the natural
restoration of the forest. They were, however, aided by the reckless waste
of man. The East India Company took possession of the island in 1651, and
about the year 1700 it began to be seen that the forests were fast
diminishing, and required some protection. Two of the native trees, redwood
and ebony, were good for tanning, and to save trouble the bark was
wastefully stripped from the trunks only, the remainder being left to rot;
while in 1709 a large quantity of the rapidly disappearing ebony was used
to burn lime for building fortifications! By the MSS. records quoted in Mr.
Melliss' interesting volume on St. Helena,[67] it is evident that the evil
consequences of allowing the trees to be destroyed were clearly foreseen,
as the following passages show: "We find the place called the Great Wood in
a flourishing condition, full of young trees, where the hoggs (of which
there is a great abundance) do not come to root them up. But the Great Wood
is miserably lessened and destroyed within our memories, and is not near
the circuit and length it was. But we believe it does not contain now less
than fifteen hundred acres of fine woodland and good ground, but no springs
of water but what is salt or brackish, which we take to be the reason that
that part was not inhabited when the people first {296} chose out their
settlements and made plantations; but if wells could be sunk, which the
governor says he will attempt when we have more hands, we should then think
it the most pleasant and healthiest part of the island. But as to
healthiness, we don't think it will hold so if the wood that keeps the land
warm were destroyed, for then the rains, which are violent here, would
carry away the upper soil, and it being a clay marl underneath would
produce but little; as it is, we think in case it were enclosed it might be
greatly improved" ... "When once this wood is gone the island will soon be
ruined" ... "We viewed the wood's end which joins the Honourable Company's
plantation called the Hutts, but the wood is so destroyed that the
beginning of the Great Wood is now a whole mile beyond that place, and all
the soil between being washed away, that distance is now entirely barren."
(MSS. records, 1716.) In 1709 the governor reported to the Court of
Directors of the East India Company that the timber was rapidly
disappearing, and that the goats should be destroyed for the preservation
of the ebony wood, and because the island was suffering from droughts. The
reply was, "The goats are not to be destroyed, being more valuable than
ebony." Thus, through the gross ignorance of those in power, the last
opportunity of preserving the peculiar vegetation of St. Helena, and
preventing the island from becoming the comparatively rocky desert it now
is, was allowed to pass away.[68] Even in a mere {297} pecuniary point of
view the error was a fatal one, for in the next century (in 1810) another
governor reports the total destruction of the great forests by the goats,
and that in consequence the cost of importing fuel for government use was
2,729l. 7s. 8d. for a single year! About this time large numbers of
European, American, Australian, and South African plants were imported, and
many of these ran wild and increased so rapidly as to drive out and
exterminate much of the relics of the native flora; so that now English
broom gorse and brambles, willows and poplars, and some common American,
Cape, and Australian weeds, alone meet the eye of the ordinary visitor.
These, in Sir Joseph Hooker's opinion, render it absolutely impossible to
restore the native flora, which only lingers in a few of the loftiest
ridges and most inaccessible precipices, and is rarely seen except by some
exploring naturalist.
This almost total extirpation of a luxuriant and highly peculiar vegetation
must inevitably have caused the destruction of a considerable portion of
the lower animals which once existed on the island, and it is rather
singular that so much as has actually been discovered should be left to
show us the nature of the aboriginal fauna. Many naturalists have made
small collections during short visits, but we owe our present complete
knowledge of the two most interesting groups of animals, the insects, and
the land-shells, mainly to the late Mr. T. Vernon Wollaston, who, after
having thoroughly explored Madeira and the Canaries, undertook a voyage to
St. Helena for the express purpose of studying its terrestrial fauna, and
resided for six months (1875-76) in a high central position, whence the
loftiest peaks could be explored. The results of his labours are contained
in two volumes,[69] which, like all that he wrote, are models of accuracy
and research, and it is to these volumes that we are indebted for the
interesting and suggestive facts which we here lay before our readers.
{298}
_Insects--Coleoptera._--The total number of species of beetles hitherto
observed at St. Helena is 203, but of these no less than seventy-four are
common and wide-spread insects, which have certainly, in Mr. Wollaston's
opinion, been introduced by human agency. There remain 129 which are
believed to be truly aborigines, and of these all but one are found nowhere
else on the globe. But in addition to this large amount of specific
peculiarity (perhaps unequalled anywhere else in the world) the beetles of
this island are equally remarkable for their generic isolation, and for the
altogether exceptional proportion in which the great divisions of the order
are represented. The species belong to thirty-nine genera, of which no less
than twenty-five are peculiar to the island; and many of these are such
isolated forms that it is impossible to find their allies in any particular
country. Still more remarkable is the fact, that more than two-thirds of
the whole number of indigenous species are Rhyncophora or weevils, while
more than two-fifths (fifty-four species) belong to one family, the
Cossonidæ. Now although the Rhyncophora are an immensely numerous group and
always form a large portion of the insect population, they nowhere else
approach such a proportion as this. For example, in Madeira they form
one-sixth of the whole of the indigenous Coleoptera, in the Azores less
than one-tenth, and in Britain one-seventh. Even more interesting is the
fact that the twenty genera to which these insects belong are every one of
them peculiar to the island, and in many cases have no near allies
elsewhere, so that we cannot but look on this group of beetles as forming
the most characteristic portion of the ancient insect fauna. Now, as the
great majority of these are wood borers, and all are closely attached to
vegetation and often to particular species of plants, we might, as Mr.
Wollaston well observes, deduce the former luxuriant vegetation of the
island from the great preponderance of this group, even had we not positive
evidence that it was at no distant epoch densely forest-clad. We will now
proceed briefly to indicate the numbers and peculiarities of each of the
families of beetles which enter into the St. Helena fauna, taking them, not
in {299} systematic order, but according to their importance in the island.
1. RHYNCOPHORA.--This great division includes the weevils and allied
groups, and, as above stated, exceeds in number of species all the other
beetles of the island. Four families are represented; the Cossonidæ, with
fifteen peculiar genera comprising fifty-four species, and one minute
insect (_Stenoscelis hylastoides_) forming a peculiar genus, but which has
been found also at the Cape of Good Hope. It is therefore impossible to say
of which country it is really a native, or whether it is indigenous to
both, and dates back to the remote period when St. Helena received its
early emigrants. All the Cossonidæ are found in the highest and wildest
parts of the island where the native vegetation still lingers, and many of
them are only found in the decaying stems of tree-ferns, box-wood,
arborescent Compositæ, and other indigenous plants. They are all
pre-eminently peculiar and isolated, having no direct affinity to species
found in any other country. The next family, the Tanyrhynchidæ, has one
peculiar genus in St. Helena, with ten species. This genus (Nesiotes) is
remotely allied to European, Australian, and Madeiran insects of the same
family: the habits of the species are similar to those of the Cossonidæ.
The Trachyphloeidæ are represented by a single species belonging to a
peculiar genus not very remote from a European form. The Anthribidæ again
are highly peculiar. There are twenty-six species belonging to three
genera, all endemic, and so extremely peculiar that they form two new
subfamilies. One of the genera, Acarodes, is said to be allied to a
Madeiran genus.
2. GEODEPHAGA.--These are the terrestrial carnivorous beetles, very
abundant in all parts of the world, especially in the temperate regions of
the northern hemisphere. In St. Helena there are fourteen species belonging
to three genera, one of which is peculiar. This is the _Haplothorax
burchellii_, the largest beetle on the island, and now very rare. It
resembles a large black Carabus. There is also a peculiar Calosoma, very
distinct, though resembling in some respects certain African species. The
rest of the {300} Geodephaga, twelve in number, belong to the wide-spread
genus Bembidium, but they are altogether peculiar and isolated, except one,
which is of European type, and alone has wings, all the rest being
wingless.
3. HETEROMERA.--This group is represented by three peculiar genera
containing four species, with two species belonging to European genera.
They belong to the families Opatridæ, Mordellidæ, and Anthicidæ.
4. BRACHYELYTRA.--Of this group there are six peculiar species belonging to
four European genera--Homalota, Philonthus, Xantholinus, and Oxytelus.
5. PRIOCERATA.--The families Elateridæ and Anobiidæ are each represented by
a peculiar species of a European genus.
6. PHYTOPHAGA.--There are only three species of this tribe, belonging to
the European genus Longitarsus.
7. LAMELLICORNIS.--Here are three species belonging to two genera. One is a
peculiar species of Trox, allied to South African forms; the other two
belong to the peculiar genus Melissius, which Mr. Wollaston considers to be
remotely allied to Australian insects.
8. PSEUDO-TRIMERA.--Here we have the fine lady-bird _Chilomenus lunata_,
also found in Africa, but apparently indigenous in St. Helena; and a
peculiar species of Euxestes, a genus only found elsewhere in Madeira.
9. TRICHOPTERYGIDÆ.--These, the minutest of beetles, are represented by one
species of the European and Madeiran genus Ptinella.
10. NECROPHAGA.--One indigenous species of Cryptophaga inhabits St. Helena,
and this is said to be very closely allied to a Cape species.
_Peculiarities and Origin of the Coleoptera of St. Helena._--We see that
the great mass of the indigenous species are not only peculiar to the
island, but so isolated in their characters as to show no close affinity
with any existing insects; while a small number (about one-third of the
whole) have some relations, though often very remote, with species now
inhabiting Europe, Madeira, or South Africa. These facts clearly point to
the very great antiquity of the insect fauna of St. Helena, which has
allowed {301} time for the modification of the originally introduced
species, and their special adaptation to the conditions prevailing in this
remote island. This antiquity is also shown by the remarkable specific
modification of a few types. Thus the whole of the Cossonidæ may be
referred to three types, one species only (_Hexacoptus ferrugineus_) being
allied to the European Cossonidæ though forming a distinct genus; a group
of three genera and seven species remotely allied to the _Stenoscelis
hylastoides_, which occurs also at the Cape; while a group of twelve genera
with forty-six species have their only (remote) allies in a few insects
widely scattered in South Africa, New Zealand, Europe, and the Atlantic
Islands. In like manner, eleven species of Bembidium form a group by
themselves; and the Heteromera form two groups, one consisting of three
genera and species of Opatridæ allied to a type found in Madeira, the
other, Anthicodes, altogether peculiar.
Now each of these types may well be descended from a single species which
originally reached the island from some other land; and the great variety
of generic and specific forms into which some of them have diverged is an
indication, and to some extent a measure, of the remoteness of their
origin. The rich insect fauna of Miocene age found in Switzerland consists
mostly of genera which still inhabit Europe, with others which now inhabit
the Cape of Good Hope or the tropics of Africa and South America; and it is
not at all improbable that the origin of the St. Helena fauna dates back to
at least as remote, and not improbably to a still earlier, epoch. But if
so, many difficulties in accounting for its origin will disappear. We know
that at that time many of the animals and plants of the tropics, of North
America, and even of Australia, inhabited Europe; while during the changes
of climate, which, as we have seen, there is good reason to believe
periodically occurred, there would be much migration from the temperate
zones towards the equator, and the reverse. If, therefore, the nearest ally
of any insular group now inhabits a particular country, we are not obliged
to suppose that it reached the island from that country, since we know that
most groups have ranged in past times over {302} wider areas than they now
inhabit. Neither are we limited to the means of transmission across the
ocean that now exist, because we know that those means have varied greatly.
During such extreme changes of conditions as are implied by glacial periods
and by warm polar climates, great alterations of winds and of
ocean-currents are inevitable, and these are, as we have already proved,
the two great agencies by which the transmission of living things to
oceanic islands has been brought about. At the present time the south-east
trade-winds blow almost constantly at St. Helena, and the ocean-currents
flow in the same direction, so that any transmission of insects by their
means must almost certainly be from South Africa. Now there is undoubtedly
a South African element in the insect-fauna, but there is no less clearly a
European, or at least a north-temperate element, and this is very difficult
to account for by causes now in action. But when we consider that this
northern element is chiefly represented by remote generic affinity, and has
therefore all the signs of great antiquity, we find a possible means of
accounting for it. We have seen that during early Tertiary times an almost
tropical climate extended far into the northern hemisphere, and a temperate
climate to the Arctic regions. But if at this time (as is not improbable)
the Antarctic regions were as much ice-clad as they are now it is certain
that an enormous change must have been produced in the winds. Instead of a
great difference of temperature between each pole and the equator, the
difference would be mainly between one hemisphere and the other, and this
might so disturb the trade winds as to bring St. Helena within the south
temperate region of storms--a position corresponding to that of the Azores
and Madeira in the North Atlantic, and thus subject it to violent gales
from all points of the compass. At this remote epoch the mountains of
equatorial Africa may have been more extensive than they are now, and may
have served as intermediate stations by which some northern insects may
have migrated to the southern hemisphere.
We must remember also that these peculiar forms are said to be northern
only because their nearest allies are {303} now found in the North Atlantic
islands and Southern Europe; but it is not at all improbable that they are
really widespread Miocene types, which have been preserved mainly in
favourable insular stations. They may therefore have originally reached St.
Helena from Southern Africa, or from some of the Atlantic islands, and may
have been conveyed by oceanic currents as well as by winds.[70] This is the
more probable, as a large proportion of the St. Helena beetles live even in
the perfect state within the stems of plants or trunks of trees, while the
eggs and larvæ of a still larger number are likely to inhabit similar
stations. Drift-wood might therefore be one of the most important agencies
by which these insects reached the island.
Let us now see how far the distribution of other groups support the
conclusions derived from a consideration of the beetles. The Hemiptera have
been studied by Dr. F. Buchanan White, and though far less known than the
beetles, indicate somewhat similar relations. Eight out of twenty-one
genera are peculiar, and the thirteen other genera are for the most part
widely distributed, while one of the peculiar genera is of African type.
The other orders of insects have not been collected or studied with {304}
sufficient care to make it worth while to refer to them in detail; but the
land-shells have been carefully collected and minutely described by Mr.
Wollaston himself, and it is interesting to see how far they agree with the
insects in their peculiarities and affinities.
_Land-shells of St. Helena._--The total number of species is only
twenty-nine, of which seven are common in Europe or the other Atlantic
islands, and are no doubt recent introductions. Two others, though
described as distinct, are so closely allied to European forms, that Mr.
Wollaston thinks they have probably been introduced and have become
slightly modified by new conditions of life; so that there remain exactly
twenty species which may be considered truly indigenous. No less than
thirteen of these, however, appear to be extinct, being now only found on
the surface of the ground or in the surface soil in places where the native
forests have been destroyed and the land not cultivated. These twenty
peculiar species belong to the following genera: Hyalina (3 sp.), Patula (4
sp.), Bulimus (7 sp.), Subulina (3 sp.), Succinea (3 sp.); of which, one
species of Hyalina, three of Patula, all the Bulimi, and two of Subulina
are extinct. The three Hyalinas are allied to European species, but all the
rest appear to be highly peculiar, and to have no near allies with the
species of any other country. Two of the Bulimi (_B. auris vulpinæ_ and _B.
darwinianus_) are said to somewhat resemble Brazilian, New Zealand, and
Solomon Island forms, while neither Bulimus nor Succinea occur at all in
the Madeira group.
Omitting the species that have probably been introduced by human agency, we
have here indications of a somewhat recent immigration of European types
which may perhaps be referred to the glacial period; and a much more
ancient immigration from unknown lands, which must certainly date back to
Miocene, if not to Eocene, times.
_Absence of Fresh-water Organisms._--A singular phenomenon is the total
absence of indigenous aquatic forms of life in St. Helena. Not a single
water-beetle or fresh-water shell has been discovered; neither do there
seem to be any water-plants in the streams, except the common {305}
water-cress, one or two species of Cyperus, and the Australian _Isapis
prolifera_. The same absence of fresh-water shells characterises the
Azores, where, however, there is one indigenous water-beetle. In the
Sandwich Islands also recent observations refer to the absence of
water-beetles, though here there are a few fresh-water shells. It would
appear therefore that the wide distribution of the same generic and
specific forms which so generally characterises fresh-water organisms, and
which has been so well illustrated by Mr. Darwin, has its limits in the
_very remote_ oceanic islands, owing to causes of which we are at present
ignorant.
The other classes of animals in St. Helena need occupy us little. There are
no indigenous mammals, reptiles, fresh-water fishes or true land-birds; but
there is one species of wader--a small plover (_Ægialitis
sanctæ-helenæ_)--very closely allied to a species found in South Africa,
but presenting certain differences which entitle it to the rank of a
peculiar species. The plants, however, are of especial interest from a
geographical point of view, and we must devote a few pages to their
consideration as supplementing the scanty materials afforded by the animal
life, thus enabling us better to understand the biological relations and
probable history of the island.
_Native Vegetation of St. Helena._--Plants have certainly more varied and
more effectual means of passing over wide tracts of ocean than any kinds of
animals. Their seeds are often so minute, of such small specific gravity,
or so furnished with downy or winged appendages, as to be carried by the
wind for enormous distances. The bristles or hooked spines of many small
fruits cause them to become easily attached to the feathers of aquatic
birds, and they may thus be conveyed for thousands of miles by these
pre-eminent wanderers; while many seeds are so protected by hard outer
coats and dense inner albumen, that months of exposure to salt water does
not prevent them from germinating, as proved by the West Indian seeds that
reach the Azores or even the west coast of Scotland, and, what is more to
the point, by the fact stated by Mr. Melliss, that large seeds which have
floated from {306} Madagascar or Mauritius round the Cape of Good Hope,
have been thrown on the shores of St. Helena and have then sometimes
germinated!
We have therefore little difficulty in understanding _how_ the island was
first stocked with vegetable forms. _When_ it was so stocked (generally
speaking), is equally clear. For as the peculiar coleopterous fauna, of
which an important fragment remains, is mainly composed of species which
are specially attached to certain groups of plants, we may be sure that the
plants were there long before the insects could establish themselves.
However ancient then is the insect fauna the flora must be more ancient
still. It must also be remembered that plants, when once established in a
suitable climate and soil, soon take possession of a country and occupy it
almost to the complete exclusion of later immigrants. The fact of so many
European weeds having overrun New Zealand and temperate North America may
seem opposed to this statement, but it really is not so. For in both these
cases the native vegetation has first been artificially removed by man and
the ground cultivated; and there is no reason to believe that any similar
effect would be produced by the scattering of any amount of foreign seed on
ground already completely clothed with an indigenous vegetation. We might
therefore conclude _à priori_, that the flora of such an island as St.
Helena would be of an excessively ancient type, preserving for us in a
slightly modified form examples of the vegetation of the globe at the time
when the island first rose above the ocean. Let us see then what botanists
tell us of its character and affinities.
The truly indigenous flowering plants are about fifty in number, besides
twenty-six ferns. Forty of the former and ten of the latter are absolutely
peculiar to the island, and, as Sir Joseph Hooker tells us, "with scarcely
an exception, cannot be regarded as very close specific allies of any other
plants at all. Seventeen of them belong to peculiar genera, and of the
others, all differ so markedly as species from their congeners, that not
one comes under the category of being an insular form of a continental
species." The affinities of this flora are, Sir Joseph Hooker thinks, {307}
mainly African and especially South African, as indicated by the presence
of the genera Phylica, Pelargonium, Mesembryanthemum, Oteospermum, and
Wahlenbergia, which are eminently characteristic of southern extra-tropical
Africa. The sixteen ferns which are not peculiar are common either to
Africa, India, or America, a wide range sufficiently explained by the
dust-like spores of ferns, capable of being carried to unknown distances by
the wind, and the great stability of their generic and specific forms, many
of those found in the Miocene deposits of Switzerland, being hardly
distinguishable from living species. This shows, that identity of _species_
of ferns between St. Helena and distant countries does not necessarily
imply a recent origin.
_The Relation of the St. Helena Compositæ._--In an elaborate paper on the
Compositæ,[71] Mr. Bentham gives us some valuable remarks on the affinities
of the seven endemic species belonging to the genera Commidendron,
Melanodendron, Petrobium, and Pisiadia, which forms so important a portion
of the existing flora of St. Helena. He says: "Although nearer to Africa
than to any other continent, those composite denizens which bear evidence
of the greatest antiquity have their affinities for the most part in South
America, while the colonists of a more recent character are South African."
... "Commidendron and Melanodendron are among the woody Asteroid forms
exemplified in the Andine Diplostephium, and in the Australian Olearia.
Petrobium is one of three genera, remains of a group probably of great
antiquity, of which the two others are Podanthus in Chile and Astemma in
the Andes. The Pisiadia is an endemic species of a genus otherwise
Mascarene or of Eastern Africa, presenting a geographical connection
analogous to that of the St. Helena Melhaniæ,[72] with the Mascarene
Trochetia."
Whenever such remote and singular cases of geographical affinity as the
above are pointed out, the first {308} impression is to imagine some mode
by which a communication between the distant countries implicated might be
effected; and this way of viewing the problem is almost universally
adopted, even by naturalists. But if the principles laid down in this work
and in my _Geographical Distribution of Animals_ are sound, such a course
is very unphilosophical. For, on the theory of evolution, nothing can be
more certain than that groups now broken up and detached were once
continuous, and that fragmentary groups and isolated forms are but the
relics of once widespread types, which have been preserved in a few
localities where the physical conditions were especially favourable, or
where organic competition was less severe. The true explanation of all such
remote geographical affinities is, that they date back to a time when the
ancestral group of which they are the common descendants had a wider or a
different distribution; and they no more imply any closer connection
between the distant countries the allied forms now inhabit, than does the
existence of living Equidæ in South Africa and extinct Equidæ in the
Pliocene deposits of the Pampas, imply a continent bridging the South
Atlantic to allow of their easy communication.
_Concluding Remarks on St. Helena._--The sketch we have now given of the
chief members of the indigenous fauna and flora of St. Helena shows, that
by means of the knowledge we have obtained of past changes in the physical
history of the earth, and of the various modes by which organisms are
conveyed across the ocean, all the more important facts become readily
intelligible. We have here an island of small size and great antiquity,
very distant from every other land, and probably at no time very much less
distant from surrounding continents, which became stocked by chance
immigrants from other countries at some remote epoch, and which has
preserved many of their more or less modified descendants to the present
time. When first visited by civilised man it was in all probability far
more richly stocked with plants and animals, forming a kind of natural
museum or vivarium in which ancient types, perhaps dating back to the
Miocene {309} period, or even earlier, had been saved from the destruction
which has overtaken their allies on the great continents. Unfortunately
many, we do not know how many, of these forms have been exterminated by the
carelessness and improvidence of its civilised but ignorant rulers; and it
is only by the extreme ruggedness and inaccessibility of its peaks and
crater-ridges that the scanty fragments have escaped by which alone we are
able to obtain a glimpse of this interesting chapter in the life-history of
our earth.
* * * * *
{310}
CHAPTER XV
THE SANDWICH ISLANDS
Position and Physical Features--Zoology of the Sandwich
Islands--Birds--Reptiles--Land-shells--Insects--Vegetation of the
Sandwich Islands--Peculiar Features of the Hawaiian Flora--Antiquity of
the Hawaiian Fauna and Flora--Concluding Observations on the Fauna and
Flora of the Sandwich Islands--General Remarks on Oceanic Islands.
The Sandwich Islands are an extensive group of large islands situated in
the centre of the North Pacific, being 2,350 miles from the nearest part of
the American coast--the bay of San Francisco, and about the same distance
from the Marquesas and the Samoa Islands to the south, and the Aleutian
Islands a little west of north. They are, therefore, wonderfully isolated
in mid-ocean, and are only connected with the other Pacific Islands by
widely scattered coral reefs and atolls, the nearest of which, however, are
six or seven hundred miles distant, and are all nearly destitute of animal
or vegetable life. The group consists of seven large inhabited islands
besides four rocky islets; the largest, Hawaii, being seventy miles across
and having an area 3,800 square miles--being somewhat larger than all the
other islands together. A better conception of this large island will be
formed by comparing it with Devonshire, with which it closely agrees both
in size and shape, though its enormous volcanic mountains rise to nearly
14,000 feet high. {311} Three of the smaller islands are each about the
size of Hertfordshire or Bedfordshire, and the whole group stretches from
north-west to south-east for a distance of about 350 miles. Though so
extensive, the entire archipelago is volcanic, and the largest island is
rendered sterile and comparatively uninhabitable by its three active
volcanoes and their widespread deposits of lava.
[Illustration: MAP OF THE SANDWICH ISLANDS.]
The light tint shows where the sea is less than 1,000 fathoms deep.
The figures show the depth in fathoms.
The ocean depths by which these islands are separated from the nearest
continents are enormous. North, east, and south, soundings have been
obtained a little over or under three thousand fathoms, and these profound
deeps extend over a large part of the North Pacific. We may {312} be quite
sure, therefore, that the Sandwich Islands have, during their whole
existence, been as completely severed from the great continents as they are
now; but on the west and south there is a possibility of more extensive
islands having existed, serving as stepping-stones to the island groups of
the Mid-Pacific. This is indicated by a few widely-scattered coral islets,
around which extend {313} considerable areas of less depth, varying from
two hundred to a thousand fathoms, and which _may_ therefore indicate the
sites of submerged islands of considerable extent. When we consider that
east of New Zealand and New Caledonia, all the larger and loftier islands
are of volcanic origin, with no trace of any ancient stratified rocks
(except, perhaps, in the Marquesas, where, according to Jules Marcou,
granite and gneiss are said to occur) it seems probable that the
innumerable coral-reefs and atolls, which occur in groups on deeply
submerged banks, mark the sites of bygone volcanic islands, similar to
those which now exist, but which, after becoming extinct, have been lowered
or destroyed by denudation, and finally have altogether disappeared except
where their sites are indicated by the upward-growing coral-reefs. If this
view is correct we should give up all idea of there ever having been a
Pacific continent, but should look upon that vast ocean as having from the
remotest geological epochs been the seat of volcanic forces, which from its
profound depths have gradually built up the islands which now dot its
surface, as well as many others which have sunk beneath its waves. The
number of islands, as well as the total quantity of land-surface, may
sometimes have been greater than it is now, and may thus have facilitated
the transfer of organisms from one group to another, and more rarely even
from the American, Asiatic, or Australian continents. Keeping these various
facts and considerations in view, we may now proceed to examine the fauna
and flora of the Sandwich Islands, and discuss the special phenomena they
present.
[Illustration: MAP OF THE NORTH PACIFIC WITH ITS SUBMERGED BANKS.]
The light tint shows where the sea is less than 1,000 fathoms deep.
The dark tint ,, ,, ,, more than 1,000 fathoms deep.
The figures show the depths in fathoms.
_Zoology of the Sandwich Islands: Birds._--It need hardly be said that
indigenous mammalia are quite unknown in the Sandwich Islands, the most
interesting of the higher animals being the birds, which are tolerably
numerous and highly peculiar. Many aquatic and wading birds which range
over the whole Pacific visit these islands, twenty-five species having been
observed, but even of these six are peculiar--a coot, _Fulica alai_; a
moorhen, _Gallinula galeata_ var _sandvichensis_; a rail with rudimentary
wings, _Pennula millei_; a stilt-plover, _Himantopus knudseni_; and {314}
two ducks, _Anas Wyvilliana_ and _Bernicla sandvichensis_. The birds of
prey are also great wanderers. Four have been found in the islands--the
short-eared owl, _Otus brachyotus_, which ranges over the greater part of
the globe, but is here said to resemble the variety found in Chile and the
Galapagos; the barn owl, _Strix flammea_, of a variety common in the
Pacific; a peculiar sparrow-hawk, _Accipiter hawaii_; and _Buteo
solitarius_, a buzzard of a peculiar species, and coloured so as to
resemble a hawk of the American subfamily Polyborinæ. It is to be noted
that the genus Buteo abounds in America, but is not found in the Pacific;
and this fact, combined with the remarkable colouration, renders it almost
certain that this peculiar species is of American origin.
The Passeres, or true perching birds, are especially interesting, being all
of peculiar species, and, all but one, belonging to peculiar genera. Their
numbers have been greatly increased since the first edition of this work
appeared, partly by the exertions of American naturalists, and very largely
by the researches of Mr. Scott B. Wilson, who visited the Sandwich Islands
for the purpose of investigating their ornithology, and collected
assiduously in the various islands of the group for a year and a half. This
gentleman is now publishing a finely illustrated work on Hawaiian birds,
and he has kindly furnished me with the following list.
PASSERES OF THE SANDWICH ISLANDS.
MUSCICAPIDÆ (Flycatchers).
1. _Chasiempis ridgwayi_ Hawaii.
2. ,, _sclateri_ Kauai.
3. ,, _dolei_ Kauai.
4. ,, _gayi_ Oahu.
5. ,, _ibidis_ Oahu.
6. _Phæornis obscura_ Hawaii.
7. ,, _myadestina_ Kauai.
MELIPHAGIDÆ (Honeysuckers).
8. _Acrulocercus nobilis_ Hawaii.
9. ,, _braccalus_ Kauai.
10. ,, _apicalis_ (extinct) Oahu or Maui.
11. _Chætoptila angustipluma_ (extinct) Hawaii.
{315}
DREPANIDIDÆ.
12. _Drepanis pacifica_ (extinct) Hawaii.
13. _Vastiaria coccinea_ All the Islands.
14. _Hiniatione vireus_ Hawaii.
15. ,, _dolii_ Maui.
16. ,, _sanguinea_ All the Islands.
17. ,, _montana_ Lanai.
18. ,, _chloris_ Oahu.
19. ,, _maculata_ Oahu.
20. ,, _parva_ Kauai.
21. ,, _stejnegeri_ Kauai.
22. _Oreomyza bairdi_ Kauai.
23. _Hemignathus obscurus_ Hawaii.
24. ,, _olivaceus_ Hawaii.
25. ,, _lichtensteini_ Oahu.
26. ,, _lucidus_ Oahu.
27. ,, _stejnegeri_ Kauai.
28. ,, _hanapepe_ Kauai.
29. _Loxops coccinea_ Hawaii.
30. ,, _flammea_ Molokai.
31. ,, _aurea_ Maui.
32. _Chrysomitridops coeruleorostris_ Kaui.
33. ,, _anna_ (extinct)
FRINGILLIDÆ (Finches).
34. _Loxioides bailleni_ Hawaii.
35. _Psittirostra psittacea_ All the Islands.
36. _Chloridops kona_ Hawaii.
CORVIDÆ (Crows).
37. _Corvus hawaiiensis_ Hawaii.
Many of the birds recently described are representative forms found in the
several islands of the group.
Taking the above in the order here given, we have, first, two peculiar
genera of true flycatchers, a family confined to the Old World, but
extending over the Pacific as far as the Marquesas Islands. Next we have
two peculiar genera (with four species) of honeysuckers, a family confined
to the Australian region, and also ranging over all the Pacific Islands to
the Marquesas. We now come to the most important group of birds in the
Sandwich Islands, comprising seven or eight peculiar genera, and twenty-two
species which are believed to form a peculiar family allied to the Oriental
flower-peckers (Diceidæ), and perhaps remotely to the American greenlets
(Vireonidæ), or {316} tanagers (Tanagridæ). They possess singularly varied
beaks, some having this organ much thickened like those of finches, to
which family some of them have been supposed to belong. In any case they
form a most peculiar group, and cannot be associated with any other known
birds. The last species, and the only one not belonging to a peculiar
genus, is the Hawaiian crow, belonging to the almost universally
distributed genus Corvus.
On the whole, the affinities of these birds are, as might be expected,
chiefly with Australia and the Pacific Islands; but they exhibit in the
buzzard, one of the owls, and perhaps in some of the Drepanididæ, slight
indications of very rare or very remote communication with America. The
amount of speciality is, however, wonderful, far exceeding that of any
other islands; the only approach to it being made by New Zealand and
Madagascar, which have a much more varied bird fauna and a smaller
_proportionate_ number of peculiar genera. The Galapagos, among the true
oceanic islands, while presenting many peculiarities have only four out of
the ten genera of Passeres peculiar. These facts undoubtedly indicate an
immense antiquity for this group of islands, or the vicinity of some very
ancient land (now submerged), from which some portion of their peculiar
fauna might be derived. For further details as to the affinities and
geographical distribution of the genera and species, the reader must
consult Mr. Scott Wilson's work _The Birds of the Sandwich Islands_,
already alluded to.
_Reptiles._--The only other vertebrate animals are two lizards. One of
these is a very widespread species, _Ablepharus poecilopleurus_, ranging
from the Pacific Islands to West Africa. The other is said to form a
peculiar genus of geckoes, but both its locality and affinities appear to
be somewhat doubtful.
_Land-shells._--The only other group of animals which has been carefully
studied, and which presents features of especial interest, are the
land-shells. These are very numerous, about thirty genera, and between
three and four hundred species having been described; and it is remarkable
that this single group contains as many species of {317} land-shells as all
the other Polynesian Islands from the Pelew Islands and Samoa to the
Marquesas. All the species are peculiar, and about three-fourths of the
whole belong to peculiar genera, fourteen of which constitute the subfamily
Achatinellinæ, entirely confined to this group of islands and constituting
its most distinguishing feature. Thirteen genera (comprising sixty-four
species) are found also in the other Polynesian Islands, but three genera
of Auriculidæ (Plecotrema, Pedipes, and Blauneria) are not found in the
Pacific, but inhabit--the former genus Australia, China, Bourbon, and Cuba,
the two latter the West Indian Islands. Another remarkable peculiarity of
these islands is the small number of Operculata, which are represented by
only one genus and five species, while the other Pacific Islands have
twenty genera and 115 species, or more than half the number of the
Inoperculata. This difference is so remarkable that it is worth stating in
a comparative form:--
Inoperculata. Operculata. Auriculidæ.
Sandwich Islands 332 5 9
Rest of Pacific Islands 200 115 16
When we remember that in the West Indian Islands the Operculata abound in a
greater proportion than even in the Pacific Islands generally, we are led
to the conclusion that limestone, which is plentiful in both these areas,
is especially favourable to them, while the purely volcanic rocks are
especially unfavourable. The other peculiarities of the Sandwich Islands,
however, such as the enormous preponderance of the strictly endemic
Achatinellinæ, and the presence of genera which occur elsewhere only beyond
the Pacific area in various parts of the great continents, undoubtedly
point to a very remote origin, at a time when the distribution of many of
the groups of mollusca was very different from that which now prevails.
A very interesting feature of the Sandwich group is the extent to which the
species and even the genera are confined to separate islands. Thus the
genera Carelia and Catinella with eight species are peculiar to the island
of Kaui; Bulimella, Apex, Frickella, and Blauneria, to Oahu; Perdicella to
Maui; and Eburnella to Lanai. {318} The Rev. John T. Gulick, who has made a
special study of the Achatinellinæ, informs us that the average range of
the species in this sub-family is five or six miles, while some are
restricted to but one or two square miles, and only very few have the range
of a whole island. Each valley, and often each side of a valley, and
sometimes even every ridge and peak possesses its peculiar species.[73] The
island of Oahu, in which the capital is situated, has furnished about half
the species already known. This is partly due to its being more
forest-clad, but also, no doubt, in part to its being better explored, so
that notwithstanding the exceptional riches of the group, we have no reason
to suppose that there are not many more species to be found in the less
explored islands. Mr. Gulick tells us that the forest region that covers
one of the mountain ranges of Oahu is about forty miles in length, and five
or six miles in width, yet this small territory furnishes about 175 species
of Achatinellidæ, represented by 700 or 800 varieties. The most important
peculiar genus, not belonging to the Achatinella group, is Carelia, with
six species and several named varieties, all peculiar to Kaui, the most
westerly of the large islands. This would seem to show that the small
islets stretching westward, and situated on an extensive bank with less
than a thousand fathoms of water over it, may indicate the position of a
large submerged island whence some portion of the Sandwich Island fauna was
derived.
_Insects._--Owing to the researches of the Rev. T. Blackburn we have now a
fair knowledge of the Coleopterous fauna of these islands. Unfortunately
some of the most productive islands in plants--Kaui and Maui--were very
little explored, but during a residence of six years the equally rich Oahu
was well worked, and the general character of the beetle fauna must
therefore be considered to be pretty accurately determined. Out of 428
species collected, many being obviously recent introductions, no {319} less
than 352 species and 99 of the genera appear to be quite peculiar to the
archipelago. Sixty of these species are Carabidæ, forty-two are
Staphylinidæ, forty are Nitidulidæ, twenty are Ptinidæ, twenty are Ciodidæ,
thirty are Aglycyderidæ, forty-five are Curculionidæ, and fourteen are
Cerambycidæ, the remainder being distributed among twenty-two other
families. Many important families, such as Cicindelidæ, Scaraboeidæ,
Buprestidæ, and the whole of the enormous series of the Phytophaga are
either entirely absent or are only represented by a few introduced species.
In the eight families enumerated above most of the species belong to
peculiar genera which usually contain numerous distinct species; and we may
therefore consider these to represent the descendants of the most ancient
immigrants into the islands.
Two important characteristics of the Coleopterous fauna are, the small size
of the species, and the great scarcity of individuals. Dr. Sharp, who has
described many of them,[74] says they are "mostly small or very minute
insects," and that "there are few--probably it would be correct to say
absolutely none--that would strike an ordinary observer as being
beautiful." Mr. Blackburn says that it was not an uncommon thing for him to
pass a morning on the mountains and to return home with perhaps two or
three specimens, having seen literally nothing else except the few species
that are generally abundant. He states that he "has frequently spent an
hour sweeping flower-covered herbage, or beating branches of trees over an
inverted white umbrella without seeing the sign of a beetle of any kind."
To those who have collected in any tropical or even temperate country on or
near a continent, this poverty of insect life must seem almost incredible;
and it affords us a striking proof of how erroneous are those now almost
obsolete views which imputed the abundance, variety, size, and colour of
insects to the warmth and sunlight and luxuriant vegetation of the tropics.
The facts become quite intelligible, however, if we consider that only
{320} minute insects of certain groups could ever reach the islands by
natural means, and that these, already highly specialised for certain
defined modes of life, could only develop slowly into slightly modified
forms of the original types. Some of the groups, however, are considered by
Dr. Sharp to be very ancient generalised forms, especially the peculiar
family Aglycyderidæ, which he looks upon as being "absolutely the most
primitive of all the known forms of Coleoptera, it being a synthetic form
linking the isolated Rhynchophagous series of families with the Clavicorn
series. About thirty species are known in the Hawaiian Islands, and they
exhibit much difference _inter se_." A few remarks on each of the more
important of the families will serve to indicate their probable mode and
period of introduction into the islands.
The Carabidæ consist chiefly of seven peculiar genera of Anchomenini
comprising fifty-one species, and several endemic species of Bembidiinæ.
They are highly peculiar and are all of small size, and may have originally
reached the islands in the crevices of the drift wood from N.W. America
which is still thrown on their shores, or, more rarely, by means of a
similar drift from the N.-Western islands of the Pacific.[75] It is
interesting to note that peculiar species of the same groups of Carabidæ
are found in the Azores, Canaries, and St. Helena, indicating that they
possess some special facilities for transmission across wide oceans and for
establishing themselves upon oceanic islands. The Staphylinidæ present many
peculiar species of known genera. Being still more minute and usually more
ubiquitous than the Carabidæ, there is no difficulty in accounting for
their presence in the islands by the same means of dispersal. The
Nitidulidæ, Ptinidæ, and Ciodidæ being very small and of varied habits,
either the perfect insects, their eggs or larvæ, may have been introduced
either by water or wind carriage, or through the agency of birds. The
Curculionidæ, being wood bark or nut borers, would have considerable
facilities for transmission by floating timber, fruits, or nuts; and the
eggs or larvæ of the {321} peculiar Cerambycidæ must have been introduced
by the same means. The absence of so many important and cosmopolitan groups
whose size or constitution render them incapable of being thus transmitted
over the sea, as well as of many which seem equally well adapted as those
which are found in the islands, indicate how rare have been the conditions
for successful immigration; and this is still further emphasized by the
extreme specialisation of the fauna, indicating that there has been no
repeated immigration of the same species which would tend, as in the case
of Bermuda, to preserve the originally introduced forms unchanged by the
effects of repeated intercrossing.
_Vegetation of the Sandwich Islands._--The flora of these islands is in
many respects so peculiar and remarkable, and so well supplements the
information derived from its interesting but scanty fauna, that a brief
account of its more striking features will not be out of place; and we
fortunately have a pretty full knowledge of it, owing to the researches of
the German botanist Dr. W. Hildebrand.[76]
Considering their extreme isolation, their uniform volcanic soil, and the
large proportion of the chief island which consists of barren lava-fields,
the flora of the Sandwich Islands is extremely rich, consisting, so far as
at present known, of 844 species of flowering plants and 155 ferns. This is
considerably richer than the Azores (439 Phanerogams and 39 ferns), which
though less extensive are perhaps better known, or than the Galapagos (332
Phanerogams), which are more strictly comparable, being equally volcanic,
while their somewhat smaller area may perhaps be compensated by their
proximity to the American continent. Even New Zealand with more than twenty
times the area of the Sandwich group, whose soil and climate are much more
varied and whose botany has been thoroughly explored, has not a very much
larger number of flowering plants (935 species), while in ferns it is
barely equal.
{322}
The following list gives the number of indigenous species in each natural
order.
_Number of Species in each Natural Order in the Hawaiian Flora, excluding
the introduced Plants._
DICOTYLEDONS. 48. Gentianaceæ (Erythræa) 1
49. Loganiaceæ 7
1. Ranunculaceæ 2 50. Apocynaceæ 4
2. Menispermaceæ 4 51. Hydrophyllaceæ (Nama ...
3. Papaveraceæ 1 allies Andes) 1
4. Cruciferæ 3 52. Oleaceæ 1
5. Capparidaceæ 2 53. Solanaceæ 12
6. Violaceæ 8 54. Convolvulaceæ 14
7. Bixaceæ 2 55. Boraginaceæ 3
8. Pittosporaceæ 10 56. Scrophulariaceæ 2
9. Caryophyllaceæ 23 57. Gesneriaceæ 24
10. Portulaceæ 3 58. Myoporaceæ 1
11. Guttiferæ 1 59. Verbenaceæ 1
12. Ternstræmiaceæ 1 60. Labiatæ 39
13. Malvaceæ 14 61. Plantaginaceæ 2
14. Sterculiaceæ 2 62. Nyctaginaceæ 5
15. Tiliaceæ 1 63. Amarantaceæ 9
16. Geraniaceæ 6 64. Phytolaccaceæ 1
17. Zygophyllaceæ 1 65. Polygonaceæ 3
18. Oxalidaceæ 1 66. Chenopodiaceæ 2
19. Rutaceæ 30 67. Lauraceæ 2
20. Ilicineæ 1 68. Thymelæaceæ 7
21. Celastraceæ 1 69. Santalaceæ 5
22. Rhamnaceæ 7 70. Loranthaceæ 1
23. Sapindaceæ 6 71. Euphorbiaceæ 12
24. Anacardiaceæ 1 72. Urticaceæ 15
25. Leguminosæ 21 73. Piperaceæ 20
26. Rosaceæ 6
27. Saxifragaceæ (trees) 2 MONOCOTYLEDONS.
28. Droseraceæ 1
29. Halorageæ 1 74. Orchidaceæ 3
30. Myrtaceæ 6 75. Scitaminaceæ 4
31. Lythraceæ 1 76. Iridaceæ 1
32. Onagraceæ 1 77. Taccaceæ 1
33. Cucurbitaceæ 8 78. Dioscoreaceæ 2
34. Ficoideæ 1 79. Liliaceæ 7
35. Begoniaceæ 1 80. Commelinaceæ 1
36. Umbelliferæ 5 81. Flagellariaceæ 1
37. Araliaceæ 12 82. Juncaceæ 1
38. Rubiaceæ 49 83. Palmaceæ 3
39. Compositæ 70 84. Pandanaceæ 2
40. Lobeliaceæ 58 85. Araceæ 2
41. Goodeniaceæ 8 86. Naiadaceæ 4
42. Vaccinaceæ 2 87. Cyperaceæ 47
43. Epacridaceæ 2 88. Graminaceæ 57
44. Sapotaceæ 3
45. Myrsinaceæ 5 VASCULAR CRYPTOGAMS.
46. Primulaceæ (Lysimachia)
shrubs 6 Ferns 136
47. Plumbaginaceæ 1 Lycopodiaceæ 17
Rhizocarpeæ 2
{323}
_Peculiar Features of the Flora._--This rich insular flora is wonderfully
peculiar, for if we deduct 115 species, which are believed to have been
introduced by man, there remain 705 species of flowering plants of which
574, or more than four-fifths, are quite peculiar to the islands. There are
no less than 38 peculiar genera out of a total of 265 and these 38 genera
comprise 254 species, so that the most isolated forms are those which most
abound and thus give a special character to the flora. Besides these
peculiar types, several genera of wide range are here represented by highly
peculiar species. Such are the Hawaiian species of Lobelia which are woody
shrubs either creeping or six feet high, while a species of one of the
peculiar genera of Lobeliaceæ is a tree reaching a height of forty feet.
Shrubby geraniums grow twelve or fifteen feet high, and some vacciniums
grow as epiphytes on the trunks of trees. Violets and plantains also form
tall shrubby plants, and there are many strange arborescent compositæ, as
in other oceanic islands.
The affinities of the flora generally are very wide. Although there are
many Polynesian groups, yet Australian, New Zealand, and American forms are
equally represented. Dr. Pickering notes the total absence of a large
number of families found in Southern Polynesia, such as Dilleniceæa,
Anonaceæ, Olacaceæ, Aurantiaceæ, Guttiferæ, Malpighiaceæ, Meliaceæ,
Combretaceæ, Rhizophoraceæ, Melastomaceæ, Passifloraceæ, Cunoniaceæ,
Jasminaceæ, Acanthaceæ, Myristicaceæ, and Casuaraceæ, as well as the genera
Clerodendron, Ficus, and epidendric orchids. Australian affinities are
shown by the genera Exocarpus, Cyathodes, Melicope, Pittosporum, and by a
phyllodinous Acacia. New Zealand is represented by Ascarina, Coprosma,
Acæna, and several Cyperaceæ; while America is represented by the genera
Nama, Gunnera, Phyllostegia, Sisyrinchium, and by a red-flowered Rubus and
a yellow-flowered Sanicula allied to Oregon species.
There is no true alpine flora on the higher summits, but several of the
temperate forms extend to a great elevation. Thus Mr. Pickering records
Vaccinium, Ranunculus, Silene, Gnaphalium and Geranium, as occurring above
ten {324} thousand feet elevation; while Viola, Drosera, Acæna, Lobelia,
Edwardsia, Dodonæa, Lycopodium, and many Compositæ, range above six
thousand feet. Vaccinium and Silene are very interesting, as they are
almost peculiar to the North Temperate zone; while many plants allied to
Antarctic species are found in the bogs of the high plateaux.
The proportionate abundance of the different families in this interesting
flora is as follows:--
1. Compositæ 70 species, 12. Urticaceæ 15 species,
2. Lobeliaceæ 58 ,, 13. Malvaceæ 14 ,,
3. Graminaceæ 57 ,, 14. Convolvulaceæ 14 ,,
4. Rubiaceæ 49 ,, 15. Araliaceæ 12 ,,
5. Cyperaceæ 47 ,, 16. Solanaceæ 12 ,,
6. Labiatæ 39 ,, 17. Euphorbiaceæ 12 ,,
7. Rutaceæ 30 ,, 18. Pittosporaceæ 10 ,,
8. Gesneriaceæ 24 ,, 19. Amarantaceæ 9 ,,
9. Caryophyllaceæ 23 ,, 20. Violaceæ 8 ,,
10. Leguminosæ 21 ,, 21. Goodeniaceæ 8 ,,
11. Piperaceæ 20 ,,
Nine other orders, Geraniaceæ, Rhamnaceæ, Rosaceæ, Myrtaceæ, Primulaceæ,
Loganiaceæ, Liliaceæ, Thymelaceæ, and Cucurbitaceæ, have six or seven
species each; and among the more important orders which have less than five
species each are Ranunculaceæ, Cruciferæ, Vaccinacæ, Apocynaceæ,
Boraginaceæ, Scrophulariaceæ, Polygonaceæ, Orchidaceæ, and Juncaceæ. The
most remarkable feature here is the great abundance of Lobeliaceæ, a
character of the flora which is probably unique; while the superiority of
Labiatæ to Leguminosæ and the scarcity of Rosaceæ and Orchidaceæ are also
very unusual. Composites, as in most temperate floras, stand at the head of
the list, and it will be interesting to note the affinities which they
indicate. Omitting eleven species which are cosmopolitan, and have no doubt
entered with civilised man, there remain nineteen genera and seventy
species of Compositæ in the islands. Sixty-one of the species are peculiar,
as are eight of the genera; while the genus Lipochæta with eleven species
is only known elsewhere in the Galapagos, where a single species occurs. We
may therefore consider that nine out of the nineteen genera of Hawaiian
{325} Compositæ are really confined to the Archipelago. The relations of
the peculiar genera and species are indicated in the following table.[77]
_Affinities of Hawaiian Composites._
No. of
Peculiar Genera. Species. External Affinities of the Genus.
Remya 2 Very peculiar. Allied to the North American
genus Grindelia.
Tetramolobium 7 South Temperate America and Australia.
Lipochæta 11 Allied to American genera.
Campylothæca 12 With Tropical American species of Bidens and
Coreopsis.
Argyroxiphium 2 With the Mexican Madieæ.
Wilkesia 2 Same affinities.
Dubantia 6 With the Mexican Raillardella.
Raillardia 12 Same affinities.
Hesperomannia 2 Allied to Stifftia and Wunderlichia of Brazil.
Peculiar Species.
Lagenophora 1 Australia, New Zealand, Antarctic America,
Fiji Islands.
Senecio 2 Universally distributed.
Artemisia 2 North Temperate Regions.
The great preponderance of American relations in the Compositæ, as above
indicated, is very interesting and suggestive, since the Compositæ of
Tahiti and the other Pacific Islands are allied to Malaysian types. It is
here that we meet with some of the most isolated and remarkable forms,
implying great antiquity; and when we consider the enormous extent and
world-wide distribution of this order (comprising about ten thousand
species), its distinctness from all others, the great specialisation of its
flowers to attract insects, and of its seeds for dispersal by wind and
other means, we can hardly doubt that its origin dates back to a very
remote epoch. We may therefore look upon the Compositæ as representing the
most ancient portion of the existing flora of the Sandwich Islands,
carrying us back to a very remote period when the facilities for
communication with America were greater than they are now. This may be
indicated by the two deep submarine banks in the North Pacific, between the
Sandwich Islands and San Francisco, which, from an ocean floor {326} nearly
3,000 fathoms deep, rise up to within a few hundred fathoms of the surface,
and seem to indicate the subsidence of two islands, each about as large as
Hawaii. The plants of North Temperate affinity may be nearly as old, but
these may have been derived from Northern Asia by way of Japan and the
extensive line of shoals which run north-westward from the Sandwich
Islands, as shown on our map. Those which exhibit Polynesian or Australian
affinities, consisting for the most part of less highly modified species,
usually of the same genera, may have had their origin at a later, though
still somewhat remote period, when large islands, indicated by the
extensive shoals to the south and south-west, offered facilities for the
transmission of plants from the tropical portions of the Pacific Ocean.
It is in the smaller and most woody islands in the westerly portion of the
group, especially in Kauai and Oahu, that the greatest number and variety
of plants are found and the largest proportion of peculiar species and
genera. These are believed to form the oldest portion of the group, the
volcanic activity having ceased and allowed a luxuriant vegetation more
completely to cover the islands, while in the larger and much newer islands
of Hawaii and Maui the surface is more barren and the vegetation
comparatively monotonous. Thus while twelve of the arborescent Lobeliaceæ
have been found on Hawaii no less than seventeen occur on the much smaller
Oahu, which has even a genus of these plants confined to it.
It is interesting to note that while the non-peculiar genera of flowering
plants have little more than two species to a genus, the endemic genera
average six and three-quarter species to a genus. These may be considered
to represent the earliest immigrants which became firmly established in the
comparatively unoccupied islands, and have gradually become modified into
such complete harmony with their new conditions that they have developed
into many diverging forms adapting them to different _habitats_. The
following is a list of the peculiar genera with the number of species in
each. {327}
_Peculiar Hawaiian Genera of Flowering Plants._
Genus. No. of Species. Natural Order.
1. Isodendrion 3 Violaceæ.
2. Schiedea (seeds rugose or muricate) 17 Caryophyllaceæ.
3. Alsinidendron 1 ,,
4. Pelea 20 Rutaceæ.
5. Platydesma 4 ,,
6. Mahoe 1 Sapindaceæ.
7. Broussaisia 2 Saxifragaceæ.
8. Hildebrandia 1 Begoniaceæ.
9. Cheirodendron (fleshy fruit) 2 Araliaceæ.
10. Pterotropia (succulent) 3 ,,
11. Triplasandra (drupe) 4 ,,
12. Kadua (small, flat, winged seeds) 16 Rubiaceæ.
13. Gouldia (berry) 5 ,,
14. Bobea (drupe) 5 ,,
15. Straussia (drupe) 5 ,,
16. Remya 2 Compositæ.
17. Tetramolobium 7 ,,
18. Lipochæta 11 ,,
19. Campylotheca 12 ,,
20. Argyroxiphium 2 ,,
21. Wilkesia 2 ,,
22. Dubautia 6 ,,
23. Raillardia 12 ,,
24. Hesperomannia 2 ,,
25. Brighamia 1 Lobeliaceæ.
26. Clermontia (berry) 11 ,,
27. Rollandia 6 ,,
28. Delissea 7 ,,
29. Cyanea 28 ,,
30. Labordea 9 Loganiaceæ.
31. Nothocestrum 4 Solanaceæ.
32. Haplostachys (nucules dry) 3 Labiatæ.
33. Phyllostegia (nucules fleshy) 16 ,,
34. Stenogyne (nucules fleshy) 16 ,,
35. Nototrichium 3 Amarantaceæ.
36. Charpentiera 2 ,,
37. Touchardia 1 Urticaceæ.
38. Neraudia 2 ,,
----
Total 254 species.
The great preponderance of the two orders Compositæ and Lobeliaceæ are what
first strike us in this list. In the former case the facilities for
wind-dispersal afforded by the structure of so many of the seeds render it
comparatively easy to account for their having reached the islands at an
early period. The Lobelias, judging from Hildebrand's descriptions, may
have been transported in several {328} different ways. Most of the endemic
genera are berry-bearers and thus offer the means of dispersal by
fruit-eating birds. The endemic species of the genus Lobelia have sometimes
very minute seeds, which might be carried long distances by wind, while
other species, especially Lobelia gaudichaudii, have a "hard, almost woody
capsule which opens late," apparently well adapted for floating long
distances. Afterwards "the calycine covering withers away, leaving a
fenestrate woody network" enclosing the capsule, and the seeds themselves
are "compressed, reniform, or orbicular, and margined," and thus of a form
well adapted to be carried to great heights and distances by gales or
hurricanes.
In the other orders which present several endemic genera indications of the
mode of transit to the islands are afforded us. The Araliaceæ are said to
have fleshy fruits or drupes more or less succulent. The Rubiaceæ have
usually berries or drupes, while one genus, Kadua, has "small, flat, winged
seeds." The two largest genera of the Labiatæ are said to have "fleshy
nucules," which would no doubt be swallowed by birds.[78]
_Antiquity of the Hawaiian Fauna and Flora._--The great antiquity implied
by the peculiarities of the fauna and flora, no less than by the
geographical conditions and surroundings, of this group, will enable us to
account for another peculiarity of its flora--the absence of so many
families found in other Pacific Islands. For the earliest immigrants would
soon occupy much of the surface, and become specially modified in
accordance with the conditions of the locality, and these would serve as a
barrier against the intrusion of many forms which at a later {329} period
spread over Polynesia. The extreme remoteness of the islands, and the
probability that they have always been more isolated than those of the
Central Pacific, would also necessarily result in an imperfect and
fragmentary representation of the flora of surrounding lands.
_Concluding Observations on the Fauna and Flora of the Sandwich
Islands._--The indications thus afforded by a study of the flora seem to
accord well with what we know of the fauna of the islands. Plants having so
much greater facilities for dispersal than animals, and also having greater
specific longevity and greater powers of endurance under adverse
conditions, exhibit in a considerable degree the influence of the primitive
state of the islands and their surroundings; while members of the animal
world, passing across the sea with greater difficulty and subject to
extermination by a variety of adverse conditions, retain much more of the
impress of a recent state of things, with perhaps here and there an
indication of that ancient approach to America so clearly shown in the
Compositæ and some other portions of the flora.
GENERAL REMARKS ON OCEANIC ISLANDS.
We have now reviewed the main features presented by the assemblages of
organic forms which characterise the more important and best known of the
Oceanic Islands. They all agree in the total absence of indigenous mammalia
and amphibia, while their reptiles, when they possess any, do not exhibit
indications of extreme isolation and antiquity. Their birds and insects
present just that amount of specialisation and diversity from continental
forms which may be well explained by the known means of dispersal acting
through long periods; their land shells indicate greater isolation, owing
to their admittedly less effective means of conveyance across the ocean;
while their plants show most clearly the effects of those changes of
conditions which we have reason to believe have occurred during the
Tertiary epoch, and preserve to us in highly specialised and archaic forms
some record of the primeval immigration by which the islands were
originally {330} clothed with vegetation. But in every case the series of
forms of life in these islands is scanty and imperfect as compared with far
less favourable continental areas, and no one of them presents such an
assemblage of animals or plants as we always find in an island which we
know has once formed part of a continent.
It is still more important to note that none of these oceanic archipelagoes
present us with a single type which we may suppose to have been preserved
from Mesozoic times; and this fact, taken in connection with the volcanic
or coralline origin of all of them, powerfully enforces the conclusion at
which we have arrived in the earlier portion of this volume, that during
the whole period of geologic time as indicated by the fossiliferous rocks,
our continents and oceans have, speaking broadly, been permanent features
of our earth's surface. For had it been otherwise--had sea and land changed
place repeatedly as was once supposed--had our deepest oceans been the seat
of great continents while the site of our present continents was occupied
by an oceanic abyss--is it possible to imagine that no fragments of such
continents would remain in the present oceans, bringing down to us some of
their ancient forms of life preserved with but little change? The
correlative facts, that the islands of our great oceans are all volcanic
(or coralline built probably upon degraded volcanic islands or extinct
submarine volcanoes), and that their productions are all more or less
clearly related to the existing inhabitants of the nearest continents, are
hardly consistent with any other theory than the permanence of our oceanic
and continental areas.
We may here refer to the one apparent exception, which, however, lends
additional force to the argument. New Zealand is sometimes classed as an
oceanic island, but it is not so really; and we shall discuss its
peculiarities and probable origin further on.
* * * * *
{331}
CHAPTER XVI
CONTINENTAL ISLANDS OF RECENT ORIGIN: GREAT BRITAIN
Characteristic Features of Recent Continental Islands--Recent Physical
Changes of the British Isles--Proofs of Former Elevation--Submerged
Forests--Buried River Channels--Time of Last Union with the
Continent--Why Britain is poor in Species--Peculiar British
Birds--Freshwater Fishes--Cause of Great Speciality in Fishes--Peculiar
British Insects--Lepidoptera Confined to the British
Isles--Peculiarities of the Isle of Man--Lepidoptera--Coleoptera
confined to the British Isles--Trichoptera Peculiar to the British
Isles--Land and Freshwater Shells--Peculiarities of the British
Flora--Peculiarities of the Irish Flora--Peculiar British Mosses and
Hepaticæ--Concluding Remarks on the Peculiarities of the British Fauna
and Flora.
We now proceed to examine those islands which are the very reverse of the
"oceanic" class, being fragments of continents or of larger islands from
which they have been separated, by subsidence of the intervening land at a
period which, geologically, must be considered recent. Such islands are
always still connected with their parent land by a shallow sea, usually
indeed not exceeding a hundred fathoms deep; they always possess mammalia
and reptiles either wholly or in large proportion identical with those of
the mainland; while their entire flora and fauna is characterised either by
the total absence or comparative scarcity of those endemic or peculiar
species and genera which are so striking a feature of almost all oceanic
islands. Such islands will, of course, differ from each {332} other in
size, in antiquity, and in the richness of their respective faunas, as well
as in their distance from the parent land and the facilities for
intercommunication with it; and these diversities of conditions will
manifest themselves in the greater or less amount of speciality of their
animal productions.
This speciality, when it exists, may have been brought about in two ways. A
species or even a genus may on a continent have had a very limited area of
distribution, and this area may be wholly or almost wholly contained in the
separated portion or island, to which it will henceforth be peculiar. Even
when the area occupied by a species is pretty equally divided at the time
of separation between the island and the continent, it may happen that it
will become extinct on the latter, while it may survive on the former,
because the limited number of individuals after division may be unable to
maintain themselves against the severer competition or more contrasted
climate of the continent, while they may flourish, under the more
favourable insular conditions. On the other hand, when a species continues
to exist in both areas, it may on the island be subjected to some
modifications by the altered conditions, and may thus come to present
characters which differentiate it from its continental allies and
constitute it a new species. We shall in the course of our survey meet with
cases illustrative of both these processes.
The best examples of recent continental islands are Great Britain and
Ireland, Japan, Formosa, and the larger Malay Islands, especially Borneo,
Java, and Celebes; and as each of these presents special features of
interest, we will give a short outline of their zoology and past history in
relation to that of the continents from which they have recently been
separated, commencing with our own islands, to which the present chapter
will be devoted.
_Recent Physical Changes in the British Isles._--Great Britain is perhaps
the most typical example of a large and recent continental island now to be
found upon the globe. It is joined to the Continent by a shallow bank which
extends from Denmark to the Bay of Biscay, the 100 fathom line from these
extreme points receding from the {333} coasts so as to include the whole of
the British Isles and about fifty miles beyond them to the westward. (_See_
Map.)
[Illustration: MAP SHOWING THE SHALLOW BANK CONNECTING THE BRITISH ISLES
WITH THE CONTINENT.]
The light tint indicates a depth of less than 100 fathoms.
The figures show the depth in fathoms.
The narrow channel between Norway and Denmark is 2,580 feet deep.
Beyond this line the sea deepens rapidly to the 500 and 1,000 fathom lines,
the distance between 100 and 1,000 {334} fathoms being from twenty to fifty
miles, except where there is a great outward curve to include the Porcupine
Bank 170 miles west of Galway, and to the north-west of Caithness where a
narrow ridge less than 500 fathoms below the surface joins the extensive
bank under 300 fathoms, on which are situated the Faroe Islands and
Iceland, and which stretches across to Greenland. In the North Channel
between Ireland and Scotland, and in the Minch between the outer Hebrides
and Skye, are a series of hollows in the sea-bottom from 100 to 150 fathoms
deep. These correspond exactly to the points between the opposing highlands
where the greatest accumulations of ice would necessarily occur during the
glacial epoch, and they may well be termed submarine lakes, of exactly the
same nature as those which occur in similar positions on land.
_Proofs of Former Elevation--Submerged Forests._--What renders Britain
particularly instructive as an example of a recent continental island is
the amount of direct evidence that exists, of several distinct kinds,
showing that the land has been sufficiently elevated (or the sea depressed)
to unite it with the Continent,--and this at a very recent period. The
first class of evidence is the existence, all round our coasts, of the
remains of submarine forests often extending far below the present
low-water mark. Such are the submerged forests near Torquay in Devonshire,
and near Falmouth in Cornwall, both containing stumps of trees in their
natural position rooted in the soil, with deposits of peat, branches, and
nuts, and often with remains of insects and other land animals. These occur
in very different conditions and situations, and some have been explained
by changes in the height of the tide, or by pebble banks shutting out the
tidal waters from estuaries; but there are numerous examples to which such
hypotheses cannot apply, and which can only be explained by an actual
subsidence of the land (or rise of the sea-level) since the trees grew.
We cannot give a better idea of these forests than by quoting the following
account by Mr. Pengelly of a visit to one which had been exposed by a
violent storm on the coast of Devonshire, at Blackpool near Dartmouth:--
{335}
"We were so fortunate as to reach the beach at spring-tide low-water, and
to find, admirably exposed, by far the finest example of a submerged forest
which I have ever seen. It occupied a rectangular area, extending from the
small river or stream at the western end of the inlet, about one furlong
eastward; and from the low-water line thirty yards up the strand. The lower
or seaward portion of the forest area, occupying about two-thirds of its
entire breadth, consisted of a brownish drab-coloured clay, which was
crowded with vegetable _débris_, such as small twigs, leaves, and nuts.
There were also numerous prostrate trunks and branches of trees, lying
partly imbedded in the clay, without anything like a prevalent direction.
The trunks varied from six inches to upwards of two feet in diameter. Much
of the wood was found to have a reddish or bright pink hue, when fresh
surfaces were exposed. Some of it, as well as many of the twigs, had almost
become a sort of ligneous pulp, while other examples were firm, and gave a
sharp crackling sound on being broken. Several large stumps projected above
the clay in a vertical direction, and sent roots and rootlets into the soil
in all directions and to considerable distances. It was obvious that the
movement by which the submergence was effected had been so uniform as not
to destroy the approximate horizontality of the old forest ground. One fine
example was noted of a large prostrate trunk having its roots still
attached, some of them sticking up above the clay, while others were buried
in it. Hazelnuts were extremely abundant--some entire, others broken, and
some obviously gnawed.... It has been stated that the forest area reached
the spring-tide low-water line; hence as the greatest tidal range on this
coast amounts to eighteen feet, we are warranted in inferring that the
subsidence amounted to eighteen feet as a minimum, even if we suppose that
some of the trees grew in a soil the surface of which was not above the
level of high water. There is satisfactory evidence that in Torbay it was
not less than forty feet, and that in Falmouth Harbour it amounted to at
least sixty-seven feet."[79]
{336}
On the coast of the Bristol Channel similar deposits occur, as well as
along much of the coast of Wales and in Holyhead Harbour. It is believed by
geologists that the whole Bristol Channel was, at a comparatively recent
period, an extensive plain, through which flowed the River Severn; for in
addition to the evidence of submerged forests there are on the coast of
Glamorganshire numerous caves and fissures in the face of high sea cliffs,
in one of which no less than a thousand antlers of the reindeer were found,
the remains of animals which had been devoured there by bears and hyænas;
facts which can only be explained by the existence of some extent of dry
land stretching seaward from the present cliffs, but since submerged and
washed away. This plain may have continued down to very recent times, since
the whole of the Bristol Channel to beyond Lundy Island is under
twenty-five fathoms deep. In the east of England we have a similar
forest-bed at Cromer in Norfolk; and in the north of Holland an old land
surface has been found fifty-six feet below high-water mark.
_Buried River Channels._--Still more remarkable are the buried river
channels which have been traced on many parts of our coasts. In order to
facilitate the study of the glacial deposits of Scotland, Dr. James Croll
obtained the details of about 250 bores put down in all parts of the mining
districts of Scotland for the purpose of discovering minerals.[80] These
revealed the interesting fact that there are ancient valleys and river
channels at depths of from 100 to 260 feet below the present sea-level.
These old rivers sometimes run in quite different directions from the
present lines of drainage, connecting what are now distinct valleys; and
they are so completely filled up and hidden by boulder clay, drift, and
sands, that there is no indication of their presence on the surface, which
often consists of mounds or low hills more than 100 feet high. One of these
old valleys connects the Clyde near Dumbarton with the Forth at
Grangemouth, and appears to have contained two streams flowing in opposite
directions from a watershed about midway at Kilsith. At {337} Grangemouth
the old channel is 260 feet below the sea-level. The watershed at Kilsith
is now 160 feet above the sea, the old valley bottom being 120 feet deep or
forty feet above the sea. In some places the old valley was a ravine with
precipitous rocky walls, which have been found in mining excavations. Sir
A. Geikie, who has himself discovered many similar buried valleys, is of
opinion that "they unquestionably belong to the period of the boulder
clay."
We have here a clear proof that, when these rivers were formed, the land
must have stood in relation to the sea _at least_ 260 feet higher than it
does now, and probably much more; and this is sufficient to join England to
the continent. Supporting this evidence, we have freshwater or littoral
shells found at great depths off our coasts. Mr. Godwin Austen records the
dredging up of a freshwater shell (_Unio pictorum_) off the mouth of the
English Channel between the fifty fathom and 100 fathom lines, while in the
same locality gravel banks with littoral shells now lie under sixty or
seventy fathoms water.[81] More recently Mr. Gwyn Jeffreys has recorded the
discovery of eight species of fossil arctic shells off the Shetland Isles
in about ninety fathoms water, all being characteristic shallow water
species, so that their association at this great depth is a distinct
indication of considerable subsidence.[82]
_Time of Last Union with the Continent._--The period when this last union
with the continent took place was comparatively recent, as shown by the
identity of the shells with living species, and the fact that the buried
river channels are all covered with clays and gravels of the glacial
period, of such a character as to indicate that most of them were deposited
above the sea-level. From these and various other indications geologists
are all agreed that the last continental period, as it is called, was
subsequent to the greatest development of the ice, but probably before the
cold epoch had wholly passed away. But if so recent, we should naturally
expect our land still {338} to show an almost perfect community with the
adjacent parts of the continent in its natural productions; and such is
found to be the case. All the higher and more perfectly organised animals
are, with but few exceptions, identical with those of France and Germany;
while the few species still considered to be peculiar may be accounted for
either by an original local distribution, by preservation here owing to
favourable insular conditions, or by slight modifications having been
caused by these conditions resulting in a local race, sub-species, or
species.
_Why Britain is Poor in Species._--The former union of our islands with the
continent, is not, however, the only recent change they have undergone.
There have been partial submergences to the depth of from one hundred to
perhaps three hundred feet over a large part of our country; while during
the period of maximum glaciation the whole area north of the Thames was
buried in snow and ice. Even the south of England must have suffered the
rigour of an almost arctic climate, since Mr. Clement Reid has shown that
floating ice brought granite blocks from the Channel Islands to the coast
of Sussex. Such conditions must have almost exterminated our preexisting
fauna and flora, and it was only during the subsequent union of Britain
with the continent that the bulk of existing animals and plants could have
entered our islands. We know that just before and during the glacial period
we possessed a fauna almost or quite identical with that of adjacent parts
of the continent and equally rich in species. The glaciation and
submergence destroyed much of this fauna; and the permanent change of
climate on the passing away of the glacial conditions appears to have led
to the extinction or migration of many species in the adjacent continental
areas, where they were succeeded by the assemblage of animals now occupying
Central Europe. When England became continental, these entered our country;
but sufficient time does not seem to have elapsed for the migration to have
been completed before subsidence again occurred, cutting off the further
influx of purely terrestrial animals, and leaving us without the number of
species which our favourable climate and varied surface entitle us to.
{339}
To this cause we must impute our comparative poverty in mammalia and
reptiles--more marked in the latter than the former, owing to their lower
vital activity and smaller powers of dispersal. Germany, for example,
possesses nearly ninety species of land mammalia, and even Scandinavia
about sixty, while Britain has only forty, and Ireland only twenty-two. The
depth of the Irish Sea being somewhat greater than that of the German
Ocean, the connecting land would there probably be of small extent and of
less duration, thus offering an additional barrier to migration, whence has
arisen the comparative zoological poverty of Ireland. This poverty attains
its maximum in the reptiles, as shown by the following figures:--
Belgium has 22 species of reptiles and amphibia.
Britain ,, 13 ,, ,, ,,
Ireland ,, 4 ,, ,, ,,
Where the power of flight existed, and thus the period of migration was
prolonged, the difference is less marked; so that Ireland has seven bats to
twelve in Britain, and about 110 as against 130 land-birds.
Plants, which have considerable facilities for passing over the sea, are
somewhat intermediate in proportionate numbers, there being about 970
flowering plants and ferns in Ireland to 1,425 in Great Britain,--or almost
exactly two-thirds, a proportion intermediate between that presented by the
birds and the mammalia.
_Peculiar British Birds._--Among our native mammalia, reptiles, and
amphibia, it is the opinion of the best authorities that we possess neither
a distinct species nor distinguishable variety. In birds, however, the case
is different, since some of our species, in particular our coal-tit and
long-tailed tit, present well-marked differences of colour as compared with
continental specimens; and in Mr. Dresser's work on the _Birds of Europe_
they are considered to be distinct species, while Professor Newton, in his
new edition of Yarrell's _British Birds_, does not consider the difference
to be sufficiently great or sufficiently constant to warrant this, and
therefore classes {340} them as insular races of the continental species.
We have, however, one undoubted case of a bird peculiar to the British
Isles, in the red grouse (_Lagopus scoticus_), which abounds in Scotland,
Ireland, the north of England, and Wales, and is very distinct from any
continental species, although closely allied to the willow grouse of
Scandinavia. This latter species resembles it considerably in its summer
plumage, but becomes pure white in winter; whereas our species retains its
dark plumage throughout the year, becoming even darker in winter than in
summer. We have here therefore a most interesting example of an insular
form in our own country; but it is difficult to determine how it
originated. On the one hand, it may be an old continental species which
during the glacial epoch found a refuge here when driven from its native
haunts by the advancing ice; or, on the other hand, it may be a descendant
of the Northern willow grouse, which has lost its power of turning white in
winter owing to its long residence in the lowlands of an island where there
is little permanent snow, and where assimilation in colour to the heather
among which it lurks is at all times its best protection. In either case it
is equally interesting, as the one large and handsome bird which is
peculiar to our islands notwithstanding their recent separation from the
continent.
The following is a list of the birds now held to be peculiar to the British
Isles:--
1. Parus ater, _sub. sp._ BRITANNICUS Closely allied to _P. ater_ of
the continent; a local race or
sub-species.
2. Acredula caudata, _sub. sp._ ROSEA Allied to _A. caudata_ of the
continent.
3. LAGOPUS SCOTICUS Allied to _L. albus_ of
Scandinavia, a distinct species.
_Freshwater Fishes._--Although the productions of fresh waters have
generally, as Mr. Darwin has shown, a wide range, fishes appear to form an
exception, many of them being extremely limited in distribution. Some are
confined to particular river valleys or even to single rivers, others
inhabit the lakes of a limited district only, while some are {341} confined
to single lakes, often of small area, and these latter offer examples of
the most restricted distribution of any organisms whatever. Cases of this
kind are found in our own islands, and deserve our especial attention. It
has long been known that some of our lakes possessed peculiar species of
trout and charr, but how far these were unknown on the continent, and how
many of those in different parts of our islands were really distinct, had
not been ascertained till Dr. Günther, so well known for his extensive
knowledge of the species of fishes, obtained numerous specimens from every
part of the country, and by comparison with all known continental species
determined their specific differences. The striking and unexpected result
has thus been attained, that no less than fifteen well-marked species of
freshwater fishes are altogether peculiar to the British Islands. The
following is the list, with their English names and localities:--[83]
_Freshwater Fishes peculiar to the British Isles._
_Latin Name._ | _English Name._ | _Locality._
| |
1. SALMO BRACHYPOMA |Short-headed salmon|Firth of Forth, Tweed,
| |Ouse.
| |
2. ,, GALLIVENSIS |Galway sea-trout |Galway, West Ireland.
| |
3. ,, ORCADENSIS |Loch Stennis trout |Lakes of Orkney.
| |
4. ,, FEROX |Great lake trout |Larger lakes of Scotland,
| |Ireland, the N. of England,
| |and Wales.
| |
5. ,, STOMACHICUS |Gillaroo trout |Lakes of Ireland.
| |
6. ,, NIGRIPINNIS |Black-finned trout |Mountain lochs of Wales
| |and Scotland.
| |
7. ,, LEVENENSIS |Loch Leven Trout |Loch Leven, Loch Lomond,
| |Windermere.
| |
8. ,, PERISII |Welsh charr |Llanberris lakes, N.
| |Wales.
| |
9. ,, WILLUGHBII |Windermere charr |Lake Windermere and
| |others in N. of England,
| |and Lake Bruiach in
| |Scotland.
| |
10. ,, KILLINENSIS |Lock Killin charr |Killin lake in
| |Inverness-shire.
| |
11. ,, COLII |Cole's charr |Lough Eske and Lough
| |Dan, Ireland.
| |
12. ,, GRAYI |Gray's charr |Lough Melvin, Leitrim,
| |N.W. Ireland.
| |
{342}
13. COREGONUS CLUPEOIDES |The gwyniad, or |Loch Lomond, Ulleswater,
|schelly |Derwentwater,
| |Haweswater, and Bala
| |lake.
| |
14. ,, VANDESIUS |The vendace |Loch Maben, Dumfriesshire.
| |
15. ,, POLLAN |The pollan |Lough Neagh and Lough
| |Earne, N. of Ireland.
These fifteen peculiar fishes differ from each other and from all British
and continental species, not in colour only, but in such important
structural characters as the number and size of the scales, form and size
of the fins, and the form or proportions of the head, body, or tail. Some
of them, like _S. killinensis_ and the Coregoni are in fact, as Dr. Günther
assures me, just as good and distinct species as any other recognised
species of fish. It may indeed be objected that, until all the small lakes
of Scandinavia are explored, and their fishes compared with ours, we cannot
be sure that we have any peculiar species. But this objection has very
little weight if we consider how our own species vary from lake to lake and
from island to island, so that the Orkney species is not found in Scotland,
and only one of the peculiar British species extends to Ireland, which has
no less than five species altogether peculiar to it. If the species of our
own two islands are thus distinct, what reason have we for believing that
they will be otherwise than distinct from those of Scandinavia? At all
events, with the amount of evidence we already possess of the very
restricted ranges of many of our species, we must certainly hold them to be
peculiar till they have been proved to be otherwise.
The great speciality of the Irish fishes is very interesting, because it is
just what we should expect on the theory of evolution. In Ireland the two
main causes of specific change--isolation and altered conditions--are each
more powerful than in Britain. Whatever difficulty continental fishes may
have in passing over to Britain, that difficulty will certainly be
increased by the second sea passage to Ireland; and the latter country has
been longer isolated, for the Irish Sea with its northern and southern
channels is considerably deeper than the German Ocean and the {343} Eastern
half of the English Channel, so that, when the last subsidence occurred,
Ireland would have been an island for some length of time while England and
Scotland still formed part of the continent. Again, whatever differences
have been produced by the exceptional climate of our islands will have been
greater in Ireland, where insular conditions are at a maximum, the
abundance of moisture and the equability of temperature being far more
pronounced than in any other part of Europe.
Among the remarkable instances of limited distribution afforded by these
fishes, we have the Loch Stennis trout confined to the little group of
lakes in the mainland of Orkney, occupying altogether an area of about ten
miles by three; the Welsh charr confined to the Llanberris lakes, about
three miles in length; Gray's charr confined to Lough Melvin, about seven
miles long; while the Loch Killin charr, known only from a small mountain
lake in Inverness-shire, and the vendace, from the equally small lakes at
Loch Maben in Scotland, are two examples of restricted distribution which
can hardly be surpassed.
_Cause of Great Speciality in Fishes._--The reason why fishes alone should
exhibit such remarkable local modifications in lakes and islands is
sufficiently obvious. It is due to the extreme rarity of their transmission
from one lake to another. Just as we found to be the case in Oceanic
Islands, where the means of transmission were ample hardly any modification
of species occurred, while where these means were deficient and individuals
once transported remained isolated during a long succession of ages, their
forms and characters became so much changed as to bring about what we term
distinct species or even distinct genera,--so these lake fishes have become
modified because the means by which they are enabled to migrate so rarely
occur. It is quite in accordance with this view that some of the smaller
lakes contain no fishes, because none have ever been conveyed to them.
Others contain several; and some fishes which have peculiarities of
constitution or habits which render their transmission somewhat less
difficult occur in several lakes over a wide area of country, though only
one appears to be common to the British and Irish lakes. {344}
The manner in which fishes are enabled to migrate from lake to lake is
unknown, but many suggestions have been made. It is a fact that whirlwinds
and waterspouts sometimes carry living fish in considerable numbers and
drop them on the land. Here is one mode which might certainly have acted
now and then in the course of thousands of years, and the eggs of fishes
may have been carried with even greater ease. Again we may well suppose
that some of these fish have once inhabited the streams that enter or flow
out of the lakes as well as the lakes themselves; and this opens a wide
field for conjecture as to modes of migration, because we know that rivers
have sometimes changed their courses to such an extent as to form a union
with distinct river basins. This has been effected either by floods rising
over low watersheds, by elevations of the land changing lines of drainage,
or by ice blocking up valleys and compelling the streams to flow over
watersheds to find an outlet. This is known to have occurred during the
glacial epoch, and is especially manifest in the case of the Parallel Roads
of Glenroy, and it probably affords the true solution of many of the cases
in which existing species of fish inhabit distinct river basins whether in
streams or lakes. If a fish thus wandered out of one river-basin into
another, it might then retire up the streams to some of the lakes, where
alone it might find conditions favourable to it. By a combination of the
modes of migration here indicated it is not difficult to understand how so
many species are now common to the lakes of Wales, Cumberland, and
Scotland, while others less able to adapt themselves to different
conditions have survived only in one or two lakes in a single district; or
these last may have been originally identical with other forms, but have
become modified by the particular conditions of the lake in which they have
found themselves isolated.
_Peculiar British Insects._--We now come to the class of insects, and here
we have much more difficulty in determining what are the actual facts,
because new species are still being yearly discovered and considerable
portions of Europe are but imperfectly explored. It often happens that an
insect is discovered in our islands, and for some {345} years Britain is
its only recorded locality; but at length it is found on some part of the
continent, and not unfrequently has been all the time known there, but
disguised by another name, or by being classed as a variety of some other
species. This has occurred so often that our best entomologists have come
to take it for granted that _all_ our supposed peculiar British species are
really natives of the continent and will one day be found there; and owing
to this feeling little trouble has been taken to bring together the names
of such as from time to time remain known from this country only. The view
of the probable identity of our entire insect-fauna with that of the
continent has been held by such well-known authorities as the late Mr.
E. C. Rye and Dr. D. Sharp for the beetles, and by Mr. H. T. Stainton for
butterflies and moths; but as we have already seen that among two orders of
vertebrates--birds and fishes--there are undoubtedly peculiar British
species, it seems to me that all the probabilities are in favour of there
being a much larger number of peculiar species of insects. In every other
island where some of the vertebrates are peculiar--as in the Azores, the
Canaries, the Andaman Islands, and Ceylon--the insects show an equal if not
a higher proportion of speciality, and there seems no reason whatever why
the same law should not apply to us. Our climate is undoubtedly very
distinct from that of any part of the continent, and in Scotland, Ireland,
and Wales we possess extensive tracts of wild mountainous country where a
moist uniform climate, an alpine or northern vegetation, and a considerable
amount of isolation, offer all the conditions requisite for the
preservation of some species which may have become extinct elsewhere, and
for the slight modification of others since our last separation from the
continent. I think, therefore, that it will be very interesting to take
stock, as it were, of our recorded peculiarities in the insect world, for
it is only by so doing that we can hope to arrive at any correct solution
of the question on which there is at present so much difference of opinion.
For the list of Coleoptera with the accompanying notes I was originally
indebted to the late Mr. E. C. Rye; and Dr. Sharp also gave me valuable
information as to the recent {346} occurrence of some of the supposed
peculiar species on the continent. The list has now been revised by the
Rev. Canon Fowler, author of the best modern work on the British
Coleoptera, who has kindly furnished some valuable notes.
For the Lepidoptera I first noted all the species and varieties marked as
British only in Staudinger's Catalogue of European Lepidoptera. This list
was carefully corrected by Mr. Stainton, who weeded out all the species
known by him to have been since discovered, and furnished me with valuable
information on the distribution and habits of the species. This information
often has a direct bearing on the probability of the insect being peculiar
to Britain, and in some cases may be said to explain why it should be so.
For example, the larvæ of some of our peculiar species of Tineina feed
during the winter, which they are enabled to do owing to our mild and
insular climate, but which the severer continental winters render
impossible. A curious example of the effect this habit may have on
distribution is afforded by one of our commonest British species,
_Elachista rufocinerea_, the larva of which mines in the leaves of _Holcus
mollis_ and other grasses from December to March. This species, though
common everywhere with us, extending to Scotland and Ireland, is quite
unknown in similar latitudes on the continent, but appears again in Italy,
the South of France, and Dalmatia, where the mild winters enable it to live
in its accustomed manner.
Such cases as this afford an excellent illustration of those changes of
distribution, dependent probably on recent changes of climate, which may
have led to the restriction of certain species to our islands. For should
any change of climate lead to the extinction of the species in South
Europe, where it is far less abundant than with us, we should have a common
and wide-spread species entirely restricted to our islands. Other species
feed in the larva state on our common gorse, a plant found only in limited
portions of Western and Southern Europe; and the presence of this plant in
a mild and insular climate such as ours may well be supposed to have led to
the preservation of some of the numerous species which are or have been
dependent on it. Since the first edition was {347} published many new
British species have been discovered, while some of the supposed peculiar
species have been found on the continent. Information as to these has been
kindly furnished by Mr. W. Warren, Mr. C. G. Barrett, Lord Walsingham, and
other students of British Lepidoptera, and the first-named gentleman has
also looked over the proofs.
Mr. McLachlan has kindly furnished me with some valuable information on
certain species of Trichoptera or Caddis flies which seem to be peculiar to
our islands; and this completes the list of orders which have been studied
with sufficient care to afford materials for such a comparison. We will now
give the list of peculiar British Insects, beginning with the Lepidoptera
and adding such notes as have been supplied by the gentlemen already
referred to.
_List of the Species or Varieties of Lepidoptera which, so far as at
present known, are confined to the British Islands. (The figures show the
dates when the species was first described. Species added since the first
edition are marked with an asterisk.)_
DIURNI.
1. POLYOMMATUS DISPAR. "The large copper." This fine insect, once
common in the fens, but now extinct owing to extensive drainage, is
generally admitted to be peculiar to our island, at all events as a
variety or local form. Its continental ally differs constantly in being
smaller and in having smaller spots; but the difference, though
constant, is so slight that it is now classed as a variety under the
name of _rutilus_. Our insect may therefore be stated to be a
well-marked local form of a continental species.
2. Lycæna astrarche, _var._ ARTAXERXES. This very distinct form is
confined to Scotland and the north of England. The species of which it
is considered a variety (more generally known to English entomologists
as _P. agestis_) is found in the southern half of England, and almost
everywhere on the continent.
BOMBYCES.
3. Lithosia complana, _var._ SERICEA. North of England (1861).
4. Hepialus humuli, _var._ HETHLANDICA. Shetland Islands (1865). A
remarkable form, in which the male is usually yellow and buff instead
of pure white, as in the common form, but exceedingly variable in tint
and markings.
5. EPICHNOPTERYX RETICELLA. Sheerness, Gravesend, and other localities
along the Thames (1847); Hayling Island, Sussex.
6. E. pulla, _var._ RADIELLA. Near London, rare (1830?); the species in
Central and Southern Europe. (Doubtfully peculiar in Mr. Stainton's
opinion.) {348}
NOCTUÆ.
7. Acronycta euphorbiæ, _var._ MYRICÆ. Scotland only (1852). A melanic
form of a continental species.
8. AGROTIS SUBROSEA. Cambridgeshire and Huntingdonshire fens, perhaps
extinct (1835). The _var._ _subcærulea_ is found in Finland and
Livonia.
9. Agrotis candelarum _var._ ASHWORTHII. South and West (1855).
Distinct and not uncommon.
10. Luperina luteago, _var._ BARRETTI. Ireland (1864).
11. Aporophyla australis, _var._ PASCUEA. South of England (1830). A
variety of a species otherwise confined to South Europe.
12. Hydræcia nictitans, _var._ PALUDRIS.
GEOMETRÆ.
13. Boarmia gemmaria, _var._ PERFUMARIA. Near London and elsewhere. A
large dark variety of a common species.
14. *B. repandata, _var._ SODORENSIUM. Outer Hebrides.
15. *Emmelesia albulata, _var._ HEBRIDIUM. Outer Hebrides.
16. *E. albulata, _var._ THULES. Shetland Islands.
17. *Melanippe montanata, _var._ SHETLANDICA. Shetland Islands.
18. *M. sociata, _var._ OBSCURATA. Outer Hebrides. A dark form.
19. Cidaria albulata, _var._ GRISEATA. East of England (1835). A
variety of a species otherwise confined to Central and Southern Europe.
20. EUPITHECIA CONSTRICTATA.. Widely spread, but local (1835). Larva on
thyme.
21. *E. satyrata, _var._ CURZONI. N. Scotland.
22. *E. nanata _var._ CURZONI. Shetland Islands.
PYRALIDINA.
23. Aglossa pinguinalis, _var._ STREATFIELDI. Mendip Hills (1830). A
remarkable variety of the common "tabby."
24. *Scoparia cembræ, _var._ SCOTICA. Scotland (1872).
25. *Myelois ceratoniæ, _var._ PRYERELLA. North London (1871).
26. *Howoeosoma nimbella, _var._ SAXICOLA. England, Scotland, Isle of
Man (1871).
27. *Epischnia bankesiella. Isle of Portland (1888).
TORTRICINA.
28. APHELIA NIGROVITTANA. Scotland (1852). A local form of the
generally distributed _A. lanceolana_.
29. GRAPHOLITA PARVULANA. Isle of Wight (1858). Rare. A distinct
species.
30. CONCHYLIS ERIGERANA. South-east of England (1866).
31. *BRACHYTÆNIA WOODIANA. Herefordshire (1882).
32. *Eupoecilia angustana, _var._ THULEANA. Shetland Islands.
33. *TORTRIX DONELANA. Connemara, Ireland (1890).
TINEINA.
34. TINEA COCHYLIDELLA. Sanderstead, near Croydon (1854). Unique!
35. ACROLEPIA BETULÆTELLA. Yorkshire and Durham (1840). Rare.
36. ARGYRESTHIA SEMIFUSCA. North and West of England (1829). Rather
scarce. A distinct species.
37. GELECHIA DIVISELLA. A fen insect (1856). Rare. {349}
38. G. CELERELLA. West of England (1854). A doubtful species.
39. *G. TETRAGONELLA. Yorkshire. Norfolk. Salt marshes.
40. *G. SPARSICILIELLA. Pembroke.
41. *G. PLANTAGINELLA. A salt-marsh species.
42. G. OCELLATELLA (Barrett _nec_ Stainton). Bred from _Beta maritima_.
Very distinct.
43. BRYOTROPHA POLITELLA. Moors of North of England. Norfolk (1854).
44. *B. PORTLANDICELLA. Isle of Portland (1890).
45. LITA FRATERNELLA. Widely scattered (1834). Larva feeds on shoots of
_Stellaria uliginosa_ in spring.
46. L. BLANDULELLA. Kent.
47. ANACAMPSIS SIRCOMELLA. North and West England (1854). Perhaps a
melanic variety of the more widely spread _A. tæniolella_.
48. A. IMMACULATELLA. West Wickham (1834). Unique! A distinct species.
49. *OECOPHORA WOODIELLA?
50. GLYPHIPTERYX CLADIELLA. Eastern Counties (1859). Abundant.
51. G. SCHOENICOLELLA. In several localities (1859).
52. GRACILARIA STRAMINEELLA. (1850). On birch. Perhaps a local form of
_G. elongella_, found on alder.
53. ORNIX LOGANELLA. Scotland (1848). Abundant, and a distinct species.
54. O. DEVONIELLA. In Devonshire (1854). Unique!
55. COLEOPHORA SATURATELLA. South of England (1850). Abundant on broom.
56. C. INFLATÆ. South and East of England. On _Silene inflata._ ?
continental.
57. C. SQUAMOSELLA. Surrey (1856). Very rare, but an obscure species.
58. C. SALINELLA. On Sea-coast (1859). Abundant.
59. *C. POTENTILLÆ. South of England.
60. *C. ADJUNCTELLA. Essex salt marshes. ? Lancashire (1882).
61. *C. LIMONIELLA. Isle of Wight. Feeds on _Statice limonium_.
62. ELACHISTA FLAVICOMELLA. Dublin (1856). Excessively rare, two
specimens only known.
63. *E. SCIRPI. Wales and Sussex. Salt marshes.
64. E. CONSORTELLA. Scotland (1854). A doubtful species.
65. E. MEGERLELLA. Widely distributed (1854). Common. Larva feeds in
grass during winter and early spring.
66. E. OBLIQUELLA. Near London (1854). Unique!
67. E. TRISERIATELLA. South of England (1854). Very local; an obscure
species.
68. *TINAGMA BETULÆ. East Dorset (1891).
69. LITHOCOLLETIS NIGRESCENTELLA. Northumberland (1850). Rare; a dark
form of _L. Bremiella_, which is widely distributed.
70. *L. ANDERIDÆ. Sussex. Dorset (1886).
71. L. IRRADIELLA. North Britain (1854). A northern form of the more
southern and wide-spread _L. lautella_.
72. L. TRIGUTTELLA. Sanderstead, near Croydon (1848). Unique! very
peculiar.
73. L. ULICICOLELLA. In a few wide-spread localities (1854). A peculiar
form.
74. L. CALEDONIELLA. North Britain (1854). A local variety of the more
widespread _L. corylifoliella_. {350}
75. L. DUNNINGIELLA. North of England (1852). A somewhat doubtful
species.
76. BUCCULATRIX DEMARYELLA. Widely distributed (1848). Rather common.
77. TRIFURCULA SQUAMATELLA. South of England (1854). A doubtful
species.
78. NEPTICULA IGNOBILIELLA. Widely scattered (1854). On hawthorn, not
common. ? on continent.
79. N. POTERII. South of England (1858). Bred from Larvæ in _Poterium
sanguisorba_.
80. N. QUINQUELLA. South of England (1848). On oak leaves, very local.
? continental.
81. N. APICELLA. Local (1854). Probably confused with allied species on
the continent.
82. N. HEADLEYELLA. Local (1854). A rare species.
83. *N. HODGKINSONI. Lancashire.
84. *N. WOOLHOPIELLA. Herefordshire.
85. *N. SERELLA. Westmoreland and S. England.
86. *N. AUROMARGINELLA. Dorset (1890).
87. *MICROPTERYX SANGII. (1891).
88. *M. SALOPIELLA.
PTEROPHORINA.
89. AGDISTIS BENNETTI. East coast. I. of Wight (1840). Common on
_Statice limonium_.
We have here a list of eighty-nine species, which, according to the best
authorities, are, in the present state of our knowledge, peculiar to
Britain. It is a curious fact that no less than fifty of these have been
described more than twenty-five years; and as during all that time they
have not been recognised on the continent, notwithstanding that good
coloured figures exist of almost all of them, it seems highly probable that
many of them are really confined to our island. At the same time we must
not apply this argument too rigidly, for the very day before my visit to
Mr. Stainton he had received a letter from Professor Zeller announcing the
discovery on the continent of a species of our last family, Pterophorina,
which for more than forty years had been considered to be exclusively
British. This insect, _Platyptilia similidactyla_ (_Pterophorus
isodactylus_, Stainton's _Manual_), had been taken rarely in the extreme
north and south of our islands--Teignmouth and Orkney, a fact which seemed
somewhat indicative of its being a straggler. Again, seven of the species
are unique, that is, have only been captured once; and it may be supposed
that, as they are so rare as to have been found only once in England, they
may be all {351} equally rare and not yet found on the continent. But this
is hardly in accordance with the laws of distribution. Widely scattered
species are generally abundant in some localities; while, when a species is
on the point of extinction, it must for a time be very rare in the single
locality where it last maintains itself. It is then more probable that some
of these unique species represent such as are almost extinct, than that
they have a wide range and are equally rare everywhere; and the peculiarity
of our insular climate, combined with our varied soil and vegetation, offer
conditions which may favour the survival of some species with us after they
have become extinct on the continent.
Of the sixty-nine species recorded in my first edition fourteen have been
since discovered on the continent, while no less than twenty-two species
and eleven varieties have been added to the list. As we can hardly suppose
continental entomologists to be less thorough collectors than ourselves, it
ought to be more and more difficult to find any insects which are unknown
on the continent if all ours really exist there; and the fact that the list
of apparently peculiar British species is an increasing one renders it
probable that many of them are not only apparently but really so. Both
general considerations dependent on the known laws of distribution, and the
peculiar habits, conspicuous appearance, and restricted range, of many of
our species, alike indicate that some considerable proportion of them will
remain permanently as peculiar British species.
We will now pass on to the Coleoptera, or beetles, an order which has been
of late years energetically collected and carefully studied by British
entomologists.
_List of the Species and Varieties of Beetles which, so far as at present
known, are confined to the British Islands. Those added since the first
edition are marked with an asterisk._
CARABIDÆ.
1. *Bembidium saxatile, _var._ VECTENSIS (Fowler). Isle of Wight.
2. DROMIUS VECTENSIS (Rye). Common in the Isle of Wight, also in Kent,
and at Weymouth and Seaton. Closely allied to _D. sigma_.
3. Harpalus latus, _var._ METALLESCENS (Rye). Unique, but very marked!
South coast. "Perhaps a sport or a hybrid" (Fowler).
4. ACUPALPUS DERELICTUS (Dawson). Unique! North Kent. Canon Fowler
thinks it may be a variety of _A. dorsalis_. {352}
DYTICIDÆ.
5. *Acilius sulcatus, _var._ SCOTICUS (Curtis). Scotland. A melanic
variety.
HELOPHORIDÆ.
6. OCHTHEBIUS POWERI (Rye). Very marked. S. coast. A few specimens
only.
7. *O. ÆNEUS (Steph).
BRACHYELYTRA.
8. OCYUSA HIBERNICA (Rye). Ireland, mountain tops, and at Braemar.
9. *OXYPODA TARDA (Sharp).
10. ,, PECTITA (Sharp). Scotland.
11. ,, VERECUNDA (Sharp). Scotland, also London districts.
12. HOMALOTA DIVERSA (Sharp).
13. ,, FULVIPENNIS (Rye).
14. ,, OBLONGIUSCULA (Sharp). Scotland, also England and Ireland.
15. ,, PRINCEPS (Sharp). A coast insect.
16. ,, CURTIPENNIS (Sharp). Scotland and near Birmingham.
17. H. levana, _var._ SETIGERA (Sharp).
18. STENUS OSCILLATOR (Rye). Unique! South coast. May be a hybrid.
19. TROGOPHLÆUS SPINICOLLIS (Rye). Mersey estuary, unique! Most
distinguishable, nothing like it in Europe. Perhaps imported from
another continent.
20. EUDECTUS WHITEI (Sharp). Scotch hills. A variety of _E. Giraudi_ of
Germany (the only European species) _fide_ Kraatz (Sharp).
21. HOMALIUM RUGULIPENNE (Rye). Exceedingly marked form. Northern and
western coasts; rare.
22. *MYCETOPORUS MONTICOLA (Fowler). Cheviots and Inverness-shire.
SCYDMÆNIDÆ.
23. *SCYDMÆNUS POWERI (Fowler) S. England. A recent discovery.
24. *S. PLANIFRONS (Fowler). ,, ,,
PSELAPHIDÆ.
25. BRYAXIS COTUS (De Sauley). Scotland.
26. BYTHINUS GLABRATUS (Rye). Sussex coast; also Isle of Wight; a few
specimens; very distinguishable; myrmecophilous (lives in ants' nests).
TRICHOPTERYGIDÆ.
27. PTINELLA MARIA (Matthews) Derbyshire.
28. TRICHOPTERYX SARÆ ( ,, ) Notts.
29. ,, POWERI ( ,, ) Oxon.
30. ,, EDITHIA ( ,, ) Kent.
31. ,, *ANGUSTA ( ,, ) Leicestershire.
32. ,, KIRBII ( ,, ) Norfolk.
33. ,, FRATERCULA ( ,, )
34. ,, WATERHOUSII ( ,, )
35. ,, CHAMPIONIS ( ,, ) Wicken Fen.
36. ,, JANSONI ( ,, ) Leicestershire.
37. ,, SUFFOCATA (Haliday). Ireland, Co. Cork.
38. ,, CARBONARIA (Matthews). Notts.
{353} 39. Ptilium halidayi (Matthews). Sherwood Forest.
40. ,, caledonicum (Sharp). Scotland; very marked form.
41. ,, insigne (Matthews). London district.
42. *ORTHOPERUS MUNDUS (Matthews). Oxfordshire.
43. *O. PUNCTULATUS (Matthews). Lincolnshire.
ANISOTOMIDÆ.
44. AGATHIDIUM RHINOCEROS (Sharp). Old fir-woods in Perthshire; local,
many specimens; a very marked species.
45. ANISOTOMA SIMILATA (Rye). South of England. Two specimens.
46. ,, LUNICOLLIS (Rye). North-east and South of England, a very
marked form; several specimens.
PHALACRIDÆ.
47. PHALACRUS BRISOUTI (Rye). South of England. Rare. "Perhaps a small
form of _P. coruscus_" (Fowler).
CRYPTOPHAGIDÆ.
48. ATOMARIA DIVISA (Rye). Unique! South of England.
LATHRIDIIDÆ.
49. Melanopthalma transversalis, _var._ WOLLASTONI (Waterhouse). South
coast, and Lincolnshire.
BYRRHIDÆ.
50. SYNCALYPTA HIRSUTA (Sharp). South of England, local. "Closely
allied to _S. setigera_" (Fowler).
MORDELLIDÆ.
51. *ANASPIS SEPTENTRIONALIS. Scotland (1891). (Champion.)
52. * ,, GARNEYSI (Fowler). London District. (1890.)
TELEPHORIDÆ.
53. TELEPHORUS DARWINIANUS (Sharp). Scotland, sea-coast. A stunted form
of abnormal habits. Perhaps a variety of _T. lituratus_.
CYPHONIDÆ.
54. CYPHON PUNCTIPENNIS (Sharp). Scotland.
ANTHICIDÆ.
55. ANTHICUS SALINUS (Crotch). South coast.
56. ,, SCOTICUS (Rye). Loch Leven; very distinct; many specimens.
CIOIDÆ.
57. *CIS BILAMELLATUS (Wood). West Wickham, Kent. "Perhaps imported.
Has the appearance of an exotic Cis" (Fowler).
TOMICIDÆ.
58. *Pityopthorus lichtensteinii, _var._ SCOTICUS (Blandford).
Scotland.
CURCULIONIDÆ.
59. Ceuthorhynchus contractus, _var._ PALLIPES (Crotch). Lundy Island;
several specimens. A curious variety only known from this island.
60. LIOSOMUS TROGLODYTES (Rye). A very queer form. Two or three
specimens. South of England.
61. *Orcheites ilicis, _var._ NIGRIPES (Fowler). London District.
(1890.)
{354}
62. APION RYEI (Blackburn). Shetland Islands. Several specimens.
Perhaps a _var._ of _A. fagi_.
CHRYSOMELIDÆ.
63. Chrysomela staphylea, _var._ SHARPI (Fowler). Solway district.
HALTICIDÆ.
64. LONGITARSUS AGILIS (Rye). South of England; many specimens.
65. ,, DISTINGUENDA (Rye). South of England; many specimens.
66. PSYLLIODES LURIDIPENNIS (Kutschera). Lundy Island. A very curious
form, not uncommon in this small island, to which it appears to be
confined. "An extreme and local variety of _P. chrysocephala_"
(Fowler).
COCCINELLIDÆ.
67. SCYMNUS LIVIDUS (Bold). Northumberland. A doubtful species.
Of the sixty-seven species and varieties of beetles in the preceding list,
a considerable number no doubt owe their presence there to the fact that
they have not yet been discovered or recognised on the continent. This is
almost certainly the case with many of those which have been separated from
other species by very minute and obscure characters, and especially with
the excessively minute Trichopterygidæ described by Mr. Matthews. There are
others, however, to which this mode of getting rid of them will not apply,
as they are so marked as to be at once recognised by any competent
entomologist, and often so plentiful that they can be easily obtained when
searched for. The peculiar species of Apion in the Shetland Islands is
interesting, and may be connected with the very peculiar climatal
conditions there prevailing, which have led in some cases to a change of
habits, so that a species of weevil (_Otiorhynchus maurus_) always found on
mountain sides in Scotland here occurs on the sea-shore. Still more curious
is the occurrence of two distinct forms (a species and a well-marked
variety) on the small granitic Lundy Island in the Bristol Channel. This
island is about three miles long and twelve from the coast of Devonshire,
consisting mainly of granite with a little of the Devonian formation, and
the presence here of peculiar insects can only be due to isolation with
special conditions, and immunity from enemies or competing forms. When we
consider the similar islands off {355} the coast of Scotland and Ireland,
with the Isle of Man and the Scilly Islands, none of which have been yet
thoroughly explored for beetles, it is probable that many similar examples
of peculiar isolated forms remain to be discovered.
Looking, then, at what seem to me the probabilities of the case from the
standpoint of evolution and natural selection, and giving due weight to the
facts of local distribution as they are actually presented to us, I am
forced to differ from the opinion held by our best entomological
authorities, and to believe that some at least, perhaps many, of the
species which, in the present state of our knowledge, appear to be peculiar
to our islands, are, not only apparently, but really, so peculiar.
I am indebted to Mr. Robert McLachlan for the following information on
certain Trichopterous Neuroptera (or caddis-flies) which appear to be
confined to our islands. The peculiar aquatic habits of the larvæ of these
insects, some living in ponds or rivers, others in lakes, and others again
only in clear mountain streams, render it not improbable that some of them
should have become isolated and preserved in our islands, or that they
should be modified owing to such isolation.
_Trichoptera peculiar to the British Isles._
1. PHILOPOTAMUS INSULARIS. (? A variety of _P. montanus_.)--This can
hardly be termed a British species or variety, because, so far as at
present known, it is peculiar to the Island of Guernsey. It agrees
structurally with _P. montanus_, a species found both in Britain and on
the continent, but it differs in its strikingly yellow colour, and less
pronounced markings. All the specimens from Guernsey are alike, and
resident entomologists assured Mr. McLachlan that no other kind is
known. Strange to say, some examples from Jersey differ considerably,
resembling the common European and British form. Even should this
peculiar variety be at some future time found on the continent it would
still be a remarkable fact that the form of insect inhabiting two small
islands only twenty miles apart should constantly differ; but as Jersey
is between Guernsey and the coast, it seems just possible that the more
insular conditions, and perhaps some peculiarity of the soil and water
in the former island, have really led to the production or preservation
of a well-marked variety of insect. In the first edition of this work
two other species were named as then, peculiar to Britain--Setodes
argentipunctella and Rhyacophila munda, but both have now been taken on
the continent.
2. MESOPHYLAX IMPUNCTATUS, _var._ ZETLANDICUS.--A variety of a South
and Central European species, one specimen of which has been found in
Dumfriesshire. The variety is distinguished by its small size and dark
colour.
{356}
_Land and Freshwater Shells._--In the first edition of this work four
species were noted as being, so far as was then known, exclusively British.
Two of these, _Cyclas pisidioides_ (now called _Sphærium pisidioides_) and
_Geomalacus maculosus_, have been discovered on the continent, but the
other two remain still apparently confined to these islands; and to these
another has been added by the discovery of a new species of Hydrobia in the
estuary of the Thames. The peculiar species now stands as follows:--
1. LIMNEA INVOLUTA.--A pond snail with a small polished amber-coloured
shell found only in a small alpine lake and its inflowing stream on
Cromagloun mountain near the lakes of Killarney. It was discovered in
1838, and has frequently been obtained since in the same locality. It
is sometimes classed as a variety of _Limnea peregra_, and is at all
events closely allied to that species.
2. HYDROBIA JENKINSII.--A small shell of the family Rissoidæ inhabiting
the Thames estuary both in Essex and Kent. It was discovered only a few
years ago, and was first described in 1889.
3. ASSIMINEA GRAYANA.--A small estuarine pulmonobranch found on the
banks of the Thames between Greenwich and Gravesend, on mud at the
roots of aquatic plants. It has been discovered more than sixty years.
But besides the above-named species there are a considerable number of
well-marked varieties of shells which seem to be peculiar to our islands. A
list of these has been kindly furnished me by Mr. Theo. D. A. Cockerell,
who has paid much attention to the subject; and after omitting all those
whose peculiarities are very slight or whose absence from the continent is
doubtful, there remain a series of forms some of which are in all
probability really endemic with us. This is the more probable from the fact
that an introduced colony of _Helix nemoralis_ at Lexington, Virginia,
presents numerous varieties among which are several which do not occur in
Europe.[84] The following list is therefore given in the hope that it may
be useful in calling attention to those varieties which are not yet
positively known to occur elsewhere than in our islands, and {357} thus
lead, ultimately, to a more accurate knowledge of the facts. It is only by
obtaining a full knowledge of varieties, their distribution and their
comparative stability, that we can ever hope to detect the exact process by
which nature works in the formation of species.
LIST OF THE SPECIES AND VARIETIES OF LAND AND FRESHWATER SHELLS WHICH, SO
FAR AS AT PRESENT KNOWN, ARE BELIEVED TO BE PECULIAR TO THE BRITISH ISLES
OR NOT FOUND ON THE CONTINENT.
LIMACIDÆ.
1. Limax marginatus, _var._ MACULATUS. Ireland; frequent, very
distinct.
2. ,, ,, ,, DECIPIENS. Ireland and England.
3. ,, flavus, _var._ SUFFUSUS. England; Melanic form.
4. ,, ,, ,, GRISEUS. England; Melanic form.
5. Agriolimax agrestis, _var._ NIGER. Yorkshire. Melanic. Azores.
6. ,, ,, ,, GRISEUS. England. Melanic.
7. Amalia gagates, _var._ RAVA. W. of England.
8. ,, sowerbyi, _var._ RUSTICA. England.
9. ,, ,, ,, NIGRESCENS. Surrey and Middlesex.
10. ,, ,, ,, BICOLOR. Ealing.
11. Hyalina crystallina, _var._ COMPLANATA. Near Bristol.
12. ,, fulva, _var._ ALDERI.
13. Vitrina pellucida, _var._ DEPRESSIUSCULA. S. England, Wales.
HELICIDÆ.
14. Arion ater, _var._ ALBO-LATERALIS. England, Wales, Isle of Man;
very distinct.
15. ,, hortensis, _var._ FALLAX. England. Common at Boxhill.
16. GEOMALACUS MACULOSUS. Kerry and Cork. Three varieties have been
described, one of which occurs in Portugal.
17. Helix aspersa, _var._ LUTESCENS. England. Not rare perhaps in
France.
18. ,, nemoralis, _var._ HIBERNICA. Ireland.
19. ,, rufescens, _var._ MANCHESTERIENSIS. England.
20. ,, hispida, _var._ SUBGLOBOSA. England.
21. ,, ,, ,, DEPILATA. England.
22. ,, ,, ,, MINOR. England, Ireland.
23. ,, granulata, _var._ CORNEA. Lulworth, Dorset.
24. ,, virgata, _var._ SUBAPERTA. Bath.
25. ,, ,, ,, SUBGLOBOSA. England, Wales, Bantry Bay.
26. ,, ,, ,, CARINATA. Wareham, Dorset.
27. ,, caperata, _var._ MAJOR. England, Wales, Scotland. Distinct.
28. ,, ,, ,, NANA. England.
29. ,, ,, ,, SUBSCALARIS. Wales, Ireland.
30. ,, ,, ,, ALTERNATA. England, Kent.
31. ,, acuta, _var._ NIGRESCENS. England.
PUPIDÆ.
32. Pupa anglica, _var._ PALLIDA. Not rare.
33. ,, lilljeborgi, _var._ BIDENTATA. Ireland.
{358} 34. ,, pygmea, _var._ PALLIDA. Dorset and Devon.
35. Clausilia rugosa, _var._ PARVULA. Ireland.
STENOGYRIDÆ.
36. Cochlicopa lubrica, _var._ HYALINA. Wales, Scotland.
37. Coecilianella acicula, _var._ ANGLICA. England.
SUCCINEIDÆ.
38. Succinea putris, _var._ SOLIDULA. Wiltshire.
39. ,, virescens, _var._ AUREA. Ireland.
40. ,, pfeifferi, ,, RUFESCENS. England, Ireland.
41. ,, ,, ,, MINOR. England.
LIMNÆIDÆ.
42. Planorbis fontanus, _var._ MINOR. England.
43. ,, carinatus, ,, DISCIFORMIS. England.
44. ,, contortus, ,, EXCAVATUS. Ireland.
45. ,, ,, ,, MINOR.
46. Physa fontinalus, _var._ OBLONGA. England, Wales, Ireland.
47. LIMNÆA INVOLUTA. Ireland.
48. Limnæa glutinosa, _var._ MUCRONATA.
49. ,, peregra, _var._ BURNETTI. Scotland. Very distinct.
50. ,, ,, ,, LACUSTRIS. Perhaps in C. Verde Islands.
51. ,, ,, ,, MARITIMA. Great Britain.
52. ,, ,, ,, LINEATA. England.
53. ,, ,, ,, STAGNALIFORMIS. England.
54. ,, stagnalis, _var._ ELAGANTULA. Curious. In a pond at
Chislehurst.
55. ,, palustris, _var._ CONICA. England, Ireland.
56. ,, ,, ,, TINCTA. England, Wales.
57. ,, ,, ,, ALBIDA. England.
58. ,, truncatula, _var._ ELEGANS. England, Ireland. Distinct.
59. ,, ,, ,, FUSCA. Wales.
60. Ancylus lacustris, _var._ COMPRESSUS. England.
PALUDINIDÆ.
61. Paludina vivipara, _var._ EFASCIATA. England. Not uncommon.
62. ,, ,, ,, ATROPURPUREA. Pontypool.
RISSOIDÆ.
63. HYDROBIA JENKINSII. Thames Estuary.
64. ,, ventrosa, _var._ MINOR.
65. ,, ,, ,, DECOLLATA.
66. ,, ,, ,, OVATA.
67. ,, ,, ,, ELONGATA.
68. ,, ,, ,, PELLUCIDA.
CYRENIDÆ.
69. Sphærium corneum, _var._ COMPRESSUM.
70. ,, ,, ,, MINOR.
71. ,, ,, ,, STAGNICOLA.
72. ,, ovale, _var._ PALLIDUM. England.
73. ,, lacustre, _var._ ROTUNDUM. Wales.
74. Pisidium pusillum, _var._ GRANDIS.
75. ,, ,, ,, CIRCULARE. Wales.
76. ,, nitidum, _var._ GLOBOSUM.
{359} UNIONIDÆ.
77. Unio tumidus, _var._ RICHENSIS. Regent's Park. Peculiar form.
78. ,, pictorum, _var._ LATIOR. England.
79. ,, ,, ,, COMPRESSUS. England.
80. ,, margaritifer, _var._ OLIVACEUS.
81. Anodonta cygnæa, _var._ INCRASSATA. England.
82. ,, ,, ,, PALLIDA. England, Ireland.
ESTUARINE OR MARINE PULMONOTRANCHS.
83. ASSIMINEA GRAYANA. Thames Estuary.
_Peculiarities of the British Flora._--Thinking it probable that there must
also be some peculiar British plants, but not finding any enumeration of
such in the _British Floras_ of Babington, Hooker, or Bentham, I applied to
the greatest living authority on the distribution of British plants--the
late Mr. H. C. Watson, who very kindly gave me the information I required,
and I cannot do better than quote his words: "It may be stated pretty
confidently that there is no 'species' (generally accepted among botanists
as a good species) peculiar to the British Isles. True, during the past
hundred years, nominally new species have been named and described on
British specimens only, from time to time. But these have gradually come to
be identified with species described elsewhere under other names--or they
have been reduced in rank by succeeding botanists, and placed or replaced
as varieties of more widely distributed species. In his _British Rubi_
Professor Babington includes as good species, some half-dozen which he has,
apparently, not identified with any foreign species or variety. None of
these are accepted as 'true species,' nor even as 'sub-species' in the
_Students' Flora_, where the brambles are described by Baker, a botanist
well acquainted with the plants of Britain. And as all these nominal
species of Rubi are of late creation, they have truly never been subjected
to real or critical tests as 'species.'"
In my first edition I was only able to name four species, sub-species, or
varieties of flowering plants which were believed to be unknown on the
continent. But much attention has of late years been paid to the critical
examination of British plants in comparison with continental specimens, and
I am now enabled to give a much more {360} extensive list of the species or
forms which at present seem to be peculiar. For the following list I am
primarily indebted to Mr. Arthur Bennett of Croydon. Sir Joseph Hooker has
been so kind as to examine it carefully and to give me his conclusions on
the relative value of the differences of the several forms, and Mr. Baker,
of Kew, has also assisted with his extensive knowledge of British plants.
LIST OF SPECIES, SUB-SPECIES, AND VARIETIES OF FLOWERING PLANTS FOUND
IN GREAT BRITAIN OR IRELAND, BUT NOT AT PRESENT KNOWN IN CONTINENTAL
EUROPE. BY ARTHUR BENNETT, F.L.S. THE MOST DISTINCT AND BEST DETERMINED
FORMS ARE MARKED WITH AN ASTERISK.
1. *Caltha radicans (Forst.). "A much disputed species, or form of _C.
palustris_. It is a relatively rare plant." (J. D. H.) "Certainly
distinct from the Scandinavian form." (Ar. Bennett.)
2. *Arabis petræa (Lam.) _var._ grandifolia (Druce). Scotch mountains.
"The larger flowers alone distinguish this." (J. D. H.)
3. Arabis ciliata (R. Br.). In Nyman's _Conspectus Floræ Europææ_ this
species is given as found in England and Ireland only. "A very much
disputed form of a plant of very wide distribution in Europe and North
America." (J. D. H.)
4. Brassica monensis (Huds.). "This and the continental _B.
cheiranthus_ (also found in Cornwall) are barely distinguishable from
one another." (J. D. H.)
5. Diplotaxis muralis (D. C.) _var._ Babingtonii (Syme). South of
England. "A biennial or perennial form; considered to be a denizen by
Watson." (J. D. H.)
6. *Helianthemum guttatum (Mill), _var._ Breweri (Planch). Anglesea.
"Very doubtful local plant. _H. guttatum_ (true) has lately been found
in the same locality." (J. D. H.)
7. *Polygala vulgaris (L.), _var._ grandiflora (Bab). Sligo, Ireland.
"A very distinct variety." (J. D. H.)
8. Viola lutea (Huds.), _var._ amoena (Symons). "_V. lutea_ itself is
considered to be a form of _V. tricolor_, and _V. amoena_ the better
coloured of the two forms of _V. lutea_." (J. D. H.)
9. *Cerastium arcticum (Lange), _var._ Edmonstonii (Beeby). Shetland
Is. "But _C. arcticum_ is referable to the very variable _C. alpinum_."
(J. D. H.) "Near to the European _C. latifolium_." (Ar. Bennett.)
10. *Geranium sanguineum (L.), _var._ Lancastriense (With.).
Lancashire. "A prostrate local form growing out of its native soil in
sand by the sea." (J. D. H.) Mr. Bennett writes: "I have grown _G.
sanguineum_ and its prostrate variety in sand, and neither became
Lancastriense."
11. Genista tinctoria (L.), _var._ humifusa (Dickson). Cornwall. "A
decumbent hairy form confined to the Lizard." (J. D. H.)
12. Cytisus scoparius (Link.), _var._ prostratus (Bailey). Cornwall. "A
prostrate form." (J. D. H.)
13. Anthyllis vulneraria (L.), _var._ ovata (Bab.). Shetland Is. "A
slight variety." (J. D. H.)
14. *Trifolium repens (L.), _var._ Townsendii (Bab.). Scilly Isles. "A
{361} well-marked form by its rose-purple flowers. Confined to the
Scilly Isles." (J. D. H.)
15. *Rosa involuta (Sm.), _var._ Wilsoni. (Borrer.) Wales. "There are a
multitude of forms or varieties of _R. involuta_, and _R. wilsoni_ is
one of the best-marked, found on the Menai Straits and Derry."
(J. D. H.)
16. Rosa involuta _var._ gracilis (Woods). "This is considered by many
as one of the commonest forms of _R. involuta_." (J. D. H.)
17. Rosa involuta _var._ Nicholsoni (Crepin). "Another slight variety
of _R. involuta_." (J. D. H.)
18. Rosa involuta _var._ Woodsiana (Groves). "A Wimbledon Common
variety of _R. villosa_." (J. D. H.)
19. Rosa involuta _var._ Grovesii (Baker). "Mr. Baker thinks this of no
account." (J. D. H.)
20. Rubus echinatus (Lind.). "A variety of the widely spread _R.
Radula_, itself a form of _R. fruticosus_." (J. D. H.)
21. *Rubus longithyrsiger (Lees). "Mr. Baker informs me that this is a
very distinct plant never yet found on the continent." (J. D. H.)
22. Pyrus aria (Sm.) _var._ rupicola (Syme). "A very local form,
confined to Gt. Britain, and owing its characters to its starved
position." (Baker.)
23. Callitriche obtusangula (Le Gall), _var._ Lachii (Warren).
Cheshire. "This is intermediate between two sub-species of _C. verna_."
(J. D. H.)
24. *Oenanthe fluviatilis (Coleman). South of England. "The fluitant
form of _Æ. Phellandrium_." (J. D. H.)
25. Anthemis arvensis (L.), _var._ anglica (Spreng). N. Coast of
England. "A maritime form with more fleshy leaves formerly found near
Durham. It has other very trifling characters." (J. D. H.)
26. Arctium intermedium (Bab.). "There are two sub-species of _A.
lappa_, _majus_ and _minus_, each with varieties, and this is one of
the intermediates." (J. D. H.)
27. Hieracium holosericium (Backh.). Scotch Alps.
28. H. gracilentum (Backh.). ,,
29. H. lingulatum (Backh.). ,, A var. of this in
Scandinavia.
30. H. senescens (Backh.). ,,
31. H. chrysanthenum (Backh.). ,,
32. H. iricum (Fr.). Teesdale and Scotland.
33. H. gibsoni (Backh.). Yorkshire and Westmoreland.
34. Hieracium nitidum (Backh.). Lower glens of the Scotch Alps. Mr.
Bennett writes:--"The following Hieracia have been named by Mr. F. J.
Hanbury _as endemic forms_. One can only safely say they are certainly
not known in Scandinavia, as they have all been submitted to Dr.
Lindeberg. But usually Scotch species are not represented in Central
Europe to any great extent, though several do occur. Still these new
forms ought to be critically compared with all Dr. Peters' new
species."
35. H. Langewellense (Hanb.). Caithness.
36. H. pollinarium (Hanb.). Sutherland.
37. H. scoticum (Hanb.). Sutherland and Caithness.
38. H. Backhousei (Hanb.). Aberdeen, Banff, Inverness.
39. H. caledonicum (Hanb.). Caithness and Sutherland.
40. H. Farrense (Hanb.). Sutherland and Shetland Is.
41. H. proximum (Hanb.). Caithness. With regard to all these {362}
Hieracia Sir Joseph Hooker and Mr. Baker say:--"No case can be made of
these. They are local forms with the shadowest of shady characters."
Mr. Bennett writes: "H. iricum and H. Gibsoni are the best marked
forms."
42. *Campanula rotundifolia (L.), _var._ speciosa (A. G. More). W.
Ireland. "Very well distinguished by its large flowers and small calyx
lobes, approaching the Swiss C. Scheuzeri." (J. D. H.)
43. Statice reticulata (Sm.). "Baker agrees with me that this is also a
Mediterranean species." (J. D. H.)
44. Erythræa capitata (Willd.), _var._ sphærocephala (Towns.). Isle of
Wight. "A form of _E. centaurium_ utterly anomalous in its genus in the
insertion of the stamens. A monster rather than a species." (J. D. H.)
45. *Erythræa latifolia (Sm.). On the sandy dunes near Liverpool. "A
local form." (J. D. H.)
46. Myosotis collina (Hoffim.), _var._ Mittenii (Baker). Sussex.
47. Veronica officinalis (L.), _var._ hirsuta (Hopk.). Ayr, Scotland.
48. Veronica arvensis (L.), _var._ eximia (Towns.). Hampshire.
49. Mentha alopecuroides (Hull). Nearest to _M. dulcissima_ (Dum.).
50. Mentha pratensis (Sole). Only once found.
51. Chenopodium rubrum (L.), _var._ pseudobotryoides (H. C. Watson).
52. Salix ferruginea (Forbes). England, Scotland. "Probably a hybrid
between _S. viminalis_ and _S. cinerea_." (J. D. H.)
53. Salix Grahami (Borr.). Sutherland, Perth. "A hybrid?" (J. D. H.)
54. Salix Sadleri (Syme). Aberdeen. "A hybrid?" (J. D. H.)
55. *Spiranthes Romanzoviana (Cham.). Ireland (N. America).
56. *Sisyrinchium angustifolium (Mill.). Ireland. (Arctic and Temp. N.
America.)
57. Allium Babingtonii (Borrer). West England, West Ireland. "A form of
_A. ampeloprasum_, itself a naturalised species." (J. D. H.)
58. *POTAMOGETON LANCEOLATUS (Sm.). Anglesea, Cambridgeshire, Ireland.
Mr. Bennett writes:--"Endemic! I have taken a good amount of trouble to
ascertain this. Nearly 400 specimens I have distributed all over the
world with requests for information as to anything like it. The
response is everywhere the same, 'nothing.' The nearest to it occurs in
the Duchy of Lauenberg but is referable to _P. heterophyllus_."
59. Potamogeton Griffithii (Ar. Bennett). Carnarvon. "Nearest to this
is a probable hybrid from N. America, but not identical." (Ar.
Bennett.)
60. Potamogeton pusillus (L.), _sub-sp._ Sturrockii (Ar. Benn.). Perth.
61. Potamogeton pusillus (L.), _var._ rigidus (Ar. Benn.). Orkneys,
Shetlands.
62. Ruppia rostellata (Koch.), _var._ nana (Bosw.). Orkneys.
63. *Eriocaulon septangulare (With.). Hebrides, Ireland. N. America.
64. Scirpus uniglumis (Link), _var._ Watsoni (Bab.). Scotland, England.
"This is a variety of a sub-species of the common _S. palustris_."
(J. D. H.)
65. Luzula pilosa (Willd.), _var._ Borreri (Bromf).
66. *Carex involuta (Bab.). Cheshire. "A distinct enough plant but
probably a hybrid between _C. vesicaria_ and _C. ampullacea_, found in
one place only." (J. D. H.)
67. Carex glauca (Murr.), _var._ stictocarpa (Sm.). Scotland.
{363} 68. Carex precox (Jacq.), _var._ capitata (Ar. Benn.). Ireland.
"A remarkable plant (monstrosity?) simulating _C. capitata_ (L.)." (Ar.
Bennett.)
69. *Carex Grahami (Boott). "A mountain form of _C. vesicaria_."
(J. D. H.)
70. *Spartina Townsendi (Groves). Hampshire. "A distinct but very local
form of _S. stricta_, found in one place only." (J. D. H.)
71. Agrostis nigra (With.).
72. Deschampsia flexuosa (Trin.), _var._ Voirlichensis (J. C. Melvill).
Perth.
73. *Deyeuxia neglecta (Kunth), _var._ Hookeri (Syme). Ireland. "A
distinct variety confined to Lough Neagh." (J. D. H.)
74. Glyceria maritima (Willd.), _var._ riparia (Towns.). Hampshire.
75. Poa Balfouri (Bab.). Scotland. "An alpine sub-variety of a variety
of the protean _P. nemoralis_." (J. D. H.)
In his comments on this extensive list of supposed peculiar British plants,
Sir Joseph Hooker arrives at the following conclusions:--
1. There are four unquestionably distinct species which do not occur in
continental Europe: viz.--
_One_ absolutely endemic species, POTAMOGETON LANCEOLATUS.
_Three_ American species, SISYRINCHIUM ANGUSTIFOLIUM, SPIRANTHES
ROMANZOVIANA, ERIOCAULON SEPTANGULARE.
2. There are sixteen endemic varieties of British species, viz.--
_Eleven_ of more or less variable species, Caltha palustris, _var._
RADICANS; Polygala vulgaris, _var._ GRANDIFLORA; Cerastium arcticum,
_var._ EDMONSTONII; Trifolium repens, _var._ TOWNSENDII; Rosa involuta,
_var._ WILSONI; Rubus fruticosus, _sub-sp._ LONGITHYRSIGER; Campanula
rotundifolia, _var._ SPECIOSA; Erythræa centaurium, _sub-sp._
LATIFOLIA; Carex involuta, (? Hyb.); Carex vesicaria, _var._ GRAHAMI;
Deyeuxia neglecta, _var._ HOOKERI.
_Five_ of comparatively well limited species. Arabis petræa, _var._
GRANDIFOLIA; Helianthemum guttatum, _var._ BREWERI; Geranium
sanguineum, _var._ LANCASTRIENSE; Oenanthe Phellandrium, _var._
FLUVIATILIS; Spartium stricta, _var._ TOWNSENDI.
The above twenty species are marked in the list with an asterisk. Of the
remaining fifty-five, Sir Joseph Hooker says, "that for various reasons it
would not be safe to rely on them as evidence. In most cases the varietal
form is so very trifling a departure from the type that this may be safely
set down to a local cause, and is probably not constant. In others the
plant is doubtfully endemic; in still others a hybrid."
Even should it ultimately prove that of the whole number of the fifty-five
doubtful forms none are established as peculiar British varieties, the
number admitted after so {364} rigorous an examination is about what we
should expect in comparison with the limited amount of speciality we have
seen to exist in other groups. The three American species which inhabit the
extreme west and north-west of the British Isles, but are not found on the
continent of Europe are especially interesting, because they demonstrate
the existence of some peculiar conditions such as would help to explain the
presence of the other peculiar species. Whether we suppose these American
forms to have migrated from America to Europe before the glacial epoch, or
to be the remnants of a vegetation once spread over the north temperate
zone, we can only explain their presence with us and not further east by
something favourable either in our insular climate or in the limited
competition due to our comparative poverty in species.
About half of the peculiar forms are found in the extreme west or north of
Britain or in Ireland, where peculiar insular conditions are at a maximum;
and the influence of these conditions is further shown by the number of
species of West or South European plants which occur in the same districts.
We may here notice the interesting fact that Ireland possesses no less than
twenty species or sub-species of flowering plants not found in Britain, and
some of these _may_ be altogether peculiar. As a whole they show the effect
of the pre-eminently mild and insular climate of Ireland in extending the
range of some south European species. The following list of these plants,
for which I am indebted to Mr. A. G. More, with a few remarks on their
distribution, will be found interesting:--
LIST OF IRISH FLOWERING PLANTS WHICH ARE NOT FOUND IN BRITAIN.
1. _Polygala vulgaris_ (_var._ grandiflora). Sligo.
2. _Campanula rotundifolia_ (_var._ speciosa). W. Ireland.
3. _Arenaria ciliata._ W. Ireland (also Auvergne, Pyrenees, Crete).
4. _Saxifraga umbrosa._ W. Ireland (also Pyrenees, N. Spain, Portugal).
5. ,, _geum._ S. W. Ireland (also Pyrenees).
6. ,, _hirsuta._ S. W. Ireland (also Pyrenees).
7. _Inula salicina._ W. Ireland (Scandinavia, Middle and South Europe).
8. _Erica mediterranea._ W. Ireland (W. France, Spain, Portugal).
9. ,, _mackaiana_ (_tetralix_ sub.-sp.) W. Ireland (Spain).
10. _Arbutus unedo._ S. W. Ireland (W. of France, Spain, Portugal and
shores of Mediterranean).
11. _Dabeocia polifolia._ W. Ireland (W. of France, Spain and
Portugal).
{365} 12. _Pinguicula grandiflora._ S. W. Ireland (Spain, Pyrenees,
Alps of France and Switzerland).
13. _Neotinea intacta._ W. Ireland (S. France, Portugal, Spain, and
shores of Mediterranean).
14. _Spiranthes romanzoviana._ S. W. Ireland (North America).
15. _Sisyrinchium angustifolium._ W. Ireland (North America, Arctic and
Temp.).
16. _Potamogeton lonchites._ Ireland, Mr. Arthur Bennett informs me
that this is certainly not British or European, but may possibly be
identical with _P. fluitans_ _var._ _Americanus_ of the U. States.
17. _Potamogeton kirkii_ (_natans_ sub.-sp.). W. Ireland. (Arctic
Europe?)
18. _Eriocaulon septangulare._ W. Ireland, Skye, Hebrides (North
America).
19. _Carex buxbaumii._ N. E. Ireland, on an island in Lough Neagh
(Arctic and Alpine Europe, North America).
20. _Deyeuxia neglecta_ (_var._ _Hookeri_). On the shores and islands
of Lough Neagh. (And in Germany, Arctic Europe, and North America.)
We find here nine south-west European species which probably had a wider
range in mild preglacial times, and have been preserved in the south and
west of Ireland owing to its milder climate. It must be remembered that
during the height of the glacial epoch Ireland was continental, so that
these plants may have followed the retreating ice to their present stations
and survived the subsequent depression. This seems more probable than that
so many species should have reached Ireland for the first time during the
last union with the continent subsequent to the glacial epoch. The Arctic,
Alpine, and American plants may all be examples of species which once had a
wider range, and which, owing to the more favourable conditions, have
continued to exist in Ireland while becoming extinct in the adjacent parts
of Britain and Western Europe.
As contrasted with the extreme scarcity of peculiar species among the
flowering plants, it is the more interesting and unexpected to find a
considerable number of peculiar mosses and Hepaticæ, some of which present
us with phenomena of distribution of a very remarkable character. For the
following lists and the information as to the distribution of the genera
and species I am indebted to Mr. William Mitten, one of the first
authorities on these beautiful little plants. That of the mosses has been
corrected for this edition by Dr. R. Braithwaite, and several species of
hepaticæ have been added by Mr. Mitten. {366}
LIST OF THE SPECIES OF MOSSES AND HEPATICÆ WHICH ARE PECULIAR TO THE
BRITISH ISLES (OR NOT FOUND IN EUROPE).
(_Those belonging to non-European genera in Italics._)
MOSSES.
1. Systegium Mittenii South England.
2. Campylopus Shawii North Britain.
3. ,, setifolius Ireland, Wales, and Hebrides.
4. Seligeria calcicola South England.
5. Pottia viridifolia South England.
6. Leptodontium recurvifolium Ireland and Scotland.
7. Tortula Hybernica Ireland.
8. _Streptopogon gemmascens_ Sussex.
9. Bryum barbatum Scotland.
10. _Bartramidula Wilsoni_ Ireland, Wales, and Scotland.
11. _Daltonia splachnoides_ Ireland, Antilles, and Mexico.
12. _Hookeria laetevirens_ Ireland, Cornwall, and Madeira.
13. Hypnum micans Ireland.
14. Myurium Hebridarium Hebrides and Atlantic Islands.
15. Hedwigia ciliata _var._ striata Wales and Scotland.
HEPATICÆ.
1. Frullania germana Ireland.
2. ,, Hutchinsiæ Ireland, Scotland, Wales, Devon,
Tropical regions.
3. Lejeunia flava Ireland, Atlantic Islands, S. America,
Africa, &c.
4. ,, microscopica Ireland, Wales, Cumberland, Madeira.
5. ,, Holtii Ireland (Killarney).
6. ,, diversiloba Ireland (Killarney), Mexico?
7. ,, patens Ireland.
8. Radula tenax Ireland.
9. ,, Holtii Ireland.
10. ,, voluta Ireland, Wales, Cumberland, Mexico?
11. ,, Carringtonii Ireland.
12. Lepidozia Pearsoni Wales.
13. Adilocolia decipiens Ireland, Wales, Africa, and S. America.
14. Cephalozia aeraria Wales.
15. Lophocolia spicata Ireland, Cornwall, Anglesea.
16. Martinellia nimbosa Ireland (Brandon Mountain).
17. Plagiochila spinulosa Wales, Ireland, and Scotland, Atlantic
Islands.
18. ,, ambagiosa Ireland, India.
19. Jamesoniella Carringtonii Scotland.
20. Gymnocolea Nevicensis Scotland.
21. Jungermannia Doniana Scotland.
22. Cesia crenulata Ireland, Wales.
23. Chasmatocolea cuneifolia Ireland.
24. Aerobolbus Wilsoni Ireland, S. America, New Zealand.
25. Petalophyllum Ralfsii Ireland, Cornwall, Devon.
{367}
Many of the above are minute or obscure plants, and are closely allied to
other European species with which they may have been confounded. We cannot
therefore lay any stress on these individually as being absent from the
continent of Europe so much of which is imperfectly explored, though it is
probable that several of them are really confined to Britain. But there are
a few--indicated by italics--which are in a very different category; for
they belong to genera which are altogether unknown in any other part of
Europe, and their nearest allies are to be found in the tropics or in the
southern hemisphere. The four non-European genera of mosses to which we
refer all have their maximum of development in the Andes, while the three
non-European Hepaticæ appear to have their maximum in the temperate regions
of the southern hemisphere. Mr. Mitten has kindly furnished me with the
following particulars of the distribution of these genera:--
BARTRAMIDULA. Asia, Africa, S. America and Australia, but not Europe or
N. America.
STREPTOPOGON is a comparatively small genus, with seven species in the
Andes, one in the Himalayas, and three in the south temperate zone,
besides our English species.
DALTONIA is a large genus of inconspicuous mosses, having seventeen
species in the Andes, two in Brazil, two in Mexico, one in the
Galapagos, six in India and Ceylon, five in Java, two in Africa, and
three in the Antarctic Islands, and one in Ireland.
HOOKERIA (restricting that term to the species referable to
Cyclodictyon) is still a large genus of handsome and remarkable mosses,
having twenty-six species in the Andes, eleven in Brazil, eight in the
Antilles, one in Mexico, two in the Pacific Islands, one in New
Zealand, one in Java, one in India, and five in Africa--besides our
British species, which is found also in Madeira and the Azores but in
no part of Europe proper.
These last two are very remarkable cases of distribution, since Mr. Mitten
assures me that the plants are so markedly different from all other mosses
that they would scarcely be overlooked in Europe.
The distribution of the non-European genera of Hepaticæ is as follows:--
CHASMATOCOLIA. South America and Ireland.
ACROBOLBUS. A small genus found only in New Zealand and the adjacent
islands, besides Ireland.
{368} PETALOPHYLLUM. A small genus confined to Australia and New
Zealand in the southern hemisphere, Algeria, and Ireland in the
northern. We have also one of the Hepaticæ--_Mastigophora
Woodsii_--found in Ireland and the Himalayas, but unknown in any part
of continental Europe. The genus is most developed in New Zealand.
These are certainly very interesting facts, but they are by no means so
exceptional in this group of plants as to throw any doubt upon their
accuracy. The Atlantic islands present very similar phenomena in the
_Rhamphidium purpuratum_, whose nearest allies are in the West Indies and
South America; and in three species of Sciaromium, whose only allies are in
New Zealand, Tasmania, and the Andes of Bogota. An analogous and equally
curious fact is the occurrence in the Drontheim mountains in Central
Norway, of a little group of four or five peculiar species of mosses of the
genus Mnium, which are found nowhere else; although the genus extends over
Europe, India, and the southern hemisphere, but always represented by a
very few wide-ranging species except in this one mountain group![85]
Such facts show us the wonderful delicacy of the balance of conditions
which determine the existence of particular species in any locality. The
spores of mosses and Hepaticæ are so minute that they must be continually
carried through the air to great distances, and we can hardly doubt that,
so far as its powers of diffusion are concerned, any species which fruits
freely might soon spread itself over the whole world. That they do not do
so must depend on peculiarities of habit and constitution, which fit the
different species for restricted stations and special climatic conditions;
and according as the adaptation is more general, or the degree of
specialisation extreme, species will have wide or restricted ranges.
Although their fossil remains have been rarely detected, we can hardly
doubt that mosses have as high an antiquity as ferns or Lycopods; and
coupling this antiquity with their great powers of dispersal we may
understand how many of the genera have come to occupy a number of detached
areas scattered over the whole earth, but {369} always such as afford the
peculiar conditions of climate and soil best suited to them. The repeated
changes of temperature and other climatic conditions, which, as we have
seen, occurred through all the later geological epochs, combined with those
slower changes caused by geographical mutations, must have greatly affected
the distribution of such ubiquitous yet delicately organised plants as
mosses. Throughout countless ages they must have been in a constant state
of comparatively rapid migration, driven to and fro by every physical and
organic change, often subject to modification of structure or habit, but
always seizing upon every available spot in which they could even
temporarily maintain themselves.[86]
Here then we have a group in which there is no question of the means of
dispersal; and where the difficulties that present themselves are not how
the species reached the remote localities in which they are now found, but
rather why they have not established themselves in {370} many other
stations which, so far as we can judge, seem equally suitable to them. Yet
it is a curious fact, that the phenomena of distribution actually presented
by this group do not essentially differ from those presented by the higher
flowering plants which have apparently far less diffusive power, as we
shall find when we come to treat of the floras of oceanic islands; and we
believe that the explanation of this is, that the life of _species_, and
especially of _genera_, is often so prolonged as to extend over whole
cycles of such terrestrial mutations as we have just referred to; and that
thus the majority of plants are afforded means of dispersal which are
usually sufficient to carry them into all suitable localities on the globe.
Hence it follows that their actual existence in such localities depends
mainly upon vigour of constitution and adaptation to conditions just as it
does in the case of the lower and more rapidly diffused groups, and only
partially on superior facilities for diffusion. This important principle
will be used further on to afford a solution of some of the most difficult
problems in the distribution of plant life.[87]
_Concluding Remarks on the Peculiarities of the British Fauna and
Flora._--The facts, now I believe for the first time brought together,
respecting the peculiarities of the British fauna and flora, are sufficient
to show that there is considerable scope for the study of geographical
distribution even in so apparently unpromising a field as one of the most
recent of continental islands. Looking at the general bearing of these
facts, they prove, that the idea so generally entertained as to the
biological identity of the British Isles with the adjacent continent is not
altogether correct. Among birds we have undoubted peculiarities in at least
three instances; peculiar fishes are much more numerous, and in this case
the fact that the Irish species {371} are almost all different from the
British, and those of the Orkneys distinct from those of Scotland, renders
it almost certain that the great majority of the fifteen peculiar British
fishes are really peculiar and will never be found on the European
Continent. The mosses and Hepaticæ also have been sufficiently collected in
Europe to render it pretty certain that the more remarkable of the peculiar
British forms are not found there; why therefore, it may be well asked,
should there not be a proportionate number of peculiar British insects? It
is true that numerous species have been first discovered in Britain, and,
subsequently, on the continent; but we have many species which have been
known for twenty, thirty, or forty years, some of which are not rare with
us, and yet have never been found on the continent. We have also the
curious fact of our outlying islands, such as the Shetland Isles, the Isle
of Man, and the little Lundy Island, possessing each some peculiar forms
which, _certainly_, do not exist on our principal island which has been so
very thoroughly worked. Analogy, therefore, would lead us to conclude that
many other species or varieties would exist on our islands and not on the
continent; and when we find that a very large number (150) in three orders
only, are so recorded, we may I think be sure that some considerable
portion of these (though how many we cannot say) are really endemic British
species.
The general laws of distribution also lead us to expect such phenomena.
Very rare and very local species are such as are becoming extinct; and it
is among insects, which are so excessively varied and abundant, which
present so many isolated forms, and which, even on continents, afford
numerous examples of very rare species confined to restricted areas, that
we should have the best chance of meeting with every degree of rarity down
to the point of almost complete extinction. But we know that in all parts
of the world islands are the refuge of species or groups which have become
extinct elsewhere; and it is therefore in the highest degree probable that
some species which have ceased to exist on the continent should be
preserved in some part or other of our islands, especially {372} as these
present favourable climatic conditions such as do not exist elsewhere.
There is therefore a considerable amount of harmony in the various facts
adduced in this chapter, as well as a complete accordance with what the
laws of distribution in islands would lead us to expect. In proportion to
the species of birds and fresh-water fishes, the number of insect-forms is
enormously great, so that the numerous species or varieties here recorded
as not yet known on the continent are not to be wondered at; while it
would, I think, be almost an anomaly if, with peculiar birds and fishes
there were _not_ a fair proportion of peculiar insects. Our entomologists
should, therefore, give up the assumption, that all our insects do exist on
the continent, and will some time or other be found there, as not in
accordance either with the evidence or the probabilities of the case; and
when this is done, and the interesting peculiarities of some of our smaller
islands are remembered, the study of our native animals and plants, in
relation to those of other countries, will acquire a new interest. The
British Isles are said to consist of more than a thousand islands and
islets. How many of these have ever been searched for insects? With the
case of Lundy Island before us, who shall say that there is not yet scope
for extensive and interesting investigations into the British fauna and
flora?
* * * * *
{373}
CHAPTER XVII
BORNEO AND JAVA
Position and Physical Features of Borneo--Zoological Features of
Borneo: Mammalia--Birds--The Affinities of the Bornean Fauna--Java, its
Position and Physical Features--General Character of the Fauna of
Java--Differences Between the Fauna of Java and that of the other Malay
Islands--Special Relations of the Javan Fauna to that of the Asiatic
Continent--Past Geographical Changes of Java and Borneo--The Philippine
Islands--Concluding Remarks on the Malay Islands.
As a representative of recent continental islands situated in the tropics,
we will take Borneo, since, although perhaps not much more ancient than
Great Britain, it presents a considerable amount of speciality; and, in its
relations to the surrounding islands and the Asiatic continent, offers us
some problems of great interest and considerable difficulty.
The accompanying map shows that Borneo is situated on the eastern side of a
submarine bank of enormous extent, being about 1,200 miles from north to
south, and 1,500 from east to west, and embracing Java, Sumatra, and the
Malay Peninsula. This vast area is all included within the 100 fathom line,
but by far the larger part of it--from the Gulf of Siam to the Java Sea--is
under fifty fathoms, or about the same depth as the sea that separates our
own island from the continent. The distance from Borneo to the southern
extremity of the Malay Peninsula is about 350 miles, and it is nearly as
far from Sumatra and Java, while it is more than 600 miles from the Siamese
Peninsula, opposite to which its long northern coast extends. There is, I
believe, nowhere else upon the globe, an island so far from a continent,
yet separated from it by so shallow a sea. Recent changes of sea and land
must have occurred here on a grand scale, and this adds to the interest
attaching to the study of this large island.
{374}
[Illustration: MAP OF BORNEO AND JAVA, SHOWING THE GREAT SUBMARINE BANK OF
SOUTH-EASTERN ASIA.]
The light tint shows a less depth than 100 fathoms.
The figures show the depth of the sea in fathoms.
{375} The internal geography of Borneo is somewhat peculiar. A large
portion of its surface is lowland, consisting of great alluvial valleys
which penetrate far into the interior; while the mountains except in the
north, are of no great elevation, and there are no extensive plateaux. A
subsidence of 500 feet would allow the sea to fill the great valleys of the
Pontianak, Banjarmassing, and Coti rivers, almost to the centre of the
island, greatly reducing its extent, and causing it to resemble in form the
island of Celebes to the east of it.
In geological structure Borneo is thoroughly continental, possessing
formations of all ages, with basalt and crystalline rocks, but no recent
volcanoes. It possesses vast beds of coal of Tertiary age; and these, no
less than the great extent of alluvial deposits in its valleys, indicate
great changes of level in recent geological times.
Having thus briefly indicated those physical features of Borneo which are
necessary for our inquiry, let us turn to the organic world.
Neither as regards this great island nor those which surround it, have we
the amount of detailed information in a convenient form that is required
for a full elucidation of its past history. We have, however, a tolerable
acquaintance with the two higher groups--mammalia and birds, both of Borneo
and of all the surrounding countries, and to these alone will it be
necessary to refer in any detail. The most convenient course, and that
which will make the subject easiest for the reader, will be to give, first,
a connected sketch of what is known of the zoology of Borneo itself, with
the main conclusions to which they point; and then to discuss the mutual
relations of some of {376} the adjacent islands, and the series of
geographical changes that seem required to explain them.
ZOOLOGICAL FEATURES OF BORNEO.
_Mammalia._--Nearly a hundred and forty species of mammalia have been
discovered in Borneo, and of these more than three-fourths are identical
with those of the surrounding countries, and more than one half with those
of the continent. Among these are two lemurs, nine civets, five cats, five
deer, the tapir, the elephant, the rhinoceros, and many squirrels, an
assemblage which could certainly only have reached the country by land. The
following species of mammalia are supposed to be peculiar to Borneo:--
QUADRUMANA.
1. Simia morio. A small orangutan
with large incisor teeth.
2. Hylobates mulleri.
3. Nasalis larvatus.
4. Semnopithecus rubicundus.
5. " chrysomelas.
6. " frontatus.
7. " hosei. (Thomas.) Kini Balu.
CARNIVORA.
8. Herpestes semitorquatus.
9. Felis badia.
UNGULATA.
10. Sus barbatus.
RODENTIA.
11. Pteromys phæomelas.
12. Sciurus jentinki. (Th.) Kini Balu.
13. Sciurus whiteheadi. (Th.) Kini Balu.
14. " everetti.
15. Rheithrosciurus macrotis.
16. Hystrix crassispinis.
17. Trichys guentheri.
18. Mus infraluteus. (Th.) Kini Balu.
19. " alticola. (Th.) Kini Balu.
INSECTIVORA.
20. Tupaia splendidula.
21. " minor.
22. " dorsalis.
23. Dendrogale murina.
CHIROPTERA.
24. Vesperugo stenopterus.
25. " doriæ
26. Cynopterus brachyotus.
27. " lucasii.
28. " spadiceus.
29. Hipposideros doriæ.
Of the twenty-nine peculiar species here enumerated it is possible that a
few may be found to be identical with those of Malacca or Sumatra; but
there are also four peculiar genera which are less likely to be discovered
elsewhere. These are Nasalis, the remarkable long-nosed monkey;
Rheithrosciurus, a peculiar form of squirrel; and Trichys, a tailless
porcupine. These peculiar forms do not, however, imply that the separation
of the island from the continent is of very ancient date, for the country
is so vast and {377} so much of the once connecting land is covered with
water, that the amount of speciality is hardly, if at all, greater than
occurs in many continental areas of equal extent and remoteness. This will
be more evident if we consider that Borneo is as large as the Indo-Chinese
Peninsula, or as the Indian Peninsula south of Bombay, and if either of
these countries were separated from the continent by the submergence of the
whole area north of them as far as the Himalayas, they would be found to
contain quite as many peculiar genera and species as Borneo actually does
now. A more decisive test of the lapse of time since the separation took
place is to be found in the presence of a number of representative species
closely allied to those of the surrounding countries, such as the tailed
monkeys and the numerous squirrels. These relationships, however, are best
seen among the birds, which have been more thoroughly collected and more
carefully studied than the mammalia.
_Birds._--About 580 species of birds are now known to inhabit Borneo, of
which 420 species are land-birds.[88] One hundred and eight species are
supposed to be peculiar to the island, and of these one half have been
noted, either by Count Salvadori or Mr. Everett, as being either
representative species of, or closely allied to birds inhabiting other
islands or countries. The majority of these are, as might be expected,
allied to species inhabiting the surrounding countries, especially Sumatra,
the Malay Peninsula, or Java, a smaller number having their representative
forms in the Philippine Islands or Celebes. But there is another group of
eight species whose nearest allies are found in such remote lands as
Ceylon, North India, Burma, or China. These last have been indicated in the
following list by a double star (**) while those which are representative
of forms found in the immediately surrounding area, and are in many cases
very slightly differentiated from their allies, are indicated by a single
star (*). {378}
LIST OF BIRDS WHICH ARE SUPPOSED TO BE PECULIAR TO BORNEO.
TURDIDÆ (Thrushes).
1. **Cettia oreophila.
2. *Merula seebohmi.
3. **Geocichla aurata.
4. **Myiophoneus borneensis.
5. Brachypteryx erythrogyna.
6. Copsychus niger.
7. *Cittocincla suavis.
8. * ,, stricklandi.
9. *Henicurus borneensis.
10. *Phyllergates cinereicollis.
11. Burnesia superciliaris.
TIMELIIDÆ (Babbling Thrushes).
12. *Garrulax schistochlamys.
13. Rhinocichla treacheri.
14. Allocotops calvus.
15. **Stachyris borneensis.
16. Cyanoderma bicolor.
17. Chlorocharis æmiliæ.
18. Androphilus accentor.
19. Malacopterum cinereocapillum.
20. **Staphidia everetti.
21. *Herporius brunnescens.
22. *Mixornis borneensis.
23. * ,, montana.
24. *Turdinus canicapillus.
25. ,, atrigularis.
26. *Drymocataphus capistratoides.
27. Ptilophaga rufiventris.
28. ,, leucogrammica.
29. *Corythocichla crassa.
30. *Turdinulus exsul.
31. Orinthocichla whiteheadi.
BRACHYPODIDÆ (Bulbuls).
32. *Hemixus connectens.
33. Criniger diardi.
34. * ,, ruficrissus.
35. Tricophoropsis typus.
36. Oreostictes leucops.
37. Rubigula montis.
38. * ,, paroticalis.
39. Chloropsis kinabaluensis.
40. * ,, irridinucha.
ORIOLIDÆ (Orioles).
41. Oriolus consobrinus.
42. *Oriolus vulneratus.
PARIDÆ (Tits).
43. Parus sarawakensis.
44. *Dendrophila corallipes.
LANIIDÆ (Shrikes).
45. Pityriasis gymnocephala.
46. *Hyloterpe hypoxantha.
DICRURIDÆ (Drongo-shrikes).
47. *Chibia borneensis.
CAMPOPHAGIDÆ (Caterpillar-catchers).
48. Chlamodychæra jeffreyi.
49. *Artamides normani.
50. Pericrocotus cinereigula.
MUSCICAPIDÆ (Flycatchers).
51. **Hemichelidon cinereiceps.
52. *Rhinomyias gularis.
53. * ,, ruficrissa.
54. Cryptolopha schwaneri.
55. ,, montis.
56. *Stoparola cerviniventris.
57. Siphia coeruleata.
58. ,, beccariana.
59. ,, clopurensis.
60. ,, obscura.
61. ,, everetti.
62. ,, nigrogularis.
NECTARINEIDÆ (Sun-birds).
63. Arachnothera juliæ.
{379}
DICÆIDÆ (Flower-peckers).
64. *Diceum monticolum.
65. * ,, pryeri.
66. *Prionochilus xanthopygius.
67. **Prionochilus everetti.
68. *Zosterops clara.
PLOCEIDÆ (Weavers).
69. Chlorura borneensis.
70. Munia fuscans.
CORVIDÆ (Crows).
71. *Dendrocitta cinerascens.
72. Cissa jeffreyi.
73. *Platysmurus aterrimus.
PITTIDÆ (Ground Thrushes).
74. Pitta bertæ.
75. ,, arcuata.
76. ,, baudi.
77. *Pitta usheri.
78. * ,, granatina.
79. * ,, schwaneri.
EURYLÆMIDÆ (Gapers).
80. Calyptomena whiteheadi.
CYPSELIDÆ (Swifts).
81. Cypselus lowi.
PODARGIDÆ (Frogmouths).
82. *Batrachostomus adspersus.
CAPRIMULGIDAE (Goatsuckers).
83. Caprimulgus borneensis.
84. Caprimulgus concretus.
PICIDÆ (Woodpeckers).
85. *Jyngipicus aurantiiventris.
86. ,, picatus.
87. *Micropternus badiosus.
88. Sasia everetti.
ALCEDINIDÆ (Kingfishers).
89. *Pelargopsis leucocephala.
90. *Carcineutes melanops.
TROGONIDÆ (Trogons).
91. Harpactes whiteheadi.
CUCULIDÆ (Cuckoos).
92. *Rhopodytes borneensis.
CAPITONIDÆ (Barbets).
93. Cyanops pulcherrimus.
94. ,, monticulus.
95. *Megalæma chrysopsis.
BUBONIDÆ (Owls).
96. Heteroscops luciæ.
97. *Syrnium leptogrammicum.
FALCONIDÆ (Hawks, &c.).
98. Spilornis pallidus.
99. *Accipiter nigrotibialis.
100. Microhierax latifrons.
PHASIANIDÆ (Pheasants).
101. Polyplectron schliermacheri.
102. Lobiophasis bulweri.
103. *Argusianus grayi.
104. *Euplocamus pyrronotus.
{380}
TETRAONIDÆ (Grouse, &c.).
105. Bambusicola hyperythra.
106. ,, erythrophrys.
107. Hæmatortyx sanguiniceps.
RALLIDÆ (Rails).
108. Rallina rufigenys.
Representative forms of the same character as those noted above are found
in all extensive continental areas, but they are rarely so numerous. Thus,
in Mr. Elwes' paper on the "Distribution of Asiatic Birds," he states that
12.5 per cent. of the land birds of Burmah and Tenasserim are peculiar
species, whereas we find that in Borneo they are about 25 per cent., and
the difference may fairly be imputed to the greater proportion of slightly
modified representative species due to a period of complete isolation. Of
peculiar genera, the Indo-Chinese Peninsula has one--Ampeliceps, a
remarkable yellow-crowned starling, with bare pink-coloured orbits; while
two others, Temnurus and Crypsirhina--singular birds allied to the
jays--are found in no other part of the Asiatic continent though they occur
in some of the Malay Islands. Borneo has seven peculiar genera of
passeres,[89] as well as Hæmatortyx, a crested partridge; and Lobiophasis,
a pheasant hardly distinct from Euplocamus; while two others, Pityriasis,
an extraordinary bare-headed bird between a jay and a shrike, and
Carpococcyx, a pheasant-like ground cuckoo formerly thought to be peculiar,
are said to have been discovered also in Sumatra.
The insects and land-shells of Borneo and of the surrounding countries are
too imperfectly known to enable us to arrive at any accurate results with
regard to their distribution. They agree, however, with the birds and
mammals in their general approximation to Malayan forms, but the number of
peculiar species is perhaps larger.
The proportion here shown of less than one-fourth peculiar species of
mammalia and fully one-fourth peculiar species of land-birds, teaches us
that the possession of the power of flight affects but little the
distribution of {381} land-animals, and gives us confidence in the results
we may arrive at in those cases where we have, from whatever cause, to
depend on a knowledge of the birds alone. And if we consider the wide range
of certain groups of powerful flight--as the birds of prey, the swallows
and swifts, the king-crows, and some others, we shall be forced to conclude
that the majority of forest-birds are restricted by even narrow watery
barriers, to an even greater extent than mammalia.
_The Affinities of the Bornean Fauna._--The animals of Borneo exhibit an
almost perfect identity in general character, and a close similarity in
species, with those of Sumatra and the Malay Peninsula. So great is this
resemblance that it is a question whether it might not be quite as great
were the whole united; for the extreme points of Borneo and Sumatra are
1,500 miles apart--as far as from Madrid to Constantinople, or from the
Missouri valley to California. In such an extent of country we always meet
with some local species, and representative forms, so that we hardly
require any great lapse of time as an element in the production of the
peculiarities we actually find. So far as the forms of life are concerned,
Borneo, as an island, may be no older than Great Britain; for the time that
has elapsed since the glacial epoch would be amply sufficient to produce
such a redistribution of the species, consequent on their mutual relations
being disturbed, as would bring the islands into their present zoological
condition. There are, however, other facts to be considered, which seem to
imply much greater and more complex revolutions than the recent separation
of Borneo from Sumatra and the Malay Peninsula, and that these changes must
have been spread over a considerable lapse of time. In order to understand
what these changes probably were, we must give a brief sketch of the fauna
of Java, the peculiarities of which introduce a new element into the
question we have to discuss. {382}
JAVA.
The rich and beautiful island of Java, interesting alike to the politician,
the geographer, and the naturalist, is more especially attractive to the
student of geographical distribution, because it furnishes him with some of
the most curious anomalies and difficult problems in a place where such
would be least expected. As Java forms with Sumatra one almost unbroken
line of volcanoes and volcanic mountains, interrupted only by the narrow
Straits of Sunda, we should naturally expect a close resemblance between
the productions of the two islands. But in point of fact there is a much
greater difference between them than between Sumatra and Borneo, so much
further apart, and so very unlike in physical features.[90] Java differs
from the three great land masses--Borneo, Sumatra, and the Malay Peninsula,
far more than either of these do from each other; and this is the first
anomaly we encounter. But a more serious difficulty than this remains to be
stated. Java has certain close resemblances to the Siamese Peninsula, and
also to the Himalayas, which Borneo and Sumatra do not exhibit to so great
a proportionate extent; and looking at the relative position of these lands
respectively, this seems most incomprehensible. In order fully to
appreciate the singularity and difficulty of the problem, it will be
necessary to point out the exact nature and amount of these peculiarities
in the fauna of Java.
_General Character of the Fauna of Java._--If we were only to take account
of the number of peculiar species in Java, and the relations of its fauna
generally to that of the surrounding lands, we might pass it over as a less
interesting island than Borneo or Sumatra. Its mammalia (ninety species)
are nearly as numerous as those of Borneo, but are apparently less
peculiar, none of the genera and only five or six of the species being
confined to the island. In land-birds it is decidedly less rich, having
only 300 species, of which about forty-five are peculiar, and only one
{383} or two belong to peculiar genera; so that here again the amount of
speciality is considerably less than in Borneo. It is only when we proceed
to analyse the species of the Javan fauna, and trace their distribution and
affinities, that we discover its interesting nature.
_Difference Between the Fauna of Java and that of the other great Malay
Islands._--Comparing the fauna of Java with that which may be called the
typical Malayan fauna as exhibited in Borneo, Sumatra, and the Malay
Peninsula, we find the following differences. No less than thirteen genera
of mammalia, each of which is known to inhabit at least two, and generally
all three, of the above-named Malayan countries, are totally absent from
Java; and they include such important forms as the elephant, the tapir, and
the Malay bear. It cannot be said that this difference depends on imperfect
knowledge, for Java is one of the oldest European settlements in the East,
and has been explored by a long succession of Dutch and English
naturalists. Every part of it is thoroughly well known, and it would be
almost as difficult to find a new mammal of any size in Europe as in Java.
Of birds there are twenty-five genera, all typically Malayan and occurring
at least in two, and for the most part in all three of the Malay countries,
which are yet absent from Java. Most of these are large and conspicuous
forms, such as jays, gapers, bee-eaters, woodpeckers, hornbills, cuckoos,
parrots, pheasants, and partridges, as impossible to have remained
undiscovered in Java as the large mammalia above referred to.
Besides these absent _genera_ there are some curious illustrations of Javan
isolation in the _species_; there being several cases in which the same
species occurs in all three of the typical Malay countries, while in Java
it is represented by an allied species. These occur chiefly among birds,
there being no less than seven species which are common to the three great
Malay countries but are represented in Java by distinct though closely
allied species.
From these facts it is impossible to doubt that Java has had a history of
its own, quite distinct from that of the other portions of the Malayan
area. {384}
_Special Relations of the Javan Fauna to that of the Asiatic
Continent._--These relations are indicated by comparatively few examples,
but they are very clear and of great importance. Among mammalia, the genus
Helictis is found in Java but in no other Malay country, though it inhabits
also North India; while two species, _Rhinoceros javanicus_ and _Lepus
kurgosa_, are natives of Indo-Chinese countries and Java, but not of
typical Malaya. In birds there are five genera or sub-genera--Zoothera,
Notodela, Crypsirhina, Allotrius, and Cochoa, which inhabit Java, the
Himalayas, and Indo-China, all but the last extending south to Tenasserim,
but none of them occurring in Malacca, Sumatra, or Borneo. There are also
two species of birds--a trogon (_Harpactes oreskios_), and the Javanese
peacock (_Pavo muticus_), which inhabit only Java and the Indo-Chinese
countries, the former reaching Tenasserim and the latter Perak in the Malay
Peninsula.
Here, then, we find a series of remarkable similarities between Java and
the Asiatic continent, quite independent of the typical Malay
countries--Borneo, Sumatra, and the Malay Peninsula, which latter have
evidently formed one connected land, and thus appear to preclude any
independent union of Java and Siam.
The great difficulty in explaining these facts is, that all the required
changes of sea and land must have occurred within the period of existing
species of mammalia. Sumatra, Borneo, and Malacca have, as we have seen, a
great similarity as regards their species of mammals and birds, while Java,
though it differs from them in so curious a manner, has no greater degree
of speciality, since its species, when not Malayan, are almost all North
Indian or Siamese.
There is, however, one consideration which may help us over this
difficulty. It seems highly probable that in the equatorial regions species
have changed less rapidly than in the north temperate zone, on account of
the equality and stability of the equatorial climate. We have seen, in
Chapter X., how important an agent in producing extinction and modification
of species must have been the repeated changes from cold to warm, and from
warm to cold {385} conditions, with the migrations and crowding together
that must have been their necessary consequence. But in the lowlands, near
the equator, these changes would be very little if at all felt, and thus
one great cause of specific modification would be wanting. Let us now see
whether we can sketch out a series of not improbable changes which may have
brought about the existing relations of Java and Borneo to the continent.
_Past Geographical Changes of Java and Borneo._--Although Java and Sumatra
are mainly volcanic, they are by no means wholly so. Sumatra possesses in
its great mountain masses ancient crystalline rocks with much granite,
while there are extensive Tertiary deposits of Eocene age, overlying which
are numerous beds of coal now raised up many thousand feet above the
sea.[91] The volcanoes appear to have burst through these older mountains,
and to have partly covered them as well as great areas of the lowlands with
the products of their eruptions. In Java either the fundamental strata were
less extensive and less raised above the sea, or the period of volcanic
action has been of longer duration; for here no crystalline rocks have been
found except a few boulders of granite in the western part of the island,
perhaps the relics of a formation destroyed by denudation or covered up by
volcanic deposits. In the southern part of Java, however, there is an
extensive range of low mountains, about 3,000 feet high, consisting of
basalt with limestone, apparently of Miocene age.
During this last named period, then, Java would have been at least 3,000
feet lower than it is now, and such a depression would probably extend to
considerable parts of Sumatra and Borneo, so as to reduce them all to a few
small islands. At some later period a gradual elevation occurred, which
ultimately united the whole of the islands with the continent. This may
have continued till the glacial period of the northern hemisphere, during
the severest part of which a few Himalayan species of birds and mammals may
have been driven southward, and {386} have ranged over suitable portions of
the whole area. Java then became separated by subsidence, and these species
were imprisoned in the island; while those in the remaining part of the
Malayan area again migrated northward when the cold had passed away from
their former home, the equatorial forests of Borneo, Sumatra, and the Malay
Peninsula being more especially adapted to the typical Malayan fauna which
is there developed in rich profusion. A little later the subsidence may
have extended farther north, isolating Borneo and Sumatra, in which a few
other Indian or Indo-Chinese forms have been retained, but probably leaving
the Malay Peninsula as a ridge between them as far as the islands of Banca
and Biliton. Other slight changes of climate followed, when a further
subsidence separated these last-named islands from the Malay Peninsula, and
left them with two or three species which have since become slightly
modified. We may thus explain how it is that a species is sometimes common
to Sumatra and Borneo, while the intervening island (Banca) possesses a
distinct form.[92]
In my _Geographical Distribution of Animals_, Vol. I., p. 357, I have given
a somewhat different hypothetical explanation of the relations of Java and
Borneo to the continent, in which I took account of changes of land and sea
only; but a fuller consideration of the influence of changes of climate on
the migration of animals, has led me to the much simpler, and, I think,
more probable, explanation above given. The amount of the relationship
between Java and Siam, as well as of that between Java and the Himalayas,
is too small to be well accounted for by an independent geographical
connection in which Borneo and Sumatra did not take part. It is, at the
same time, too distinct and indisputable to be ignored; and a change of
climate which should drive a portion of the Himalayan fauna southward,
leaving a few species in Java and Borneo from which they could not return
owing to the subsequent isolation of those islands by subsidence, seems
{387} to be a cause exactly adapted to produce the kind and amount of
affinity between these distant countries that actually exists.
THE PHILIPPINE ISLANDS.
A general account of the fauna of these islands, and of their biological
relations to the countries which form the subject of this chapter, has been
given in my _Geographical Distribution of Animals_, Vol. I. pp. 345-349;
but since the publication of that work considerable additions have been
made to their fauna, having the effect of somewhat diminishing their
isolation from the other islands. Four genera have been added to the
terrestrial mammalia--Crocidura, Felis, Pteromys, and Mus, as well as two
additional squirrels; while the black ape (_Cynopithecus niger_) has been
struck out as not inhabiting the Philippines. This brings the true land
mammalia to twenty-one species, of which fourteen are peculiar to the
islands; but to these we must add no less than thirty-three species of bats
of which only ten are peculiar.[93] In these estimates the Palawan {388}
group has been omitted as these islands contain so many Bornean species
that if included they obscure the special features of the fauna.
_Birds._--The late Marquis of Tweeddale made a special study of Philippine
birds, and in 1873 published a catalogue in the _Transactions of the
Zoological Society_ (Vol. IX. Pt. 2, pp. 125-247). But since that date
large collections have been made by Everett, Steere, and other travellers,
the result of which has been to more than double the known species, and to
render the ornithological fauna an exceedingly rich one. Many of the
Malayan genera which were thought to be absent when the first edition of
this work was published have since been discovered, among which are
Phyllornis, Criniger, Diceum, Prionochilus, and Batrachostomus. But there
still remain a large number of highly characteristic Malayan genera whose
absence gives a distinctive feature to the Philippine bird fauna. Among
these are Tiga and Meiglyptes, genera of woodpeckers; Phænicophaes and
Centropus, remarkable cuckoos; the long-tailed paroquets, Palæornis; all
the genera of Barbets except Xantholæma; the small but beautiful family
Eurylæmidæ; many genera allied to Timalia and Ixos; the mynahs, Gracula;
the long-tailed flycatchers, Tchitrea; the fire-backed pheasants,
Euplocamus; the argus pheasants, the jungle-fowl, and many others.
The following tabular statement will illustrate the rapid growth of our
knowledge of the birds of the Philippines:--
|Land-birds.|Water-birds.|Total.
+-----------+------------+------
Lord Tweeddale's Catalogue (1873) | 158 | 60 | 218
Mr. Wardlaw Ramsay's List (1881) | 265 | 75 | 340
Mr. Everett's MSS. List of Additions (1891)| 370 | 102 | 472
The number of peculiar species is very large, there being about 300 land
and forty-two water birds, which are not {389} known to occur beyond the
group. We have here, still more pronounced than in the case of Borneo, the
remarkable fact of the true land birds presenting a larger amount of
speciality than the land mammals; for while more than four-fifths of the
birds are peculiar, only a little more than half the mammals are so, and if
we exclude the bats only two-thirds.
The general character of the fauna of this group of islands is evidently
the result of their physical conditions and geological history. The
Philippines are almost surrounded by deep sea, but are connected with
Borneo by means of two narrow submarine banks, on the northern of which is
situated Palawan, and on the southern the Sulu Islands. Two small groups of
islands, the Bashees and Babuyanes, have also afforded a partial connection
with the continent by way of Formosa. It is evident that the Philippines
once formed part of the great Malayan extension of Asia, but that they were
separated considerably earlier than Java; and having been since greatly
isolated and much broken up by volcanic disturbances, their species have
for the most part become modified into distinct local forms, representative
species often occurring in the different islands of the group. They have
also received a few Chinese types by the route already indicated, and a few
Australian forms owing to their proximity to the Moluccas. Their
comparative poverty in genera and species of the mammalia is perhaps due to
the fact that they have been subjected to a great amount of submersion in
recent times, greatly reducing their area and causing the extinction of a
considerable portion of their fauna. This is not a mere hypothesis, but is
supported by direct evidence; for I am informed by Mr. Everett, who has
made extensive explorations in the islands, that almost everywhere are
found large tracts of elevated coral-reefs, containing shells similar to
those living in the adjacent seas, an indisputable proof of recent
elevation.
_Concluding Remarks on the Malay Islands._--This completes our sketch of
the great Malay islands, the seat of the typical Malayan fauna. It has been
shown that the peculiarities presented by the individual islands may be all
{390} sufficiently well explained by a very simple and comparatively
unimportant series of geographical changes, combined with a limited amount
of change of climate towards the northern tropic. Beginning in late Miocene
times when the deposits on the south coast of Java were upraised, we
suppose a general elevation of the whole of the extremely shallow seas
uniting what are now Sumatra, Java, Borneo, and the Philippines with the
Asiatic continent, and forming that extended equatorial area in which the
typical Malayan fauna was developed. After a long period of stability,
giving ample time for the specialisation of so many peculiar types, the
Philippines were first separated; then at a considerably later period Java;
a little later Sumatra and Borneo; and finally the islands south of
Singapore to Banca and Biliton. This one simple series of elevations and
subsidences, combined with the changes of climate already referred to, and
such local elevations and depressions as must undoubtedly have occurred,
appears sufficient to have brought about the curious, and at first sight
puzzling, relations, of the faunas of Java and the Philippines, as compared
with those of the larger islands.
We will now pass on to the consideration of two other groups which offer
features of special interest, and which will complete our illustrative
survey of recent continental islands.
* * * * *
{391}
CHAPTER XVIII
JAPAN AND FORMOSA
Japan, its Position and Physical Features--Zoological Features of
Japan--Mammalia--Birds--Birds Common to Great Britain and Japan--Birds
Peculiar to Japan--Japan Birds Recurring in Distant
Areas--Formosa--Physical Features of Formosa--Animal Life of
Formosa--Mammalia--Land-birds Peculiar to Formosa--Formosan Birds
Recurring in India or Malaya--Comparison of Faunas of Hainan, Formosa,
and Japan--General Remarks on Recent Continental Islands.
JAPAN.
The Japanese Islands occupy a very similar position on the eastern shore of
the great Euro-Asiatic continent to that of the British Islands on the
western, except that they are about sixteen degrees further south, and
having a greater extension in latitude enjoy a more varied as well as a
more temperate climate. Their outline is also much more irregular and their
mountains loftier, the volcanic peak of Fusiyama being 14,177 feet high;
while their geological structure is very complex, their soil extremely
fertile, and their vegetation in the highest degree varied and beautiful.
Like our own islands, too, they are connected with the continent by a
marine bank less than a hundred fathoms below the surface--at all events
towards the north and south; but in the intervening space the Sea of Japan
opens out to a width of six hundred miles, and in its central portion is
very deep, and this may be an indication that the connection between the
islands and the continent is of rather ancient date. At the Straits of
Corea the distance from the main land is about 120 miles, while at the
northern extremity of Yesso it is about 200. The island of Saghalien,
however, separated from Yesso by a strait only twenty-five miles wide,
forms a connection with Amoorland in about 52° N. Lat. A southern warm
current flowing a little to the eastward of the islands, ameliorates their
climate much in the same way as the Gulf Stream does ours, and added to
their insular position enables them to support a more tropical vegetation
and more varied forms of life than are found at corresponding latitudes in
China.
{392}
[Illustration: MAP OF JAPAN AND FORMOSA (with depths in fathoms).
Light tint, sea under 100 fathoms. Medium tint, under 1,000 fathoms. Dark
tint, over 1,000 fathoms. The figures show the depth in fathoms.]
{393}
_Zoological Features of Japan._--As we might expect from the conditions
here sketched out, Japan exhibits in all its forms of animal life a close
general resemblance to the adjacent continent, but with a considerable
element of specific individuality; while it also possesses some remarkable
isolated groups. Its fauna presents indications of there having been two or
more lines of migration at different epochs. The majority of its animals
are related to those of the temperate or cold regions of the continent,
either as identical or allied species; but a smaller number have a tropical
character, and these have in several instances no allies in China but occur
again only in Northern India or the Malay Archipelago. There is also a
slight American element in the fauna of Japan, a relic probably of the
period when a land communication existed between the two continents over
what are now the shallow seas of Japan, Ochotsk, and Kamschatka. We will
now proceed to examine the peculiarities and relations of the fauna.
_Mammalia._--The mammalia of Japan at present known are forty in number;
not very many when compared with the rich fauna of China and Manchuria, but
containing monkeys, bears, deer, wild goats and wild boars, as well as
foxes, badgers, moles, squirrels, and hares, so that there can be no doubt
whatever that they imply a land connection with the continent. No complete
account of Japan mammals has been given by any competent zoologist since
the publication of Von Siebold's _Fauna Japonica_ in 1844, {394} but by
collecting together most of the scattered observations since that period
the following list has been drawn up, and will, it is hoped, be of use to
naturalists. The species believed to be peculiar to Japan are printed in
italics. These are very numerous, but it must be remembered that Corea and
Manchuria (the portions of the continent opposite Japan) are comparatively
little known, while in very few cases have the species of Japan and of the
continent been critically compared. Where this has been done, however, the
peculiar species established by the older naturalists have been in many
cases found to be correct.
LIST OF THE MAMMALIA OF THE JAPANESE ISLANDS.
1. _Macacus speciosus._ A monkey with rudimentary tail and red face,
allied to the Barbary ape. It inhabits the island of Niphon up to 41°
N. Lat., and has thus the most northern range of any living monkey.
2. _Pteropus dasymallus._ A peculiar fruit-bat, found in Kiusiu Island
only (Lat. 33° N.), and thus ranging further north of the equator than
any other species of the genus.
3. Rhinolophus ferrum-equinum. The great horse-shoe bat, ranges from
Britain across Europe and temperate Asia to Japan. It is the _R.
nippon_ of the Fauna Japonica according to Mr. Dobson's _Monograph of
Asiatic Bats_.
4. R. minor. Found also in Burma, Yunan, Java, Borneo, &c.
5. Vesperugo pipistrellus. From Britain across Europe and Asia.
6. V. abramus. Also in India and China.
7. V. noctula. From Britain across Europe and Asia.
8. V. molossus. Also in China.
9. Vespertilio capaccinii. Philippine Islands, and Italy! This is _V.
macrodactylus_ of the Fauna Japonica according to Mr. Dobson.
10. Miniopterus schreibersii. Philippines, Burma, Malay Islands. This
is _Vespertilio blepotis_ of the Fauna Japonica.
11. _Talpa wogura._ Closely resembles the common mole of Europe, but
has six incisors instead of eight in the lower jaw.
12. _Talpa mizura._ Günth. Allied to _T. wogura_.
13. _Urotrichus talpoides._ A peculiar genus of moles confined to
Japan. An American species has been named _Urotrichus gibsii_, and Mr.
Lord after comparing the two says that he "can find no difference
whatever, either generic or specific. In shape, size, and colour, they
are exactly alike." But Dr. Günther (_P. Z. S._ 1880, p. 441) states
that _U. gibsii_ differs so much in dentition from the Japanese species
that it should be placed in a distinct genus, which he calls
Neurotrichus.
14. Sorex myosurus. A shrew, found also in India and Malaya.
15. _Sorex dzi-nezumi._
16. _S. umbrinus._
17. _S. platycephalus._ {395}
18. Ursus arctos. var. A peculiar variety of the European brown bear
which inhabits also Amoorland and Kamschatka. It is the _Ursus ferox_
of the Fauna Japonica.
19. _Ursus japonicus._ A peculiar species allied to the Himalayan and
Formosan species. Named _U. tibetanus_ in the Fauna Japonica.
20. _Meles anakuma._ Differs from the European and Siberian badgers in
the form of the skull.
21. _Mustela brachyura._ A peculiar martin found also in the Kurile
Islands.
22. _Mustela melanopus._ The Japanese sable.
23. _M. Japonica._ A peculiar martin (See _Proc. Zool. Soc._ 1865, p.
104).
24. _M. Sibericus._ Also Siberia and China. This is the _M. italsi_ of
the Fauna Japonica according to Dr. Gray.
25. _Lutronectes whiteleyi._ A new genus and species of otter
(_P. Z. S._ 1867, p. 180). In the Fauna Japonica named _Lutra
vulgaris_.
26. Enhydris marina. The sea-otter of California and Kamschatka.
27. _Canis hodophylax._ According to Dr. Gray allied to _Cuon
sumatranus_ of the Malay Islands, and _C. alpinus_ of Siberia, if not
identical with one of them (_P. Z. S._ 1868, p. 500).
28. _Vulpes japonica._ A peculiar fox. _Canis vulpes_ of Fauna
Japonica.
29. Nyctereutes procyonoides. The racoon-dog of N. China and Amoorland.
30. _Lepus brachyurus._ A peculiar hare.
31. _Sciurus lis._ A peculiar squirrel.
32. _Pteromys leucogenys._ The white-cheeked flying squirrel.
33. _P. momoga._ Perhaps identical with a Cambojan species (_P. Z. S._
1861, p. 137).
34. _Myoxus japonicus._ A peculiar dormouse. _M. elegans_ of the Fauna
Japonica; _M. javanicus_, Schinz (_Synopsis Mammalium_, ii. p. 530).
35. _Mus argenteus._ China.
36. _Mus molossinus._
37. _M. nezumi._
38. _M. speciosus._
39. _Cervus sika._ A peculiar deer allied to _C. pseudaxis_ of Formosa
and _C. mantchuricus_ of Northern China.
40. _Nemorhedus crispa._ A goat-like antelope allied to _N. sumatranus_
of Sumatra, and _N. Swinhoei_ of Formosa.
41. _Sus leucomystax._ A wild boar allied to _S. taeranus_ of Formosa.
We thus find that no less than twenty-six out of the forty-one Japanese
mammals are peculiar, and if we omit the aërial bats (nine in number), as
well as the marine sea-otter, we shall have remaining only thirty strictly
land mammalia, of which twenty-five are peculiar, or five-sixths of the
whole. Nor does this represent all their speciality; for we have a mole
differing in its dentition from the European mole; another superficially
resembling but quite distinct from an American species; a peculiar genus of
otters; and an antelope whose nearest allies are in Formosa and Sumatra.
The importance of these facts will {396} be best understood when we have
examined the corresponding affinities of the birds of Japan.
_Birds._--Owing to the recent researches of some English residents we have
probably a fuller knowledge of the birds than of the mammalia; yet the
number of true land-birds ascertained to inhabit the islands either as
residents or migrants is only 200, which is less than might be expected
considering the highly favourable conditions of mild climate, luxuriant
vegetation, and abundance of insect-life, and the extreme riches of the
adjacent continent,--Mr. Swinhoe's list of the birds of China containing
more than 400 land species, after deducting all which are peculiar to the
adjacent islands. Only seventeen species, or about one-twelfth of the
whole, are now considered to be peculiar to Japan proper; while seventeen
more are peculiar to the various outlying small islands constituting the
Bonin and Loo Choo groups. Even of these, six or seven are classed by Mr.
Seebohm as probably sub-species or slightly modified forms of continental
birds, so that ten only are well-marked species, undoubtedly distinct from
those of any other country.
The great majority of the birds are decidedly temperate forms identical
with those of Northern Asia and Europe; while no less than forty of the
species of land-birds are also found in Britain, or are such slight
modifications of British species that the difference is only perceptible to
a trained ornithologist. The following list of the land-birds common to
Britain and Japan is very interesting, when we consider that these
countries are separated by the whole extent of the European and Asiatic
continents, or by almost exactly one-fourth of the circumference of the
globe:--
LAND BIRDS COMMON TO GREAT BRITAIN AND JAPAN.[94]
(_Either Identical Species or Representative sub-species._)
1. Goldcrest _Regulus cristatus_ sub-sp. _orientalis_.
2. Marsh tit _Parus palustris_ sub-sp. _japonicus_.
3. Coal tit _Parus ater_ sub-sp. _pekinensis_.
4. Long-tailed tit _Acredula caudata_ (the sub-sp. _rosea_, is
British).
{397}
5. Common creeper _Certhia familiaris._
6. Nuthatch _Sitta europæa_ sub-sp. _amurensis._
7. Carrion crow _Corvus corone._
8. Nutcracker _Nucifraga caryocatactes._
9. Magpie _Pica caudata._
10. Pallass' grey shrike _Lanius excubitor_ sub-sp. _major._
11. Waxwing _Ampelis garrulus._
12. Grey wagtail _Motacilla boarula_ sub-sp. _melanope._
13. Alpine Pipit _Anthus spinoletta_ sub-sp. _japonicus._
14. Skylark _Alauda arvensis_ sub-sp. _japonica._
15. Common hawfinch _Coccothraustes vulgaris._
16. Common Crossbill _Loxia curvirostra._
17. Siskin _Fringilla spinus._
18. Mealy redpole ,, _linaria._
19. Brambling ,, _montifringilla._
20. Tree sparrow _Passer montanus._
21. Reed bunting _Emberiza schoeniculus_ sub-sp.
_palustris._
22. Rustic bunting ,, _rustica._
23. Snow bunting ,, _nivalis._
24. Chimney swallow _Hirundo rustica_ sub-sp. _gutturalis._
25. Sand martin _Cotyle riparia._
26. Great spotted woodpecker _Picus major_ sub-sp. _japonicus._
27. Lesser spotted woodpecker ,, _minor._
28. Wryneck _Jynx torquilla._
29. Hoopoe _Upupa epops._
30. Blue rock pigeon _Columba livia._
31. Cuckoo _Cuculus canorus._
32. Kingfisher _Alcedo ispida_ sub-sp. _bengalensis._
33. Eagle owl _Bubo maximus._
34. Snowy owl _Surnia nyctea._
35. Long-eared owl _Strix otus._
36. Short-eared owl ,, _brachyotus._
37. Scops owl _Scops scops._
38. Jer falcon _Falco gyrfalco._
39. Peregrine falcon ,, _peregrinus._
40. Hobby ,, _subbuteo._
41. Merlin _Falco æsalon._
42. Kestrel _Tinnunculus alaudarius_ sub-sp.
_japonicus._
43. Osprey _Pandion haliäctus._
44. Honey-buzzard _Pernis apivorus._
45. White-tailed eagle _Haliäetus albicilla._
46. Golden eagle _Aquila chrysäetus._
47. Common buzzard _Buteo vulgaris_ sub-sp. _plumipes._
48. Hen-harrier _Circus cyaneus._
49. Marsh-harrier ,, _æruginosus._
50. Gos-hawk _Astur palumbarius._
51. Sparrow-hawk _Accipiter nisus._
52. Ptarmigan _Tetrao mutus._
53. Common quail _Coturnix communis._
But even these fifty-three species by no means fairly represent the amount
of _resemblance_ between Britain and {398} Japan as regards birds; for
there are also thrushes, robins, stonechats, wrens, hedge-sparrows,
sedge-warblers, jays, starlings, swifts, goatsuckers, and some others,
which, though distinct _species_ from our own, have the same general
appearance, and give a familiar aspect to the ornithology. There remains,
however, a considerable body of Chinese and Siberian species, which link
the islands to the neighbouring parts of the continent; and there are also
a few which are Malayan or Himalayan rather than Chinese, and thus afford
us an interesting problem in distribution.
The seventeen species and sub-species which are altogether peculiar to
Japan proper, are for the most part allied to birds of North China and
Siberia, but three are decidedly tropical, and one of them--a fruit pigeon
(_Treron sieboldi_)--has no close ally nearer than Burmah and the
Himalayas. In the following list the affinities of the species are
indicated wherever they have been ascertained:--
LIST OF THE SPECIES OF LAND BIRDS PECULIAR TO JAPAN.
1. _Accentor rubidus._ Nearly allied to our hedge-sparrow, and less
closely to the Central Asian _A. immaculatus._
(1a. _Hypsipetes amaurotis._ Migrates to the Corea, otherwise
peculiar.)
2. _Zosterops japonica._ Allied to two Chinese species.
3. _Lusciniola pryeri._
4. _Garrulus japonicus._ Allied to the Siberian and British Jays.
5. _Fringilla kawarahiba._ Allied to the Chinese greenfinch.
6. _Emberiza ciopsis._ Allied to the E. Siberian bunting _E. cioides_,
of which it may be considered a sub-species.
7. ,, _yessoensis._ A distinct species.
8. ,, _personata._ A sub-species of _E. spodocephala._
9. _Gecinus awokera._ A distinct species of green woodpecker.
10. _Picus namiyei._ Allied to a Formosan species.
11. _Treron sieboldi._ Allied to _T. sphenura_ of the Himalayas, and to
a Formosan species.
12. _Carpophaga ianthina._ A distinct species of fruit-pigeon.
13. _Bubo blakistoni._ Allied to a Philippine eagle-owl.
14. _Scops semitorgues._ A distinct species.
15. _Phasianus versicolor._ A distinct species.
16. ,, _soemmeringi._ A distinct species.
17. ,, _scintillaus._ A sub-species of the last.
The large number of seventeen peculiar species in the outlying Bonin and
Loo Choo Islands is an interesting feature of Japanese ornithology. The
comparative remoteness of {399} these islands, their mild sub-tropical
climate and luxuriant vegetation, and perhaps the absence of violent storms
and their being situated out of the line of continental migration, seem to
be the conditions that have favoured the specialisation of modified types
adapted to the new environment.
_Japan Birds Recurring in Distant Areas._--The most interesting feature in
the ornithology of Japan is, undoubtedly, the presence of several species
which indicate an alliance with such remote districts as the Himalayas, the
Malay Islands, and Europe. Among the peculiar species, the most remarkable
of this class are,--the fruit-pigeon of the genus Treron, entirely unknown
in China, but reappearing in Formosa and Japan; the Hypsipetes, whose
nearest ally is in South China at a distance of nearly 500 miles; and the
jay (_Garrulus japonicus_), whose near ally (_G. glandarius_) inhabits
Europe only, at a distance of 3,700 miles. But even more extraordinary are
the following non-peculiar species:--_Spizaetus orientalis_, a crested
eagle, inhabiting the Himalayas, Formosa, and Japan, but unknown in
Southern or Eastern China; _Ceryle guttata_, a spotted kingfisher, almost
confined to the Himalayas and Japan, though occurring rarely in Central
China; and _Halcyon coromanda_, a brilliant red kingfisher inhabiting
Northern India, the Malay Islands to Celebes, Formosa, and Japan. We have
here an excellent illustration of the favourable conditions which islands
afford both for species which elsewhere live further south (_Halcyon
coromanda_), and for the preservation in isolated colonies of species which
are verging towards extinction; for such we must consider the above-named
eagle and kingfisher, both confined to a very limited area on the
continent, but surviving in remote islands. Referring to our account of the
birth, growth, and death of a species (in Chapter IV.) it can hardly be
doubted that the _Ceryle guttata_ formerly ranged from the Himalayas to
Japan, and has now almost died out in the intervening area owing to
geographical and physical changes, a subject which will be better discussed
when we have examined the interesting fauna of the island of Formosa. {400}
The other orders of animals are not yet sufficiently known to enable us to
found any accurate conclusions upon them. The main facts of their
distribution have already been given in my _Geographical Distribution of
Animals_ (Vol I., pp. 227-231), and they sufficiently agree with the birds
and mammalia in showing a mixture of temperate and tropical forms with a
considerable proportion of peculiar species. Owing to the comparatively
easy passage from the northern extremity of Japan through the island of
Saghalien to the mainland of Asia, a large number of temperate forms of
insects and birds are still able to enter the country, and thus diminish
the proportionate number of peculiar species. In the case of mammals this
is more difficult; and the large proportion of specific difference in their
case is a good indication of the comparatively remote epoch at which Japan
was finally separated from the continent. How long ago this separation took
place we cannot of course tell, but we may be sure it was much longer than
in the case of our own islands, and therefore probably in the earlier
portion of the Pliocene period.
FORMOSA.
Among recent continental islands there is probably none that surpasses in
interest and instructiveness the Chinese island named by the Portuguese,
Formosa, or "The Beautiful." Till quite recently it was a _terra incognita_
to naturalists, and we owe almost all our present knowledge of it to a
single man, the late Mr. Robert Swinhoe, who, in his official capacity as
one of our consuls in China, visited it several times between 1856 and
1866, besides residing on it for more than a year. During this period he
devoted all his spare time and energy to the study of natural history, more
especially of the two important groups, birds and mammals; and by employing
a large staff of native collectors and hunters, he obtained a very complete
knowledge of its fauna. In this case, too, we have the great advantage of a
very thorough knowledge of the adjacent parts of the continent, in great
part due to Mr. Swinhoe's own exertions during the twenty years of his
service in {401} that country. We possess, too, the further advantage of
having the whole of the available materials in these two classes collected
together by Mr. Swinhoe himself after full examination and comparison of
specimens; so that there is probably no part of the world (if we except
Europe, North America, and British India) of whose warm-blooded vertebrates
we possess fuller or more accurate knowledge than we do of those of the
coast districts of China and its islands.[95]
_Physical Features of Formosa._--The island of Formosa is nearly half the
size of Ireland, being 220 miles long, and from twenty to eighty miles
wide. It is traversed down its centre by a fine mountain range, which
reaches an altitude of about 8,000 feet in the south and 12,000 feet in the
northern half of the island, and whose higher slopes and valleys are
everywhere clothed with magnificent forests. It is crossed by the line of
the Tropic of Cancer a little south of its centre; and this position,
combined with its lofty mountains, gives it an unusual variety of tropical
and temperate climates. These circumstances are all highly favourable to
the preservation and development of animal life, and from what we already
know of its productions, it seems probable that few, if any islands of
approximately the same size and equally removed from a continent will be
found to equal it in the number and variety of their higher animals. The
outline map (at page 392) shows that Formosa is connected with the mainland
by a submerged bank, the hundred-fathom line including it along with Hainan
to the south-west and Japan on the north-east; while the line of
two-hundred fathoms includes also the Madjico-Sima and Loo-Choo Islands,
and may, perhaps, mark out approximately the last great extension of the
Asiatic continent, the submergence of which isolated these islands from the
mainland.
_Animal Life of Formosa._--We are at present acquainted {402} with 35
species of mammalia, and 128 species of land-birds from Formosa, fourteen
of the former and forty-three of the latter being peculiar, while the
remainder inhabit also some part of the continent or adjacent islands. This
proportion of peculiar species is perhaps (as regards the birds) the
highest to be met with in any island which can be classed as both
continental and recent, and this, in all probability, implies that the
epoch of separation is somewhat remote. It was not, however, remote enough
to reach back to a time when the continental fauna was very different from
what it is now, for we find all the chief types of living Asiatic mammalia
represented in this small island. Thus we have monkeys; insectivora;
numerous carnivora; pigs, deer, antelopes, and cattle among ungulata;
numerous rodents, and the edentate Manis,--a very fair representation of
Asiatic mammals, all being of known genera, and of species either
absolutely identical with some still living elsewhere or very closely
allied to them. The birds exhibit analogous phenomena, with the exception
that we have here two peculiar and very interesting genera.
But besides the amount of specific and generic modification that has
occurred, we have another indication of the lapse of time in the peculiar
relations of a large proportion of the Formosan animals, which show that a
great change in the distribution of Asiatic species must have taken place
since the separation of the island from the continent. Before pointing
these out it will be advantageous to give lists of the mammalia and
peculiar birds of the island, as we shall have frequent occasion to refer
to them.
LIST OF THE MAMMALIA OF FORMOSA. (The peculiar species are printed in
italics.)
1. _Macacus cyclopis._ A rock-monkey more allied to _M. rhesus_ of
India than to _M. sancti-johannis_ of South China.
2. _Pteropus formosus._ A fruit-bat closely allied to the Japanese
species. None of the genus are found in China.
3. Vesperugo abramus. China.
4. Vespertilio formosus. Black and orange Bat. China.
5. Nyctinomus cestonii. Large-eared Bat. China, S. Europe.
6. _Talpa insularis._ A blind mole of a peculiar species.
{403} 7. Sorex murinus. Musk Rat. China.
8. Sorex sp. A shrew, undescribed.
9. Erinaceus sp. A Hedgehog, undescribed.
10. Ursus tibetanus. The Tibetan Bear. Himalayas and North China.
11. _Helictis subaurantiaca._ The orange-tinted Tree Civet. Allied to
_H. nipalensis_ of the Himalayas more than to _H. moschata_ of
China.
12. Martes flavigula, var. The yellow-necked Marten. India, China.
13. Felis macroscelis. The clouded Tiger of Siam and Malaya.
14. Felis viverrina. The Asiatic wild Cat. Himalayas and Malacca.
15. Felis chinensis. The Chinese Tiger Cat. China.
16. Viverricula malaccensis. Spotted Civet. China, India.
17. Paguma larvata. Gem-faced Civet. China.
18. _Sus taivanus._ Allied to the wild Pig of Japan.
19. Cervulus reevesii. Reeve's Muntjac. China.
20. _Cervus pseudaxis._ Formosan Spotted Deer. Allied to _C. sika_ of
Japan.
21. _Cervus swinhoii._ Swinhoe's Rusa Deer. Allied to Indian and
Malayan species.
22. _Nemorhedus swinhoii._ Swinhoe's Goat-antelope. Allied to the
species of Sumatra and Japan.
23. Bos chinensis. South China wild Cow.
24. Mus bandicota. The Bandicoot Rat. Perhaps introduced from India.
25. Mus indicus. Indian Rat.
26. _Mus coxinga._ Spinous Country-rat.
27. _Mus canna._ Silken Country-rat.
28. _Mus losca_. Brown Country-rat.
29. Sciurus castaneoventris. Chestnut-bellied Squirrel. China and
Hainan.
30. Sciurus m'clellandi. McClelland's Squirrel. Himalayas, China.
31. _Sciuropterus kaleensis._ Small Formosan Flying Squirrel. Allied to
_S. alboniger_ of Nepal.
32. _Pteromys grandis._ Large Red Flying Squirrel. Allied to Himalayan
and Bornean species. From North Formosa.
33. _Pteromys pectoralis._ White-breasted Flying Squirrel. From South
Formosa.
34. Lepus sinensis. Chinese Hare. Inhabits South China.
35. Manis dalmanni. Scaly Ant-eater. China and the Himalayas.
The most interesting and suggestive feature connected with these Formosan
mammals is the identity or affinity of several of them, with Indian or
Malayan rather than with Chinese species. We have the rock-monkey of
Formosa allied to the rhesus monkeys of India and Burma, not to those of
South China and Hainan. The tree civet (_Helictis subaurantiaca_), and the
small flying squirrel (_Sciuropterus kaleensis_), are both allied to
Himalayan species. Swinhoe's deer and goat-antelope are nearest to Malayan
species, as are the red and white-breasted flying squirrels; while the
fruit-bat, the wild pig, {404} and the spotted deer are all allied to
peculiar Japanese species. The clouded tiger is a Malay species unknown in
China, while the Asiatic wild cat is a native of the Himalayas and Malacca.
It is clear, therefore, that before Formosa was separated from the mainland
the above named animals or their ancestral types must have ranged over the
intervening country as far as the Himalayas on the west, Japan on the
north, and Borneo or the Philippines on the south; and that after that
event occurred, the conditions were so materially changed as to lead to the
extinction of these species in what are now the coast provinces of China,
while they or their modified descendants continued to exist in the dense
forests of the Himalayas and the Malay Islands, and in such detached
islands as Formosa and Japan. We will now see what additional light is
thrown upon this subject by an examination of the birds.
LIST OF THE LAND BIRDS PECULIAR TO FORMOSA.
TURDIDÆ (Thrushes).
1. _Turdus albiceps._ Allied to Chinese species.
SYLVIDIÆ (Warblers).
2. _Cisticola volitans._ Allied to _C. schoenicola_ of India and
China.
3. _Herbivox cantans._ Sub-species of _H. cantillaus_ of N. China and
Japan.
4. _Notodela montium._ Allied to _N. leucura_ of the Himalayas; no ally
in China.
TIMALIIDÆ (Babblers).
5. _Pomatorhinus musicus._ Allies in S. China and the Himalayas.
6. _P. erythroenemis._ Do. do.
7. _Garrulax ruficeps._ Allied to _G. albogularis_ of N. India and East
Thibet, not to the species of S. China (_G. sannio_).
8. _Janthocincla poecilorhyncha._ Allied to _J. coerulata_ of the
Himalayas. None of the genus in China.
9. _Trochalopteron taivanus._ Allied to a Chinese species.
10. _Alcippe morrisoniana._} Near the Himalayan _A. nipalensis_.
11. _A. brunnea._ } None of the genus in China.
12. _Sibia auricularis._ Allied to the Himalayan _S. capistrata_. The
genus not known in China.
PANURIDÆ (Bearded Tits, &c.).
13. _Suthora bulomachus._ Allied to the Chinese _S. suffusa_.
CINCLIDÆ (Dippers and Whistling Thrushes).
14. _Myiophoneus insularis._ Allied to _M. horsfieldi_ of South India.
{405}
PARIDÆ (Tits).
15. _Parus insperatus._ Sub-species of _P. monticola_ of the Himalayas
and East Thibet.
16. _P. castaneiventris._ Allied to _P. varius_ of Japan.
LIOTRICHIDÆ (Hill Tits).
17. _Liocichla steerii._ A peculiar genus of a specially Himalayan
family, quite unknown in China.
PYCNONOTIDÆ (Bulbuls).
18. _Pycnonotus (Spizixos) cinereicapillus_. Very near _P. semitorques_
of China.
19. _Hypsipetes nigerrimus._ Allied to _H. concolor_ of Assam, not to
_H. macclellandi_ of China.
ORIOLIDÆ (Orioles).
20. _Analcipus ardens._ Allied to _A. traillii_ of the Himalayas and
Tenasserim.
CAMPEPHAGIDÆ (Caterpillar Shrikes).
21. _Graucalus rex-pineti._ Closely allied to the Indian _G. macei_. No
ally in China.
DICRURIDÆ (King Crows).
22. _Chaptia brauniana._ Closely allied to _C. ænea_ of Assam. No ally
in China.
MUSCICAPIDÆ (Flycatchers).
23. _Cyornis vivida._ Allied to _C. rubeculoides_ of India.
CORVIDÆ (Jays and Crows).
24. _Garrulus taivanus._ Allied to _G. sinensis_ of S. China.
25. _Urocissa coerulea._ A very distinct species from its Indian and
Chinese allies.
26. _Dendrocitta formosæ._ A sub-species of the Chinese _D. sinensis_.
PLOCEIDÆ (Weaver Finches).
27. _Munia formosana._ Allied to _M. rubronigra_ of India and Burmah.
ALAUDIDÆ (Larks).
28. _Alauda sala._}Allies in South China.
29. _A. wattersi._}
PITTIDÆ (Pittas).
30. _Pitta oreas._ Allied to _P. cyanoptera_ of Malaya and S. China.
PICIDÆ (Woodpeckers).
31. _Picus insularis._ Allied to _P. leuconotus_ of Japan and Siberia.
MEGALÆMIDÆ.
32. _Megalæma nuchalis._ Allied to _M. oortii_ of Sumatra and _M.
faber_ of Hainan. No allies in China.
CAPRIMULGIDÆ (Goatsuckers).
33. _Caprimulgus stictomus._ A sub-species of _C. monticolus_ of India
and China.
{406}
COLUMBIDÆ (Pigeons).
34. _Treron formosæ._ Allied to Malayan species.
35. _Sphenocercus sororius._ Allied to Malay species and to _S.
sieboldi_ of Japan. No allies of these two birds inhabit China.
36. _Chalcophaps formosana._ Allied to the Indian species which extends
to Tenasserim and Hainan.
TETRAONIDÆ (Grouse and Partridges).
37. _Orcoperdix crudigularis._ A peculiar genus of partridges.
38. _Bambusicola sonorivox._ Allied to the Chinese _B. thoracica_.
39. _Arcoturnix rostrata._ Allied to the Chinese _A. blakistonii_.
PHASIANIDÆ (Pheasants).
40. _Phasianus formosanus._ Allied to _P. torquatus_ of China.
41. _Euplocamus swinhoii._ A very peculiar and beautiful species allied
to the tropical fire-backed pheasants, and to the silver pheasant of
North China.
STRIGIDÆ (Owls).
42. _Athene pardalota._ Closely allied to a Chinese species.
43. _Lempigius hambroekii._ Allied to a Chinese species.
This list exhibits to us the marvellous fact that more than half the
peculiar species of Formosan birds have their nearest allies in such remote
regions as the Himalayas, South India, the Malay Islands, or Japan, rather
than in the adjacent parts of the Asiatic continent. Fourteen species have
Himalayan allies, and six of these belong to genera which are unknown in
China. One has its nearest ally in the Nilgherries, and five in the Malay
Islands; and of these six, four belong to genera which are not Chinese. Two
have their only near allies in Japan. Perhaps more curious still are those
cases in which, though the genus is Chinese, the nearest allied species is
to be sought for in some remote region. Thus we have the Formosan babbler
(_Garrulax ruficeps_) not allied to the species found in South China, but
to one inhabiting North India and East Thibet; while the black bulbul
(_Hypsipetes nigerrimus_), is not allied to the Chinese species but to an
Assamese form.
In the same category as the above we must place eight species not peculiar
to Formosa, but which are Indian or Malayan rather than Chinese, so that
they offer examples of discontinuous distribution somewhat analogous to
what {407} we found to occur in Japan. These are enumerated in the
following list.
SPECIES OF BIRDS COMMON TO FORMOSA AND INDIA OR MALAYA, BUT NOT FOUND IN
CHINA.
1. _Siphia superciliaris._ The Rufous-breasted Flycatcher of the S. E.
Himalayas.
2. _Halcyon coromanda._ The Great Red Kingfisher of India, Malaya, and
Japan.
3. _Palumbus pulchricollis._ The Darjeeling Wood-pigeon of the S. E.
Himalayas.
4. _Turnix dussumieri._ The larger Button-quail of India.
5. _Spizaetus nipalensis._ The Spotted Hawk-eagle of Nepal and Assam.
6. _Lophospiza trivirgata._ The Crested Gos-hawk of the Malay Islands.
7. _Bulaca newarensis._ The Brown Wood-owl of the Himalayas.
8. _Strix candida._ The Grass-owl of India and Malaya.
The most interesting of the above are the pigeon and the flycatcher, both
of which are, so far as yet known, strictly confined to the Himalayan
mountains and Formosa. They thus afford examples of discontinuous specific
distribution exactly parallel to that of the great spotted kingfisher,
already referred to as found only in the Himalayas and Japan.
_Comparison of the Faunas of Hainan, Formosa, and Japan._--The island of
Hainan on the extreme south of China, and only separated from the mainland
by a strait fifteen miles wide, appears to have considerable similarity to
Formosa, inasmuch as it possesses seventeen peculiar land-birds (out of 130
obtained by Mr. Swinhoe), two of which are close allies of Formosan
species, while two others are identical. We also find four species whose
nearest allies are in the Himalayas. Our knowledge of this island and of
the adjacent coast of China is not yet sufficient to enable us to form an
accurate judgment of its relations, but it seems probable that it was
separated from the continent at, approximately, the same epoch as Formosa
and Japan, and that the special features of each of these islands are
mainly due to their geographical position. Formosa, being more completely
isolated than either of the others, possesses a larger proportion of
peculiar species of birds, while its tropical situation and lofty mountain
ranges {408} have enabled it to preserve an unusual number of Himalayan and
Malayan forms. Japan, almost equally isolated towards the south, and having
a much greater variety of climate as well as a much larger area, possesses
about an equal number of mammalia with Formosa, and an even larger
proportion of peculiar species. Its birds, however, though more numerous
are less peculiar; and this is probably due to the large number of species
which migrate northwards in summer, and find it easy to enter Japan through
the Kurile Isles or Saghalien.[96] Japan too, is largely peopled by those
northern types which have an unusually wide range, and which, being almost
all migratory, are accustomed to cross over seas of moderate extent. The
regular or occasional influx of these species prevents the formation of
special insular races, such as are almost always produced when a portion of
the population of a species remains for a considerable time completely
isolated. We thus have explained the curious fact, that while the mammalia
of the two islands are almost equally peculiar, (those of Japan being most
so in the present state of our knowledge), the birds of Formosa show a far
greater number of peculiar species than those of Japan.
_General Remarks on Recent Continental Islands._--We have now briefly
sketched the zoological peculiarities of an illustrative series of recent
continental islands, commencing with one of the most recent--Great
Britain--in which the process of formation of peculiar species has only
just commenced, and terminating with Formosa, probably one of the most
ancient of the series, and which accordingly presents us with a very large
proportion of peculiar species, not only in its mammalia, which have no
means of crossing the wide strait which separates it from the mainland, but
also in its birds, many of which are quite able to cross over.
Here, too, we obtain a glimpse of the way in which {409} species die out
and are replaced by others, which quite agrees with what the theory of
evolution assures us must have occurred. On a continent, the process of
extinction will generally take effect on the circumference of the area of
distribution, because it is there that the species comes into contact with
such adverse conditions or competing forms as prevent it from advancing
further. A very slight change will evidently turn the scale and cause the
species to contract its range, and this usually goes on till it is reduced
to a very restricted area, and finally becomes extinct. It may conceivably
happen (and almost certainly has sometimes happened) that the process of
restriction of range by adverse conditions may act in one direction only,
and over a limited district, so as ultimately to divide the specific area
into two separated parts, in each of which a portion of the species will
continue to maintain itself. We have seen that there is reason to believe
that this has occurred in a very few cases both in North America and in
Northern Asia. (_See_ pp. 65-68.) But the same thing has certainly occurred
in a considerable number of cases, only it has resulted in the divided
areas being occupied by _representative forms_ instead of by the very same
species. The cause of this is very easy to understand. We have already
shown that there is a large amount of local variation in a considerable
number of species, and we may be sure that were it not for the constant
intermingling and intercrossing of the individuals inhabiting adjacent
localities this tendency to local variation in adaptation to slightly
different conditions, would soon form distinct races. But as soon as the
area is divided into two portions the intercrossing is stopped, and the
usual result is that two closely allied races, classed as representative
species, become formed. Such pairs of allied species on the two sides of a
continent, or in two detached areas, are very numerous; and their existence
is only explicable on the supposition that they are descendants of a parent
form which once occupied an area comprising that of both of them,--that
this area then became discontinuous,--and, lastly, that, as a consequence
of the discontinuity, the two sections of the parent species became
segregated into distinct races or new species. {410}
Now, when the division of the area leaves one portion of the species in an
island, a similar modification of the species, either in the island or in
the continent, occurs, resulting in closely-allied but distinct forms; and
such forms are, as we have seen, highly characteristic of island-faunas.
But islands also favour the occasional preservation of the unchanged
species--a phenomenon which very rarely occurs in continents. This is
probably due to the absence of competition in islands, so that the parent
species there maintains itself unchanged, while the continental portion, by
the force of that competition, is driven back to some remote mountain area,
where it also obtains a comparative freedom from competition. Thus may be
explained the curious fact, that the species common to Formosa and India
are generally confined to limited areas in the Himalayas, or in other cases
are found only in remote islands, as Japan or Hainan.
The distribution and affinities of the animals of continental islands thus
throws much light on that obscure subject--the decay and extinction of
species; while the numerous and delicate gradations in the modification of
the continental species, from perfect identity, through slight varieties,
local forms, and insular races, to well-defined species and even distinct
genera, afford an overwhelming mass of evidence in favour of the theory of
"descent with modification."
We shall now pass on to another class of islands, which, though originally
forming parts of continents, were separated from them at very remote
epochs. This antiquity is clearly manifested in their existing faunas,
which present many peculiarities, and offer some most curious problems to
the student of distribution.
* * * * *
{411}
CHAPTER XIX
ANCIENT CONTINENTAL ISLANDS: THE MADAGASCAR GROUP
Remarks on Ancient Continental Islands--Physical Features of
Madagascar--Biological Features of
Madagascar--Mammalia--Reptiles--Relation of Madagascar to Africa--Early
History of Africa and Madagascar--Anomalies of Distribution and How to
Explain Them--The Birds of Madagascar as Indicating a Supposed Lemurian
Continent--Submerged Islands between Madagascar and India--Concluding
Remarks on "Lemuria"--The Mascarene Islands--The Comoro Islands--The
Seychelles Archipelago--Birds of the Seychelles--Reptiles and
Amphibia--Freshwater Fishes--Land Shells--Mauritius, Bourbon, and
Rodriguez--Birds--Extinct Birds and their Probable
Origin--Reptiles--Flora of Madagascar and the Mascarene
Islands--Curious Relations of Mascarene Plants--Endemic Genera of
Mauritius and Seychelles--Fragmentary Character of the Mascarene
Flora--Flora of Madagascar Allied to that of South
Africa--Preponderance of Ferns in the Mascarene Flora--Concluding
Remarks on the Madagascar Group.
We have now to consider the phenomena presented by a very distinct class of
islands--those which, although once forming part of a continent, have been
separated from it at a remote epoch when its animal forms were very unlike
what they are now. Such islands preserve to us the record of a by-gone
world,--of a period when many of the higher types had not yet come into
existence and when the distribution of others was very different from what
prevails at the present day. The problem presented by these ancient islands
is often complicated by the changes they themselves have undergone since
the period of their separation. A partial subsidence will have led to the
{412} extinction of some of the types that were originally preserved, and
may leave the ancient fauna in a very fragmentary state; while subsequent
elevations may have brought it so near to the continent that some
immigration even of mammalia may have taken place. If these elevations and
subsidences occurred several times over, though never to such an extent as
again to unite the island with the continent, it is evident that a very
complex result might be produced; for besides the relics of the ancient
fauna, we might have successive immigrations from surrounding lands
reaching down to the era of existing species. Bearing in mind these
possible changes, we shall generally be able to arrive at a fair
conjectural solution of the phenomena of distribution presented by these
ancient islands.
Undoubtedly the most interesting of such islands, and that which exhibits
their chief peculiarities in the greatest perfection, is Madagascar, and we
shall therefore enter somewhat fully into its biological and physical
history.
_Physical Features of Madagascar._--This great island is situated about 250
miles from the east coast of Africa, and extends from 12° to 25½° S. Lat.
It is almost exactly 1,000 miles long, with an extreme width of 360 and an
average width of more than 260 miles. A lofty granitic plateau, from eighty
to 160 miles wide and from 3,000 to 5,000 feet high, occupies its central
portion, on which rise peaks and domes of basalt and granite to a height of
nearly 9,000 feet; and there are also numerous extinct volcanic cones and
craters. All round the island, but especially developed on the south and
west, are plains of a few hundred feet elevation, formed of rocks which are
shown by their fossils to be of Jurassic age, or at all events to belong to
somewhere near the middle portion of the Secondary period. The higher
granitic plateau consists of bare undulating moors, while the lower
Secondary plains are more or less wooded; and there is here also a
continuous belt of dense forest, varying from six or eight to fifty miles
wide, encircling the whole island, usually at about thirty miles distance
from the coast but in the north-east coming down to the sea-shore. {413}
[Illustration]
{414}
The sea around Madagascar, when the shallow bank on which it stands is
passed, is generally deep. This 100-fathom bank is only from one to three
miles wide on the east side, but on the west it is much broader, and
stretches out opposite Mozambique to a distance of about eighty miles. The
Mozambique Channel is rather more than 1,000 fathoms deep, but there is
only a narrow belt of this depth opposite Mozambique, and still narrower
where the Comoro Islands and adjacent shoals seem to form stepping-stones
to the continent of Africa. The 1,000-fathom line includes Aldabra and the
small Farquhar Islands to the north of Madagascar; while to the east the
sea deepens rapidly to the 1,000-fathom line and then more slowly, a
profound channel of 2,400 fathoms separating Madagascar from Bourbon and
Mauritius. To the north-east of Mauritius are a series of extensive shoals
forming four large banks less than 100 fathoms below the surface, while the
1,000-fathom line includes them all, with an area about half that of
Madagascar itself. A little further north is the Seychelles group, also
standing on an extensive 1,000-fathom bank, while all round the sea is more
than 2,000 fathoms deep.
It seems probable, then, that to the north-east of Madagascar there was
once a series of very large islands, separated from it by not very wide
straits; while eastward across the Indian Ocean we find the Chagos and
Maldive coral atolls, perhaps marking the position of other large islands,
which together would form a line of communication, by comparatively easy
stages of 400 or 500 miles each between Madagascar and India. These
submerged islands, as shown in our map at p. 424, are of great importance
in explaining some anomalous features in the zoology of this great island.
If the rocks of Secondary age which form a belt around the island are held
to indicate that Madagascar was once of less extent than it is now (though
this by no means necessarily follows), we have also evidence that it has
recently been considerably larger; for along the east coast there is an
extensive barrier coral-reef about 350 miles in length, and varying in
distance from the land from a quarter of a mile to three or four miles.
This seems to indicate recent subsidence; while we have no record of raised
coral rocks inland which would certainly mark any recent elevation, though
fringing coral reefs surround a considerable portion of the northern,
eastern, and south-western coasts. We may therefore conclude that during
Tertiary times the island was usually as large as, and often probably much
larger than, it is now. {415}
[Illustration: MAP OF THE MADAGASCAR GROUP, SHOWING DEPTHS OF SEA.]
In this Map the depth of the sea is shown by three tints; the lightest tint
indicating from 0 to 100 fathoms, the medium tint from 100 to 1,000
fathoms, the dark tint more than 1,000 fathoms.
{416}
_Biological Features of Madagascar._--Madagascar possesses an exceedingly
rich and beautiful fauna and flora, rivalling in some groups most tropical
countries of equal extent, and even when poor in species, of surpassing
interest from the singularity, the isolation, or the beauty of its forms of
life. In order to exhibit the full peculiarity of its natural history and
the nature of the problems it offers to the biological student, we must
give an outline of its more important animal forms in systematic order.
_Mammalia._--Madagascar possesses no less than sixty-six species of
mammals--a certain proof in itself that the island has once formed part of
a continent; but the character of these animals is very extraordinary and
altogether different from the assemblage now found in Africa or in any
other existing continent. Africa is now most prominently characterised by
its monkeys, apes, and baboons; by its lions, leopards, and hyænas; by its
zebras, rhinoceroses, elephants, buffaloes, giraffes, and numerous species
of antelopes. But no one of these animals, nor any thing like them, is
found in Madagascar, and thus our first impression would be that it could
never have been united with the African continent. But, as the tigers, the
bears, the tapirs, the deer, and the numerous squirrels of Asia are equally
absent, there seems no probability of its having been united with that
continent. Let us then see to what groups the mammalia of Madagascar
belong, and where we must look for their probable allies.
First and most important are the lemurs, consisting of six genera and
thirty-three species, thus comprising just half the entire mammalian
population of the island. This group of lowly-organised and very ancient
creatures {417} still exists scattered over a wide area; but they are
nowhere so abundant as in the island of Madagascar. They are found from
West Africa to India, Ceylon, and the Malay Archipelago, consisting of a
number of isolated genera and species, which appear to maintain their
existence by their nocturnal and arboreal habits, and by haunting dense
forests. It can hardly be said that the African forms of lemurs are more
nearly allied to those of Madagascar than are the Asiatic, the whole series
appearing to be the disconnected fragments of a once more compact and
extensive group of animals.
Next, we have about a dozen species of Insectivora, consisting of one
shrew, a group distributed over all the great continents; and five genera
of a peculiar family, Centetidæ, which family exists nowhere else on the
globe except in the two largest West Indian Islands, Cuba and Hayti, thus
adding still further to our embarrassment in seeking for the original home
of the Madagascar fauna.
We then come to the Carnivora, which are represented by a peculiar cat-like
animal, Cryptoprocta, forming a distinct family, and having no close allies
in any part of the globe; and eight civets belonging to four peculiar
genera. Here we first meet with some decided indications of an African
origin; for the civet family is more abundant in this continent than in
Asia, and some of the Madagascar genera seem to be decidedly allied to
African groups--as, for example, Eupleres to Suricata and Crossarchus.[97]
The Rodents consist only of four rats and mice of peculiar genera, one of
which is said to be allied to an American genus; and lastly we have a
river-hog of the African genus Potamochærus, and a small sub-fossil
hippopotamus, both of which being semi-aquatic animals might easily have
reached the island from Africa, by way of the Comoros, without any actual
land connection.[98]
_Reptiles of Madagascar._--Passing over the birds for the present, as not
so clearly demonstrating {418} land-connection, let us see what indications
are afforded by the reptiles. The large and universally distributed family
of Colubrine snakes is represented in Madagascar, not by African or Asiatic
genera, but by two American genera--Philodryas and Heterodon, and by
Herpetodryas, a genus found in America and China. The other genera are all
peculiar, and belong mostly to widespread tropical families; but two
families--Lycodontidæ and Viperidæ, both abundant in Africa and the Eastern
tropics--are absent. Lizards are mostly represented by peculiar genera of
African or tropical families, but several African genera are represented by
peculiar species, and there are also some species belonging to two American
genera of the Iguanidæ, a family which is exclusively American; while a
genus of geckoes, inhabiting America and Australia, also occurs in
Madagascar.
_Relation of Madagascar to Africa._--These facts taken all together are
certainly very extraordinary, since they show in a considerable number of
cases as much affinity with America as with Africa; while the most striking
and characteristic groups of animals now inhabiting Africa are entirely
wanting in Madagascar. Let us first deal with this fact, of the absence of
so many of the most dominant African groups. The explanation of this
deficiency is by no means difficult, for the rich deposits of fossil
mammals of Miocene or Pliocene age in France, Germany, Greece, and
North-west India, have demonstrated the fact that all the great African
mammals then inhabited Europe and temperate Asia. We also know that a
little earlier (in Eocene times) tropical Africa was cut off from Europe
and Asia by a sea stretching from the Atlantic to the Bay of Bengal, at
which time Africa must have formed a detached island-continent such as
Australia is now, and probably, like it, very poor in the higher forms of
life. Coupling these two facts, the inference seems clear, that all the
higher types of mammalia were developed in the great Euro-Asiatic continent
(which then included Northern Africa), and that they only migrated into
tropical Africa when the two continents became united by the upheaval of
the sea-bottom, probably {419} in the latter portion of the Miocene or
early in the Pliocene period.[99]
It is clear, therefore, that if Madagascar had once formed part of Africa,
but had been separated from it before Africa was united to Europe and Asia,
it would not contain any of those kinds of animals which then first entered
the country. But, besides the African mammals, we know that some birds now
confined to Africa then inhabited Europe, and we may therefore fairly
assume that all the more important groups of birds, reptiles, and insects,
now abundant in Africa but absent from Madagascar, formed no part of the
original African fauna, but entered the country only after it was joined to
Europe and Asia.
_Early History of Africa and Madagascar._--We have seen that Madagascar
contains an abundance of mammals, and that most of them are of types either
peculiar to, or existing also in, Africa; it follows that that continent
must have had an earlier union with Europe, Asia, or America, or it could
never have obtained any mammals at all.
{420} Now these ancient African mammals are Lemurs, Insectivora, and small
Carnivora, chiefly Viverridæ; and all these groups are known to have
inhabited Europe in Eocene and Miocene times; and that the union was with
Europe rather than with America is clearly proved by the fact that even the
insectivorous Centetidæ, now confined to Madagascar and the West Indies,
inhabited France in the Lower Miocene period, while the Viverridæ, or
civets, which form so important a part of the fauna of Madagascar as well
as of Africa, were abundant in Europe throughout the whole Tertiary period,
but are not known to have ever lived in any part of the American continent.
We here see the application of the principle which we have already fully
proved and illustrated (Chapter IV., p. 60), that all extensive groups have
a wide range at the period of their maximum development; but as they decay
their area of distribution diminishes or breaks up into detached fragments,
which one after another disappear till the group becomes extinct. Those
animal forms which we now find isolated in Madagascar and other remote
portions of the globe all belong to ancient groups which are in a decaying
or nearly extinct condition, while those which are absent from it belong to
more recent and more highly-developed types, which range over extensive and
continuous areas, but have had no opportunity of reaching the more ancient
continental islands.
_Anomalies of Distribution and How to Explain Them._--If these
considerations have any weight, it follows that there is no reason whatever
for supposing any former direct connection between Madagascar and the
Greater Antilles merely because the insectivorous Centetidæ now exist only
in these two groups of islands; for we know that the ancestors of this
family must once have had a much wider range, which almost certainly
extended over the great northern continents. We might as reasonably suppose
a land-connection across the Pacific to account for the camels of Asia
having their nearest existing allies in the llamas and alpacas of the
Peruvian Andes, and another between Sumatra and Brazil, in order that the
ancestral tapir of one country might have passed over to the other. In both
{421} these cases we have ample proof of the former wide extension of the
group. Extinct camels of numerous species abounded in North America in
Miocene, Pliocene, and even Post-pliocene times, and one has also been
found in North-western India, but none whatever among all the rich deposits
of mammalia in Europe. We are thus told, as clearly as possible, that from
the North American continent as a centre the camel tribe spread westward,
over now-submerged land at the shallow Behring Straits and Kamschatka Sea,
into Asia, and southward along the Andes into South America. Tapirs are
even more interesting and instructive. Their remotest known ancestors
appear in Western Europe in the early portion of the Eocene period; in the
latter Eocene and the Miocene other forms occur both in Europe and North
America. These seem to have become extinct in North America, while in
Europe they developed largely into many forms of true tapirs, which at a
much later period found their way again to North, and thence to South,
America, where their remains are found in caves and gravel deposits. It is
an instructive fact that in the Eastern continent, where they were once so
abundant, they have dwindled down to a single species, existing in small
numbers in the Malay Peninsula, Sumatra, and Borneo only; while in the
Western continent, where they are comparatively recent immigrants, they
occupy a much larger area, and are represented by three or four distinct
species. Who could possibly have imagined such migrations, and extinctions,
and changes of distribution as are demonstrated in the case of the tapirs,
if we had only the distribution of the existing species to found an opinion
upon? Such cases as these--and there are many others equally striking--show
us with the greatest distinctness how nature has worked in bringing about
the examples of anomalous distribution that everywhere meet us; and we
must, on every ground of philosophy and common sense, apply the same method
of interpretation to the more numerous instances of anomalous distribution
we discover among such groups as reptiles, birds, and insects, where we
rarely have any direct evidence of their past migrations through the
discovery of {422} fossil remains. Whenever we can trace the past history
of any group of terrestrial animals, we invariably find that its actual
distribution can be explained by migrations effected by means of
comparatively slight modifications of our existing continents. In no single
case have we any direct evidence that the distribution of land and sea has
been radically changed during the whole lapse of the Tertiary and Secondary
periods, while, as we have already shown in our fifth chapter, the
testimony of geology itself, if fairly interpreted, upholds the same theory
of the stability of our continents and the permanence of our oceans. Yet so
easy and pleasant is it to speculate on former changes of land and sea with
which to cut the gordian knot offered by anomalies of distribution, that we
still continually meet with suggestions of former continents stretching in
every direction across the deepest oceans, in order to explain the presence
in remote parts of the globe of the same genera even of plants or of
insects--organisms which possess such exceptional facilities both for
terrestrial, aërial, and oceanic transport, and of whose distribution in
early geological periods we generally know little or nothing.
_The Birds of Madagascar, as Indicating a Supposed Lemurian
Continent._--Having thus shown how the distribution of the land mammalia
and reptiles of Madagascar may be well explained by the supposition of a
union with Africa before the greater part of its existing fauna had reached
it, we have now to consider whether, as some ornithologists think, the
distribution and affinities of the birds present an insuperable objection
to this view, and require the adoption of a hypothetical
continent--Lemuria--extending from Madagascar to Ceylon and the Malay
Islands.
There are about one hundred and fifty land birds known from the island of
Madagascar, of which a hundred and twenty-seven are peculiar; and about
half of these peculiar species belong to peculiar genera, many of which are
extremely isolated, so that it is often difficult to class them in any of
the recognised families, or to determine their affinities to any living
birds.[100] Among the other moiety, {423} belonging to known genera, we
find fifteen which have undoubted African affinities, while five or six are
as decidedly Oriental, the genera or nearest allied species being found in
India or the Malay Islands. It is on the presence of these peculiar Indian
types that Dr. Hartlaub, in his recent work on the _Birds of Madagascar and
the Adjacent Islands_, lays great stress, as proving the former existence
of "Lemuria"; while he considers the absence of such peculiar African
families as the plantain-eaters, glossy-starlings, ox-peckers, barbets,
honey-guides, hornbills, and bustards--besides a host of peculiar African
genera--as sufficiently disproving the statement in my _Geographical
Distribution of Animals_ that Madagascar is "more nearly related to the
Ethiopian than to any other region," and that its fauna was evidently
"mainly derived from Africa."
But the absence of the numerous peculiar groups of African birds is so
exactly parallel to the same phenomenon among mammals, that we are
justified in imputing it to the same cause, the more especially as some of
the very groups that are wanting--the plantain-eaters and the trogons, for
example,--are actually known to have inhabited Europe along with the large
mammalia which subsequently migrated to Africa. As to the peculiarly
Eastern genera--such as Copsychus and Hypsipetes, with a Dicrurus, a
Ploceus, a Cisticola, and a Scops, all closely allied to Indian or Malayan
species--although very striking to the ornithologist, they certainly do not
outweigh the fourteen African genera found in Madagascar. Their presence
may, moreover, be accounted for more satisfactorily than by means of an
ancient Lemurian continent, which, even if granted, would not explain the
very facts adduced in its support.
Let us first prove this latter statement.
The supposed "Lemuria" must have existed, if at all, at so remote a period
that the higher animals did not then inhabit either Africa or Southern
Asia, and it must have {424} become partially or wholly submerged before
they reached those countries; otherwise we should find in Madagascar many
other animals besides Lemurs, Insectivora, and Viverridæ, especially such
active arboreal creatures as monkeys and squirrels, such hardy grazers as
deer or antelopes, or such wide-ranging carnivores as foxes or bears. This
obliges us to date the disappearance of the hypothetical continent about
the earlier part of the Miocene epoch at latest, for during the latter part
of that period we know that such animals existed in abundance in every part
of the great northern continents wherever we have found organic remains.
But the Oriental birds in Madagascar, by whose presence Dr. Hartlaub
upholds the theory of a Lemuria, are slightly modified forms of _existing
Indian genera_, or sometimes, as Dr. Hartlaub himself points out, _species
hardly distinguishable from those of India_. Now all the evidence at our
command leads us to conclude that, even if these genera and species were in
existence in the early Miocene period, they must have had a widely
different distribution from what they have now. Along with so many African
and Indian genera of mammals they then probably inhabited Europe, which at
that epoch enjoyed a sub-tropical climate; and this is rendered almost
certain by the discovery in the Miocene of France of fossil remains of
trogons and jungle-fowl. If, then, these Indian birds date back to the very
period during which alone Lemuria could have existed, that continent was
quite unnecessary for their introduction into Madagascar, as they could
have followed the same track as the mammalia of Miocene Europe and Asia;
while if, as I maintain, they are of more recent date, then Lemuria had
ceased to exist, and could not have been the means of their introduction.
_Submerged Islands between Madagascar and India._--Looking at the
accompanying map of the Indian Ocean, we see that between Madagascar and
India there are now extensive shoals and coral reefs, such as are usually
held to indicate subsidence; and we may therefore fairly postulate the
former existence here of several large islands, some of them not much
inferior to Madagascar itself. These reefs are all separated from each
other by very deep {425} sea--much deeper than that which divides
Madagascar from Africa, and we have therefore no reason to imagine their
former union. But they would nevertheless greatly facilitate the
introduction of Indian birds into the Mascarene Islands and Madagascar; and
these facilities existing, such an immigration would be sure to take place,
just as surely as American birds have entered the Galapagos and Juan
Fernandez, as European birds now reach the Azores, and as Australian birds
reach such a distant island as New Zealand. This would take place the more
certainly because the Indian Ocean is a region of violent periodical storms
at the changes of the monsoons, and we have seen in the case of the Azores
and Bermuda how important a factor this is in determining the transport of
birds across the ocean.
[Illustration: MAP OF THE INDIAN OCEAN.
Showing the position of banks less than 1,000 fathoms deep between Africa
and the Indian Peninsula.]
{426}
The final disappearance of these now sunken islands does not, in all
probability, date back to a very remote epoch; and this exactly accords
with the fact that some of the birds, as well as the fruit-bats of the
genus Pteropus, are very closely allied to Indian species, if not actually
identical, others being distinct species of the same genera. The fact that
not one closely-allied species or even genus of Indian or Malayan mammals
is found in Madagascar, sufficiently proves that it is no land-connection
that has brought about this small infusion of Indian birds and bats; while
we have sufficiently shown, that, when we go back to remote geological
times no land-connection in this direction was necessary to explain the
phenomena of the distribution of the Lemurs and Insectivora. A
land-connection with _some_ continent was undoubtedly necessary, or there
would have been no mammalia at all in Madagascar; and the nature of its
fauna on the whole, no less than the moderate depth of the intervening
strait and the comparative approximation of the opposite shores, clearly
indicate that the connection was with Africa.
_Concluding Remarks on "Lemuria."_--I have gone into this question in some
detail, because Dr. Hartlaub's criticism on my views has been reproduced in
a scientific periodical,[101] and the supposed Lemurian continent is
constantly referred to by quasi-scientific writers, as well as by
naturalists and geologists, as if its existence had been demonstrated by
facts, or as if it were absolutely necessary to postulate such a land in
order to account for the entire series of phenomena connected with the
Madagascar fauna, and especially with the distribution of the
Lemuridæ.[102] I {427} think I have now shown, on the other hand, that it
was essentially a provisional hypothesis, very useful in calling attention
to a remarkable series of problems in geographical distribution, but not
affording the true solution of those problems, any more than the hypothesis
of an Atlantis solved the problems presented by the Atlantic Islands and
the relations of the European and North American flora and fauna. The
Atlantis is now rarely introduced seriously except by the absolutely
unscientific, having received its death-blow by the chapter on Oceanic
Islands in the _Origin of Species_, and the researches of Professor Asa
Gray on the affinities of the North American and Asiatic floras. But
"Lemuria" still keeps its place--a good example of the survival of a
provisional hypothesis which offers what seems an easy solution of a
difficult problem, and has received an appropriate and easily remembered
name, long after it has been proved to be untenable.
It is now more than fifteen years since I first showed, by a careful
examination of all the facts to be accounted for, that the hypothesis of a
Lemurian continent was alike unnecessary to explain one portion of the
facts, and inadequate to explain the remaining portion.[103] Since that
time I have seen no attempt even to discuss the question on general grounds
in opposition to my views, nor on the other hand have those who have
hitherto supported the hypothesis taken any opportunity of acknowledging
its weakness and inutility. I have therefore here explained my reasons for
rejecting it somewhat more fully and in a more popular form, in the hope
that a check may thus be placed on the continued re-statement of this
unsound theory as if it were one of the accepted conclusions of modern
science.
{428}
_The Mascarene Islands._[104]--In the _Geographical Distribution of
Animals_, a summary is given of all that was known of the zoology of the
various islands near Madagascar, which to some extent partake of its
peculiarities, and with it form the Malagasy sub-region of the Ethiopian
region. As no great additions have since been made to our knowledge of the
fauna of these islands, and my object in this volume being more especially
to illustrate the mode of solving distributional problems by means of the
most suitable examples, I shall now confine myself to pointing out how far
the facts presented by these outlying islands support the views already
enunciated with regard to the origin of the Madagascar fauna.
_The Comoro Islands._--This group of islands is situated nearly midway
between the northern extremity of Madagascar and the coast of Africa. The
four chief islands vary between sixteen and forty miles in length, the
largest being 180 miles from the coast of Africa, while one or two smaller
islets are less than 100 miles from Madagascar. All are volcanic, Great
Comoro being an active volcano 8,500 feet high; and, as already stated,
they are situated on a submarine bank with less than 500 fathoms soundings,
connecting Madagascar with Africa. There is reason to believe, however,
that these islands are of comparatively recent origin, and that the bank
has been formed by matter ejected by the volcanoes or by upheaval. Anyhow,
there is no indication whatever of there having been here a land-connection
between Madagascar and Africa; while the islands themselves have been
mainly colonised from Madagascar, some of them making a near approach to
the 100-fathom bank which surrounds that island.
The Comoros contain two land mammals, a lemur and a civet, both of
Madagascar genera and the latter an identical species, and there is also a
peculiar species of fruit-bat (_Pteropus comorensis_), a group which ranges
from Australia to Asia and Madagascar but is unknown in Africa. Of
land-birds forty-one species are known, of {429} which sixteen are peculiar
to the islands, twenty-one are found also in Madagascar, and three found in
Africa and not in Madagascar; while of the peculiar species, six belong to
Madagascar or Mascarene genera. A species of Chameleon is also peculiar to
the islands.
These facts point to the conclusion that the Comoro Islands have been
formerly more nearly connected with Madagascar than they are now, probably
by means of intervening islets and the former extension of the latter
island to the westward, as indicated by the extensive shallow bank at its
northern extremity, so as to allow of the easy passage of birds, and the
occasional transmission of small mammalia by means of floating trees.[105]
_The Seychelles Archipelago._--This interesting group consists of about
thirty small islands situated 700 miles N.N.E. of Madagascar, or almost
exactly in the line formed by continuing the central ridge of that great
island. The Seychelles stand upon a rather extensive shallow bank, the
100-fathom line around them enclosing an area nearly 200 miles long by 100
miles wide, while the 500-fathom line shows an extension of nearly 100
miles in a southern direction. All the larger islands are of granite, with
mountains rising to 3,000 feet in Mahé, and to from 1,000 to 2,000 feet in
several of the other islands. We can therefore hardly doubt that they form
a portion of the great line of upheaval which produced the central granitic
mass of Madagascar, intervening points being indicated by the Amirantes,
the Providence, and the Farquhar Islands, which, though all coralline,
probably rest on a granitic basis. Deep channels of more than 1,000 fathoms
now separate these islands from each other, and if they were ever
sufficiently elevated to be united, it was probably at a very remote epoch.
The Seychelles may thus have had ample facilities for receiving from
Madagascar such immigrants as can pass over narrow seas; and, on the other
hand, they were equally favourably situated as regards the extensive Saya
de Malha and Cargados banks, which were probably once {430} large islands,
and may have supported a rich insular flora and fauna of mixed Mascarene
and Indian type. The existing fauna and flora of the Seychelles must
therefore be looked upon as the remnants which have survived the partial
submergence of a very extensive island; and the entire absence of
non-aërial mammalia may be due, either to this island having never been
actually united to Madagascar, or to its having since undergone so much
submergence as to have led to the extinction of such mammals as may once
have inhabited it. The birds and reptiles, however, though few in number,
are very interesting, and throw some further light on the past history of
the Seychelles.
_Birds of the Seychelles._--Fifteen indigenous land-birds are known to
inhabit the group, thirteen of which are peculiar species,[106] belonging
to genera which occur also in Madagascar or Africa. The genera which are
more peculiarly Indian are,--Copsychus and Hypsipetes, also found in
Madagascar; and Palæornis, which has species in Mauritius and Rodriguez, as
well as one on the continent of Africa. A black parrot (Coracopsis),
congeneric with two species that inhabit Madagascar and with one that is
peculiar to the Comoros; and a beautiful red-headed blue pigeon
(_Alectorænas pulcherrimus_) allied to those of Madagascar and Mauritius,
but very distinct, are the most remarkable species characteristic of this
group of islands.
_Reptiles and Amphibia of the Seychelles._--The reptiles and amphibia are
rather numerous and very interesting, indicating clearly that the islands
can hardly be classed as oceanic. There are seven species of lizards, three
being peculiar to the islands, while the others have rather a wide range.
The first is a chameleon--defenceless {431} slow-moving lizards, especially
abundant in Madagascar, from which no less than eighteen species are now
known, about the same number as on the continent of Africa. The Seychelles
species (_Chamæleon tigris_) also occurs at Zanzibar. The next are skinks
(Scincidæ), small ground-lizards with a wide distribution in the Eastern
hemisphere. Two species are however peculiar to the islands--_Mabuia
seychellensis_ and _M. wrightii_. The other peculiar species is one of the
geckoes (Geckotidæ) named _Æluronyx seychellensis_, and there are also
three other geckoes, _Phelsuma madagascarensis_, _Gehyra mutilata_ and
_Hemidactylus frenatus_, the two latter having a wide distribution in the
tropical regions of both hemispheres. These lizards, clinging as they do to
trees and timber, are exceedingly liable to be carried in ships from one
country to another, and I am told by Dr. Günther that some are found almost
every year in the London Docks. It is therefore probable, that when species
of this family have a very wide range they have been assisted in their
migrations by man, though their habit of clinging to trees also renders
them likely to be floated with large pieces of timber to considerable
distances. Dr. Percival Wright, to whom I am indebted for much information
on the productions of the Seychelles Archipelago, informs me that the
last-named species varies greatly in colour in the different islands, so
that he could always tell from which particular island a specimen had been
brought. This is analogous to the curious fact of certain lizards on the
small islands in the Mediterranean being always very different in colour
from those of the mainland, usually becoming rich blue or black (see
_Nature_, Vol. XIX. p. 97); and we thus learn how readily in some cases
differences of colour are brought about, either directly or indirectly, by
local conditions.
Snakes, as is usually the case in small or remote islands, are far less
numerous than lizards, only two species being known. One, _Dromicus
seychellensis_, is a peculiar species of the family Colubridæ, the rest of
the genus being found in Madagascar and South America. The other, _Boodon
geometricus_, one of the Lycodontidæ, or fanged ground-snakes, is also
peculiar. So far, then, as the reptiles are {432} concerned, there is
nothing but what is easily explicable by what we know of the general means
of distribution of these animals.
We now come to the Amphibia, which are represented in the Seychelles by two
tailless and two serpent-like forms. The frogs are _Rana mascareniensis_,
found also in Mauritius, Bourbon, Angola, and Abyssinia, and probably all
over tropical Africa; and _Megalixalus seychellensis_ a peculiar tree-frog
having allies in Madagascar and tropical Africa. It is found, Dr. Wright
informs me, on the Pandani or screw-pines; and as these form a very
characteristic portion of the vegetation of the Mascarene Islands, all the
species being peculiar and confined each to a single island or small group,
we may perhaps consider it as a relic of the indigenous fauna of that more
extensive land of which the present islands are the remains.
The serpentine Amphibia are represented by two species of Cæcilia. These
creatures externally resemble large worms, except that they have a true
head with jaws and rudimentary eyes, while internally they have of course a
true vertebrate skeleton. They live underground, burrowing by means of the
ring-like folds of the skin which simulate the jointed segments of a worm's
body, and when caught they exude a viscid slime. The young have external
gills which are afterwards replaced by true lungs, and this peculiar
metamorphosis shows that they belong to the amphibia rather than to the
reptiles. The Cæcilias are widely but very sparingly distributed through
all the tropical regions; a fact which may, as we have seen, be taken as an
indication of the great antiquity of the group, and that it is now verging
towards extinction. In the Seychelles Islands there appear to be three
species of these singular animals. _Cryptopsophis multiplicatus_ is
confined to the islands; _Herpele squalostoma_ is found also in Western
India and in Africa; while _Hypogeophis rostratus_ inhabits both West
Africa and South America.[107] This last is certainly one of the most
remarkable cases of the wide and discontinuous distribution of a species;
and {433} when we consider the habits of life of these animals and the
extreme slowness with which it is likely they can migrate into new areas,
we can hardly arrive at any other conclusion than that this species once
had an almost world-wide range, and that in the process of dying out it has
been left stranded, as it were, in these three remote portions of the
globe. The extreme stability and long persistence of specific form which
this implies is extraordinary, but not unprecedented, among the lower
vertebrates. The crocodiles of the Eocene period differ but slightly from
those of the present day, while a small freshwater turtle from the Pliocene
deposits of the Siwalik Hills is absolutely identical with a still living
Indian species, _Emys tectus_. The mud-fish of Australia, _Ceratodus
forsteri_ is a very ancient type, and may well have remained specifically
unchanged since early Tertiary times. It is not, therefore, incredible that
this Seychelles Cæcilia may be the oldest land vertebrate now living on the
globe; dating back to the early part of the Tertiary period, when the warm
climate of the northern hemisphere in high latitudes and the union of the
Asiatic and American continents allowed of the migration of such types over
the whole northern hemisphere, from which they subsequently passed into the
southern hemisphere, maintaining themselves only in certain limited areas,
where the physical conditions were especially favourable, or where they
were saved from the attacks of enemies or the competition of higher forms.
_Fresh-water Fishes._--The only other vertebrates in the Seychelles are two
fresh-water fishes abounding in the streams and rivulets. One, _Haplochilus
playfairii_ is peculiar to the islands, but there are allied species in
Madagascar. It is a pretty little fish about four inches long, of an olive
colour, with rows of red spots, and is very abundant in some of the
mountain streams. The fishes of this genus, as I am informed by Dr.
Günther, often inhabit both sea and fresh water, so that their migration
from {434} Madagascar to the Seychelles and subsequent modification, offers
no difficulty. The other species is _Fundulus orthonotus_, found also on
the east coast of Africa; and as both belong to the same
family--Cyprinodontidæ--this may possibly have migrated in a similar
manner.
_Land-shells._--The only other group of animals inhabiting the Seychelles
which we know with any approach to completeness, are the land and
fresh-water mollusca, but they do not furnish any facts of special
interest. About forty species are known, and Mr. Geoffrey Nevill, who has
studied them, thinks their meagre number is chiefly owing to the
destruction of so much of the forests which once covered the islands. Seven
of the species--and among them one of the most conspicuous, _Achatina
fulica_--have almost certainly been introduced; and the remainder show a
mixture of Madagascar and Indian forms, with a preponderance of the latter.
Five genera--Streptaxis, Cyathoponea, Onchidium, Helicina and Paludomus,
are mentioned as being especially Indian, while only two--Tropidophora and
Gibbus, are found in Madagascar but not in India.[108] About two-thirds of
the species appear to be peculiar to the islands.
_Mauritius, Bourbon and Rodriguez._--These three islands are somewhat out
of place in this chapter, because they really belong to the oceanic group,
being of volcanic formation, surrounded by deep sea, and possessing no
indigenous mammals or amphibia. Yet their productions are so closely
related to those of Madagascar, to which they may be considered as
attendant satellites, that it is absolutely necessary to associate them
together if we wish to comprehend and explain their many interesting
features.
Mauritius and Bourbon are lofty volcanic islands, evidently of great
antiquity. They are about 100 miles apart, and the sea between them is less
than 1,000 fathoms deep, while on each side it sinks rapidly to depths of
2,400 and 2,600 fathoms. We have therefore no reason to believe that they
have ever been connected with {435} Madagascar, and this view is strongly
supported by the character of their indigenous fauna. Of this, however, we
have not a very complete or accurate knowledge, for though both islands
have long been occupied by Europeans, the study of their natural products
was for a long time greatly neglected, and owing to the rapid spread of
sugar cultivation, the virgin forests, and with them no doubt many native
animals, have been almost wholly destroyed. There is, however, no good
evidence of there ever having been any indigenous mammals or amphibia,
though both are now found and are often recorded among the native
animals.[109]
The smaller and more remote island, Rodriguez, is also volcanic; but it
has, besides a good deal of coralline rock, an indication of partial
submergence helping to account for the poverty of its fauna and flora. It
stands on a 100-fathom bank of considerable extent, but beyond this the
{436} sea rapidly deepens to more than 2,000 fathoms, so that it is truly
oceanic like its larger sister isles.
_Birds._--The living birds of these islands are few in number and consist
mainly of peculiar species of Mascarene types, together with two peculiar
genera--Oxynotus belonging to the Campephagidæ or caterpillar-catchers, a
family abundant in the old-world tropics; and a dove, Trocazza, forming a
peculiar sub-genus. The origin of these birds offers no difficulty, looking
at the position of the islands and of the surrounding shoals and islets.
_Extinct Birds._--These three islands are, however, preeminently remarkable
as having been the home of a group of large ground-birds, quite incapable
of flight, and altogether unlike anything found elsewhere on the globe; and
which, though once very abundant, have become totally extinct within the
last two hundred years. The best known of these birds is the dodo, which
inhabited Mauritius; while allied species certainly lived in Bourbon and
Rodriguez, abundant remains of the species of the latter island--the
"solitaire," having been discovered, corresponding with the figure and
description given of it by Legouat, who resided in Rodriguez in 1692. These
birds constitute a distinct family, Dididæ, allied to the pigeons but very
isolated. They were quite defenceless, and were rapidly exterminated when
man introduced dogs, pigs, and cats into the island, and himself sought
them for food. The fact that such perfectly unprotected creatures survived
in great abundance to a quite recent period in these three islands only,
while there is no evidence of their ever having inhabited any other
countries whatever, is itself almost demonstrative that Mauritius, Bourbon,
and Rodriguez are very ancient but truly oceanic islands. From what we know
of the general similarity of Miocene birds to living genera and families,
it seems clear that the origin of so remarkable a type as the dodos must
date back to early Tertiary times. If we suppose some ancestral
ground-feeding pigeon of large size to have reached the group by means of
intervening islands afterwards submerged, and to have thenceforth remained
to increase and multiply unchecked by the attacks of any more {437}
powerful animals, we can well understand that the wings, being useless,
would in time become almost aborted.[110] It is also not improbable that
this process would be aided by natural selection, because the use of wings
might be absolutely prejudicial to the birds in their new home. Those that
flew up into trees to roost, or tried to cross over the mouths of rivers,
might be blown out to sea and destroyed, especially during the hurricanes
which have probably always more or less devastated the islands; while on
the other hand the more bulky and short-winged individuals, who took to
sleeping on the ground in the forest, would be preserved from such dangers,
and perhaps also from the attacks of birds of prey which may always have
visited the islands. But whether or no this was the mode by which these
singular birds acquired their actual form and structure, it is perfectly
certain that their existence and development depended on complete isolation
and on freedom from the attacks of enemies. We have no single example of
such defenceless birds having ever existed on a continent at any geological
period, whereas analogous though totally distinct forms do exist in New
Zealand, where enemies are equally wanting. On the other hand, every
continent has always produced abundance of carnivora adapted to prey upon
the herbivorous animals inhabiting it at the same period; and we may
therefore be sure that {438} these islands have never formed part of a
continent during any portion of the time when the dodos inhabited them.
It is a remarkable thing that an ornithologist of Dr. Hartlaub's
reputation, looking at the subject from a purely ornithological point of
view, should yet entirely ignore the evidence of these wonderful and unique
birds against his own theory, when he so confidently characterises Lemuria
as "that sunken land, which, containing parts of Africa, must have extended
far eastward over Southern India and Ceylon, and the highest points of
which we recognise in the volcanic peaks of Bourbon and Mauritius, and in
the central range of Madagascar itself--the last resorts of the mostly
extinct Lemurine race which formerly peopled it."[111] It is here implied
that lemurs formerly inhabited Bourbon and Mauritius, but of this there is
not a particle of evidence, and we feel pretty sure that had they done so
the dodos would never have been developed there. In Madagascar there are no
traces of dodos, while there are remains of extinct gigantic struthious
birds of the genus Æpyornis, which were no doubt as well able to protect
themselves against the smaller carnivora as are the ostriches, emus, and
cassowaries in their respective countries at the present day.
The whole of the evidence at our command, therefore, tends to establish in
a very complete manner the "oceanic" character of the three
islands--Mauritius, Bourbon, and Rodriguez, and that they have never formed
part of "Lemuria" or of any continent.
_Reptiles._--Mauritius, like Bourbon, has lizards, some of which are
peculiar species; but no snakes, and no frogs or toads but such as have
been introduced.[112] Strange to say, however, a small islet called Round
Island, only about a mile across, and situated about fourteen miles
north-east of Mauritius, possesses a snake which is not only unknown in
Mauritius, but also in any other part of the world, being {439} altogether
confined to this minute islet! It belongs to the boa family, and forms a
peculiar and very distinct genus, Casaria, whose nearest allies seem to be
the Ungalia of Cuba and Bolyeria of Australia. It is hardly possible to
believe that this serpent has very long maintained itself on so small an
island; and though we have no record of its existence on Mauritius, it may
very well have inhabited the lowland forests without being met with by the
early settlers; and the introduction of swine, which soon ran wild and
effected the final destruction of the dodo, may also have been fatal to
this snake. It is, however, now almost certainly confined to the one small
islet, and is probably the land-vertebrate of most restricted distribution
on the globe.
On the same island there is a small lizard, _Scelotes bojeri_, recorded
also from Mauritius and Bourbon, though it appears to be rare in both
islands; but a gecko, _Phelsuma guentheri_, is restricted to the island. As
Round Island is connected with Mauritius by a bank under a hundred fathoms
below the surface, it has probably been once joined to it, and when first
separated would have been both much larger and much nearer the main island,
circumstances which would greatly facilitate the transmission of these
reptiles to their present dwelling-place, where they have been able to
maintain themselves owing to the complete absence of competition, while
some of them have become extinct in the larger island.
_Flora of Madagascar and the Mascarene Islands._--The botany of the great
island of Madagascar has been perhaps more thoroughly explored than that of
the opposite coasts of Africa, so that its peculiarities may not be really
so great as they now appear to be. Yet there can be no doubt of its extreme
richness and grandeur, its remarkable speciality, and its anomalous
external relations. It is characterised by a great abundance of
forest-trees and shrubs of peculiar genera or species, and often adorned
with magnificent flowers. Some of these are allied to African forms, others
to those of Asia, and it is said that of the two affinities the latter
preponderates. But there are also, as in the animal world, some decided
South {440} American relations, while other groups point to Australia, or
are altogether isolated.
No less than 3,740 flowering plants are now known from Madagascar with 360
ferns and fern-allies. The most abundant natural orders are the following:
Species.
Leguminosæ 346
Ferns 318
Compositæ 281
Euphorbiaceæ 228
Orchideæ 170
Cyperaceæ 160
Rubiaceæ 147
Acanthaceæ 131
Gramineæ 130
The flora contains representatives of 144 natural orders and 970 genera,
one of the former and 148 of the latter being peculiar to the island. The
peculiar order, Chælnaceæ, comprises seven genera and twenty-four species;
while Rubiaceæ and Compositæ have the largest number of peculiar genera,
followed by Leguminosæ and Melastomaceæ. Nearly three-fourths of the
species are endemic.
Beautiful flowers are not conspicuous in the flora of Madagascar, though it
contains several magnificent flowering plants. A shrub with the dreadful
name _Harpagophytum Grandidieri_ has bunches of gorgeous red flowers;
_Tristellateia madagascariensis_ is a climbing plant with spikes of rich
yellow flowers; while _Poinciana regia_, a tall tree, _Rhodolæna altivola_
and _Astrapoea Wallichii_, shrubs, are among the most magnificent flowering
plants in the world. _Disa Buchenaviana_, _Commelina madagascarica_, and
_Tachiadenus platypterus_ are fine blue-flowered plants, while the superb
orchid _Angræcum sesquipedale_, _Vinca rosea_, _Euphorbia splendens_, and
_Stephanotis floribunda_, have been long cultivated in our hot-houses.
There are also many handsome Combretaceæ, Rubiaceæ, and Leguminosæ; but, as
in most tropical regions, this wealth of floral beauty has to be searched
for, and produces little effect in the landscape.
The affinities of the Madagascar flora are to a great extent in accordance
with those of the fauna. The tropical portion of the flora agrees closely
with that of tropical Africa, while the plants of the highlands are {441}
equally allied to those of the Cape and of the mountains of Central Africa.
Some Asiatic types are present which do not occur in Africa; and even the
curious American affinities of some of the animals are reproduced in the
vegetable kingdom. These last are so interesting that they deserve to be
enumerated. An American genus of Euphorbiaceæ, Omphalea, has one species in
Madagascar, and Pedilanthus, another genus of the same natural order, has a
similar distribution. Myrosma, an American genus of Scitamineæ has one
Madagascar species; while the celebrated "travellers' tree," _Ravenala
madagascariensis_, belonging to the order Musaceæ, has its nearest ally in
a plant inhabiting N. Brazil and Guiana. Echinolæna, a genus of grasses,
has the same distribution.[113]
Of the flora of the smaller Madagascarian islands we possess a fuller
account, owing to the recent publication of Mr. Baker's _Flora of the
Mauritius and the Seychelles_, including also Rodriguez. The total number
of species in this flora is 1,058, more than half of which (536) are
exclusively Mascarene--that is, found only in some of the islands of the
Madagascar group, while nearly a third (304) are endemic or confined to
single islands. Of the widespread plants sixty-six are found in Africa but
not in Asia, and eighty-six in Asia but not in Africa, showing a similar
Asiatic preponderance to what is said to occur in Madagascar. With the
genera, however, the proportions are different, for I find by going through
the whole of the generic distributions as given by Mr. Baker, that out of
the 440 genera of wild plants fifty are endemic, twenty-two are Asiatic but
not African, while twenty-eight are African but not Asiatic. This implies
that the more ancient connection has been on the side of Africa, while a
more recent immigration, shown by identity of species, has come from the
side of Asia; and it is already certain that when the flora of Madagascar
is more thoroughly worked out, a still greater African preponderance will
be found in that island.
{442}
A few Mascarene genera are found elsewhere only in South America,
Australia, or Polynesia; and there are also a considerable number of genera
whose metropolis is South America, but which are represented by one or more
species in Madagascar, and by a single often widely distributed species in
Africa. This fact throws light upon the problem offered by those mammals,
reptiles, and insects of Madagascar which now have their only allies in
South America, since the two cases would be exactly parallel were the
African plants to become extinct. Plants, however, are undoubtedly more
long-lived specifically than animals--especially the more highly organised
groups, and are less liable to complete extinction through the attacks of
enemies or through changes of climate or of physical geography; hence we
find comparatively few cases in which groups of Madagascar plants have
their _only_ allies in such distant regions as America and Australia, while
such cases are numerous among animals, owing to the extinction of the
allied forms in intervening areas, for which extinction, as we have already
shown, ample cause can be assigned.
_Curious Relations of Mascarene Plants._--Among the curious affinities of
Mascarene plants we have culled the following from Mr. Baker's volume.
Trochetia, a genus of Sterculiaceæ, has four species in Mauritius, one in
Madagascar, and one in the remote island of St. Helena. Mathurina, a genus
of Turneraceæ, consisting of a single species peculiar to Rodriguez, has
its nearest ally in another monotypic genus, Erblichia, confined to Central
America. Siegesbeckia, one of the Compositæ, consists of two species, one
inhabiting the Mascarene islands, the other Peru. Labourdonasia, a genus of
Sapotaceæ, has two species in Mauritius, one in Natal, and one in Cuba.
Nesogenes, belonging to the verbena family, has one species in Rodriguez
and one in Polynesia. Mespilodaphne, an extensive genus of Lauraceæ, has
six species in the Mascarene islands, and all the rest (about fifty
species) in South America. Nepenthes, the well-known pitcher plants, are
found chiefly in the Malay Islands, South China, and Ceylon, with species
in the Seychelles Islands, {443} and in Madagascar. Milla, a large genus of
Liliaceæ, is exclusively American, except one species found in Mauritius
and Bourbon. Agauria, a genus of Ericaceæ, is found in Madagascar, the
Mascarene islands, the plateau of Central Africa, and the Camaroon
Mountains in West Africa. An acacia, found in Mauritius and Bourbon (_A.
heterophylla_), can hardly be separated specifically from _Acacia koa_ of
the Sandwich Islands. The genus Pandanus, or screw-pine, has sixteen
species in the three islands--Mauritius, Rodriguez, and the Seychelles--all
being peculiar, and none ranging beyond a single island. Of palms there are
fifteen species belonging to ten genera, and all these genera are peculiar
to the islands. We have here ample evidence that plants exhibit the same
anomalies of distribution in these islands as do the animals, though in a
smaller proportion; while they also exhibit some of the transitional stages
by which these anomalies have, in all probability, been brought about,
rendering quite unnecessary any other changes in the distribution of sea
and land than physical and geological evidence warrants.[114]
{444}
_Fragmentary Character of the Mascarene Flora._--Although the peculiar
character and affinities of the vegetation of these islands is sufficiently
apparent, there can be little doubt that we only possess a fragment of the
rich flora which once adorned them. The cultivation of sugar, and other
tropical products, has led to the clearing away of the virgin forests from
all the lowlands, plateaus, and accessible slopes of the mountains, so that
remains of the aboriginal woodlands only linger in the recesses of the
hills, and numbers of forest-haunting plants must inevitably have been
exterminated. The result is, that nearly three hundred species of foreign
plants have run wild in Mauritius, and have in their turn helped to
extinguish the native {445} species. In the Seychelles, too, the indigenous
flora has been almost entirely destroyed in most of the islands, although
the peculiar palms, from their longevity and comparative hardiness, have
survived. Mr. Geoffrey Nevill tells us, that at Mahé, and most of the other
islands visited by him, it was only in a few spots near the summits of the
hills that he could perceive any remains of the ancient flora. Pine-apples,
cinnamon, bamboos, and other plants have obtained a firm footing, covering
large tracts of country and killing the more delicate native flowers and
ferns. The pine-apple, especially, grows almost to the tops of the
mountains. Where the timber and shrubs have been destroyed, the water
falling on the surface immediately cuts channels, runs off rapidly, and
causes the land to become dry and arid; and the same effect is largely seen
both in Mauritius and Bourbon, where, originally, dense forest covered the
entire surface, and perennial moisture, with its ever-accompanying
luxuriance of vegetation, prevailed.
_Flora of Madagascar Allied to that of South Africa._--In my _Geographical
Distribution of Animals_ I have remarked on the relation between the
insects of Madagascar and those of south temperate Africa, and have
speculated on a great _southern_ extension of the continent at the time
when Madagascar was united with it. As supporting this view I now quote Mr.
Bentham's remarks on the Compositæ. He says: "The connections of the
Mascarene endemic Compositæ, especially those of Madagascar itself, are
eminently with the southern and sub-tropical African races; the more
tropical races, Plucheineæ, &c., may be rather more of an Asiatic type." He
further says that the Composite flora is almost as strictly endemic as that
of the Sandwich Islands, and that it is much diversified, with evidences of
great antiquity, while it shows insular characteristics in the tendency to
tall shrubby or arborescent forms in several of the endemic or prevailing
genera.
_Preponderance of Ferns in the Mascarene Flora._--A striking character of
the flora of these smaller Mascarene islands is the great preponderance of
ferns, and next to them of orchideæ. The following figures are taken from
{446} Mr. Baker's _Flora_ for Mauritius and the Seychelles, and from an
estimate by M. Frappier of the flora of Bourbon given in Maillard's volume
already quoted:--
_Mauritius, &c._ _Bourbon._
Ferns 168 Ferns 240
Orchideæ 79 Orchideæ 120
Gramineæ 69 Gramineæ 60
Cyperaceæ 62 Compositæ 60
Rubiaceæ 57 Leguminosæ 36
Euphorbiaceæ 45 Rubiaceæ 24
Compositæ 43 Cyperaceæ 24
Leguminosæ 41 Euphorbiaceæ 18
The cause of the great preponderance of ferns in oceanic islands has
already been discussed in my book on _Tropical Nature_; and we have seen
that Mauritius, Bourbon, and Rodriguez must be classed as such, though from
their proximity to Madagascar they have to be considered as satellites to
that great island. The abundance of orchids, the reverse of what occurs in
remoter oceanic islands, may be in part due to analogous causes. Their
usually minute and abundant seeds would be as easily carried by the wind as
the spores of ferns, and their frequent epiphytic habit affords them an
endless variety of stations on which to vegetate, and at the same time
removes them in a great measure from the competition of other plants. When,
therefore, the climate is sufficiently moist and equable, and there is a
luxuriant forest vegetation, we may expect to find orchids plentiful on
such tropical islands as possess an abundance of insects adapted to
fertilise them, and which are not too far removed from other lands or
continents from which their seeds might be conveyed.
_Concluding Remarks on Madagascar and the Mascarene Islands._--There is
probably no portion of the globe that contains within itself so many and
such varied features of interest connected with geographical distribution,
or which so well illustrates the mode of solving the problems it presents,
as the comparatively small insular region which comprises the great island
of Madagascar and the smaller islands and island-groups which immediately
surround it. In Madagascar we have a continental island of the first rank,
and undoubtedly of immense antiquity; we have detached fragments of this
island in the Comoros and {447} Aldabra; in the Seychelles we have the
fragments of another very ancient island, which may perhaps never have been
continental; in Mauritius, Bourbon, and Rodriguez we have three undoubtedly
oceanic islands; while in the extensive banks and coral reefs of Cargados,
Saya de Malha, the Chagos, and the Maldive Isles, we have indications of
the submergence of many large islands which may have aided in the
transmission of organisms from the Indian Peninsula. But between and around
all these islands we have depths of 2,500 fathoms and upwards, which
renders it very improbable that there has ever been here a continuous land
surface, at all events during the Tertiary or Secondary periods of geology.
It is most interesting and satisfactory to find that this conclusion,
arrived at solely by a study of the form of the sea-bottom and the general
principle of oceanic permanence, is fully supported by the evidence of the
organic productions of the several islands; because it gives us confidence
in those principles, and helps to supply us with a practical demonstration
of them. We find that the entire group contains just that amount of Indian
forms which could well have passed from island to island; that many of
these forms are slightly modified species, indicating that the migration
occurred during late Tertiary times, while others are distinct genera,
indicating a more ancient connection; but in no one case do we find animals
which necessitate an actual land-connection, while the numerous Indian
types of mammalia, reptiles, birds, and insects, which must certainly have
passed over had there been such an actual land-connection, are totally
wanting. The one fact which has been supposed to require such a
connection--the distribution of the lemurs--can be far more naturally
explained by a general dispersion of the group from Europe, where we know
it existed in Eocene times; and such an explanation applies equally to the
affinity of the Insectivora of Madagascar and Cuba; the snakes
(Herpetodryas, &c.) of Madagascar and America; and the lizards
(Cryptoblepharus) of Mauritius and Australia. To suppose, in all these
cases, and in many others, a direct land-connection, is really absurd,
because {448} we have the evidence afforded by geology of wide differences
of distribution directly we pass beyond the most recent deposits; and when
we go back to Mesozoic--and still more to Palæozoic--times, the majority of
the groups of animals and plants appear to have had a world-wide range. A
large number of our European Miocene genera of vertebrates were also Indian
or African, or even American; the South American Tertiary fauna contained
many European types; while many Mesozoic reptiles and mollusca ranged from
Europe and North America to Australia and New Zealand.
By very good evidence (the occurrence of wide areas of marine deposits of
Eocene age), geologists have established the fact that Africa was cut off
from Europe and Asia by an arm of the sea in early Tertiary times, forming
a large island-continent. By the evidence of abundant organic remains we
know that all the types of large mammalia now found in Africa (but which
are absent from Madagascar) inhabited Europe and Asia, and many of them
also North America, in the Miocene period. At a still earlier epoch Africa
may have received its lower types of mammals--lemurs, insectivora, and
small carnivora, together with its ancestral struthious birds, and its
reptiles and insects of American or Australian affinity; and at this period
it was joined to Madagascar. Before the later continental period of Africa,
Madagascar had become an island; and thus, when the large mammalia from the
northern continent overran Africa, they were prevented from reaching
Madagascar, which thenceforth was enabled to develop its singular forms of
low-type mammalia, its gigantic ostrich-like Æpyornis, its isolated birds,
its remarkable insects, and its rich and peculiar flora. From it the
adjacent islands received such organisms as could cross the sea; while they
transmitted to Madagascar some of the Indian birds and insects which had
reached them.
The method we have followed in these investigations is to accept the
results of geological and palæontological science, and the ascertained
facts as to the powers of dispersal of the various animal groups; to take
full account of the laws of evolution as affecting distribution, {449} and
of the various ocean depths as implying recent or remote union of islands
with their adjacent continents; and the result is, that wherever we possess
a sufficient knowledge of these various classes of evidence, we find it
possible to give a connected and intelligible explanation of all the most
striking peculiarities of the organic world. In Madagascar we have
undoubtedly one of the most difficult of these problems; but we have, I
think, fairly met and conquered most of its difficulties. The complexity of
the organic relations of this island is due, partly to its having derived
its animal forms from two distinct sources--from one continent through a
direct land-connection, and from another by means of intervening islands
now submerged; but, mainly to the fact of its having been separated from a
continent which is now, zoologically, in a very different condition from
that which prevailed at the time of the separation; and to its having been
thus able to preserve a number of types which may date back to the Eocene,
or even to the Cretaceous, period. Some of these types have become
altogether extinct elsewhere; others have spread far and wide over the
globe, and have survived only in a few remote countries--and especially in
those which have been more or less secured by their isolated position from
the incursions of the more highly-developed forms of later times. This
explains why it is that the nearest allies of the Madagascar fauna and
flora are now so often to be found in South America or Australia--countries
in which low forms of mammalia and birds still largely prevail;--it being
on account of the long-continued isolation of all these countries that
similar forms (descendants of ancient types) are preserved in them. Had the
numerous suggested continental extensions connecting these remote
continents at various geological periods been realities, the result would
have been that all these interesting archaic forms, all these defenceless
insular types, would long ago have been exterminated, and one comparatively
monotonous fauna have reigned over the whole earth. So far from explaining
the anomalous facts, the alleged continental extensions, had they existed,
would have left no such facts to be explained.
* * * * *
{450}
CHAPTER XX
ANOMALOUS ISLANDS: CELEBES
Anomalous Relations of Celebes--Physical Features of the
Island--Zoological Character of the Islands Around Celebes--The Malayan
and Australian Banks--Zoology of Celebes: Mammalia--Probable Derivation
of the Mammals of Celebes--Birds of Celebes--Bird-types Peculiar to
Celebes--Celebes not Strictly a Continental Island--Peculiarities of
the Insects of Celebes--Himalayan Types of Birds and Butterflies in
Celebes--Peculiarities of Shape and Colour of Celebesian
Butterflies--Concluding Remarks--Appendix on the Birds of Celebes.
The only other islands of the globe which can be classed as "ancient
continental" are the larger Antilles (Cuba, Haiti, Jamaica, and Porto
Rico), Iceland, and perhaps Celebes. The Antilles have been so fully
discussed and illustrated in my former work, and there is so little fresh
information about them, that I do not propose to treat of them here,
especially as they fall short of Madagascar in all points of biological
interest, and offer no problems of a different character from such as have
already been sufficiently explained.
Iceland, also, must apparently be classed as belonging to the "Ancient
Continental Islands," for though usually described as wholly volcanic, it
is, more probably, an island of varied geological structure buried under
the lavas of its numerous volcanoes. But of late years extensive Tertiary
deposits of Miocene age have been discovered, showing that it is not a mere
congeries of {451} volcanoes; it is connected with the British Islands and
with Greenland by seas less than 500 fathoms deep; and it possesses a few
mammalia, one of which is peculiar, and at least three peculiar species of
birds. It was therefore almost certainly united with Greenland, and
probably with Europe by way of Britain, in the early part of the Tertiary
period, and thus afforded one of the routes by which that intermigration of
American and European animals and plants was effected which we know
occurred during some portion of the Eocene and Miocene periods, and
probably also in the Pliocene. The fauna and flora of this island are,
however, so poor, and offer so few peculiarities, that it is unnecessary to
devote more time to their consideration.
There remains the great Malay island--Celebes, which, owing to its
possession of several large and very peculiar mammalia, must be classed,
zoologically, as "ancient continental"; but whose central position and
relations both to Asia and to Australia render it very difficult to decide
in which of the primary zoological regions it ought to be placed, or
whether it has ever been united with either of the great continents.
Although I have pretty fully discussed its zoological peculiarities and
past history in my _Geographical Distribution of Animals_, it seems
advisable to review the facts on the present occasion, more especially as
the systematic investigation of the characteristics of continental islands
we have now made will place us in a better position for determining its
true zoo-geographical relations.
_Physical Features of Celebes._--This large and still comparatively
unexplored island is interesting to the geographer on account of its
remarkable outline, but much more so to the zoologist for its curious
assemblage of animal forms. The geological structure of Celebes is almost
unknown. The extremity of the northern peninsula is volcanic; while in the
southern peninsula there are extensive deposits of a crystalline limestone,
in some places overlying basalt. Gold is found in the northern peninsula
and in the central mass, as well as iron, tin, and copper in small
quantities; so that there can be little {452} doubt that the mountain
ranges of the interior consist of ancient stratified rocks.
[Illustration: MAP OF CELEBES AND THE SURROUNDING ISLANDS.
The depth of sea is shown by three tints: the lightest indicating less than
100 fathoms, the medium tint less than 1,000 fathoms, and the dark tint
more than 1,000 fathoms. The figures show depths in fathoms.]
It is not yet known whether Celebes is completely separated from the
surrounding islands by a deep sea, but {453} the facts at our command
render it probable that it is so. The northern and eastern portions of the
Celebes Sea have been ascertained to be from 2,000 to 2,600 fathoms deep,
and such depths may extend over a considerable portion of it, or even be
much exceeded in the centre. In the Molucca passage a single sounding on
the Gilolo side gave 1,200 fathoms, and a large part of the Molucca and
Banda Seas probably exceed 2,000 fathoms. The southern portion of the
Straits of Macassar is full of coral reefs, and a shallow sea of less than
100 fathoms extends from Borneo to within about forty miles of the western
promontory of Celebes; but farther north there is deep water close to the
shore, and it seems probable that a deep channel extends quite through the
straits, which have no doubt been much shallowed by the deposits from the
great Bornean rivers as well as by those of Celebes itself. Southward
again, the chain of volcanic islands from Bali to Timor appears to rise out
of a deep ocean, the few soundings we possess showing depths of from 670 to
1,300 fathoms almost close to their northern shores. We seem justified,
therefore, in concluding that Celebes is entirely surrounded by a deep sea,
which has, however, become partially filled up by river deposits, by
volcanic upheaval, or by coral reefs. Such shallows, where they exist, may
therefore be due to antiquity and isolation, instead of being indications
of a former union with any of the surrounding islands.
_Zoological Character of the Islands around Celebes._--In order to have a
clear conception of the peculiar character of the Celebesian fauna, we must
take into account that of the surrounding countries from which we may
suppose it to have received immigrants. These we may divide broadly into
two groups, those on the west belonging to the Oriental region of our
zoological geography, and those on the east belonging to the Australian
region. Of the first group Borneo is a typical representative; and from its
proximity and the extent of its opposing coasts it is the island which we
should expect to show most resemblance to Celebes. We have already seen
that the fauna of Borneo is essentially the same as that of Southern Asia,
and that it is excessively rich in all the Malayan types of {454} mammalia
and birds. Java and Bali closely resemble Borneo in general character,
though somewhat less rich and with several peculiar forms; while the
Philippine Islands, though very much poorer, and with a greater amount of
speciality, yet exhibit essentially the same character. These islands,
taken as a whole, may be described as having a fauna almost identical with
that of Southern Asia; for no family of mammalia is found in the one which
is absent from the other, and the same may be said, with very few and
unimportant exceptions, of the birds; while hundreds of genera and of
species are common to both.
In the islands east and south of Celebes--the Moluccas, New Guinea, and the
Timor group from Lombok eastward--we find, on the other hand, the most
wonderful contrast in the forms of life. Of twenty-seven families of
terrestrial mammals found in the great Malay islands, all have disappeared
but four, and of these it is doubtful whether two have not been introduced
by man. We also find here four families of Marsupials, all totally unknown
in the western islands. Even birds, though usually more widely spread, show
a corresponding difference, about eleven Malayan families being quite
unknown east of Celebes, where six new families make their appearance which
are equally unknown to the westward.[115]
We have here a radical difference between two sets of islands not very far
removed from each other, the one set belonging zoologically to Asia, the
other to Australia. The Asiatic or Malayan group is found to be bounded
strictly by the eastward limits of the great bank (for the most part less
than fifty fathoms below the surface) which {455} stretches out from the
Siamese and Malayan peninsula as far as Java, Sumatra, Borneo, and the
Philippines. To the east another bank unites New Guinea and the Papuan
Islands as far as Aru, Mysol, and Waigiou, with Australia; while the
Moluccas and Timor groups are surrounded by much deeper water, which forms,
in the Banda and Celebes Seas and perhaps in other parts of this area,
great basins of enormous depths (2,000 to 3,000 fathoms or even more)
enclosed by tracts under a thousand fathoms, which separate the basins from
each other and from the adjacent Pacific and Indian Oceans (see map). This
peculiar formation of the sea-bottom probably indicates that this area has
been the seat of great local upheavals and subsidences; and it is quite in
accordance with this view that we find the Moluccas, while closely agreeing
with New Guinea in their forms of life, yet strikingly deficient in many
important groups, and exhibiting an altogether poverty-stricken appearance
as regards the higher animals. It is a suggestive fact that the Philippine
Islands bear an exactly parallel relation to Borneo, being equally
deficient in many of the higher groups; and here too, in the Sooloo Sea, we
find a similar enclosed basin of great depth. Hence we may in both cases
connect, on the one hand, the extensive area of land-surface and of
adjacent shallow sea with a long period of stability and a consequent rich
development of the forms of life; and, on the other hand, a highly broken
land-surface with the adjacent seas of great but very unequal depths, with
a period of disturbance, probably involving extensive submersions of the
land, resulting in a scanty and fragmentary vertebrate fauna.
_Zoology of Celebes._--The zoology of Celebes differs so remarkably from
that of both the great divisions of the Archipelago above indicated, that
it is very difficult to decide in which to place it. It possesses only
about sixteen species of terrestrial mammalia, so that it is at once
distinguished from Borneo and Java by its extreme poverty in this class. Of
this small number four belong to the Moluccan and Australian fauna--there
being two marsupials of the genus Cuscus, and two forest rats said to be
allied to Australian types. {456}
The remaining twelve species are, generally speaking, of Malayan or Asiatic
types, but some of them are so peculiar that they have no near allies in
any part of the world; while the rest are of the ordinary Malay type or
even identical with Malayan species, and some of these may be recent
introductions through human agency. These twelve species of Asiatic type
will be now enumerated. They consist of five peculiar squirrels--a group
unknown farther east; a peculiar species of wild pig; a deer so closely
allied to the _Cervus hippelaphus_ of Borneo that it may well have been
introduced by man both here and in the Moluccas; a civet, _Viverra
tangalunga_, common in all the Malay Islands, and also perhaps introduced;
the curious Malayan tarsier (_Tarsius spectrum_) said to be only found in a
small island off the coast;--and besides these, three remarkable animals,
all of large size and all quite unlike anything found in the Malay Islands
or even in Asia. These are a black and almost tailless baboon-like ape
(_Cynopithecus nigrescens_); an antelopean buffalo (_Anoa depressicornis_),
and the strange babirusa (_Babirusa alfurus_).
None of these three animals last mentioned has any close allies elsewhere,
and their presence in Celebes may be considered the crucial fact which must
give us the clue to the past history of the island. Let us then see what
they teach us. The ape is apparently somewhat intermediate between the
great baboons of Africa and the short-tailed macaques of Asia, but its
cranium shows a nearer approach to the former group, in its flat projecting
muzzle, large superciliary crests, and maxillary ridges. The anoa, though
anatomically allied to the buffaloes, externally more resembles the bovine
antelopes of Africa; while the babirusa is altogether unlike any other
living member of the swine family, the canines of the upper jaws growing
directly upwards like horns, forming a spiral curve over the eyes, instead
of downwards, as in all other mammalia. An approach to this peculiarity is
made by the African wart-hogs, in which the upper tusk grows out laterally
and then curves up; but these animals are not otherwise closely allied to
the babirusa. {457}
_Probable Derivation of the Mammals of Celebes._--It is clear that we have
here a group of extremely peculiar, and, in all probability, very ancient
forms, which have been preserved to us by isolation in Celebes, just as the
monotremes and marsupials have been preserved in Australia, and so many of
the lemurs and Insectivora in Madagascar. And this compels us to look upon
the existing island as a fragment of some ancient land, once perhaps
forming part of the great northern continent, but separated from it far
earlier than Borneo, Sumatra, and Java. The exceeding scantiness of the
mammalian fauna, however, remains to be accounted for. We have seen that
Formosa, a much smaller island, contains more than twice as many species;
and we may be sure that at the time when such animals as apes and buffaloes
existed, the Asiatic continent swarmed with varied forms of mammals to
quite as great an extent as Borneo does now. If the portion of separated
land had been anything like as large as Celebes now is, it would certainly
have preserved a far more abundant and varied fauna. To explain the facts
we have the choice of two theories:--either that the original island has
since its separation been greatly reduced by submersion, so as to lead to
the extinction of most of the higher land animals; or, that it originally
formed part of an independent land stretching eastward, and was only united
with the Asiatic continent for a short period, or perhaps even never united
at all, but so connected by intervening islands separated by narrow straits
that a few mammals might find their way across. The latter supposition
appears best to explain the facts. The three animals in question are such
as might readily pass over narrow straits from island to island; and we are
thus better enabled to understand the complete absence of the arboreal
monkeys, of the Insectivora, and of the very numerous and varied Carnivora
and Rodents of Borneo, all of which except the squirrels are entirely
unrepresented in Celebes by any peculiar and ancient forms.
The question at issue can only be finally determined by geological
investigations. If Celebes has once formed part of Asia, and participated
in its rich mammalian fauna, which has been since destroyed by submergence,
then some {458} remains of this fauna must certainly be preserved in caves
or late Tertiary deposits, and proofs of the submergence itself will be
found when sought for. If, on the other hand, the existing animals fairly
represent those which have ever reached the island, then no such remains
will be discovered, and there need be no evidence of any great and
extensive subsidence in late Tertiary times.
_Birds of Celebes._--Having thus clearly placed before us the problem
presented by the mammalian fauna of Celebes, we may proceed to see what
additional evidence is afforded by the birds and any other groups of which
we have sufficient information. About 164 species of true land-birds are
now known to inhabit the island of Celebes itself. Considerably more than
half of these (ninety-four species) are peculiar to it; twenty-nine are
found also in Borneo and the other Malay Islands, to which they specially
belong; while sixteen are common to the Moluccas or other islands of the
Australian region; the remainder being species of wide range and not
characteristic of either division of the Archipelago. We have here a large
preponderance of western over eastern species of birds inhabiting Celebes,
though not to quite so great an extent as in the mammalia; and the
inference to be drawn from this fact is, simply, that more birds have
migrated from Borneo than from the Moluccas--which is exactly what we might
expect both from the greater extent of the coast of Borneo opposite that of
Celebes, and also from the much greater richness in species of the Bornean
than the Moluccan bird-fauna.
It is, however, to the relations of the peculiar species of Celebesian
birds that we must turn, in order to ascertain the origin of the fauna in
past times; and we must look to the source of the generic types which they
represent to give us this information. The ninety-four peculiar species
above noted belong to about sixty-six genera, of which about twenty-three
are common to the whole Archipelago, and have therefore little
significance. Of the remainder, twelve are altogether peculiar to Celebes;
twenty-one are Malayan, but not Moluccan or Australian; while ten are
Moluccan or Australian, but not Malayan. This {459} proportion does not
differ much from that afforded by the non-peculiar species; and it teaches
us that, for a considerable period, Celebes has been receiving immigrants
from all sides, many of which have had time to become modified into
distinct representative species. These evidently belong to the period
during which Borneo on the one side, and the Moluccas on the other, have
occupied very much the same relative position as now. There remain the
twelve peculiar Celebesian genera, to which we must look for some further
clue as to the origin of the older portion of the fauna; and as these are
especially interesting we must examine them somewhat closely.
_Bird-types Peculiar to Celebes._--First we have Artamides, one of the
Campephaginæ or caterpillar-shrikes--a not very well-marked genus, and
which may have been derived, either from the Malayan or the Moluccan side
of the Archipelago. Two peculiar genera of kingfishers--Monachalcyon and
Cittura--seem allied, the former to the widespread Todiramphus and to the
Caridonax of Lombok, the latter to the Australian Melidora. Another
kingfisher, Ceycopsis, combines the characters of the Malayan Ceyx and the
African Ispidina, and thus forms an example of an ancient generalised form
analogous to what occurs among the mammalia. Streptocitta is a peculiar
form allied to the magpies; while Basilornis (found also in Ceram), Enodes,
and Scissirostrum, are very peculiar starlings, the latter altogether
unlike any other bird, and perhaps forming a distinct sub-family. Meropogon
is a peculiar bee-eater, allied to the Malayan Nyctiornis; Rhamphococyx is
a modification of Phænicophaes, a Malayan genus of cuckoos; Prioniturus
(found also in the Philippines) is a genus of parrots distinguished by
raquet-formed tail feathers, altogether unique in the order; while
Megacephalon is a remarkable and very isolated form of the Australian
Megapodiidæ, or mound-builders.
Omitting those whose affinity may be pretty clearly traced to groups still
inhabiting the islands of the western or the eastern half of the
Archipelago, we find four birds which have no near allies at all, but
appear to be either ancestral forms, or extreme modifications, of Asiatic
or {460} African birds--Basilornis, Enodes, Scissirostrum, Ceycopsis. These
may fairly be associated with the baboon-ape, anoa, and babirusa, as
indicating extreme antiquity and some communication with the Asiatic
continent at a period when the forms of life and their geographical
distribution differed considerably from what they are at the present time.
But here again we meet with exactly the same difficulty as in the mammalia,
in the comparative poverty of the types of birds now inhabiting Celebes.
Although the preponderance of affinity, especially in the case of its more
ancient and peculiar forms, is undoubtedly with Asia rather than with
Australia; yet, still more decidedly than in the case of the mammalia, are
we forbidden to suppose that it ever formed a part of the old Asiatic
continent, on account of the _total_ absence of so many important and
extensive groups of Asiatic birds. It is not single species or even genera,
but whole families that are thus absent, and among them families which are
pre-eminently characteristic of all tropical Asia. Such are the Timaliidæ,
or babblers, of which there are twelve genera in Borneo, and nearly thirty
genera in the Oriental Region, but of which one species only, hardly
distinguishable from a Malayan form, inhabits Celebes; the Phyllornithidæ,
or green bulbuls, and the Pycnonotidæ, or bulbuls, both absolutely
ubiquitous in tropical Asia and Malaya, but unknown in Celebes; the
Eurylæmidæ, or gapers, found everywhere in the great Malay Islands; the
Megalæmidæ, or barbets; the Trogonidæ, or trogons; and the Phasianidæ, or
pheasants, all pre-eminently Asiatic and Malayan but all absent from
Celebes, with the exception of the common jungle-fowl, which, owing to the
passion of Malays for cock-fighting, may have been introduced. To these
important _families_ may be added Asiatic and Malayan _genera_ by the
score; but, confining ourselves to these seven ubiquitous families, we must
ask,--Is it possible, that, at the period when the ancestors of the
peculiar Celebes mammals entered the island, and when the forms of life,
though distinct, could not have been quite unlike those now living, it
could have actually formed a part of the continent without {461} possessing
representatives of the greater part of these extensive and important
families of birds? To get rid altogether of such varied and dominant types
of bird-life by any subsequent process of submersion is more difficult than
to exterminate mammalia; and we are therefore again driven to our former
conclusion--that the present land of Celebes has never (in Tertiary times)
been united to the Asiatic continent, but has received its population of
Asiatic forms by migration across narrow straits and intervening islands.
Taking into consideration the amount of affinity on the one hand, and the
isolation on the other, of the Celebesian fauna, we may probably place the
period of this earlier migration in the early part of the latter half of
the Tertiary period, that is, in middle or late Miocene times.
_Celebes not Strictly a Continental Island._--A study of the mammalian and
of the bird-fauna of Celebes thus leads us in both cases to the same
conclusion, and forbids us to rank it as a strictly continental island on
the Asiatic side. But facts of a very similar character are equally opposed
to the idea of a former land-connection with Australia or New Guinea, or
even with the Moluccas. The numerous marsupials of those countries are all
wanting in Celebes, except the phalangers of the genus Cuscus, and these
arboreal creatures are very liable to be carried across narrow seas on
trees uprooted by earthquakes or floods. The terrestrial cassowaries are
equally absent; and thus we can account for the presence of all the
Moluccan or Australian types actually found in Celebes without supposing
any land-connection on this side during the Tertiary period. The presence
of the Celebes ape in the island of Batchian, and of the babirusa in Bouru,
can be sufficiently explained by a somewhat closer approximation of the
respective lands, or by a few intervening islands which have since
disappeared, or it may even be due to human agency.
If the explanation now given of the peculiar features presented by the
fauna of Celebes be the correct one, we are fully justified in classing it
as an "anomalous island," since it possesses a small but very remarkable
mammalian fauna, without ever having been directly united with any {462}
continent or extensive land; and, both by what it has and what it wants,
occupies such an exactly intermediate position between the Oriental and
Australian regions that it will perhaps ever remain a mere matter of
opinion with which it should properly be associated. Forming, as it does,
the western limit of such typical Australian groups as the Marsupials among
mammalia, and the Trichoglossidæ and Meliphagidæ among birds, and being so
strikingly deficient in all the more characteristic Oriental families and
genera of both classes, I have always placed it in the Australian Region;
but it may perhaps with equal propriety be left out of both till a further
knowledge of its geology enables us to determine its early history with
more precision.
_Peculiarities of the Insects of Celebes._--The only other class of animals
in Celebes, of which we have a tolerable knowledge, is that of insects,
among which we meet with peculiarities of a very remarkable kind, and such
as are found in no other island on the globe. Having already given a full
account of some of these peculiarities in a paper read before the Linnean
Society--republished in my _Contributions to the Theory of Natural
Selection_,--while others have been discussed in my _Geographical
Distribution of Animals_ (Vol. I. p. 434)--I will only here briefly refer
to them in order to see whether they accord with, or receive any
explanation from, the somewhat novel view of the past history of the island
here advanced.
The general distribution of the two best known groups of insects--the
butterflies and the beetles--agrees very closely with that of the birds and
mammalia, inasmuch as Celebes forms the eastern limit of a number of
Asiatic and Malayan genera, and at the same time the western limit of
several Moluccan and Australian genera, the former perhaps preponderating
as in the higher animals.
_Himalayan Types of Birds and Butterflies in Celebes._--A curious fact of
distribution exhibited both among butterflies and birds, is the occurrence
in Celebes of species and genera unknown to the adjacent islands, but only
found again when we reach the Himalayan mountains or the Indian Peninsula.
Among birds we have a small yellow {463} flycatcher (_Myialestes
helianthea_), a flower-pecker (_Pachyglossa aureolimbata_), a finch (_Munia
brunneiceps_), and a roller (_Coracias temminckii_), all closely allied to
Indian (not Malayan) species,--all the genera, except Munia, being, in
fact, unknown in any Malay island. An exactly parallel case is that of a
butterfly of the genus Dichorrhagia, which has a very close ally in the
Himalayas, but nothing like it in any intervening country. These facts call
to mind the similar case of Formosa, where some of its birds and mammals
occurred again, under identical or closely allied forms, in the Himalayas;
and in both instances they can only be explained by going back to a period
when the distribution of these forms was very different from what it is
now.
_Peculiarities of Shape and Colour in Celebesian Butterflies._--Even more
remarkable are the peculiarities of shape and colour in a number of
Celebesian butterflies of different genera. These are found to vary all in
the same manner, indicating some general cause of variation able to act
upon totally distinct groups, and produce upon them all a common result.
Nearly thirty species of butterflies, belonging to three different
families, have a common modification in the shape of their wings, by which
they can be distinguished at a glance from their allies in any other island
or country whatever; and all these are larger than the representative forms
inhabiting most of the adjacent islands.[116] No such remarkable local
modification as this is known to occur in any other part of the globe; and
whatever may have been its cause, that cause must certainly have been long
in action, and have been confined to a limited area. We have here,
therefore, another argument in favour of the long-continued isolation of
Celebes from all the surrounding islands and continents--a hypothesis which
we have seen to afford the best, if not the only, explanation of its
peculiar vertebrate fauna.
_Concluding Remarks._--If the view here given of the origin of the
remarkable Celebesian fauna is correct, we have in this island a fragment
of the great eastern {464} continent which has preserved to us, perhaps
from Miocene times, some remnants of its ancient animal forms. There is no
other example on the globe of an island so closely surrounded by other
islands on every side, yet preserving such a marked individuality in its
forms of life; while, as regards the special features which characterise
its insects, it is, so far as yet known, absolutely unique. Unfortunately
very little is known of the botany of Celebes, but it seems probable that
its plants will to some extent partake of the speciality which so markedly
distinguishes its animals; and there is here a rich field for any botanist
who is able to penetrate to the forest-clad mountains of its interior.
{465}
APPENDIX TO CHAPTER XX
The following list of the Land Birds of Celebes and the adjacent islands
which partake of its zoological peculiarities, in which are incorporated
all the species discovered up to 1890, has been drawn up from the following
sources:--
1. A List of the Birds known to inhabit the Island of Celebes, By
Arthur, Viscount Walden, F.R.S. (Trans. Zool. Soc. 1872. Vol. viii. pt.
ii.)
2. Intorno al Genere Hermotimia. (Rchb.) Nota di Tommaso Salvadori.
(Atti della Reale Accademia delle Scienze di Torino. Vol x. 1874.)
3. Intorno a due Collezioni di Ucelli di Celebes--Note di Tommaso
Salvadori. (Annali del Mus. Civ. di St. Nat. di Genova. Vol. vii.
1875.)
4. Beiträge zur Ornithologie von Celebes und Sangir. Von Dr. Friedrich
Brüggemann. Bremen, 1876.
5. Intorno a due piccole Collezioni di Ucelli di Isole Sanghir e di
Tifore. Nota di Tommaso Salvadori. (Annali del Mus. Civ. di St. Nat. di
Genova. Vol. ix. 1876-77.)
6. Intorno alle Specie di Nettarinie delle Molucche e del Gruppo di
Celebes. Note di Tommaso Salvadori. (Atti della Reale Accad. delle
Scienze di Torino. Vol. xii. 1877.)
7. Descrizione di tre Nuove Specie di Ucelli, e note intorno ad altre
poco conosciute delle Isole Sanghir. Per Tommaso Salvadori. (L. c. Vol.
xiii. 1878.)
8. Field Notes on the Birds of Celebes. By A. B. Meyer, M.D., &c.
(Ibis, 1879.)
9. On the Collection of Birds made by Dr. Meyer during his Expedition
to New Guinea and some neighbouring Islands. By R. Boulder Sharpe.
(Mitth. d. kgl. Zool. Mus. Dresden, 1878. Heft 3.) New species from the
Sula and Sanghir Islands are described.
10. List of Birds from the Sula Islands (East of Celebes) with
Descriptions of the New Species. By Alfred Russel Wallace, F.Z.S.
(_Proc. Zool. Soc._ 1862, p. 333.)
11. The Zoological Record, and "The Ibis" to 1890.
{466}
LIST OF LAND BIRDS OF CELEBES
_N.B.--The Species marked with an * are not included in Viscount Walden's
list. For these only, an authority is usually given._
--------------------------------+-------+-------+-------+-------------
|Celebes| Sula |Sanghir| Range and
| | Is. | Is. | Remarks
--------------------------------+-------+-------+-------+-------------
TURDIDÆ. | | | |
1. Geocichla erythronota | X | | |
2. Monticola solitaria | X | | X |Phil., China,
| | | | Japan
| | | |
SYLVIIDÆ. | | | |
3. Cisticola cursitans | X | | |Assam
4 ,, grayi | X | | |
5. Acrocephalus orientalis | X | | |China, Japan
*6. ,, insularis | -- | -- | X |Moluccas
| | |(Salv.)|
7. Pratincola caprata | X | | |Asia, Java,
| | | | Timor
*8. Gerygone flaveola (Cab.) | X | | |(Near G.
|(Meyer)| | |_sulphurea_,
| | | |Timor)
| | | |
TIMALIIDÆ. | | | |
9. Trichostoma celebense | X | | |
| | | |
PYCNONOTIDÆ. | | | |
*10. Criniger longirostris | | | |
(Wall.) | | X | |Oriental
| | | | genus (near
| | | | Bouru sp.)
11. ,, aureus (Wald.) | X | | |
| | | |
ORIOLIDÆ. | | | |
12. Oriolus celebensis | X | | |(Var of O.
| | | | _coronatus_,
| | | | Java)
13. ,, formosus (Cab.) | -- | -- | X |(Var. of
| | |(Brugg.) Philipp.
| | | | sp.)
14. ,, frontalis (Wall.) | -- | X | |
| | | |
CAMPEPHAGIDÆ. | | | |
15. Graucalus atriceps | X | | |Ceram, Flores
16. ,, leucopygius | X | | |
17. ,, temminckii | X | X | |
18. Campephaga morio | X | | |
*19. ,, melanotis | -- | X | |Moluccas
*20. ,, salvadorii | |(Wall.)| |
(Sharpe) | -- | -- | X |
21. Lalage leucopygialis | X | | |
*22. ,, dominica | X | -- | -- |Java
|(Meyer)| | |
23. Artamides bicolor | X | | |
*24. ,, schistaceus | | | |
(Sharpe) | -- | X | |
| | | |
DICRURIDÆ. | | | |
25. Dicrurus leucops | X | | |
*26. ,, axillaris (Salv.) | -- | -- | X |
*27. ,, pectoralis (Wall.) | | X | |
{467}
| | | |
MUSCICAPIDÆ. | | | |
28. Cyornis rufigula | X | | |
29. ,, banyumas | X | | |Java and Borneo
30. Myialestes helianthea | X | | |(Indian ally)
31. Hypothymis puella | X | X | |
32. ,, menadensis? | X | | |
*33. Monarcha commutata | | | |
(Brugg.) | X | | |
*34. ,, cinerascens | -- | X | |Moluccas
| |(Wall.)| |
PACHYCEPHALIDÆ. | | | |
35. Hylocharis sulfuriventra | X | | |
*36. Pachycephala lineolata | | | |
(Wall.) | -- | X | -- |Bouru
*37. Pachycephala rufescens | | | |
(Wall.) | -- | X | -- |Bouru
*38. Pachycephala clio (Wall.) | -- | X | -- |Bouru
| | | |
LANIIDÆ. | | | |
*39. Lanius magnirostris (Meyer)| X | -- | -- |Java
| | | |
CORVIDÆ. | | | |
40. Corvus enca | X | X var.| |Java
*41. ,, annectens (Brugg.) | X | | |
42. ,,(Gazzola) typica | X | | |
43. Streptocitta caledonica | X | | |
44. ,, torquata | X | | |
*45(Charitornis) albertiæ(Schl.)| -- | X | |
| | | |
MELIPHAGIDÆ. | | | |
46. Myzomela chloroptera | X | | |(Nearest _M.
| | | |sanguinolenta_
| | | |of Australia)
NECTARINIIDÆ. | | | |
47. Anthreptes celebensis | | | |
(Shelley) | X | X | X |Siam, Malaya
48. Chalcostethia porphyolæma | X | | |
*49. ,, auriceps | -- | X | -- |Ternate
| |(Wall.)| |
*50. ,, sangirensis | -- | -- | X |
(Meyer) | | | |
51. Cyrtostomus frenatus | X | X | -- |Moluccas and N.
| | | | Guinea
52. Nectarophila grayi | X | | |
53. Æthopyga flavostriata | X | | |(An Oriental
| | | | genus)
*54. ,, beccarii (Salv.) | X | | |
*55. ,, duyvenbodei (Schl.)| -- | -- | X |
| | | |
DICÆIDÆ. | | | |
56. Zosterops intermedia | X | | |Lombock
57. ,, atrifrons | X | | |
58. Dicæum celebicum | X | X | |
*59. ,, sanghirense (Salv.) | -- | -- | X |
*60. ,, nehrkorni (Blas.) | X | | |
61. Pachyglossa aureolimbata | X | -- | X |
| | | |
HIRUNDINIDÆ. | | | |
62. Hirundo gutturalis | X | | X |Indian region
63. ,, javanica | X | X | |Indo-Malaya
| | | |
PLOCEIDÆ. | | | |
64. Munia oryzivora | X | | |Java
65. ,, nisoria | X | | |Java
66. ,, molucca | X | | |Moluccas
{468}
67. ,, brunneiceps | X | | |(Near _M.
| | | |rubronigra_,
| | | |India)
*68. ,, jagori | X | | |Philippines
|(Meyer)| | |
STURNIDÆ. | | | |
69. Basilornis celebensis | X | | |
70. Acridotheres cinereus | X | | |
71. Sturnia pyrrhogenys | X | | |Malaya
72. Calornis neglecta | X | X | X var.|
*73. ,, metallica | X | X | |Moluccas
|(Brugg.)(Wall.)| |
74. Enodes crythrophrys | X | | |
75. Scissirostrum pagei | X | | |
| | | |
ARTAMIDÆ. | | | |
76. Artamus monachus | X | X | |
77. ,, leucorhynchus | X | | |Malay Archipel.
| | | |
MOTACILLIDÆ. | | | |
78. Corydalla gustavi | X | | |
79. Budytes viridis | X | | |Java, Moluccas
*80. Calobates melanope | | | |
(= Motac. sulfurea, Brugg.) | X | | |China, Phillipp.
| | | |
PITTIDÆ. | | | |
81. Pitta forsteni | X | | |
*82. ,, sanghirana (Schl.) | | | X |
83. ,, celebensis | X | | |
*84. ,, palliceps (Brugg.) | | | X |
*85. ,, coeruleitorques (Salv.) | | X |
*86. ,, irena (= crassirostris) | X | |Timor, Ternate?
| |(Wall.)| |
PICIDÆ. | | | |
87. Alophonerpes fulvus | X | | |
*88. ,, wallacei | | | |
89. Yungipicus temminckii | X | | |
| | | |
CUCULIDÆ. | | | |
90. Rhamphococcyx calorhynchus | X | | |
91. Pyrrhocentor celebensis | X | | |
92. Centropus affinis | X | | |Java
93. ,, javanensis | X | | |Java, Borneo
94. Cuculus canorus | X | | |
95. Cacomantes lanceolatus | X | | |Java
96. ,, sepulchralis | X | | |
97. Hierococcyx crassirostris | X | | |
98. Eudynamis melanorhyncha | X | | |
*99. ,, facialis (Wall.) | | X | |
*100. ,, orientalis | | | X |Moluccas?
| | |(Brugg.)
101. Scythrops novæhollandiæ | X | | |Moluccas, &c.
| | | |
CORACIIDÆ. | | | |
102. Coracias temminckii | X | | |
103. Eurystomus orientalis | X | X | X |Asia
| | | |
MEROPIDÆ. | | | |
104. Meropogon forsteni | X | | |
105. Merops philippinus | X | | |Oriental region
106. ,, ornatus | X | X | |Java, Australia
| | | |
ALCEDINIDÆ. | | | |
107. Alcedo moluccensis | X | | X |Moluccas
108. ,, asiatica | X | | |Indo-Malaya
{469}
109. Pelargopsis melanorhyncha | X | X | |
*110. Ceyx wallacei (Sharpe) | | X | |(Allied to Mol.
| | | | sp.)
111. Ceycopsis fallax | X | | |
112. Halcyon chloris | X | X | X |All Archipel.
113. ,, sancta | X | X | |All Archipel.
114. ,, forsteni | X | | |
115. ,, rufa | X | X | |
116. Monachalcyon princeps | X | | |
*117. ,, cyanocephala (Brugg.) | X | | |
118. Cittura cyanotis | X | | |
*119. ,, sanghirensis (Schl.)| | | X |
| | | |
BUCEROTIDÆ. | | | |
120. Hydrocissa exarata | X | | |
121. Cranorhinus cassidix | X | | |
| | | |
CAPRIMULGIDÆ. | | | |
122. Caprimulgus affinis | X | | |
123. ,, sp. | X | | |
124. Lyncornis macropterus. | X | | |
| | | |
CYPSELIDÆ. | | | |
125. Dendrochelidon wallacei | X | X | |
126. Collocalia esculenta | X | | |Mol. to Arn Is.
127. ,, fuciphaga | X | | |India, Java
128. Chætura gigantea | X | | |India, Java
| | | |
PSITTACI. | | | |
129. Cacatua sulphurea | X | | |Lombock, Flores
130. Prioniturus platurus | X | | |
131. ,, flavicans | X | | |
*132. Platycercus dorsalis, var.| | X | |N. Guinea?
| |(Wall.)| |
133. Tanygnathus mulleri | X | X | |
*134. ,, megalorhynchus | X | | X |Moluccas. An
| | | |island near
| | | |Menado (Meyer)
*135. ,, luzoniensis | | | X |
| | |(Brugg.)
136. Loriculus stigmatus | X | | |
*137. ,, quadricolor (Wald.)| X | | |Togian Is., Gulf
| | | |of Tomini
138. ,, sclateri | ? | X | |
139. ,, exilis | X | | |
*140. ,, catamene (Schl.) | | | X |
141. Trichoglossus ornatus | X | | |
*142. ,, flavoviridis (Wall.)| | X | |
143. ,, meyeri | X | | |
*144. Eos histrio = E. coccinea | | | X |
| | | |
COLUMBÆ. | | | |
145. Treron vernans | X | | |Malacca, Java,
| | | |Philipp.
146. ,, griseicauda | X | X | X var.|
| | |Sanghir-
| | | ensis |
147. Ptilopus formosus | X | | |
148. ,, melanocephalus | X | X | X var.|Java, Lombock
| | |Xantho-|
| | | rrhoa,|
| | |Salv. |
149. ,, gularis | X | | |
*150. ,, fischeri (Brugg.)| X | | |
151. Carpophaga paulina | X | X | |
{470}
*152. ,, pulchella | X | | |Togian Is.
(Wald.) | | | |(_Ann. and
| | | |Mag. Nat. Hst._,
| | | |1874.)
153. ,, concinna | | | X |Ké Goram
| | |(Salv.)|
154. ,, rosacea | X | | |Gilolo, Timor
*155. ,, pæcilorrhoa (Brugg) | X | | |
156. ,, luctuosa | X | X | |
*157. ,, bicolor | X | | X |New Guin.,
|(Meyer)| | |Moluccas
158. ,, radiata | X | | X |
159. ,, forsteni | X | | |
160. Macropygia albicapilla | X | X | |
161. ,, macassariensis | X | | |
*162. ,, sanghirensis (Salv.) | | | X |
163. Turacoena menadensis | X | X | |
*164. Reinwardtænas reinwardti |X Meyer| | |Moluccas & New
| | | |Guin.
165. Turtur tigrina | X | | |Malaya, Moluccas
166. Chalcophaps stephani | X | | |New Guinea
167. ,, indica | X | X var.| X |India and
| | | |Archipel.
168. Phlogænas tristigmata | X | | |
169. Geopelia striata | X | | |China, Java,
| | | |Lombock
170. Calænas nicobarica | X | | |Malacca and New
| | | |Guinea
| | | |
GALLINÆ. | | | |
171. Gallus bankiva | X | | |Java, Timor
172. Coturnix minima | X | | |(Var. of _C.
| | | |Chinensis_)
173. Turnix rufilatus | X | | |
*174. ,, beccarii (Salv.) | X | | |
175. Megapodius gilberti | X | | |
176. Megacephalon malleo | X | | X |
| | | |
ACCIPITRES. | | | |
177. Circus assimilis | X | | |Australia
178. Astur griseiceps | X | | |
*179. ,, tenuirostris (Brugg.) X | | |
180. ,, rhodogastra | X | | |
181. ,, trinotata | X | | |
182. Accipiter sulaensis (Schl.) X | | |
183. ,, soloensis | X | | |Malacca & New
| | | |Guin.
184. Neopus malayensis | X | | |Nepaul, Sum.,
| | | |Java, Moluccas
185. Spizaetus lanceolatus | X | X | |
186. Haliactus leucogaster | X | | |Oriental region
187. Spilornis rufipectus | X | X | |
188. Butastur liventer | X | | |Java, Timor
189. ,, indicus | X | | X |India, Java
190. Haliastur leucosternus | X | | |Moluccas, New
| | | |Guin.
191. Milvus affinis | X | | |Australia
192. Elanus hypoleucus | X | | |? Java, Borneo
193. Pernis ptilorhyncha (var. | | | |
celebensis) | X | | |(Var. Java, &c.)
194. Baza erythrothorax | X | X | |
195. Falco severus | X | | |All Archipel.
196. Cerchneis moluccensis | X | | |Java, Moluccas
197. Polioaetus humilis | X | | |India, Malaya
| | | |
STRIGIDÆ. | | | |
198. Athene punctulata | X | | |
199. ,, ochracea | X | | |
200. Scops magicus | X | | |Amboyna, &c.?
201. ,, menadensis | X | | |Flores,
| | | |Madagascar
202. Ninox japonicus | X | | |China, Japan
*203. ,, scutulata | | | X |Malacca
| | |(Salv.)|
204. Strix rosenbergi | X | | |
--------------------------------+-------+-------+-------+--------------------
* * * * *
{471}
CHAPTER XXI
ANOMALOUS ISLANDS: NEW ZEALAND
Position and Physical Features of New Zealand--Zoological Character of
New Zealand--Mammalia--Wingless Birds Living and Extinct--Recent
Existence of the Moa--Past Changes of New Zealand deduced from its
Wingless Birds--Birds and Reptiles of New Zealand--Conclusions from the
Peculiarities of the New Zealand Fauna.
The fauna of New Zealand has been so recently described, and its bearing on
the past history of the islands so fully discussed in my large work already
referred to, that it would not be necessary to introduce the subject again,
were it not that we now approach it from a somewhat different point of
view, and with some important fresh material, which will enable us to
arrive at more definite conclusions as to the nature and origin of this
remarkable fauna and flora. The present work is, besides, addressed to a
wider class of readers than my former volumes, and it would be manifestly
incomplete if all reference to one of the most remarkable and interesting
of insular faunas was omitted.
The two great islands which mainly constitute New Zealand are together
about as large as the kingdom of Italy. They stretch over thirteen degrees
of latitude in the warmer portion of the south-temperate zone, their
extreme points corresponding to the latitudes of Vienna and Cyprus. Their
climate throughout is mild and {472} equable, their vegetation is
luxuriant, and deserts or uninhabitable regions are as completely unknown
as in our own islands.
The geological structure of these islands has a decidedly continental
character. Ancient sedimentary rocks, granite, and modern volcanic
formations abound; gold, silver, copper, tin, iron, and coal are plentiful;
and there are also some considerable deposits of early or late Tertiary
age. The Secondary rocks alone are very scantily developed, and such
fragments as exist are chiefly of Cretaceous age, often not clearly
separated from the succeeding Eocene beds.
[Illustration: MAP SHOWING DEPTHS OF SEA AROUND AUSTRALIA AND NEW ZEALAND.]
The light tint indicates a depth of less than 1,000 fathoms.
The dark tint ,, ,, more than 1,000 fathoms.
The position of New Zealand, in the great Southern Ocean, about 1,200 miles
distant from the Australian {473} continent, is very isolated. It is
surrounded by a moderately deep ocean; but the form of the sea-bottom is
peculiar, and may help us in the solution of some of the anomalies
presented by its living productions. The line of 200 fathoms encloses the
two islands and extends their area considerably; but the 1,000-fathom line,
which indicates the land-area that would be produced if the sea-bottom were
elevated 6,000 feet, has a very remarkable conformation, extending in a
broad mass westward and northward, then sending out a great arm reaching to
beyond Lord Howe's Island. Norfolk Island is situated on a moderate-sized
bank, while two others, much more extensive, to the north-west approach the
great barrier reef, which here carries the 1,000-fathom line more than 300
miles from the coast. It is probable that a bank, less than 1,500 fathoms
below the surface, extends over this area, thus forming a connection with
tropical Australia and New Guinea. Temperate Australia, on the other hand,
is divided from New Zealand by an oceanic gulf about 700 miles wide and
between 2,000 and 3,000 fathoms deep. The 2,000-fathom line embraces all
the islands immediately round New Zealand as far as the Fijis to the north,
while a submarine plateau at a depth somewhere between one and two thousand
fathoms stretches southward to the Antarctic continent. Judging from these
indications, we should say that the most probable ancient connections of
New Zealand were with tropical Australia, New Caledonia, and the Fiji
Islands, and perhaps at a still more remote epoch, with the great Southern
continent by means of intervening lands and islands; and we shall find that
a land-connection or near approximation in these two directions, at remote
periods, will serve to explain many of the remarkable anomalies which these
islands present.
_Zoological Character of New Zealand._--We see, then, that both
geologically and geographically New Zealand has more of the character of a
"continental" than of an "oceanic" island, yet its zoological
characteristics are such as almost to bring it within the latter
category--and it is this which gives it its anomalous character. It is
usually {474} considered to possess no indigenous mammalia; it has no
snakes, and only one frog; it possesses (living or quite recently extinct)
an extensive group of birds incapable of flight; and its productions
generally are wonderfully isolated, and seem to bear no predominant or
close relation to those of Australia or any other continent. These are the
characteristics of an oceanic island; and thus we find that the inferences
from its physical structure and those from its forms of life directly
contradict each other. Let us see how far a closer examination of the
latter will enable us to account for this apparent contradiction.
_Mammalia of New Zealand._--The only undoubtedly indigenous mammalia appear
to be two species of bats, one of which (_Scotophilus tuberculatus_) is,
according to Mr. Dobson, identical with an Australian form, while the other
(_Mystacina tuberculata_) forms a very remarkable and isolated genus of
Emballonuridæ, a family which extends throughout all the tropical regions
of the globe. The genus Mystacina was formerly considered to belong to the
American Phyllostomidæ, but this has been shown to be an error.[117] The
poverty of New Zealand in bats is very remarkable when compared with our
own islands where there are at least twelve distinct species, though we
have a far less favourable climate.
Of the existence of truly indigenous land mammals in New Zealand there is
at present no positive evidence, but there is some reason to believe that
one if not two species may be found there. The Maoris say that before
Europeans came to their country a forest-rat abounded and was largely used
for food. They believe that their ancestors brought it with them when they
first came to the country; but it has now become almost, if not quite,
exterminated by the European brown rat. What this native animal was is
still somewhat doubtful. Several specimens have been caught at different
times which have been declared by the natives to be the true _Kiore
Maori_--as they term it, but these have usually proved on examination to be
either the European black rat or some of the native Australian rats which
now {475} often find their way on board ships. But within the last few
years many skulls of a rat have been obtained from the old Maori
cooking-places, and from a cave associated with moa bones; and Captain
Hutton, who has examined them, states that they belong to a true Mus, but
differ from the _Mus rattus_. This animal might have been on the islands
when the Maoris first arrived, and in that case would be truly indigenous;
while the Maori legend of their "ancestors" bringing the rat from their
Polynesian home may be altogether a myth invented to account for its
presence in the islands, because the only other land mammal which they
knew--the dog--was certainly so brought. The question can only be settled
by the discovery of remains of a rat in some deposit of an age decidedly
anterior to the first arrival of the Maori race in New Zealand.[118]
Much more interesting is the reported existence in the mountains of the
South Island of a small otter-like animal. Dr. Haast has seen its tracks,
resembling those of our European otter, at a height of 3,000 feet above the
sea in a region never before trodden by man; and the animal itself was seen
by two gentlemen near Lake Heron, about seventy miles due west of
Christchurch. It was described as being dark brown and the size of a large
rabbit. On being struck at with a whip, it uttered a shrill yelping sound
and disappeared in the water.[119] An animal seen so closely as to be
struck at with a whip could hardly have been mistaken for a dog--the only
other animal that it could possibly be supposed to have been, and a dog
would certainly not have "disappeared in the water." This account, as well
as the footsteps, point to an aquatic animal; and if it now frequents only
the high alpine lakes and streams, this might explain why it has never yet
been captured. Hochstetter also states that it has a native
name--Waitoteke--a striking evidence of its actual existence, while a
gentleman who lived many years in the district assures me that {476} it is
universally believed in by residents in that part of New Zealand. The
actual capture of this animal and the determination of its characters and
affinities could not fail to aid us greatly in our speculations as to the
nature and origin of the New Zealand fauna.[120]
_Wingless Birds, Living and Extinct._--Almost equally valuable with
mammalia in affording indications of geographical changes are the wingless
birds for which New Zealand is so remarkable. These consist of four species
of Apteryx, called by the natives "kiwis,"--creatures which hardly look
like birds owing to the apparent absence (externally) of tail or wings and
the dense covering of hair-like feathers. They vary in size from that of a
small fowl up to that of a turkey, and have a long slightly curved bill,
somewhat resembling that of the snipe or ibis. Two species appear to be
confined to the South Island, and one to the North Island, but all are
becoming scarce, and they will no doubt gradually become extinct. These
birds are generally classed with the Struthiones or ostrich tribe, but they
form a distinct family, and in many respects differ greatly from all other
known birds.
But besides these, a number of other wingless birds, called "moas,"
inhabited New Zealand during the period of human occupation, and have only
recently become extinct. These were much larger birds than the kiwis, and
some of them were even larger than the ostrich, a specimen {477} of
_Dinornis maximus_ mounted in the British Museum in its natural attitude
being eleven feet high. They agreed, however, with the living Apteryx in
the character of the pelvis and some other parts of the skeleton, while in
their short bill and in some important structural features they resembled
the emu of Australia and the cassowaries of New Guinea.[121] No less than
eleven distinct species of these birds have now been discovered; and their
remains exist in such abundance--in recent fluviatile deposits, in old
native cooking places, and even scattered on the surface of the
ground--that complete skeletons of several of them have been put together,
illustrating various periods of growth from the chick up to the adult bird.
Feathers have also been found attached to portions of the skin, as well as
the stones swallowed by the birds to assist digestion, and eggs, some
containing portions of the embryo bird; so that everything confirms the
statements of the Maoris--that their ancestors found these birds in
abundance on the islands, that they hunted them for food, and that they
finally exterminated them only a short time before the arrival of
Europeans.[122] Bones of Apteryx are also found fossil, but apparently of
the same species as the living birds. {478} How far back in geological time
these creatures or their ancestral types lived in New Zealand we have as
yet no evidence to show. Some specimens have been found under a
considerable depth of fluviatile deposits which may be of Quaternary or
even of Pliocene age; but this evidently affords us no approximation to the
time required for the origin and development of such highly peculiar
insular forms.
_Past Changes of New Zealand deduced from its Wingless Birds._--It has been
well observed by Captain Hutton, in his interesting paper already referred
to, that the occurrence of such a number of species of Struthious birds
living together in so small a country as New Zealand is altogether
unparalleled elsewhere on the globe. This is even more remarkable when we
consider that the species are not equally divided between the two islands,
for remains of no less than ten out of the eleven known species of Dinornis
have been found in a single swamp in the South Island, where also three of
the species of Apteryx occur. The New Zealand Struthiones, in fact, very
nearly equal in number those of all the rest of the world, and nowhere else
do more than three species occur in any one continent or island, while no
more than two ever occur in the same district. Thus, there appear to be two
closely allied species of ostriches inhabiting Africa and South-western
Asia respectively. South America has three species of Rhea, each in a
separate district. Australia has an eastern and a western variety of emu,
and a cassowary in the north; while eight other cassowaries are known from
the islands north of Australia--one from Ceram, two from the Aru Islands,
one from Jobie, one from New Britain, and three from New Guinea--but of
these last one is confined to the northern and another to the southern part
of the island.
This law, of the distribution of allied species in separate areas--which is
found to apply more or less accurately to all classes of animals--is so
entirely opposed to the crowding together of no less that fifteen species
of wingless birds in the small area of New Zealand, that the idea is at
once suggested of great geographical changes. Captain Hutton points out
that if the islands from Ceram to New Britain {479} were to become joined
together, we should have a large number of species of cassowary (perhaps
several more than are yet discovered) in one land area. If now this land
were gradually to be submerged, leaving a central elevated region, the
different species would become crowded together in this portion just as the
moas and kiwis were in New Zealand. But we also require, at some remote
epoch, a more or less complete union of the islands now inhabited by the
separate species of cassowaries, in order that the common ancestral form
which afterwards became modified into these species, could have reached the
places where they are now found; and this gives us an idea of the complete
series of changes through which New Zealand is believed to have passed in
order to bring about its abnormally dense population of wingless birds.
First, we must suppose a land connection with some country inhabited by
struthious birds, from which the ancestral forms might be derived;
secondly, a separation into many considerable islands, in which the various
distinct species might become differentiated; thirdly, an elevation
bringing about the union of these islands to unite the distinct species in
one area; and fourthly, a subsidence of a large part of the area, leaving
the present islands with the various species crowded together.
If New Zealand has really gone through such a series of changes as here
suggested, some proofs of it might perhaps be obtained in the outlying
islands which were once, presumably, joined with it. And this gives great
importance to the statement of the aborigines of the Chatham Islands, that
the Apteryx formerly lived there but was exterminated about 1835. It is to
be hoped that some search will be made here and also in Norfolk Island, in
both of which it is not improbable remains either of Apteryx or Dinornis
might be discovered.
So far we find nothing to object to in the speculations of Captain Hutton,
with which, on the contrary, we almost wholly concur; but we cannot follow
him when he goes on to suggest an Antarctic continent uniting New Zealand
and Australia with South America, and probably also with South Africa, in
order to explain the existing distribution {480} of struthious birds. Our
best anatomists, as we have seen, agree that both Dinornis and Apteryx are
more nearly allied to the cassowaries and emus than to the ostriches and
rheas; and we see that the form of the sea-bottom suggests a former
connection with North Australia and New Guinea--the very region where these
types most abound, and where in all probability they originated. The
suggestion that all the struthious birds of the world sprang from a common
ancestor at no very remote period, and that their existing distribution is
due to direct land communication between the countries they _now_ inhabit,
is one utterly opposed to all sound principles of reasoning in questions of
geographical distribution. For it depends upon two assumptions, both of
which are at least doubtful, if not certainly false--the first, that their
distribution over the globe has never in past ages been very different from
what it is now; and the second, that the ancestral forms of these birds
never had the power of flight. As to the first assumption, we have found in
almost every case that groups now scattered over two or more continents
formerly lived in intervening areas of existing land. Thus the marsupials
of South America and Australia are connected by forms which lived in North
America and Europe; the camels of Asia and the llamas of the Andes had many
extinct common ancestors in North America; the lemurs of Africa and Asia
had their ancestors in Europe, as had the trogons of South America, Africa,
and tropical Asia. But besides this general evidence we have direct proof
that the struthious birds had a wider range in past times than now. Remains
of extinct rheas have been found in Central Brazil, and those of ostriches
in North India; while remains, believed to be of struthious birds, are
found in the Eocene deposits of England; and the Cretaceous rocks of North
America have yielded the extraordinary toothed bird, Hesperornis, which
Professor O. Marsh declares to have been "a carnivorous swimming ostrich."
As to the second point, we have the remarkable fact that all known birds of
this group have not only the rudiments of wing-bones, but also the
rudiments of wings, that is, an external limb bearing rigid quills or
largely-developed {481} plumes. In the cassowary these wing-feathers are
reduced to long spines like porcupine-quills, while even in the Apteryx,
the minute external wing bears a series of nearly twenty stiff quill-like
feathers.[123] These facts render it almost certain that the struthious
birds do not owe their imperfect wings to a direct evolution from a
reptilian type, but to a retrograde development from some low form of
winged birds, analogous to that which has produced the dodo and the
solitaire from the more highly-developed pigeon-type. Professor Marsh has
proved, that so far back as the Cretaceous period, the two great forms of
birds--those with a keeled sternum and fairly-developed wings, and those
with a convex keel-less sternum and rudimentary wings--already existed side
by side; while in the still earlier Archæopteryx of the Jurassic period we
have a bird with well-developed wings, and therefore probably with a keeled
sternum. We are evidently, therefore, very far from a knowledge of the
earliest stages of bird life, and our acquaintance with the various forms
that have existed is scanty in the extreme; but we may be sure that birds
acquired wings, and feathers, and some power of flight, before they
developed a keeled sternum, since we see that bats with no such keel fly
very well. Since, therefore, the struthious birds all have perfect
feathers, and all have rudimentary wings, which are anatomically those of
true birds, not the rudimentary fore-legs of reptiles, and since we know
that in many higher groups of birds--as the pigeons and the rails--the
wings have become more or less aborted, and the keel of the sternum greatly
reduced in size by disuse, it seems probable that the very remote ancestors
of the rhea, the cassowary, and the apteryx, were true flying birds,
although not perhaps provided with a keeled sternum, or possessing very
great powers of flight. But in addition to the possible ancestral power of
flight, we have the undoubted fact that the rhea and the emu both swim
freely, the former having been seen swimming from island to island off the
coast of Patagonia. This, taken in connection with the wonderful aquatic
ostrich of the Cretaceous period discovered by Professor Marsh, opens {482}
up fresh possibilities of migration; while the immense antiquity thus given
to the group and their universal distribution in past time, renders all
suggestions of special modes of communication between the parts of the
globe in which their scattered remnants _now_ happen to exist, altogether
superfluous and misleading.
The bearing of this argument on our present subject is, that so far as
accounting for the presence of wingless birds in New Zealand is concerned,
we have nothing whatever to do with any possible connection, by way of a
southern continent or antarctic islands, with South America and South
Africa, because the nearest allies of its moas and kiwis are the
cassowaries and emus, and we have distinct indications of a former land
extension towards North Australia and New Guinea, which is exactly what we
require for the original entrance of the struthious type into the New
Zealand area.
_Winged Birds and Lower Vertebrates of New Zealand._--Having given a pretty
full account of the New Zealand fauna elsewhere[124] I need only here point
out its bearing on the hypothesis now advanced, of the former
land-connection having been with North Australia, New Guinea, and the
Western Pacific Islands, rather than with the temperate regions of
Australia.
Of the Australian genera of birds, which are found also in New Zealand,
almost every one ranges also into New Guinea or the Pacific Islands, while
the few that do not extend beyond Australia are found in its northern
districts. As regards the peculiar New Zealand genera, all whose affinities
can be traced are allied to birds which belong to the tropical parts of the
Australian region; while the starling family, to which four of the most
remarkable New Zealand birds belong (the genera Creadion, Heterolocha, and
Callæas), is totally wanting in temperate Australia and is comparatively
scarce in the entire Australian region, but is abundant in the Oriental
region, with which New Guinea and the Moluccas are in easy communication.
It is certainly a most suggestive fact that there are more than sixty {483}
genera of birds peculiar to the Australian continent (with Tasmania), many
of them almost or quite confined to its temperate portions, and that no
single one of these should be represented in temperate New Zealand.[125]
The affinities of the living and more highly organised, no less than those
of the extinct and wingless birds, strikingly accord with the line of
communication indicated by the deep submarine bank connecting these
temperate islands with the tropical parts of the Australian region.
The reptiles, so far as they go, are quite in accordance with the birds.
The lizards belong to two genera, Lygosoma, which has a wide range in all
the tropics as well as in Australia; and Naultinus, a genus peculiar to New
Zealand, but belonging to a family--Geckonidæ--spread over the whole of the
warmer parts of the world. Australia, with New Guinea, on the other hand,
has a peculiar family, and no less than twenty-one peculiar genera of
lizards, many of which are confined to its temperate regions, but no one of
them extends to temperate New Zealand.[126] The extraordinary lizard-like
_Hatteria punctata_ of New Zealand forms of itself a distinct order of
reptiles, in some respects intermediate between lizards and crocodiles, and
having therefore no affinity with any living animal.
The only representative of the Amphibia in New Zealand is a solitary frog
of a peculiar genus (_Liopelma hochstetteri_); but it has no affinity for
any of the Australian frogs, which are numerous, and belong to eleven
different families; while the Liopelma belongs {484} to a very distinct
family (Discoglossidæ), confined to the Palæarctic region.
Of the fresh-water fishes we need only say here, that none belong to
peculiar Australian types, but are related to those of temperate South
America or of Asia.
The Invertebrate classes are comparatively little known, and their modes of
dispersal are so varied and exceptional that the facts presented by their
distribution can add little weight to those already adduced. We will,
therefore, now proceed to the conclusions which can fairly be drawn from
the general facts of New Zealand natural history already known to us.
_Deductions from the Peculiarities of the New Zealand Fauna._--The total
absence (or extreme scarcity) of mammals in New Zealand obliges us to place
its union with North Australia and New Guinea at a very remote epoch. We
must either go back to a time when Australia itself had not yet received
the ancestral forms of its present marsupials and monotremes, or we must
suppose that the portion of Australia with which New Zealand was connected
was then itself isolated from the mainland, and was thus without a
mammalian population. We shall see in our next chapter that there are
certain facts in the distribution of plants, no less than in the geological
structure of the country, which favour the latter view. But we must on any
supposition place the union very far back, to account for the total want of
identity between the winged birds of New Zealand and those peculiar to
Australia, and a similar want of accordance in the lizards, the fresh-water
fishes, and the more important insect-groups of the two countries. From
what we know of the long geological duration of the generic types of these
groups we must certainly go back to the earlier portion of the Tertiary
period at least, in order that there should be such a complete disseverance
as exists between the characteristic animals of the two countries; and we
must further suppose that, since their separation, there has been no
subsequent union or sufficiently near approach to allow of any important
intermigration, even of winged birds, between them. It seems probable,
therefore, that {485} the Bampton shoal west of New Caledonia, and Lord
Howe's Island further south, formed the western limits of that extensive
land in which the great wingless birds and other isolated members of the
New Zealand fauna were developed. Whether this early land extended eastward
to the Chatham Islands and southward to the Macquaries we have no means of
ascertaining, but as the intervening sea appears to be not more than about
1,500 fathoms deep it is quite possible that such an amount of subsidence
may have occurred. It is possible, too, that there may have been an
extension northward to the Kermadec Islands, and even further to the Tonga
and Fiji Islands, though this is hardly probable, or we should find more
community between their productions and those of New Zealand.
A southern extension towards the Antarctic continent at a somewhat later
period seems more probable, as affording an easy passage for the numerous
species of South American and Antarctic plants, and also for the identical
and closely allied fresh-water fishes of these countries.
The subsequent breaking up of this extensive land into a number of separate
islands in which the distinct species of moa and kiwi were developed--their
union at a later period, and the final submergence of all but the existing
islands, is a pure hypothesis, which seems necessary to explain the
occurrence of so many species of these birds in a small area but of which
we have no independent proof. There are, however, some other facts which
would be explained by it, as the presence of three peculiar but allied
genera of starlings, the three species of parrots of the genus Nestor, and
the six distinct rails of the genus Ocydromus, as well as the numerous
species in some of the peculiar New Zealand genera of plants, which seem
less likely to have been developed in a single area than when isolated, and
thus preserved from the counteracting influence of intercrossing.
In the present state of our knowledge these seem all the conclusions we can
arrive at from a study of the New Zealand fauna; but as we fortunately
possess a tolerably {486} full and accurate knowledge of the flora of New
Zealand, as well as of that of Australia and the south temperate lands
generally, it will be well to see how far these conclusions are supported
by the facts of plant distribution, and what further indications they
afford us of the early history of these most interesting countries. This
inquiry is of sufficient importance to occupy a separate chapter.
* * * * *
{487}
CHAPTER XXII
THE FLORA OF NEW ZEALAND: ITS AFFINITIES AND PROBABLE ORIGIN
Relations of the New Zealand Flora to that of Australia--General
Features of the Australian Flora--The Floras of South-eastern and
South-western Australia--Geological Explanation of the Differences of
these two Floras--The Origin of the Australian Element in the New
Zealand Flora--Tropical Character of the New Zealand Flora
Explained--Species Common to New Zealand and Australia mostly Temperate
Forms--Why Easily Dispersed Plants have often Restricted
Ranges--Summary and Conclusion on the New Zealand Flora.
Although plants have means of dispersal far exceeding those possessed by
animals, yet as a matter of fact comparatively few species are carried for
very great distances, and the flora of a country taken as a whole usually
affords trustworthy indications of its past history. Plants, too, are more
numerous in species than the higher animals, and are almost always better
known; their affinities have been more systematically studied; and it may
be safely affirmed that no explanation of the origin of the fauna of a
country can be sound, which does not also explain, or at least harmonise
with, the distribution and relations of its flora. The distribution of the
two may be very different, but both should be explicable by the same series
of geographical changes.
The relations of the flora of New Zealand to that of Australia have long
formed an insoluble enigma for {488} botanists. Sir Joseph Hooker, in his
most instructive and masterly essay on the flora of Australia,
says:--"Under whatever aspect I regard the flora of Australia and of New
Zealand, I find all attempts to theorise on the possible causes of their
community of feature frustrated by anomalies in distribution, such as I
believe no two other similarly situated countries in the globe present.
Everywhere else I recognise a parallelism or harmony in the main common
features of contiguous floras, which conveys the impression of their
generic affinity, at least, being affected by migration from centres of
dispersion in one of them, or in some adjacent country. In this case it is
widely different. Regarding the question from the Australian point of view,
it is impossible in the present state of science to reconcile the fact of
Acacia, Eucalyptus, Casuarina, Callitris, &c., being absent in New Zealand,
with any theory of transoceanic migration that may be adopted to explain
the presence of other Australian plants in New Zealand; and it is very
difficult to conceive of a time or of conditions that could explain these
anomalies, except by going back to epochs when the prevalent botanical as
well as geographical features of each were widely different from what they
are now. On the other hand, if I regard the question from the New Zealand
point of view, I find such broad features of resemblance, and so many
connecting links that afford irresistible evidence of a close botanical
connection, that I cannot abandon the conviction that these great
differences will present the least difficulties to whatever theory may
explain the whole case." I will now state, as briefly as possible, what are
the facts above referred to as being of so anomalous a character, and there
is little difficulty in doing so, as we have them fully set forth, with
admirable clearness, in the essay above alluded to, and in the same
writer's _Introduction to the Flora of New Zealand_, only requiring some
slight modifications, owing to the later discoveries which are given in the
_Handbook of the New Zealand Flora_.
Confining ourselves always to flowering plants, we find that the flora of
New Zealand is a very poor one, considering the extent of surface, and the
favourable conditions of {489} soil and climate. It consists of 1,085
species (our own islands possessing about 1,500), but a very large
proportion of these are peculiar, there being no less than 800 endemic
species, and thirty-two endemic genera.
Out of the 285 species not peculiar to New Zealand, no less than 215 are
Australian, but a considerable number of these are also Antarctic, South
American, or European; so that there are only about 100 _species_
absolutely confined to New Zealand and Australia, and, what is important as
indicating a somewhat recent immigration, only some half-dozen of these
belong to _genera_ which are peculiar to the two countries, and hardly any
to the larger and more important Australian genera. Many, too, are rare
species in both countries and are often alpines.
Far more important are the relations of the genera and families of the two
countries. All the Natural Orders of New Zealand are found in Australia
except three--Coriariæ, a widely-scattered group found in South Europe, the
Himalayas, and the Andes; Escallonieæ, a widely distributed group; and
Chloranthaceæ, found in Tropical Asia, Japan, Polynesia, and South America.
Out of a total of 310 New Zealand genera, no less than 248 are Australian,
and sixty of these are almost peculiar to the two countries, only
thirty-two however being absolutely confined to them.[127] In the three
large orders--Compositæ, Orchideæ, and Gramineæ, the genera are almost
identical in the two countries, while the species--in the two former
especially--are mostly distinct.
Here then we have apparently a wonderful resemblance between the New
Zealand flora and that of Australia, indicated by more than two-thirds of
the non-peculiar species, and more than nine-tenths of the non-peculiar
genera (255) being Australian. But now let us look at the other side of the
question.
There are in Australia seven great genera of plants, each containing more
than 100 species, all widely spread over {490} the country, and all highly
characteristic Australian forms,--Acacia, Eucalyptus, Melaleuca,
Leucopogon, Stylidium, Grevillea, and Hakea. These are entirely absent from
New Zealand, except one species of Leucopogon, a genus which also has
representatives in the Malayan and Pacific Islands. Sixteen more Australian
genera have over fifty species each, and of these eight are totally absent
from New Zealand, five are represented by one or two species, and only two
are fairly represented; but these two--Drosera and Helichrysum--are very
widespread genera, and might have reached New Zealand from other countries
than Australia.
But this by no means exhausts the differences between New Zealand and
Australia. No less than seven Australian Natural Orders--Dilleniaceæ,
Buettneriaceæ, Polygaleæ, Tremandreæ, Casuarineæ, Hæmodoraceæ, and Xyrideæ
are entirely wanting in New Zealand, and several others which are
excessively abundant and highly characteristic of the former country are
very poorly represented in the latter. Thus, Leguminosæ are extremely
abundant in Australia, where there are over 1,000 species belonging to
about 100 genera, many of them altogether peculiar to the country; yet in
New Zealand this great order is most scantily represented, there being only
five genera and thirteen species; and only two of these genera, Swainsonia
and Clianthus, are Australian, and as the latter consists of but two
species it may as well have passed from New Zealand to Australia as the
other way, or more probably from some third country to them both.[128]
Goodeniaceæ with ten genera and 220 species Australian, has but two species
in New Zealand--and one of these is a salt-marsh plant found also in
Tasmania and in Chile; and four other large Australian orders--Rhamneæ,
Myoporineæ, Proteaceæ and Santalaceæ, have very few representatives in New
Zealand.
We find, then, that the great fact we have to explain and account for is,
the undoubted affinity of the New {491} Zealand flora to that of Australia,
but an affinity almost exclusively confined to the least predominant and
least peculiar portion of that flora, leaving the most predominant, most
characteristic, and most widely distributed portion absolutely
unrepresented. We must however be careful not to exaggerate the amount of
affinity with Australia, apparently implied by the fact that nearly
six-sevenths of the New Zealand genera are also Australian, for, as we have
already stated, a very large number of these are European, Antarctic, South
American or Polynesian genera, whose presence in the two contiguous areas
only indicates a common origin. About one-eighth, only, are absolutely
confined to Australia and New Zealand (thirty-two genera), and even of
these several are better represented in New Zealand than in Australia, and
may therefore have passed from the former to the latter. No less than 174
of the New Zealand genera are temperate South American, many being also
Antarctic or European; while others again are especially tropical or
Polynesian; yet undoubtedly a larger proportion of the Natural Orders and
genera are common to Australia than to any other country, so that we may
say that the basis of the flora is Australian with a large intermixture of
northern and southern temperate forms and others which have remote
world-wide affinities.
_General Features of the Australian Flora and its Probable Origin._--Before
proceeding to point out how the peculiarities of the New Zealand flora may
be best accounted for, it is necessary to consider briefly what are the
main peculiarities of Australian vegetation, from which so important a part
of that of New Zealand has evidently been derived.
The actual Australian flora consists of two great divisions--a temperate
and a tropical, the temperate being again divisible into an eastern and a
western portion. All that is most characteristic of the Australian flora
belongs to the temperate division (though these often overspread the whole
continent), in which are found almost all the remarkable Australian types
of vegetation and the numerous genera peculiar to this part of the world.
Contrary to what occurs in most other countries, the {492} tropical appears
to be less rich in species and genera than the temperate region, and what
is still more remarkable it contains fewer peculiar species, and very few
peculiar genera. Although the area of tropical Australia is about equal to
that of the temperate portions, and it has now been pretty well explored
botanically, it has probably not more than half as many species.[129]
Nearly 500 of its species are identical with Indian or Malayan plants, or
are very close representatives of them; while there are more than 200
Indian genera, confined for the most part to the tropical portion of
Australia. The remainder of the tropical flora consists of a few species
and many genera of temperate {493} Australia which range over the whole
continent, but these form only a small portion of the peculiarly Australian
genera.
These remarkable facts clearly point to one conclusion--that the flora of
tropical Australia is, comparatively, recent and derivative. If we imagine
the greater part of North Australia to have been submerged beneath the
ocean, from which it rose in the middle or latter part of the Tertiary
period, offering an extensive area ready to be covered by such suitable
forms of vegetation as could first reach it, something like the present
condition of things would inevitably arise. From the north, widespread
Indian and Malay plants would quickly enter, while from the south the most
dominant forms of warm-temperate Australia, and such as were best adapted
to the tropical climate and arid soil, would intermingle with them. Even if
numerous islands had occupied the area of Northern Australia for long
periods anterior to the final elevation, very much the same state of things
would result.
The existence in North and North-east Australia of enormous areas covered
with Cretaceous and other Secondary deposits, as well as extensive Tertiary
formations, lends support to the view, that during very long epochs
temperate Australia was cut off from all close connection with the tropical
and northern lands by a wide extent of sea; and this isolation is exactly
what was required, in order to bring about the wonderful amount of
specialisation and the high development manifested by the typical
Australian flora. Before proceeding further, however, let us examine this
flora itself, so far as regards its component parts and probable past
history.
_The Floras of South-eastern and South-western Australia._--The
peculiarities presented by the south-eastern and south-western subdivisions
of the flora of temperate Australia are most interesting and suggestive,
and are, perhaps, unparalleled in any other part of the world. South-west
Australia is far less extensive than the south-eastern division--less
varied in soil and climate, with no lofty mountains, and much sandy desert;
yet, strange to say, it contains an equally rich flora and a far greater
proportion of peculiar species and genera of plants. As Sir {494} Joseph
Hooker remarks:--"What differences there are in conditions would, judging
from analogy with other countries, favour the idea that South-eastern
Australia, from its far greater area, many large rivers, extensive tracts
of mountainous country and humid forests, would present much the most
extensive flora, of which only the drier types could extend into
South-western Australia. But such is not the case; for though the far
greater area is much the best explored, presents more varied conditions,
and is tenanted by a larger number of Natural Orders and genera, these
contain fewer species by several hundreds."[130]
The fewer genera of South-western Australia are due almost wholly to the
absence of the numerous European, Antarctic, and South-American types found
in the south-eastern region, while in purely Australian types it is far the
richer, for while it contains most of those found in the east it has a
large number altogether peculiar to it; and Sir Joseph Hooker states that
"there are about 180 genera, out of 600 in South-western Australia, that
are either not found at all in South-eastern, or that are represented there
by a very few species only, and these 180 genera include nearly 1,100
species."
_Geological Explanation of the Differences of these Two Floras._--These
facts again clearly point to the conclusion that South-western Australia is
the remnant of the more extensive and more isolated portion of the
continent in which the peculiar Australian flora was principally developed.
The existence there of a very large area of granite--800 miles in length by
nearly 500 in maximum width with detached masses 200 miles to the north and
500 miles to the east--indicates such an extension; for these {495}
granitic masses were certainly once buried under piles of stratified rock,
since denuded, and then formed the nucleus of the old Western Australian
continent. If we take the 1000-fathom line around the southern part of
Australia to represent the probable extension of this old land we shall see
that it would give a wide additional area south of the Great Australian
Bight, and form a continent which, even if the greater part of tropical
Australia were submerged, would be sufficient for the development of a
peculiar and abundant flora. We must also remember that an elevation of
6000 feet, added to the vast amount which has been taken away by
denudation, would change the whole country, including what are now the
deserts of the interior, into a mountainous and well-watered region.
But while this rich and peculiar flora was in process of formation, the
eastern portion of the continent must either have been widely separated
from the western or had perhaps not yet risen from the ocean. The whole of
this part of the country consists of Palæozoic and Secondary formations
with granite and metamorphic rocks, the Secondary deposits being largely
developed on both sides of the central range, extending the whole length of
the continent from Tasmania to Cape York, and constituting the greater part
of the plateau of the Blue Mountains and other lofty ranges. During some
portion of the Secondary and Tertiary periods therefore, this side of
Australia must have been almost wholly submerged beneath the ocean; and if
we suppose that during this time the western part of the continent was at
nearly its maximum extent and elevation, we shall have a sufficient
explanation of the great difference between the flora of Western and
Eastern Australia, since the latter would only have been able to receive
immigrants from the former, at a later period, and in a more or less
fragmentary manner.
If we examine the geological map of Australia (given in Stanford's
Compendium of Geography and Travel, volume _Australasia_), we shall see
good reason to conclude that the eastern and the western divisions of the
country first existed as separate islands, and only became united at a
comparatively recent epoch. This is indicated by an {496} enormous stretch
of Cretaceous and Tertiary formations extending from the Gulf of
Carpentaria completely across the continent to the mouth of the Murray
River. During the Cretaceous period, therefore, and probably throughout a
considerable portion of the Tertiary epoch,[131] there must have been a
wide arm of the sea occupying this area, dividing the great mass of land on
the west--the true seat and origin of the typical Australian flora--from a
long but narrow belt of land on the east, indicated by the continuous mass
of Secondary and Palæozoic formations already referred to which extend
uninterruptedly from Tasmania to Cape York. Whether this formed one
continuous land, or was broken up into islands, cannot be positively
determined; but the fact that no marine Tertiary beds occur in the whole of
this area, renders it probable that it was almost, if not quite,
continuous, and that it not improbably extended across to what is now New
Guinea. At this epoch, then (as shown in the accompanying map), Australia
may, not improbably, have consisted of a very large and fertile western
island, almost or quite extratropical, and extending from the Silurian
rocks of the Flinders range in South Australia, to about 150 miles west of
the present west coast, and southward to about 350 miles south of the Great
Australian Bight. To the east of this, at a distance of from 250 to 400
miles, extended in a north and south direction a long but comparatively
narrow island, stretching from far south of Tasmania to New Guinea; while
the crystalline and Secondary formations of central North Australia
probably indicate the existence of one or more large islands in that
direction.
{497}
The white portions represent land; the shaded parts sea.
The existing land of Australia is shown in outline.]
The eastern and the western islands--with which we are now chiefly
concerned--would then differ considerably in their vegetation and animal
life. The western and more ancient land already possessed, in its main
features, the peculiar Australian flora, and also the ancestral forms of
its strange marsupial fauna, both of which it had probably received at some
earlier epoch by a temporary union with the Asiatic continent over what is
now the Java sea. Eastern Australia, on the other hand, possessed only the
rudiments of its existing mixed flora, derived from three distinct sources.
Some important fragments of the typical Australian vegetation had reached
it across the marine {498} strait, and had spread widely owing to the soil,
climate and general conditions being exactly suited to it: from the north
and north-east a tropical vegetation of Polynesian type had occupied
suitable areas in the north; while the extension southward of the Tasmanian
peninsula, accompanied, probably, as now, with lofty mountains, favoured
the immigration of south-temperate forms from whatever Antarctic lands or
islands then existed. This supposition is strikingly in harmony with what
is known of the ancient flora of this portion of Australia. In deposits
supposed to be of Eocene age in New South Wales and Victoria fossil plants
have been found showing a very different vegetation from that now existing.
Along with a few Australian types--such as Pittosporum, Knightia, and
Eucalyptus, there occur birches, alders, oaks, and beeches; while in
Tasmania in freshwater limestone, apparently of Miocene age, are found
willows, alders, birches, oaks, and beeches,[132] all except the latter
genus (Fagus) now quite extinct in Australia.[133] These temperate forms
probably indicate a more oceanic climate, cooler and moister than at
present. The union with Western Australia and the establishment of an arid
interior by modifying the climate may have led to the extinction of many of
these forms and their replacement by special Australian types more suited
to the new conditions.
At this time the marsupial fauna had not yet reached this eastern land,
which was, however, occupied in the north by some ancestral struthious
birds, which had entered it by way of New Guinea through some very ancient
continental extension, and of which the emu, the cassowaries, the extinct
Dromornis of Queensland, and the moas and kiwis of New Zealand, are the
modified descendants.
_The Origin of the Australian Element in the New Zealand Flora._--We have
now brought down the history of Australia, as deduced from its geological
structure and the main features of its existing and Tertiary flora, to the
period {499} when New Zealand was first brought into close connection with
it, by means of a great north-western extension of that country, which, as
already explained in our last chapter, is so clearly indicated by the form
of the sea bottom (See Map, p. 471). The condition of New Zealand previous
to this event is very obscure. That it had long existed as a more or less
extensive land is indicated by its ancient sedimentary rocks; while the
very small areas occupied by Jurassic and Cretaceous deposits, imply that
much of the present land was then also above the sea-level. The country had
probably at that time a scanty vegetation of mixed Antarctic and Polynesian
origin; but now, for the first time, it would be open to the free
immigration of such Australian types as were suitable to its climate, and
which _had already reached the tropical and sub-tropical portions of the
Eastern Australian island_. It is here that we obtain the clue to those
strange anomalies and contradictions presented by the New Zealand flora in
its relation to Australia, which have been so clearly set forth by Sir
Joseph Hooker, and which have so puzzled botanists to account for. But
these apparent anomalies cease to present any difficulty when we see that
the Australian plants in New Zealand were acquired, not directly, but, as
it were, at second hand, by union with an island which itself had as yet
only received a portion of its existing flora. And then, further
difficulties were placed in the way of New Zealand receiving such an
adequate representation of that portion of the flora which had reached East
Australia as its climate and position entitled it to, by the fact of the
union being, not with the temperate, but with the tropical and sub-tropical
portions of that island, so that only those groups could be acquired which
were less exclusively temperate, and had already established themselves in
the warmer portion of their new home.[134]
{500}
It is therefore no matter of surprise, but exactly what we should expect,
that the great mass of pre-eminently temperate Australian genera should be
absent from New Zealand, including the whole of such important families as,
Dilleniaceæ, Tremandreæ, Buettneriacæ, Polygaleæ, Casuarineæ and
Hæmodoraceæ; while others, such as Rutaceæ, Stackhousieæ, Rhamneæ,
Myrtaceæ, Proteaceæ, and Santalaceæ, are represented by only a few species.
Thus, too, we can explain the absence of _all_ the peculiar Australian
Leguminosæ; for these were still mainly confined to the great western
island, along with the peculiar Acacias and Eucalypti, which at a later
period spread over the whole continent. It is equally accordant with the
view we are maintaining, that among the groups which Sir Joseph Hooker
enumerates as "keeping up the features of extra tropical Australia in its
tropical quarter," several should have reached New Zealand, such as
Drosera, some Pittosporeæ and Myoporineæ, with a few Proteaceæ, Loganiaceæ,
and Restiaceæ; for most of these are not only found in tropical Australia,
but also in the Malayan and Pacific islands.
_Tropical Character of the New Zealand Flora Explained._--In this origin of
the New Zealand fauna by a north-western route from North-eastern
Australia, we find also an explanation of the remarkable number of tropical
groups of plants found there: for though, as Sir Joseph Hooker has {501}
shown, a moist and uniform climate favours the extension of tropical forms
in the temperate zone, yet some means must be afforded them for reaching a
temperate island. On carefully going through the _Handbook_, and comparing
its indications with those of Bentham's _Flora Australiensis_, I find that
there are in New Zealand thirty-eight thoroughly tropical genera,
thirty-three of which are found in Australia--mostly in the tropical
portion of it, though a few are temperate, and these may have reached it
through New Zealand[135]. To these we must add thirty-two more genera,
which, though chiefly developed in temperate Australia, extend into the
tropical or sub-tropical portions of it, and may well have reached New
Zealand by the same route.
On the other hand we find but few New Zealand genera certainly derived from
Australia which are especially temperate, and it may be as well to give a
list of such as {502} do occur with a few remarks. They are sixteen in
number, as follows:--
1. Pennantia (1 sp.). This genus has a species in Norfolk Island,
indicating perhaps its former extension to the north-west.
2. Pomaderris (3 sp.). One _species_ inhabits Victoria and New Zealand,
indicating recent trans-oceanic migration.
3. Quintinia (2 sp.). This genus has winged seeds facilitating
migration.
4. Olearia (20 sp.). Seeds with pappus.
5. Craspedia (2 sp.). Seeds with pappus. Alpine; identical with
Australian species, and therefore of comparatively recent introduction.
6. Celmisia (25 sp.). Seeds with pappus. Only three Australian species,
two of which are identical with New Zealand forms, probably therefore
derived from New Zealand.
7. Ozothamnus (5 sp.). Seeds with pappus.
8. Epacris (4 sp.). Minute seeds. Some species are sub-tropical, and
they are all found in the northern (warmer) island of New Zealand.
9. Archeria (2 sp.). Minute seeds. A species common to E. Australia and
New Zealand.
10. Logania (3 sp.). Small seeds. Alpine plants.
11. Hedycarya (1 sp.).
12. Chiloglottis (1 sp.). Minute seeds. In Auckland Islands; alpine in
Australia.
13. Prasophyllum (1 sp.). Minute seeds. Identical with Australian
species, indicating recent transmission.
14. Orthoceras (1 sp.). Minute seeds. Identical with an Australian
species.
15. Alepyrum (1 sp.). Alpine, moss-like. An Antarctic type.
16. Dichelachne (3 sp.). Identical with Australian species. An awned
grass.
We thus see that there are special features in most of these plants that
would facilitate transmission across the sea between temperate Australia
and New Zealand, or to both from some Antarctic island; and the fact that
in several of them the species are absolutely identical shows that such
transmission has occurred in geologically recent times.
_Species Common to New Zealand and Australia Mostly Temperate Forms._--Let
us now take the _species_ which are common to New Zealand and Australia,
but found nowhere else, and which must therefore have passed from one
country to the other at a more recent period than the mass of _genera_ with
which we have hitherto been dealing. These are ninety-six in number, and
they present a striking contrast to the similarly restricted _genera_ in
being wholly temperate in character, the entire list presenting only a
{503} single species which is confined to sub-tropical East Australia--a
grass (_Apera arundinacea_) only found in a few localities on the New
Zealand coast.
Now it is clear that the larger portion, if not the whole, of these plants
must have reached New Zealand from Australia (or in a few cases Australia
from New Zealand), by transmission across the sea, because we know there
has been no actual land connection during the Tertiary period, as proved by
the absence of all the Australian mammalia, and almost all the most
characteristic Australian birds, insects, and plants. The form of the
sea-bed shows that the distance could not have been less than 600 miles,
even during the greatest extension of Southern New Zealand and Tasmania;
and we have no reason to suppose it to have been less, because in other
cases an equally abundant flora of identical species has reached islands at
a still greater distance--notably in the case of the Azores and Bermuda.
The character of the plants is also just what we should expect: for about
two-thirds of them belong to genera of world-wide range in the temperate
zones, such as Ranunculus, Drosera, Epilobium, Gnaphalium, Senecio,
Convolvulus, Atriplex, Luzula, and many sedges and grasses, whose
exceptionally wide distribution shows that they possess exceptional powers
of dispersal and vigour of constitution, enabling them not only to reach
distant countries, but also to establish themselves there. Another set of
plants belong to especially Antarctic or south temperate groups, such as
Colobanthus, Acæna, Gaultheria, Pernettya, and Muhlenbeckia, and these may
in some cases have reached both Australia and New Zealand from some now
submerged Antarctic island. Again, about one-fourth of the whole are alpine
plants, and these possess two advantages as colonisers. Their lofty
stations place them in the best position to have their seeds carried away
by winds; and they would in this case reach a country which, having derived
the earlier portion of its flora from the side of the tropics, would be
likely to have its higher mountains and favourable alpine stations to a
great extent unoccupied, or occupied by plants unable to compete with
specially adapted alpine groups. {504}
Fully one-third of the exclusively Australo-New Zealand species belong to
the two great orders of the sedges and the grasses; and there can be no
doubt that these have great facilities for dispersion in a variety of ways.
Their seeds, often enveloped in chaffy glumes, would be carried long
distances by storms of wind, and even if finally dropped into the sea would
have so much less distance to reach the land by means of surface currents;
and Mr. Darwin's experiments show that even cultivated oats germinated
after 100 days' immersion in sea-water. Others have hispid awns by which
they would become attached to the feathers of birds, and there is no doubt
this is an effective mode of dispersal. But a still more important point
is, probably, that these plants are generally, if not always,
wind-fertilised, and are thus independent of any peculiar insects, which
might be wanting in the new country.
_Why Easily-Dispersed Plants have often Restricted Ranges._--This last
consideration throws light on a very curious point, which has been noted as
a difficulty by Sir Joseph Hooker, that plants which have most clear and
decided powers of dispersal by wind or other means, have _not_ generally
the widest specific range; and he instances the small number of Compositæ
common to New Zealand and Australia. But in all these cases it will, I
think, be found that although the _species_ have not a wide range the
_genera_ often have. In New Zealand, for instance, the Compositæ are very
abundant, there being no less than 167 species, almost all belonging to
Australian genera, yet only about one-sixteenth of the whole are identical
in the two countries. The explanation of this is not difficult. Owing to
their great powers of dispersal, the Australian Compositæ reached New
Zealand at a very remote epoch, and such as were adapted to the climate and
the means of fertilisation established themselves; but being highly
organised plants with great flexibility of organisation, they soon became
modified in accordance with the new conditions, producing many special
forms in different localities; and these, spreading widely, soon took
possession of all suitable stations. Henceforth immigrants from Australia
had to compete {505} with these indigenous and well-established plants, and
only in a few cases were able to obtain a footing; whence it arises that we
have many Australian types, but few Australian species, in New Zealand, and
both phenomena are directly traceable to the combination of great powers of
dispersal with a high degree of adaptability. Exactly the same thing occurs
with the still more highly specialised Orchideæ. These are not
proportionally so numerous in New Zealand (thirty-eight species), and this
is no doubt due to the fact that so many of them require
insect-fertilisation often by a particular family or genus (whereas almost
any insect will fertilise Compositæ), and insects of all orders are
remarkably scarce in New Zealand.[136] This would at once prevent the
establishment of many of the orchids which may have reached the islands,
while those which did find suitable fertilisers and other favourable
conditions would soon become modified into new species. It is thus quite
intelligible why only three species of orchids are identical in Australia
and New Zealand, although their minute and abundant seeds must be dispersed
by the wind almost as readily as the spores of ferns.
Another specialised group--the Scrophularineæ--abounds in New Zealand,
where there are sixty-two species; but though almost all the genera are
Australian only three species are so. Here, too, the seeds are usually very
small, and the powers of dispersal great, as shown by several European
genera--Veronica, Euphrasia, and Limosella, being found in the southern
hemisphere.
Looking at the whole series of these Australo-New Zealand plants, we find
the most highly specialised groups--Compositæ, Scrophularineæ,
Orchideæ--with a small proportion of identical species (one-thirteenth to
one twentieth), the less highly specialised--Ranunculaceæ, Onagrariæ and
Ericeæ--with a higher proportion (one-ninth to one-sixth), and the least
specialised--Junceæ, {506} Cyperaceæ and Gramineæ--with the high proportion
in each case of one-fourth. These nine are the most important New Zealand
orders which contain species common to that country and Australia and
confined to them; and the marked correspondence they show between high
specialisation and want of _specific_ identity, while the _generic_
identity is in all cases approximately equal, points to the conclusion that
the means of diffusion are, in almost all plants ample, when long periods
of time are concerned, and that diversities in this respect are not so
important in determining the peculiar character of a derived flora, as
adaptability to varied conditions, great powers of multiplication, and
inherent vigour of constitution. This point will have to be more fully
discussed in treating of the origin of the Antarctic and north temperate
members of the New Zealand flora.
_Summary and Conclusion on the New Zealand Flora._--Confining ourselves
strictly to the direct relations between the plants of New Zealand and of
Australia, as I have done in the preceding discussion, I think I may claim
to have shown that the union between the two countries in the latter part
of the Secondary epoch at a time when Eastern Australia was widely
separated from Western Australia (as shown by its geological formation and
by the contour of the sea-bottom) does sufficiently account for all the
main features of the New Zealand flora. It shows why the basis of the flora
is fundamentally Australian both as regards orders and genera, for it was
due either to a direct land connection or a somewhat close approximation
between the two countries. It shows also why the great mass of typical
Australian forms are unrepresented, for the Australian flora is typically
_western_ and _temperate_, and New Zealand received its immigrants from the
_eastern_ island which had itself received only a fragment of this flora,
and from the _tropical_ end of this island, and thus could only receive
such forms as were not exclusively temperate in character. It shows,
further, why New Zealand contains such a very large proportion of tropical
forms, for we see that it derived the main portion of its flora directly
from the tropics. Again, this hypothesis shows us why, though {507} the
specially Australian _genera_ in New Zealand are largely tropical or
sub-tropical, the specially Australian _species_ are wholly temperate or
alpine; for these are comparatively recent arrivals, they must have
migrated across the sea in the temperate zone, and these temperate and
alpine forms are exactly such as would be best able to establish themselves
in a country already stocked mainly by tropical forms and their modified
descendants. This hypothesis further fulfils the conditions implied in Sir
Joseph Hooker's anticipation that--"these great differences (of the floras)
will present the least difficulties to whatever theory may explain the
whole case,"--for it shows that these differences are directly due to the
history and development of the Australian flora itself, while the
resemblances depend upon the most certain cause of all such broad
resemblances--close proximity or actual land connection.
One objection will undoubtedly be made to the above theory,--that it does
not explain why some species of the prominent Australian genera Acacia,
Eucalyptus, Melaleuca, Grevillea, &c., have not reached New Zealand in
recent times along with the other temperate forms that have established
themselves. But it is doubtful whether any detailed explanation of such a
negative fact is possible, while general explanations sufficient to cover
it are not wanting. Nothing is more certain than that numerous plants never
run wild and establish themselves in countries where they nevertheless grow
freely if cultivated; and the explanation of this fact given by Mr.
Darwin--that they are prevented doing so by the competition of better
adapted forms--is held to be sufficient. In this particular case, however,
we have some very remarkable evidence of the fact of their non-adaptation.
The intercourse between New Zealand and Europe has been the means of
introducing a host of common European plants,--more than 150 in number, as
enumerated at the end of the second volume of the _Handbook_; yet, although
the intercourse with Australia has probably been greater, only two or three
Australian plants have similarly established themselves. More remarkable
still, Sir Joseph Hooker states: {508} "I am informed that the late Mr.
Bidwell habitually scattered Australian seeds during his extensive travels
in New Zealand." We may be pretty sure that seeds of such excessively
common and characteristic groups as _Acacia_ and _Eucalyptus_ would be
among those so scattered, yet we have no record of any plants of these or
other peculiar Australian genera ever having been found wild, still less of
their having spread and taken possession of the soil in the way that many
European plants have done. We are, then, entitled to conclude that the
plants above referred to have not established themselves in New Zealand
(although their seeds may have reached it) because they could not
successfully compete with the indigenous flora which was already well
established and better adapted to the conditions of climate and of the
organic environment. This explanation is so perfectly in accordance with a
large body of well-known facts, including that which is known to every
one--how few of our oldest and hardiest garden plants ever run wild--that
the objection above stated will, I feel convinced, have no real weight with
any naturalists who have paid attention to this class of questions.
* * * * *
{509}
CHAPTER XXIII
ON THE ARCTIC ELEMENT IN SOUTH TEMPERATE FLORAS
European Species and Genera of Plants in the Southern
Hemisphere--Aggressive Power of the Scandinavian Flora--Means by which
Plants have Migrated from North to South--Newly moved Soil as Affording
Temporary Stations to Migrating Plants--Elevation and Depression of the
Snow-line as Aiding the Migration of Plants--Changes of Climate
Favourable to Migration--The Migration from North to South has been
long going on--Geological Changes as Aiding Migration--Proofs of
Migration by way of the Andes--Proofs of Migration by way of the
Himalayas and Southern Asia--Proofs of Migration by way of the African
Highlands--Supposed Connection of South Africa and Australia--The
Endemic Genera of Plants in New Zealand--The Absence of Southern Types
from the Northern Hemisphere--Concluding Remarks on the New Zealand and
South Temperate Floras.
We have now to deal with another portion of the New Zealand flora which
presents perhaps equal difficulties--that which appears to have been
derived from remote parts of the north and south temperate zones; and this
will lead us to inquire into the origin of the northern or Arctic element
in all the south temperate floras.
More than one-third of the entire number of New Zealand genera (115) are
found also in Europe, and even fifty-eight species are identical in these
remote parts of the world. Temperate South America has seventy-four genera
in common with New Zealand, and there are even eleven species identical in
the two countries, as well as thirty-two which are close allies or
representative species. {510} A considerable number of these northern or
Antarctic plants and many more which are representative species, are found
also in Tasmania and in the mountains of temperate Australia; and Sir
Joseph Hooker gives a list of thirty-eight species very characteristic of
Europe and Northern Asia, but almost or quite unknown in the warmer
regions, which yet reappear in temperate Australia. Other genera seem
altogether Antarctic--that is, confined to the extreme southern lands and
islands; and these often have representative species in Southern America,
Tasmania, and New Zealand, while others occur only in one or two of these
areas. Many north temperate genera also occur in the mountains of South
Africa. On the other hand, few if any of the peculiar Australian or
Antarctic types have spread northwards, except some of the former which
have reached the mountains of Borneo, and a few of the latter which spread
along the Andes to Mexico.
On these remarkable facts, of which I have given but the barest outline,
Sir Joseph Hooker makes the following suggestive observations:--
"When I take a comprehensive view of the vegetation of the Old World, I am
struck with the appearance it presents of there being a continuous current
of vegetation (if I may so fancifully express myself) from Scandinavia to
Tasmania; along, in short, the whole extent of that arc of the terrestrial
sphere which presents the greatest continuity of land. In the first place
Scandinavian genera, and even species, reappear everywhere from Lapland and
Iceland to the tops of the Tasmanian Alps, in rapidly diminishing numbers
it is true, but in vigorous development throughout. They abound on the Alps
and Pyrenees, pass on to the Caucasus and Himalayas, thence they extend
along the Khasia Mountains, and those of the peninsulas of India to those
of Ceylon and the Malayan Archipelago (Java and Borneo), and after a hiatus
of 30° they appear on the Alps of New South Wales, Victoria, and Tasmania,
and beyond these again on those of New Zealand and the Antarctic Islands,
many of the species remaining unchanged throughout! It matters not what the
vegetation of the bases and flanks of these mountains may be; the northern
species may be {511} associated with alpine forms of Germanic, Siberian,
Oriental, Chinese, American, Malayan, and finally Australian, and Antarctic
types; but whereas these are all, more or less, local assemblages, the
Scandinavian asserts his prerogative of ubiquity from Britain to beyond its
antipodes."[137]
It is impossible to place the main facts more forcibly before the reader
than in the above striking passage. It shows clearly that this portion of
the New Zealand flora is due to wide-spread causes which have acted with
even greater effect in other south temperate lands, and that in order to
explain its origin we must grapple with the entire problem of the transfer
of the north temperate flora to the southern hemisphere. Taking, therefore,
the facts as given by Sir Joseph Hooker in the works already referred to, I
shall discuss the whole question broadly, and shall endeavour to point out
the general laws and subordinate causes that, in my opinion, have been at
work in bringing about the anomalous phenomena of distribution he has done
so much to make known and to elucidate.
_Aggressive Power of the Scandinavian Flora._--The first important fact
bearing upon this question is the wonderful aggressive and colonising power
of the Scandinavian flora, as shown by the way in which it establishes
itself in any temperate country to which it may gain access. About 150
species have thus established themselves in New Zealand, often taking
possession of large tracts of country; about the same number are found in
Australia, and nearly as many in the Atlantic states of America, where they
form the commonest weeds. Whether or not we accept Mr. Darwin's explanation
of this power as due to development in the most extensive land area of the
globe where competition has been most severe and long-continued, the fact
of the existence of this power remains, and we can see how important an
agent it must be in the formation of the floras of any lands to which these
aggressive plants have been able to gain access.
But not only are these plants pre-eminently capable of holding their own in
any temperate country in the world, but they also have exceptional powers
of migration and {512} dispersal over seas and oceans. This is especially
well shown by the case of the Azores, where no less than 400 out of a total
of 478 flowering plants are identical with European species. These islands
are more than 800 miles from Europe, and, as we have already seen in
Chapter XII., there is no reason for supposing that they have ever been
more nearly connected with it than they are now, since an extension of the
European coast to the 1,000-fathom line would very little reduce the
distance. Now it is a most interesting and suggestive fact that more than
half the European genera which occur in the Australian flora occur also in
the Azores, and in several cases even the species are identical in
both.[138] The importance of such a case as this cannot be exaggerated,
because it affords a demonstration of the power of the very plants in
question to pass over wide areas of sea, some no doubt wholly through the
air, carried by storms in the same way as the European birds and insects
which annually reach the Azores, others by floating on the waters, or by a
combination of the two methods; while some may have been carried by aquatic
birds, to whose feathers many seeds have the power of attaching themselves,
and some even in the stomachs of fruit or seed eating birds. We have in
such facts as these a complete disproof of the necessity for those great
changes of sea and land which are continually appealed to by those who
think land-connection the only efficient means of accounting for the
migration of animals or plants; but at the same time we do not neglect to
make the fullest use of such moderate changes as all the evidence at our
command leads us to believe have actually occurred, and especially of the
former existence of intermediate islands, so often indicated by shoals in
the midst of the deepest oceans.
_Means by which Plants have migrated from North to South._--But if plants
can thus pass in considerable numbers and variety over wide seas and
oceans, it must be yet more easy for them to traverse continuous areas of
land, whereever mountain-chains offer suitable stations at moderate {513}
intervals on which they might temporarily establish themselves. The
facilities afforded for the transmission of plants by mountains has hardly
received sufficient attention. The numerous land-slips, the fresh surfaces
of broken rock and precipice, the _debris_ of torrents, and the moraines
deposited by glaciers, afford numerous unoccupied stations on which
wind-borne seeds have a good chance of germinating. It is a well-known fact
that fresh surfaces of soil or rock, such as are presented by railway
cuttings and embankments, often produce plants strange to the locality,
which survive for a few years, and then disappear as the normal vegetation
gains strength and permanence.[139] But such a surface {514} will, in the
meantime, have acted as a fresh centre of dispersal; and thus a plant might
pass on step by step, by means of stations temporarily occupied, till it
reached a district {515} where, the general conditions being more
favourable, it was able to establish itself as a permanent member of the
flora. Such, generally speaking, was probably the process by which the
Scandinavian flora has made its way to the southern hemisphere; but it
could hardly have done so to any important extent without the aid of those
powerful causes explained in our eighth chapter--causes which acted as a
constantly recurrent motive-power to produce that "continuous current of
vegetation" from north to south across the whole width of the tropics
referred to by Sir Joseph Hooker. Those causes were, the repeated changes
{516} of climate which, during all geological time, appear to have occurred
in both hemispheres, culminating at rare intervals in glacial epochs, and
which have been shown to depend upon changes of excentricity of the earth's
orbit and the occurrence of summer or winter in _aphelion_, in conjunction
with the slower and more irregular changes of geographical conditions;
these combined causes acting chiefly through the agency of heat-bearing
oceanic currents, and of snow- and ice-collecting highlands. Let us now
briefly consider how such changes would act in favouring the dispersal of
plants.
_Elevation and Depression of the Snow Line as Aiding the Migration of
Plants._--We have endeavoured to show (in an earlier portion of this
volume) that wherever geographical or physical conditions were such as to
produce any considerable amount of perpetual snow, this would be increased
whenever a high degree of excentricity concurred with winter in _aphelion_,
and diminished during the opposite phase. On all mountain ranges,
therefore, which reached above the snow-line, there would be a periodical
increase and decrease of snow, and when there were extensive areas of
plateau at about the same level, the lowering of the snow-line might cause
such an increased accumulation of snow as to produce great glaciers and
ice-fields, such as we have seen occurred in South Africa during the last
period of high excentricity. But along with such depression of the line of
perpetual snow there would be a corresponding depression of the alpine and
sub-alpine zones suitable for the growth of an arctic and temperate
vegetation, and, what is perhaps more important, the depression would
necessarily produce a great _extension_ of the area of these zones on all
high mountains, because as we descend the average slopes become less
abrupt,--thus affording a number of new stations suitable for such
temperate plants as might first reach them. But just above and below the
snow-line is the area of most powerful disintegration and denudation, from
the alternate action of frost and sun, of ice and water; and thus the more
extended area would be subject to the constant occurrence of land-slips,
berg-falls, and floods, with their {517} accompanying accumulations of
_débris_ and of alluvial soil, affording innumerable stations in which
solitary wind-borne seeds might germinate and temporarily establish
themselves.
This lowering and rising of the snow-line each 10,500 years during periods
of high excentricity, would occur in the northern and southern hemispheres
alternately; and where there were high mountains within the tropics the two
would probably overlap each other, so that the northern depression would
make itself felt in a slight degree even across the equator some way into
the southern hemisphere, and _vice versâ_; and even if the difference of
the height of perpetual snow at the two extremes did not average more than
a few hundred feet, this would be amply sufficient to supply the new and
unoccupied stations needful to facilitate the migration of plants. It is
well known that all great mountain ranges have undergone such fluctuations,
as proved by ice-marks below the present level of snow and ice.
But the differences of temperature in the two hemispheres caused by the sun
being in _perihelion_ in the winter of the one while it was in _aphelion_
during the same season in the other, would necessarily lead to increased
aërial and marine currents, as already explained; and whenever geographical
conditions were such as to favour the production of glaciation in any area
these effects would become more powerful, and would further aid in the
dispersal of the seeds of plants.
_Changes of Climate Favourable to Migration._--It is clear then, that
during periods when no glacial epochs were produced in the northern
hemisphere, and even when a mild climate extended over the whole polar
area, alternate changes of climate favouring the dispersal of plants would
occur on all high mountains, and with particular force on such as rise
above the snow-line. But during that long-continued, though comparatively
recent, phase of high excentricity which produced an extensive glaciation
in the northern hemisphere and local glaciations in the southern, these
risings and lowerings of the snow-line on all mountain ranges would have
been at a maximum, and {518} would have been increased by the depression of
the ocean which must have arisen from such a vast bulk of water being
locked up in land-ice, and which depression would have produced the same
effect as a general elevation of all the continents. At this time, too,
aërial currents would have attained their maximum of force in both
hemispheres; and this would greatly facilitate the dispersal of all
wind-borne seeds as well as of those carried in the plumage or in the
stomachs of birds, since we have seen, by the cases of the Azores and
Bermuda, how vastly the migratory powers of birds are increased by a stormy
atmosphere.
_Migration from North to South has been long going on._--Now, if each phase
of colder and warmer mountain-climate--each alternate depression and
elevation of the snow-line, only helped on the migration of a few species
some stages of the long route from the north to the south temperate
regions, yet, during the long course of the Tertiary period there might
well have arisen that representation of the northern flora in the southern
hemisphere which is now so conspicuous. For it is very important to remark
that it is not the existing flora alone that is represented, such as might
have been conveyed during the last glacial epoch only; but we find a whole
series of northern types evidently of varying degrees of antiquity, while
even some genera characteristic of the southern hemisphere appear to have
been originally derived from Europe. Thus Eucalyptus and Metrosideros have
been determined by Dr. Ettingshausen from their fruits in the Eocene beds
of Sheppey, while Pimelea, Leptomeria and four genera of Proteaceæ have
been recognised by Professor Heer in the Miocene of Switzerland; and the
former writer has detected fifty-five Australian forms in the Eocene plant
beds of Häring (? Belgium).[140] Then we have such peculiar genera {519} as
Pachychladon and Notothlaspi of New Zealand said to have affinities with
Arctic plants, while Stilbocarpa--another peculiar New Zealand genus--has
its nearest allies in the Himalayan and Chinese Aralias. Following these
are a whole host of very distinct species of northern genera which may date
back to any part of the Tertiary period, and which occur in every south
temperate land. Then we have closely allied representative species of
European or Arctic plants; and, lastly, a number of identical species,--and
these two classes are probably due entirely to the action of the last great
glacial epoch, whose long continuance, and the repeated fluctuations of
climate with which it commenced and terminated, rendered it an agent of
sufficient power to have brought about this result.
Here, then, we have that constant or constantly recurrent process of
dispersal acting throughout long periods with varying power--that
"continuous current of vegetation" as it has been termed, which the facts
demand; and the extraordinary phenomenon of the species and genera of
European and even of Arctic plants being represented abundantly in South
America, Australia, and New Zealand, thus adds another to the long series
of phenomena which are rendered intelligible by frequent alternations of
warmer and colder climates in either hemisphere, culminating, at long
intervals and in favourable situations, in actual glacial epochs.
_Geological Changes as Aiding Migration._--It will be well also to notice
here, that there is another aid to dispersion dependent upon the changes
effected by denudation during the long periods included in the duration of
the species and genera of plants. A considerable number of {520} the plants
of the Miocene period of Europe were so much like existing species that
although they have generally received fresh names they may well have been
identical; and a large proportion of the vegetation during the whole
Tertiary period consisted of genera which are still living.[141] But from
what is now known of the rate of sub-aërial denudation, we are sure, that
during each division of this period many mountain chains must have been
considerably lowered, while we know that some of the existing ranges have
been greatly elevated. Ancient volcanoes, too, have been destroyed by
denudation, and new ones have been built up, so that we may be quite sure
that ample means for the transmission of temperate plants across the
tropics, may have existed in countries where they are now no longer to be
found. The great mountain masses of Guiana and Brazil, for example, must
have been far more lofty before the sedimentary covering was denuded from
their granitic bosses and metamorphic peaks, and may have aided the
southern migration of plants before the final elevation of the Andes. And
if Africa presents us with an example of a continent of vast antiquity, we
may be sure that its great central plateaux once bore far loftier mountain
ranges before they were reduced to their present condition by long ages of
denudation.
_Proofs of Migration by Way of the Andes._--We are now prepared to apply
the principles above laid down to the explanation of the character and
affinities of the various portions of the north temperate flora in the
southern hemisphere, and especially in Australia and New Zealand.
At the present time the only unbroken chain of highlands and mountains
connecting the Arctic and north temperate with the Antarctic lands is to be
found in the American continent, the only break of importance being the
comparatively low Isthmus of Panama, where there is {521} a distance of
about 300 miles occupied by rugged forest-clad hills, between the lofty
peaks of Veragua and the northern extremity of the Andes of New Grenada.
Such distances are, as we have already seen, no barrier to the diffusion of
plants; and we should accordingly expect that this great continuous
mountain-chain has formed the most effective agent in aiding the southward
migration of the Arctic and north temperate vegetation. We do find, in
fact, not only that a large number of northern genera and many species are
scattered all along this line of route, but that at the end of the long
journey, in Southern Chile and Fuegia, they have established themselves in
such numbers as to form an important part of the flora of those countries.
From the lists given in the works already referred to, it appears that
there are between sixty and seventy northern genera in Fuegia and Southern
Chile, while about forty of the species are absolutely identical with those
of Europe and the Arctic regions. Considering how comparatively little the
mountains of South Temperate America are yet known, this is a very
remarkable result, and it proves that the transmission of species must have
gone on up to comparatively recent times. Yet, as only a few of these
species are now found along the line of migration, we see that they only
occupied such stations temporarily; and we may connect their disappearance
with the passing away of the last glacial period which, by raising the
snow-line, reduced the area on which alone they could exist, and exposed
them to the competition of indigenous plants from the belt of country
immediately below them.
Now, just as these numerous species and genera have undoubtedly passed
along the great American range of mountains, although only now found at its
two extremes, so others have doubtless passed on further; and have found
more suitable stations or less severe competition in the Antarctic
continent and islands, in New Zealand, in Tasmania, and even in Australia
itself. The route by which they may have reached these countries is easily
marked out. Immediately south of Cape Horn, at a distance of only 500
miles, are the South Shetland Islands and Graham's Land, whence the
Antarctic continent or a {522} group of large islands probably extends
across or around the south polar area to Victoria Land and thence to Adélie
Land. The outlying Young Island, 12,000 feet high, is about 750 miles south
of the Macquarie Islands, which may be considered a southern outlier of the
New Zealand group; and the Macquarie Islands are about the same distance
from the 1,000-fathom line at a point marking the probable southern
extension of Tasmania. Other islands may have existed at intermediate
points; but, even as it is, these distances are not greater than we know
are traversed by plants both by flotation and by aërial currents,
especially in such a stormy atmosphere as that of the Antarctic regions.
Now, we may further assume, that what we know occurred within the Arctic
circle also took place in the Antarctic--that is, that there have been
alternations of climate during which some portion of what are now ice-clad
lands became able to support a considerable amount of vegetation.[142]
During such periods there would be a steady migration of plants from all
southern circumpolar countries to people the comparatively unoccupied
continent, and the southern extremity of America being considerably the
nearest, and also being the best stocked with those northern types which
have such great powers of migration and colonisation, such plants would
form the bulk of the Antarctic vegetation, and during the continuance of
the milder southern climate would occupy the whole area.
When the cold returned and the land again became ice-clad, these plants
would be crowded towards the outer margins of the Antarctic land and its
islands, and some of them would find their way across the sea to such
countries as offered on their mountain summits suitable cool stations; and
as this process of alternately receiving plants from Chile and Fuegia and
transmitting them in all directions from the central Antarctic land may
have been {523} repeated several times during the Tertiary period, we have
no difficulty in understanding the general community between the European
and Antarctic plants found in all south temperate lands. Kerguelen's Land
and The Crozets are within about the same distance from the Antarctic
continent as New Zealand and Tasmania, and we need not therefore be
surprised at finding in each of these islands some Fuegian species which
have not reached the others. Of course, there will remain difficulties of
detail, as there always must remain, so long as our knowledge of the past
changes of the earth's surface and the history of the particular plants
concerned is so imperfect. Sir Joseph Hooker notes, for example, the
curious fact that several Compositæ common to three such remote localities
as the Auckland Islands, Fuegia, and Kerguelen's Land, have no pappus or
seed-down, while such as have pappus are in no case common even to two of
these islands. Without knowing the exact history and distribution of the
genera to which these plants belong it would be useless to offer any
conjecture, except that they are ancient forms which may have survived
great geographical changes, or may have some peculiar and exceptional means
of dispersion.
_Proofs of Migration by way of the Himalayas and Southern Asia._--But
although we may thus explain the presence of a considerable portion of the
European element in the floras of New Zealand and Australia, we cannot
account for the whole of it by this means, because Australia itself
contains a host of European and Asiatic genera of which we find no trace in
New Zealand or South America, or any other Antarctic land. We find, in
fact, in Australia two distinct sets of European plants. First we have a
number of species identical with those of Northern Europe or Asia (of the
most characteristic of which--thirty-eight in number--Sir Joseph Hooker
gives a list); and in the second place a series of European genera usually
of a somewhat more southern character, mostly represented by very distinct
species, and all absent from New Zealand; such as Clematis, Papaver,
Cleome, Polygala, Lavatera, Ajuga, &c. Now of the first set--the North
European _species_--about three-fourths occur in some parts of America,
{524} and about half in South Temperate America or New Zealand; whence we
may conclude that most of these, as well as some others, have reached
Australia by the route already indicated. The second set of
Australo-European genera, however, and many others characteristic of the
South European or the Himalayan flora, have probably reached Australia by
way of the mountains of Southern Asia, Borneo, the Moluccas, and New
Guinea, at a somewhat remote period when loftier ranges and some
intermediate peaks may have existed, sufficient to carry on the migration
by the aid of the alternate climatal changes which are known to have
occurred. The long belt of Secondary and Palæozoic formations in East
Australia from Tasmania to Cape York continued by the lofty ranges of New
Guinea, indicates the route of this immigration, and sufficiently explains
how it is that these northern types are almost wholly confined to this part
of the Australian continent. Some of the earlier immigrants of this class
no doubt passed over to New Zealand and now form a portion of the peculiar
genera confined to these two countries; but most of them are of later date,
and have thus remained in Australia only.
_Proofs of Migration by way of the African Highlands._--It is owing to this
twofold current of vegetation flowing into Australia by widely different
routes that we have in this distant land a better representation of the
European flora, both as regards species and genera, than in any other part
of the southern hemisphere; and, so far as I can judge of the facts, there
is no general phenomenon--that is, nothing in the distribution of genera
and other groups of plants as opposed to cases of individual species--that
is not fairly accounted for by such an origin. It further receives support
from the case of South Africa, which also contains a large and important
representation of the northern flora. But here we see no indications (or
very slight ones) of that southern influx which has given Australia such a
community of vegetation with the Antarctic lands. There are no less than
sixty _genera_ of strictly north temperate plants in South Africa, none of
which occur in Australia; while very few of the _species_, so
characteristic of Australia, New Zealand, and Fuegia, are found there. It
{525} is clear, therefore, that South Africa has received its European
plants by the direct route through the Abyssinian highlands and the lofty
equatorial mountains, and mostly at a distant period when the conditions
for migration were somewhat more favourable than they are now. The much
greater directness of the route from Northern Europe to South Africa than
to Australia; and the existence even now of lofty mountains and extensive
highlands for a large portion of the distance, will explain (what Sir
Joseph Hooker notes as "a very curious fact") why South Africa has more
very northern European _genera_ than Australia, while Australia has more
identical _species_ and a better representation on the whole of the
European flora--this being clearly due to the large influx of species it
has received from the Antarctic Islands, in addition to those which have
entered it by way of Asia. The greater distance of South Africa even now
from any of these islands, and the much deeper sea to the south of the
African continent, than in the case of Tasmania and New Zealand, indicating
a smaller recent extension southward, is all quite in harmony with the
facts of distribution of the northern flora above referred to.
_Supposed Connection of South Africa and Australia._--There remains,
however, the small amount of direct affinity between the vegetation of
South Africa and that of Australia, New Zealand, and Temperate South
America, consisting in all of fifteen genera, five of which are confined to
Australia and South Africa, while several natural orders are better
represented in these two countries than in any other part of the world.
This resemblance has been supposed to imply some former land-connection of
all the great southern lands, but it appears to me that any such
supposition is wholly unnecessary. The differences between the faunas and
floras of these countries are too great and too radical to render it
possible that any such connection should have existed except at a very
remote period. But if we have to go back so far for an explanation, a much
simpler one presents itself, and one more in accordance with what we have
learnt of the general permanence of deep oceans and the great changes that
have taken place {526} in the distribution of all forms of life. Just as we
explain the presence of marsupials in Australia and America and of
Centetidæ in Madagascar and the Antilles, by the preservation in these
localities of remnants of once wide-spread types, so we should prefer to
consider the few genera common to Australia and South Africa as remnants of
an ancient vegetation, once spread over the northern hemisphere, driven
southward by the pressure of more specialised types, and now finding a
refuge in these two widely separated southern lands. It is suggestive of
such an explanation that these genera are either of very ancient groups--as
Conifers and Cycads--or plants of low organisation as the Restiaceæ--or of
world-wide distribution, as Melanthaceæ.
_The Endemic Genera of Plants in New Zealand._--Returning now to the New
Zealand flora, with which we are more especially concerned, there only
remains to be considered the peculiar or endemic genera which characterise
it. These are thirty-two in number, and are mostly very isolated. A few
have affinities with Arctic groups, others with Himalayan, or Australian
genera; several are tropical forms, but the majority appear to be
altogether peculiar types of world-wide groups--as Leguminosæ, Saxifrageæ,
Compositæ, Orchideæ, &c. We must evidently trace back these peculiar forms
to the earliest immigrants, either from the north or from the south; and
the great antiquity we are obliged to give to New Zealand--an antiquity
supported by every feature in its fauna and flora, no less than by its
geological structure, and its extinct forms of life[143]--affords ample
time for the changes in the general distribution of plants, and for those
due to isolation and modification under {527} the influence of changed
conditions, which are manifested by the extreme peculiarity of many of
these interesting endemic forms.
_The Absence of Southern Types from the Northern Hemisphere._--We have now
only to notice the singular want of reciprocity in the migrations of
northern and southern types of vegetation. In return for the vast number of
European plants which have reached Australia, not one single Australian
plant has entered any part of the north temperate zone, and the same may be
said of the typical southern vegetation in general, whether developed in
the Antarctic lands, New Zealand, South America, or South Africa. The
furthest northern outliers of the southern flora are a few genera of
Antarctic type on the Bornean Alps; the genus Acæna which has a species in
California; two representatives of the Australian flora--Casuarina and
Stylidium, in the peninsula of India; while China and the Philippines have
two strictly Australian genera of Orchideæ--Microtis and Thelymitra, as
well as a Restiaceous genus. Several distinct causes appear to have
combined to produce this curious inability of the southern flora to make
its way into the northern hemisphere. The primary cause is, no doubt, the
totally different distribution of land in the two hemispheres, so that in
the south there is the minimum of land in the colder parts of the temperate
zone and in the north the maximum. This is well shown by the fact that on
the parallel of Lat. 50° N. we pass over 240° of land or shallow sea, while
on the same parallel of south latitude we have only 4°, where we cross the
southern part of Patagonia. Again the three most important south temperate
land-areas--South Temperate America, South Africa, and Australia--are
widely separated from each other, and have in all probability always been
so; whereas the whole of the north temperate lands are practically
continuous. It follows that, instead of the enormous northern area, in
which highly organised and dominant groups of plants have been developed
gifted with great colonising and aggressive powers, we have in the south
three comparatively small and detached areas, in which rich floras have
been developed with _special_ {528} adaptations to soil, climate, and
organic environment, but comparatively impotent and inferior beyond their
own domain.
Another circumstance which makes the contest between the northern and
southern forms still more unequal, is the much greater hardiness of the
former, from having been developed in a colder region, and one where alpine
and arctic conditions extensively prevail; whereas the southern floras have
been mainly developed in mild regions to which they have been altogether
confined. While the northern plants have been driven north or south by each
succeeding change of climate, the southern species have undergone
comparatively slight changes of this nature, owing to the areas they occupy
being unconnected with the ice-bearing Antarctic continent. It follows,
that whereas the northern plants find in all these southern lands a milder
and more equable climate than that to which they have been accustomed, and
are thus often able to grow and flourish even more vigorously than in their
native land, the southern plants would find in almost every part of Europe,
North America or Northern Asia, a more severe and less equable climate,
with winters that usually prove fatal to them even under cultivation. These
causes, taken separately, are very powerful, but when combined they must, I
think, be held to be amply sufficient to explain why examples of the
typical southern vegetation are almost unknown in the north temperate zone,
while a very few of them have extended so far as the northern tropic.[144]
{529}
_Concluding Remarks on the Last Two Chapters._--Our inquiry into the
external relations and probable origin of the fauna and flora of New
Zealand, has thus led us on to a general theory as to the cause of the
peculiar biological relations between the northern and the southern
hemispheres; and no better or more typical example could be found of the
wide range and great interest of the study of the geographical distribution
of animals and plants.
The solution which has here been given of one of the most difficult of this
class of problems, has been rendered possible solely by the knowledge very
recently obtained of the form of the sea-bottom in the southern ocean, and
of the geological structure of the great Australian continent. Without this
knowledge we should have nothing but a series of guesses or probabilities
on which to found our hypothetical explanation, which we have now been able
to build up on a solid foundation of fact. The complete separation of East
from West Australia during a portion of the Cretaceous and Tertiary
periods, could never have been guessed till it was established by the
laborious explorations of the Australian geologists; while the hypothesis
of a comparatively shallow sea, uniting New Zealand by a long route with
tropical Australia, while a profoundly deep ocean always separated it from
temperate Australia, would have been rejected as too improbable a
supposition for the foundation of even the most enticing theory. Yet it is
mainly by means of these two facts, that we are enabled to give an adequate
explanation of the strange anomalies in the flora of Australia and its
relation to that of New Zealand.
In the more general explanation of the relations of the various northern
and southern floras, I have shown what an important aid to any such
explanation is the theory of repeated changes of climate, not necessarily
of great amount, given in Chapters VIII. and IX.; while the whole
discussion justifies the importance attached to the theory of the general
permanence of continents and oceans, as demonstrated in Chapter VI., since
any rational explanation based upon facts (as opposed to mere unsupported
{530} conjecture) must take such general permanence as a starting-point.
The whole inquiry into the phenomena presented by islands, which forms the
main subject of the present volume has, I think, shown that this theory
does afford a firm foundation for the discussion of questions of
distribution and dispersal; and that by its aid, combined with a clear
perception of the wonderful powers of dispersion and modification in the
organic world when long periods are considered, the most difficult problems
connected with this subject cease to be insoluble.
* * * * *
{531}
CHAPTER XXIV
SUMMARY AND CONCLUSION
The Present Volume is the Development and Application of a
Theory--Statement of the Biological and Physical Causes of
Dispersal--Investigation of the Facts of Dispersal--of the Means of
Dispersal--of Geographical Changes Affecting Dispersal--of Climatal
Changes Affecting Dispersal--The Glacial Epoch and its Causes--Alleged
Ancient Glacial Epochs--Warm Polar Climates and their
Causes--Conclusions as to Geological Climates--How far Different from
those of Mr. Croll--Supposed Limitations of Geological Time--Time Amply
Sufficient both for Geological and Biological Development--Insular
Faunas and Floras--The North Atlantic Islands--The Galapagos--St.
Helena and the Sandwich Islands--Great Britain as a Recent Continental
Island--Borneo and Java--Japan and Formosa--Madagascar as an Ancient
Continental Island--Celebes and New Zealand as Anomalous Islands--The
Flora of New Zealand and its Origin--The European Element in the South
Temperate Floras--Concluding Remarks.
The present volume has gone over a very wide field both of facts and
theories, and it will be well to recall these to the reader's attention and
point out their connection with each other, in a concluding chapter. I hope
to be able to show that, although at first sight somewhat fragmentary and
disconnected, this work is really the development of a clear and definite
theory, and its application to the solution of a number of biological
problems. That theory is, briefly, that the distribution of the various
species and groups of living things over the earth's surface, and their
aggregation in definite assemblages in certain areas, is the {532} direct
result and outcome of a complex set of causes, which may be grouped as
"biological" and "physical." The biological causes are mainly of two
kinds--firstly, the constant tendency of all organisms to increase in
numbers and to occupy a wider area, and their various powers of dispersion
and migration through which, when unchecked, they are enabled to spread
widely over the globe; and, secondly, those laws of evolution and
extinction which determine the manner in which groups of organisms arise
and grow, reach their maximum, and then dwindle away, often breaking up
into separate portions which long survive in very remote regions. The
physical causes are also mainly of two kinds. We have, first, the
geographical changes which at one time isolate a whole fauna and flora, at
another time lead to their dispersal and intermixture with adjacent faunas
and floras--and it was here important to ascertain and define the exact
nature and extent of these changes, and to determine the question of the
general stability or instability of continents and oceans; in the second
place, it was necessary to determine the exact nature, extent and frequency
of the changes of climate which have occurred in various parts of the
earth,--because such changes are among the most powerful agents in causing
the dispersal and extinction of plants and animals. Hence the importance
attached to the question of geological climates and their causes, which
have been here investigated at some length with the aid of the most recent
researches of geologists, physicists, and explorers. These various
inquiries led on to an investigation of the mode of formation of stratified
deposits, with a view to fix within some limits their probable age; and
also to an estimate of the probable rate of development of the organic
world; and both these processes are shown to involve, so far as we can
judge, periods of time less vast than have generally been thought
necessary.
The numerous facts and theories established in the First Part of the work
are then applied to explain the phenomena presented by the floras and
faunas of the chief islands of the globe, which are classified, in
accordance with their physical origin, in three groups or classes, each
{533} of which are shown to exhibit certain well-marked biological
features.
Having thus shown that the work is a connected whole, founded on the
principle of tracing out the more recondite causes of the distribution of
organisms, we will briefly indicate the scope and object of the several
chapters, by means of which this general conception has been carried out.
Beginning with simple and familiar facts relating to British and European
quadrupeds and birds, I have defined and shown the exact character of
"areas of distribution," as applied to species, genera, and families, and
have illustrated the subject by maps showing the peculiarities of
distribution of some well-known groups of birds. Taking then our British
mammals and land-birds, I follow them over the whole area they inhabit, and
thus obtain a foundation for the establishment of "zoological regions," and
a clear insight into their character as distinct from the usual
geographical divisions of the globe.
The facts thus far established are then shown to be necessary results of
the "law of evolution." The nature and amount of "variation" is exhibited
by a number of curious examples; the origin, growth, and decay of species
and genera are traced, and all the interesting phenomena of isolated groups
and discontinuous generic and specific areas are shown to follow as logical
consequences.
The next subject investigated is the means by which the various groups of
animals are enabled to overcome the natural barriers which often seem to
limit them to very restricted areas, how far those barriers are themselves
liable to be altered or abolished, and what is the exact nature and amount
of the changes of sea and land which our earth has undergone in past times.
This latter part of the inquiry is shown to be the most important as it is
the most fundamental; and as it is still a subject of controversy, and many
erroneous views prevail in regard to it, it is discussed at some length.
Several distinct classes of evidence are adduced to prove that the grand
features of our globe--the position of the great oceans {534} and the chief
land-areas--have remained, on the whole, unchanged throughout geological
time. Our continents are shown to be built up mainly of "shore-deposits";
and even the chalk, which is so often said to be the exact equivalent of
the "globigerina ooze" now forming in mid-Atlantic, is shown to be a
comparatively shallow-water deposit formed in inland seas, or in the
immediate vicinity of land. The general stability of continents has,
however, been accompanied by constant changes of form, and insular
conditions have prevailed over every part in succession; and the effect of
such changes on the distribution of organisms is pointed out.
We then approach the consideration of another set of changes--those of
climate--which have probably been agents of the first importance in
modifying the specific forms as well as the distribution of animals. Here
again we find ourselves in the midst of fierce controversies. The
occurrence of a recent glacial epoch of great severity in the northern
hemisphere is now universally admitted, but the causes which brought it on
are matter of dispute. But unless we can arrive at these causes, as well as
at those which produced the equally well demonstrated mild climate in the
Arctic regions, we shall be quite unable to determine the nature and amount
of the changes of climate which have occurred throughout past ages, and
shall thus be left without a most important clue to the explanation of many
of the anomalies in the distribution of animals and plants.
I have therefore devoted three chapters to a full investigation of this
question. I have first given such a sketch of the most salient facts as to
render the phenomena of the glacial epoch clear and intelligible. I then
review the various suggested explanations, and, taking up the two which
alone seem tenable, I endeavour to determine the true principles of each.
While adopting generally Mr. Croll's views as to the causes of the "glacial
epoch," I have introduced certain limitations and modifications. I have
pointed out, I believe, more clearly than has hitherto been done, the very
different effects on climate of water in the liquid and in the solid state;
and I have {535} shown, by a variety of evidence, that without high land
there can be no permanent snow and ice. From these facts and principles the
very important conclusion is reached, that the alternate phases of
precession--causing the winter of each hemisphere to be in _aphelion_ and
_perihelion_ each 10,500 years--would produce a complete change of climate
only where a country was _partially_ snow-clad; while, whenever a large
area became almost _wholly_ buried in snow and ice--as was certainly the
case with Northern Europe and America during the glacial epoch--then the
glacial conditions would be continued and perhaps even intensified when the
sun approached nearest to the earth in winter, instead of there being at
that time, as Mr. Croll maintains, an almost perpetual spring. This
important result is supported by reference to the existing differences
between the climates of the northern and southern hemispheres, and by what
is known to have occurred during the last glacial epoch; and it is shown to
be in complete harmony with the geological evidence as to interglacial mild
periods.
Discussing next the evidence for glacial epochs in earlier times, it is
shown that Mr. Croll's views are opposed by a vast body of facts, and that
the geological evidence leads irresistibly to the conclusion that during a
large portion of the Secondary and Tertiary periods, uninterrupted warm
climates prevailed in the north temperate zone, and so far ameliorated the
climate of the Arctic regions as to admit of the growth of a luxuriant
vegetation in the highest latitudes yet explored. The geographical
condition of the northern hemisphere at these periods is then investigated,
and it is shown to have been probably such as to admit the warm tropical
waters freely to penetrate the land, and to reach the Arctic seas by
several channels; and, adopting Mr. Croll's calculations as to the enormous
quantity of heat that would thus be conveyed northwards, it is maintained
that the mild Arctic climates are amply accounted for. With such favourable
geographical conditions, it is shown, that changes of excentricity and of
the phases of precession would have no other effect than to cause greater
differences {536} of temperature between summer and winter; but, wherever
there was a considerable extent of very lofty mountains the snow-line would
be lowered, and the snow-collecting area being thus largely increased a
considerable amount of local glaciation might result. Thus may be explained
the presence of enormous ice-borne rocks in Eocene and Miocene times in
Central Europe, while at the very same period all the surrounding country
enjoyed a tropical or sub-tropical climate.
The general conclusion is thus reached, that geographical conditions are
the essential causes of great changes of climate, and that the radically
different distribution of land and sea in the northern and southern
hemispheres has generally led to great diversity of climate in the Arctic
and Antarctic regions. The form and arrangement of the continents is shown
to be such as to favour the transfer of warm oceanic currents to the north
far in excess of those which move towards the south, and whenever these
currents had free passage _through_ the northern land-masses to the polar
area, a mild climate must have prevailed over the whole northern
hemisphere. It is only in very recent times that the great northern
continents have become so completely consolidated as they now are, thus
shutting out the warm water from their interiors, and rendering possible a
wide-spread and intense glacial epoch. But this great climatal change was
actually brought about by the high excentricity which occurred about
200,000 years ago; and it is doubtful if a similar glaciation in equally
low latitudes could be produced by means of any such geographical
combinations as actually occur, without the concurrence of a high
excentricity.
A survey of the present condition of the earth supports this view, for
though we have enormous mountain ranges in every latitude, there is no
glaciated country south of Greenland in N. Lat. 61°. But directly we go
back a very short period, we find the superficial evidences of glaciation
to an enormous extent over three-fourths of the globe. In the Alps and
Pyrenees, in the British Isles and Scandinavia, in Spain and the Atlas, in
the Caucasus {537} and the Himalayas, in Eastern North America and west of
the Rocky Mountains, in the Andes of South Temperate America, in South
Africa, and in New Zealand, huge moraines and other unmistakable ice-marks
attest the universal descent of the snow-line for several thousand feet
below its present level. If we reject the influence of high excentricity as
the cause of this almost universal glaciation, we must postulate a general
elevation of _all_ these mountains about the same time, geologically
speaking--for the general similarity in the state of preservation of the
ice-marks and the known activity of denudation as a destroying agent,
forbid the idea that they belong to widely separated epochs. It has,
indeed, been suggested, that denudation alone has lowered these mountains
so much during the post-tertiary epoch, that they were previously of
sufficient height to account for the glaciation of all of them; but this
hardly needs refutation, for it is clear that denudation could not at the
same time have removed some thousands of feet of rock from many hundreds of
square miles of lofty snow-collecting plateaus, and yet have left moraines,
and blocks, and even glacial striæ, undisturbed and uneffaced on the slopes
and in the valleys of these same mountains.
The theory of geological climates set forth in this volume, while founded
on Mr. Croll's researches, differs from all that have yet been made public,
in clearly tracing out the comparative influence of geographical and
astronomical revolutions, showing that, while the former have been the
chief, if not the exclusive, causes of the long-continued mild climates of
the Arctic regions, the concurrence of the latter has been essential to the
production of glacial epochs in the temperate zones, as well as of those
local glaciations in low latitudes, of which there is such an abundance of
evidence.
The next question discussed is that of geological time as bearing on the
development of the organic world. The periods of time usually demanded by
geologists have been very great, and it was often assumed that there was no
occasion to limit them. But the theory of development demands far more; for
the earliest fossiliferous rocks {538} prove the existence of many and
varied forms of life which require unrecorded ages for their
development--ages probably far longer than those which have elapsed from
that period to the present day. The physicists, however, deny that any such
indefinitely long periods are available. The sun is ever losing heat far
more rapidly than it can be renewed from any known or conceivable source.
The earth is a cooling body, and must once have been too hot to support
life; while the friction of the tides is checking the earth's rotation, and
this cannot have gone on indefinitely without making our day much longer
than it is. A limit is therefore placed to the age of the habitable earth,
and it has been thought that the time so allowed is not sufficient for the
long processes of geological change and organic development. It is
therefore important to inquire whether these processes are either of them
so excessively slow as has been supposed, and I devote a chapter to the
inquiry.
Geologists have measured with some accuracy the maximum thickness of all
the known sedimentary rocks. The rate of denudation has also been recently
measured by a method which, if not precise, at all events gives results of
the right order of magnitude and which err on the side of being too slow
rather than too fast. If, then, the _maximum_ thickness of the _known_
sedimentary rocks is taken to represent the _average_ thickness of _all_
the sedimentary rocks, and we also know the _amount_ of sediment carried to
the sea or lakes, and the _area_ over which that sediment is spread, we
have a means of calculating the _time_ required for the building up of all
the sedimentary rocks of the geological system. I have here inquired how
far the above suppositions are correct, or on which side they probably err;
and the conclusion arrived at is, that the time required is very much less
than has hitherto been supposed.
Another estimate is afforded by the date of the last glacial epoch if
coincident with the last period of high excentricity, while the Alpine
glaciation of the Miocene period is assumed to have been caused by the next
earlier phase of very high excentricity. Taking these as data, the {539}
proportionate change of the species of mollusca affords a means of arriving
at the whole lapse of time represented by the fossiliferous rocks; and
these two estimates agree in the _order_ of their magnitudes.
It is then argued that the changes of climate every 10,500 years during the
numerous periods of high excentricity have acted as a motive power in
hastening on both geological and biological change. By raising and lowering
the snow-line in all mountain ranges it has caused increased denudation;
while the same changes have caused much migration and disturbance in the
organic world, and have thus tended to the more rapid modification of
species. The present epoch being a period of very low excentricity, the
earth is in a phase of _exceptional stability_ both physical and organic;
and it is from this period of exceptional stability that our notions of the
very slow rate of change have been derived.
The conclusion is, on the whole, that the periods allowed by physicists are
not only far in excess of such as are required for geological and organic
change, but that they allow ample margin for a lapse of time anterior to
the deposit of the earliest fossiliferous rocks several times longer than
the time which has elapsed since their deposit to the present day.
Having thus laid the foundation for a scientific interpretation of the
phenomena of distribution, we proceed to the Second Part of our work--the
discussion of a series of typical Insular Faunas and Floras with a view to
explain the interesting phenomena they present. Taking first two North
Atlantic groups--the Azores and Bermuda--it is shown how important an agent
in the dispersal of most animals and plants is a stormy atmosphere.
Although 900 and 700 miles respectively from the nearest continents, their
productions are very largely identical with those of Europe and America;
and, what is more important, fresh arrivals of birds, insects, and plants,
are now taking place almost annually. These islands afford, therefore, test
examples of the great dispersive powers of certain groups of organisms, and
thus serve as a basis on which to found our explanations of many anomalies
of distribution. Passing {540} on to the Galapagos we have a group less
distant from a continent and of larger area, yet, owing to special
conditions, of which the comparatively stormless equatorial atmosphere is
the most important, exhibiting far more speciality in its productions than
the more distant Azores. Still, however, its fauna and flora are as
unmistakably derived from the American continent as those of the Azores are
from the European.
We next take St. Helena and the Sandwich Islands, both wonderfully isolated
in the midst of vast oceans, and no longer exhibiting in their productions
an exclusive affinity to one continent. Here we have to recognise the
results of immense antiquity, and of those changes of geography, of
climate, and in the general distribution of organisms which we know have
occurred in former geological epochs, and whose causes and consequences we
have discussed in the first part of our volume. This concludes our review
of the Oceanic Islands.
Coming now to Continental Islands we consider first those of most recent
origin and offering the simplest phenomena; and begin with the British
Isles as affording the best example of very recent and well known
Continental Islands. Reviewing the interesting past history of Britain, we
show why it is comparatively poor in species and why this poverty is still
greater in Ireland. By a careful examination of its fauna and flora it is
then shown that the British Isles are not so completely identical,
biologically, with the continent as has been supposed. A considerable
amount of speciality is shown to exist, and that this speciality is real
and not apparent is supported by the fact, that small outlying islands,
such as the Isle of Man, the Shetland Isles, Lundy Island, and the Isle of
Wight, all possess certain species or varieties not found elsewhere.
Borneo and Java are next taken, as illustrations of tropical islands which
may be not more ancient than Britain, but which, owing to their much larger
area, greater distance from the continent, and the extreme richness of the
equatorial fauna and flora, possess a large proportion of peculiar species,
though these are in general very closely allied to those of the adjacent
parts of Asia. The {541} preliminary studies we have made enable us to
afford a simpler and more definite interpretation of the peculiar relations
of Java to the continent and its differences from Borneo and Sumatra, than
was given in my former work (_The Geographical Distribution of Animals_).
Japan and Formosa are next taken, as examples of islands which are
decidedly somewhat more ancient than those previously considered, and which
present a number of very interesting phenomena, especially in their
relations to each other, and to remote rather than to adjacent parts of the
Asiatic continent.
We now pass to the group of Ancient Continental Islands, of which
Madagascar is the most typical example. It is surrounded by a number of
smaller islands which may be termed its satellites since they partake of
many of its peculiarities; though some of these--as the Comoros and
Seychelles--may be considered continental, while others--as Bourbon,
Mauritius, and Rodriguez--are decidedly oceanic. In order to understand the
peculiarities of the Madagascar fauna we have to consider the past history
of the African and Asiatic continents, which it is shown are such as to
account for all the main peculiarities of the fauna of these islands
without having recourse to the hypothesis of a now-submerged Lemurian
continent. Considerable evidence is further adduced to show that "Lemuria"
is a myth, since not only is its existence unnecessary, but it can be
proved that it would not explain the actual facts of distribution. The
origin of the interesting Mascarene wingless birds is discussed, and the
main peculiarities of the remarkable flora of Madagascar and the Mascarene
islands pointed out; while it is shown that all these phenomena are to be
explained on the general principles of the permanence of the great oceans
and the comparatively slight fluctuations of the land area, and by taking
account of established palæontological facts.
There remain two other islands--Celebes and New Zealand--which are classed
as "anomalous," the one because it is almost impossible to place it in any
of the six zoological regions, or determine whether it has ever been
actually joined to a continent--the other because it {542} combines the
characteristics of continental and oceanic islands.
The peculiarities of the Celebesian fauna have already been dwelt upon in
several previous works, but they are so remarkable and so unique that they
cannot be omitted in a treatise on "Insular Faunas"; and here, as in the
case of Borneo and Java, fuller consideration and the application of the
general principles laid down in our First Part, lead to a solution of the
problem at once more simple and more satisfactory than any which have been
previously proposed. I now look upon Celebes as an outlying portion of the
great Asiatic continent of Miocene times, which either by submergence or
some other cause had lost the greater portion of its animal inhabitants,
and since then has remained more or less completely isolated from every
other land. It has thus preserved a fragment of a very ancient fauna along
with a number of later types which have reached it from surrounding islands
by the ordinary means of dispersal. This sufficiently explains all the
peculiar _affinities_ of its animals, though the peculiar and distinctive
_characters_ of some of them remain as mysterious as ever.
New Zealand is shown to be so completely continental in its geological
structure, and its numerous wingless birds so clearly imply a former
connection with some other land (as do its numerous lizards and its
remarkable reptile, the Hatteria), that the total absence of indigenous
land-mammalia was hardly to be expected. Some attention is therefore given
to the curious animal which has been seen but never captured, and this is
shown to be probably identical with an animal referred to by Captain Cook.
The more accurate knowledge which has recently been obtained of the sea
bottom around New Zealand enables us to determine that the former
connection of that island with Australia was towards the north, and this is
found to agree well with many of the peculiarities of its fauna.
The flora of New Zealand and that of Australia are now both so well known,
and they present so many peculiarities, and relations of so anomalous a
character, {543} as to present in Sir Joseph Hooker's opinion an almost
insoluble problem. Much additional information on the physical and
geological history of these two countries has, however, been obtained since
the appearance of Sir Joseph Hooker's works, and I therefore determined to
apply to them the same method of discussion and treatment which has been
usually successful with similar problems in the case of animals. The fact
above noted, that New Zealand was connected with Australia in its northern
and tropical portion only, of itself affords a clue to one portion of the
specialities of the New Zealand flora--the presence of an unusual number of
tropical families and genera, while the temperate forms consist mainly of
species either identical with those found in Australia or closely allied to
them. But a still more important clue is obtained in the geological
structure of Australia itself, which is shown to have been for long periods
divided into an eastern and a western island, in the latter of which the
highly peculiar flora of temperate Australia was developed. This is found
to explain with great exactness the remarkable absence from New Zealand of
all the most abundant and characteristic Australian genera, both of plants
and of animals, since these existed at that time only in the _western_
island, while New Zealand was in connection with the _eastern_ island alone
and with the tropical portion of it. From these geological and physical
facts, and the known powers of dispersal of plants, all the main features,
and many of the detailed peculiarities of the New Zealand flora are shown
necessarily to result.
Our last chapter is devoted to a wider, and if possible more interesting
subject--the origin of the European element in the floras of New Zealand
and Australia, and also in those of South America and South Africa. This is
so especially a botanical question, that it was with some diffidence I
entered upon it, yet it arose so naturally from the study of the New
Zealand and Australian floras, and seemed to have so much light thrown upon
it by our preliminary studies as to changes of climate and the causes which
have favoured the distribution of plants, that I felt my work would be
incomplete without a consideration of {544} it. The subject will be so
fresh in the reader's mind that a complete summary of it is unnecessary. I
venture to think, however, that I have shown, not only the several routes
by which the northern plants have reached the various southern lands, but
have pointed out the special aids to their migration, and the motive power
which has urged them on.
In this discussion, if nowhere else, will be found a complete justification
of that lengthy investigation of the exact nature of past changes of
climate, which to some readers may have seemed unnecessary and unsuited to
such a work as the present. Without the clear and definite conclusions
arrived at by that discussion, and those equally important views as to the
permanence of the great features of the earth's surface, and the wonderful
dispersive powers of plants which have been so frequently brought before us
in our studies of insular floras, I should not have ventured to attack the
wide and difficult problem of the northern element in southern floras.
In concluding a work dealing with subjects which have occupied my attention
for many years, I trust that the reader who has followed me throughout will
be imbued with the conviction that ever presses upon myself, of the
complete interdependence of organic and inorganic nature. Not only does the
marvellous structure of each organised being involve the whole past history
of the earth, but such apparently unimportant facts as the presence of
certain types of plants or animals in one island rather than in another,
are now shown to be dependent on the long series of past geological
changes--on those marvellous astronomical revolutions which cause a
periodic variation of terrestrial climates--on the apparently fortuitous
action of storms and currents in the conveyance of germs--and on the
endlessly varied actions and reactions of organised beings on each other.
And although these various causes are far too complex in their combined
action to enable us to follow them out in the case of any one species, yet
their broad results are clearly recognisable; and we are thus encouraged to
study more completely every detail and {545} every anomaly in the
distribution of living things, in the firm conviction that by so doing we
shall obtain a fuller and clearer insight into the course of nature, and
with increased confidence that the "mighty maze" of Being we see everywhere
around us is "not without a plan."
{549}
INDEX
A.
Acacia, wide range of in Australia, 185
_Acacia heterophylla_, and _Acacia koa_, 443
Acæna in California, 527
_Accipiter hawaii_, 314
Achatinellinæ, average range of, 317
_Ægialitis sanctæ-helenæ_, 305
Africa, characteristic mammalia of, 416
former isolation of, 418
Africa and Madagascar, relations of, 418
early history of, 419
African highlands as aiding the migration of plants, 524
African reptiles absent from Madagascar, 418
Aggressive power of the Scandinavian flora, 511
Air and water, properties of, in relation to climate, 131
_Alectorænas pulcherrimus_, 429
Allen, Mr. J. A., on variation, 58
Allied species occupy separate areas, 478
Alpine plants, their advantages as colonisers, 503
Alternations of climate in Switzerland and North America, 121
Alternations of climate, palæontological evidence of, 119
Amazon, limitation of species by, 18
_Amblyrhynchus cristatus_, 279
American genera of reptiles in Madagascar, 417
Amphibia, dispersal of, 76
of the Seychelles, 432
introduced, of Mauritius, 435
of New Zealand, 483
Amphioxus, 63
Amphisbænidæ, 28
_Amydrus Tristramii_, restricted range of, 16
_Anas Wyvilliana_, 314
Ancient continental islands, 244, 411
Ancient glacial epochs, 169
what evidence of may be expected, 175
Ancient groups in Madagascar, 419
Andersson, N. J., on the flora of the Galapagos, 287
Andes, migration of plants along the, 520
_Angræcum sesquipedale_, 440
Animal life, effects of glacial epoch on, 117
Animal life of Formosa, 401
_Anoa depressicornis_, 456
Antarctic continent as a means of plant-dispersion, 521
Antarctic islands, with perpetual snow, 136
Antelopes, overlapping genera of, 29
Antiquity of Hawaiian fauna and flora, 328
of land-shells, 79
of New Zealand, 526
of plants as affecting their dispersal, 82
_Apera arundinacea_, 503
_Apium graveolens_ in New Zealand, 515
Apteryx, species of, 476
_Arabis hirsuta_ on railway arch, 514
Archaic forms still existing, 229
Arctic and Antarctic regions, contrasts of, 135
Arctic current, effects of a stoppage of, 150
Arctic plants in the southern hemisphere, 509
Arctic regions, mild climates of, 181
recent interglacial mild period in, 182
Arctic warm climates of Secondary and Palæozoic times, 201
Areas of distribution, 13
separate and overlapping, 17, 28
Ascension, former climate and productions of, 303
Astronomical and geographical causes, comparative effects of, on climate,
207
Astronomical causes of change of climate, 126
of glaciation, 140
Atlantic isles, peculiar mosses of, 368
Atlantosaurus, the largest land-animal, 98
_Atriplex patula_ on a railway bank, 515
Auchenia, 27
Austen, Mr. Godwin, on littoral shells in deep water, 337
Australia, two sets of Northern plants in, 523
South European plants in, 523
Australia and South Africa, supposed connection of, 525
{550}
Australian Alps, indications of glaciation in, 163
birds absent from New Zealand, 483
flora, general features of, 491
richest in temperate zone, 491
recent and derivative in the tropics, 492
its south-eastern and south-western divisions, 493
Sir Joseph Hooker on, 494
geological explanation of, 494
its presence in New Zealand, 498
natural orders of, wanting in New Zealand, 490
orchideæ in China, 527
genera of plants in India, 524
plants absent from New Zealand, 488, 490
none in north temperate zone, 527
running wild in Neilgherrie mountains, 528
region, definition of, 45
mammals and birds of, 46
seeds scattered in New Zealand, 508
Aylward, Captain, on glaciation of South Africa, 163
Azores, 247
absence from, of large-fruited trees or shrubs, 260
zoological features of, 248
birds of, 249
insects of, 253
beetles of, 253
land-shells of, 256
flora of, 256
Azores and New Zealand, identical plants in both, 512
Azorean bird-fauna, origin of, 250
fauna and flora, deductions from, 261
plants, facilities for the dispersal of, 260
B.
_Babirusa alfurus_ in Celebes, 456
Badgers, 41
Bahamas contrasted with Florida, 5
Baker, Mr., on flora of Mauritius and the Seychelles, 441
Bali and Lombok, contrasts of, 4
Banca, peculiar species of, 386
_Barbarea precox_ on railway bank, 514
Barn-owl, wide range of, 15
Baron, Rev. R., on the flora of Madagascar, 441
Barriers to dispersal, 73
Batrachia, 30
Bats in Bermuda, 269
Bears of Europe and America, 14
Beaver of Europe and America, 14
Beetles of the Azores, 253
remote affinities of some of, 255
of the Galapagos, 284
of St. Helena, 298
of the Sandwich Islands, 318
peculiar British species of, 351
Bell-birds, distribution of, 24
Bennett, Mr. Arthur, on peculiar British plants, 360
on the vegetation of railway banks, 514
Bentham, Mr., on the compositæ of the Galapagos, 288
on the compositæ of St. Helena, 307
on the Mascarene compositæ, 445
on Sandwich Island compositæ, 325
Bermuda, 262
soundings around, 263
red clay of, 265
zoology of, 266
reptiles of, 266
birds of, 266
insects of, 269
land-mollusca of, 270
flora of, 271
Bermuda and Azores, comparison of bird-faunas of, 268
_Bernicla sandvichensis_, 314
Biological causes which determine distribution, 532
Biological features of Madagascar, 416
Birds as plant-dispersers, 81
as seed-carriers, 81, 258
common to Great Britain and Japan, 396
common to India and Japan, 399
specific range of, 15
range of British, 34
range of East Asian, 38
variation in N. American, 58
dispersal of, 75
of the Azores, 249
of Bermuda, 266
of Bermuda and Azores compared, 268
of the Galapagos, 280
of the Sandwich Islands, 313
peculiar to Britain, 340
of Borneo, 377
of Java, 382
of the Philippines, 388
of Japan, 396
peculiar to Japan, 398
peculiar to Formosa, 404
common to Formosa and India or Malaya, 407
of Madagascar, and their teachings, 422
of Comoro Islands, 429
of the Seychelles, 430
of the Mascarene islands, 436
of islands east and west of Celebes, 454
of Celebes, 458
peculiar to Celebes, 459
Himalayan types of, in Celebes, 462
list of, in Celebes, 466
of New Zealand, 476, 482
wingless, of New Zealand, 476
Blackburn, Mr. T., on the beetles of the Sandwich Islands, 318
Blakiston and Pryer on birds of Japan, 396
{551}
Bland, Mr., on land-shells of Bermuda, 270
Blanford, Mr. W. T., on small effect of marine denudation, 225
Blanford, Mr. H. F., on former connection of Africa and India, 426
Blocks, travelled and perched, 109
Blue magpies, range of, 15
Borneo, geology of, 375
mammalia of, 376
birds of, 377
affinities of fauna of, 381
Borneo and Asia, resemblance of, 6
Borneo and Java, 373
Boulder-beds of the carboniferous formation, 201
Boulder clays of east of England, 118
Bovidæ, 29
Brady, Mr. H. B., on habitat of globigerinæ, 92
Braithwaite, Dr. R., on peculiar British mosses, 365
Britain, probable climate of, with winter in _aphelion_, 156
British birds, range of, 34-38
British Columbia, interglacial warm periods in, 121
British fauna and flora, peculiarities of, 370
British Isles, recent changes in, 332
proofs of former elevation of, 334
submerged forests of, 335
buried river channels of, 336
last union of, with continent, 337
why poor in species, 338
peculiar birds of, 339
fresh-water fishes of, 340
peculiar insects of, 344
peculiar Lepidoptera of, 347
peculiar Coleoptera of, 351
peculiar Trichoptera of, 355
peculiar land and fresh-water shells of, 356
peculiarities of the flora of, 360
peculiar mosses and Hepaticæ of, 366
British mammals as indicating a zoological region, 33
Buller, Sir W. L., on the New Zealand rat, 475
Buried river-channels, 336
_Buteo solitarius_, 314
Butterflies of Celebes, peculiar shape of, 463
Butterflies, peculiar British, 347
C.
Caddis-flies peculiar to Britain, 355
Cæcilia, species of, in the Seychelles, 432
wide distribution of, 432
Cæciliadæ, 28
_Callithea Leprieuri_, distribution of, 18
_Callithea sapphira_, 18
Camels as destroyers of vegetation, 296
former wide distribution of, 421
Camelus, 17, 27
_Campanula vidalii_, 261
Canis, 17, 26
Carabus, numerous species of, 42
Carboniferous boulder-beds, 201
warm Arctic climate, 201
Carnivora in Madagascar, 417
Carpenter, Dr., on habitat of globigerinæ, 92
Carpenter, Mr. Edward, on Mars and glacial periods, 164
_Carduus marianus_ in New Zealand, 515
_Carpodacus purpureus_ and _P. californicus_, 68
Castor, 17
Casuarina, 185
in India, 527
Cause of extinction, 63
Caves of Glamorganshire, 336
Cebibæ, overlapping genera of, 29
Celebes, physical features of, 451
islands around, 452
zoology of, 455
derivation of mammals of, 457
birds of, 458
not a continental island, 461
insect peculiarities of, 462
Himalayan types in, 462
peculiarity of butterflies of, 463
list of land-birds of, 466
Centetidæ, 27
Centetidæ, formerly inhabited Europe, 420
Central America, mixed fauna of, 53
Ceratodus, or mud-fish, 69
Cervus, 17, 26
Chalk a supposed oceanic formation, 89
Chalk at Oahu, analysis of, 90
Chalk, analysis of, 91
Chalk mollusca indicative of shallow water, 93
Chalk sea, extent of, in Europe, 93
Chalk-formation, land-plants found in, 94
deposited in an inland sea, 93
of Faxoe an ancient coral-reef, 94
modern formation of, 95
supposed oceanic origin of, erroneous, 96
"Challenger" soundings and shore-deposits, 86
"Challenger" ridge in the Atlantic, 101
Chameleons very abundant in Madagascar, 430
Chamois, distribution of, 13
Changes of land and sea, 83
Chasmorhynchus, distribution of, 24
_C. nudicollis_, 24
_C. tricarunculatus_, 24
_C. variegatus_, 24
_C. niveus_, 24
_Chilomenus lunata_, 300
Chinchillas, 26
Chrysochloridæ, 29
Cicindela, 17
Cicindelidæ common to South America and Madagascar, 28
Clay, red, of Bermuda, 265
Climate, astronomical causes of changes of, 126
{552}
properties of snow and ice in relation to, 131
of Britain with winter in _aphelion_, 156
of Tertiary period in Europe and N. America, 178
temperate in Arctic regions, 181
causes of mild Arctic, 190
of Tertiary and Secondary periods, 199, 202
of the Secondary and Palæozoic epochs, 200
change of, during Tertiary and Secondary Periods, 200
affected by arrangement of the great continents, 205
nature of changes of, caused by high excentricity, 230
exceptional stability of the present, 232
changes of, as affecting migration of plants, 517
Climatal changes, 106
change, its essential principle restated, 158
changes as modifying organisms, 229
Clouds cut off the sun's heat, 145
Coal in Sumatra, 385
Coast line of globe, extent of, 221
Cochoa, distribution of, 25
Cockerell, Mr. Th. D. A., on slugs of Bermuda, 271
on British land and fresh-water shells, 356
Cold alone does not cause glaciation, 135
how it can be stored up, 133
Coleoptera of the Azores, 253
of St. Helena, 298
of the Sandwich Islands, 318
peculiar British species of, 351
Comoro Islands, 428
mammals and birds of, 428
Compositæ of the Galapagos, 288
of St. Helena, 307
of the Sandwich Islands, 325
of the Mascarene Islands, 445
species often have restricted ranges, 504
Conclusions on the New Zealand flora, 506
Contemporaneous formation of Lower Greensand and Wealden, 221
Continental conditions throughout geological time, 97-99
changes and animal distribution, 102
extensions will not explain anomalous facts of distribution, 449
Continental islands, 243
of recent origin, 331
general remarks on recent, 408
ancient, 411
Continental period, date of, 337
Continents, movements of, 88
permanence of, 97
general stability of, 101, 103
geological development of, 205
Continuity of land, 74
Continuity of now isolated groups, proof of, 70
Cook, Captain, on a native quadruped in New Zealand, 476
Cope, Professor, on the Bermuda lizard, 266
_Coracias temminckii_, in Celebes, 463
Corvus, 17
Cossonidæ, in St. Helena, 299
Cretaceous deposits in North Australia, 493, 496
Cretaceous flora of Greenland, 185
of the United States, 189
Croll, Dr. James, on Antarctic icebergs, 136
on winter temperature of Britain in glacial epoch, 141
on diversion of gulf-stream during the glacial epoch, 143
on loss of heat by clouds and fogs, 145
on geographical causes as affecting climate, 148
on ancient glacial epochs, 170
on universality of glacial markings in Scotland, 174
on mild climates of Arctic regions, 189
on ocean-currents, 190, 204
on age of the earth, 213
on mean thickness of sedimentary rocks, 220
on small amount of marine denudation, 225
on buried river-channels, 336
Ctenodus, 69
Cyanopica, distribution of, 24
_Cyanopica cooki_, restricted range of, 15, 24
_Cyanopica cyanus_, 24
_Cynopithecus nigrescens_, in Celebes, 456
D.
Dacelo, 47
Dana on continental upheavals, 88
on chalk in the Sandwich Islands, 90
on elevation of land causing the glacial epoch, 152
on elevation of Western America, 194
on the development of continents, 205
on shore-deposits, 222
on life extermination by cold epochs, 230
Darwin, experiment on _Helix pomatia_, 78
on the permanence of oceans, 100
on cloudy sky of Antarctic regions, 146
on glaciers of the Southern Andes, 147
on geological time, 211
on complex relations of organisms, 226
on oceanic islands, 242
on seeds carried by birds, 257
{553}
experiments on seed-dispersal, 258
on natural history of the Keeling Islands, 286
theory of formation of atolls, 397
on cultivated plants not running wild, 507
Dawkins, Professor Boyd, on animal migrations during the glacial epoch,
120
Dawson, Mr. G. M., on alternations of climate in British Columbia, 121
Professor, on Palæozoic boulder-beds in Nova Scotia, 201
De Candolle on dispersal of seeds, 80
Deep-sea deposits, 219
Deer in Celebes, 456
_Delphinium ajacis_, on a railway bank, 515
_Dendroeca_, 19
_D. coerulea_, 19
_D. discolor_, 19
_D. dominica_, 19
_Dendroeca coronata_, variation of, 58
Dendrophidæ, 29
Denudation destroys the evidences of glaciation, 172
Denudation and deposition as a measure of time, 213
Denudation in river basins, measurement of, 215
Denudation, marine as compared with sub-aerial, 225
Deposition of sediments, how to estimate the average, 221
Deserts, cause of high temperature of, 132
Diagram of excentricity and precession, 129
Diagram of excentricity for three million years, 171
Dididæ, how exterminated, 436
Didunculus, keeled sternum of, 437
Diospyros, in upper greensand of Greenland, 186
_Diplotaxis muralis_, on railway banks, 513
Dipnoi, discontinuity of, 69
Dipterus, 69
Discontinuity among North American birds, 67
Discontinuity a proof of antiquity, 69
Discontinuous generic areas, 23
Discontinuous areas, 64
why rare, 64
Dispersal of animals, 72
of land animals, how effected, 73, 76
along mountain-chains, 81
of seeds by wind, 80, 257
by birds, 81, 258
by ocean-currents, 81, 258
of Azorean plants, facilities for, 260
Distribution, changes of, shown by extinct animals, 102
how to explain anomalies of, 420
Drontheim mountains, peculiar mosses of, 368
Dobson, Mr., on bats of Japan, 394
on the affinities of _Mystacina tuberculata_, 474
Dodo, the, 436
aborted wings of, 437
Dryiophidæ, 28
Dumeril, Professor, on lizards of Bourbon, 435
Duncan, Professor P. M., on ancient sea of central Australia, 496
E.
Early history of New Zealand, 484
Earth's age, 210
East Asian birds, range of, 38
East and West Australian floras, geological explanation of, 494
Echidna, 30
Echimyidæ, 27
Elevation of North America during glacial period, 154
causing diversion of gulf-stream, 154
Elwes, Mr. H. J., on distribution of Asiatic birds, 380
_Emberiza schoeniclus_, discontinuity of, 66
_E. passerina_, range of, 66
_E. pyrrhulina_, 66
Endemic genera of plants in Mauritius, &c., 443
Endemic genera of plants in New Zealand, 526
English plants in St. Helena, 297
Environment, change of, as modifying organisms, 225
_Eriocaulon septangulare_, 363
Ethiopian Region, definition of, 42
birds of, 43
Ettingshausen, Baron von, on the fossil flora of New Zealand, 499
on Australian plants in England, 518
Eucalyptus, wide range of, in Australia, 185
Eucalyptus and Acacia, why not in New Zealand, 507
Eucalyptus in Eocene of Sheppey, 518
Eupetes, distribution of, 25
Europe, Asia, &c., as zoological terms, 32
European birds, range of, 16
in Bermuda, 269
European occupation, effects of, in St. Helena, 294
European plants in New Zealand, 507
in Chile and Fuegia, 521
Everett, Mr., on Bornean birds, 377
on mammalia of the Philippines, 387
on Philippine birds, 388
on raised coral-reefs in the Philippines, 389
Evolution necessitates continuity, 70
Excentricity and precession, diagram of, 129
Excentricity, variations of, during three million years, 171
Excentricity a test of rival theories of climate, 171
Excentricity, high, its effects on warm and cold climates, 198
Explanation of peculiarities of the fauna of Celebes, 460
{554}
Extinct animals showing changes of distribution, 102
Extinct birds of the Mascarene Islands, 436
of New Zealand, 476
Extinction caused by glacial epoch, 122
F.
Families, restricted areas of, 29
distribution and antiquity of, 68
Fauna and flora, peculiarities of British, 370
Fauna of Borneo, affinities of, 381
of Java, 382
of Java and Asia compared, 384
Faunas of Hainan, Formosa, and Japan compared, 407
Felis, 17, 26
Ferns, abundance of, in Mascarene flora, 445
Ficus, fossil Arctic, 186
Fire-weed, the, of Tasmania, 513
Fisher, Rev. O., on temperature of space, 131
Fishes, dispersal of, 76
peculiar British, 340
cause of great speciality in, 343
mode of migration of fresh-water, 344
fresh-water, of New Zealand, 484
Floating islands, and the dispersal of animals, 74
Flora of the Azores, 256
of Bermuda, 271
of the Galapagos, 287
of St. Helena, 305
of the Sandwich Islands, 321;
peculiar features of, 323
peculiarities of the British, 360
of Madagascar and the Mascarene Islands, 439
of Madagascar and South Africa allied, 445
of New Zealand, 487
very poor, 488
its resemblance to the Australian, 489
its differences from the Australian, 490
origin of Australian element in, 498
tropical character of, explained, 500
summary and conclusion on, 506
Floras of New Zealand and Australia, summary of conclusion as to, 542
Florida and Canada, resemblances of, 5
and Bahamas, contrasts of, 5
Fogs cut off the sun's heat in glaciated countries, 145
Forbes, Mr. D., analysis of chalk, 91
Forbes, Mr. H. O., on plants of the Keeling Islands, 286
Formosa, 400
physical features of, 401
animal life of, 401
list of mammalia of, 402
list of land-birds peculiar to, 404
Forests, submerged, 335
Fowler, Rev. Canon, on peculiar British coleoptera, 346, 351
Freezing water liberates low-grade heat, 145
Fresh-water deposits, extent of, 97
organisms absent in St. Helena, 304
snail peculiar to Ireland, 356
fishes of the Seychelles, 433
Frogs of the Seychelles, 432
of New Zealand, 483
Fuegia, European plants in, 521
_Fulica alai_, 313
G.
Galapagos Islands, 275
Galapagos, absence of mammalia and amphibia from, 278
reptiles of, 278
birds of, 280
insects of, 284
land-shells of, 285
flora of, 287
and Azores contrasted, 290
_Galbula cyaneicollis_, distribution of, 18
_rufoviridis_, 18
_viridis_, 18
Galeopithecus, 63
_Gallinula sandvichensis_, 313
Gardner, Mr. J. S., on Tertiary changes of climate, 203
Garrulus, distribution of species of, 20
_Garrulus glandarius_, 21, 23, 65
_G. cervicalis_, 21
_G. krynicki_, 21
_G. atricapillus_, 21
_G. hyrcanus_, 21
_G. brandti_, 21, 23
_G. lanceolatus___, 22
_G. bispecularis_, 22
_G. sinensis_, 22
_G. taivanus_, 22
_G. japonicus_, 22, 65
Geikie, Dr. James, on interglacial deposits, 121
Sir Archibald, on age of buried river-channels, 337
on stratified rocks being found near shores, 87
on formation of chalk in shallow water, 96
on permanence of continents, 104
on variation in rate of denudation, 173
on the rate of denudation, 215
on small amount of marine denudation, 225
Genera, extent of, 17
origin of, 61
rise and decay of, 64
Generic areas, 17
Generic and Family distribution, 25
Genus, defined and illustrated, 17
Geographical change as a cause of glaciation, 148
changes, influence of, on climate, 150, 152
{555}
changes, effect of, on Arctic climates, 195
changes of Java and Borneo, 385
changes as modifying organisms, 228
Geological climates and geographical conditions, 204
time, 210
change, probably quicker in remote times, 223
time, value of the estimate of, 224
time, measurement of, 235
changes as aiding the migration of plants, 519
climates as affecting distribution, 534
climates, summary of causes of, 536
time, summary of views on, 539
Geology of Borneo, 375
of Madagascar, 412
of Celebes, 451
of New Zealand, 472
of Australia, 494
_Geomalacus maculcosus_, 356
Glacial climate not local, 113
deposits of Scotland, 112
Glacial epoch, proofs of, 107
effects of, on animal life, 117
alternations of climate during, 118
as causing migration and extinction, 122
causes of, 125
the essentials to the production of, 136
probable date of the, 160
and the climax of continental development, 206
date of last, 233
Glacial phenomena in North America, 116
Glaciation was greatest where rainfall is now greatest, 139
action of meteorological causes on, 142
summary of chief causes of, 144
in Northern Hemisphere, the only efficient cause of, 144
of New Zealand and South Africa, 162
local, due to high excentricity, 207
widespread in recent times, 536
Gleichenia in Greenland, 186
in relation to chalk, 89
Globigerina-ooze, analysis of, 91
Globigerinæ, where found, 92
Glyptostrobus, fossil, 186
Goats, destructiveness of, in St. Helena, 295
Godman, Mr., on birds reaching the Azores, 248, 250
Gray, Professor Asa, on extinction of European plants by the glacial
epoch, 123
Great Britain and Japan, birds common to, 396
Greene, Dr. J. Reay, on chameleons in Bourbon and Mauritius, 435
Greenland, loss of sun-heat by clouds in, 147
an anomaly in the Northern Hemisphere, 154
Miocene flora of, 183
Cretaceous flora of, 186
flora of ice-surrounded rocks of, 522
Grinnell Land, fossil flora of, 184
Guernsey, peculiar caddis-fly in, 355
Gulick, Rev. J. T., on Achatinellinæ, 318
Günther, Dr., on gigantic tortoises, 279
on peculiar British fishes, 341
on _Urotrichus gibsii_, 394
on lizards in the London Docks, 431
on Indian toads in Mauritius, 438
Guppy, Mr., on chalk of Solomon Islands, 91
H.
Haast, Dr., on otter-like mammal in New Zealand, 475
Habitability of globe due to disproportion of land and water, 209
_Haplothorax burchellii_, 299
Hartlaub, Dr., on "Lemuria," 423, 426
_Hatteria punctata_, 483
Haughton, Professor, on heat carried by ocean-currents, 194
comparison of Miocene and existing climates, 197
on geological time, 211, 219
on thickness of sedimentary rocks, 219
Hawaiian fauna and flora, antiquity of, 328
Heat and cold, how dispersed or stored up, 131
Heat required to melt snow, 134
evolved by frozen water, its nature and effects, 145
cut off by cloud and fogs, 145
Hector, Dr., on Triassic and Jurassic flora of New Zealand, 526
Heer, Professor, on chalk sea in Central Europe, 93
Heilprin, Professor, on insects of Bermuda, 269
on land-shells of Bermuda, 270
_Helianthemum Breweri_, 360, 363
Heliodus, an American fossil, 69
Helix, 17
Hemiptera of St. Helena, 303
Hepaticæ, peculiar British, 366
non-European genera of, in Britain, 367
Hesperomys, 26
Hesperornis allied to ostriches, 481
_Hieracium iricum_, 362
High land essential to the production of a glacial epoch, 195
Hildebrand, Dr. W., on flora of the Sandwich Islands, 321
Himalayan birds and insects in Celebes, 462
Hippopotamus in Yorkshire as proving a mild climate, 119
Hochstetter on the aquatic mammal of New Zealand, 475
{556}
Hooker, Sir Joseph, on the Galapagos flora, 287
on affinities of St. Helena plants, 306
on peculiar British plants, 360, 363
on the flora of New Zealand, 488
on proportion of temperate and tropical Australian floras, 492
on current of vegetation from north to south, 510
on supposed occurrence of Australian plants in England in the Tertiary
period, 518
Horne, Mr. John, on ice-sheet covering the Isle of Man, 115
Hull, Professor, on Permian breccias in Ireland indicating ice-action,
201
Humming-birds, restricted ranges of, 16
Hutton, Captain, on struthious birds of New Zealand, 479
Huxley, Professor, on geological time, 211
on European origin of African animals, 419
Hyomoschus, 27
Hyracoidea, restricted range of, 30
I.
Ice-action, what evidences of, during the Tertiary period, 178
indications of ancient, 200
Ice-borne rocks, a test of a glacial epoch, 176
in Miocene of N. Italy, 178
in Eocene of Alps, 178
in Eocene of Carpathians and Apennines, 179
absence of, in English and N. American Tertiaries, 180
Ice-cap, why improbable or impossible, 161
Iceland, a continental island, 450
Icteridæ, 50
Iguanidæ, 50
Indian birds in Formosa, 407
Indian Ocean as a source of heat in Tertiary times, 192
Indian genera of plants in Australia, 492
Indicator, distribution of, 25
Insectivora in Madagascar, 417
Insects, dispersal of, 77
of the Miocene period, 77
restriction of range of, 78
of the Azores, 253
of Bermuda, 269
of the Galapagos, 284
of St. Helena, 298
of the Sandwich Islands, 318
peculiar British, 344
of Celebes, peculiarities of, 462
scarcity of, in New Zealand, 505
Insular faunas, summary of conclusions as to, 539, 542
Interglacial warm periods on the continent and in North America, 121
Interglacial periods and their probable character, 152
Interglacial periods will not occur during an epoch of extreme
glaciation, 155
Interglacial climates never very warm, 159
Ireland, poverty of, in reptiles, 339
in plants, 339
peculiar fishes of, 342
plants of, not found in Great Britain, 364
Islands, classification of, 242
importance of, in study of distribution, 241
remote, how stocked with plants and animals, 261
submerged between Madagascar and India, 425
Isle of Wight, peculiar beetle of, 351
_Isatis tinctoria_, on railway bank, 513
Ithaginis, 26
J.
Japan, zoological features of, 393
mammalia of, 394
birds of, 396
birds peculiar to, 398
birds in distant areas, 399
Japan and Formosa, 391
Java, fauna of, 382
Asiatic species in, 384
Java and Borneo, past changes of, 385
Jays, distribution of species of, 20
of Europe and Japan, 67
Jeffreys, Dr. Gwyn, on shallow-water mollusca in chalk, 92
on fossil shallow-water shells in deep water, 337
Jones, Mr., on migration of birds to Bermuda, 268
on vegetation of the Bermudas, 272
Juan Fernandez, flora and fauna of, 287
Judd, Prof. J. W., on absence of glaciation in east Europe, 139
on glaciation of the Alps produced by elevation, 179
_Juniperus barbadensis_, 272
Jura, travelled blocks on, 110
Jurassic warm Arctic climate, 202
K.
Keeling Islands, animals of, 286
Kirk, Mr. T., on temporary introduced plants, 515
Knowledge of various kinds required for study of geographical
distribution, 7, 9
L.
_Lagopus scoticus_, 340
Land as a barrier to ocean-currents, 150
{557}
Land and sea, changes of, 83
how changes of, affect climate, 148, 150
Land and water, disproportion of, renders globe habitable, 209
Land-birds of Celebes, list of, 466
Land-connection, how far necessary to dispersal of mammals, 73
Land-shells, great antiquity of, 79
universal distribution of, 79
causes favouring the abundance of, 79
of the Azores, 256
of Bermuda, 270
of the Galapagos, 284
of St. Helena, 304
of the Sandwich Islands, 316
of the Seychelles, 434
_Laurus canariensis_, 260
Leguat on animals of Bourbon, 435
on the Solitaire, 436
Leguminosæ, abundance of, in Australia, 490
"Lemuria," a supposed submerged continent, 422-426
Lemurs in Madagascar, 416
Lendenfeld, Dr. R. von, on glaciation in the Australian Alps, 163
Leopard, enormous range of, 14
Lepidoptera, list of peculiar British, 347
Lepidosiren, 63
_Lepidosiren paradoxa_ and _L. annectens_, 69
Lepidosternidæ, 27
Limestone as indicating change of sea and land, 84
_Limnæa involuta_, 356
_Linaria purpurea_, on railway bank, 514
_Liopelma hochstetteri_, in New Zealand, 483
Liotrichidæ, 29
List of the land-birds of Celebes, 466
Lizard peculiar to the Mascarene Islands, 438
Lizards of the Galapagos, 278
local variation of colour of, 431
of New Zealand, 483
Lobeliaceæ, abundance of, in the Sandwich Islands, 324
Locality of a species, importance of, 12
_Loddigesia mirabilis_, rarity of, 16
Lord, Mr., on species of Urotrichus, 394
Low-grade and high-grade heat, 145
Lowlands nowhere covered with perpetual snow, 136
Lundy Island, peculiar beetles of, 354
Lyell, Sir Charles, on permanence of continents, 84
on calcareous mud, 90
on the distribution of chalk, 93
on geographical causes as modifying climate, 148
on estimate of geological time, 211, 235
on classification of sedimentary rocks, 217
Lynxes, a Palæarctic group, 41
M.
McLachlan, Mr., on peculiar British caddis-flies, 355
Madagascar, physical features of, 412
former condition of, 414
biological features of, 416
mammalia of, 416
reptiles of, 417
relation of, to Africa, 418
early history of, 419
birds of, in relation to "Lemuria," 422
flora of, 439
conclusion on fauna and flora of, 446
great antiquity of, 446
Madagascar and Africa, contrast of, 6
Maillard on animals of Bourbon, 435
Malay Islands, local peculiarities of flora in, 187
past history of, 389
Malayan birds in Formosa, 406
Mammalia of East Asia, range of, 34
of North Africa, range of, 34
Mammalia, dispersal of, 73
of Britain, range of, 33
poverty of, 329
of Borneo, 376
of Java, 382
of the Philippines, 387
of Japan, 393
of Formosa, 402
common to Formosa and India, 403
of Madagascar, 416
of Comoro Islands, 428
of Celebes, 455; whence derived, 457
of New Zealand, 474
Maori legend of origin of the forest-rat, 475
Maoris, their accounts of the moa, 477
Map of the old Rhone glacier, 110
of North and South Polar Regions, 138
of the Azores, 248
of Bermuda, 263
of the Galapagos, 276, 277
of the South Atlantic Ocean, 293
of the Sandwich Islands, 311
of the North Pacific with its submerged banks, 312
of British Isles and the 100-fathom bank, 333
of Borneo and Java, 374
of Japan and Formosa, 392
physical, of Madagascar, 413
of the Madagascar group, 415
of the Indian Ocean, 425
of Celebes, 452
of sea-bottom around New Zealand, 472
of Australia in Cretaceous period, 497
Marcou, Professor Jules, on the Pliocene and glacial epochs, 233
Marmot, range of, 15
Mars as illustrating glacial theories, 164, 168
{558}
Mars, no true ice-cap on, 166
Marsupials, range of, 30
Marsh, Prof. O. C., on the Atlantosaurus, 98
on Hesperornis, 481
Marsh, Mr., on camels as desert-makers, 296
Mascarene Islands, 428-445
Mascarene plants, curious relations of, 442
endemic genera of, 443
Mascarene flora, fragmentary character of, 444
abundance of ferns in, 445
Mauritius, Bourbon, and Rodriguez, 434
Measurements of geological time, 233
agreement of various estimates of, 235
concluding remarks on, 236
_Medicago sativa_ in New Zealand, 515
Megalæmidæ, 27
Meleagris, 50
_Melilotus vulgaris_, on railway banks, 513
Meliphagidæ, 47
Melliss, Mr., on the early history of St. Helena, 295
_Melospiza melodia_, variation of, 58
Merycotherium, 123
Meteorological causes as intensifying glaciation, 142
Migration caused by glacial epoch, 122
of birds to Bermuda, 267
of plants from north to south, 512
of plants and alterations of snow line, 516
of plants due to changes of climate, 517
of plants from north to south, long continued, 518
of plants aided by geological changes, 519
of plants by way of the Andes, 520
of plants by way of Himalayas and South Asia, 523
of plants through Africa, 524
Mild Arctic climates, stratigraphical evidence of, 187
causes of, 190
dependent on geographical changes, 191
effects of high excentricity on, 198
summary of causes of, 537
Miocene Arctic flora, 183
flora of Europe, 123
or Eocene floras, 185
deposits of Java, 385
fauna of Europe and North India, 419
Mississippi, matter carried away by, 172
Mitten, Mr. William, on peculiar British mosses and hepaticæ, 365, 368
on temporary appearance of plants, 513
Mniotiltidæ, a nearctic group, 49
Mnium, peculiar species of, in the Drontheim mountains, 368
Moas of New Zealand, 476
Mollusca, dispersal of, 78
Monotremata, restricted range of, 30
Moraines, 108
of Ivrea, 116
More, Mr. A. G., on peculiar Irish plants, 364
Morgan, Mr. C. Lloyd, on thickness of formations not affected by
denudation, 220
Moseley, Mr. H. N., on seeds carried by birds, 259
on the flora of Bermuda, 272
Mosses, peculiar British, 366
non-European genera of, in Britain, 367
how diffused and why restricted, 368
Mt. St. Elias, why not ice-clad, 154
Mountain chains aiding the dispersal of plants, 81
as aids to migration of plants, 513
Mueller, Baron von, census of Australian plants, 492
_Munia brunneiceps_, in Celebes, 463
Murray, Mr. J., on oceanic deposits, 86
on chalk-like globigerina-ooze, 92
on mean height of continents, 216
on land-area of the globe, 221
Mus, 17, 26
_Mygale pyrenaica_, range of, 15, 24
_M. muscovitica_, 24
_Myialestes helianthea_ in Celebes, 463
_Myrica faya_, 260
Myrsine, fossil in Greenland, 186
_Mytilus edulis_, sub-fossil in Spitzbergen, 182
N.
Nares, Capt. Sir G., on snow and ice in high latitudes, 135
on abrupt elevation of Bermuda, 264
Nearctic Region, definition of, 48
mammalia of, 48
birds of, 49
reptiles of, 50
_Nectarinea osea_, restricted range of, 16
Neilgherries, Australian plants naturalized in, 528
Neotropical Region, definition of, 51
low types of, 52
Nevill, Mr. Geoffrey, on land-shells of the Seychelles, 434
on destruction of Seychelles flora, 445
New species, origin of, 56
Newton, Mr. E., on short wings of the Seychelles dove, 437
Newton, Professor, on recently extinct birds, 437
Newts, restricted range of, 30
New Zealand, recent glaciation of, 163
New Zealand, 471
geology of, 472
form of sea-bottom around, 473
zoological character of, 473
mammalia of, 474
{559}
wingless birds of, 476
past changes of, 478
winged birds and lower vertebrates of, 482
deductions from peculiarities of fauna of, 484
period of its union with N. Australia, 484
the flora of, 487, 506
origin of Australian element in the flora of, 498
tropical character of flora, 500
tropical genera common to Australia, 501
temperate species common to Australia, 502
route of Arctic plants to, 521
European plants in, 509
endemic genera of plants in, 526
great antiquity of, 526
Nordenskjöld, Prof., on absence of perpetual snow in N. Asia, 135
on recent milder climate in Spitzbergen, 182
on former Polar climates, 187
on geology of Spitzbergen, 188
North America, glacial phenomena in, 116
interglacial warm periods in, 121
condition of, in Tertiary period, 194
Northern genera of plants in S. temperate America, 521
hemisphere, absence of southern plants from, 527
flora, hardiness of, 528
O.
Ocean-currents as carriers of plants, 81
as affecting interglacial periods, 152
as determining climate, 153
effects of, in Tertiary times, 196
Ocean, Darwin on permanence of, 100
Oceanic and continental islands, 242
Oceanic islands a proof of the permanence of oceans, 100
Oceanic islands, 244
--the Azores, 247
general remarks on, 329
Octodontidæ, 27
_Oenanthe fluviatilis_, 361
Oeninghen, Miocene flora of, 183
_Oenothera odorata_, on a railway bank, 514
Oliver, Professor, on peculiar Bermudan plants, 272
Operculata, scarcity of, in the Sandwich Islands, 317
_Ophrys apifera_, temporary appearance of, 514
Orchideæ, species have restricted ranges, 505
Orchids, abundance of, in Bourbon and Mauritius, 446
why almost universal in the tropics, 446
Orders, distribution of, 30
Organic change dependent on change of conditions, 225, 228
Oriental Region, definition of, 44
mammals and birds of, 44
reptiles of, 45
insects of, 45
Origin of new species, 56, 60
of new genera, 61
of the Galapagos flora, 288
of the beetles of St. Helena, 298
of Australian element in the New Zealand flora, 498
Orkney, peculiar fishes of, 341
Orthonyx not a New Zealand genus, 483
Osprey, wide range of, 15
Ostriches, limitation of, 30
Otter-like mammal in New Zealand, 475
Overlapping and discontinuous areas, 28
P.
_Pachyglossa aureolimbata_, in Celebes, 463
Palæarctic Region, limits of, 39
characteristic features of, 41
Palæozoic formations, depth of, round London, 218
Palm confined to Round Island, 444
Panax, fossil in Greenland, 186
Papilio, 17
Paraguay, no wild horses or cattle in, 226
Parnassius, Palæarctic, 42
_Parus ater_, 19
_P. borealis_, 19, 64
_P. britannicus_, 321
_P. camtschatkensis_, 19
_P. cinctus_, 20
_P. coeruleus_, 20
_P. cyaneus_, 20
_P. cristatus_, 20
_P. ledouci_, 20
_P. lugubris_, 20
_P. major_, 19
_P. palustris_, 19; discontinuous area of, 65
_P. rosea_, 340
_P. teneriffæ_, 20
Passeres of the Sandwich Islands, 314
Past changes of New Zealand, 478
Payer, Lieut., on evaporation of ice during the Arctic summer, 140
Peculiar fauna of New Zealand, deductions from, 484
Pengelly, Mr., on submerged forests, 335
_Pennula millei_, in Sandwich Islands, 313
Permanence of continents, summary of evidence for, 103
Permian formation, indications of ice-action in, 200
Perodicticus, a local genus, 26
_Petroselinum segetum_, on railway bank, 514
{560}
Philippine Islands, 387
mammalia of, 387
birds of, 388
past history of, 389
_Phyllodactylus galapagensis_, 279
_Phylloscopus borealis_, range of, 15
Physical causes which determine distribution, 533
features of Formosa, 401
Pica, 17
Pickering, Dr., on the flora of the Sandwich Islands, 323
on temperate forms on mountains of the Sandwich Islands, 323
_Pithecia monachus_, distribution of, 18
_P. rufibarbata_, 18
Pitta, distribution of, 25
Plants, dispersal of, 80
seeds of, adapted for dispersal, 80
wide range of species and genera of, 185
poverty of, in Ireland, 339
peculiar British, 359
of Ireland not in Great Britain, 364
cause of their wide diffusion and narrow restriction, 369
easily dispersed often have restricted ranges, 504
how they migrate from north to south, 512
of existing genera throughout the Tertiary period, 520
southern migration of, by way of the Himalayas, 523
southern migration of, through Africa, 524
endemic genera of, in New Zealand, 526
Platypus, 30
_Plestiodon longirostris_ of Bermuda, 266
Po, matter carried away by, 173
Podargus, Australian genus, 47
Poecilozonites, peculiar to Bermuda, 270
_Poinciana regia_ in Madagascar, 440
Populus, fossil in Spitzbergen, 184
Pourtales, Count, on modern formation of chalk, 95
on sedimentary deposits in Gulf of Mexico, 222
Poverty in species of Britain, 338
Precession of Equinoxes, influence of, on climate, 126
Preservation of species, 63
Proboscidea, range of, 30
Proteus, why preserved, 63
Psophia, range of species of, 18
Pteroptochidæ, 29
Pyrenean ibex, restricted range of, 15
R.
Railways, new plants on, 513
Ramsay, Mr. Wardlaw, on Philippine birds, 388
Professor, on ancient land surfaces, 99
on geological time 212
on thickness of sedimentary rocks, 219
Rat, native, of New Zealand, 475
Rate of organic change usually measured by an incorrect scale, 232
Rats in the Galapagos, 278
Raven, wide range of, 15
Reade, T. Mellard, on changes of sea and land, 84
Recent continental islands, 243, 331
Red clay of Bermuda, 265
Reptiles, dispersal of, 75
of the Galapagos, 278
of the Sandwich Islands, 316
cause of scarcity of, in British Isles, 339
of Madagascar, 417
of the Seychelles, 430
of Mauritius and Round Island, 438
of New Zealand, 483
_Rhodolæna altivola_ in Madagascar, 440
_Rhus toxicodendron_ in Bermuda, 272
Ridgway, Mr., on birds of Galapagos, 281
River-channels, buried, 336
_Roches moutonnées_, 108
Rodents in Madagascar, 417
Round Island, a snake and a palm peculiar to, 438, 444
_Rumex pulcher_ in New Zealand, 515
Rye, Mr. E. C., on peculiar British insects, 345, 351
S.
St. Helena, 292
effects of European occupation on the vegetation of, 294
insects of, 298
land-shells of, 304
absence of fresh-water organisms in, 304
native vegetation of, 305
Salvin, Mr., on the birds of the Galapagos, 280
Sandwich Islands, the, 310
zoology of, 313
birds of, 313
reptiles of, 316
land-shells of, 316
insects of, 318
vegetation of, 321
antiquity of fauna and flora of, 328
Sassafras, in Swiss Miocene, 183
Scandinavian flora, aggressive power of, 511
Scientific voyages, comparative results of, 7
Sciurus, 26
Sclater, Mr. P. L., on zoological region, 32, 39
Scotland, glacial deposits of, 112-115
probable rate of denudation in, 173
Miocene flora of, 184
peculiar fishes of, 341
{561}
_Scotophilus tuberculatus_ in New Zealand, 474
Scrophularincæ, why few species are common to Australia and New Zealand,
505
Sea, depth of, around Madagascar, 414
depth of, around Celebes, 452
Sea-bottom around New Zealand and Australia, 473
Sea-level, changes of, dependent on glaciation, 161
complex effects of glaciation on, 162, 164
rise of, a cause of denudation, 174
Seas, inland, in Tertiary period, 191
Section of sea-bottom near Bermuda, 264
Sedges and grasses common to Australia and New Zealand, 504
Sedimentary rocks, how to estimate thickness of, 217
thinning out of, 217
how formed, 218
thickness of, 217, 221
summary of conclusions on the rate of formation of the, 221
Seebohm, Mr., on _Parus palustris_, 65
on _Emberiza schoeniclus_, 66
on snow in Siberia, 166
on birds of Japan, 396
Seeds, dispersal of, 257
carried by birds, 258
_Senecio australis_, on burnt ground, 513
Sericinus, Palæarctic, 42
Seychelles Archipelago, 429
birds of, 430
reptiles and amphibia of, 430
fresh-water fishes of, 433
land-shells of, 434
Sharp, Dr. D., on beetles of the Sandwich Islands, 319
on peculiar British beetles, 345
Shells, peculiar to Britain, 356
Shetland Isles, peculiar beetle of, 354
Shore deposits, 85, 211
proving the permanence of continents, 97
distance from coast of, 221
_Sialia sialis_, variation of, 58
Siberia, amount of snow and its sudden disappearance in, 166
Silurian boulder-beds, 201
warm Arctic climate, 202
Simiidae, 27
_Sisyrinchium bermudianum_, 272
Skertchley, Mr., on four distinct boulder-clays, 118
on Tertiary deposits in Egypt and Nubia, 191
on climatic stability of present epoch, 233
Slug peculiar to Ireland, 356
Snake peculiar to Round Island, 438
Snakes of the Galapagos, 280
of the Seychelles, 431
Snow and ice, properties of, in relation to climate, 131
Snow, effects of, on climate, 133
Snow, quantity of heat required to melt, 134
often of small amount in high latitudes, 135
never perpetual on lowlands, 136
conditions determining perpetual, 137
maintains cold by reflecting the solar heat, 144
Snow-line, alterations of, causing migration of plants, 516
Sollas, Mr. J. W., on greater intensity of telluric action in past time,
223
South Africa, recent glaciation of, 163
many northern genera of plants in, 524
its supposed connection with Australia, 525
South American plants in New Zealand, 521
South Temperate America, poor in species, 53
climate of, 146
Southern flora, comparative tenderness of, 528
Southern plants, why absent in the Northern Hemisphere, 527
Space, temperature of, 129
Specialisation antagonistic to diffusion of _species_, 505
Species, origin of new, 56
extinction of, 63
rise and decay of, 64
epoch of exceptional stability of, 232
dying out and replacement of, 409
preservation of, in islands, 410
Specific areas, 14; discontinuous, 64
_Spiranthes romanzoviana_, 364
Spitzbergen, Miocene flora of, 184
absence of boulder-beds in, 187
Spruce, Dr. Richard, on the dispersion of hepaticæ, 309
Stability of extreme glacial conditions, 159
Stainton, Mr. H. T., on peculiar British moths, 346-350
Stanivoi mountains, why not ice-clad, 154
Starlings, genera of, in New Zealand, 482
_Stellaria media_, temporary appearance of, 515
Sternum, process of abortion of keel of, 437
Stow, Mr. G. W., on glacial phenomena in South Africa, 163
Stratified rocks formed near shores, 85, 87
deposits, how formed, 218
Striated rocks, 107
blocks in the Permian formation, 200
_Striæ flammea_, range of, 15
Struthiones, 30
Struthious birds of New Zealand as indicating past changes, 478
Stylidium, wide range of, 185
Submerged forests, 334
{562}
Subsidence of isthmus of Panama, 151
Sumatra, geology of, 385
Sweden, two deposits of "till" in, 121
Swimming powers of mammalia, 74
Swinhoe, Mr. Robert, researches in Formosa, 400
Switzerland, interglacial warm periods in, 121
Sylviadæ, overlapping genera of, 29
T.
Talpidæ, a Palæarctic group, 41
Tapirs, distribution of, 25
former wide range of, 393
Tarsius, 63
_Tarsius spectrum_ in Celebes, 456
Tasmania and North Australia, resemblance of, 5
route of Arctic plants to, 520
_Taxodium distichum_ in Spitzbergen, 184
Temperate climates in Arctic regions, 181
Australian genera of plants in New Zealand, 502
Australian species of plants in New Zealand, 502
Temperature, how dependent on sun's distance, 129
of space, 129
Tertiary glacial epochs, evidence against, 179
warm climates, continuous, 187
Test of glaciation at any period, 175
_Testudo abingdonii_, 279
_T. microphyes_, 278
Tetraogallus, distribution of, 24
Thais, a Palæarctic genus, 42
Thomson, Sir William, on age of the earth, 213
Sir Wyville, on organisms in the globigerina-ooze, 89
analysis of globigerina-ooze, 91
_Thryothorus bewickii_, discontinuity of, 68
"Till" of Scotland, 112
several distinct formations of, 121
Tits, distribution of species of, 19
Torreya, fossil in Spitzbergen, 186
Tortoises of the Galapagos, 278
Trade-winds, how modified by a glacial epoch, 142
Tragulidæ, 27
Travelled blocks, 109
Tremarctos, an isolated genus, 29
Triassic warm Arctic climate, 200
Tribonyx not a New Zealand genus, 483
Trichoptera peculiar to Britain, 355
Trogons, distribution of, 28
Tropical affinities of New Zealand birds, 483
character of the New Zealand flora, cause of, 500
genera common to New Zealand and Australia, 501
Turdus, 17, 26
_Turdus fuscescens_, variation of, 58, 59
Tylor, A., on estimating the rate of denudation, 214
Tyrannidæ, an American family, 50
U.
Uraniidæ, 28
Uropeltidæ, 30
Urotrichus, distribution of, 25
Ursus, 26
V.
Variation in animals, 57
amount of, in N. American birds, 58
Vegetation, local peculiarities of, 185
effects of Polar night on, 198
_Vesperugo serotinus_, range of, 14
_Vireo bellii_, supposed discontinuity of, 68
Vireonidæ, an American family, 49
W.
Wallich, Dr., on habitat of globigerinæ, 92
Warren, Mr. W., information on British lepidoptera, 347
Water, properties of, in relation to climate, 131, 133
Waterhouse, Mr., on Galapagos beetles, 284
Wales, peculiar fish of, 341
Warm climates of northern latitudes, long persistence of, 201
Watson, Mr. H. C., on the flora of the Azores, 256
on peculiar British plants, 359
on vegetation of railway banks, 513
Webb, Mr., on comparison of Mars and the Earth, 166
West Australia, rich flora of, 494
former extent and isolation of, 497
West Indies, a Neotropical district, 53
White, Dr. F. Buchanan, on the Hemiptera of St. Helena, 303
Mr. John, on native accounts of the moa, 477
Whitehead, Mr. John, on Bornean birds, 377
Wilson, Mr. Scott B., on birds of the Sandwich Islands, 314
Winged birds of New Zealand, 482
Wingless birds never inhabit continents, 437
their evidence against "Lemuria," 438
of New Zealand, 476
Wings of struthious birds show retrograde development, 437
{563}
Winter temperature of Europe and America, 196
Wolf, range of, 14
Wollaston, Mr. T. V., on insular character of St. Helena, 294
on St. Helena shells and insects, 297
Wood, Mr. Searles V., jun., on formation of "till," 114
on alternations of climate, 118
on causes of glacial epochs, 125
conclusive objection to the excentricity theory, 160
on continuous warm Tertiary climates, 180
Woodward, Dr. S. P., on Ammonites living in shallow water, 95
Woodward, Mr., on "Lemuria," 426
Wright, Dr. Percival, on lizards of the Seychelles, 431
Y.
Young, Professor J., on contemporaneous formation of deposits, 221
Young Island, lofty Antarctic, 522
Z.
Zoology of the Azores, 248
of Bermuda, 262
of the Sandwich Islands, 313
of Borneo, 376
of Madagascar, 416
of islands round Celebes, 453
of Celebes, 455
Zoological and geographical regions compared, 32, 54
Zoological features of Japan, 393
character of New Zealand, 473
THE END
{564}
RICHARD CLAY AND SONS, LIMITED,
LONDON AND BUNGAY.
* * * * *
[1] A small number of species belonging to the West Indies are found in the
extreme southern portion of the Florida Peninsula.
[2] I cannot avoid here referring to the enormous waste of labour and money
with comparatively scanty and unimportant results to natural history of
most of the great scientific voyages of the various civilized governments
during the present century. All these expeditions combined have done far
less than private collectors in making known the products of remote lands
and islands. They have brought home fragmentary collections, made in widely
scattered localities, and these have been usually described in huge folios
or quartos, whose value is often in inverse proportion to their bulk and
cost. The same species have been collected again and again, often described
several times over under new names, and not unfrequently stated to be from
places they never inhabited. The result of this wretched system is that the
productions of some of the most frequently visited and most interesting
islands on the globe are still very imperfectly known, while their native
plants and animals are being yearly exterminated, and this is the case even
with countries under the rule or protection of European governments. Such
are the Sandwich Islands, Tahiti, the Marquesas, the Philippine Islands,
and a host of smaller ones; while Bourbon and Mauritius, St. Helena, and
several others, have only been adequately explored after an important
portion of their productions has been destroyed by cultivation or the
reckless introduction of goats and pigs. The employment in each of our
possessions, and those of other European powers, of a resident naturalist
at a very small annual expense, would have done more for the advancement of
knowledge in this direction than all the expensive expeditions that have
again and again circumnavigated the globe.
[3] The general facts of Palæontology, as bearing on the migrations of
animal groups, are summarised in my _Geographical Distribution of Animals_,
Vol. I. Chapters VI., VII., and VIII.
[4] Since these lines were written, a fine series of specimens of this rare
humming-bird has been obtained from the same locality. (See _Proc. Zool.
Soc._ 1881, pp. 827-834.)
[5] Many of these large genera are now subdivided, the divisions being
sometimes termed genera, sometimes sub-genera.
[6] The Palæarctic region includes temperate Asia and Europe, as will be
explained in the next chapter.
[7] The following list of the genera of reptiles and amphibia peculiar to
the Palæarctic Region has been furnished me by Mr. G. A. Boulenger, of the
British Museum:--
SNAKES. FROGS AND TOADS.
_Achalinus_--China, Japan. _Pelobates_--Eur., S.W. Asia.
_Coelopeltis_--S. Eur., N. Af., _Pelodytes_--W. Europe.
S.W. Asia. _Discoglossus_--S. Eur., N.W. Af.
_Macroprotodon_--S. Eur., N. Af. _Bombinator_--Eur., Temp. Asia.
_Taphrometopon_--Cent. Asia. _Alytus_--Cent. and W. Eur.
LIZARDS. NEWTS.
_Phrynocephalus_--Cent. and S.W. _Salamandra_--Eur., N. Af., S.W.
Asia. Asia.
_Anguis_--Europe, W. Asia. _Chioglossa_--Spain and Portugal.
_Blanus_--S.W. Eur., N.W. Africa, _Salamandrina_--Italy.
S.W. Asia. _Pachytriton_--East Thibet.
_Trogonophis_--N.W. Africa. _Hynobius_--China and Japan.
_Lacerta_--Eur., Temp. Asia, N. _Geomolge_--E. Manchuria.
Africa (one sp. in _Onychodactylus_--Japan.
W. Af.). _Salamandrella_--Siberia.
_Psammodromus_--S.W. Eur., N.W. _Ranidens_--Siberia.
Africa. _Batrachyperus_--East Thibet.
_Algiroides_--S. Eur. _Myalobatrachus_--China, Japan.
_Proteus_--Caverns of S. Austria.
[8] Remains of the dingo have been found fossil in Pleistocene deposits but
the antiquity of man in Australia is not known. It is not, however,
improbable that it may be as great as in Europe. My friend A. C. Swinton,
Esq., while working in the then almost unknown gold-field of Maryborough,
Victoria, in January, 1855, found a fragment of a well-formed stone axe
resting on the metamorphic schistose bed-rock about five feet beneath the
surface. It was overlain by the compact gravel drift called by the miners
"cement," and by an included layer of hard iron-stained sandstone. The
fragment is about an inch and three-eighths wide and the same length, and
is of very hard fine-grained black basalt. One side is ground to a very
smooth and regular surface, terminating in a well-formed cutting edge more
than an inch long, the return face of the cutting part being about a
quarter of an inch wide. The other side is a broken surface. The weapon
appears to have been an axe or tomahawk closely resembling that figured at
p. 335 of Lumholtz's _Among Cannibals_, from Central Queensland. The
fragment was discovered by Mr. Swinton and the late Mr. Mackworth Shore,
one of the discoverers of the gold-field, before any rush to it had taken
place, and it seems impossible to avoid the conclusion that it was formed
prior to the deposit of the gravel drift and iron-stained sandstone under
which it lay. This would indicate a great antiquity of man in Australia,
and would enable us to account for the fossilised remains of the dingo in
Pleistocene deposits as those of an animal introduced by man.
[9] These facts are taken from a memoir on _The Mammals and Winter Birds of
Florida_, by J. A. Allen; forming Vol. II., No. 3, of the Bulletin of the
Museum of Comparative Zoology at Harvard College, Cambridge, Massachusetts.
[10] The great variation in wild animals is more fully discussed and
illustrated in the author's _Darwinism_ (Chapter III.).
[11] See _Ibis_, 1879, p. 32.
[12] In Mr. Seebohm's latest work, _Birds of the Japanese Empire_ (1890),
he says, "Examples from North China are indistinguishable from those
obtained in Greece" (p. 82).
[13] _Ibis_, 1879, p. 40. In his _Birds of the Japanese Empire_ (1890), Mr.
Seebohm classes the Japanese and European forms as _E. schoeniclus_, and
thinks that their range is probably continuous across the two continents.
[14] Lyell's _Principles of Geology_, ii., p. 369.
[15] Mr. Darwin found that the large _Helix pomatia_ lived after immersion
in sea-water for twenty days. It is hardly likely that this is the extreme
limit of their powers of endurance, but even this would allow of their
being floated many hundred miles at a stretch, and if we suppose the shell
to be partially protected in the crevice of a log of wood, and to be thus
out of water in calm weather, the distance might extend to a thousand miles
or more. The eggs of fresh-water mollusca, as well as the young animals,
are known to attach themselves to the feet of aquatic birds, and this is
probably the most efficient cause of their very wide diffusion.
[16] _Principles of Geology_, 11th Ed., Vol. I., p. 258.
[17] On Limestone as an Index of Geological Time.
[18] In his _Preliminary Report on Oceanic Deposit_, Mr. Murray says:--"It
has been found that the deposits taking place near continents and islands
have received their chief characteristics from the presence of the _debris_
of adjacent lands. In some cases these deposits extend to a distance of
over 150 miles from the coast." (_Proceedings of the Royal Society_, Vol.
XXIV. p. 519.)
"The materials in suspension appear to be almost entirely deposited within
200 miles of the land." (_Proceedings of the Royal Society of Edinburgh_,
1876-77, p. 253.)
[19] _Geographical Evolution. (Proceedings of the Royal Geographical
Society._ 1879, p. 426.)
[20] Professor Dana was, I believe, the first to point out that the regions
which, after long undergoing subsidence and accumulating vast piles of
sedimentary deposit have been elevated into mountain ranges, thereby become
stiff and unyielding, and that the next depression and subsequent upheaval
will be situated on one or the other sides of it; and he has shown that, in
North America, this is the case with all the mountains of the successive
geological formations. Thus, depressions, and elevations of extreme
slowness but often of vast amount, have occurred successively in restricted
adjacent areas; and the effect has been to bring each portion in succession
beneath the ocean but always bordered on one or both sides by the remainder
of the continent, from the denudation of which the deposits are formed
which, on the subsequent upheaval, become mountain ranges. (_Manual of
Geology_, 2nd Ed., p. 751.)
[21] _Nature_, Vol. II., p. 297.
[22] Sir W. Thomson, _Voyage of Challenger_, Vol. II., p. 374.
[23] The following is the analysis of the chalk at Oahu:--
Carbonate of Lime 92.800 per cent.
Carbonate of Magnesia 2.385 ,,
Alumina 0.250 ,,
Oxide of Iron 0.543 ,,
Silica 0.750 ,,
Phosphoric Acid and Fluorine 2.113 ,,
Water and loss 1.148 ,,
This chalk consists simply of comminuted corals and shells of the reef. It
has been examined microscopically and found to be destitute of the minute
organisms abounding in the chalk of England. (_Geology of the United States
Exploring Expedition_, p. 150.) Mr. Guppy also found chalk-like coral
limestones containing 95 p.c. of carbonate of lime in the Solomon Islands.
The absence of _Globigerinæ_ is a local phenomenon. They are quite absent
in the Arafura Sea, and no _Globigerina_-ooze was found in any of the
enclosed seas of the Pacific, but with these exceptions the _Globigerinæ_
"are really found all over the bottom of the ocean." (Murray on Oceanic
Deposits--_Proceedings of Royal Society_, Vol. XXIV., p. 523.)
The above analysis shows a far closer resemblance to chalk than that of the
_Globigerina_-ooze of the Atlantic, four specimens of which given by Sir W.
Thomson (_Voyage of the Challenger_ Vol. II. Appendix, pp. 374-376, Nos. 9,
10, 11 and 12) from the mid-Atlantic, show the following proportions:--
Carbonate of Lime 43.93 to 79.17 per cent.
Carbonate of Magnesia 1.40 to 2.58 ,,
Alumina and Oxide of Iron 6.00? to 32.98 ,,
Silica 4.60 to 11.23 ,,
In addition to the above there is a quantity of insoluble residue
consisting of small particles of sanidine, augite, hornblende, and
magnetite, supposed to be the product of volcanic dust or ashes carried
either in the air or by ocean currents. This volcanic matter amounts to
from 4.60 to 8.33 per cent. of the _Globigerina_-ooze of the mid-Atlantic,
where it seems to be always present; and the small proportion of similar
matter in true chalk is another proof that its origin is different, and
that it was deposited far more rapidly than the oceanic ooze.
The following analysis of chalk by Mr. D. Forbes will show the difference
between the two formations:--
Grey Chalk, White Chalk,
_Folkestone_. _Shoreham_.
Carbonate of Lime 94.09 98.40
Carbonate of Magnesia 0.31 0.08
Alumina and Phosphoric Acid a trace 0.42
Chloride of Sodium 1.29 --
Insoluble débris 3.61 1.10
(From _Quarterly Journal of the Geological Society_, Vol. XXVII.)
The large proportion of carbonate of lime, and the very small quantity of
silica, alumina, and insoluble _débris_, at once distinguish true chalk
from the _Globigerina_-ooze of the deep ocean bed.
[24] Notes on Reticularian Rhizopoda; in _Microscopical Journal_, Vol.
XIX., New Series, p. 84.
[25] _Proceedings of the Royal Society_, Vol. XXIV. p. 532.
[26] See Presidential Address in Sect. D. of British Association at
Plymouth, 1877.
[27] _Geological Magazine_, 1871, p. 426.
[28] In his lecture on _Geographical Evolution_ (which was published after
the greater part of this chapter had been written) Sir Archibald Geikie
expresses views in complete accordance with those here advocated. He
says:--"The next long era, the Cretaceous, was more remarkable for slow
accumulation of rock under the sea than for the formation of new land.
During that time the Atlantic sent its waters across the whole of Europe
and into Asia. But they were probably nowhere more than a few hundred feet
deep over the site of our continent, even at their deepest part. Upon their
bottom there gathered a vast mass of calcareous mud, composed in great part
of foraminifera, corals, echinoderms, and molluscs. Our English chalk,
which ranges across the north of France, Belgium, Denmark, and the north of
Germany, represents a portion of the deposits of that sea-floor." The
weighty authority of the Director-General of the Geological Survey may
perhaps cause some geologists to modify their views as to the deep-sea
origin of chalk, who would have treated any arguments advanced by myself as
not worthy of consideration.
[29] _Introduction and Succession of Vertebrate Life in America_, by
Professor O. C. Marsh. Reprinted from the _Popular Science Monthly_, March,
April, 1878.
[30] _Physical Geography and Geology of Great Britain_, 5th Ed. p. 61.
[31] Of late it has been the custom to quote the so-called "ridge" down the
centre of the Atlantic as indicating an extensive ancient land. Even
Professor Judd at one time adopted this view, speaking of the great belt of
Tertiary volcanoes "which extended through Greenland, Iceland, the Faroe
Islands, the Hebrides, Ireland, Central France, the Iberian Peninsula, the
Azores, Madeira, Canaries, Cape de Verde Islands, Ascension, St. Helena,
and Tristan d'Acunha, and which constituted as shown by the recent
soundings of H.M.S. _Challenger_ a mountain-range, comparable in its
extent, elevation, and volcanic character with the Andes of South America"
(_Geological Mag._ 1874, p. 71). On examining the diagram of the Atlantic
Ocean in the _Challenger Reports_, No. 7, a considerable part of this ridge
is found to be more than 1,900 fathoms deep, while the portion called the
"Connecting Ridge" seems to be due in part to the deposits carried out by
the River Amazon. In the neighbourhood of the Azores, St. Paul's Rocks,
Ascension, and Tristan d'Acunha are considerable areas varying from 1,200
to 1,500 fathoms deep, while the rest of the ridge is usually 1,800 or
1,900 fathoms. The shallower water is no doubt due to volcanic upheaval and
the accumulation of volcanic ejections, and there may be many other deeply
submerged old volcanoes on the ridge; but that it ever formed a chain of
mountains "comparable in elevation with the Andes," there seems not a
particle of evidence to prove. It is however probable that this ridge
indicates the former existence of some considerable Atlantic islands, which
may serve to explain the presence of a few identical genera, and even
species of plants and insects in Africa and South America, while the main
body of the fauna and flora of these two continents remains radically
distinct.
In my _Darwinism_ (pp. 344-5) I have given an additional argument founded
on the comparative height and area of land with the depth and area of
ocean, which seems to me to add considerably to the weight of the evidence
here submitted for the permanence of oceanic and continental areas.
[32] In a review of Mr. T. Mellard Reade's _Chemical Denudation and
Geological Time_, in _Nature_ (Oct. 2nd, 1879), the writer remarks as
follows:--"One of the funny notions of some scientific thinkers meets with
no favour from Mr. Reade, whose geological knowledge is practical as well
as theoretical. They consider that because the older rocks contain nothing
like the present red clays, &c., of the ocean floor, that the oceans have
always been in their present positions. Mr. Reade points out that the first
proposition is not yet proved, and the distribution of animals and plants
and the fact that the bulk of the strata on land are of marine origin are
opposed to the hypothesis." We must leave it to our readers to decide
whether the "notion" developed in this chapter is "funny," or whether such
hasty and superficial arguments as those here quoted from a "practical
geologist" have any value as against the different classes of facts, all
pointing to an opposite conclusion, which have now been briefly laid before
them, supported as they are by the expressed opinion of so weighty an
authority as Sir Archibald Geikie, who, in the lecture already quoted
says:--"From all this evidence we may legitimately conclude that the
present land of the globe, though formed in great measure of marine
formations, has never lain under the deep sea; but that its site must
always have been near land. Even its thick marine limestones are the
deposits of comparatively shallow water."
[33] _Antiquity of Man_, 4th Ed. pp. 340-348.
[34] _The Great Ice Age and its Relation to the Antiquity of Man._ By James
Geikie, F.R.S. (Isbister and Co., 1874.)
[35] This view of the formation of "till" is that adopted, by Dr. Geikie,
and upheld by almost all the Scotch, Swiss, and Scandinavian geologists.
The objection however is made by many eminent English geologists, including
the late Mr. Searles V. Wood, Jun., that mud ground off the rocks cannot
remain beneath the ice, forming sheets of great thickness, because the
glacier cannot at the same time grind down solid rock and yet pass over the
surface of soft mud and loose stones. But this difficulty will disappear if
we consider the numerous fluctuations in the glacier with increasing size,
and the additions it must have been constantly receiving as the ice from
one valley after another joined together, and at last produced an ice-sheet
covering the whole country. The grinding power is the motion and pressure
of the ice, and the pressure will depend on its thickness. Now the points
of maximum thickness must have often changed their positions, and the
result would be that the matter ground out in one place would be forced
into another place where the pressure was less. If there were no lateral
escape for the mud, it would necessarily support the ice over it just as a
water-bed supports the person lying on it; and when there was little
drainage water, and the ice extended, say, twenty miles in every direction
from a given part of a valley where the ice was of less than the average
thickness, the mud would necessarily accumulate at this part simply because
there was no escape for it. Whenever the pressure all round any area was
greater than the pressure on that area, the _débris_ of the surrounding
parts would be forced into it, and would even raise up the ice to give it
room. This is a necessary result of hydrostatic pressure. During this
process the superfluous water would no doubt escape through fissures or
pores of the ice, and would leave the mud and stones in that excessively
compressed and tenacious condition in which the "till" is found. The
unequal thickness and pressure of the ice above referred to would be a
necessary consequence of the inequalities in the valleys, now narrowing
into gorges, now opening out into wide plains, and again narrowed lower
down; and it is just in these openings in the valleys that the "till" is
said to be found, and also in the lowlands where an ice-sheet must have
extended for many miles in every direction. In these lowland valleys the
"till" is both thickest and most wide-spread, and this is what we might
expect. At first, when the glaciers from the mountains pushed out into
these valleys, they would grind out the surface beneath them into hollows,
and the drainage-water would carry away the _débris_. But when they spread
all over the surface from sea to sea, and there was little or no drainage
water compared to the enormous area covered with ice, the great bulk of the
_débris_ must have gathered under the ice wherever the pressure was least,
and the ice would necessarily rise as it accumulated. Some of the mud would
no doubt be forced out along lines of least resistance to the sea, but the
friction of the stone-charged "till" would be so enormous that it would be
impossible for any large part of it to be disposed of in this way.
[36] That the ice-sheet was continuous from Scotland to Ireland is proved
by the glacial phenomena in the Isle of Man, where "till" similar to that
in Scotland abounds, and rocks are found in it which must have come from
Cumberland and Scotland, as well as from the north of Ireland. This would
show that glaciers from each of these districts reached the Isle of Man,
where they met and flowed southwards down the Irish Sea. Ice-marks are
traced over the tops of the mountains which are nearly 2,000 feet high.
(See _A Sketch of the Geology of the Isle of Man_, by John Horne, F.G.S.
_Trans. of the Edin. Geol. Soc._ Vol. II. pt. 3, 1874.)
[37] _The Great Ice Age_, p. 177.
[38] These are named, in descending order, Hessle Boulder Clay, Purple
Boulder Clay, Chalky Boulder Clay, and Lower Boulder Clay--below which is
the Norwich Crag.
[39] "On the Climate of the Post-Glacial Period." _Geological Magazine_,
1872, pp. 158, 160.
[40] _Geological Magazine_, 1876, p. 396.
[41] _Early Man in Britain and his Place in the Tertiary Period_, p. 113.
[42] Heer's _Primæval World of Switzerland_ Vol. II., pp. 148-168.
[43] Dr. James Geikie in _Geological Magazine_, 1878, p. 77.
[44] This subject is admirably discussed in Professor Asa Gray's Lecture on
"Forest Geography and Archæology" in the _American Journal of Science and
Arts_, Vol. XVI. 1878.
[45] In a letter to _Nature_ of October 30th, 1879, the Rev. O. Fisher
calls attention to a result arrived at by Pouillet, that the temperature
which the surface of the ground would assume if the sun were extinguished
would be -128° F. instead of -239° F. If this corrected amount were used in
our calculations, the January temperature of England during the glacial
epoch would come out 17° F., and this Mr. Fisher thinks not low enough to
cause any extreme difference from the present climate. In this opinion,
however, I cannot agree with him. On the contrary, it would, I think, be a
relief to the theory were the amounts of decrease of temperature in winter
and increase in summer rendered more moderate, since according to the usual
calculation (which I have adopted) the differences are unnecessarily great.
I cannot therefore think that this modification of the temperatures, should
it be ultimately proved to be correct (which is altogether denied by Dr.
Croll), would be any serious objection to the adoption of Dr. Croll's
theory of the Astronomical and Physical causes of the Glacial Epoch.
The reason of the theoretical increase of summer heat being greater than
the decrease of winter cold is because we are now nearest the sun in winter
and farthest in summer, whereas we calculate the temperatures of the
glacial epoch for the phase of precession when the _aphelion_ was in
winter. A large part of the increase of temperature would no doubt be used
up in melting ice and evaporating water, so that there would be a much less
increase of sensible heat; while only a portion of the theoretical lowering
of temperature in winter would be actually produced owing to equalising
effect of winds and currents, and the storing up of heat by the earth and
ocean.
[46] Dr. Croll says this "is one of the most widespread and fundamental
errors within the whole range of geological climatology." The temperature
of the snow itself is, he says, one of the main factors. (_Climate and
Cosmology_, p. 85.) But surely the temperature of the snow must depend on
the temperature of the air through which it falls.
[47] In an account of Prof. Nordenskjöld's recent expedition round the
northern coast of Asia, given in _Nature_, November 20th, 1879, we have the
following passage, fully supporting the statement in the text. "Along the
whole coast, from the White Sea to Behring's Straits, no glacier was seen.
During autumn the Siberian coast is nearly free of ice and snow. There are
no mountains covered all the year round with snow, although some of them
rise to a height of more than 2,000 feet." It must be remembered that the
north coast of Eastern Siberia is in the area of supposed greatest winter
cold on the globe.
[48] Dr. Croll objects to this argument on the ground that Greenland and
the Antarctic continent are probably lowlands or groups of islands.
(_Climate and Cosmology_, Chap. V.)
[49] "On the Glacial Epoch," by James Croll. _Geol. Mag._ July, August,
1874.
[50] "The general absence of recent marks of glacial action in Eastern
Europe is well known; and the series of changes which have been so well
traced and described by Prof. Szabó as occurring in those districts seems
to leave no room for those periodical extensions of 'ice-caps' with which
some authors in this country have amused themselves and their readers. Mr.
Campbell, whose ability to recognise the physical evidence of glaciers will
scarcely be questioned, finds quite the same absence of the proof of
extensive ice-action in North America, westward of the meridian of
Chicago." (Prof. J. W. Judd in _Geol. Mag._ 1876, p. 535.)
The same author notes the diminution of marks of ice-action on going
eastward in the Alps; and the Altai Mountains far in Central Asia show no
signs of having been largely glaciated. West of the Rocky Mountains,
however, in the Sierra Nevada and the coast ranges further north, signs of
extensive old glaciers again appear; all which phenomena are strikingly in
accordance with the theory here advocated, of the absolute dependence of
glaciation on abundant rainfall and elevated snow-condensers and
accumulators.
[51] I have somewhat modified this whole passage in the endeavour to
represent more accurately the difference between the views of Dr. Croll and
Sir Charles Lyell.
[52] For numerous details and illustrations see the paper--"On Ocean
Currents in Relation to the Physical Theory of Secular Changes of
Climate"--in the _Philosophical Magazine_, 1870.
[53] See _Darwin's Naturalist's Voyage Round the World_, 2nd Edition, pp.
244-251.
[54] The influence of geographical changes on climate is now held by many
geologists who oppose what they consider the extravagant hypotheses of Dr.
Croll. Thus, Prof. Dana imputes the glacial epoch chiefly, if not wholly,
to elevation of the land caused by the lateral pressure due to shrinking of
the earth's crust that has caused all other elevations and depressions. He
says: "Now, that elevation of the land over the higher latitudes which
brought on the glacial era is a natural result of the same agency, and a
natural, and almost necessary, counterpart of the coral-island subsidence
which must have been then in progress. The accumulating, folding,
solidification, and crystallisation of rocks attending all the rock-making
and mountain-making through the Palæozoic, Mesozoic, and Cenozoic eras, had
greatly stiffened the crust in these parts; and hence in after times, the
continental movements resulting from the lateral pressure necessarily
appeared over the more northern portions of the continent, where the
accumulations and other changes had been relatively small. To the
subsidence which followed the elevation the weight of the ice-cap may have
contributed in some small degree. But the great balancing movements of the
crust of the continental and oceanic areas then going forward must have had
a greatly preponderating effect in the oscillating agency of all
time--lateral pressure within the crust." (_American Journal of Science and
Arts_, 3rd Series, Vol. IX. p. 318.)
"In the 2nd edition of his _Manual of Geology_, Professor Dana suggests
elevation of Arctic lands sufficient to exclude the Gulf Stream, as a
source of cold during glacial epochs. This, he thinks, would have made an
epoch of cold at any era of the globe. A deep submergence of Behring's
Strait, letting in the Pacific warm current to the polar area, would have
produced a mild Arctic climate like that of the Miocene period. When the
warm current was shut out from the polar area it would yet reach near to
it, and bring with it that abundant moisture necessary for glaciation."
(_Manual of Geology_, 2nd Edition, pp. 541-755, 756.)
[55] Dana's _Manual of Geology_, 2nd Edition, p. 540.
[56] Dr. Croll says that I here assume an impossible state of things. He
maintains "that the change from the distant sun in winter, and near sun in
summer to the near sun in winter and distant sun in summer, aided by the
change in the physical causes which this would necessarily bring about,
would certainly be sufficient to cause the snow and ice to disappear."
(_Climate and Cosmology_, p. 106.) But I demur to his "necessarily." It is
not the _direct_ effect of the nearer sun in winter that is supposed to
melt the snow and ice, but the "physical causes," such as absence of fogs
and increase of warm equatorial currents. But the near sun in winter acting
on an ice-clad surface would only increase the fogs and snow, while the
currents could only change if a large portion of the ice were first melted,
in which case they would no doubt be modified so as to cause a further
melting of the ice. Dr. Croll says: "The warm and equable conditions of
climate which would then prevail, and the enormous quantity of
intertropical water carried into the Southern Ocean, would soon produce a
melting of the ice." (_Loc. cit._ p. 111.) This seems to me to be assuming
the very point at issue. He has himself shown that the presence of large
quantities of ice prevents "a warm and equable climate" however great may
be the sun-heat; the ice therefore would _not_ be melted, and there would
be no increased flow of intertropical water to the Southern Ocean. The
ocean currents are mainly due to the difference of temperature of the polar
and equatorial areas combined with the peculiar form and position of the
continents, and some one or more of these factors must be altered _before_
the ocean currents towards the north pole can be increased. The only factor
available is the Antarctic ice, and if this were largely increased, the
northward-flowing currents might be so increased as to melt some of the
Arctic ice. But the very same argument applies to both poles. Without some
geographical change the Antarctic ice could not materially diminish during
its winter in _perihelion_, nor increase to any important extent during the
opposite phase. We therefore seem to have no available agency by which to
get rid of the ice over a glaciated hemisphere, _so long as the
geographical conditions remained unchanged and the excentricity continued
high_.
[57] In the _Geological Magazine_, April, 1880, Mr. Searles V. Wood adduces
what he considers to be the "conclusive objection" to Dr. Croll's
excentricity theory, which is, that during the last glacial epoch Europe
and North America were glaciated very much in proportion to their
respective climates now, which are generally admitted to be due to the
distribution of oceanic currents. But Dr. Croll admits his theory "to be
baseless unless there was a complete diversion of the warm ocean currents
from the hemisphere glaciated," in which case there ought to be no
difference in the extent of glaciation in Europe and North America. Whether
or not this is a correct statement of Dr. Croll's theory, the above
objection certainly does not apply to the views here advocated; but as I
also hold the "excentricity theory" in a modified form, it may be as well
to show why it does not apply. In the first place I do not believe that the
Gulf Stream was "completely diverted" during the glacial epoch, but that it
was diminished in force, and (as described at p. 144) _partly_ diverted
southward. A portion of its influence would, however, still remain to cause
a difference between the climates of the two sides of the Atlantic; and to
this must be added two other causes--the far greater penetration of warm
sea-water into the European than into the North American continent, and the
proximity to America of the enormous ice-producing mass of Greenland. We
have thus three distinct causes, all combining to produce a more severe
winter climate on the west than on the east of the Atlantic during the
glacial epoch, and though the first of these--the Gulf Stream--was not
nearly so powerful as it is now, neither is the difference indicated by the
ice-extension in the two countries so great as the present difference of
winter-temperature, which is the essential point to be considered. The
ice-sheet of the United States is usually supposed to have extended about
ten, or, at most, twelve, degrees further south than it did in Western
Europe, whereas we must go twenty degrees further south in the former
country to obtain the same mean winter-temperature we find in the latter,
as may be seen by examining any map of winter isothermals. This difference
very fairly corresponds to the difference of conditions existing during the
glacial epoch and the present time, so far as we are able to estimate them,
and it certainly affords no grounds of objection to the theory by which the
glaciation is here explained.
[58] Dr. Croll objects to this argument, and adduces the case of Greenland
as showing that ice may accumulate far from sea. But the width of Greenland
is small compared with that of the supposed Antarctic ice-cap. (_Climate
and Cosmology_, p. 78.)
[59] The recent extensive glaciation of New Zealand is generally imputed by
the local geologists to a greater elevation of the land; but I cannot help
believing that the high phase of excentricity which caused our own glacial
epoch was at all events an assisting cause. This is rendered more probable
if taken in connection with the following very definite statement of
glacial markings in South Africa. Captain Aylward in his _Transvaal of
To-day_ (p. 171) says:--"It will be interesting to geologists and others to
learn that the entire country, from the summits of the Quathlamba to the
junction of the Vaal and Orange rivers, shows marks of having been swept
over, and that at no very distant period, by vast masses of ice from east
to west. The striations are plainly visible, scarring the older rocks, and
marking the hill-sides--getting lower and lower and less visible as,
descending from the mountains, the kopjies (small hills) stand wider apart;
but wherever the hills narrow towards each other, again showing how the
vast ice-fields were checked, thrown up, and raised against their Eastern
extremities."
This passage is evidently written by a person familiar with the phenomena
of glaciation, and as Captain Aylward's preface is dated from Edinburgh, he
has probably seen similar markings in Scotland. The country described
consists of the most extensive and lofty plateau in South Africa, rising to
a mountain knot with peaks more than 10,000 feet high, thus offering an
appropriate area for the condensation of vapour and the accumulation of
snow. At present, however, the mountains do not reach the snow-line, and
there is no proof that they have been much higher in recent times, since
the coast of Natal is now said to be rising. It is evident that no slight
elevation would now lead to the accumulation of snow and ice in these
mountains, situated as they are between 27° and 30° S. Lat.; since the
Andes, which in 32° S. Lat. reach 23,300 feet high, and in 28° S. Lat.
20,000, with far more extensive plateaus, produce no ice-fields. We cannot,
therefore, believe that a few thousand feet of additional elevation, even
if it occurred so recently as indicated by the presence of striations,
would have produced the remarkable amount of glaciation above described;
while from the analogy of the northern hemisphere, we may well believe that
it was mainly due to the same high excentricity that led to the glaciation
of Western and Central Europe, and Eastern North America.
These observations confirm those of Mr. G. W. Stow, who, in a paper
published in the _Quarterly Journal of the Geological Society_ (Vol. XXVII.
p. 539), describes similar phenomena in the same mountains, and also mounds
and ridges of unstratified clay packed with angular boulders; while further
south the Stormberg mountains are said to be similarly glaciated, with
immense accumulations of morainic matter in all the valleys. We have here
most of the surface phenomena characteristic of a glaciated country, only a
few degrees south of the tropic; and taken in connection with the
indications of recent glaciation in New Zealand, and those discovered by
Dr. R. von Lendenfeld in the Australian Alps between 6,000 and 7,000 feet
elevation (_Nature_, Vol. XXXII. p. 69), we can hardly doubt the occurrence
of some general and wide-spread cause of glaciation in the southern
hemisphere at a period so recent that the superficial phenomena are almost
as well preserved as in Europe. Other geologists however deny that there
are any distinct indications of glacial action in South Africa; but the
recent discovery by Dr. J. W. Gregory, F.G.S., of the former extension of
glaciers on Mount Kenya 5,000 feet below their present limits, renders
probable the former glaciation of the South African Highlands.
[60] The astronomical facts connected with the motions and appearance of
the planet are taken from a paper by Mr. Edward Carpenter, M.A., in the
_Geological Magazine_ of March, 1877, entitled, "Evidence Afforded by Mars
on the Subject of Glacial Periods," but I arrive at somewhat different
conclusions from those of the writer of the paper.
[61] In an article in _Nature_ of Jan. 1, 1880, the Rev. T. W. Webb states
that in 1877 the pole of Mars (? the south pole) was, according to
Schiaparelli, entirely free of snow. He remarks also on the regular contour
of the supposed snows of Mars as offering a great contrast to ours, and
also the strongly marked dark border which has often been observed. On the
whole Mr. Webb seems to be of opinion that there can be no really close
resemblance between the physical condition of the Earth and Mars, and that
any arguments founded on such supposed similarity are therefore
untrustworthy.
[62] _London, Edinburgh and Dublin Philosophical Magazine_, Vol. XXXVI.,
pp. 144-150 (1868).
[63] _Climate and Time in their Geological Relations_, p. 341.
[64] _Nature_, Vol. XXI., p. 345, "The Interior of Greenland."
[65] Prof. J. W. Judd says: "In the case of the Alps I know of no glacial
phenomena which are not capable of being explained, like those of New
Zealand, by a great extension of the area of the tracts above the snow-line
which would collect more ample supplies for the glaciers protruded into
surrounding plains. And when we survey the grand panoramas of ridges,
pinnacles, and peaks produced for the most part by sub-aërial action, we
may well be prepared to admit that before the intervening ravines and
valleys were excavated, the glaciers shed from the elevated plateaux must
have been of vastly greater magnitude than at present." (Contributions to
the Study of Volcanoes, _Geological Magazine_, 1876, p. 536.) Professor
Judd applies these remarks to the last as well as to previous glacial
periods in the Alps; but surely there has been no such extensive alteration
and lowering of the surface of the country since the erratic blocks were
deposited on the Jura and the great moraines formed in North Italy, as this
theory would imply. We can hardly suppose wide areas to have been lowered
thousands of feet by denudation, and yet have left other adjacent areas
apparently untouched; and it is even very doubtful whether such an
extension of the snow-fields would alone suffice for the effects which were
certainly produced.
[66] _Geological Magazine_, 1876, p. 392.
[67] Colonel Fielden thinks that these trees have all been brought down by
rivers, and have been stranded on shores which have been recently elevated.
See _Trans. of Norfolk Nat. Hist. Soc., Vol. III._, 1880.
[68] _Geological Magazine_, 1876, "Geology of Spitzbergen," p. 267.
[69] The preceding account is mostly derived from Professor Heer's great
work _Flora Fossilis Arctica_.
[70] _Geological Magazine_, 1875, p. 531.
[71] _Geological Magazine_, 1876, p. 266. In his recent work--_Climate and
Cosmology_ (pp. 164, 172)--the late Dr. Croll has appealed to the
imperfection of the geological record as a reply to these arguments; in
this case, as it appears to me, a very unsuccessful one.
[72] It is interesting to observe that the Cretaceous flora of the United
States (that of the Dakota group), indicates a somewhat cooler climate than
that of the following Eocene period. Mr. De Rance (in the geological
appendix to Capt. Sir G. Nares's _Narrative of a Voyage to the Polar Sea_)
remarks as follows: "In the overlying American Eocenes occur types of
plants occurring in the European Miocenes and still living, proving the
truth of Professor Lesquereux's postulate, that the plant types appear in
America a stage in advance of their advent in Europe. These plants point to
a far higher mean temperature than those of the Dakota group, to a dense
atmosphere of vapour, and a luxuriance of ferns and palms." This is very
important as adding further proof to the view that the climates of former
periods are not due to any general refrigeration, but to causes which were
subject to change and alternation in former ages as now.
[73] Mr. S. B. J. Skertchley informs me that he has himself observed thick
Tertiary deposits, consisting of clays and anhydrous gypsum, at Berenice on
the borders of Egypt and Nubia, at a height of about 600 feet above the
sea-level; but these may have been of fresh-water origin.
[74] By referring to our map of the Indian Ocean showing the submarine
banks indicating ancient islands (Chap. XIX.), it will be evident that the
south-east trade-winds--then exceptionally powerful--would cause a vast
body of water to enter the deep Arabian Sea.
[75] In his recently published _Lectures on Physical Geography_, Professor
Haughton calculates, that more than half the solar heat of the torrid zone
is carried to the temperate zones by ocean currents. The Gulf Stream itself
carries one-twelfth of the total amount, but it is probable that a very
small fraction of this quantity of heat reaches the polar seas owing to the
wide area over which the current spreads in the North Atlantic. The
corresponding stream of the Indian Ocean in Miocene times would have been
fully equal to the Gulf Stream in heating power, while, owing to its being
so much more concentrated, a large proportion of its heat may have reached
the polar area. But the Arctic Ocean occupies less than one-tenth of the
area of the tropical seas; so that, whatever proportion of the heat of the
tropical zone was conveyed to it, would, by being concentrated into
one-tenth of the surface, produce an enormously increased effect. Taking
this into consideration, we can hardly doubt that the opening of a
sufficient passage from the Indian Ocean to the Arctic seas would produce
the effects above indicated.
[76] For an account of the resemblances and differences of the mammalia of
the two continents during the Tertiary epoch, see my _Geographical
Distribution of Animals_, Vol. I. pp. 140-156.
[77] Professor Haughton has made an elaborate calculation of the difference
between existing climates and those of Miocene times, for all the places
where a Miocene flora has been discovered, by means of the actual range of
corresponding species and genera of plants. Although this method is open to
the objection that the ranges of plants and animals are not determined by
temperature only, yet the results may be approximately correct, and are
very interesting. The following table which summarizes these results is
taken from his Lectures on Physical Geography (p. 344):--
_______________________________________________________________________
| | | Present | Miocene | |
| |Latitude.|Temperature.|Temperature.|Difference.|
|_____________________|_________|____________|____________|___________|
| 1. Switzerland | 47d.00 | 53d.6 F | 69d.8 F | 16d.2 F |
| 2. Dantzig | 54d.21 | 45d.7 ,, | 62d.6 ,, | 16d.9 ,, |
| 3. Iceland | 65d.30 | 35d.6 ,, | 48d.2 ,, | 12d.6 ,, |
| 4. Mackenzie River | 65d.00 | 19d.4 ,, | 48d.2 ,, | 28d.8 ,, |
| 5. Disco (Greenland)| 70d.00 | 19d.6 ,, | 55d.6 ,, | 36d.0 ,, |
| 6. Spitzbergen | 78d.00 | 16d.5 ,, | 51d.8 ,, | 35d.3 ,, |
| 7. Grinnell Land | 81d.44 | 1d.7 ,, | 42d.3 ,, | 44d.0 ,, |
|_____________________|_________|____________|____________|___________|
It is interesting to note that Iceland, which is now exposed to the full
influence of the Gulf Stream, was only 12°.6 F. warmer in Miocene times,
while Mackenzie River, now totally removed from its influence was 28°
warmer. This, as well as, the greater increase of temperature as we go
northward and the polar area becomes more limited, is quite in accordance
with the view of the causes which brought about the Miocene climate which
is here advocated.
[78] The objection has been made, that the long polar night would of itself
be fatal to the existence of such a luxuriant vegetation as we know to have
existed as far as 80° N. Lat., and that there must have been some
alteration of the position of the pole, or diminution of the obliquity of
the ecliptic, to permit such plants as magnolias and large-leaved maples to
flourish. But there appears to be really no valid grounds for such an
objection. Not only are numbers of Alpine and Arctic evergreens deeply
buried in the snow for many months without injury, but a variety of
tropical and sub-tropical plants are preserved in the hot-houses of St.
Petersburg and other northern cities, which are closely matted during
winter, and are thus exposed to as much darkness as the night of the Arctic
regions. We have besides no proof that any of the Arctic trees or large
shrubs were evergreens, and the darkness would certainly not be prejudical
to deciduous plants. With a suitable temperature there is nothing to
prevent a luxuriant vegetation up to the pole, and the long continued day
is known to be highly favourable to the development of foliage, which in
the same species is larger and better developed in Norway than in the south
of England.
[79] _Geological Magazine_, 1873, p. 320.
[80] _Geological Magazine_, 1877, p. 137.
[81] _Manual of Geology_, 2nd Ed. p. 525. See also letter in _Nature_, Vol.
XXIII. p. 410.
[82] _Nature_, Vol. XVIII. (July, 1878), p. 268.
[83] "On the Comparative Value of certain Geological Ages considered as
items of Geological Time." (_Proceedings of the Royal Society_, 1874, p.
334.)
[84] _Trans. Royal Society of Edinburgh_, Vol. XXIII. p. 161. _Quarterly
Journal of Science_, 1877. (Croll on the "Probable Origin and Age of the
Sun.")
[85] _Philosophical Magazine_, April, 1853.
[86] It has usually been the practice to take the amount of denudation in
the Mississippi valley, or one foot in six thousand years, as a measure of
the rate of denudation in Europe, from an idea apparently of being on the
"safe side," and of not over-estimating the rate of change. But this
appears to me a most unphilosophical mode of proceeding and unworthy of
scientific inquiry. What should we think of astronomers if they always took
the lowest estimates of planetary or stellar distances, instead of the mean
results of observation, "in order to be on the safe side!"? As if error in
one direction were any worse than error in another. Yet this is what
geologists do systematically. Whenever any calculations are made involving
the antiquity of man, it is those that give the _lowest_ results that are
always taken, for no reason apparently except that there was, for so long a
time, a prejudice, both popular and scientific, against the great antiquity
of man; and now that a means has been found of measuring the rate of
denudation, they take the slowest rate instead of the mean rate, apparently
only because there is now a scientific prejudice in favour of extremely
slow geological change. I take the mean of the whole; and as this is almost
exactly the same as the mean of the three great European rivers--the Rhone,
Danube, and Po--I cannot believe that this will not be nearer the truth for
Europe than taking one North American river as the standard.
[87] "On the Height of the Land and the Depth of the Ocean," in the
_Scottish Geographical Magazine_, 1888.
[88] These figures are merely used to give an idea of the rate at which
denudation is actually going on now; but if no elevatory forces were at
work, the rate of denudation would certainly diminish as the mountains were
lowered and the slope of the ground everywhere rendered flatter. This would
follow not only from the diminished power of rain and rivers, but because
the climate would become more uniform, the rainfall probably less, and no
rocky peaks would be left to be fractured and broken up by the action of
frosts. It is certain, however, that no continent has ever remained long
subject to the influences of denudation alone, for, as we have seen in our
sixth chapter, elevation and depression have always been going on in one
part or other of the surface.
[89] The following statement of the depths at which the Palæozoic
formations have been reached in various localities in and round London was
given by Mr. H. B. Woodward in his address to the Norwich Geological
Society in 1879:--
_Deep Wells through the Tertiary and Cretaceous Formations._
Harwich at 1,022 feet reached Carboniferous Rock.
Kentish Town ,, 1,114 ,, ,, Old Red Sandstone.
Tottenham Court Road ,, 1,064 ,, ,, Devonian.
Blackwall ,, 1,004 ,, ,, Devonian or Old Red Sandstone.
Ware ,, 800 ,, ,, Silurian (Wenlock Shale).
We thus find that over a wide area, extending from London to Ware and
Harwich, the whole of the formations from the Oolite to the Permian are
wanting, the Cretaceous resting on the Carboniferous or older Palæozoic
rocks; and the same deficiency extends across to Belgium, where the
Tertiary beds are found resting on Carboniferous at a depth of less than
400 feet.
[90] _Geological Magazine_, Vol. VIII., March, 1871.
[91] Mr. C. Lloyd Morgan has well illustrated this point by comparing the
generally tilted-up strata denuded on their edges, to a library in which a
fire had acted on the exposed edges of the books, destroying a great mass
of literature but leaving a portion of each book in its place, which
portion represents the thickness but not the size of the book. (_Geological
Magazine_, 1878, p. 161.)
[92] Professor J. Young thinks it highly probable that--"the Lower
Greensand is contemporaneous with part of the Chalk, so were parts of the
Wealden; nay, even of the Purbeck a portion must have been forming while
the Cretaceous sea was gradually deepening southward and westward." Yet
these deposits are always arranged successively, and their several
thicknesses added together to obtain the total thickness of the formations
of the country. (See Presidential Address, Sect. C. British Association,
1876.)
[93] Mr. John Murray in his more careful estimate makes it about 51½
millions.
[94] As by far the larger portion of the denuded matter of the globe passes
to the sea through comparatively few great rivers, the deposits must often
be confined to very limited areas. Thus the denudation of the vast
Mississippi basin must be almost all deposited in a limited portion of the
Gulf of Mexico, that of the Nile within a small area of the Eastern
Mediterranean, and that of the great rivers of China--the Hoang Ho and
Yang-tse-kiang, in a small portion of the Eastern Sea. Enormous lengths of
coast, like those of Western America and Eastern Africa, receive very
scanty deposits; so that thirty miles in width along the whole of the
coasts of the globe will probably give an area greater than that of the
area of _average_ deposit, and certainly greater than that of _maximum_
deposit, which is the basis on which I have here made my estimates. In the
case of the Mississippi, it is stated by Count Pourtales that along the
plateau between the mouth of the river and the southern extremity of
Florida for two hundred and fifty miles in width the bottom consists of
clay with some sand and but few Rhizopods; but beyond this distance the
soundings brought up either Rhizopod shells alone, or these mixed with
coral sand, Nullipores, and other calcareous organisms (Dana's _Manual of
Geology_, 2nd Ed. p. 671). It is probable, therefore, that a large
proportion of the entire mass of sediment brought down by the Mississippi
is deposited on the limited area above indicated.
Professor Dana further remarks: "Over interior oceanic basins as well as
off a coast in quiet depths, fifteen or twenty fathoms and beyond, the
deposits are mostly of fine silt, fitted for making fine argillaceous
rocks, as shales or slates. When, however, the depth of the ocean falls off
below a hundred fathoms, the deposition of silt in our existing oceans
mostly ceases, unless in the case of a great bank along the border of a
continent."
[95] From the same data Professor Haughton estimates a minimum of 200
million years for the duration of geological time; but he arrives at this
conclusion by supposing the products of denudation to be uniformly spread
over the _whole sea-bottom_ instead of over a narrow belt near the coasts,
a supposition entirely opposed to all the known facts, and which had been
shown by Dr. Croll, five years previously, to be altogether erroneous. (See
_Nature_, Vol. XVIII., p. 268, where Professor Haughton's paper is given as
read before the Royal Society.)
[96] See _Geological Magazine_ for 1877, p. 1.
[97] In his reply to Sir W. Thomson, Professor Huxley _assumed_ one foot in
a thousand years as a not improbable rate of deposition. The above estimate
indicates a far higher rate; and this follows from the well-ascertained
fact, that the area of deposition is many times smaller than the area of
denudation.
[98] Dr. Croll and Sir Archibald Geikie have shown that marine denudation
is very small in amount as compared with sub-aërial, since it acts only
locally on the _edge_ of the land, whereas the latter acts over every foot
of the _surface_. Mr. W. T. Blanford argues that the difference is still
greater in tropical than in temperate latitudes, and arrives at the
conclusion that--"If over British India the effects of marine to those of
fresh-water denudation in removing the rocks of the country be estimated at
1 to 100, I believe that the result of marine action will be greatly
overstated" (_Geology and Zoology of Abyssinia_, p. 158, note). Now, as our
estimate of the rate of sub-aërial denudation cannot pretend to any precise
accuracy, we are justified in neglecting marine denudation altogether,
especially as we have no method of estimating it for the whole earth with
any approach to correctness.
[99] Agassiz appears to have been the first to suggest that the principal
epochs of life extermination were epochs of cold; and Dana thinks that two
at least such epochs may be recognised, at the close of the Palæozoic and
of the Cretaceous periods--to which we may add the last glacial epoch.
[100] This view was, I believe, first put forth by myself in a paper read
before the Geological Section of the British Association in 1869, and
subsequently in an article in _Nature_, Vol. I. p. 454. It was also stated
by Mr. S. B. J. Skertchley in his _Physical System of the Universe_, p. 363
(1878); but we both founded it on what I now consider the erroneous
doctrine that actual glacial epochs recurred each 10,500 years during
periods of high excentricity.
[101] Explication d'une seconde édition de la _Carte Géologique de la
Terre_ (1875), p. 64.
[102] For most of the facts as to the zoology and botany of these islands,
I am indebted to Mr. Godman's valuable work--_Natural History of the Azores
or Western Islands_, by Frederick Du Cane Godman, F.L.S., F.Z.S., &c.,
London, 1870.
[103] See Chap. V. p. 78.
[104] Some of Mr. Darwin's experiments are very interesting and suggestive.
Ripe hazel-nuts sank immediately, but when dried they floated for ninety
days, and afterwards germinated. An asparagus-plant with ripe berries, when
dried, floated for eighty-five days, and the seeds afterwards germinated.
Out of ninety-four dried plants experimented with, eighteen floated for
more than a month, and some for three months, and their powers of
germination seem never to have been wholly destroyed. Now, as oceanic
currents vary from thirty to sixty miles a day, such plants under the most
favourable conditions might be carried 90 X 60 = 5,400 miles! But even half
of this is ample to enable them to reach any oceanic island, and we must
remember that till completely water-logged they might be driven along at a
much greater rate by the wind. Mr. Darwin calculates the distance by the
average time of flotation to be 924 miles; but in such a case as this we
are entitled to take the extreme cases, because such countless thousands of
plants and seeds must be carried out to sea annually that the extreme cases
in a single experiment with only ninety-four plants, must happen hundreds
or thousands of times and with hundreds or thousands of species, naturally,
and thus afford ample opportunities for successful migration. (See _Origin
of Species_, 6th Edition, p. 325.)
[105] The following remarks, kindly communicated to me by Mr. H. N.
Moseley, naturalist to the _Challenger_, throw much light on the agency of
birds in the distribution of plants:--"Grisebach (_Veg. der Erde_, Vol. II.
p. 496) lays much stress on the wide ranging of the albatross (Diomedea)
across the equator from Cape Horn to the Kurile Islands, and thinks that
the presence of the same plants in Arctic and Antarctic regions may be
accounted for, possibly, by this fact. I was much struck at Marion Island
of the Prince Edward group, by observing that the great albatross breeds in
the midst of a dense, low herbage, and constructs its nest of a mound of
turf and herbage. Some of the indigenous plants, _e.g._ Acæna, have
flower-heads which stick like burrs to feathers, &c., and seem specially
adapted for transposition by birds. Besides the albatrosses, various
species of Procellaria and Puffinus, birds which range over immense
distances may, I think, have played a great part in the distribution of
plants, and especially account, in some measure, for the otherwise
difficult fact (when occurring in the tropics), that widely distant islands
have similar mountain plants. The Procellaria and Puffinus in nesting,
burrow in the ground, as far as I have seen choosing often places where the
vegetation is the thickest. The birds in burrowing get their feathers
covered with vegetable mould, which must include spores, and often seeds.
In high latitudes the birds often burrow near the sea-level, as at Tristan
d'Acunha or Kerguelen's Land, but in the tropics they choose the mountains
for their nesting-place (Finsch and Hartlaub, _Orn. der Viti- und
Tonga-Inseln_, 1867, Einleitung, p. xviii.). Thus, _Puffinus megasi_ nests
at the top of the Korobasa basaga mountain, Viti Levu, fifty miles from the
sea. A Procellaria breeds in like manner in the high mountains of Jamaica,
I believe at 7,000 feet. Peale describes the same habit of _Procellaria
rostrata_ at Tahiti, and I saw the burrows myself amidst a dense growth of
fern, &c., at 4,400 feet elevation in that island. Phaethon has a similar
habit. It nests at the crater of Kilauea, Hawaii, at 4,000 feet elevation,
and also high up in Tahiti. In order to account for the transportation of
the plants, it is not of course necessary that the same species of
Procellaria or Diomedea should now range between the distant points where
the plants occur. The ancestor of the now differing species might have
carried the seeds. The range of the genus is sufficient."
[106] _Nature_, Vol. VI. p. 262, "Recent Observations in the Bermudas," by
Mr. J. Matthew Jones.
[107] "The late Sir C. Wyville Thomson was of opinion that the 'red earth'
which largely forms the soil of Bermuda had an organic origin, as well as
the 'red clay' which the _Challenger_ discovered in all the greater depths
of the ocean basins. He regarded the red earth and red clay as an ash left
behind after the gradual removal of the lime by water charged with carbonic
acid. This ash he regarded as a constituent part of the shells of
Foraminifera, skeletons of Corals, and Molluscs, [_vide_ _Voyage of the
Challenger_, Atlantic, Vol. I. p. 316]. This theory does not seem to be in
any way tenable. Analysis of carefully selected shells of Foraminifera,
Heteropods, and Pteropods, did not show the slightest trace of alumina, and
none has as yet been discovered in coral skeletons. It is most probable
that a large part of the clayey matter found in red clay and the red earth
of Bermuda is derived from the disintegration of pumice, which is
continually found floating on the surface of the sea. [See Murray, "On the
Distribution of Volcanic Débris Over the Floor of the Ocean;" _Proc. Roy.
Soc. Edin._ Vol. IX. pp. 247-261. 1876-1877.] The naturalists of the
_Challenger_ found it among the floating masses of gulf weed, and it is
frequently picked up on the reefs of Bermuda and other coral islands. The
red earth contains a good many fragments of magnetite, augite, felspar, and
glassy fragments, and when a large quantity of the rock of Bermuda is
dissolved away with acid, a small number of fragments are also met with.
These mineral particles most probably came originally from the pumice which
had been cast up on the island for long ages (for it is known that these
minerals are present in pumice), although possibly some of them may have
come from the volcanic rock, which is believed to form the nucleus of the
island." _The Voyage of H.M.S. Challenger_, Narrative of the Cruise, Vol.
I. 1885, pp. 141-142.
[108] Four bats occur rarely, two being N. American, and two West Indian
Species. _The Bermuda Islands_, by Angelo Heilprin, Philadelphia, 1889.
[109] Fourteen species of Spiders were collected by Prof. A. Heilprin, all
American or cosmopolitan species except one, _Lycosa atlantica_, which Dr.
Marx of Washington describes as new and as peculiar to the islands.
(Heilprin's _The Bermudas_, p. 93.)
[110] Mr. Theo. D. A. Cockerell informs me that there are two slugs in
Bermuda of which specimens exist in the British Museum,--_Amalia gagates_
Drap. common in Europe, and _Agriolimax campestris_ of the United States.
Both may therefore have been introduced by human agency. Also _Vaginulus
Morelete var. schivelyæ_ which seems to be a variety of a Mexican species;
perhaps imported.
[111] "Notes on the Vegetation of Bermuda," by H. N. Moseley. (_Journal of
the Linnean Society_, Vol. XIV., _Botany_, p. 317.)
[112] _Gigantic Land Tortoises Living and Extinct in the Collection of the
British Museum._ By A. C. L. G. Günther, F.R.S. 1877.
[113] The following list of the beetles yet known from the Galapagos shows
their scanty proportions and accidental character; the forty species
belonging to thirty-three genera and eighteen families. It is taken from
Mr. Waterhouse's enumeration in the _Proceedings of the Zoological Society_
for 1877 (p. 81), with a few additions collected by the U. S. Fish
Commission Steamer _Albatross_, and published by the U. S. National Museum
in 1889.
CARABIDÆ. ELATERIDÆ.
Feronia calathoides. Physorhinus galapagoensis
,, insularis. HETEROMERA.
,, galapagoensis. Allecula n. s.
Amblygnathus obscuricornis. Stomion helopoides.
Solenophorus galapagoensis. ,, lævigatum.
Notaphus galapagoensis. Ammophorus obscurus.
DYTISCIDÆ. ,, cooksoni.
Eunectes occidentalis. ,, bifoveatus.
Acilius incisus. Pedonoeces galapagoensis.
Copelatus galapagoensis. ,, pubescens.
PALPICORNES. Phaleria manicata.
Tropisternus lateralis. CURCULIONIDÆ.
Philhydrus sp. Otiorhynchus cuneiformis.
STAPHYLINIDÆ. Anchonus galapagoensis.
Creophilus villosus. LONGICORNIA.
NECROPHAGA. Mallodou sp.
Acribis serrativentris. Eburia amabilis.
Phalacrus darwinii. ANTHRIBIDÆ.
Dermestes vulpinus. Ormiscus variegatus.
MALACODERMS. PHYTOPHAGA
Ablechrus darwinii. Diabrotica limbata.
Corynetes rufipes. Docema galapagoensis.
Bostrichus unciniatus. Longitarsus lunatus.
Tetrapriocerca sp. SECURIPALPES.
LAMELLICORNES. Scymuns galapagoensis.
Copris lugubris.
Oryctes galapagoensis.
[114] Mr. H. O. Forbes, who visited these islands in 1878, increased the
number of wild plants to thirty-six, and these belonged to twenty-six
natural orders.
[115] Juan Fernandez is a good example of a small island which, with time
and favourable conditions, has acquired a tolerably rich and highly
peculiar flora and fauna. It is situated in 34° S. Lat., 400 miles from the
coast of Chile, and so far as facilities for the transport of living
organisms are concerned is by no means in a favourable position, for the
ocean-currents come from the south-west in a direction where there is no
land but the Antarctic continent, and the prevalent winds are also
westerly. No doubt, however, there are occasional storms, and there may
have been intermediate islands, but its chief advantages are its antiquity,
its varied surface, and its favourable soil and climate, offering many
chances for the preservation and increase of whatever plants and animals
have chanced to reach it. The island consists of basalt, greenstone, and
other ancient rocks, and though only about twelve miles long its mountains
are three thousand feet high. Enjoying a moist and temperate climate it is
especially adapted to the growth of ferns, which are very abundant; and as
the spores of these plants are as fine as dust, and very easily carried for
enormous distances by winds, it is not surprising that there are nearly
fifty species on the island, while the remote period when it first received
its vegetation may be indicated by the fact that nearly half the species
are quite peculiar; while of 102 species of flowering plants seventy are
peculiar, and there are ten peculiar genera. The same general character
pervades the fauna. For so small an island it is rich, containing four true
land-birds, about fifty species of insects, and twenty of land-shells.
Almost all these belong to South American genera, and a large proportion
are South American species; but several of the insects, half the birds, and
the whole of the land-shells are peculiar. This seems to indicate that the
means of transmission were formerly greater than they are now, and that in
the case of land-shells none have been introduced for so long a period that
all have become modified into distinct forms, or have been preserved on the
island while they have become extinct on the continent. For a detailed
examination of the causes which have led to the modification of the humming
birds of Juan Fernandez see the chapter on Humming Birds in the author's
_Natural Selection and Tropical Nature_, p. 324; while a general account of
the fauna of the island is given in his _Geographical Distribution of
Animals_, Vol. II. p. 49.
[116] No additions appear to have been made to this flora down to 1885,
when Mr. Hemsley published his _Report on the Present State of our
Knowledge of Insular Floras_.
[117] _Journal of the Linnean Society_, Vol. XIII., "Botany," p. 556.
[118] _Geographical Distribution of Animals_, Vol. II. p. 81.
[119] _St. Helena: a Physical, Historical, and Topographical Description of
the Island, &c._ By John Charles Melliss, F.G.S., &c. London: 1875.
[120] Mr. Marsh in his interesting work entitled _The Earth as Modified by
Human Action_ (p. 51), thus remarks on the effect of browsing quadrupeds in
destroying and checking woody vegetation.--"I am convinced that forests
would soon cover many parts of the Arabian and African deserts if man and
domestic animals, especially the goat and the camel, were banished from
them. The hard palate and tongue, and strong teeth and jaws of this latter
quadruped enable him to break off and masticate tough and thorny branches
as large as the finger. He is particularly fond of the smaller twigs,
leaves, and seed-pods of the _Sont_ and other acacias, which, like the
American robinia, thrive well on dry and sandy soils, and he spares no tree
the branches of which are within his reach, except, if I remember right,
the tamarisk that produces manna. Young trees sprout plentifully around the
springs and along the winter water-courses of the desert, and these are
just the halting stations of the caravans and their routes of travel. In
the shade of these trees annual grasses and perennial shrubs shoot up, but
are mown down by the hungry cattle of the Bedouin as fast as they grow. A
few years of undisturbed vegetation would suffice to cover such points with
groves, and these would gradually extend themselves over soils where now
scarcely any green thing but the bitter colocynth and the poisonous
foxglove is ever seen."
[121] _Coleoptera Sanctæ Helenæ_, 1877; _Testacea Atlantica_, 1878.
[122] On Petermann's map of Africa, in _Stieler's Hand-Atlas_ (1879), the
Island of Ascension is shown as seated on a much larger and shallower
submarine bank than St. Helena. The 1,000 fathom line round Ascension
encloses an oval space 170 miles long by 70 wide, and even the 300 fathom
line, one over 60 miles long; and it is therefore probable that a much
larger island once occupied this site. Now Ascension is nearly equidistant
between St. Helena and Liberia, and such an island might have served as an
intermediate station through which many of the immigrants to St. Helena
passed. As the distances are hardly greater than in the case of the Azores,
this removes whatever difficulty may have been felt of the possibility of
_any_ organisms reaching so remote an island. The present island of
Ascension is probably only the summit of a huge volcanic mass, and any
remnant of the original fauna and flora it might have preserved may have
been destroyed by great volcanic eruptions. Mr. Darwin collected some
masses of tufa which were found to be mainly organic, containing, besides
remains of fresh-water infusoria, the siliceous tissue of plants! In the
light of the great extent of the submarine bank on which the island stands,
Mr. Darwin's remark, that--"we may feel sure, that at some former epoch,
the climate and productions of Ascension were very different from what they
are now,"--has received a striking confirmation. (See _Naturalist's Voyage
Round the World_, p. 495.)
[123] "Notes on the Classification, History, and Geographical Distribution
of Compositæ."--_Journal of the Linnean Society_, Vol. XIII. p. 563 (1873).
[124] The Melhaniæ comprise the two finest timber trees of St. Helena, now
almost extinct, the redwood and native ebony.
[125] _Journal of the Linnean Society_, 1873, p. 496. "On Diversity of
Evolution under one set of External Conditions." _Proceedings of the
Zoological Society of London_, 1873, p. 80. "On the Classification of the
Achitinellidæ."
[126] "Memoirs on the Coleoptera of the Hawaiian Islands." By the Rev. T.
Blackburn, B.A., and Dr. D. Sharp. _Scientific Transactions of the Royal
Dublin Society._ Vol. III. Series II. 1885.
[127] See Hildebrand's _Flora of the Hawaiian Islands_, Introduction, p.
xiv.
[128] _Flora of the Hawaiian Islands_, by W. Hildebrand, M.D., annotated
and published after the author's death by W. F. Hildebrand, 1888.
[129] These are obtained from Hildebrand's _Flora_ supplemented by Mr.
Bentham's paper in the _Journal of the Linnean Society_.
[130] Among the curious features of the Hawaiian flora is the extraordinary
development of what are usually herbaceous plants into shrubs or trees.
Three species of Viola are shrubs from three to five feet high. A shrubby
Silene is nearly as tall; and an allied endemic genus, Schiedea, has
numerous shrubby species. _Geranium arboreum_ is sometimes twelve feet
high. The endemic Compositæ are mostly shrubs, while several are trees
reaching twenty or thirty feet in height. The numerous Lobeliaceæ, all
endemic, are mostly shrubs or trees, often resembling palms or yuccas in
habit, and sometimes twenty-five or thirty feet high. The only native genus
of Primulaceæ--Lysimachia--consists mainly of shrubs; and even a plantain
has a woody stem sometimes six feet high.
[131] _Geological Magazine_, 1870, p. 155.
[132] _Transactions of the Edinburgh Geological Society_, Vol. I. p. 330.
[133] _Quarterly Journal of Geological Society_, 1850, p. 96.
[134] _British Association Report_, Dundee, 1867, p. 431.
[135] The list of names was furnished to me by Dr. Günther, and I have
added the localities from the papers containing the original descriptions,
and from Dr. Haughton's _British Freshwater Fishes_.
[136] See "The Virginia Colony of Helix nemoralis," T. D. A. Cockerell, in
_The Nautilus_, Vol. III. No. 7, p. 73.
[137] I am indebted to Mr. Mitten for this curious fact.
[138] The following remarks by Dr. Richard Spruce, who has made a special
study of mosses and especially of hepaticæ, are of interest. "From what
precedes, I conclude that no existing agency is capable of transporting the
germs of our hepatics of tropical type from the torrid zone to Britain, and
I venture to suppose that their existence at Killarney dates from the
remote period when the vegetation of the whole northern hemisphere partook
of a tropical character. If I am challenged to account for their survival
through the last glacial period, I reply that, granting even the existence
of a universal ice-cap down to the latitude of 40° in America and 50° in
Europe, it is not to be assumed that the whole extent, even of land, was
_perennially_ entombed 'in thrilling regions of thick-ribbed ice.' Towards
the southern margin of the ice the climate was probably very similar to
that of Greenland and the northern part of Norway at the present day. The
summer sun would have great power, and on the borders of sheltered fjords
the frozen snow would disappear completely, if only for a very short
period, and I ask only for a month or two, not doubting the capacity of our
hepatics to survive in a dormant state under the snow for at least ten
months in the year. I have gathered mosses in the Pyrenees where the snow
had barely left them on August 2nd; by September 25th they were re-covered
with snow, and would not be again uncovered till the following year. The
mosses of Killarney might even enjoy a longer summer than this; for the
gulf-stream laves both sides of the south-western angle of Ireland, and its
tepid waters would exert great melting power on the ice-bound coast,
preventing at the same time any formation of ice in the sea itself." This
passage is the conclusion of a very interesting discussion on the
distribution of hepaticæ in a paper on "A New Hepatic from Killarney," in
the _Journal of Botany_, vol. 25, (Feb. 1887), pp. 33-82, in which many
curious facts are given as to the habits and distribution of these curious
and beautiful little plants.
[139] While these pages are passing through the press I am informed by my
friend Mr. W. H. Beeby that in the Shetland Isles, where he has been
collecting for five summers, he has found several plants new to the British
flora, and a few altogether undescribed. Among these latter is a very
distinct species of Hieracium (_H. Zetlandicum_), which is quite unknown in
Scandinavia, and is almost certainly peculiar to the British Islands. Here
we have another proof that entirely new species are still to be discovered
in the remoter portions of our country.
[140] In the first edition of this work the numbers were 400 and 340,
showing the great increase of our knowledge during the last ten years,
chiefly owing to the researches of Mr. A. H. Everett in Sarawak and Mr.
John Whitehead in North Borneo and the great mountain Kini Balu.
[141] These are Allocotops, Chlorocharis, Androphilus, and Ptilopyga, among
the Timeliidæ; Tricophoropsis and Oreoctistes among the Brachypodidæ;
Chlamydochoera among the Campophagidæ.
[142] In a letter from Darwin he says:--"Hooker writes to me, 'Miguel has
been telling me that the flora of Sumatra and Borneo are identical, and
that of Java quite different.'"
[143] "On the Geology of Sumatra," by M. R. D. M. Verbeck. _Geological
Magazine_, 1877.
[144] _Pitta megarhynchus_ (Banca) allied to _P. brachyurus_ (Borneo,
Sumatra, Malacca); and _Pitta bangkanus_ (Banca) allied to _P. sordidus_
(Borneo and Sumatra).
[145] The following list of the mammalia of the Philippines and the Sulu
Islands has been kindly furnished me by Mr. Everett.
QUADRUMANA.
1. Macacus cynomolgus.
2. Tarsius spectrum.
CARNIVORA.
3. Viverra tangalunga.
4. Paradoxurus philippinensis. Also in Palawan.
5. Felis bengalensis. In Negros Island.
UNGULATA.
6. Bubalus mindorensis. Peculiar species.
7. Cervus philippinus. Peculiar species.
8. " alfredi. Peculiar species.
9. " nigricans. Peculiar species.
10. " pseudaxis. Sulu only. Probably introduced.
11. Sus marchesi. Peculiar species.
RODENTIA.
12. Sciurus philippinensis. Peculiar species.
13. Sciurus cagos. Peculiar species.
14. " concinnus. Peculiar. Mindanao and Basilan.
15. Phlæomys cummingi. Peculiar genus.
16. Mus ephippium.
17. " everetti. Peculiar species.
INSECTIVORA.
18. Crocidura luzoniensis. Peculiar species.
19. Crocidura edwardsiana. Peculiar species.
20. Dendrogale sp.
21. Galeopithecus philippinensis. Peculiar species.
CHIROPTERA.
22. Pteropus leucopterus.
23. " edulis.
24. " hypomelanus.
25. " jubatus.
26. Xantharpyia amplexicaule.
27. Cynopterus marginatus.
28. " jagorii. Peculiar species.
29. Carponycteris australis.
30. Rhinolophus luctus.
31. " philippinensis. Peculiar species.
32. Rhinolophus rufus. Peculiar species.
33. Hipposideros diadema.
34. " pygmæus. Peculiar species.
35. Hipposideros larvatus.
36. " obscurus. Peculiar species.
37. Hipposideros coronatus. Peculiar species.
38. Hipposideros bicolor.
39. Megaderma spasma.
40. Vesperugo pachypus.
41. " tenuis.
42. Vesperugo abramus.
43. Nycticejus kuhlii.
44. Vespertilio macrotarsus. Peculiar species.
45. Vespertilio capaccinii.
46. Harpiocephalus cyclotis.
47. Kerivoula hardwickii.
48. Kerivoula pellucida. Peculiar species.
49. " jagorii. Peculiar species.
50. Miniopterus schreibersii.
51. " tristis. Peculiar species.
52. Emballonura monticola.
53. Taphyzous melanopogon.
54. Nyctinomus plicatus.
[146] Extracted from Messrs. Blakiston and Pryer's _Catalogue of Birds of
Japan_ (_Ibis_, 1878, p. 209), with Mr. Seebohm's additions and corrections
in his _Birds of the Japanese Empire_ 1890. Accidental stragglers are not
reckoned as British birds.
[147] Mr. Swinhoe died in October, 1877, at the early age of forty-two. His
writings on natural history are chiefly scattered through the volumes of
the _Proceedings of the Zoological Society_ and _The Ibis_; the whole being
summarised in his _Catalogue of the Mammals of South China and Formosa_
(_P. Z. S._, 1870, p. 615), and his _Catalogue of the Birds of China and
its Islands_ (_P. Z. S._, 1871, p. 337).
[148] Captain Blakiston has shown that the northern island--Yezo--is much
more temperate and less peculiar in its zoology than the central and
southern islands. This is no doubt dependent chiefly on the considerable
change of climate that occurs on passing the Tsu-garu strait.
[149] See Dr. J. E. Gray's "Revision of the Viverridæ," in _Proc. Zool.
Soc._ 1864, p. 507.
[150] Some of the Bats of Madagascar and East Africa are said to have their
nearest allies in Australia. (See Dobson in _Nature_, Vol. XXX. p. 575.)
[151] This view was, I believe, first advanced by Professor Huxley in his
"Anniversary Address to the Geological Society," in 1870. He says:--"In
fact the Miocene mammalian fauna of Europe and the Himalayan regions
contain, associated together, the types which are at present separately
located in the South African and Indian provinces of Arctogæa. Now there is
every reason to believe, on other grounds, that both Hindostan south of the
Ganges, and Africa south of the Sahara, were separated by a wide sea from
Europe and North Asia during the Middle and Upper Eocene epochs. Hence it
becomes highly probable that the well-known similarities, and no less
remarkable differences, between the present faunæ of India and South Africa
have arisen in some such fashion as the following: Some time during the
Miocene epoch, the bottom of the nummulitic sea was upheaved and converted
into dry land in the direction of a line extending from Abyssinia to the
mouth of the Ganges. By this means the Dekkan on the one hand and South
Africa on the other, became connected with the Miocene dry land and with
one another. The Miocene mammals spread gradually over this intermediate
dry land; and if the condition of its eastern and western ends offered as
wide contrasts as the valleys of the Ganges and Arabia do now, many forms
which made their way into Africa must have been different from those which
reached the Dekkan, while others might pass into both these sub-provinces."
This question is fully discussed in my _Geographical Distribution of
Animals_ (Vol. I., p. 285), where I expressed views somewhat different from
those of Professor Huxley, and made some slight errors which are corrected
in the present work. As I did not then refer to Professor Huxley's prior
statement of the theory of Miocene immigration into Africa (which I had
read but the reference to which I could not recall) I am happy to give his
views here.
[152] The total number of Madagascar birds is 238, of which 129 are
absolutely peculiar to the island, as are thirty-five of the genera. All
the peculiar birds but two are land birds. These are the numbers given in
M. Grandidier's great work on Madagascar.
[153] _The Ibis_, 1877, p. 334.
[154] In a paper read before the Geological Society in 1874, Mr. H. F.
Blanford, from the similarity of the fossil plants and reptiles, supposed
that India and South Africa had been connected by a continent, "and
remained so connected with some short intervals from the Permian up to the
end of the Miocene period," and Mr. Woodward expressed his satisfaction
with "this further evidence derived from the fossil flora of the Mesozoic
series of India in corroboration of the former existence of an old
submerged continent--Lemuria."
Those who have read the preceding chapters of the present work will not
need to have pointed out to them how utterly inconclusive is the
fragmentary evidence derived from such remote periods (even if there were
no evidence on the other side) as indicating geographical changes. The
notion that a similarity in the productions of widely separated continents
at any past epoch is only to be explained by the existence of a _direct_
land-connection, is entirely opposed to all that we know of the wide and
varying distribution of _all_ types at different periods, as well as to the
great powers of dispersal over moderate widths of ocean possessed by all
animals except mammalia. It is no less opposed to what is now known of the
general permanency of the great continental and oceanic areas; while in
this particular case it is totally inconsistent (as has been shown above)
with the actual facts of the distribution of animals.
[155] _Geographical Distribution of Animals_, Vol. I., pp. 272-292.
[156] The term "Mascarene" is used here in an extended sense, to include
all the islands near Madagascar which resemble it in their animal and
vegetable productions.
[157] For the birds of the Comoro Islands see _Proc. Zool. Soc._, 1877, p.
295, and 1879, p. 673.
[158] The following is a list of these peculiar birds. (See the _Ibis_, for
1867, p. 359; and 1879, p. 97.)
PASSERES.
_Ellisia seychelensis._
_Copsychus seychellarum._
_Hypsipetes crassirostris._
_Tchitrea corvina._
_Nectarinia dussumieri._
_Zosterops modesta._
" _semiflava._
_Foudia seychellarum._
PSITTACI.
_Coracopsis barklyi._
_Palæornis wardi._
COLUMBÆ.
_Alectorænas pulcherrimus._
_Turtur rostratus._
ACCIPITRES.
_Tinnunculus gracilis._
[159] Specimens are recorded from West Africa in the _Proceedings of the
Academy of Natural Science_, Philadelphia, 1857, p. 72, while specimens in
the Paris Museum were brought by D'Orbigny from S. America. Dr. Wright's
specimens from the Seychelles have, as he informs me, been determined to be
the same species by Dr. Peters of Berlin.
[160] "Additional Notes on the Land-shells of the Seychelles Islands." By
Geoffrey Nevill, C.M.Z.S. _Proc. Zool. Soc._ 1869, p. 61.
[161] In Maillard's _Notes sur l'Isle de Réunion_, a considerable number of
mammalia are given as "wild," such as _Lemur mongoz_ and _Centetes
setosus_, both Madagascar species, with such undoubtedly introduced animals
as a wild cat, a hare, and several rats and mice. He also gives two species
of frogs, seven lizards, and two snakes. The latter are both Indian species
and certainly imported, as are most probably the frogs. Legouat, who
resided some years in the island nearly two centuries ago, and who was a
closer observer of nature, mentions numerous birds, large bats,
land-tortoises, and lizards, but no other reptiles or venomous animals
except scorpions. We may be pretty sure, therefore, that the land-mammalia,
snakes, and frogs, now found wild, have all been introduced. Of lizards, on
the other hand, there are several species, some peculiar to the island,
others common to Africa and the other Mascarene Islands. The following list
by Prof. Dumeril is given in Maillard's work:--
_Platydactylus cepedianus._
" _ocellatus._
_Hemidactylus peronii._
" _mutilatus._
_Hemidactylus frenatus._
_Gongylus bojerii._
_Ablepharus peronii._
Four species of chameleon are now recorded from Bourbon and one from
Mauritius (J. Reay Greene, M.D., in _Pop. Science Rev._ April, 1880), but
as they are not mentioned by the old writers, it is pretty certain that
these creatures are recent introductions, and this is the more probable as
they are favourite domestic pets.
Darwin informed me that in a work entitled _Voyage à l'Isle de France, par
un Officier du Roi_, published in 1770, it is stated that a fresh-water
fish had been introduced from Batavia and had multiplied. The writer also
says (p. 170): "_On a essayé, mais sans succcès, d'y transporter des
grenouilles qui mangent les oeufs que les moustigues deposent sur les eaux
stagnantes._" It thus appears that there were then no frogs on the island.
[162] That the dodo is really an abortion from a more perfect type, and not
a direct development from some lower form of wingless bird, is shown by its
possessing a keeled sternum, though the keel is exceedingly reduced, being
only three-quarters of an inch deep in a length of seven inches. The most
terrestrial pigeon--the Didunculus of the Samoan Islands, has a far deeper
and better developed keel, showing that in the case of the dodo the
degradation has been extreme. We have also analogous examples in other
extinct birds of the same group of islands, such as the flightless
Rails--Aphanapteryx of Mauritius and Erythromachus of Rodriguez, as well as
the large parrot--Lophopsittacus of Mauritius, and the Night Heron,
_Nycticorax megacephala_ of Rodriguez, the last two birds probably having
been able to fly a little. The commencement of the same process is to be
seen in the peculiar dove of the Seychelles, _Turtur rostratus_, which, as
Mr. Edward Newton has shown, has much shorter wings than its close ally,
_T. picturatus_, of Madagascar. For a full and interesting account of these
and other recently extinct birds see Professor Newton's article on "Fossil
Birds" in the _Encyclopædia Britannica_, ninth edition, vol. iii., p. 732;
and that on "The Extinct Birds of Rodriguez," by Dr. A. Günther and Mr. E.
Newton, in the Royal Society's volume on the Transit of Venus Expedition.
[163] See _Ibis_, 1877, p. 334.
[164] A common Indian and Malayan toad (_Bufo melanostictus_) has been
introduced into Mauritius and also some European toads, as I am informed by
Dr. Günther.
[165] This brief account of the Madagascar flora has been taken from a very
interesting paper by the Rev. Richard Baron, F.L.S., F.G.S., in the
_Journal of the Linnean Society_, Vol. XXV., p. 246; where much information
is given on the distribution of the flora within the island.
[166] It may be interesting to botanists and to students of geographical
distribution to give here an enumeration of the endemic genera of the
_Flora of the Mauritius and the Seychelles_, as they are nowhere separately
tabulated in that work.
Aphloia (Bixaceæ) 1 sp., a shrub, Maur., Rod., Sey., also
Madagascar.
Medusagyne (Ternströmiaceæ) 1 sp., a shrub, Seychelles.
Astiria (Sterculiaceæ) 1 sp., a shrub, Mauritius.
Quivisia (Meliaceæ) 3 sp., shrubs, Mauritius (2 sp.),
Rodriguez (1 sp.), also Bourbon.
Cossignya (Sapindaceæ) 1 sp., a shrub, Mauritius, also Bourbon.
Hornea ,, 1 sp., a shrub, Mauritius.
Stadtmannia ,, 1 sp., a shrub, Mauritius.
Doratoxylon ,, 1 sp., a shrub, Mauritius and Bourbon.
Gagnebina (Leguminosæ) 1 sp., a shrub, Mauritius, also
Madagascar.
Roussea (Saxifragaceæ) 1 sp., a climbing shrub, Mauritius and
Bourbon.
Tetrataxis (Lythraceæ) 1 sp., a shrub, Mauritius.
Psiloxylon ,, 1 sp., a shrub, Mauritius and Bourbon.
Mathurina (Turneraceæ) 1 sp., a shrub, Rodriguez.
Foetidia (Myrtaceæ) 1 sp., a tree, Mauritius.
Danais (Rubiaceæ) 4 sp., climbing shrubs, Maur. (1 sp.),
Rodr. (1 sp.), also Bourbon and
Madagascar.
Fernelia (Rubiaceæ) 1 sp., a shrub, Mauritius and Rodriguez.
Pyrostria ,, 6 sp., shrubs, Mauritius (3 sp.), also
Bourbon and Madagascar.
Scyphochlamys (Rubiaceæ) 1 sp., a shrub, Rodriguez.
Myonima ,, 3 sp., shrubs, Mauritius, also Bourbon.
Cylindrocline (Compositæ) 1 sp., a shrub, Mauritius.
Monarrhenus ,, 2 sp., shrubs, Mauritius, also Bourbon
and Madagascar.
Faujasia (Compositæ) 3 sp., shrubs, Mauritius, also Bourbon
and Madagascar.
Heterochænia (Campanulaceæ) 1 sp., a shrub, Mauritius, also Bourbon.
Tanulepis (Asclepiadaceæ) 1 sp., a climber, Rodriguez.
Decanema ,, 1 sp., a climber, Mauritius, also
Madagascar.
Nicodemia (Loganiaceæ) 2 sp., shrubs, Mauritius (1 sp.), also
Comoro Islands and Madagascar.
Bryodes (Scrophulariaceæ) 1 sp., herb, Mauritius.
Radamæa ,, 2 sp., herb, Seychelles (1 sp.), and
Madagascar.
Colea (Bignoniaceæ) 10 sp., Mauritius (1 sp.), Seychelles (1
sp.), also Bourbon and Madagascar.
(Shrubs, trees, or climbers.)
Obetia (Urticaceæ) 2 sp., shrubs, Mauritius, Seychelles,
and Madagascar.
Bosquiea (Moreæ) 3 sp., trees, Seychelles (1 sp.), also
Madagascar.
Monimia (Monimiaceæ) 3 sp., trees, Mauritius (2 sp.), also
Bourbon.
Cynorchis (Orchideæ) 3 sp., herb, ter., Mauritius.
Amphorchis ,, 1 sp., herb, ter., Mauritius, also
Bourbon.
Arnottia ,, 2 sp., herb, ter., Mauritius, also
Bourbon.
Aplostellis ,, 1 sp., herb, ter., Mauritius.
Cryptopus ,, 1 sp., herb, Epiphyte, Mauritius, also
Bourbon and Madagascar.
Lomatophyllum (Liliaceæ) 3 sp., shrubs (succulent), Mauritius,
also Bourbon.
Lodoicea (Palmæ) 1 sp., tree, Seychelles.
Latania ,, 3 sp., trees, Mauritius (2 sp.),
Rodriguez, also Bourbon.
Hyophorbe ,, 3 sp., trees, Mauritius (2 sp.),
Rodriguez, also Bourbon.
Dictyosperma ,, 1 sp., tree, Mauritius, Rodriguez,
also Bourbon.
Acanthophænix ,, 2 sp., trees, Mauritius, also Bourbon.
Deckenia ,, 1 sp., tree, Seychelles.
Nephrosperma ,, 1 sp., tree, Seychelles.
Roscheria ,, 1 sp., tree, Seychelles.
Verschaffeltia ,, 1 sp., tree, Seychelles.
Stevensonia ,, 1 sp., tree, Seychelles.
Ochropteris (Filices) 1 sp., herb, Mauritius, also Bourbon and
Madagascar.
Among the curious features in this list are the great number of endemic
shrubs in Mauritius, and the remarkable assemblage of five endemic genera
of palms in the Seychelles Islands. We may also notice that one palm
(_Latania loddigesii_) is confined to Round Island and two other adjacent
islets offering a singular analogy to the peculiar snake also found there.
[167]
_Families of Malayan Birds not found in islands East of Celebes._
Troglodytidæ.
Sittidæ.
Paridæ.
Liotrichidæ.
Phyllornithidæ.
Eurylæmidæ.
Picidæ.
Indicatoridæ.
Megalænidæ.
Trogonidæ.
Phasianidæ.
_Families of Moluccan Birds not found in islands West of Celebes._
Paradiseidæ.
Meliphagidæ.
Cacatuidæ.
Platycercidæ.
Trichoglossidæ.
Nestoridæ.
[168] For outline figures of the chief types of these butterflies, see my
_Malay Archipelago_, Vol. I. p. 441, or p. 216 of the tenth edition.
[169] Dobson on the Classification of Chiroptera (_Ann. and Mag. of Nat.
Hist._ Nov. 1875).
[170] See Buller, "On the New Zealand Rat," _Trans. of the N. Z. Institute_
(1870), Vol. III. p. 1, and Vol. IX. p. 348; and Hutton, "On the
Geographical Relations of the New Zealand Fauna," _Trans. N. Z. Instit._
1872, p. 229.
[171] Hochstetter's _New Zealand_, p. 161, note.
[172] The animal described by Captain Cook as having been seen at
Pickersgill Harbour in Dusky Bay (Cook's 2nd Voyage, Vol. I. p. 98) may
have been the same creature. He says, "A four-footed animal was seen by
three or four of our people, but as no two gave the same description of it,
I cannot say what kind it is. All, however, agreed that it was about the
size of a cat, with short legs, and of a mouse colour. One of the seamen,
and he who had the best view of it, said it had a bushy tail, and was the
most like a jackal of any animal he knew." It is suggestive that, so far as
the points on which "all agreed"--the size and the dark colour--this
description would answer well to the animal so recently seen, while the
"short legs" correspond to the otter-like tracks, and the thick tail of an
otter-like animal may well have appeared "bushy" when the fur was dry. It
has been suggested that it was only one of the native dogs; but as none of
those who saw it took it for a dog, and the points on which they all agreed
are not dog-like, we can hardly accept this explanation; while the actual
existence of an unknown animal in New Zealand of corresponding size and
colour is confirmed by this account of a similar animal having been seen
about a century ago.
[173] Owen, "On the Genus Dinornis," _Trans. Zool. Soc._ Vol. X. p. 184.
Mivart, "On the Axial Skeleton of the Struthionidæ," _Trans. Zool. Soc._
Vol. X. p. 51.
[174] The recent existence of the Moa and its having been exterminated by
the Maoris appears to be at length set at rest by the statement of Mr. John
White, a gentleman who has been collecting materials for a history of the
natives for thirty-five years, who has been initiated by their priests into
all their mysteries, and is said to "know more about the history, habits,
and customs of the Maoris than they do themselves." His information on this
subject was obtained from old natives long before the controversy on the
subject arose. He says that the histories and songs of the Maoris abound in
allusions to the Moa, and that they were able to give full accounts of "its
habits, food, the season of the year it was killed, its appearance,
strength, and all the numerous ceremonies which were enacted by the natives
before they began the hunt, the mode of hunting, how cut up, how cooked,
and what wood was used in the cooking, with an account of its nest, and how
the nest was made, where it usually lived, &c." Two pages are occupied by
these details, but they are only given from memory, and Mr. White promises
a full account from his MSS. Many of the details given correspond with
facts ascertained from the discovery of native cooking places with Moas'
bones; and it seems quite incredible that such an elaborate and detailed
account should be all invention. (See _Transactions of the New Zealand
Institute_, Vol. VIII. p. 79.)
[175] See fig. in _Trans. of N. Z. Institute_, Vol. III., plate 12_b._ fig.
2.
[176] _Geographical Distribution of Animals_, Vol. I., p. 450.
[177] In my _Geographical Distribution of Animals_ (I. p. 541) I have given
two peculiar Australian genera (_Orthonyx_ and _Tribonyx_) as occurring in
New Zealand. But the former has been found in New Guinea, while the New
Zealand bird is considered to form a distinct genus, _Clitonyx_; and the
latter inhabits Tasmania, and was recorded from New Zealand through an
error. (See _Ibis_, 1873, p. 427.)
[178] The peculiar genera of Australian lizards according to Boulenger's
British Museum Catalogue, are as follows:--Family GECKONIDÆ: Nephrurus,
Rhynchoedura, Heteronota, Diplodactylus, Oedura. Family PYGOPODIDÆ
(peculiar): Pygopus, Cryptodelma, Delma, Pletholax, Aprasia. Family
AGAMIDÆ: Chelosania, Amphibolurus, Tympanocryptis, Diporophora,
Chlamydosaurus, Moloch, Oreodeira. Family SCINCIDÆ: Egerina, Trachysaurus,
Hemisphænodon. Family doubtful: Ophiopsiseps.
[179] These figures are taken from Mr. G. M. Thomson's address "On the
Origin of the New Zealand Flora," _Trans. N. Z. Institute_, XIV. (1881),
being the latest that I can obtain. They differ somewhat from those given
in the first edition, but not so as to affect the conclusions drawn from
them.
[180] This accords with the general scarcity of Leguminosæ in Oceanic
Islands, due probably to their usually dry and heavy seeds, not adapted to
any of the forms of aërial transmission; and it would indicate either that
New Zealand was never absolutely united with Australia, or that the union
was at a very remote period when Leguminosæ were either not differentiated
or comparatively rare.
[181] Sir Joseph Hooker informs me that the number of tropical Australian
plants discovered within the last twenty years is very great, and that the
statement as above made may have to be modified. Looking, however, at the
enormous disproportion of the figures given in the "Introductory Essay" in
1859 (2,200 tropical to 5,800 temperate species) it seems hardly possible
that a great difference should not still exist, at all events as regards
species. In Baron von Müeller's latest summary of the Australian Flora
(_Second Systematic Census of Australian Plants_, 1889), he gives the total
species at 8,839, of which 3,560 occur in West Australia, and 3,251 in New
South Wales. On counting the species common to these two colonies in fifty
pages of the _Census_ taken at random, I find them to be about one-tenth of
the total species in both. This would give the number of distinct species
in these areas as about 6,130. Adding to these the species peculiar to
Victoria and South Australia, we shall have a flora of near 6,500 in the
temperate parts of Australia. It is true that West Australia extends far
into the tropics, but an overwhelming majority of the species have been
discovered in the south-western portion of the colony, while the species
that may be exclusively tropical will be more than balanced by those of
temperate Queensland, which have not been taken account of, as that colony
is half temperate and half tropical. It thus appears probable that full
three fourths of the species of Australian plants occur in the temperate
regions, and are mainly characteristic of it. Sir Joseph Hooker also doubts
the generally greater richness of tropical over temperate floras which I
have taken as almost an axiom. He says: "Taking similar areas to Australia
in the Western World, _e.g._, tropical Africa north of 20° S. Lat. as
against temperate Africa and Europe up to 47°--I suspect that the latter
would present more genera and species than the former." This, however,
appears to me to be hardly a case in point, because Europe is a distinct
continent from Africa and has had a very different past history, and it is
not a fair comparison to take the tropical area in one continent while the
temperate is made up of widely separated areas in two continents. A closer
parallel may perhaps be found in equal areas of Brazil and south temperate
America, or of Mexico and the Southern United States, in both of which
cases I suppose there can be little doubt that the tropical areas are far
the richest. Temperate South Africa is, no doubt, always quoted as richer
than an equal area of tropical Africa or perhaps than any part of the world
of equal extent, but this is admitted to be an exceptional case.
[182] Sir Joseph Hooker thinks that later discoveries in the Australian
Alps and other parts of East and South Australia may have greatly modified
or perhaps reversed the above estimate, and the figures given in the
preceding note indicate that this is so. But still, the small area of
South-west Australia will be, proportionally, far the richer of the two. It
is much to be desired that the enormous mass of facts contained in Mr.
Bentham's _Flora Australiensis_ and Baron von Müeller's _Census_ should be
tabulated and compared by some competent botanist, so as to exhibit the
various relations of its wonderful vegetation in the same manner as was
done by Sir Joseph Hooker with the materials available twenty-one years
ago.
[183] From an examination of the fossil corals of the South-west of
Victoria, Professor P. M. Duncan concludes--"that, at the time of the
formation of these deposits the central area of Australia was occupied by
sea, having open water to the north, with reefs in the neighbourhood of
Java." The age of these fossils is not known, but as almost all are extinct
species, and some are almost identical with European Pliocene and Miocene
species, they are supposed to belong to a corresponding period. (_Journal
of Geol. Soc._, 1870.)
[184] "On the Origin of the Fauna and Flora of New Zealand," by Captain
F. W. Hutton, in _Annals and Mag. of Nat. Hist._ Fifth series, p. 427
(June, 1884).
[185] To these must now be added the genera Sequoia, Myrica, Aralia, and
Acer, described by Baron von Ettingshausen. (_Trans. N.Z. Institute_, xix.,
p. 449.)
[186] The large collection of fossil plants from the Tertiary beds of New
Zealand which have been recently described by Baron von Ettingshausen
(_Trans. N. Z. Inst._, vol. xxiii., pp. 237-310), prove that a change in
the vegetation has occurred similar to that which has taken place in
Eastern Australia, and that the plants of the two countries once resembled
each other more than they do now. We have, first, a series of groups now
living in Australia, but which have become extinct in New Zealand, as
Cassia, Dalbergia, Eucalyptus, Diospyros, Dryandra, Casuarina, and Ficus;
and also such northern genera as Acer, Planera, Ulmus, Quercus, Alnus,
Myrica, and Sequoia. All these latter, except Ulmus and Planera, have been
found also in the Eastern-Australian Tertiaries, and we may therefore
consider that at this period the northern temperate element in both floras
was identical. If this flora entered both countries from the south, and was
really Antarctic, its extinction in New Zealand may have been due to the
submergence of the country to the south, and its elevation and extension
towards the tropics, admitting of the incursion of the large number of
Polynesian and tropical Australian types now found there; while the
Australian portion of the same flora may have succumbed at a somewhat later
period, when the elevation of the Cretaceous and Tertiary sea united it
with Western Australia, and allowed the rich typical Australian flora to
overrun the country. Of course we are assuming that the identification of
these genera is for the most part correct, though almost entirely founded
on leaves only. Fuller knowledge, both of the extinct flora itself and of
the geological age of the several deposits, is requisite before any
trustworthy explanation of the phenomena can be arrived at.
[187] The following are the tropical genera common to New Zealand and
Australia:--
1. _Melicope._ Queensland, Pacific Islands.
2. _Eugenia._ Eastern and Tropical Australia, Asia, and America.
3. _Passiflora._ N.S.W. and Queensland, Tropics of Old World and America.
4. _Myrsine._ Tropical and Temperate Australia, Tropical and Sub-tropical
regions.
5. _Sapota._ Australia, Norfolk Islands, Tropics.
6. _Cyathodes._ Australia and Pacific Islands.
7. _Parsonsia._ Tropical Australia and Asia.
8. _Geniostoma._ Queensland, Polynesia, Asia.
9. _Mitrasacme._ Tropical and Temperate Australia, India.
10. _Ipomoea._ Tropical Australia, Tropics.
11. _Mazus._ Temperate Australia, India, China.
12. _Vitex._ Tropical Australia, Tropical and Sub-tropical.
13. _Pisonia._ Tropical Australia, Tropical and Sub-tropical.
14. _Alternanthera._ Tropical Australia, India, and S. America.
15. _Tetranthera._ Tropical Australia, Tropics.
16. _Santalum._ Tropical and Sub-tropical Australia, Pacific, Malay
Islands.
17. _Carumbium._ Tropical and Sub-tropical Australia, Pacific Islands.
18. _Elatostemma._ Sub-tropical Australia, Asia, Pacific Islands.
19. _Peperomia._ Tropical and Sub-tropical Australia, Tropics.
20. _Piper._ Tropical and Sub-tropical Australia, Tropics.
21. _Dacrydium._ Tasmania, Malay, and Pacific Islands.
22. _Dammara._ Tropical Australia, Malay, and Pacific Islands.
23. _Dendrobium._ Tropical Australia, Eastern Tropics.
24. _Bolbophyllum._ Tropical and Sub-tropical Australia, Tropics.
25. _Sarcochilus._ Tropical and Sub-tropical Australia, Fiji, and Malay
Islands.
26. _Freycinetia._ Tropical Australia, Tropical Asia.
27. _Cordyline._ Tropical Australia, Pacific Islands.
28. _Dianella._ Australia, India, Madagascar, Pacific Islands.
29. _Cyperus._ Australia, Tropical regions mainly.
30. _Fimbristylis._ Tropical Australia, Tropical regions.
31. _Paspalum._ Tropical and Sub-tropical grasses.
32. _Isachne._ Tropical and Sub-tropical grasses.
33. _Sporobolus._ Tropical and Sub-tropical grasses.
[188] Insects are tolerably abundant in the open mountain regions, but very
scarce in the forests. Mr. Meyrick says that these are "strangely deficient
in insects, the same species occurring throughout the islands;" and Mr.
Pascoe remarked that "the forests of New Zealand were the most barren
country, entomologically, he had ever visited." (_Proc. Ent. Soc._, 1883.
p. xxix.)
[189] Introductory Essay _On the Flora of Australia_, p. 130.
[190] Hooker, _On the Flora of Australia_, p. 95.--H. C. Watson, in
Godman's _Azores_, pp. 278-286.
[191] As this is a point of great interest in its bearing on the dispersal
of plants by means of mountain ranges, I have endeavoured to obtain a few
illustrative facts:--
1. Mr. William Mitten, of Hurstpierpoint, Sussex, informs me that when the
London and Brighton railway was in progress in his neighbourhood,
_Melilotus vulgaris_ made its appearance on the banks, remained for several
years, and then altogether disappeared. Another case is that of _Diplotaxis
muralis_, which formerly occurred only near the sea-coast of Sussex, and at
Lewes; but since the railway was made has spread along it, and still
maintains itself abundantly on the railway banks though rarely found
anywhere else.
2. A correspondent in Tasmania informs me that whenever the virgin forest
is cleared in that island there invariably comes up a thick crop of a plant
locally known as fire-weed--a species of Senecio, probably _S. Australis_.
It never grows except where the fire has gone over the ground, and is
unknown except in such places. My correspondent adds:--"This autumn I went
back about thirty-five miles through a dense forest, along a track marked
by some prospectors the year before, and in one spot where they had camped,
and the fire had burnt the fallen logs, &c., there was a fine crop of
'fire-weed.' All around for many miles was a forest of the largest trees
and dense scrub." Here we have a case in which burnt soil and ashes favour
the germination of a particular plant, whose seeds are easily carried by
the wind, and it is not difficult to see how this peculiarity might favour
the dispersal of the species for enormous distances, by enabling it
temporarily to grow and produce seeds on burnt spots.
3. In answer to an inquiry on this subject, Mr. H. C. Watson has been kind
enough to send me a detailed account of the progress of vegetation on the
railway banks and cuttings about Thames Ditton. This account is written
from memory, but as Mr. Watson states that he took a great interest in
watching the process year by year, there can be no reason to doubt the
accuracy of his memory. I give a few extracts which bear especially on the
subject we are discussing.
"One rather remarkable biennial plant appeared early (the second year, as I
recollect) and renewed itself either two or three years, namely, _Isatis
tinctoria_--a species usually supposed, to be one of our introduced, but
pretty well naturalised, plants. The nearest stations then or since known
to me for this _Isatis_ are on chalk about Guildford, twenty miles distant.
There were two or three plants of it at first, never more than half a
dozen. Once since I saw a plant of _Isatis_ on the railway bank near
Vauxhall.
"Close by Ditton Station three species appeared which may be called
interlopers. The biennial _Barbarea precox_, one of these, is the least
remarkable, because it might have come as seed in the earth from some
garden, or possibly in the Thames gravel (used as ballast). At first it
increased to several plants, then became less numerous, and will soon, in
all probability, become extinct, crowded out by other plants. The biennial
_Petroselinum segetum_ was at first one very luxuriant plant on the slope
of the embankment. It increased by seed into a dozen or a score, and is now
nearly if not quite extinct. The third species is _Linaria purpurea_, not
strictly a British plant, but one established in some places on old walls.
A single root of it appeared on the chalk facing of the embankment by
Ditton Station. It has remained there several years and grown into a
vigorous specimen. Two or three smaller examples are now seen by it,
doubtless sprung from some of the hundreds or thousands of seeds shed by
the original one plant. The species is not included in Salmon and Brewer's
_Flora of Surrey_.
"The main line of the railway has introduced into Ditton parish the
perennial _Arabis hirsuta_, likely to become a permanent inhabitant. The
species is found on the chalk and greensand miles away from Thames Ditton;
but neither in this parish nor in any adjacent parish, so far as known to
myself or to the authors of the flora of the county, does it occur. Some
years after the railway was made a single root of this _Arabis_ was
observed in the brickwork of an arch by which the railway is carried over a
public road. A year or two afterwards there were three or four plants. In
some later year I laid some of the ripened seed-pods between the bricks in
places where the mortar had partly crumbled out. Now there are several
scores of specimens in the brickwork of the arch. It is presumable that the
first seed may have been brought from Guildford. But how could it get on to
the perpendicular face of the brickwork?
"The Bee Orchis (_Ophrys apifera_), plentiful on some of the chalk lands in
Surrey, is not a species of Thames Ditton, or (as I presume) of any
adjacent parish. Thus, I was greatly surprised some years back to see about
a hundred examples of it in flower in one clayey field either on the
outskirts of Thames Ditton or just within the limits of the adjoining
parish of Cobham. I had crossed this same field in a former year without
observing the Ophrys there. And on finding it in the one field I closely
searched the surrounding fields and copses, without finding it anywhere
else. Gradually the plants became fewer and fewer in that one field, and
some six or eight years after its first discovery there the species had
quite disappeared again. I guessed it had been introduced with chalk, but
could obtain no evidence to show this."
4. Mr. A. Bennett, of Croydon, has kindly furnished me with some
information on the temporary vegetation of the banks and cuttings on the
railway from Yarmouth to Caistor in Norfolk, where it passes over extensive
sandy Denes with a sparse vegetation. The first year after the railway was
made the banks produced abundance of _Oenothera odorata_ and _Delphinium
Ajacis_ (the latter only known thirty miles off in cornfields in
Cambridgeshire), with _Atriplex patula_ and _A. deltoidea_. Gradually the
native sand plants--Carices, Grasses, _Galium verum_, &c., established
themselves, and year by year covered more ground till the new introductions
almost completely disappeared. The same phenomenon was observed in
Cambridgeshire between Chesterton and Newmarket, where, the soil being
different, _Stellaria media_ and other annuals appeared in large patches;
but these soon gave way to a permanent vegetation of grasses, composites,
&c., so that in the third year no _Stellaria_ was to be seen.
5. Mr. T. Kirk (writing in 1878) states that--"in Auckland, where a dense
sward of grass is soon formed, single specimens of the European milk
Thistle (_Carduus marianus_) have been known for the past fifteen years;
but although they seeded freely, the seeds had no opportunity of
germinating, so that the thistle did not spread. A remarkable exception to
this rule occurred during the formation of the Onehunga railway, where a
few seeds fell on disturbed soil, grew up and flowered. The railway works
being suspended, the plant increased rapidly, and spread wherever it could
find disturbed soil."
Again:--"The fiddle-dock (_Rumex pulcher_) occurs in great abundance on the
formation of new streets, &c., but soon becomes comparatively rare. It
seems probable that it was one of the earliest plants naturalised here, but
that it partially died out, its buried seeds retaining their vitality."
_Medicago sativa_ and _Apium graveolens_, are also noted as escapes from
cultivation which maintain themselves for a time but soon die out.
(_Transactions of the New Zealand Institute_, Vol. X. p. 367.)
The preceding examples of the _temporary_ establishment of plants on newly
exposed soil, often at considerable distances from the localities they
usually inhabit, might, no doubt, by further inquiry be greatly multiplied;
but, unfortunately, the phenomenon has received little attention, and is
not even referred to in the elaborate work of De Candolle (_Géographie
Botanique Raisonnée_) in which almost every other aspect of the dispersion
and distribution of plants is fully discussed. Enough has been advanced,
however, to show that it is of constant occurrence, and from the point of
view here advocated it becomes of great importance in explaining the almost
world-wide distribution of many common plants of the north temperate zone.
[192] Sir Joseph Hooker informs me that he considers these identifications
worthless, and Mr. Bentham has also written very strongly against the value
of similar identifications by Heer and Unger. Giving due weight to the
opinions of these eminent botanists we must admit that Australian genera
have not yet been _demonstrated_ to have existed in Europe during the
Tertiary period; but, on the other hand, the evidence that they did so
appears to have some weight, on account of the improbability that the
numerous resemblances to Australian plants which have been noticed by
different observers should _all_ be illusory; while the well established
fact of the former wide distribution of many tropical or now restricted
types of plants and animals, so frequently illustrated in the present
volume, removes the antecedent improbability which is supposed to attach to
such identifications. I am myself the more inclined to accept them,
because, according to the views here advocated, such migrations must have
taken place at remote as well as at recent epochs; and the preservation of
some of these types in Australia while they have become extinct in Europe,
is exactly paralleled by numerous facts in the distribution of animals
which have been already referred to in Chapter XIX., and elsewhere in this
volume, and also repeatedly in my larger work.
[193] Out of forty-two genera from the Eocene of Sheppey enumerated by Dr.
Ettingshausen in the _Geological Magazine_ for January 1880, only two or
three appear to be extinct, while there is a most extraordinary
intermixture of tropical and temperate forms--Musa, Nipa, and Victoria,
with Corylus, Prunus, Acer, &c. The rich Miocene flora of Switzerland,
described by Professor Heer, presents a still larger proportion of living
genera.
[194] The recent discovery by Lieutenant Jensen of a rich flora on rocky
peaks rising out of the continental ice of Greenland, as well as the
abundant vegetation of the highest northern latitudes, renders it possible
that even now the Antarctic continent may not be wholly destitute of
vegetation, although its climate and physical condition are far less
favourable than those of the Arctic lands. (See _Nature_, Vol. XXI. p.
345.)
[195] Dr. Hector notes the occurrence of the genus _Dammara_ in Triassic
deposits, while in the Jurassic period New Zealand possessed the genera
_Palæozamia_, _Oleandrium_, _Alethopteris_, _Camptopteris_, _Cycadites_,
_Echinostrobus_, &c., all Indian forms of the same age. Neocomian beds
contain a true dicotyledonous leaf with _Dammara_ and _Araucaria_. The
Cretaceous deposits have produced a rich flora of dicotyledonous plants,
many of which are of the same genera as the existing flora; while the
Miocene and other Tertiary deposits produce plants almost identical with
those now inhabiting the country, together with many North Temperate genera
which have since become extinct. (See p. 499, footnote, and _Trans. New
Zealand Inst._, Vol. XI. 1879, p. 536.)
[196] The fact stated in the last edition of the _Origin of Species_ (p.
340) on the authority of Sir Joseph Hooker, that Australian plants are
rapidly sowing themselves and becoming naturalised on the Neilgherrie
mountains in the southern part of the Indian Peninsula, though an exception
to the rule of the inability of Australian plants to become naturalised in
the Northern Hemisphere, is yet quite in harmony with the hypothesis here
advocated. For not only is the climate of the Neilgherries more favourable
to Australian plants than any part of the North Temperate zone, but the
entire Indian Peninsula has existed for unknown ages as an _island_ and
thus possesses the "insular" characteristic of a comparatively poor and
less developed flora and fauna as compared with the truly "continental"
Malayan and Himalayan regions. Australian plants are thus enabled to
compete with those of the Indian Peninsula highlands with a fair chance of
success.
* * * * *
Corrections made to printed original.
Page 10. "the general stability of continents": 'sontinents' in original.
Pages 35, 250, 361, 363 "oenanthe" read for "ænanthe" throughout for
consistency
Page 50. "some others of the lower animals": 'animials' in original.
Page 82. "transmission along mountain chains": 'mountains chains' in
original.
Page 99. "our present land masses": 'massses' in original.
Page 149. "the whole earth should theoretically be": 'thoretically' in
original.
Page 200. "the flora and fauna, in the British area": 'Brittish' in
original.
Page 234. "the indications of an uninterrupted warm climate": 'indic-tions'
on line break in original.
Page 306. "artificially removed by man": 'artifically' in original.
Page 346. "Elachista rufocinerea, the larva of which ...": 'lava' in
original.
Page 456. "Cynopithecus nigrescens": 'Cynopitheus' in original.
Footnote 100. "S. B. J. Skertchley": 'S. B. K.' in original. I have left
the name as Skertchley as Wallace uses this spelling almost consistently,
although Skertchly (as on p. 118) appears to be correct.--Tr.
Footnote 105. "the transportation of the plants": 'transporation' in
original.
Footnote 110. "Agriolimax campestris": 'Agriolimaoe' (ligand oe) in
original.
*** End of this LibraryBlog Digital Book "Island Life - Or the Phenomena and Causes of Insular Faunas and Floras" ***
Copyright 2023 LibraryBlog. All rights reserved.