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Title: Life's Dawn on Earth - Being the history of the oldest known fossil remains, and - their relations to geological time and to the development - of the animal kingdom
Author: Dawson, John William, Sir, William, John
Language: English
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Transcriber Notes
Text emphasis denoted as _Italics_.
[Illustration:
Plate I.
From a Photo. by Henderson Vincent Brooke, Day & Son. Lith.
CAPE TRINITY ON THE SAGUENAY.
A CLIFF OF LAURENTIAN GNEISS.
_Frontispiece_]
LIFE'S DAWN ON EARTH:
BEING THE
History of the Oldest Known Fossil Remains,
AND
THEIR RELATIONS TO GEOLOGICAL TIME
AND TO THE DEVELOPMENT OF
THE ANIMAL KINGDOM.
BY
J. W. DAWSON, LL.D., F.R.S., F.G.S., Etc.,
PRINCIPAL AND VICE-CHANCELLOR OF M'GILL UNIVERSITY, MONTREAL;
AUTHOR OF
"ARCHAIA," "ACADIAN GEOLOGY," "THE STORY OF
THE EARTH AND MAN," ETC.
_SECOND THOUSAND._
LONDON:
HODDER & STOUGHTON,
27, PATERNOSTER ROW.
MDCCCLXXV.
Butler & Tanner,
The Selwood Printing Works,
Frome, and London.
To the Memory of
SIR WILLIAM EDMOND LOGAN,
LL.D., F.R.S., F.G.S.,
THIS WORK IS DEDICATED,
Not merely as a fitting acknowledgment of his long and successful
labours in the geology of those most ancient rocks, first named by
him Laurentian, and which have afforded the earliest known traces
of the beginning of life, but also as a tribute of sincere personal
esteem and regard to the memory of one who, while he attained to the
highest eminence as a student of nature, was also distinguished by his
patriotism and public spirit, by the simplicity and earnestness of his
character, and by the warmth of his friendships.
PREFACE.
An eminent German geologist has characterized the discovery of fossils
in the Laurentian rocks of Canada as "the opening of a new era in
geological science." Believing this to be no exaggeration, I have
felt it to be a duty incumbent on those who have been the apostles of
this new era, to make its significance as widely known as possible to
all who take any interest in scientific subjects, as well as to those
naturalists and geologists who may not have had their attention turned
to this special topic.
The delivery of occasional lectures to popular audiences on this and
kindred subjects, has convinced me that the beginning of life in the
earth is a theme having attractions for all intelligent persons;
while the numerous inquiries on the part of scientific students with
reference to the fossils of the Eozoic age, show that the subject
is yet far from being familiar to their minds. I offer no apology
therefore for attempting to throw into the form of a book accessible
to general readers, what is known as to the dawn of life, and cannot
doubt that the present work will meet with at least as much acceptance
as that in which I recently endeavoured to picture the whole series of
the geological ages.
I have to acknowledge my obligations to Sir W. E. Logan for most
of the Laurentian geology in the second chapter, and also for the
beautiful map which he has kindly had prepared at his own expense as
a contribution to the work. To Dr. Carpenter I am indebted for much
information as to foraminiferal structures, and to Dr. Hunt for the
chemistry of the subject. Mr. Selwyn, Director of the Geological
Survey of Canada, has kindly given me access to the materials in its
collections. Mr. Billings has contributed specimens and illustrations
of Palæozoic Protozoa; and Mr. Weston has aided greatly by the
preparation of slices for the microscope, and of photographs, as well
as by assistance in collecting.
J. W. D.
McGill College, Montreal.
_April, 1875._
CONTENTS.
PAGE
Chapter I. Introductory 1
Chapter II. The Laurentian System 7
Notes:--Logan on Structure of Laurentian; Hunt
on Life in the Laurentian; Laurentian Graphite;
Western Laurentian; Metamorphism 24
Chapter III. The History of a Discovery 35
Notes:--Logan on Discovery of Eozoon, and on
Additional Specimens 48
Chapter IV. What is Eozoon? 59
Notes:--Original Description; Note by Dr. Carpenter;
Specimens from Long Lake; Additional
Structural Facts 76
Chapter V. Preservation of Eozoon 93
Notes:--Hunt on Mineralogy of Eozoon; Silicified
Fossils in Silurian Limestones; Minerals
associated with Eozoon; Glauconites 115
Chapter VI. Contemporaries and Successors 127
Notes:--On Stromatoporidæ; Localities of Eozoon 165
Chapter VII. Opponents and Objections 169
Notes:--Objections and Replies; Hunt on
Chemical Objections; Reply by Dr. Carpenter 184
Chapter VIII. The Dawn-Animal as a Teacher in Science 207
Appendix 235
Index 237
LIST OF ILLUSTRATIONS.
FULL PAGE ILLUSTRATIONS.
TO FACE
PAGE
I. Cape Trinity, from a Photograph (_Frontispiece_).
II. Map of the Laurentian Region on the River Ottawa 7
III. Weathered Specimen of Eozoon, from a Photograph 35
IV. Restoration of Eozoon 59
V. Nature-print of Eozoon 93
VI. Canals of Eozoon, Magnified, from Photographs 127
VII. Nature-print of Large Laminated Specimen 169
VIII. Eozoon With Chrysotile, etc. 207
WOODCUTS.
FIG. PAGE
1. General Section 9
2. Laurentian Hills 11
3. Section of Laurentian 13
4. Laurentian Map 16
5. Section at St. Pierre 22
6. Sketch of Rocks at St. Pierre 22
7. Eozoon from Burgess 36
8, 9. Eozoon from Calumet 39
10. Canals of Eozoon 41
11. Nummuline Wall 43
12. Amœba 60
13. Actinophrys 60
14. Entosolenia 62
15. Biloculina 62
16. Polystomella 62
17. Polymorphina 63
18. Archæospherinæ 67
19. Nummulites 73
20. Calcarina 73
21. Foraminiferal Rock-builders 75
21_a_. Casts of Cells of Eozoon 92
22. Modes of Mineralization 96
23. Silurian Organic Limestone 98
24. Wall of Eozoon Penetrated with Canals 98
25. Crinoid Infiltrated with Silicate 103
26. Shell Infiltrated with Silicate 104
27. Diagram of Proper Wall, etc. 106
28, 29. Casts of Canals 107
30. Eozoon from Tudor 111
31. Acervuline Variety of Eozoon 135
32, 33, 34. Archæospherinæ 137, 138
35. Annelid Burrows 140
36. Archæospherinæ 148
37. Eozoon Bavaricum 149
38, 39, 40. Archæocyathus 152, 153
41. Archæocyathus (Structure of) 154
42. Stromatopora 157
43. Stromatopora (Structure of) 158
44. Caunopora 159
45. Cœnostroma 160
46. Receptaculites 162
47, 48. Receptaculites (Structure of) 163
49. Laminæ of Eozoon 176
THE DAWN OF LIFE.
CHAPTER I.
INTRODUCTORY.
Every one has heard of, or ought to have heard of, _Eozoon Canadense_,
the Canadian Dawn-animal, the sole fossil of the ancient Laurentian
rocks of North America, the earliest known representative on our planet
of those wondrous powers of animal life which culminate and unite
themselves with the spirit-world in man himself. Yet few even of those
to whom the name is familiar, know how much it implies, and how strange
and wonderful is the story which can be evoked from this first-born of
old ocean.
No one probably believes that animal life has been an eternal
succession of like forms of being. We are familiar with the idea that
in some way it was introduced; and most men now know, either from the
testimony of Genesis or geology, or of both, that the lower forms
of animal life were introduced first, and that these first living
creatures had their birth in the waters, which are still the prolific
mother of living things innumerable. Further, there is a general
impression that it would be the most appropriate way that the great
procession of animal existence should commence with the humblest types
known to us, and should march on in successive bands of gradually
increasing dignity and power, till man himself brings up the rear.
Do we know the first animal? Can we name it, explain its structure,
and state its relations to its successors? Can we do this by inference
from the succeeding types of being; and if so, do our anticipations
agree with any actual reality disinterred from the earth's crust? If we
could do this, either by inference or actual discovery, how strange it
would be to know that we had before us even the remains of the first
creature that could feel or will, and could place itself in vital
relation with the great powers of inanimate nature. If we believe in a
Creator, we shall feel it a solemn thing to have access to the first
creature into which He breathed the breath of life. If we hold that all
things have been evolved from collision of dead forces, then the first
molecules of matter which took upon themselves the responsibility of
living, and, aiming at the enjoyment of happiness, subjected themselves
to the dread alternatives of pain and mortality, must surely evoke
from us that filial reverence which we owe to the authors of our own
being, if they do not involuntarily draw forth even a superstitious
adoration. The veneration of the old Egyptian for his sacred animals
would be a comparatively reasonable idolatry, if we could imagine any
of these animals to have been the first that emerged from the domain
of dead matter, and the first link in a reproductive chain of being
that produced all the population of the world. Independently of any
such hypotheses, all students of nature must regard with surpassing
interest the first bright streaks of light that break on the long reign
of primeval night and death, and presage the busy day of teeming animal
existence.
No wonder then that geologists have long and earnestly groped in the
rocky archives of the earth in search of some record of this patriarch
of the animal kingdom. But after long and patient research, there still
remained a large residuum of the oldest rocks, destitute of all traces
of living beings, and designated by the hopeless name "Azoic,"--the
formations destitute of remains of life, the stony records of a
lifeless world. So the matter remained till the Laurentian rocks of
Canada, lying at the base of these old Azoic formations, afforded
forms believed to be of organic origin. The discovery was hailed
with enthusiasm by those who had been prepared by previous study to
receive it. It was regarded with feeble and not very intelligent faith
by many more, and was met with half-concealed or open scepticism by
others. It produced a copious crop of descriptive and controversial
literature, but for the most part technical, and confined to scientific
transactions and periodicals, read by very few except specialists.
Thus, few even of geological and biological students have clear ideas
of the real nature and mode of occurrence of these ancient organisms,
and of their relations to better known forms of life; while the crudest
and most inaccurate ideas have been current in lectures and popular
books, and even in text-books, although to the minds of those really
acquainted with the facts, all the disputed points have long ago been
satisfactorily settled, and the true nature and affinities of Eozoon
are distinctly and satisfactorily understood.
This state of things has long ceased to be desirable in the interests
of science, since the settlement of the questions raised is in the
highest degree important to the history of life. We cannot, it is true,
affirm that Eozoon is in reality the long sought prototype of animal
existence; but it is for us at present the last organic foothold, on
which we can poise ourselves, that we may look back into the abyss
of the infinite past, and forward to the long and varied progress of
life in geological time. Its consideration, therefore, is certain,
if properly entered into, to be fruitful of interesting and valuable
thought, and to form the best possible introduction to the history of
life in connection with geology.
It is for these reasons, and because I have been connected with this
great discovery from the first, and have for the last ten years given
to it an amount of labour and attention far greater than could be
adequately represented by short and technical papers, that I have
planned the present work. In it I propose to give a popular, yet
as far as possible accurate, account of all that is known of the
Dawn-animal of the Laurentian rocks of Canada. This will include,
firstly: a descriptive notice of the Laurentian formation itself.
Secondly: a history of the steps which led to the discovery and proper
interpretation of this ancient fossil. Thirdly: the description of
Eozoon, and the explanation of the manner in which its remains have
been preserved. Fourthly: inquiries as to forms of animal life, its
contemporaries and immediate successors, or allied to it by zoological
affinity. Fifthly: the objections which have been urged against its
organic nature. And sixthly: the summing up of the lessons in science
which it is fitted to teach. On these points, while I shall endeavour
to state the substance of all that has been previously published, I
shall bring forward many new facts illustrative of points hitherto more
or less obscure, and shall endeavour so to picture these in themselves
and their relations, as to give distinct and vivid impressions to the
reader.
For the benefit of those who may not have access to the original
memoirs, or may not have time to consult them, I shall append to the
several chapters some of the technical details. These may be omitted by
the general reader; but will serve to make the work more complete and
useful as a book of reference.
The only preparation necessary for the unscientific reader of this
work, will be some little knowledge of the division of geological time
into successive ages, as represented by the diagram of formations
appended to this chapter, and more full explanations may be obtained by
consulting any of the numerous elementary manuals on geology, or "The
Story of the Earth and Man," by the writer of the present work.
TABULAR VIEW OF THE EARTH'S GEOLOGICAL HISTORY.
_Animal Kingdom._ _Geological Periods._ _Vegetable Kingdom._
Age of Man. CENOZOIC, OR Modern. Age of Angiosperms
NEOZOIC, OR Post-Pliocene, and Palms.
TERTIARY or Pleistocene.
Pliocene.
Miocene.
Age of Mammals. Eocene.
Age of Reptiles. MESOZOIC Cretaceous. Age of Cycads and
Jurassic. Pines.
Triassic.
Age of Amphibians PALÆOZOIC Permian. Age of Acrogens
and Fishes. Carboniferous. and Gymnosperms.
Erian, or Devonian.
Age of Mollusks, Upper Silurian.
Corals, and Lower Silurian, or
Crustaceans. Siluro-Cambrian.
Cambrian or
Primordial. Age of Algæ.
Age of Protozoa, EOZOIC Huronian. Beginning of Age
and dawn of Upper Laurentian. of Algæ.
Animal Life. Lower Laurentian.
[Illustration:
Plate II.
MAP SHEWING THE DISTRIBUTION OF THE LAURENTIAN LIMESTONES HOLDING EOZOON
IN THE COUNTIES OF OTTAWA & ARGENTEUIL.
_Drawn by M. R. Barlow_ _Stanford's Geog. Estab^t. Charing Cross, London._
Reprinted with additions from the Report of the Geology of Canada,
by Sir W. Logan, F.R.S., 1863.]
CHAPTER II.
THE LAURENTIAN ROCKS.
As we descend in depth and time into the earth's crust, after passing
through nearly all the vast series of strata constituting the monuments
of geological history, we at length reach the Eozoic or Laurentian
rocks, deepest and oldest of all the formations known to the geologist,
and more thoroughly altered or metamorphosed by heat and heated
moisture than any others. These rocks, at one time known as Azoic,
being supposed destitute of all remains of living things, but now more
properly Eozoic, are those in which the first bright streaks of the
dawn of life make their appearance.[A]
[Footnote A: Dana has recently proposed the term "_Archæan_," on the
ground that some of these rocks are as yet unfossiliferous but as the
oldest known part of them contains fossils, there seems no need for
this new name.]
The name Laurentian, given originally to the Canadian development of
these rocks by Sir William Logan, but now applied to them throughout
the world, is derived from a range of hills lying north of the
St. Lawrence valley, which the old French geographers named the
Laurentides. In these hills the harder rocks of this old formation
rise to considerable heights, and form the highlands separating the
St. Lawrence valley from the great plain fronting on Hudson's Bay
and the Arctic Sea. At first sight it may seem strange that rocks so
ancient should anywhere appear at the surface, especially on the tops
of hills; but this is a necessary result of the mode of formation of
our continents. The most ancient sediments deposited in the sea were
those first elevated into land, and first altered and hardened by heat.
Upheaved in the folding of the earth's crust into high and rugged
ridges, they have either remained uncovered with newer sediments, or
have had such as were deposited on them washed away; and being of a
hard and resisting nature, they have remained comparatively unworn when
rocks much more modern have been swept off by denuding agencies.
But the exposure of the old Laurentian skeleton of mother earth is not
confined to the Laurentide Hills, though these have given the formation
its name. The same ancient rocks appear in the Adirondack mountains
of New York, and in the patches which at lower levels protrude from
beneath the newer formations along the American coast from Newfoundland
to Maryland. The older gneisses of Norway, Sweden, and the Hebrides,
of Bavaria and Bohemia, belong to the same age, and it is not unlikely
that similar rocks in many other parts of the old continent will be
found to be of as great antiquity. In no part of the world, however,
are the Laurentian rocks more extensively distributed or better
known than in North America; and to this as the grandest and most
instructive development of them, and that which first afforded organic
remains, we may more especially devote our attention. Their general
relations to the other formations of America may be learned from the
rough generalised section (fig. 1); in which the crumpled and contorted
Laurentian strata of Canada are seen to underlie unconformably the
comparatively flat Silurian beds, which are themselves among the oldest
monuments of the geological history of the earth.
[Illustration: Fig. 1. _General Section, showing the Relations of
the Laurentian and Palæozoic Rocks in Canada._ (L.) Laurentian. (1.)
Cambrian, or Primordial. (2.) Lower Silurian. (3.) Upper Silurian. (4.)
Devonian and Carboniferous.]
The Laurentian rocks, associated with another series only a little
younger, the Huronian, form a great belt of broken and hilly country,
extending from Labrador across the north of Canada to Lake Superior,
and thence bending northward to the Arctic Sea. Everywhere on the lower
St. Lawrence they appear as ranges of billowy rounded ridges on the
north side of the river; and as viewed from the water or the southern
shore, especially when sunset deepens their tints to blue and violet,
they present a grand and massive appearance, which, in the eye of
the geologist, who knows that they have endured the battles and the
storms of time longer than any other mountains, invests them with a
dignity which their mere elevation would fail to give. (Fig. 2.) In the
isolated mass of the Adirondacks, south of the Canadian frontier, they
rise to a still greater elevation, and form an imposing mountain group,
almost equal in height to their somewhat more modern rivals, the White
Mountains, which face them on the opposite side of Lake Champlain.
The grandeur of the old Laurentian ranges is, however, best displayed
where they have been cut across by the great transverse gorge of the
Saguenay, and where the magnificent precipices, known as Capes Trinity
and Eternity, look down from their elevation of 1500 feet on a fiord,
which at their base is more than 100 fathoms deep (see frontispiece).
The name Eternity applied to such a mass is geologically scarcely a
misnomer, for it dates back to the very dawn of geological time, and is
of hoar antiquity in comparison with such upstart ranges as the Andes
and the Alps.
[Illustration: Fig. 2. _Laurentian Hills opposite Kamouraska, Lower St.
Lawrence._
The islands in front are Primordial.]
On a nearer acquaintance, the Laurentian country appears as a broken
and hilly upland and highland district, clad in its pristine state
with magnificent forests, but affording few attractions to the
agriculturist, except in the valleys, which follow the lines of its
softer beds, while it is a favourite region for the angler, the hunter,
and the lumberman. Many of the Laurentian townships of Canada are,
however, already extensively settled, and the traveller may pass
through a succession of more or less cultivated valleys, bounded by
rocks or wooded hills and crags, and diversified by running streams and
romantic lakes and ponds, constituting a country always picturesque
and often beautiful, and rearing a strong and hardy population. To
the geologist it presents in the main immensely thick beds of gneiss,
and similar metamorphic and crystalline rocks, contorted in the most
remarkable manner, so that if they could be flattened out they would
serve as a skin much too large for mother earth in her present state,
so much has she shrunk and wrinkled since those youthful days when the
Laurentian rocks were her outer covering. (Fig. 3.)
The elaborate sections of Sir William Logan show that these old rocks
are divisible into two series, the Lower and Upper Laurentian; the
latter being the newer of the two, and perhaps separated from the
former by a long interval of time; but this Upper Laurentian being
probably itself older than the Huronian series, and this again older
than all the other stratified rocks. The Lower Laurentian, which
attains to a thickness of more than 20,000 feet, consists of stratified
granitic rocks or gneisses, of indurated sandstone or quartzite, of
mica and hornblende schist, and of crystalline limestones or marbles,
and iron ores, the whole interstratified with each other. The Upper
Laurentian, which is 10,000 feet thick at least, consists in part of
similar rocks, but associated with great beds of triclinic feldspar,
especially of that peculiar variety known as labradorite, or Labrador
feldspar, and which sometimes by its wonderful iridescent play of
colours becomes a beautiful ornamental stone.
I cannot describe such rocks, but their names will tell something to
those who have any knowledge of the older crystalline materials of the
earth's crust. To those who have not, I would advise a visit to some
cliff on the lower St. Lawrence, or the Hebridean coasts, or the shore
of Norway, where the old hard crystalline and gnarled beds present
their sharp edges to the ever raging sea, and show their endless
alternations of various kinds and colours of strata often diversified
with veins and nests of crystalline minerals. He who has seen and
studied such a section of Laurentian rock cannot forget it.
[Illustration: Fig. 3. _Section from Petite Nation Seigniory to St.
Jerome_ (60 miles). _After Sir W. E. Logan._
(_a, b._) Upper Laurentian. (_c._) Fourth gneiss. (_d´._) Third
limestone. (_d._) Third gneiss. (_e´._) Second limestone. (_x._)
Porphyry. (_y._) Granite.]
All the constituents of the Laurentian series are in that state known
to geologists as metamorphic. They were once sandstones, clays, and
limestones, such as the sea now deposits, or such as form the common
plebeian rocks of everyday plains and hills and coast sections. Being
extremely old, however, they have been buried deep in the bowels of
the earth under the newer deposits, and hardened by the action of
pressure and of heat and heated water. Whether this heat was part
of that originally belonging to the earth when a molten mass, and
still existing in its interior after aqueous rocks had begun to form
on its surface, or whether it is a mere mechanical effect of the
intense compression which these rocks have suffered, may be a disputed
question; but the observations of Sorby and of Hunt (the former in
connection with the microscopic structure of rocks, and the latter
in connection with the chemical conditions of change) show that no
very excessive amount of heat would be required. These observations
and those of Daubrée indicate that crystallization like that of the
Laurentian rocks might take place at a temperature of not over 370° of
the centigrade thermometer.
The study of those partial alterations which take place in the
vicinity of volcanic and older aqueous masses of rock confirms these
conclusions, so that we may be said to know the precise conditions
under which sediments may be hardened into crystalline rocks, while
the bedded character and the alternations of different layers in the
Laurentian rocks, as well as the indications of contemporary marine
life which they contain, show that they actually are such altered
sediments. (See Note D.)
It is interesting to notice here that the Laurentian rocks thus
interpreted show that the oldest known portions of our continents were
formed in the waters. They are oceanic sediments deposited perhaps when
there was no dry land or very little, and that little unknown to us
except in so far as its debris may have entered into the composition
of the Laurentian rocks themselves. Thus the earliest condition of the
earth known to the geologist is one in which old ocean was already
dominant on its surface; and any previous condition when the surface
was heated, and the water constituted an abyss of vapours enveloping
its surface, or any still earlier condition in which the earth was
gaseous or vaporous, is a matter of mere inference, not of actual
observation. The formless and void chaos is a deduction of chemical and
physical principles, not a fact observed by the geologist. Still we
know, from the great dykes and masses of igneous or molten rock which
traverse the Laurentian beds, that even at that early period there were
deep-seated fires beneath the crust; and it is quite possible that
volcanic agencies then manifested themselves, not only with quite as
great intensity, but also in the same manner, as at subsequent times.
It is thus not unlikely that much of the land undergoing waste in the
earlier Laurentian time was of the same nature with recent volcanic
ejections, and that it formed groups of islands in an otherwise
boundless ocean.
However this may be, the distribution and extent of these
pre-Laurentian lands is, and probably ever must be, unknown to us; for
it was only after the Laurentian rocks had been deposited, and after
the shrinkage of the earth's crust in subsequent times had bent and
contorted them, that the foundations of the continents were laid. The
rude sketch map of America given in fig. 4 will show this, and will
also show that the old Laurentian mountains mark out the future form of
the American continent.
[Illustration: Fig. 4. _The Laurentian Nucleus of the American
Continent._]
Rocks so highly altered as the Laurentian beds can scarcely be expected
to hold well characterized fossil remains, and those geologists who
entertained any hope that such remains might have been preserved, long
looked in vain for their actual discovery. Still, as astronomers have
suspected the existence of unknown planets from observing perturbations
not accounted for, and as voyagers have suspected the approach to
unknown regions by the appearance of floating wood or stray land birds,
anticipations of such discoveries have been entertained and expressed
from time to time. Lyell, Dana, and Sterry Hunt more especially, have
committed themselves to such speculations. The reasons assigned may be
stated thus:--
Assuming the Laurentian rocks to be altered sediments, they must, from
their great extent, have been deposited in the ocean; and if there had
been no living creatures in the waters, we have no reason to believe
that they would have consisted of anything more than such sandy and
muddy debris as may be washed away from wasting rocks originally of
igneous origin. But the Laurentian beds contain other materials than
these. No formations of any geological age include thicker or more
extensive limestones. One of the beds measured by the officers of the
Geological Survey, is stated to be 1500 feet in thickness, another is
1250 feet thick, and a third 750 feet; making an aggregate of 3500
feet.[B] These beds may be traced, with more or less interruption,
for hundreds of miles. Whatever the origin of such limestones, it
is plain that they indicate causes equal in extent, and comparable
in power and duration, with those which have produced the greatest
limestones of the later geological periods. Now, in later formations,
limestone is usually an organic rock, accumulated by the slow gathering
from the sea-water, or its plants, of calcareous matter, by corals,
foraminifera, or shell-fish, and the deposition of their skeletons,
either entire or in fragments, in the sea-bottom. The most friable
chalk and the most crystalline limestones have alike been formed in
this way. We know of no reason why it should be different in the
Laurentian period. When, therefore, we find great and conformable
beds of limestone, such as those described by Sir William Logan in
the Laurentian of Canada, we naturally imagine a quiet sea-bottom, in
which multitudes of animals of humble organization were accumulating
limestone in their hard parts, and depositing this in gradually
increasing thickness from age to age. Any attempts to account otherwise
for these thick and greatly extended beds, regularly interstratified
with other deposits, have so far been failures, and have arisen either
from a want of comprehension of the nature and magnitude of the
appearances to be explained, or from the error of mistaking the true
bedded limestones for veins of calcareous spar.
[Footnote B: Logan: _Geology of Canada_, p. 45.]
The Laurentian rocks contain great quantities of carbon, in the form of
graphite or plumbago. This does not occur wholly, or even principally,
in veins or fissures, but in the substance of the limestone and gneiss,
and in regular layers. So abundant is it, that I have estimated the
amount of carbon in one division of the Lower Laurentian of the Ottawa
district at an aggregate thickness of not less than twenty to thirty
feet, an amount comparable with that in the true coal formation itself.
Now we know of no agency existing in present or in past geological
time capable of deoxidizing carbonic acid, and fixing its carbon as
an ingredient in permanent rocks, except vegetable life. Unless,
therefore, we suppose that there existed in the Laurentian age a vast
abundance of vegetation, either in the sea or on the land, we have no
means of explaining the Laurentian graphite.
The Laurentian formation contains great beds of oxide of iron,
sometimes seventy feet in thickness. Here again we have an evidence of
organic action; for it is the deoxidizing power of vegetable matter
which has in all the later formations been the efficient cause in
producing bedded deposits of iron. This is the case in modern bog and
lake ores, in the clay iron-stones of the coal measures, and apparently
also in the great ore beds of the Silurian rocks. May not similar
causes have been at work in the Laurentian period?
Any one of these reasons might, in itself, be held insufficient to
prove so great and, at first sight, unlikely a conclusion as that of
the existence of abundant animal and vegetable life in the Laurentian;
but the concurrence of the whole in a series of deposits unquestionably
marine, forms a chain of evidence so powerful that it might command
belief even if no fragment of any organic and living form or structure
had ever been recognised in these ancient rocks.
Such was the condition of the matter until the existence of supposed
organic remains was announced by Sir W. Logan, at the American
Association for the Advancement of Science, in Springfield, in 1859;
and we may now proceed to narrate the manner of this discovery, and how
it has been followed up.
Before doing so, however, let us visit Eozoon in one of its haunts
among the Laurentian Hills. One of the most noted repositories of its
remains is the great Grenville band of limestone (see section, fig. 3,
and map), the outcrop of which may be seen in our map of the country
near the Ottawa, twisting itself like a great serpent in the midst of
the gneissose rocks; and one of the most fruitful localities is at a
place called Côte St. Pierre on this band. Landing, as I did, with
Mr. Weston, of the Geological Survey, last autumn, at Papineauville,
we find ourselves on the Laurentian rocks, and pass over one of the
great bands of gneiss for about twelve miles, to the village of St.
André Avelin. On the road we see on either hand abrupt rocky ridges,
partially clad with forest, and sometimes showing on their flanks the
stratification of the gneiss in very distinct parallel bands, often
contorted, as if the rocks, when soft, had been wrung as a washer-woman
wrings clothes. Between the hills are little irregular valleys, from
which the wheat and oats have just been reaped, and the tall Indian
corn and yellow pumpkins are still standing in the fields. Where not
cultivated, the land is covered with a rich second growth of young
maples, birches, and oaks, among which still stand the stumps and tall
scathed trunks of enormous pines, which constituted the original
forest. Half way we cross the Nation River, a stream nearly as large as
the Tweed, flowing placidly between wooded banks, which are mirrored in
its surface; but in the distance we can hear the roar of its rapids,
dreaded by lumberers in their spring drivings of logs, and which we
were told swallowed up five poor fellows only a few months ago. Arrived
at St. André, we find a wider valley, the indication of the change to
the limestone band, and along this, with the gneiss hills still in view
on either hand, and often encroaching on the road, we drive for five
miles more to Côte St. Pierre. At this place the lowest depression of
the valley is occupied by a little pond, and, hard by, the limestone,
protected by a ridge of gneiss, rises in an abrupt wooded bank by
the roadside, and a little further forms a bare white promontory,
projecting into the fields. Here was Mr. Love's original excavation,
whence some of the greater blocks containing Eozoon were taken, and a
larger opening made by an enterprising American on a vein of fibrous
serpentine, yielding "rock cotton," for packing steam pistons and
similar purposes. (Figs. 5 and 6.)
[Illustration: Fig. 5. _Attitude of Limestone at St. Pierre._
(_a._) Gneiss band in the Limestone. (_b._) Limestone with Eozoon.
(_c._) Diorite and Gneiss.]
[Illustration: Fig. 6. _Gneiss and Limestone at St. Pierre._
(_a._) Limestone. (_b._) Gneiss and Diorite.]
The limestone is here highly inclined and much contorted, and in all
the excavations a thickness of about 100 feet of it may be exposed.
It is white and crystalline, varying much however in coarseness in
different bands. It is in some layers pure and white, in others it
is traversed by many gray layers of gneissose and other matter, or
by irregular bands and nodules of pyroxene and serpentine, and it
contains subordinate beds of dolomite. In one layer only, and this
but a few feet thick, does the Eozoon occur in any abundance in a
perfect state, though fragments and imperfectly preserved specimens
abound in other parts of the bed. It is a great mistake to suppose
that it constitutes whole beds of rock in an uninterrupted mass.
Its true mode of occurrence is best seen on the weathered surfaces
of the rock, where the serpentinous specimens project in irregular
patches of various sizes, sometimes twisted by the contortion of the
beds, but often too small to suffer in this way. On such surfaces
the projecting patches of the fossil exhibit laminæ of serpentine so
precisely like the _Stromatoporæ_ of the Silurian rocks, that any
collector would pounce upon them at once as fossils. In some places
these small weathered specimens can be easily chipped off from the
crumbling surface of the limestone; and it is perhaps to be regretted
that they have not been more extensively shown to palæontologists, with
the cut slices which to many of them are so problematical. One of the
original specimens, brought from the Calumet, and now in the Museum
of the Geological Survey of Canada, was of this kind, and much finer
specimens from Côte St. Pierre are now in that collection and in my
own. A very fine example is represented, on a reduced scale, in Plate
III., which is taken from an original photograph.[C] In some of the
layers are found other and more minute fossils than Eozoon, and these,
together with its fragmental remains, as ingredients in the limestone,
will be discussed in the sequel. We may merely notice here that the
most abundant layer of Eozoon at this place, occurs near the base of
the great limestone band, and that the upper layers in so far as seen
are less rich in it. Further, there is no necessary connection between
Eozoon and the occurrence of serpentine, for there are many layers
full of bands and lenticular masses of that mineral without any Eozoon
except occasional fragments, while the fossil is sometimes partially
mineralized with pyroxene, dolomite, or common limestone. The section
in fig. 5 will serve to show the attitude of the limestone at this
place, while the more general section, fig. 3, taken from Sir William
Logan, shows its relation to the other Laurentian rocks, and the sketch
in fig. 6 shows its appearance as a feature on the surface of the
country.
[Footnote C: By Mr. Weston, of the Geological Survey of Canada.]
NOTES TO CHAPTER II.
(A.) Sir William E. Logan on the Laurentian System.
[_Journal of Geological Society of London_, February, 1865.]
After stating the division of the Laurentian series into the two
great groups of the Upper and Lower Laurentian, Sir William goes on
to say:--
"The united thickness of these two groups in Canada cannot be less
than 30,000 feet, and probably much exceeds it. The Laurentian of
the west of Scotland, according to Sir Roderick Murchison, also
attains a great thickness. In that region the Upper Laurentian or
Labrador series, has not yet been separately recognised; but from
Mr. McCulloch's description, as well as from the specimens collected
by him, and now in the Museum of the Geological Society of London,
it can scarcely be doubted that the Labrador series occurs in Skye.
The labradorite and hypersthene rocks from that island are identical
with those of the Labrador series in Canada and New York, and unlike
those of any formation at any other known horizon. This resemblance
did not escape the notice of Emmons, who, in his description of the
Adirondack Mountains, referred these rocks to the hypersthene rock
of McCulloch, although these observers, on the opposite sides of
the Atlantic, looked upon them as unstratified. In the _Canadian
Naturalist_ for 1862, Mr. Thomas Macfarlane, for some time resident
in Norway, and now in Canada, drew attention to the striking
resemblance between the Norwegian primitive gneiss formation, as
described by Naumann and Keilhau, and observed by himself, and the
Laurentian, including the Labrador group; and the equally remarkable
similarity of the lower part of the primitive slate formation
to the Huronian series, which is a third Canadian group. These
primitive series attain a great thickness in the north of Europe, and
constitute the main features of Scandinavian geology.
"In Bavaria and Bohemia there is an ancient gneissic series. After
the labours in Scotland, by which he was the first to establish a
Laurentian equivalent in the British Isles, Sir Roderick Murchison,
turning his attention to this central European mass, placed it on the
same horizon. These rocks, underlying Barrande's Primordial zone,
with a great development of intervening clay-slate, extend southward
in breadth to the banks of the Danube, with a prevailing dip towards
the Silurian strata. They had previously been studied by Gümbel and
Crejci, who divided them into an older reddish gneiss and a newer
grey gneiss. But, on the Danube, the mass which is furthest removed
from the Silurian rocks being a grey gneiss, Gümbel and Crejci
account for its presence by an inverted fold in the strata; while
Sir Roderick places this at the base, and regards the whole as a
single series, in the normal fundamental position of the Laurentian
of Scotland and of Canada. Considering the colossal thickness given
to the series (90,000 feet), it remains to be seen whether it may
not include both the Lower and Upper Laurentian, and possibly, in
addition, the Huronian.
"This third Canadian group (the Huronian) has been shown by my
colleague, Mr. Murray, to be about 18,000 feet thick, and to consist
chiefly of quartzites, slate-conglomerates, diorites, and limestones.
The horizontal strata which form the base of the Lower Silurian in
western Canada, rest upon the upturned edges of the Huronian series;
which, in its turn, unconformably overlies the Lower Laurentian. The
Huronian is believed to be more recent than the Upper Laurentian
series, although the two formations have never yet been seen in
contact.
"The united thickness of these three great series may possibly
far surpass that of all the succeeding rocks from the base of the
Palæozoic series to the present time. We are thus carried back to a
period so far remote, that the appearance of the so-called Primordial
fauna may by some be considered a comparatively modern event. We,
however, find that, even during the Laurentian period, the same
chemical and mechanical processes which have ever since been at
work disintegrating and reconstructing the earth's crust were in
operation as now. In the conglomerates of the Huronian series there
are enclosed boulders derived from the Laurentian, which seem to show
that the parent rock was altered to its present crystalline condition
before the deposit of the newer formation; while interstratified with
the Laurentian limestones there are beds of conglomerate, the pebbles
of which are themselves rolled fragments of a still older laminated
sand-rock, and the formation of these beds leads us still further
into the past.
"In both the Upper and Lower Laurentian series there are several
zones of limestone, each of sufficient volume to constitute an
independent formation. Of these calcareous masses it has been
ascertained that three, at least, belong to the Lower Laurentian. But
as we do not as yet know with certainty either the base or the summit
of this series, these three may be conformably followed by many more.
Although the Lower and Upper Laurentian rocks spread over more than
200,000 square miles in Canada, only about 1500 square miles have yet
been fully and connectedly examined in any one district, and it is
still impossible to say whether the numerous exposures of Laurentian
limestone met with in other parts of the province are equivalent to
any of the three zones, or whether they overlie or underlie them all."
(B.) Dr. Sterry Hunt on the Probable Existence of Life in the
Laurentian Period.
Dr. Hunt's views on this subject were expressed in the _American
Journal of Science_, [2], vol. xxxi., p. 395. From this article,
written in 1861, after the announcement of the existence of laminated
forms supposed to be organic in the Laurentian, by Sir W. E. Logan,
but before their structure and affinities had been ascertained, I
quote the following sentences:--
"We see in the Laurentian series beds and veins of metallic
sulphurets, precisely as in more recent formations; and the extensive
beds of iron ore, hundreds of feet thick, which abound in that
ancient system, correspond not only to great volumes of strata
deprived of that metal, but, as we may suppose, to organic matters
which, but for the then great diffusion of iron-oxyd in conditions
favourable for their oxidation, might have formed deposits of mineral
carbon far more extensive than those beds of plumbago which we
actually meet in the Laurentian strata. All these conditions lead us
then to conclude the existence of an abundant vegetation during the
Laurentian period."
(C.) The Graphite of the Laurentian.
The following is from a paper by the author, in the _Journal of the
Geological Society_, for February, 1870:--
"The graphite of the Laurentian of Canada occurs both in beds and in
veins, and in such a manner as to show that its origin and deposition
are contemporaneous with those of the containing rock. Sir William
Logan states[D] that 'the deposits of plumbago generally occur in the
limestones or in their immediate vicinity, and granular varieties
of the rock often contain large crystalline plates of plumbago. At
other times this mineral is so finely disseminated as to give a
bluish-gray colour to the limestone, and the distribution of bands
thus coloured, seems to mark the stratification of the rock.' He
further states:--'The plumbago is not confined to the limestones;
large crystalline scales of it are occasionally disseminated in
pyroxene rock or pyrallolite, and sometimes in quartzite and in
feldspathic rocks, or even in magnetic oxide of iron.' In addition
to these bedded forms, there are also true veins in which graphite
occurs associated with calcite, quartz, orthoclase, or pyroxene,
and either in disseminated scales, in detached masses, or in
bands or layers 'separated from each other and from the wall rock
by feldspar, pyroxene, and quartz.' Dr. Hunt also mentions the
occurrence of finely granular varieties, and of that peculiarly
waved and corrugated variety simulating fossil wood, though really a
mere form of laminated structure, which also occurs at Warrensburgh,
New York, and at the Marinski mine in Siberia. Many of the veins
are not true fissures, but rather constitute a network of shrinkage
cracks or segregation veins traversing in countless numbers the
containing rock, and most irregular in their dimensions, so that
they often resemble strings of nodular masses. It has been supposed
that the graphite of the veins was originally introduced as a liquid
hydrocarbon. Dr. Hunt, however, regards it as possible that it
may have been in a state of aqueous solution;[E] but in whatever
way introduced, the character of the veins indicates that in the
case of the greater number of them the carbonaceous material must
have been derived from the bedded rocks traversed by these veins,
while there can be no doubt that the graphite found in the beds has
been deposited along with the calcareous matter or muddy and sandy
sediment of which these beds were originally composed.
[Footnote D: _Geology of Canada_, 1863.]
[Footnote E: _Report of the Geological Survey of Canada_, 1866.]
"The quantity of graphite in the Lower Laurentian series is enormous.
In a recent visit to the township of Buckingham, on the Ottawa
River, I examined a band of limestone believed to be a continuation
of that described by Sir W. E. Logan as the Green Lake Limestone.
It was estimated to amount, with some thin interstratified bands
of gneiss, to a thickness of 600 feet or more, and was found to
be filled with disseminated crystals of graphite and veins of the
mineral to such an extent as to constitute in some places one-fourth
of the whole; and making every allowance for the poorer portions,
this band cannot contain in all a less vertical thickness of pure
graphite than from twenty to thirty feet. In the adjoining township
of Lochaber Sir W. E. Logan notices a band from twenty-five to thirty
feet thick, reticulated with graphite veins to such an extent as
to be mined with profit for the mineral. At another place in the
same district a bed of graphite from ten to twelve feet thick, and
yielding twenty per cent. of the pure material, is worked. When it
is considered that graphite occurs in similar abundance at several
other horizons, in beds of limestone which have been ascertained by
Sir W. E. Logan to have an aggregate thickness of 3500 feet, it is
scarcely an exaggeration to maintain that the quantity of carbon in
the Laurentian is equal to that in similar areas of the Carboniferous
system. It is also to be observed that an immense area in Canada
appears to be occupied by these graphitic and Eozoon limestones, and
that rich graphitic deposits exist in the continuation of this system
in the State of New York, while in rocks believed to be of this age
near St. John, New Brunswick, there is a very thick bed of graphitic
limestone, and associated with it three regular beds of graphite,
having an aggregate thickness of about five feet.[F]
[Footnote F: Matthew, in _Quart. Journ. Geol. Soc._, vol. xxi., p. 423.
_Acadian Geology_, p. 662.]
"It may fairly be assumed that in the present world and in those
geological periods with whose organic remains we are more familiar
than with those of the Laurentian, there is no other source of
unoxidized carbon in rocks than that furnished by organic matter,
and that this has obtained its carbon in all cases, in the first
instance, from the deoxidation of carbonic acid by living plants. No
other source of carbon can, I believe, be imagined in the Laurentian
period. We may, however, suppose either that the graphitic matter
of the Laurentian has been accumulated in beds like those of coal,
or that it has consisted of diffused bituminous matter similar to
that in more modern bituminous shales and bituminous and oil-bearing
limestones. The beds of graphite near St. John, some of those in the
gneiss at Ticonderoga in New York, and at Lochaber and Buckingham
and elsewhere in Canada, are so pure and regular that one might
fairly compare them with the graphitic coal of Rhode Island. These
instances, however, are exceptional, and the greater part of the
disseminated and vein graphite might rather be compared in its mode
of occurrence to the bituminous matter in bituminous shales and
limestones.
"We may compare the disseminated graphite to that which we find in
those districts of Canada in which Silurian and Devonian bituminous
shales and limestones have been metamorphosed and converted into
graphitic rocks not dissimilar to those in the less altered portions
of the Laurentian.[G] In like manner it seems probable that the
numerous reticulating veins of graphite may have been formed by
the segregation of bituminous matter into fissures and planes of
least resistance, in the manner in which such veins occur in modern
bituminous limestones and shales. Such bituminous veins occur in
the Lower Carboniferous limestone and shale of Dorchester and
Hillsborough, New Brunswick, with an arrangement very similar to that
of the veins of graphite; and in the Quebec rocks of Point Levi,
veins attaining to a thickness of more than a foot, are filled with a
coaly matter having a transverse columnar structure, and regarded by
Logan and Hunt as an altered bitumen. These palæozoic analogies would
lead us to infer that the larger part of the Laurentian graphite
falls under the second class of deposits above mentioned, and that,
if of vegetable origin, the organic matter must have been thoroughly
disintegrated and bituminized before it was changed into graphite.
This would also give a probability that the vegetation implied was
aquatic, or at least that it was accumulated under water.
[Footnote G: Granby, Melbourne, Owl's Head, etc., _Geology of Canada_,
1863, p. 599.]
"Dr. Hunt has, however, observed an indication of terrestrial
vegetation, or at least of subaërial decay, in the great beds of
Laurentian iron ore. These, if formed in the same manner as more
modern deposits of this kind, would imply the reducing and solvent
action of substances produced in the decay of plants. In this case
such great ore beds as that of Hull, on the Ottawa, seventy feet
thick, or that near Newborough, 200 feet thick,[H] must represent
a corresponding quantity of vegetable matter which has totally
disappeared. It may be added that similar demands on vegetable matter
as a deoxidizing agent are made by the beds and veins of metallic
sulphides of the Laurentian, though some of the latter are no doubt
of later date than the Laurentian rocks themselves.
[Footnote H: _Geology of Canada_, 1863.]
"It would be very desirable to confirm such conclusions as those
above deduced by the evidence of actual microscopic structure. It is
to be observed, however, that when, in more modern sediments, algæ
have been converted into bituminous matter, we cannot ordinarily
obtain any structural evidence of the origin of such bitumen, and in
the graphitic slates and limestones derived from the metamorphosis of
such rocks no organic structure remains. It is true that, in certain
bituminous shales and limestones of the Silurian system, shreds of
organic tissue can sometimes be detected, and in some cases, as in
the Lower Silurian limestone of the La Cloche mountains in Canada,
the pores of brachiopodous shells and the cells of corals have been
penetrated by black bituminous matter, forming what may be regarded
as natural injections, sometimes of much beauty. In correspondence
with this, while in some Laurentian graphitic rocks, as, for
instance, in the compact graphite of Clarendon, the carbon presents
a curdled appearance due to segregation, and precisely similar to
that of the bitumen in more modern bituminous rocks, I can detect in
the graphitic limestones occasional fibrous structures which may be
remains of plants, and in some specimens vermicular lines, which I
believe to be tubes of Eozoon penetrated by matter once bituminous,
but now in the state of graphite.
"When palæozoic land-plants have been converted into graphite,
they sometimes perfectly retain their structure. Mineral charcoal,
with structure, exists in the graphitic coal of Rhode Island. The
fronds of ferns, with their minutest veins perfect, are preserved
in the Devonian shales of St. John, in the state of graphite; and
in the same formation there are trunks of Conifers (_Dadoxylon
ouangondianum_) in which the material of the cell-walls has been
converted into graphite, while their cavities have been filled with
calcareous spar and quartz, the finest structures being preserved
quite as well as in comparatively unaltered specimens from the
coal-formation.[I] No structures so perfect have as yet been detected
in the Laurentian, though in the largest of the three graphitic beds
at St. John there appear to be fibrous structures which I believe may
indicate the existence of land-plants. This graphite is composed of
contorted and slickensided laminæ, much like those of some bituminous
shales and coarse coals; and in these there are occasional small
pyritous masses which show hollow carbonaceous fibres, in some cases
presenting obscure indications of lateral pores. I regard these
indications, however, as uncertain; and it is not as yet fully
ascertained that these beds at St. John are on the same geological
horizon with the Lower Laurentian of Canada, though they certainly
underlie the Primordial series of the Acadian group, and are
separated from it by beds having the character of the Huronian.
[Footnote I: _Acadian Geology_, p. 535. In calcified specimens the
structures remain in the graphite after decalcification by an acid.]
"There is thus no absolute impossibility that distinct organic
tissues may be found in the Laurentian graphite, if formed from
land-plants, more especially if any plants existed at that time
having true woody or vascular tissues; but it cannot with certainty
be affirmed that such tissues have been found. It is possible,
however, that in the Laurentian period the vegetation of the land may
have consisted wholly of cellular plants, as, for example, mosses and
lichens; and if so, there would be comparatively little hope of the
distinct preservation of their forms or tissues, or of our being able
to distinguish the remains of land-plants from those of Algæ.
"We may sum up these facts and considerations in the following
statements:--First, that somewhat obscure traces of organic structure
can be detected in the Laurentian graphite; secondly, that the
general arrangement and microscopic structure of the substance
corresponds with that of the carbonaceous and bituminous matters
in marine formations of more modern date; thirdly, that if the
Laurentian graphite has been derived from vegetable matter, it has
only undergone a metamorphosis similar in kind to that which organic
matter in metamorphosed sediment of later age has experienced;
fourthly, that the association of the graphitic matter with organic
limestone, beds of iron ore, and metallic sulphides, greatly
strengthens the probability of its vegetable origin; fifthly, that
when we consider the immense thickness and extent of the Eozoonal
and graphitic limestones and iron ore deposits of the Laurentian, if
we admit the organic origin of the limestone and graphite, we must
be prepared to believe that the life of that early period, though it
may have existed under low forms, was most copiously developed, and
that it equalled, perhaps surpassed, in its results, in the way of
geological accumulation, that of any subsequent period."
(D.) Western and other Laurentian Rocks, etc.
In the map of the Laurentian nucleus of America (fig. 4,) I have
not inserted the Laurentian rocks believed to exist in the Rocky
Mountains and other western ranges. Their distribution is at present
uncertain, as well as the date of their elevation. They may indicate
an old line of Laurentian fracture or wrinkling, parallel to the west
coast, and defining its direction. In the map there should be a patch
of Laurentian in the north of Newfoundland, and it should be wider at
the west end of lake Superior.
Full details as to the Laurentian rocks of Canada and sectional
lists of their beds will be found in the _Reports of the Geological
Survey_, and Dr. Hunt has discussed very fully their chemical
characters and metamorphism in his _Chemical and Geological Essays_.
The recent reports of Hitchcock on New Hampshire, and Hayden on
the Western Territories, contain some new facts of interest.
The former recognises in the White Mountain region a series of
gneisses and other altered rocks of Lower Laurentian age, and,
resting unconformably on these, others corresponding to the Upper
Laurentian; while above the latter are other pre-silurian formations
corresponding to the Huronian and probably to the Montalban series of
Hunt. These facts confirm Logan's results in Canada; and Hitchcock
finds many reasons to believe in the existence of life at the time of
the deposition of these old rocks. Hayden's report describes granitic
and gneissose rocks, probably of Laurentian age, as appearing over
great areas in Colorado, Arizona, Utah, and Nevada--showing the
existence of this old metamorphic floor over vast regions of Western
America.
The metamorphism of these rocks does not imply any change of
their constituent elements, or interference with their bedded
arrangement. It consists in the alteration of the sediments by merely
molecular changes re-arranging their particles so as to render them
crystalline, or by chemical reactions producing new combinations of
their elements. Experiment shows that the action of heat, pressure,
and waters containing alkaline carbonates and silicates, would
produce such changes. The amount and character of change would depend
on the composition of the sediment, the heat applied, the substances
in solution in the water, and the lapse of time. (See _Hunt's
Essays_, p. 24.)
[Illustration:
Plate III.
From a Photo by Weston. Vincent Brooks, Day & Son, Lith.
WEATHERED SPECIMEN OF EOZOON CANADENSE.
(ONE-HALF NATURAL SIZE.)
_To face Chap. 3_]
CHAPTER III.
THE HISTORY OF A DISCOVERY.
It is a trite remark that most discoveries are made, not by one
person, but by the joint exertions of many, and that they have their
preparations made often long before they actually appear. In this
case the stable foundations were laid, years before the discovery
of Eozoon, by the careful surveys made by Sir William Logan and his
assistants, and the chemical examination of the rocks and minerals
by Dr. Sterry Hunt. On the other hand, Dr. Carpenter and others in
England were examining the structure of the shells of the humbler
inhabitants of the modern ocean, and the manner in which the pores of
their skeletons become infiltrated with mineral matter when deposited
in the sea-bottom. These laborious and apparently dissimilar branches
of scientific inquiry were destined to be united by a series of happy
discoveries, made not fortuitously but by painstaking and intelligent
observers. The discovery of the most ancient fossil was thus not the
chance picking up of a rare and curious specimen. It was not likely
to be found in this way; and if so found, it would have remained
unnoticed and of no scientific value, but for the accumulated stores of
zoological and palæontological knowledge, and the surveys previously
made, whereby the age and distribution of the Laurentian rocks and
the chemical conditions of their deposition and metamorphism were
ascertained.
[Illustration: Fig. 7. _Eozoon mineralized by Loganite and Dolomite._
(Collected by Dr. Wilson, of Perth.)]
The first specimens of Eozoon ever procured, in so far as known, were
collected at Burgess in Ontario by a veteran Canadian mineralogist,
Dr. Wilson of Perth, and were sent to Sir William Logan as mineral
specimens. Their chief interest at that time lay in the fact that
certain laminæ of a dark green mineral present in the specimens were
found, on analysis by Dr. Hunt, to be composed of a new hydrous
silicate, allied to serpentine, and which he named loganite: one of
these specimens is represented in fig. 7. The form of this mineral was
not suspected to be of organic origin. Some years after, in 1858, other
specimens, differently mineralized with the minerals serpentine and
pyroxene, were found by Mr. J. McMullen, an explorer in the service
of the Geological Survey, in the limestone of the Grand Calumet on
the River Ottawa. These seem to have at once struck Sir W. E. Logan
as resembling the Silurian fossils known as _Stromatopora_, and he
showed them to Mr. Billings, the palæontologist of the survey, and to
the writer, with this suggestion, confirming it with the sagacious
consideration that inasmuch as the Ottawa and Burgess specimens were
mineralized by different substances, yet were alike in form, there was
little probability that they were merely mineral or concretionary. Mr.
Billings was naturally unwilling to risk his reputation in affirming
the organic nature of such specimens; and my own suggestion was that
they should be sliced, and examined microscopically, and that if
fossils, as they presented merely concentric laminæ and no cells,
they would probably prove to be protozoa rather than corals. A few
slices were accordingly made, but no definite structure could be
detected. Nevertheless Sir William Logan took some of the specimens to
the meeting of the American Association at Springfield, in 1859, and
exhibited them as possibly Laurentian fossils; but the announcement was
evidently received with some incredulity. In 1862 they were exhibited
by Sir William to some geological friends in London, but he remarks
that "few seemed disposed to believe in their organic character, with
the exception of my friend Professor Ramsay." In 1863 the General
Report of the Geological Survey, summing up its work to that time,
was published, under the name of the _Geology of Canada_, and in this,
at page 49, will be found two figures of one of the Calumet specimens,
here reproduced, and which, though unaccompanied with any specific
name or technical description, were referred to as probably Laurentian
fossils. (Figs. 8 and 9.)
About this time Dr. Hunt happened to mention to me, in connection with
a paper on the mineralization of fossils which he was preparing, that
he proposed to notice the mode of preservation of certain fossil woods
and other things with which I was familiar, and that he would show me
the paper in proof, in order that he might have any suggestions that
occurred to me. On reading it, I observed, among other things, that
he alluded to the supposed Laurentian fossils, under the impression
that the organic part was represented by the serpentine or loganite,
and that the calcareous matter was the filling of the chambers. I took
exception to this, stating that though in the slices before examined
no structure was apparent, still my impression was that the calcareous
matter was the fossil, and the serpentine or loganite the filling. He
said--"In that case, would it not be well to re-examine the specimens,
and to try to discover which view is correct?" He mentioned at the same
time that Sir William had recently shown him some new and beautiful
specimens collected by Mr. Lowe, one of the explorers on the staff of
the Survey, from a third locality, at Grenville, on the Ottawa. It was
supposed that these might throw further light on the subject; and
accordingly Dr. Hunt suggested to Sir William to have additional slices
of these new specimens made by Mr. Weston, of the Survey, whose skill
as a preparer of these and other fossils has often done good service to
science. A few days thereafter, some slices were sent to me, and were
at once put under the microscope. I was delighted to find in one of the
first specimens examined a beautiful group of tubuli penetrating one of
the calcite layers. Here was evidence, not only that the calcite layers
represented the true skeleton of the fossil, but also of its affinities
with the Foraminifera, whose tubulated supplemental skeleton, as
described and figured by Dr. Carpenter, and represented in specimens
in my collection presented by him, was evidently of the same type with
that preserved in the canals of these ancient fossils. Fig. 10 is an
accurate representation of the first seen group of canals penetrated by
serpentine.
[Illustration: Fig. 8. _Weathered Specimen of Eozoon from the Calumet._
(Collected by Mr. McMullen.)]
[Illustration: Fig. 9. _Cross Section of the Specimen represented in
Fig. 8._
The dark parts are the laminæ of calcareous matter converging to the
outer surface.]
On showing the structures discovered to Sir William Logan, he entered
into the matter with enthusiasm, and had a great number of slices and
afterwards of decalcified specimens prepared, which were placed in my
hands for examination.
Feeling that the discovery was most important, but that it would be
met with determined scepticism by a great many geologists, I was
not content with examining the typical specimens of Eozoon, but had
slices prepared of every variety of Laurentian limestone, of altered
limestones from the Primordial and Silurian, and of serpentine
marbles of all the varieties furnished by our collections. These were
examined with ordinary and polarized light, and with every variety
of illumination. Dr. Hunt, on his part, undertook the chemical
investigation of the various associated minerals. An extensive series
of notes and camera tracings were made of all the appearances observed;
and of some of the more important structures beautiful drawings
were executed by the late Mr. H. S. Smith, the then palæontological
draughtsman of the Survey. The result of the whole investigation was a
firm conviction that the structure was organic and foraminiferal, and
that it could be distinguished from any merely mineral or crystalline
forms occurring in these or other limestones.
[Illustration: Fig. 10. _Group of Canals in the Supplemental Skeleton
of Eozoon._
Taken from the specimen in which they were first recognised.
Magnified.]
At this stage of the matter, and after exhibiting to Sir William all
the characteristic appearances in comparison with such concretionary,
dendritic, and crystalline structures as most resembled them, and also
with the structure of recent and fossil Foraminifera, I suggested that
the further prosecution of the matter should be handed over to Mr.
Billings, as palæontologist of the Survey, and as our highest authority
on the fossils of the older rocks. I was engaged in other researches,
and knew that no little labour must be devoted to the work and to its
publication, and that some controversy might be expected. Mr. Billings,
however, with his characteristic caution and modesty, declined. His
hands, he said, were full of other work, and he had not specially
studied the microscopic appearances of Foraminifera or of mineral
substances. It was finally arranged that I should prepare a description
of the fossil, which Sir William would take to London, along with Dr.
Hunt's notes, the more important specimens, and lists of the structures
observed in each. Sir William was to submit the manuscript and
specimens to Dr. Carpenter, or failing him to Prof. T. Rupert Jones, in
the hope that these eminent authorities would confirm our conclusions,
and bring forward new facts which I might have overlooked or been
ignorant of. Sir William saw both gentlemen, who gave their testimony
in favour of the organic and foraminiferal character of the specimens;
and Dr. Carpenter in particular gave much attention to the subject, and
worked out the structure of the primary cell-wall, which I had not
observed previously through a curious accident as to specimens.[J] Mr.
Lowe had been sent back to the Ottawa to explore, and just before Sir
William's departure had sent in some specimens from a new locality at
Petite Nation, similar in general appearance to those from Grenville,
which Sir William took with him unsliced to England. These showed in
a perfect manner the tubuli of the primary cell-wall, which I had in
vain tried to resolve in the Grenville specimens, and which I did
not see until after it had been detected by Dr. Carpenter in London.
Dr. Carpenter thus contributed in a very important manner to the
perfecting of the investigations begun in Canada, and on him has fallen
the greater part of their illustration and defence,[K] in so far as
Great Britain is concerned. Fig. 11, taken from one of Dr. Carpenter's
papers, shows the tubulated primitive wall as described by him.
[Footnote J: In papers by Dr. Carpenter, subsequently referred to.
Prof. Jones published an able exposition of the facts in the _Popular
Science Monthly_.]
[Footnote K: In _Quarterly Journal of Geological Society_, vol. xxii.;
_Proc. Royal Society_, vol. xv.; _Intellectual Observer_, 1865. _Annals
and Magazine of Natural History_, 1874; and other papers and notices.]
[Illustration: Fig. 11. _Portion of Eozoon magnified 100 diameters,
showing the original Cell-wall with Tubulation, and the Supplemental
Skeleton with Canals._ (_After Carpenter._)
(_a._) Original tubulated wall or "Nummuline layer," more magnified in
fig. 2. (_b, c._) "Intermediate skeleton," with canals.]
The immediate result was a composite paper in the _Proceedings of the
Geological Society_, by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and
myself, in which the geology, palæontology, and mineralogy of _Eozoon
Canadense_ and its containing rocks were first given to the world.[L]
It cannot be wondered at that when geologists and palæontologists were
thus required to believe in the existence of organic remains in rocks
regarded as altogether Azoic and hopelessly barren of fossils, and
to carry back the dawn of life as far before those Primordial rocks,
which were supposed to contain its first traces, as these are before
the middle period of the earth's life history, some hesitation should
be felt. Further, the accurate appreciation of the evidence for such a
fossil as Eozoon required an amount of knowledge of minerals, of the
more humble types of animals, and of the conditions of mineralization
of organic remains, possessed by few even of professional geologists.
Thus Eozoon has met with some negative scepticism and a little positive
opposition,--though the latter has been small in amount, when we
consider the novel and startling character of the facts adduced.
[Footnote L: _Journal Geological Society_, February, 1865.]
"The united thickness," says Sir William Logan, "of these three great
series, the Lower and Upper Laurentian and Huronian, may possibly far
surpass that of all succeeding rocks, from the base of the Palæozoic
to the present time. We are thus carried back to a period so far
remote that the appearance of the so-called Primordial fauna may
be considered a comparatively modern event." So great a revolution
of thought, and this based on one fossil, of a character little
recognisable by geologists generally, might well tax the faith of a
class of men usually regarded as somewhat faithless and sceptical. Yet
this new extension of life has been generally received, and has found
its way into text-books and popular treatises. Its opponents have
been under the necessity of inventing the most strange and incredible
pseudomorphoses of mineral substances to account for the facts; and
evidently hold out rather in the spirit of adhesion to a lost cause
than with any hope of ultimate success. As might have been expected,
after the publication of the original paper, other facts developed
themselves. Mr. Vennor found other and scarcely altered specimens in
the Upper Laurentian or Huronian of Tudor. Gümbel recognised the
organism in Laurentian Rocks in Bavaria and elsewhere in Europe, and
discovered a new species in the Huronian of Bavaria.[M] Eozoon was
recognised in Laurentian limestones in Massachusetts[N] and New York,
and there has been a rapid growth of new facts increasing our knowledge
of Foraminifera of similar types in the succeeding Palæozoic rocks.
Special interest attaches to the discovery by Mr. Vennor of specimens
of Eozoon contained in a dark micaceous limestone at Tudor, in Ontario,
and really as little metamorphosed as many Silurian fossils. Though in
this state they show their minute structures less perfectly than in
the serpentine specimens, the fact is most important with reference
to the vindication of the animal nature of Eozoon. Another fact whose
significance is not to be over-estimated, is the recognition both by
Dr. Carpenter and myself of specimens in which the canals are occupied
by calcite like that of the organism itself. Quite recently I have, as
mentioned in the last chapter, been enabled to re-examine the locality
at Petite Nation originally discovered by Mr. Lowe, and am prepared to
show that all the facts with reference to the mode of occurrence of
the forms in the beds, and their association with layers of fragmental
Eozoon, are strictly in accordance with the theory that these old
Laurentian limestones are truly marine deposits, holding the remains of
the sea animals of their time.
[Footnote M: _Ueber das Vorkommen von Eozoon_, 1866.]
[Footnote N: By Mr. Bicknell at Newbury, and Mr. Burbank at Chelmsford.
The latter gentleman has since maintained that the limestones at the
latter place are not true beds; but his own descriptions and figures,
lead to the belief that this is an error of observation on his part.
The Eozoon in the Chelmsford specimens and in those of Warren, New
York, is in small and rare fragments in serpentinous limestone.]
Eozoon is not, however, the only witness to the great fact of
Laurentian life, of which it is the most conspicuous exponent. In many
of the Laurentian limestones, mixed with innumerable fragments of
Eozoon, there are other fragments with traces of organic structure of
a different character. There are also casts in silicious matter which
seem to indicate smaller species of Foraminifera. There are besides to
be summoned in evidence the enormous accumulations of carbon already
referred to as existing in the Laurentian rocks, and the worm-burrows,
of which very perfect traces exist in rocks probably of Upper Eozoic
age.
Other discoveries also are foreshadowed here. The microscope may
yet detect the true nature and affinities of some of the fragments
associated with Eozoon. Less altered portions of the Laurentian rocks
may be found, where even the vegetable matter may retain its organic
forms, and where fossils may be recognised by their external outlines
as well as by their internal structure. The Upper Laurentian and the
Huronian have yet to yield up their stores of life. Thus the time may
come when the rocks now called Primordial shall not be held to be so
in any strict sense, and when swarming dynasties of Protozoa and other
low forms of life may be known as inhabitants of oceans vastly ancient
as compared with even the old Primordial seas. Who knows whether even
the land of the Laurentian time may not have been clothed with plants,
perhaps as much more strange and weird than those of the Devonian and
Carboniferous, as those of the latter are when compared with modern
forests?
NOTES TO CHAPTER III.
(A.) Sir William E. Logan on the Discovery and Characters of Eozoon.
[_Journal of Geological Society_, February, 1865.]
"In the examination of these ancient rocks, the question has often
naturally occurred to me, whether during these remote periods, life
had yet appeared on the earth. The apparent absence of fossils from
the highly crystalline limestones did not seem to offer a proof in
the negative, any more than their undiscovered presence in newer
crystalline limestones where we have little doubt they have been
obliterated by metamorphic action; while the carbon which, in the
form of graphite, constitutes beds, or is disseminated through the
calcareous or siliceous strata of the Laurentian series, seems to be
an evidence of the existence of vegetation, since no one disputes the
organic character of this mineral in more recent rocks. My colleague,
Dr. T. Sterry Hunt, has argued for the existence of organic matters
at the earth's surface during the Laurentian period from the presence
of great beds of iron ore, and from the occurrence of metallic
sulphurets;[O] and finally, the evidence was strengthened by the
discovery of supposed organic forms. These were first brought to me,
in October, 1858, by Mr. J. McMullen, then attached as an explorer to
the Geological Survey of the province, from one of the limestones of
the Laurentian series occurring at the Grand Calumet, on the river
Ottawa.
[Footnote O: _Quarterly Journal of the Geological Society_, xv., 493.]
"Any organic remains which may have been entombed in these limestones
would, if they retained their calcareous character, be almost
certainly obliterated by crystallization; and it would only be by the
replacement of the original carbonate of lime by a different mineral
substance, or by an infiltration of such a substance into all the
pores and spaces in and about the fossil, that its form would be
preserved. The specimens from the Grand Calumet present parallel or
apparently concentric layers resembling those of Stromatopora, except
that they anastomose at various points. What were first considered
the layers are composed of crystallized pyroxene, while the then
supposed interstices consist of carbonate of lime. These specimens,
one of which is figured in _Geology of Canada_, p. 49, called to
memory others which had some years previously been obtained from Dr.
James Wilson, of Perth, and were then regarded merely as minerals.
They came, I believe, from masses in Burgess, but whether in place
is not quite certain; and they exhibit similar forms to those of the
Grand Calumet, composed of layers of a dark green magnesian silicate
(loganite); while what were taken for the interstices are filled with
crystalline dolomite. If the specimens from both these places were to
be regarded as the result of unaided mineral arrangement, it appeared
to me strange that identical forms should be derived from minerals
of such different composition. I was therefore disposed to look
upon them as fossils, and as such they were exhibited by me at the
meeting of the American Association for the Advancement of Science,
at Springfield, in August, 1859. See _Canadian Naturalist_, 1859,
iv., 300. In 1862 they were shown to some of my geological friends
in Great Britain; but no microscopic structure having been observed
belonging to them, few seemed disposed to believe in their organic
character, with the exception of my friend Professor Ramsay.
"One of the specimens had been sliced and submitted to microscopic
observation, but unfortunately it was one of those composed of
loganite and dolomite. In these, the minute structure is rarely
seen. The true character of the specimens thus remained in suspense
until last winter, when I accidentally observed indications of
similar forms in blocks of Laurentian limestone which had been
brought to our museum by Mr. James Lowe, one of our explorers, to
be sawn up for marble. In this case the forms were composed of
serpentine and calc-spar; and slices of them having been prepared
for the microscope, the minute structure was observed in the first
one submitted to inspection. At the request of Mr. Billings, the
palæontologist of our Survey, the specimens were confided for
examination and description to Dr. J. W. Dawson, of Montreal, our
most practised observer with the microscope; and the conclusions at
which he has arrived are appended to this communication. He finds
that the serpentine, which was supposed to replace the organic form,
really fills the interspaces of the calcareous fossil. This exhibits
in some parts a well-preserved organic structure, which Dr. Dawson
describes as that of a Foraminifer, growing in large sessile patches
after the manner of Polytrema and Carpenteria, but of much larger
dimensions, and presenting minute points which reveal a structure
resembling that of other Foraminiferal forms, as, for example
Calcarina and Nummulina.
"Dr. Dawson's description is accompanied by some remarks by Dr.
Sterry Hunt on the mineralogical relations of the fossil. He
observes that while the calcareous septa which form the skeleton of
the Foraminifer in general remain unchanged, the sarcode has been
replaced by certain silicates which have not only filled up the
chambers, cells, and septal orifices, but have been injected into
the minute tubuli, which are thus perfectly preserved, as may be
seen by removing the calcareous matter by an acid. The replacing
silicates are white pyroxene, serpentine, loganite, and pyrallolite
or rensselaerite. The pyroxene and serpentine are often found
in contact, filling contiguous chambers in the fossil, and were
evidently formed in consecutive stages of a continuous process. In
the Burgess specimens, while the sarcode is replaced by loganite, the
calcareous skeleton, as has already been stated, has been replaced
by dolomite, and the finer parts of the structure have been almost
wholly obliterated. But in the other specimens, where the skeleton
still preserves its calcareous character, the resemblance between
the mode of preservation of the ancient Laurentian Foraminifera, and
that of the allied forms in Tertiary and recent deposits (which,
as Ehrenberg, Bailey, and Pourtales have shown, are injected with
glauconite), is obvious.
"The Grenville specimens belong to the highest of the three already
mentioned zones of Laurentian limestone, and it has not yet been
ascertained whether the fossil extends to the two conformable lower
ones, or to the calcareous zones of the overlying unconformable
Upper Laurentian series. It has not yet either been determined
what relation the strata from which the Burgess and Grand Calumet
specimens have been obtained bear to the Grenville limestone or
to one another. The zone of Grenville limestone is in some places
about 1500 feet thick, and it appears to be divided for considerable
distances into two or three parts by very thick bands of gneiss.
One of these occupies a position towards the lower part of the
limestone, and may have a volume of between 100 and 200 feet. It is
at the base of the limestone that the fossil occurs. This part of
the zone is largely composed of great and small irregular masses of
white crystalline pyroxene, some of them twenty yards in length by
four or five wide. They appear to be confusedly placed one above
another, with many ragged interstices, and smoothly-worn, rounded,
large and small pits and sub-cylindrical cavities, some of them
pretty deep. The pyroxene, though it appears compact, presents a
multitude of small spaces consisting of carbonate of lime, and many
of these show minute structures similar to that of the fossil.
These masses of pyroxene may characterize a thickness of about 200
feet, and the interspaces among them are filled with a mixture of
serpentine and carbonate of lime. In general a sheet of pure dark
green serpentine invests each mass of pyroxene; the thickness of the
serpentine, varying from the sixteenth of an inch to several inches,
rarely exceeding half a foot. This is followed in different spots
by parallel, waving, irregularly alternating plates of carbonate of
lime and serpentine, which become gradually finer as they recede
from the pyroxene, and occasionally occupy a total thickness of
five or six inches. These portions constitute the unbroken fossil,
which may sometimes spread over an area of about a square foot, or
perhaps more. Other parts, immediately on the outside of the sheet of
serpentine, are occupied with about the same thickness of what appear
to be the ruins of the fossil, broken up into a more or less granular
mixture of calc-spar and serpentine, the former still showing minute
structure; and on the outside of the whole a similar mixture appears
to have been swept by currents and eddies into rudely parallel and
curving layers; the mixture becoming gradually more calcareous as it
recedes from the pyroxene. Sometimes beds of limestone of several
feet in thickness, with the green serpentine more or less aggregated
into layers, and studded with isolated lumps of pyroxene, are
irregularly interstratified in the mass of rock; and less frequently
there are met with lenticular patches of sandstone or granular
quartzite, of a foot in thickness and several yards in diameter,
holding in abundance small disseminated leaves of graphite.
"The general character of the rock connected with the fossil produces
the impression that it is a great Foraminiferal reef, in which the
pyroxenic masses represent a more ancient portion, which having
died, and having become much broken up and worn into cavities and
deep recesses, afforded a seat for a new growth of Foraminifera,
represented by the calcareo-serpentinous part. This in its turn
became broken up, leaving in some places uninjured portions of the
general form. The main difference between this Foraminiferal reef and
more recent coral-reefs seems to be that, while in the latter are
usually associated many shells and other organic remains, in the more
ancient one the only remains yet found are those of the animal which
built the reef."
(B.) NOTE BY SIR WILLIAM E. LOGAN, ON ADDITIONAL SPECIMENS OF EOZOON.
[_Journal of Geological Society_, August, 1867.]
"Since the subject of Laurentian fossils was placed before this
Society in the papers of Dr. Dawson, Dr. Carpenter, Dr. T. Sterry
Hunt, and myself, in 1865, additional specimens of Eozoon have been
obtained during the explorations of the Geological Survey of Canada.
These, as in the case of the specimens first discovered, have been
submitted to the examination of Dr. Dawson; and it will be observed,
from his remarks contained in the paper which is to follow, that one
of them has afforded further, and what appears to him conclusive,
evidence of their organic character. The specimens and remarks have
been submitted to Dr. Carpenter, who coincides with Dr. Dawson;
and the object of what I have to say in connection with these new
specimens is merely to point out the localities in which they have
been procured.
"The most important of these specimens was met with last summer by
Mr. G. H. Vennor, one of the assistants on the Canadian Geological
Survey, in the township of Tudor and county of Hastings, Ontario,
about forty-five miles inland from the north shore of Lake Ontario,
west of Kingston. It occurred on the surface of a layer, three inches
thick, of dark grey micaceous limestone or calc-schist, near the
middle of a great zone of similar rock, which is interstratified
with beds of yellowish-brown sandstone, gray close grained silicious
limestone, white coarsely granular limestone, and bands of dark
bluish compact limestone and black pyritiferous slates, to the whole
of which Mr. Vennor gives a thickness of 1000 feet. Beneath this zone
are gray and pink dolomites, bluish and grayish mica slates, with
conglomerates, diorites, and beds of magnetite, a red orthoclase
gneiss lying at the base. The whole series, according to Mr. Vennor's
section, which is appended, has a thickness of more than 12,000
feet; but the possible occurrence of more numerous folds than have
hitherto been detected, may hereafter render necessary a considerable
reduction.
"These measures appear to be arranged in the form of a trough,
to the eastward of which, and probably beneath them, there are
rocks resembling those of Grenville, from which the former differ
considerably in lithological character; it is therefore supposed
that the Hastings series may be somewhat higher in horizon than
that of Grenville. From the village of Madoc, the zone of gray
micaceous limestone, which has been particularly alluded to, runs
to the eastward on one side of the trough, in a nearly vertical
position into Elzivir, and on the other side to the northward,
through the township of Madoc into that of Tudor, partially and
unconformably overlaid in several places by horizontal beds of Lower
Silurian limestone, but gradually spreading, from a diminution of
the dip, from a breadth of half a mile to one of four miles. Where
it thus spreads out in Tudor it becomes suddenly interrupted for a
considerable part of its breadth by an isolated mass of anorthosite
rock, rising about 150 feet above the general plain, and supposed to
belong to the unconformable Upper Laurentian."
[Subsequent observations, however, render it probable that some of
the above beds may be Huronian.]
"The Tudor limestone is comparatively unaltered: and, in the specimen
obtained from it, the general form or skeleton of the fossil
(consisting of white carbonate of lime) is imbedded in the limestone,
without the presence of serpentine or other silicate, the colour of
the skeleton contrasting strongly with that of the rock. It does not
sink deep into the rock, the form having probably been loose and much
abraded on what is now the under part, before being entombed. On what
was the surface of the bed, the form presents a well-defined outline
on one side; in this and in the arrangement of the septal layers
it has a marked resemblance to the specimen first brought from the
Calumet, eighty miles to the north-east, and figured in the _Geology
of Canada_, p. 49; while all the forms from the Calumet, like that
from Tudor, are isolated, imbedded specimens, unconnected apparently
with any continuous reef, such as exists at Grenville and the Petite
Nation. It will be seen, from Dr. Dawson's paper, that the minute
structure is present in the Tudor specimen, though somewhat obscure;
but in respect to this, strong subsidiary evidence is derived from
fragments of Eozoon detected by Dr. Dawson in a specimen collected
by myself from the same zone of limestone near the village of Madoc,
in which the canal-system, much more distinctly displayed, is filled
with carbonate of lime, as quoted from Dr. Dawson by Dr. Carpenter
in the Journal of this Society for August, 1866.
"In Dr. Dawson's paper mention is made of specimens from Wentworth,
and others from Long Lake. In both of these localities the rock
yielding them belongs to the Grenville band, which is the uppermost
of the three great bands of limestone hitherto described as
interstratified in the Lower Laurentian series. That at Long Lake,
situated about twenty-five miles north of Côte St. Pierre in the
Petite Nation seigniory, where the best of the previous specimens
were obtained, is in the direct run of the limestone there: and like
it the Long Lake rock is of a serpentinous character. The locality
in Wentworth occurs on Lake Louisa, about sixteen miles north of
east from that of the first Grenville specimens, from which Côte St.
Pierre is about the same distance north of west, the lines measuring
these distances running across several important undulations in
the Grenville band in both directions. The Wentworth specimens are
imbedded in a portion of the Grenville band, which appears to have
escaped any great alteration, and is free from serpentine, though a
mixture of serpentine with white crystalline limestone occurs in the
band within a mile of the spot. From this grey limestone, which has
somewhat the aspect of a conglomerate, specimens have been obtained
resembling some of the figures given by Gümbel in his _Illustrations_
of the forms met with by him in the Laurentian rocks of Bavaria.
"In decalcifying by means of a dilute acid some of the specimens
from Côte St. Pierre, placed in his hands in 1864-65, Dr. Carpenter
found that the action of the acid was arrested at certain portions
of the skeleton, presenting a yellowish-brown surface; and he showed
me, two or three weeks ago, that in a specimen recently given him,
from the same locality, considerable portions of the general form
remained undissolved by such an acid. On partially reducing some
of these portions to a powder; however, we immediately observed
effervescence by the dilute acid; and strong acid produced it without
bruising. There is little doubt that these portions of the skeleton
are partially replaced by dolomite, as more recent fossils are
often known to be, of which there is a noted instance in the Trenton
limestone of Ottawa. But the circumstance is alluded to for the
purpose of comparing these dolomitized portions of the skeleton with
the specimens from Burgess, in which the replacement of the septal
layers by dolomite appears to be the general condition. In such of
these specimens as have been examined the minute structure seems to
be wholly, or almost wholly, destroyed; but it is probable that upon
a further investigation of the locality some spots will be found
to yield specimens in which the calcareous skeleton still exists
unreplaced by dolomite; and I may safely venture to predict that in
such specimens the minute structure, in respect both to canals and
tubuli, will be found as well preserved as in any of the specimens
from Côte St. Pierre.
"It was the general form on weathered surfaces, and its strong
resemblance to Stromatopora, which first attracted my attention to
Eozoon; and the persistence of it in two distinct minerals, pyroxene
and loganite, emboldened me, in 1857, to place before the Meeting of
the American Association for the Advancement of Science specimens of
it as probably a Laurentian fossil. After that, the form was found
preserved in a third mineral, serpentine; and in one of the previous
specimens it was then observed to pass continuously through two
of the minerals, pyroxene and serpentine. Now we have it imbedded
in limestone, just as most fossils are. In every case, with the
exception of the Burgess specimens, the general form is composed of
carbonate of lime; and we have good grounds for supposing it was
originally so in the Burgess specimens also. If, therefore, with such
evidence, and without the minute structure, I was, upon a calculation
of chances, disposed, in 1857, to look upon the form as organic, much
more must I so regard it when the chances have been so much augmented
by the subsequent accumulation of evidence of the same kind, and
the addition of the minute structure, as described by Dr. Dawson,
whose observations have been confirmed and added to by the highest
British authority upon the class of animals to which the form has
been referred, leaving in my mind no room whatever for doubt of its
organic character. Objections to it as an organism have been made by
Professors King and Rowney: but these appear to me to be based upon
the supposition that because some parts simulating organic structure
are undoubtedly mere mineral arrangement, therefore all parts are
mineral. Dr. Dawson has not proceeded upon the opposite supposition,
that because some parts are, in his opinion, undoubtedly organic,
therefore all parts simulating organic structure are organic; but
he has carefully distinguished between the mineral and organic
arrangements. I am aware, from having supplied him with a vast number
of specimens prepared for the microscope by the lapidary of the
Canadian Survey, from a series of rocks of Silurian and Huronian,
as well as Laurentian age, and from having followed the course of
his investigation as it proceeded, that nearly all the points of
objection of Messrs. King and Rowney passed in review before him
prior to his coming to the conclusions which he has published."
_Ascending Section of the Eozoic Rocks in the County of Hastings,
Ontario._ By Mr. H. G. Vennor.
Feet.
1. Reddish and flesh-coloured granitic gneiss, the thickness
of which is unknown; estimated at not less than 2,000
2. Grayish and flesh-coloured gneiss, sometimes hornblendic,
passing towards the summit into a dark mica-schist,
and including portions of greenish-white diorite;
mean of several pretty closely agreeing measurements, 10,400
3. Crystalline limestone, sometimes magnesian, including
lenticular patches of quartz, and broken and
contorted layers of quartzo-felspathic rock, rarely above
a few inches in thickness. This limestone, which includes
in Elzivir a one-foot bed of graphite, is sometimes
very thin, but in other places attains a thickness
of 750 feet; estimated as averaging 400
4. Hornblendic and dioritic rocks, massive or schistose,
occasionally associated near the base with dark
micaceous schists, and also with chloritic and epidotic
rocks, including beds of magnetite; average thickness 4,200
5. Crystalline and somewhat granular magnesian
limestone, occasionally interstratified with diorites, and
near the base with silicious slates and small beds of
impure steatite 330
This limestone, which is often silicious and ferruginous,
is metalliferous, holding disseminated copper
pyrites, blende, mispickel, and iron pyrites, the latter
also sometimes in beds of two or three feet. Gold occurs
in the limestone at the village of Madoc, associated with
an argentiferous gray copper ore, and in irregular veins
with bitter-spar, quartz, and a carbonaceous matter, at
the Richardson mine in Madoc.
6. Gray silicious or fined-grained mica-slates, with
an interstratified mass of about sixty feet of yellowish-white
dolomite divided into beds by thin layers of the
mica-slate, which, as well as the dolomite, often becomes
conglomerate, including rounded masses of gneiss and
quartzite from one to twelve inches in diameter 400
7. Bluish and grayish micaceous slate, interstratified
with layers of gneiss, and occasionally holding crystals
of magnetite. The whole division weathers to a rusty-brown 500
8. Gneissoid micaceous quartzites, banded gray and
white, with a few interstratified beds of silicious
limestone, and, like the last division, weathering rusty
brown 1,900
9. Gray micaceous limestone, sometimes plumbaginous,
becoming on its upper portion a calc-schist, but
more massive towards the base, where it is interstratified
with occasional layers of diorite, and layers of a
rusty-weathering gneiss like 8 1,100
This division in Tudor is traversed by numerous
N.W. and S.E. veins, holding galena in a gangue of
calcite and barytine. The Eozoon from Tudor here
described was obtained from about the middle of this
calcareous division, which appears to form the summit
of the Hastings series.
------
Total thickness 21,130
[Illustration:
PLATE IV.
_Magnified and Restored Section of a portion of Eozoon Canadense._
The portions in brown show the animal matter of the Chambers, Tubuli,
Canals, and Pseudopodia; the portions uncoloured, the calcareous skeleton.]
[Illustration: Fig. 12. _Amœba._ Fig. 13. _Actinophrys._
From original sketches.]
CHAPTER IV.
WHAT IS EOZOON?
The shortest answer to this question is, that this ancient fossil
is the skeleton of a creature belonging to that simple and humbly
organized group of animals which are known by the name Protozoa. If
we take as a familiar example of these the gelatinous and microscopic
creature found in stagnant ponds, and known as the _Amœba_[P] (fig.
12), it will form a convenient starting point. Viewed under a low
power, it appears as a little patch of jelly, irregular in form, and
constantly changing its aspect as it moves, by the extension of parts
of its body into finger-like processes or pseudopods which serve as
extempore limbs. When moving on the surface of a slip of glass under
the microscope, it seems, as it were, to flow along rather than creep,
and its body appears to be of a semi-fluid consistency. It may be taken
as an example of the least complex forms of animal life known to us,
and is often spoken of by naturalists as if it were merely a little
particle of living and scarcely organized jelly or protoplasm. When
minutely examined, however, it will not be found so simple as it at
first sight appears. Its outer layer is clear or transparent, and more
dense than the inner mass, which seems granular. It has at one end a
curious vesicle which can be seen gradually to expand and become filled
with a clear drop of liquid, and then suddenly to contract and expel
the contained fluid through a series of pores in the adjacent part of
the outer wall. This is the so-called pulsating vesicle, and is an
organ both of circulation and excretion. In another part of the body
may be seen the nucleus, which is a little cell capable, at certain
times, of producing by its division new individuals. Food when taken
in through the wall of the body forms little pellets, which become
surrounded by a digestive liquid exuded from the enclosing mass into
rounded cavities or extemporised stomachs. Minute granules are seen
to circulate in the gelatinous interior, and may be substitutes for
blood-cells, and the outer layer of the body is capable of protrusion
in any direction into long processes, which are very mobile, and used
for locomotion and prehension. Further, this creature, though destitute
of most of the parts which we are accustomed to regard as proper to
animals, seems to exercise volition, and to show the same appetites
and passions with animals of higher type. I have watched one of these
animalcules endeavouring to swallow a one-celled plant as long as its
own body; evidently hungry and eager to devour the tempting morsel, it
stretched itself to its full extent, trying to envelope the object of
its desire. It failed again and again; but renewed the attempt, until
at length, convinced of its hopelessness, it flung itself away as if in
disappointment, and made off in search of something more manageable.
With the Amœba are found other types of equally simple Protozoa, but
somewhat differently organized. One of these, _Actinophrys_ (fig. 13),
has the body globular and unchanging in form, the outer wall of greater
thickness; the pulsating vesicle like a blister on the surface, and the
pseudopods long and thread-like. Its habits are similar to those of the
Amœba, and I introduce it to show the variations of form and structure
possible even among these simple creatures.
[Footnote P: The alternating animal, alluding to its change of form.]
[Illustration: Fig. 14. _Entosolenia._
A one-celled Foraminifer. Magnified as a transparent object.]
[Illustration: Fig. 15. _Biloculina._
A many-chambered Foraminifer. Magnified as a transparent object.]
[Illustration: Fig. 16. _Polystomella._
A spiral Foraminifer. Magnified as an opaque object.]
The Amœba and Actinophrys are fresh water animals, and are destitute
of any shell or covering. But in the sea there exist swarms of similar
creatures, equally simple in organization, but gifted with the power of
secreting around their soft bodies beautiful little shells or crusts of
carbonate of lime, having one orifice, and often in addition multitudes
of microscopic pores through which the soft gelatinous matter can ooze,
and form outside finger-like or thread-like extensions for collecting
food. In some cases the shell consists of a single cavity only, but in
most, after one cell is completed, others are added, forming a series
of cells or chambers communicating with each other, and often arranged
spirally or otherwise in most beautiful and symmetrical forms. Some of
these creatures, usually named Foraminifera, are locomotive, others
sessile and attached. Most of them are microscopic, but some grow by
multiplication of chambers till they are a quarter of an inch or more
in breadth. (Figs. 14 to 17.)
[Illustration: Fig. 17. _Polymorphina._
A many-chambered Foraminifer. Magnified as an opaque object. Figs. 14
to 17 are from original sketches of Post-pliocene specimens.]
The original skeleton or primary cell-wall of most of these creatures
is seen under the microscope to be perforated with innumerable pores,
and is extremely thin. When, however, owing to the increased size of
the shell, or other wants of the creature, it is necessary to give
strength, this is done by adding new portions of carbonate of lime to
the outside, and to these Dr. Carpenter has given the appropriate name
of "supplemental skeleton;" and this, when covered by new growths,
becomes what he has termed an "intermediate skeleton." The supplemental
skeleton is also traversed by tubes, but these are often of larger size
than the pores of the cell-wall, and of greater length, and branched in
a complicated manner. (Fig. 20.) Thus there are microscopic characters
by which these curious shells can be distinguished from those of
other marine animals; and by applying these characters we learn that
multitudes of creatures of this type have existed in former periods of
the world's history, and that their shells, accumulated in the bottom
of the sea, constitute large portions of many limestones. The manner in
which such accumulation takes place we learn from what is now going on
in the ocean, more especially from the result of the recent deep-sea
dredging expeditions. The Foraminifera are vastly numerous, both near
the surface and at the bottom of the sea, and multiply rapidly; and
as successive generations die, their shells accumulate on the ocean
bed, or are swept by currents into banks, and thus in process of time
constitute thick beds of white chalky material, which may eventually
be hardened into limestone. This process is now depositing a great
thickness of white ooze in the bottom of the ocean; and in times past
it has produced such vast thicknesses of calcareous matter as the chalk
and the nummulitic limestone of Europe and the orbitoidal limestone
of America. The chalk, which alone attains a maximum thickness of 1000
feet, and, according to Lyell, can be traced across Europe for 1100
geographical miles, may be said to be entirely composed of shells
of Foraminifera imbedded in a paste of still more minute calcareous
bodies, the Coccoliths, which are probably products of marine
vegetable life, if not of some animal organism still simpler than the
Foraminifera.
Lastly, we find that in the earlier geological ages there existed
much larger Foraminifera than any found in our present seas; and that
these, always sessile on the bottom, grew by the addition of successive
chambers, in the same manner with the smaller species. To some of these
we shall return in the sequel. In the meantime we shall see what claims
Eozoon has to be included among them.
Let us, then, examine the structure of Eozoon, taking a typical
specimen, as we find it in the limestone of Grenville or Petite Nation.
In such specimens the skeleton of the animal is represented by a white
crystalline marble, the cavities of the cells by green serpentine, the
mode of whose introduction we shall have to consider in the sequel.
The lowest layer of serpentine represents the first gelatinous coat
of animal matter which grew upon the bottom, and which, if we could
have seen it before any shell was formed upon its surface, must have
resembled, in appearance at least, the shapeless coat of living slime
found in some portions of the bed of the deep sea, which has received
from Huxley the name _Bathybius_, and which is believed to be a
protozoon of indefinite extension, though it may possibly be merely the
pulpy sarcode of sponges and similar things penetrating the ooze at
their bases. On this primary layer grew a delicate calcareous shell,
perforated by innumerable minute tubuli, and by some larger pores or
septal orifices, while supported at intervals by perpendicular plates
or pillars. Upon this again was built up, in order to strengthen it,
a thickening or supplemental skeleton, more dense, and destitute of
fine tubuli, but traversed by branching canals, through which the
soft gelatinous matter could pass for the nourishment of the skeleton
itself, and the extension of pseudopods beyond it. (Fig. 10.) So was
formed the first layer of Eozoon, which seems in some cases to have
spread by lateral extension over several inches of sea bottom. On this
the process of growth of successive layers of animal sarcode and of
calcareous skeleton was repeated again and again, till in some cases
even a hundred or more layers were formed. (Photograph, Plate III.,
and nature print, Plate V.) As the process went on, however, the
vitality of the organism became exhausted, probably by the deficient
nourishment of the central and lower layers making greater and greater
demands on those above, and so the succeeding layers became thinner,
and less supplemental skeleton was developed. Finally, toward the
top, the regular arrangement in layers was abandoned, and the cells
became a mass of rounded chambers, irregularly piled up in what Dr.
Carpenter has termed an "acervuline" manner, and with very thin walls
unprotected by supplemental skeleton. Then the growth was arrested,
and possibly these upper layers gave off reproductive germs, fitted
to float or swim away and to establish new colonies. We may have
such reproductive germs in certain curious globular bodies, like
loose cells, found in connection with irregular Eozoon in one of
the Laurentian limestones at Long Lake and elsewhere. These curious
organisms I observed some years ago, but no description of them was
published at the time, as I hoped to obtain better examples. I now
figure some of them, and give their description in a note. (Fig. 18).
I have recently obtained numerous additional examples from the beds
holding Eozoon at St. Pierre, on the Ottawa. They occur at this place
on the surface of layers of the limestone in vast numbers, as if they
had been growing separately on the bottom, or had been drifted over
it by currents. These we shall further discuss hereafter. Such was
the general mode of growth of Eozoon, and we may now consider more in
detail some questions as to its gigantic size, its precise mode of
nutrition, the arrangement of its parts, its relations to more modern
forms, and the effects of its growth in the Laurentian seas. In the
meantime a study of our illustration, Plate IV., which is intended as a
magnified restoration of the animal, will enable the reader distinctly
to understand its structure and probable mode of growth, and to avail
himself intelligently of the partial representations of its fossilized
remains in the other plates and woodcuts.
[Illustration: Fig. 18. _Minute Foraminiferal forms from the Laurentian
of Long Lake._
Highly magnified. (_a._) Single cell, showing tubulated wall. (_b, c._)
Portions of same more highly magnified. (_d._) Serpentine cast of a
similar chamber, decalcified, and showing casts of tubuli.]
With respect to its size, we shall find in a subsequent chapter that
this was rivalled by some succeeding animals of the same humble type
in the Silurian age; and that, as a whole, foraminiferal animals have
been diminishing in size in the lapse of geological time. It is indeed
a fact of so frequent occurrence that it may almost be regarded as
a law of the introduction of new forms of life, that they assume in
their early history gigantic dimensions, and are afterwards continued
by less magnificent species. The relations of this to external
conditions, in the case of higher animals, are often complex and
difficult to understand; but in organisms so low as Eozoon and its
allies, they lie more on the surface. Such creatures may be regarded
as the simplest and most ready media for the conversion of vegetable
matter into animal tissues, and their functions are almost entirely
limited to those of nutrition. Hence it is likely that they will be
able to appear in the most gigantic forms under such conditions as
afford them the greatest amount of pabulum for the nourishment of
their soft parts and for their skeletons. There is reason to believe,
for example, that the occurrence, both in the chalk and the deep-sea
mud, of immense quantities of the minute bodies known as Coccoliths
along with Foraminifera, is not accidental. The Coccoliths appear to
be grains of calcareous matter formed in minute plants adapted to a
deep-sea habitat; and these, along with the vegetable and animal debris
constantly being derived from the death of the living things at the
surface, afford the material both of sarcode and shell. Now if the
Laurentian graphite represents an exuberance of vegetable growth in
those old seas proportionate to the great supplies of carbonic acid
in the atmosphere and in the waters, and if the Eozoic ocean was even
better supplied with carbonate of lime than those Silurian seas whose
vast limestones bear testimony to their richness in such material, we
can easily imagine that the conditions may have been more favourable
to a creature like Eozoon than those of any other period of geological
time.
Growing, as Eozoon did, on the floor of the ocean, and covering wide
patches with more or less irregular masses, it must have thrown up from
its whole surface its pseudopods to seize whatever floating particles
of food the waters carried over it. There is also reason to believe,
from the outline of certain specimens, that it often grew upward in
cylindrical or club-shaped forms, and that the broader patches were
penetrated by large pits or oscula, admitting the sea-water deeply into
the substance of the masses. In this way its growth might be rapid and
continuous; but it does not seem to have possessed the power of growing
indefinitely by new and living layers covering those that had died,
in the manner of some corals. Its life seems to have had a definite
termination, and when that was reached an entirely new colony had to
be commenced. In this it had more affinity with the Foraminifera, as
we now know them, than with the corals, though practically it had the
same power with the coral polyps of accumulating limestone in the sea
bottom, a power indeed still possessed by its foraminiferal successors.
In the case of coral limestones, we know that a large proportion of
these consist not of continuous reefs but of fragments of coral mixed
with other calcareous organisms, spread usually by waves and currents
in continuous beds over the sea bottom. In like manner we find in
the limestones containing Eozoon, layers of fragmental matter which
shows in places the characteristic structures, and which evidently
represents the debris swept from the Eozoic masses and reefs by the
action of the waves. It is with this fragmental matter that the small
rounded organisms already referred to most frequently occur; and while
they may be distinct animals, they may also be the fry of Eozoon, or
small portions of its acervuline upper surface floated off in a living
state, and possibly capable of living independently and of founding new
colonies.
It is only by a somewhat wild poetical licence that Eozoon has been
represented as a "kind of enormous composite animal stretching from the
shores of Labrador to Lake Superior, and thence northward and southward
to an unknown distance, and forming masses 1500 feet in depth." We may
discuss by-and-by the question of the composite nature of masses of
Eozoon, and we see in the corals evidence of the great size to which
composite animals of a higher grade can attain. In the case of Eozoon
we must imagine an ocean floor more uniform and level than that now
existing. On this the organism would establish itself in spots and
patches. These might finally become confluent over large areas, just
as massive corals do. As individual masses attained maturity and died,
their pores would be filled up with limestone or silicious deposits,
and thus could form a solid basis for new generations, and in this way
limestone to an indefinite extent might be produced. Further, wherever
such masses were high enough to be attacked by the breakers, or where
portions of the sea bottom were elevated, the more fragile parts of the
surface would be broken up and scattered widely in beds of fragments
over the bottom of the sea, while here and there beds of mud or sand
or of volcanic debris would be deposited over the living or dead
organic mass, and would form the layers of gneiss and other schistose
rocks interstratified with the Laurentian limestone. In this way, in
short, Eozoon would perform a function combining that which corals and
Foraminifera perform in the modern seas; forming both reef limestones
and extensive chalky beds, and probably living both in the shallow and
the deeper parts of the ocean. If in connection with this we consider
the rapidity with which the soft, simple, and almost structureless
sarcode of these Protozoa can be built up, and the probability that
they were more abundantly supplied with food, both for nourishing their
soft parts and skeletons, than any similar creatures in later times, we
can readily understand the great volume and extent of the Laurentian
limestones which they aided in producing. I say aided in producing,
because I would not desire to commit myself to the doctrine that the
Laurentian limestones are wholly of this origin. There may have been
other animal limestone-builders than Eozoon, and there may have been
limestones formed by plants like the modern Nullipores or by merely
mineral deposition.
[Illustration: Fig. 19. _Section of a Nummulite, from Eocene Limestone
of Syria._
Showing chambers, tubuli, and canals. Compare this and fig. 20 with
figs. 10 and 11.]
[Illustration: Fig. 20. _Portion of shell of Calcarina._
Magnified, after Carpenter. (_a._) Cells. (_b._) Original cell-wall
with tubuli. (_c._) Supplementary skeleton with canals.]
Its relations to modern animals of its type have been very clearly
defined by Dr. Carpenter. In the structure of its proper wall and its
fine parallel perforations, it resembles the _Nummulites_ and their
allies; and the organism may therefore be regarded as an aberrant
member of the Nummuline group, which affords some of the largest and
most widely distributed of the fossil Foraminifera. This resemblance
may be seen in fig. 19. To the Nummulites it also conforms in its
tendency to form a supplemental or intermediate skeleton with canals,
though the canals themselves in their arrangement more nearly resemble
Calcarina, which is represented in fig. 20. In its superposition of
many layers, and in its tendency to a heaped up or acervuline irregular
growth it resembles _Polytrema_ and _Tinoporus_, forms of a different
group in so far as shell-structure is concerned. It may thus be
regarded as a composite type, combining peculiarities now observed in
two groups, or it may be regarded as a representative in the Nummuline
series of Polytrema and Tinoporus in the Rotaline series. At the time
when Dr. Carpenter stated these affinities, it might be objected that
Foraminifera of these families are in the main found in the Modern and
Tertiary periods. Dr. Carpenter has since shown that the curious oval
Foraminifer called _Fusulina_, found in the coal formation, is in like
manner allied to both Nummulites and Rotalines; and still more recently
Mr. Brady has discovered a true Nummulite in the Lower Carboniferous of
Belgium. This group being now fairly brought down to the Palæozoic, we
may hope finally to trace it back to the Primordial, and thus to bring
it still nearer to Eozoon in time.
[Illustration: Fig. 21. _Foraminiferal Rock Builders._
(_a._) Nummulites lævigata--Eocene. (_b._) The same, showing chambered
interior. (_c._) Milioline limestone, magnified--Eocene, Paris. (_d._)
Hard Chalk, section magnified--Cretaceous.]
Though Eozoon was probably not the only animal of the Laurentian seas,
yet it was in all likelihood the most conspicuous and important as
a collector of calcareous matter, filling the same place afterwards
occupied by the reef-building corals. Though probably less efficient
than these as a constructor of solid limestones, from its less
permanent and continuous growth, it formed wide floors and patches
on the sea-bottom, and when these were broken up vast quantities of
limestone were formed from their debris. It must also be borne in mind
that Eozoon was not everywhere infiltrated with serpentine or other
silicious minerals; quantities of its substance were merely filled
with carbonate of lime, resembling the chamber-wall so closely that
it is nearly impossible to make out the difference, and thus is likely
to pass altogether unobserved by collectors, and to baffle even the
microscopist. (Fig. 24.) Although therefore the layers which contain
well characterized Eozoon are few and far between, there is reason to
believe that in the composition of the limestones of the Laurentian
it bore no small part, and as these limestones are some of them
several hundreds of feet in thickness, and extend over vast areas,
Eozoon may be supposed to have been as efficient a world-builder as
the Stromatoporæ of the Silurian and Devonian, the Globigerinæ and
their allies in the chalk, or the Nummulites and Miliolites in the
Eocene. The two latter groups of rock-makers are represented in our
cut, fig. 21; the first will engage our attention in chapter sixth. It
is a remarkable illustration of the constancy of natural causes and of
the persistence of animal types, that these humble Protozoans, which
began to secrete calcareous matter in the Laurentian period, have been
continuing their work in the ocean through all the geological ages,
and are still busy in accumulating those chalky muds with which recent
dredging operations in the deep sea have made us so familiar.
NOTES TO CHAPTER IV.
(A.) Original Description of Eozoon Canadense.
[As given by the author in the _Journal of the Geological Society_,
February, 1865.]
"At the request of Sir W. E. Logan, I have submitted to microscopic
examination slices of certain peculiar laminated forms, consisting
of alternate layers of carbonate of lime and serpentine, and of
carbonate of lime and white pyroxene, found in the Laurentian
limestone of Canada, and regarded by Sir William as possibly fossils.
I have also examined slices of a large number of limestones from the
Laurentian series, not showing the forms of these supposed fossils.
"The specimens first mentioned are masses, often several inches in
diameter, presenting to the naked eye alternate laminæ of serpentine,
or of pyroxene, and carbonate of lime. Their general aspect, as
remarked by Sir W. E. Logan (_Geology of Canada_, 1863, p. 49),
reminds the observer of that of the Silurian corals of the genus
Stromatopora, except that the laminæ diverge from and approach each
other, and frequently anastomose or are connected by transverse septa.
"Under the microscope the resemblance to Stromatopora is seen to
be in general form merely, and no trace appears of the radiating
pillars characteristic of that genus. The laminæ of serpentine and
pyroxene present no organic structure, and the latter mineral is
highly crystalline. The laminæ of carbonate of lime, on the contrary,
retain distinct traces of structures which cannot be of a crystalline
or concretionary character. They constitute parallel or concentric
partitions of variable thickness, enclosing flattened spaces or
chambers, frequently crossed by transverse plates or septa, in some
places so numerous as to give a vesicular appearance, in others
occurring only at rare intervals. The laminæ themselves are excavated
on their sides into rounded pits, and are in some places traversed by
canals, or contain secondary rounded cells, apparently isolated. In
addition to these general appearances, the substance of the laminæ,
where most perfectly preserved, is seen to present a fine granular
structure, and to be penetrated by numerous minute tubuli, which
are arranged in bundles of great beauty and complexity, diverging
in sheaf-like forms, and in their finer extensions anastomosing so
as to form a network (figs. 10 and 28). In transverse sections, and
under high powers, the tubuli are seen to be circular in outline, and
sharply defined (fig. 29). In longitudinal sections, they sometimes
present a beaded or jointed appearance. Even where the tubular
structure is least perfectly preserved, traces of it can still be
seen in most of the slices, though there are places in which the
laminæ are perfectly compact, and perhaps were so originally.
"With respect to the nature and probable origin of the appearances
above described, I would make the following remarks:--
"1. The serpentine and pyroxene which fill the cavities of the
calcareous matter have no appearance of concretionary structure.
On the contrary, their aspect is that of matter introduced by
infiltration, or as sediment, and filling spaces previously existing.
In other words, the calcareous matter has not been moulded on the
forms of the serpentine and augite, but these have filled spaces
or chambers in a hard calcareous mass. This conclusion is further
confirmed by the fact, to be referred to in the sequel, that the
serpentine includes multitudes of minute foreign bodies, while the
calcareous matter is uniform and homogeneous. It is also to be
observed that small veins of carbonate of lime occasionally traverse
the specimen's, and in their entire absence of structures other than
crystalline, present a striking contrast to the supposed fossils.
"2. Though the calcareous laminæ have in places a crystalline
cleavage, their forms and structures have no relation to this. Their
cells and canals are rounded, and have smooth walls, which are
occasionally lined with films apparently of carbonaceous matter.
Above all, the minute tubuli are different from anything likely to
occur in merely crystalline calc-spar. While in such rocks little
importance might be attached to external forms simulating the
appearances of corals, sponges, or other organisms, these delicate
internal structures have a much higher claim to attention. Nor is
there any improbability in the preservation of such minute parts in
rocks so highly crystalline, since it is a circumstance of frequent
occurrence in the microscopic examination of fossils that the finest
structures are visible in specimens in which the general form and the
arrangement of parts have been obliterated. It is also to be observed
that the structure of the calcareous laminæ is the same, whether the
intervening spaces are filled with serpentine or with pyroxene.
"3. The structures above described are not merely definite and
uniform, but they are of a kind proper to animal organisms, and
more especially to one particular type of animal life, as likely as
any other to occur under such circumstances: I refer to that of the
Rhizopods of the order Foraminifera. The most important point of
difference is in the great size and compact habit of growth of the
specimens in question; but there seems no good reason to maintain
that Foraminifera must necessarily be of small size, more especially
since forms of considerable magnitude referred to this type are known
in the Lower Silurian. Professor Hall has described specimens of
Receptaculites twelve inches in diameter; and the fossils from the
Potsdam formation of Labrador, referred by Mr. Billings to the genus
Archæocyathus, are examples of Protozoa with calcareous skeletons
scarcely inferior in their massive style of growth to the forms now
under consideration.
"These reasons are, I think, sufficient to justify me in regarding
these remarkable structures as truly organic, and in searching for
their nearest allies among the Foraminifera.
"Supposing then that the spaces between the calcareous laminæ, as
well as the canals and tubuli traversing their substance, were once
filled with the sarcode body of a Rhizopod, comparisons with modern
forms at once suggest themselves.
"From the polished specimens in the Museum of the Canadian Geological
Survey, it appears certain that these bodies were sessile by a broad
base, and grew by the addition of successive layers of chambers
separated by calcareous laminæ, but communicating with each other by
canals or septal orifices sparsely and irregularly distributed. Small
specimens have thus much the aspect of the modern genera Carpenteria
and Polytrema. Like the first of these genera, there would also seem
to have been a tendency to leave in the midst of the structure a
large central canal, or deep funnel-shaped or cylindrical opening,
for communication with the sea-water. Where the laminæ coalesce, and
the structure becomes more vesicular, it assumes the 'acervuline'
character seen in such modern forms as Nubecularia.
"Still the magnitude of these fossils is enormous when compared with
the species of the genera above named; and from the specimens in the
larger slabs from Grenville, in the museum of the Canadian Survey,
it would seem that these organisms grew in groups, which ultimately
coalesced, and formed large masses penetrated by deep irregular
canals; and that they continued to grow at the surface, while the
lower parts became dead and were filled up with infiltrated matter or
sediment. In short, we have to imagine an organism having the habit
of growth of Carpenteria, but attaining to an enormous size, and by
the aggregation of individuals assuming the aspect of a coral reef.
"The complicated systems of tubuli in the Laurentian fossil indicate,
however, a more complex structure than that of any of the forms
mentioned above. I have carefully compared these with the similar
structures in the 'supplementary skeleton' (or the shell-substance
that carries the vascular system) of Calcarina and other forms, and
can detect no difference except in the somewhat coarser texture of
the tubuli in the Laurentian specimens. It accords well with the
great dimensions of these, that they should thus thicken their walls
with an extensive deposit of tubulated calcareous matter; and from
the frequency of the bundles of tubuli, as well as from the thickness
of the partitions, I have no doubt that all the successive walls, as
they were formed, were thickened in this manner, just as in so many
of the higher genera of more modern Foraminifera.
"It is proper to add that no spicules, or other structures indicating
affinity to the Sponges, have been detected in any of the specimens.
"As it is convenient to have a name to designate these forms, I
would propose that of Eozoon, which will be specially appropriate to
what seems to be the characteristic fossil of a group of rocks which
must now be named Eozoic rather than Azoic. For the species above
described, the specific name of Canadense has been proposed. It may
be distinguished by the following characters:--
"Eozoon Canadense; _gen. et spec. nov._
"_General form._--Massive, in large sessile patches or irregular
cylinders, growing at the surface by the addition of successive
laminæ.
"_Internal structure._--Chambers large, flattened, irregular, with
numerous rounded extensions, and separated by walls of variable
thickness, which are penetrated by septal orifices irregularly
disposed. Thicker parts of the walls with bundles of fine branching
tubuli.
"These characters refer specially to the specimens from Grenville and
the Calumet. There are others from Perth, C. W., which show more
regular laminæ, and in which the tubuli have not yet been observed;
and a specimen from Burgess, C. W., contains some fragments of laminæ
which exhibit, on one side, a series of fine parallel tubuli like
those of Nummulina. These specimens may indicate distinct species;
but on the other hand, their peculiarities may depend on different
states of preservation.
"With respect to this last point, it may be remarked that some of
the specimens from Grenville and the Calumet show the structure of
the laminæ with nearly equal distinctness, whether the chambers are
filled with serpentine or pyroxene, and that even the minute tubuli
are penetrated and filled with these minerals. On the other hand,
there are large specimens in the collection of the Canadian Survey
in which the lower and still parts of the organism are imperfectly
preserved in pyroxene, while the upper parts are more perfectly
mineralized with serpentine."
* * * * *
[The following note was added in a reprint of the paper in the
_Canadian Naturalist_, April, 1865.]
"Since the above was written, thick slices of Eozoon from Grenville
have been prepared, and submitted to the action of hydrochloric acid
until the carbonate of lime was removed. The serpentine then remains
as a cast of the interior of the chambers, showing the form of their
original sarcode-contents. The minute tubuli are found also to have
been filled with a substance insoluble in the acid, so that casts
of these also remain in great perfection, and allow their general
distribution to be much better seen than in the transparent slices
previously prepared. These interesting preparations establish the
following additional structural points:--
"1. That the whole mass of sarcode throughout the organism was
continuous; the apparently detached secondary chambers being, as
I had previously suspected, connected with the larger chambers by
canals filled with sarcode.
"2. That some of the irregular portions without lamination are not
fragmentary, but due to the acervuline growth of the animal; and that
this irregularity has been produced in part by the formation of
projecting patches of supplementary skeleton, penetrated by beautiful
systems of tubuli. These groups of tubuli are in some places very
regular, and have in their axes cylinders of compact calcareous
matter. Some parts of the specimens present arrangements of this kind
as symmetrical as in any modern Foraminiferal shell.
"3. That all except the very thinnest portions of the walls of
the chambers present traces, more or less distinct, of a tubular
structure.
"4. These facts place in more strong contrast the structure of
the regularly laminated species from Burgess, which do not show
tubuli, and that of the Grenville specimens, less regularly
laminated and tubulous throughout. I hesitated however to regard
these two as distinct species, in consequence of the intermediate
characters presented by specimens from the Calumet, which are
regularly laminated like those of Burgess, and tubulous like those
of Grenville. It is possible that in the Burgess specimens, tubuli,
originally present, have been obliterated, and in organisms of this
grade, more or less altered by the processes of fossilisation, large
series of specimens should be compared before attempting to establish
specific distinctions."
(B.) Original Description of the Specimens added by Dr. Carpenter to
the above--in a Letter to Sir W. E. Logan.
[_Journal of Geological Society_, February, 1865.]
"The careful examination which I have made, in accordance with
the request you were good enough to convey to me from Dr. Dawson
and to second on your own part, with the structure of the very
extraordinary fossil which you have brought from the Laurentian
rocks of Canada,[Q] enables me most unhesitatingly to confirm the
sagacious determination of Dr. Dawson as to its Rhizopod characters
and Foraminiferal affinities, and at the same time furnishes new
evidence of no small value in support of that determination. In
this examination I have had the advantage of a series of sections
of the fossil much superior to those submitted to Dr. Dawson; and
also of a large series of decalcified specimens, of which Dr. Dawson
had only the opportunity of seeing a few examples after his memoir
had been written. These last are peculiarly instructive; since
in consequence of the complete infiltration of the chambers and
canals, originally occupied by the sarcode-body of the animal, by
mineral matter insoluble in dilute nitric acid, the removal of the
calcareous shell brings into view, not only the internal casts of
the chambers, but also casts of the interior of the 'canal system'
of the 'intermediate' or 'supplemental skeleton,' and even casts of
the interior of the very fine parallel tubuli which traverse the
proper walls of the chambers. And, as I have remarked elsewhere,[R]
'such casts place before us far more exact representations of the
configuration of the animal body, and of the connections of its
different parts, than we could obtain even from living specimens by
dissolving away their shells with acid; its several portions being
disposed to heap themselves together in a mass when they lose the
support of the calcareous skeleton.'
[Footnote Q: The specimens submitted to Dr. Carpenter were taken from a
block of Eozoon rock, obtained in the Petite Nation seigniory, too late
to afford Dr. Dawson an opportunity of examination. They are from the
same horizon as the Grenville specimens.--W. E. L.]
[Footnote R: _Introduction to the Study of the Foraminifera_, p. 10.]
"The additional opportunities I have thus enjoyed will be found,
I believe, to account satisfactorily for the differences to be
observed between Dr. Dawson's account of the Eozoon and my own. Had
I been obliged to form my conclusions respecting its structure only
from the specimens submitted to Dr. Dawson, I should very probably
have seen no reason for any but the most complete accordance with
his description: while if Dr. Dawson had enjoyed the advantage of
examining the entire series of preparations which have come under my
own observation, I feel confident that he would have anticipated the
corrections and additions which I now offer.
"Although the general plan of growth described by Dr. Dawson, and
exhibited in his photographs of vertical sections of the fossil,
is undoubtedly that which is typical of Eozoon, yet I find that
the acervuline mode of growth, also mentioned by Dr. Dawson, very
frequently takes its place in the more superficial parts, where
the chambers, which are arranged in regular tiers in the laminated
portions, are heaped one upon another without any regularity, as is
particularly well shown in some decalcified specimens which I have
myself prepared from the slices last put into my hands. I see no
indication that this departure from the normal type of structure
has resulted from an injury; the transition from the regular to the
irregular mode of increase not being abrupt but gradual. Nor shall I
be disposed to regard it as a monstrosity; since there are many other
Foraminifera in which an originally definite plan of growth gives
place, in a later stage, to a like acervuline piling-up of chambers.
"In regard to the form and relations of the chambers, I have little
to add to Dr. Dawson's description. The evidence afforded by their
internal casts concurs with that of sections, in showing that the
segments of the sarcode-body, by whose aggregation each layer was
constituted, were but very incompletely divided by shelly partitions;
this incomplete separation (as Dr. Dawson has pointed out) having
its parallel in that of the secondary chambers in Carpenteria. But I
have occasionally met with instances in which the separation of the
chambers has been as complete as it is in Foraminifera generally; and
the communication between them is then established by several narrow
passages exactly corresponding with those which I have described and
figured in Cycloclypeus.[S]
[Footnote S: _Op. cit._, p. 294.]
"The mode in which each successive layer originates from the one
which had preceded it, is a question to which my attention has been
a good deal directed; but I do not as yet feel confident that I
have been able to elucidate it completely. There is certainly no
regular system of apertures for the passage of stolons giving origin
to new segments, such as are found in all ordinary Polythalamous
Foraminifera, whether their type of growth be rectilinear, spiral,
or cyclical; and I am disposed to believe that where one layer is
separated from another by nothing else than the proper walls of
the chambers,--which, as I shall presently show, are traversed by
multitudes of minute tubuli giving passage to pseudopodia,--the
coalescence of these pseudopodia on the external surface would
suffice to lay the foundation of a new layer of sarcodic segments.
But where an intermediate or supplemental skeleton, consisting of a
thick layer of solid calcareous shell, has been deposited between
two successive layers, it is obvious that the animal body contained
in the lower layer of chambers must be completely cut off from
that which occupies the upper, unless some special provision exist
for their mutual communication. Such a provision I believe to have
been made by the extension of bands of sarcode, through canals left
in the intermediate skeleton, from the lower to the upper tier of
chambers. For in such sections as happen to have traversed thick
deposits of the intermediate skeleton, there are generally found
passages distinguished from those of the ordinary canal-system by
their broad flat form, their great transverse diameter, and their
non-ramification. One of these passages I have distinctly traced
to a chamber, with the cavity of which it communicated through two
or three apertures in its proper wall; and I think it likely that
I should have been able to trace it at its other extremity into a
chamber of the superjacent tier, had not the plane of the section
passed out of its course. Riband-like casts of these passages are
often to be seen in decalcified specimens, traversing the void spaces
left by the removal of the thickest layers of the intermediate
skeleton.
"But the organization of a new layer seems to have not unfrequently
taken place in a much more considerable extension of the sarcode-body
of the pre-formed layer; which either folded back its margin
over the surface already consolidated, in a manner somewhat like
that in which the mantle of a Cyprœa doubles back to deposit
the final surface-layer of its shell, or sent upwards wall-like
lamellæ, sometimes of very limited extent, but not unfrequently of
considerable length, which, after traversing the substance of the
shell, like trap-dykes in a bed of sandstone, spread themselves out
over its surface. Such, at least, are the only interpretations I can
put upon the appearances presented by decalcified specimens. For
on the one hand, it is frequently to be observed that two bands of
serpentine (or other infiltrated mineral), which represent two layers
of the original sarcode-body of the animal, approximate to each other
in some part of their course, and come into complete continuity;
so that the upper layer would seem at that part to have had its
origin in the lower. Again, even where these bands are most widely
separated, we find that they are commonly held together by vertical
lamellæ of the same material, sometimes forming mere tongues, but
often running to a considerable length. That these lamellæ have not
been formed by mineral infiltration into accidental fissures in the
shell, but represent corresponding extensions of the sarcode-body,
seems to me to be indicated not merely by the characters of their
surface, but also by the fact that portions of the canal-system may
be occasionally traced into connection with them.
"Although Dr. Dawson has noticed that some parts of the sections
which he examined present the fine tubulation characteristic of
the shells of the Nummuline Foraminifera, he does not seem to have
recognised the fact, which the sections placed in my hands have
enabled me most satisfactorily to determine,--that the proper
walls of the chambers everywhere present the fine tubulation of
the Nummuline shell; a point of the highest importance in the
determination of the affinities of Eozoon. This tubulation, although
not seen with the clearness with which it is to be discerned in
recent examples of the Nummuline type, is here far better displayed
than it is in the majority of fossil Nummulites, in which the
tubuli have been filled up by the infiltration of calcareous
matter, rendering the shell-substance nearly homogeneous. In Eozoon
these tubuli have been filled up by the infiltration of a mineral
different from that of which the shell is composed, and therefore
not coalescing with it; and the tubular structure is consequently
much more satisfactorily distinguishable. In decalcified specimens,
the free margins of the casts of the chambers are often seen to be
bordered with a delicate white glistening fringe; and when this
fringe is examined with a sufficient magnifying power, it is seen to
be made up of a multitude of extremely delicate aciculi, standing
side by side like the fibres of asbestos. These, it is obvious, are
the internal casts of the fine tubuli which perforated the proper
wall of the chambers, passing directly from its inner to its outer
surface; and their presence in this situation affords the most
satisfactory confirmation of the evidence of that tubulation afforded
by thin sections of the shell-wall.
"The successive layers, each having its own proper wall, are
often superposed one upon another without the intervention of any
supplemental or intermediate skeleton such as presents itself in
all the more massive forms of the Nummuline series; but a deposit
of this form of shell-substance, readily distinguishable by its
homogeneousness from the finely tubular shell immediately investing
the segments of the sarcode-body, is the source of the great
thickening which the calcareous zones often present in vertical
sections of Eozoon. The presence of this intermediate skeleton has
been correctly indicated by Dr. Dawson; but he does not seem to have
clearly differentiated it from the proper wall of the chambers.
All the tubuli which he has described belong to that canal system
which, as I have shown,[T] is limited in its distribution to the
intermediate skeleton, and is expressly designed to supply a channel
for its nutrition and augmentation. Of this canal system, which
presents most remarkable varieties in dimensions and distribution, we
learn more from the casts presented by decalcified specimens, than
from sections, which only exhibit such parts of it as their plane may
happen to traverse. Illustrations from both sources, giving a more
complete representation of it than Dr. Dawson's figures afford, have
been prepared from the additional specimens placed in my hands.
[Footnote T: _Op. cit._, pp. 50, 51.]
"It does not appear to me that the canal system takes its origin
directly from the cavity of the chambers. On the contrary, I believe
that, as in Calcarina (which Dr. Dawson has correctly referred to as
presenting the nearest parallel to it among recent Foraminifera),
they originate in lacunar spaces on the outside of the proper
walls of the chambers, into which the tubuli of those walls open
externally; and that the extensions of the sarcode-body which
occupied them were formed by the coalescence of the pseudopodia
issuing from those tubuli.[U]
[Footnote U: _Op. cit._, p. 221.]
"It seems to me worthy of special notice, that the canal system,
wherever displayed in transparent sections, is distinguished by a
yellowish brown coloration, so exactly resembling that which I have
observed in the canal system of recent Foraminifera (as Polystomella
and Calcarina) in which there were remains of the sarcode-body, that
I cannot but believe the infiltrating mineral to have been dyed by
the remains of sarcode still existing in the canals of Eozoon at the
time of its consolidation. If this be the case, the preservation
of this colour seems to indicate that no considerable metamorphic
action has been exerted upon the rock in which this fossil occurs.
And I should draw the same inference from the fact that the organic
structure of the shell is in many instances even more completely
preserved than it usually is in the Nummulites and other Foraminifera
of the Nummulitic limestone of the early Tertiaries.
"To sum up,--That the _Eozoon_ finds its proper place in the
Foraminiferal series, I conceive to be conclusively proved by its
accordance with the great types of that series, in all the essential
characters of organization;--namely, the structure of the shell
forming the proper wall of the chambers, in which it agrees precisely
with Nummulina and its allies; the presence of an intermediate
skeleton and an elaborate canal system, the disposition of which
reminds us most of Calcarina; a mode of communication of the chambers
when they are most completely separated, which has its exact parallel
in Cycloclypeus; and an ordinary want of completeness of separation
between the chambers, corresponding with that which is characteristic
of Carpenteria.
"There is no other group of the animal kingdom to which Eozoon
presents the slightest structural resemblance; and to the suggestion
that it may have been of kin to Nullipore, I can offer the most
distinct negative reply, having many years ago carefully studied the
structure of that stony Alga, with which that of Eozoon has nothing
whatever in common.
"The objections which not unnaturally occur to those familiar with
only the ordinary forms of Foraminifera, as to the admission of
Eozoon into the series, do not appear to me of any force. These have
reference in the first place to the great _size_ of the organism; and
in the second, to its exceptional mode of growth.
"1. It must be borne in mind that all the Foraminifera normally
increase by the continuous gemmation of new segments from those
previously formed; and that we have, in the existing types, the
greatest diversities in the extent to which this gemmation may
proceed. Thus in the Globigerinæ, whose shells cover to an unknown
thickness the sea bottom of all that portion of the Atlantic Ocean
which is traversed by the Gulf Stream, only eight or ten segments
are ordinarily produced by continuous gemmation; and if new segments
are developed from the last of these, they detach themselves so
as to lay the foundation of independent Globigerinæ. On the other
hand in Cycloclypeus, which is a discoidal structure attaining two
and a quarter inches in diameter, the number of segments formed by
continuous gemmation must be many thousand. Again, the Receptaculites
of the Canadian Silurian rocks, shown by Mr. Salter's drawings[V]
to be a gigantic Orbitolite, attains a diameter of twelve inches;
and if this were to increase by vertical as well as by horizontal
gemmation (after the manner of Tinoporus or Orbitoides) so that one
discoidal layer would be piled on another, it would form a mass
equalling Eozoon in its ordinary dimensions. To say, therefore, that
Eozoon cannot belong to the Foraminifera on account of its gigantic
size, is much as if a botanist who had only studied plants and
shrubs were to refuse to admit a tree into the same category. The
very same continuous gemmation which has produced an Eozoon would
produce an equal mass of independent Globigerinæ, if after eight
or ten repetitions of the process, the new segments were to detach
themselves.
[Footnote V: _First Decade of Canadian Fossils_, pl. x.]
"It is to be remembered, moreover, that the largest masses of sponges
are formed by continuous gemmation from an original Rhizopod segment;
and that there is no _à priori_ reason why a Foraminiferal organism
should not attain the same dimensions as a Poriferal one,--the
intimate relationship of the two groups, notwithstanding the
difference between their skeletons, being unquestionable.
"2. The difficulty arising from the zoophytic plan of growth of
Eozoon is at once disposed of by the fact that we have in the recent
Polytrema (as I have shown, _op. cit._, p. 235) an organism nearly
allied in all essential points of structure to Rotalia, yet no
less aberrant in its plan of growth, having been ranked by Lamarck
among the Millepores. And it appears to me that Eozoon takes its
place quite as naturally in the Nummuline series as Polytrema in
the Rotaline. As we are led from the typical Rotalia, through the
less regular Planorbulina, to Tinoporus, in which the chambers are
piled up vertically, as well as multiplied horizontally, and thence
pass by an easy gradation to Polytrema, in which all regularity of
external form is lost; so may we pass from the typical Operculina or
Nummulina, through Heterostegina and Cycloclypeus to Orbitoides, in
which, as in Tinoporus, the chambers multiply both by horizontal and
by vertical gemmation; and from Orbitoides to Eozoon the transition
is scarcely more abrupt than from Tinoporus to Polytrema.
"The general acceptance, by the most competent judges, of my views
respecting the primary value of the characters furnished by the
intimate structure of the shell, and the very subordinate value
of plan of growth, in the determination of the affinities of
Foraminifera, renders it unnecessary that I should dwell further on
my reasons for unhesitatingly affirming the Nummuline affinities of
Eozoon from the microscopic appearances presented by the proper wall
of its chambers, notwithstanding its very aberrant peculiarities;
and I cannot but feel it to be a feature of peculiar interest in
geological inquiry, that the true relations of by far the earliest
fossil yet known should be determinable by the comparison of a
portion which the smallest pin's head would cover, with organisms at
present existing."
(C.) Note on Specimens From Long Lake and Wentworth.
[_Journal of Geological Society_, August, 1867.]
"Specimens from Long Lake, in the collection of the Geological
Survey of Canada, exhibit white crystalline limestone with light
green compact or septariiform[W] serpentine, and much resemble some
of the serpentine limestones of Grenville. Under the microscope the
calcareous matter presents a delicate areolated appearance, without
lamination; but it is not an example of acervuline Eozoon, but rather
of fragments of such a structure, confusedly aggregated together, and
having the interstices and cell-cavities filled with serpentine. I
have not found in any of these fragments a canal system similar to
that of Eozoon Canadense, though there are casts of large stolons,
and, under a high power, the calcareous matter shows in many places
the peculiar granular or cellular appearance which is one of the
characters of the supplemental skeleton of that species. In a few
places a tubulated cell-wall is preserved, with structure similar to
that of Eozoon Canadense.
[Footnote W: I use the term "septariiform" to denote the _curdled_
appearance so often presented by the Laurentian serpentine.]
"Specimens of Laurentian limestone from Wentworth, in the collection
of the Geological Survey, exhibit many rounded silicious bodies, some
of which are apparently grains of sand, or small pebbles; but others,
especially when freed from the calcareous matter by a dilute acid,
appear as rounded bodies, with rough surfaces, either separate or
aggregated in lines or groups, and having minute vermicular processes
projecting from their surfaces. At first sight these suggest the
idea of spicules; but I think it on the whole more likely that
they are casts of cavities and tubes belonging to some calcareous
Foraminiferal organism which has disappeared. Similar bodies, found
in the limestone of Bavaria, have been described by Gümbel, who
interprets them in the same way. They may also be compared with the
silicious bodies mentioned in a former paper as occurring in the
loganite filling the chambers of specimens of _Eozoon_ from Burgess."
These specimens will be more fully referred to under Chapter VI.
(D.) Additional Structural Facts.
I may mention here a peculiar and interesting structure which has
been detected in one of my specimens while these sheets were passing
through the press. It is an abnormal thickening of the calcareous
wall, extending across several layers, and perforated with large
parallel cylindrical canals, filled with dolomite, and running in
the direction of the laminæ; the intervening calcite being traversed
by a very fine and delicate canal system. It makes a nearer approach
to some of the Stromatoporæ mentioned in Chapter VI. than any other
Laurentian structure hitherto observed, and may be either an abnormal
growth of Eozoon, consequent on some injury, or a parasitic mass of
some Stromatoporoid organism overgrown by the laminæ of the fossil.
The structure of the dolomite in this specimen indicates that it
first lined the canals, and afterward filled them; an appearance
which I have also observed recently in the larger canals filled
with serpentine (Plate VIII., fig. 5). The cut below is an attempt,
only partially successful, to show the Amœba-like appearance, when
magnified, of the casts of the chambers of Eozoon, as seen on the
decalcified surface of a specimen broken parallel to the laminæ.
[Illustration: Fig. 21_a_.]
[Illustration:
Plate V.
_Nature-print of Eozoon, showing laminated, acervuline, and fragmental
portions._
This is printed from an electrotype taken from an etched slab of
Eozoon, and not touched with a graver except to remedy some accidental
flaws in the plate. The diagonal white line marks the course of a
calcite vein.]
CHAPTER V.
THE PRESERVATION OF EOZOON.
Perhaps nothing excites more scepticism as to this ancient fossil
than the prejudice existing among geologists that no organism can be
preserved in rocks so highly metamorphic as those of the Laurentian
series. I call this a prejudice, because any one who makes the
microscopic structure of rocks and fossils a special study, soon learns
that fossils undergo the most remarkable and complete chemical changes
without losing their minute structure, and that calcareous rocks if
once fossiliferous are hardly ever so much altered as to lose all
trace of the organisms which they contained, while it is a most common
occurrence to find highly crystalline rocks of this kind abounding in
fossils preserved as to their minute structure.
Let us, however, look at the precise conditions under which this takes
place.
When calcareous fossils of irregular surface and porous or cellular
texture, such as Eozoon was or corals were and are, become imbedded
in clay, marl, or other soft sediment, they can be washed out and
recovered in a condition similar to that of recent specimens, except
that their pores or cells if open may be filled with the material of
the matrix, or if not so open that they can be thus filled, they may be
more or less incrusted with mineral deposits introduced by water, or
may even be completely filled up in this way. But if such fossils are
contained in hard rocks, they usually fail, when these are broken, to
show their external surfaces, and, breaking across with the containing
rock, they exhibit their internal structure merely,--and this more
or less distinctly, according to the manner in which their cells or
cavities have been filled. Here the microscope becomes of essential
service, especially when the structures are minute. A fragment of
fossil wood which to the naked eye is nothing but a dark stone, or a
coral which is merely a piece of gray or coloured marble, or a specimen
of common crystalline limestone made up originally of coral fragments,
presents, when sliced and magnified, the most perfect and beautiful
structure. In such cases it will be found that ordinarily the original
substance of the fossil remains, in a more or less altered state. Wood
may be represented by dark lines of coaly matter, or coral by its
white or transparent calcareous laminæ; while the material which has
been introduced and which fills the cavities may so differ in colour,
transparency, or crystalline structure, as to act differently on
light, and so reveal the structure. These fillings are very curious.
Sometimes they are mere earthy or muddy matter. Sometimes they are
pure and transparent and crystalline. Often they are stained with
oxide of iron or coaly matter. They may consist of carbonate of lime,
silica or silicates, sulphate of baryta, oxides of iron, carbonate of
iron, iron pyrite, or sulphides of copper or lead, all of which are
common materials. They are sometimes so complicated that I have seen
even the minute cells of woody structures, each with several bands of
differently coloured materials deposited in succession, like the coats
of an onyx agate.
A further stage of mineralization occurs when the substance of the
organism is altogether removed and replaced by foreign matter, either
little by little, or by being entirely dissolved or decomposed,
leaving a cavity to be filled by infiltration. In this state are some
silicified woods, and those corals which have been not filled with but
converted into silica, and can thus sometimes be obtained entire and
perfect by the solution in an acid of the containing limestone, or by
its removal in weathering. In this state are the beautiful silicified
corals obtained from the corniferous limestone of Lake Erie. It may be
well to present to the eye these different stages of fossilization. I
have attempted to do this in fig. 22, taking a tabulate coral of the
genus Favosites for an example, and supposing the materials employed to
be calcite and silica. Precisely the same illustration would apply to a
piece of wood, except that the cell-wall would be carbonaceous matter
instead of carbonate of lime. In this figure the dotted parts represent
carbonate of lime, the diagonally shaded parts silica or a silicate.
Thus we have, in the natural state, the walls of carbonate of lime
and the cavities empty. When fossilized the cavities may be merely
filled with carbonate of lime, or they may be filled with silica; or
the walls themselves may be replaced by silica and the cavities may
remain filled with carbonate of lime; or both the walls and cavities
may be represented by or filled with silica or silicates. The ordinary
specimens of Eozoon are in the third of these stages, though some exist
in the second, and I have reason to believe that some have reached to
the fifth. I have not met with any in the fourth stage, though this is
not uncommon in Silurian and Devonian fossils.
[Illustration: Fig. 22. _Diagram showing different States of
Fossilization of a Cell of a Tabulate Coral._
(_a._) Natural condition--walls calcite, cell empty. (_b._) Walls
calcite, cell filled with the same. (_c._) Walls calcite, cell filled
with silica or silicate. (_d._) Walls silicified, cell filled with
calcite. (_e._) Walls silicified, cell filled with silica or silicate.]
With regard to the calcareous organisms with which we have now to do,
when these are imbedded in pure limestone and filled with the same, so
that the whole rock, fossils and all, is identical in composition, and
when metamorphic action has caused the whole to become crystalline,
and perhaps removed the remains of carbonaceous matter, it may be very
difficult to detect any traces of fossils. But even in this case
careful management of light may reveal indications of structure, as in
some specimens of Eozoon described by the writer and Dr. Carpenter. In
many cases, however, even where the limestones have become perfectly
crystalline, and the cleavage planes cut freely across the fossils,
these exhibit their forms and minute structure in great perfection.
This is the case in many of the Lower Silurian limestones of Canada,
as I have elsewhere shown.[X] The gray crystalline Trenton limestone
of Montreal, used as a building stone, is an excellent illustration
of this. To the naked eye it is a gray marble composed of cleavable
crystals; but when examined in thin slices, it shows its organic
fragments in the greatest perfection, and all the minute structures
are perfectly marked out by delicate carbonaceous lines. The only
exception in this limestone is in the case of the Crinoids, in which
the cellular structure is filled with transparent calc-spar, perfectly
identical with the original solid matter, so that they appear solid
and homogeneous, and can be recognised only by their external forms.
The specimen represented in fig. 23, is a mass of Corals, Bryozoa, and
Crinoids, and shows these under a low power, as represented in the
figure; but to the naked eye it is merely a gray crystalline limestone.
The specimen represented in fig. 24 shows the Laurentian Eozoon in a
similar state of preservation. It is from a sketch by Dr. Carpenter,
and shows the delicate canals partly filled with calcite as clear and
colourless as that of the shell itself, and distinguishable only by
careful management of the light.
[Footnote X: _Canadian Naturalist_, 1859; Microscopic Structure of
Canadian Limestones.]
[Illustration: Fig. 23. _Slice of Crystalline Lower Silurian Limestone;
showing Crinoids, Bryozoa, and Corals in fragments._]
[Illustration: Fig. 24. _Wall of Eozoon penetrated with Canals. The
unshaded portions filled with Calcite._ (_After Carpenter._)]
In the case of recent and fossil Foraminifers, these--when not so
little mineralized that their chambers are empty, or only partially
filled, which is sometimes the case even with Eocene Nummulites
and Cretaceous forms of smaller size,--are very frequently filled
solid with calcareous matter, and as Dr. Carpenter well remarks,
even well preserved Tertiary Nummulites in this state often fail
greatly in showing their structures, though in the same condition
they occasionally show these in great perfection. Among the finest
I have seen are specimens from the Mount of Olives (fig. 19), and
Dr. Carpenter mentions as equally good those of the London clay of
Bracklesham. But in no condition do modern Foraminifera or those of
the Tertiary and Mesozoic rocks appear in greater perfection than when
filled with the hydrous silicate of iron and potash called glauconite,
and which gives by the abundance of its little bottle-green concretions
the name of "green-sand" to formations of this age both in Europe and
America. In some beds of green-sand every grain seems to have been
moulded into the interior of a microscopic shell, and has retained
its form after the frail envelope has been removed. In some cases the
glauconite has not only filled the chambers but has penetrated the
fine tubulation, and when the shell is removed, either naturally or
by the action of an acid, these project in minute needles or bundles
of threads from the surface of the cast. It is in the warmer seas,
and especially in the bed of the Ægean and of the Gulf Stream, that
such specimens are now most usually found. If we ask why this mineral
glauconite should be associated with Foraminiferal shells, the answer
is that they are both products of one kind of locality. The same sea
bottoms in which Foraminifera most abound are also those in which for
some unknown chemical reason glauconite is deposited. Hence no doubt
the association of this mineral with the great Foraminiferal formation
of the chalk. It is indeed by no means unlikely that the selection
by these creatures of the pure carbonate of lime from the sea-water
or its minute plants, may be the means of setting free the silica,
iron, and potash, in a state suitable for their combination. Similar
silicates are found associated with marine limestones, as far back as
the Silurian age; and Dr. Sterry Hunt, than whom no one can be a better
authority on chemical geology, has argued on chemical grounds that the
occurrence of serpentine with the remains of Eozoon is an association
of the same character.
However this may be, the infiltration of the pores of Eozoon with
serpentine and other silicates has evidently been one main means of
the preservation of its structure. When so infiltrated no metamorphism
short of the complete fusion of the containing rock could obliterate
the minutest points of structure; and that such fusion has not
occurred, the preservation in the Laurentian rocks of the most delicate
lamination of the beds shows conclusively; while, as already stated, it
can be shown that the alteration which has occurred might have taken
place at a temperature far short of that necessary to fuse limestone.
Thus has it happened that these most ancient fossils have been
handed down to our time in a state of preservation comparable, as Dr.
Carpenter states, to that of the best preserved fossil Foraminifera
from the more recent formations that have come under his observation in
the course of all his long experience.
Let us now look more minutely at the nature of the typical specimens
of Eozoon as originally observed and described, and then turn to those
preserved in other ways, or more or less destroyed and defaced. Taking
a polished specimen from Petite Nation, like that delineated in Plate
V., we find the shell represented by white limestone, and the chambers
by light green serpentine. By acting on the surface with a dilute
acid we etch out the calcareous part, leaving a cast in serpentine
of the cavities occupied by the soft parts; and when this is done in
polished slices these may be made to print their own characters on
paper, as has actually been done in the case of Plate V., which is an
electrotype taken from an actual specimen, and shows both the laminated
and acervuline parts of the fossil. If the process of decalcification
has been carefully executed, we find in the excavated spaces delicate
ramifying processes of opaque serpentine or transparent dolomite, which
were originally imbedded in the calcareous substance, and which are
often of extreme fineness and complexity. (Plate VI. and fig. 10.)
These are casts of the canals which traversed the shell when still
inhabited by the animal. In some well preserved specimens we find the
original cell-wall represented by a delicate white film, which under
the microscope shows minute needle-like parallel processes representing
its still finer tubuli. It is evident that to have filled these tubuli
the serpentine must have been introduced in a state of actual solution,
and must have carried with it no foreign impurities. Consequently we
find that in the chambers themselves the serpentine is pure; and if we
examine it under polarized light, we see that it presents a singularly
curdled or irregularly laminated appearance, which I have designated
under the name septariiform, as if it had an imperfectly crystalline
structure, and had been deposited in irregular laminæ, beginning at
the sides of the chambers, and filling them toward the middle, and
had afterward been cracked by shrinkage, and the cracks filled with a
second deposit of serpentine. Now, serpentine is a hydrous silicate of
magnesia, and all that we need to suppose is that in the deposits of
the Laurentian sea magnesia was present instead of iron and potash,
and we can understand that the Laurentian fossil has been petrified
by infiltration with serpentine, as more modern Foraminifera have
been with glauconite, which, though it usually has little magnesia,
often has a considerable percentage of alumina. Further, in specimens
of Eozoon from Burgess, the filling mineral is loganite, a compound
of silica, alumina, magnesia and iron, with water, and in certain
Silurian limestones from New Brunswick and Wales, in which the delicate
microscopic pores of the skeletons of stalked star-fishes or Crinoids
have been filled with mineral deposits, so that when decalcified
these are most beautifully represented by their casts, Dr. Hunt has
proved the filling mineral to be a silicate of alumina, iron, magnesia
and potash, intermediate between serpentine and glauconite. We have,
therefore, ample warrant for adhering to Dr. Hunt's conclusion that
the Laurentian serpentine was deposited under conditions similar to
those of the modern green-sand. Indeed, independently of Eozoon, it is
impossible that any geologist who has studied the manner in which this
mineral is associated with the Laurentian limestones could believe it
to have been formed in any other way. Nor need we be astonished at
the fineness of the infiltration by which these minute tubes, perhaps
1/10000 of an inch in diameter, are filled with mineral matter. The
micro-geologist well knows how, in more modern deposits, the finest
pores of fossils are filled, and that mineral matter in solution
can penetrate the smallest openings that the microscope can detect.
Wherever the fluids of the living body can penetrate, there also
mineral substances can be carried, and this natural injection, effected
under great pressure and with the advantage of ample time, can surpass
any of the feats of the anatomical manipulator. Fig. 25 represents
a microscopic joint of a Crinoid from the Upper Silurian of New
Brunswick, injected with the hydrous silicate already referred to, and
fig. 26 shows a microscopic chambered or spiral shell, from a Welsh
Silurian limestone, with its cavities filled with a similar substance.
[Illustration: Fig. 25. _Joint of a Crinoid, having its pores injected
with a Hydrous Silicate._
Upper Silurian Limestone, Pole Hill, New Brunswick. Magnified 25
diameters.]
[Illustration: Fig. 26. _Shell from a Silurian Limestone, Wales; its
cavity filled with a Hydrous Silicate._
Magnified 25 diameters.]
It is only necessary to refer to the attempts which have been made to
explain by merely mineral deposits the occurrence of the serpentine
in the canals and chambers of Eozoon, and its presenting the form it
does, to see that this is the case. Prof. Rowney, for example, to avoid
the force of the argument from the canal system, is constrained to
imagine that the whole mass has at one time been serpentine, and that
this has been partially washed away, and replaced by calcite. If so,
whence the deposition of the supposed mass of serpentine, which has to
be accounted for in this way as well as in the other? How did it happen
to be eroded into so regular chambers, leaving intermediate floors and
partitions. And, more wonderful still, how did the regular dendritic
bundles, so delicate that they are removed by a breath, remain perfect,
and endure until they were imbedded in calcareous spar? Further, how
does it happen that in some specimens serpentine and pyroxene seem to
have encroached upon the structure, as if they and not calcite were the
eroding minerals? How any one who has looked at the structures can for
a moment imagine such a possibility, it is difficult to understand. If
we could suppose the serpentine to have been originally deposited as
a cellular or laminated mass, and its cavities filled with calcite in
a gelatinous or semi-fluid state, we might suppose the fine processes
of serpentine to have grown outward into these cavities in the mass,
as fibres of oxide of iron or manganese have grown in the silica of
moss-agate; but this theory would be encompassed with nearly as great
mechanical and chemical difficulties. The only rational view that any
one can take of the process is, that the calcareous matter was the
original substance, and that it had delicate tubes traversing it which
became injected with serpentine. The same explanation, and no other,
will suffice for those delicate cell-walls, penetrated by innumerable
threads of serpentine, which must have been injected into pores. It is
true that there are in some of the specimens cracks filled with fibrous
serpentine or chrysotile, but these traverse the mass in irregular
directions, and they consist of closely packed angular prisms,
instead of a matrix of limestone penetrated by cylindrical threads of
serpentine. (Fig. 27.) Here I must once for all protest against the
tendency of some opponents of Eozoon to confound these structures and
the canal system of Eozoon with the acicular crystals, and dendritic
or coralloidal forms, observed in some minerals. It is easy to make
such comparisons appear plausible to the uninitiated, but practised
observers cannot be so deceived, the differences are too marked and
essential. In illustration of this, I may refer to the highly magnified
canals in figs. 28 and 29. Further, it is evident from the examination
of the specimens, that the chrysotile veins, penetrating as they often
do diagonally or transversely across both chambers and walls, must have
originated subsequently to the origin and hardening of the rock and its
fossils, and result from aqueous deposition of fibrous serpentine in
cracks which traverse alike the fossils and their matrix. In specimens
now before me, nothing can be more plain than this entire independence
of the shining silky veins of fibrous serpentine, and the fact of their
having been formed subsequently to the fossilization of the Eozoon;
since they can be seen to run across the lamination, and to branch off
irregularly in lines altogether distinct from the structure. This,
while it shows that these veins have no connection with the fossil,
shows also that the latter was an original ingredient of the beds when
deposited, and not a product of subsequent concretionary action.
[Illustration: Fig. 27. _Diagram showing the different appearances
of the cell-wall of Eozoon and of a vein of Chrysotile, when highly
magnified._]
[Illustration: Fig. 28. _Casts of Canals of Eozoon in Serpentine,
decalcified and highly magnified._]
[Illustration: Fig. 29. _Canals of Eozoon._
Highly magnified.]
Taking the specimens preserved by serpentine as typical, we now turn
to certain other and, in some respects, less characteristic specimens,
which are nevertheless very instructive. At the Calumet some of
the masses are partly filled with serpentine and partly with white
pyroxene, an anhydrous silicate of lime and magnesia. The two minerals
can readily be distinguished when viewed with polarized light; and in
some slices I have seen part of a chamber or group of canals filled
with serpentine and part with pyroxene. In this case the pyroxene
or the materials which now compose it, must have been introduced by
infiltration, as well as the serpentine. This is the more remarkable as
pyroxene is most usually found as an ingredient of igneous rocks; but
Dr. Hunt has shown that in the Laurentian limestones and also in veins
traversing them, it occurs under conditions which imply its deposition
from water, either cold or warm. Gümbel remarks on this:--"Hunt, in
a very ingenious manner, compares this formation and deposition of
serpentine, pyroxene, and loganite, with that of glauconite, whose
formation has gone on uninterruptedly from the Silurian to the Tertiary
period, and is even now taking place in the depths of the sea; it being
well known that Ehrenberg and others have already shown that many of
the grains of glauconite are casts of the interior of foraminiferal
shells. In the light of this comparison, the notion that the serpentine
and such like minerals of the primitive limestones have been formed,
in a similar manner, in the chambers of Eozoic Foraminifera, loses any
traces of improbability which it might at first seem to possess."
In many parts of the skeleton of Eozoon, and even in the best
infiltrated serpentine specimens, there are portions of the cell-wall
and canal system which have been filled with calcareous spar or with
dolomite, so similar to the skeleton that it can be detected only under
the most favourable lights and with great care. (Fig. 24, _supra_.)
The same phenomena may be observed in joints of Crinoids from the
Palæozoic rocks, and they constitute proofs of organic origin even
more irrefragable than the filling with serpentine. Dr. Carpenter has
recently, in replying to the objections of Mr. Carter, made excellent
use of this feature of the preservation of Eozoon. It is further to
be remarked that in all the specimens of true Eozoon, as well as
in many other calcareous fossils preserved in ancient rocks, the
calcareous matter, even when its minute structures are not preserved
or are obscured, presents a minutely granular or curdled appearance,
arising no doubt from the original presence of organic matter, and not
recognised in purely inorganic calcite.
Another style of these remarkable fossils is that of the Burgess
specimens. In these the walls have been changed into dolomite
or magnesian limestone, and the canals seem to have been wholly
obliterated, so that only the laminated structure remains. The material
filling the chambers is also an aluminous silicate named loganite; and
this seems to have been introduced, not so much in solution, as in
the state of muddy slime, since it contains foreign bodies, as grains
of sand and little groups of silicious concretions, some of which are
not unlikely casts of the interior of minute foraminiferal shells
contemporary with Eozoon, and will be noticed in the sequel.
[Illustration: Fig. 30. _Eozoon from Tudor._
Two-thirds natural size. (_a._) Tubuli. (_b._) Canals. Magnified. _a_
and _b_ from another specimen.]
Still another mode of occurrence is presented by a remarkable specimen
from Tudor in Ontario, and from beds probably on the horizon of the
Upper Laurentian or Huronian.[Y] It occurs in a rock scarcely at all
metamorphic, and the fossil is represented by white carbonate of lime,
while the containing matrix is a dark-coloured coarse limestone. In
this specimen the material filling the chambers has not penetrated
the canals except in a few places, where they appear filled with dark
carbonaceous matter. In mode of preservation these Tudor specimens
much resemble the ordinary fossils of the Silurian rocks. One of
the specimens in the collection of the Geological Survey (fig. 30)
presents a clavate form, as if it had been a detached individual
supported on one end at the bottom of the sea. It shows, as does
also the original Calumet specimen, the septa approaching each other
and coalescing at the margin of the form, where there were probably
orifices communicating with the exterior. Other specimens of fragmental
Eozoon from the Petite Nation localities have their canals filled with
dolomite, which probably penetrated them after they were broken up
and imbedded in the rock. I have ascertained with respect to these
fragments of Eozoon, that they occur abundantly in certain layers of
the Laurentian limestone, beds of some thickness being in great part
made up of them, and coarse and fine fragments occur in alternate
layers, like the broken corals in some Silurian limestones.
[Footnote Y: See Note B, Chap. III.]
Finally, on this part of the subject, careful observation of many
specimens of Laurentian limestone which present no trace of Eozoon
when viewed by the naked eye, and no evidence of structure when acted
on with acids, are nevertheless organic, and consist of fragments
of Eozoon, and possibly of other organisms, not infiltrated with
silicates, but only with carbonate of lime, and consequently revealing
only obscure indications of their minute structure. I have satisfied
myself of this by long and patient investigations, which scarcely admit
of any adequate representation, either by words or figures.
Every worker in those applications of the microscope to geological
specimens which have been termed micro-geology, is familiar with the
fact that crystalline forces and mechanical movements of material
often play the most fantastic tricks with fossilized organic matter.
In fossil woods, for example, we often have the tissues disorganized,
with radiating crystallizations of calcite and little spherical
concretions of quartz, or disseminated cubes and grains of pyrite,
or little veins filled with sulphate of barium or other minerals. We
need not, therefore, be surprised to find that in the venerable rocks
containing Eozoon, such things occur in the more highly crystalline
parts of the limestones, and even in some still showing traces of
the fossil. We find many disseminated crystals of magnetite, pyrite,
spinel, mica, and other minerals, curiously curved prisms of vermicular
mica, bundles of aciculi of tremolite and similar substances, veins of
calcite and crysolite or fibrous serpentine, which often traverse the
best specimens. Where these occur abundantly we usually find no organic
structures remaining, or if they exist they are in a very defective
state of preservation. Even in specimens presenting the lamination of
Eozoon to the naked eye, these crystalline actions have often destroyed
the minute structure; and I fear that some microscopists have been
victimised by having under their consideration only specimens in which
the actual characters had been too much defaced to be discernible. I
must here state that I have found some of the specimens sold under
the name of Eozoon Canadense by dealers in microscopical objects to
be almost or quite worthless, being destitute of any good structure,
and often merely pieces of Laurentian limestone with serpentine
grains only. I fear that the circulation of such specimens has done
much to cause scepticism as to the Foraminiferal nature of Eozoon. No
mistake can be greater than to suppose that any and every specimen
of Laurentian limestone must contain Eozoon. More especially have
I hitherto failed to detect traces of it in those carbonaceous or
graphitic limestones which are so very abundant in the Laurentian
country. Perhaps where vegetable matter was very abundant Eozoon
did not thrive, or on the other hand the growth of Eozoon may have
diminished the quantity of vegetable matter. It is also to be observed
that much compression and distortion have occurred in the beds of
Laurentian limestone and their contained fossils, and also that the
specimens are often broken by faults, some of which are so small as to
appear only on microscopic examination, and to shift the plates of the
fossil just as if they were beds of rock. This, though it sometimes
produces puzzling appearances, is an evidence that the fossils were
hard and brittle when this faulting took place, and is consequently
an additional proof of their extraneous origin. In some specimens it
would seem that the lower and older part of the fossil had been wholly
converted into serpentine or pyroxene, or had so nearly experienced
this change that only small parts of the calcareous wall can be
recognised. These portions correspond with fossil woods altogether
silicified, not only by the filling of the cells, but also by the
conversion of the walls into silica. I have specimens which manifestly
show the transition from the ordinary condition of filling with
serpentine to one in which the cell-walls are represented obscurely by
one shade of this mineral and the cavities by another.
The above considerations as to mode of preservation of Eozoon concur
with those in previous chapters in showing its oceanic character;
but the ocean of the Eozoic period may not have been so deep as at
present, and its waters were probably warm and well stocked with
mineral matters derived from the newly formed land, or from hot springs
in its own bottom. On this point the interesting investigations of
Dr. Hunt with reference to the chemical conditions of the Silurian
seas, allow us to suppose that the Laurentian ocean may have been much
more richly stored, more especially with salts of lime and magnesia,
than that of subsequent times. Hence the conditions of warmth, light,
and nutriment, required by such gigantic Protozoans would all be
present, and hence, also no doubt, some of the peculiarities of its
mineralization.
NOTES TO CHAPTER V.
(A.) Dr. Sterry Hunt on the Mineralogy of Eozoon and the containing
Rocks.
It was fortunate for the recognition of Eozoon that Dr. Hunt had,
before its discovery, made so thorough researches into the chemistry
of the Laurentian series, and was prepared to show the chemical
possibilities of the preservation of fossils in these ancient
deposits. The following able summary of his views was appended to the
original description of the fossil in the _Journal of the Geological
Society_.
"The details of structure have been preserved by the introduction
of certain mineral silicates, which have not only filled up the
chambers, cells, and canals left vacant by the disappearance of the
animal matter, but have in very many cases been injected into the
tubuli, filling even their smallest ramifications. These silicates
have thus taken the place of the original sarcode, while the
calcareous septa remain. It will then be understood that when the
replacement of the Eozoon by silicates is spoken of, this is to be
understood of the soft parts only; since the calcareous skeleton is
preserved, in most cases, without any alteration. The vacant spaces
left by the decay of the sarcode may be supposed to have been filled
by a process of infiltration, in which the silicates were deposited
from solution in water, like the silica which fills up the pores of
wood in the process of silicification. The replacing silicates, so
far as yet observed, are a white pyroxene, a pale green serpentine,
and a dark green alumino-magnesian mineral, which is allied in
composition to chlorite and to pyrosclerite, and which I have
referred to loganite. The calcareous septa in the last case are found
to be dolomitic, but in the other instances are nearly pure carbonate
of lime. The relations of the carbonate and the silicates are well
seen in thin sections under the microscope, especially by polarized
light. The calcite, dolomite, and pyroxene exhibit their crystalline
structure to the unaided eye; and the serpentine and loganite are
also seen to be crystalline when examined with the microscope. When
portions of the fossil are submitted to the action of an acid, the
carbonate of lime is dissolved, and a coherent mass of serpentine is
obtained, which is a perfect cast of the soft parts of the Eozoon.
The form of the sarcode which filled the chambers and cells is
beautifully shown, as well as the connecting canals and the groups
of tubuli; these latter are seen in great perfection upon surfaces
from which the carbonate of lime has been partially dissolved. Their
preservation is generally most complete when the replacing mineral is
serpentine, although very perfect specimens are sometimes found in
pyroxene. The crystallization of the latter mineral appears, however,
in most cases to have disturbed the calcareous septa.
"Serpentine and pyroxene are generally associated in these specimens,
as if their disposition had marked different stages of a continuous
process. At the Calumet, one specimen of the fossil exhibits the
whole of the sarcode replaced by serpentine; while, in another one
from the same locality, a layer of pale green translucent serpentine
occurs in immediate contact with the white pyroxene. The calcareous
septa in this specimen are very thin, and are transverse to the plane
of contact of the two minerals; yet they are seen to traverse both
the pyroxene and the serpentine without any interruption or change.
Some sections exhibit these two minerals filling adjacent cells,
or even portions of the same cell, a clear line of division being
visible between them. In the specimens from Grenville on the other
hand, it would seem as if the development of the Eozoon (considerable
masses of which were replaced by pyroxene) had been interrupted, and
that a second growth of the animal, which was replaced by serpentine,
had taken place upon the older masses, filling up their interstices."
[Details of chemical composition are then given.]
"When examined under the microscope, the loganite which replaces the
Eozoon of Burgess shows traces of cleavage-lines, which indicate a
crystalline structure. The grains of insoluble matter found in the
analysis, chiefly of quartz-sand, are distinctly seen as foreign
bodies imbedded in the mass, which is moreover marked by lines
apparently due to cracks formed by a shrinking of the silicate, and
subsequently filled by a further infiltration of the same material.
This arrangement resembles on a minute scale that of septaria.
Similar appearances are also observed in the serpentine which
replaces the Eozoon of Grenville, and also in a massive serpentine
from Burgess, resembling this, and enclosing fragments of the fossil.
In both of these specimens also grains of mechanical impurities are
detected by the microscope; they are however, rarer than in the
loganite of Burgess.
"From the above facts it may be concluded that the various silicates
which now constitute pyroxene, serpentine, and loganite were directly
deposited in waters in the midst of which the Eozoon was still
growing, or had only recently perished; and that these silicates
penetrated, enclosed, and preserved the calcareous structure
precisely as carbonate of lime might have done. The association
of the silicates with the Eozoon is only accidental; and large
quantities of them, deposited at the same time, include no organic
remains. Thus, for example, there are found associated with the
Eozoon limestones of Grenville, massive layers and concretions of
pure serpentine; and a serpentine from Burgess has already been
mentioned as containing only small broken fragments of the fossil.
In like manner large masses of white pyroxene, often surrounded
by serpentine, both of which are destitute of traces of organic
structure, are found in the limestone at the Calumet. In some cases,
however, the crystallization of the pyroxene has given rise to
considerable cleavage-planes, and has thus obliterated the organic
structures from masses which, judging from portions visible here and
there, appear to have been at one time penetrated by the calcareous
plates of Eozoon. Small irregular veins of crystalline calcite, and
of serpentine, are found to traverse such pyroxene masses in the
Eozoon limestone of Grenville.
"It appears that great beds of the Laurentian limestones are
composed of the ruins of the Eozoon. These rocks, which are white,
crystalline, and mingled with pale green serpentine, are similar in
aspect to many of the so-called primary limestones of other regions.
In most cases the limestones are non-magnesian, but one of them
from Grenville was found to be dolomitic. The accompanying strata
often present finely crystallized pyroxene, hornblende, phlogopite,
apatite, and other minerals. These observations bring the formation
of silicious minerals face to face with life, and show that their
generation was not incompatible with the contemporaneous existence
and the preservation of organic forms. They confirm, moreover, the
view which I some years since put forward, that these silicated
minerals have been formed, not by subsequent metamorphism in
deeply buried sediments, but by reactions going on at the earth's
surface.[Z] In support of this view, I have elsewhere referred to
the deposition of silicates of lime, magnesia, and iron from natural
waters, to the great beds of sepiolite in the unaltered Tertiary
strata of Europe; to the contemporaneous formation of neolite (an
aluimino-magnesian silicate related to loganite and chlorite in
composition); and to glauconite, which occurs not only in Secondary,
Tertiary, and Recent deposits, but also, as I have shown, in Lower
Silurian strata.[AA] This hydrous silicate of protoxide of iron
and potash, which sometimes includes a considerable proportion of
alumina in its composition, has been observed by Ehrenberg, Mantell,
and Bailey, associated with organic forms in a manner which seems
identical with that in which pyroxene, serpentine, and loganite
occur with the Eozoon in the Laurentian limestones. According to the
first of these observers, the grains of green-sand, or glauconite,
from the Tertiary limestone of Alabama, are casts of the interior
of Polythalamia, the glauconite having filled them by 'a species of
natural injection, which is often so perfect that not only the large
and coarse cells, but also the very finest canals of the cell-walls
and all their connecting tubes, are thus petrified and separately
exhibited.' Bailey confirmed these observations, and extended them.
He found in various Cretaceous and Tertiary limestones of the United
States, casts in glauconite, not only of _Foraminifera_, but of
spines of _Echinus_, and of the cavities of corals. Besides, there
were numerous red, green, and white casts of minute anastomosing
tubuli, which, according to Bailey, resemble the casts of the holes
made by burrowing sponges (_Cliona_) and worms. These forms are seen
after the dissolving of the carbonate of lime by a dilute acid.
He found, moreover, similar casts of _Foraminifera_, of minute
mollusks, and of branching tubuli, in mud obtained from soundings in
the Gulf Stream, and concluded that the deposition of glauconite is
still going on in the depths of the sea.[AB] Pourtales has followed
up these investigations on the recent formation of glauconite in
the Gulf Stream waters. He has observed its deposition also in
the cavities of _Millepores_, and in the canals in the shells
of _Balanus_. According to him, the glauconite grains formed in
_Foraminifera_ lose after a time their calcareous envelopes, and
finally become 'conglomerated into small black pebbles,' sections
of which still show under a microscope the characteristic spiral
arrangement of the cells.[AC]
[Footnote Z: _Silliman's Journal_ [2], xxix., p. 284; xxxii., p. 286.
_Geology of Canada_, p. 577.]
[Footnote AA: _Silliman's Journal_ [2], xxxiii., p. 277. _Geology of
Canada_, p. 487.]
[Footnote AB: _Silliman's Journal_ [2], xxii., p. 280.]
[Footnote AC: _Report of United States Coast-Survey_, 1858, p. 248.]
"It appears probable from these observations that glauconite is
formed by chemical reactions in the ooze at the bottom of the sea,
where dissolved silica comes in contact with iron oxide rendered
soluble by organic matter; the resulting silicate deposits itself in
the cavities of shells and other vacant spaces. A process analogous
to this in its results, has filled the chambers and canals of the
Laurentian _Foraminifera_ with other silicates; from the comparative
rarity of mechanical impurities in these silicates, however, it would
appear that they were deposited in clear water. Alumina and oxide of
iron enter into the composition of loganite as well as of glauconite;
but in the other replacing minerals, pyroxene and serpentine, we
have only silicates of lime and magnesia, which were probably formed
by the direct action of alkaline silicates, either dissolved in
surface-waters, or in those of submarine springs, upon the calcareous
and magnesian salts of the sea-water."
[As stated in the text, the canals of Eozoon are sometimes filled
with dolomite, or in part with serpentine and in part with dolomite.]
(B.) Silurian Limestones holding Fossils infiltrated with Hydrous
Silicate.
Since my attention has been directed to this subject, many
illustrations have come under my notice of Silurian limestones in
which the pores of fossils are infiltrated with hydrous silicates
akin to glauconite and serpentine. A limestone of this kind,
collected by Mr. Robb, at Pole Hill, in New Brunswick, afforded not
only beautiful specimens of portions of Crinoids preserved in this
way, but a sufficient quantity of the material was collected for an
exact analysis, a note on which was published in the Proceedings of
the Royal Irish Academy, 1871.
The limestone of Pole Hill is composed almost wholly of organic
fragments, cemented by crystalline carbonate of lime, and traversed
by slender veins of the same mineral. Among the fragments may be
recognised under the microscope portions of Trilobites, and of
brachiopod and gastropod shells, and numerous joints and plates
of Crinoids. The latter are remarkable for the manner in which
their reticulated structure, which is similar to that of modern
Crinoids, has been injected with a silicious substance, which is
seen distinctly in slices, and still more plainly in decalcified
specimens. This filling is precisely similar in appearance to the
serpentine filling the canals of Eozoon, the only apparent difference
being in the forms of the cells and tubes of the Crinoids, as
compared with those of the Laurentian fossil; the same silicious
substance also occupies the cavities of some of the small shells,
and occurs in mere amorphous pieces, apparently filling interstices.
From its mode of occurrence, I have not the slightest doubt that
it occupied the cavities of the crinoidal fragments while still
recent, and before they had been cemented together by the calcareous
paste. This silicious filling is therefore similar on the one hand
to that effected by the ancient serpentine of the Laurentian, and
on the other to that which results from the depositions of modern
glauconite. The analysis of Dr. Hunt, which I give below, fully
confirms these analogies.
I may add that I have examined under the microscope portions of the
substance prepared by Dr. Hunt for analysis, and find it to retain
its form, showing that it is the actual filling of the cavities. I
have also examined the small amount of insoluble silica remaining
after his treatment with acid and alkaline solvents, and find it to
consist of angular and rounded grains of quartzose sand.
The following are Dr. Hunt's notes:--
"The fossiliferous limestone from Pole Hill, New Brunswick, probably
of Upper Silurian age, is light gray and coarsely granular. When
treated with dilute hydrochloric acid, it leaves a residue of 5·9 per
cent., and the solution gives 1·8 per cent. of alumina and oxide of
iron, and magnesia equal to 1·35 of carbonate--the remainder being
carbonate of lime. The insoluble matter separated by dilute acid,
after washing by decantation from a small amount of fine flocculent
matter, consists, apart from an admixture of quartz grains, entirely
of casts and moulded forms of a peculiar silicate, which Dr. Dawson
has observed in decalcified specimens filling the pores of crinoidal
stems; and which when separated by an acid, resembles closely under
the microscope the coralloidal forms of arragonite known as _flos
ferri_, the surfaces being somewhat rugose and glistening with
crystalline faces. This silicate is sub-translucent, and of a pale
green colour, but immediately becomes of a light reddish brown when
heated to redness in the air, and gives off water when heated in a
tube, without however, changing its form. It is partially decomposed
by strong hydrochloric acid, yielding a considerable amount of
protosalt of iron. Strong hot sulphuric acid readily and completely
decomposes it, showing it to be a silicate of alumina and ferrous
oxide, with some magnesia and alkalies, but with no trace of lime.
The separated silica, which remains after the action of the acid,
is readily dissolved by a dilute solution of soda, leaving behind
nothing but angular and partially rounded grains of sand, chiefly
of colourless vitreous quartz. An analysis effected in the way just
described on 1·187 grammes gave the following results, which give, by
calculation, the centesimal composition of the mineral:--
Silica ·3290 38·93 = 20·77 oxygen·
Alumina ·2440 28·88 = 13·46 "
Protoxyd of iron ·1593 18·86}
Magnesia ·0360 4·25} = 6·29 "
Potash ·0140 1·69}
Soda ·0042 ·48}
Water ·0584 6·91 = 6·14 "
Insoluble, quartz ·3420
------ ------
1·1869 100·00
"A previous analysis of a portion of the mixture by fusion with
carbonate of soda gave, by calculation, 18·80 p. c. of protoxide of
iron, and amounts of alumina and combined silica closely agreeing
with those just given.
"The oxygen ratios, as above calculated, are nearly as 3 : 2 : 1 : 1.
This mineral approaches in composition to the jollyte of Von Kobell,
from which it differs in containing a portion of alkalies, and only
one half as much water. In these respects it agrees nearly with the
silicate found by Robert Hoffman, at Raspenau, in Bohemia, where it
occurs in thin layers alternating with picrosmine, and surrounding
masses of Eozoon in the Laurentian limestones of that region;[AD]
the Eozoon itself being there injected with a hydrous silicate which
may be described as intermediate between glauconite and chlorite in
composition. The mineral first mentioned is compared by Hoffman to
fahlunite, to which jollyte is also related in physical characters as
well as in composition. Under the names of fahlunite, gigantolite,
pinite, etc., are included a great class of hydrous silicates, which
from their imperfectly crystalline condition, have generally been
regarded, like serpentine, as results of the alteration of other
silicates. It is, however, difficult to admit that the silicate
found in the condition described by Hoffman, and still more the
present mineral, which injects the pores of palæozoic Crinoids, can
be any other than an original deposition, allied in the mode of its
formation, to the serpentine, pyroxene, and other minerals which have
injected the Laurentian Eozoon, and the serpentine and glauconite,
which in a similar manner fill Tertiary and recent shells."
[Footnote AD: _Journ. für Prakt. Chemie_, Bd. 106 (Erster Jahrgang,
1869), p. 356.]
(C.) Various Minerals filling Cavities of Fossils in the Laurentian.
The following on this subject is from a memoir by Dr. Hunt in the
_Twenty-first Report of the Regents of the University of New York_,
1874:--
"Recent investigations have shown that in some cases the
dissemination of certain of these minerals through the crystalline
limestones is connected with organic forms. The observations
of Dr. Dawson and myself on the Eozoon Canadense showed that
certain silicates, namely serpentine, pyroxene, and loganite,
had been deposited in the cells and chambers left vacant by the
disappearance of the animal matter from the calcareous skeleton of
the foraminiferous organism; so that when this calcareous portion is
removed by an acid there remains a coherent mass, which is a cast of
the soft parts of the animal, in which, not only the chambers and
connecting canals, but the minute tubuli and pores are represented
by solid mineral silicates. It was shown that this process must have
taken place immediately after the death of the animal, and must have
depended on the deposition of these silicates from the waters of the
ocean.
"The train of investigation thus opened up, has been pursued by
Dr. Gümbel, Director of the Geological Survey of Bavaria, who, in
a recent remarkable memoir presented to the Royal Society of that
country, has detailed his results.
"Having first detected a fossil identical with the Canadian Eozoon
(together with several other curious microscopic organic forms not
yet observed in Canada), replaced by serpentine in a crystalline
limestone from the primitive group of Bavaria, which he identified
with the Laurentian system of this country, he next discovered a
related organism, to which he has given the name of Eozoon Bavaricum.
This occurs in a crystalline limestone belonging to a series of rocks
more recent than the Laurentian, but older than the Primordial zone
of the Lower Silurian, and designated by him the Hercynian clay slate
series, which he conceives may represent the Cambrian system of Great
Britain, and perhaps correspond to the Huronian series of Canada and
the United States. The cast of the soft parts of this new fossil is,
according to Gümbel, in part of serpentine, and in part of hornblende.
"His attention was next directed to the green hornblende (pargasite)
which occurs in the crystalline limestone of Pargas in Finland, and
remains when the carbonate of lime is dissolved as a coherent mass
closely resembling that left by the irregular and acervuline forms
of Eozoon. The calcite walls also sometimes show casts of tubuli....
A white mineral, probably scapolite was found to constitute some
tubercles associated with the pargasite, and the two mineral species
were in some cases united in the same rounded grain.
"Similar observations were made by him upon specimens of coccolite
or green pyroxene, occurring in rounded and wrinkled grains in a
Laurentian limestone from New York. These, according to Gümbel,
present the same connecting cylinders and branching stems as the
pargasite, and are by him supposed to have been moulded in the
same manner.... Very beautiful evidences of the same organic
structure consisting of the casts of tubuli and their ramifications,
were also observed by Gümbel in a purely crystalline limestone,
enclosing granules of chondrodite, hornblende, and garnet, from
Boden in Saxony. Other specimens of limestone, both with and without
serpentine and chondrodite, were examined without exhibiting any
traces of these peculiar forms; and these negative results are
justly deemed by Gümbel as going to prove that the structure of
the others is really, like that of Eozoon, the result of the
intervention of organic forms. Besides the minerals observed in the
replacing substance of Eozoon in Canada, viz., serpentine, pyroxene,
and loganite, Gümbel adds chondrodite, hornblende, scapolite, and
probably also pyrallolite, quartz, iolite, and dichroite."
(D.) Glauconites.
The following is from a paper by Dr. Hunt in the _Report of the
Survey of Canada_ for 1866:--
"In connection with the Eozoon it is interesting to examine more
carefully into the nature of the matters which have been called
glauconite or green-sand. These names have been given to substances
of unlike composition, which, however, occur under similar
conditions, and appear to be chemical deposits from water, filling
cavities in minute fossils, or forming grains in sedimentary rocks
of various ages. Although greenish in colour, and soft and earthy
in texture, it will be seen that the various glauconites differ
widely in composition. The variety best known, and commonly regarded
as the type of the glauconites, is that found in the green-sand of
Cretaceous age in New Jersey, and in the Tertiary of Alabama; the
glauconite from the Lower Silurian rocks of the Upper Mississippi is
identical with it in composition. Analysis shows these glauconites to
be essentially hydrous silicates of protoxyd of iron, with more or
less alumina, and small but variable quantities of magnesia, besides
a notable amount of potash. This alkali is, however, sometimes
wanting, as appears from the analysis of a green-sand from Kent in
England, by that careful chemist, the late Dr. Edward Turner, and
in another examined by Berthier, from the _calcaire grossier_, near
Paris, which is essentially a serpentine in composition, being a
hydrous silicate of magnesia and protoxyd of iron. A comparison of
these last two will show that the loganite, which fills the ancient
Foraminifer of Burgess, is a silicate nearly related in composition.
I. Green-sand from the _calcaire grossier_, near Paris. Berthier
(cited by Beudant, _Mineralogie_, ii., 178).
II. Green-sand from Kent, England. Dr. Edward Turner (cited by
Rogers, Final Report, Geol. N. Jersey, page 206).
III. Loganite from the Eozoon of Burgess.
IV. Green-sand, Lower Silurian; Red Bird, Minnesota.
V. Green-sand, Cretaceous, New Jersey.
VI. Green-sand, Lower Silurian, Orleans Island.
The last four analyses are by myself.
I. II. III. IV. V. VI.
Silica 40·0 48·5 35·14 46·58 50·70 50·7
Protoxyd of iron 24·7 22·0 8·60 20·61 22·50 8·6
Magnesia 16·6 3·8 31·47 1·27 2·16 3·7
Lime 3·3 .... .... 2·49 1·11 ....
Alumina 1·7 17·0 10·15 11·45 8·03 19·8
Potash .... traces. .... 6·96 5·80 8·2
Soda .... .... .... ·98 ·75 ·5
Water 12·6 7·0 14·64 9·66 8·95 8·5
---- ---- ------ ------ ------ -----
98·9 98·3 100·00 100·00 100·00 100·0"
[Illustration:
Plate VI.
From a Photo. by Weston. Vincent Brooks, Day & Son Lith.
CANAL SYSTEM OF EOZOON.
SLICES OF THE FOSSIL (MAGNIFIED.)
_To face Chap. 6._]
CHAPTER VI.
CONTEMPORARIES AND SUCCESSORS OF EOZOON.
The name Eozoon, or Dawn-animal, raises the question whether we shall
ever know any earlier representative of animal life. Here I think
it necessary to explain that in suggesting the name Eozoon for the
earliest fossil, and Eozoic for the formation in which it is contained,
I had no intention to affirm that there may not have been precursors
of the Dawn-animal. By the similar term, Eocene, Lyell did not mean
to affirm that there may not have been modern types in the preceding
geological periods: and so the dawn of animal life may have had its
gray or rosy breaking at a time long anterior to that in which Eozoon
built its marble reefs. When the fossils of this early auroral time
shall be found, it will not be hard to invent appropriate names for
them. There are, however, two reasons that give propriety to the
name in the present state of our knowledge. One is, that the Lower
Laurentian rocks are absolutely the oldest that have yet come under
the notice of geologists, and at the present moment it seems extremely
improbable that any older sediments exist, at least in a condition to
be recognised as such. The other is that Eozoon, as a member of the
group Protozoa, of gigantic size and comprehensive type, and oceanic in
its habitat, is as likely as any other creature that can be imagined
to have been the first representative of animal life on our planet.
Vegetable life may have preceded it, nay probably did so by at least
one great creative æon, and may have accumulated previous stores of
organic matter; but if any older forms of animal life existed, it is
certain at least that they cannot have belonged to much simpler or more
comprehensive types. It is also to be observed that such forms of life,
if they did exist, may have been naked protozoa, which may have left no
sign of their existence except a minute trace of carbonaceous matter,
and perhaps not even this.
But if we do not know, and perhaps we are not likely to know, any
animals older than Eozoon, may we not find traces of some of its
contemporaries, either in the Eozoon limestones themselves, or other
rocks associated with them? Here we must admit that a deep sea
Foraminiferal limestone may give a very imperfect indication of the
fauna of its time. A dredger who should have no other information as
to the existing population of the world, except what he could gather
from the deposits formed under several hundred fathoms of water, would
necessarily have very inadequate conceptions of the matter. In like
manner a geologist who should have no other information as to the
animal life of the Mesozoic ages than that furnished by some of the
thick beds of white chalk might imagine that he had reached a period
when the simplest kinds of protozoa predominated over all other
forms of life; but this impression would at once be corrected by the
examination of other deposits of the same age: so our inferences as to
the life of the Laurentian from the contents of its oceanic limestones
may be very imperfect, and it may yet yield other and various fossils.
Its possibilities are, however, limited by the fact that before we
reach this great depth in the earth's crust, we have already left
behind in much newer formations all traces of animal life except a
few of the lower forms of aquatic invertebrates; so that we are not
surprised to find only a limited number of living things, and those of
very low type. Do we then know in the Laurentian even a few distinct
species, or is our view limited altogether to Eozoon Canadense? In
answering this question we must bear in mind that the Laurentian itself
was of vast duration, and that important changes of life may have taken
place even between the deposition of the Eozoon limestones and that
of those rocks in which we find the comparatively rich fauna of the
Primordial age. This subject was discussed by the writer as early as
1865, and I may repeat here what could be said in relation to it at
that time:--
"In connection with these remarkable remains, it appeared desirable to
ascertain, if possible, what share these or other organic structures
may have had in the accumulation of the limestones of the Laurentian
series. Specimens were therefore selected by Sir W. E. Logan, and
slices were prepared under his direction. On microscopic examination,
a number of these were found to exhibit merely a granular aggregation
of crystals, occasionally with particles of graphite and other foreign
minerals, or a laminated mixture of calcareous and other matters, in
the manner of some more modern sedimentary limestones. Others, however,
were evidently made up almost entirely of fragments of Eozoon, or of
mixtures of these with other calcareous and carbonaceous fragments
which afford more or less evidence of organic origin. The contents of
these organic limestones may be considered under the following heads:--
1. Remains of Eozoon.
2. Other calcareous bodies, probably organic.
3. Objects imbedded in the serpentine.
4. Carbonaceous matters.
5. Perforations, or worm-burrows.
"1. The more perfect specimens of Eozoon do not constitute the mass
of any of the larger specimens in the collection of the Survey; but
considerable portions of some of them are made up of material of
similar minute structure, destitute of lamination, and irregularly
arranged. Some of this material gives the impression that there may
have been organisms similar to Eozoon, but growing in an irregular
or acervuline manner without lamination. Of this, however, I cannot
be certain; and on the other hand there is distinct evidence of the
aggregation of fragments of Eozoon in some of these specimens. In
some they constitute the greater part of the mass. In others they
are embedded in calcareous matter of a different character, or in
serpentine or granular pyroxene. In most of the specimens the cells of
the fossils are more or less filled with these minerals; and in some
instances it would appear that the calcareous matter of fragments of
Eozoon has been in part replaced by serpentine."
"2. Intermixed with the fragments of Eozoon above referred to, are
other calcareous matters apparently fragmentary. They are of various
angular and rounded forms, and present several kinds of structure. The
most frequent of these is a strong lamination varying in direction
according to the position of the fragments, but corresponding, as
far as can be ascertained, with the diagonal of the rhombohedral
cleavage. This structure, though crystalline, is highly characteristic
of crinoidal remains when preserved in altered limestones. The more
dense parts of Eozoon, destitute of tubuli, also sometimes show this
structure, though less distinctly. Other fragments are compact and
structureless, or show only a fine granular appearance; and these
sometimes include grains, patches, or fibres of graphite. In Silurian
limestones, fragments of corals and shells which have been partially
infiltrated with bituminous matter, show a structure like this. On
comparison with altered organic limestones of the Silurian system,
these appearances would indicate that in addition to the debris of
Eozoon, other calcareous structures, more like those of crinoids,
corals, and shells, have contributed to the formation of the
Laurentian limestones.
"3. In the serpentine[AE] filling the chambers of a large specimen of
Eozoon from Burgess, there are numerous small pieces of foreign matter;
and the silicate itself is laminated, indicating its sedimentary
nature. Some of the included fragments appear to be carbonaceous,
others calcareous; but no distinct organic structure can be detected
in them. There are, however, in the serpentine, many minute silicious
grains of a bright green colour, resembling green-sand concretions;
and the manner in which these are occasionally arranged in lines and
groups, suggests the supposition that they may possibly be casts of
the interior of minute Foraminiferal shells. They may, however, be
concretionary in their origin.
[Footnote AE: This is the dark green mineral named loganite by Dr.
Hunt.]
"4. In some of the Laurentian limestones submitted to me by Sir W.
E. Logan, and in others which I collected some years ago at Madoc,
Canada West, there are fibres and granules of carbonaceous matter,
which do not conform to the crystalline structure, and present forms
quite similar to those which in more modern limestones result from
the decomposition of algæ. Though retaining mere traces of organic
structure, no doubt would be entertained as to their vegetable origin
if they were found in fossiliferous limestones.
"5. A specimen of impure limestone from Madoc, in the collection of
the Canadian Geological Survey, which seems from its structure to
have been a finely laminated sediment, shows perforations of various
sizes, somewhat scalloped at the sides, and filled with grains of
rounded silicious sand. In my own collection there are specimens
of micaceous slate from the same region, with indications on their
weathered surfaces of similar rounded perforations, having the aspect
of Scolithus, or of worm-burrows.
"Though the abundance and wide distribution of Eozoon, and the
important part it seems to have acted in the accumulation of limestone,
indicate that it was one of the most prevalent forms of animal
existence in the seas of the Laurentian period, the non-existence of
other organic beings is not implied. On the contrary, independently of
the indications afforded by the limestones themselves, it is evident
that in order to the existence and growth of these large Rhizopods, the
waters must have swarmed with more minute animal or vegetable organisms
on which they could subsist. On the other hand, though this is a less
certain inference, the dense calcareous skeleton of Eozoon may indicate
that it also was liable to the attacks of animal enemies. It is also
possible that the growth of Eozoon, or the deposition of the serpentine
and pyroxene in which its remains have been preserved, or both, may
have been connected with certain oceanic depths and conditions, and
that we have as yet revealed to us the life of only certain stations
in the Laurentian seas. Whatever conjectures we may form on these more
problematic points, the observations above detailed appear to establish
the following conclusions:--
"First, that in the Laurentian period, as in subsequent geological
epochs, the Rhizopods were important agents in the accumulation of
beds of limestone; and secondly, that in this early period these low
forms of animal life attained to a development, in point of magnitude
and complexity, unexampled, in so far as yet known, in the succeeding
ages of the earth's history. This early culmination of the Rhizopods is
in accordance with one of the great laws of the succession of living
beings, ascertained from the study of the introduction and progress of
other groups; and, should it prove that these great Protozoans were
really the dominant type of animals in the Laurentian period, this fact
might be regarded as an indication that in these ancient rocks we may
actually have the records of the first appearance of animal life on our
planet."
With reference to the first of the above heads, I have now to state
that it seems quite certain that the upper and younger portions of
the masses of Eozoon often passed into the acervuline form, and the
period in which this change took place seems to have depended on
circumstances. In some specimens there are only a few regular layers,
and then a heap of irregular cells. In other cases a hundred or more
regular layers were formed; but even in this case little groups of
irregular cells occurred at certain points near the surface. This
may be seen in plate III. I have also found some masses clearly not
fragmental which consist altogether of acervuline cells. A specimen
of this kind is represented in fig. 31. It is oval in outline, about
three inches in length, wholly made up of rounded or cylindrical
cells, the walls of which have a beautiful tubular structure, but
there is little or no supplemental skeleton. Whether this is a portion
accidentally broken off from the top of a mass of Eozoon, or a
peculiar varietal form, or a distinct species, it would be difficult
to determine. In the meantime I have described it as a variety,
"_acervulina_," of the species Eozoon Canadense.[AF] Another variety
also, from Petite Nation, shows extremely thin laminæ, closely placed
together and very massive, and with little supplemental skeleton. This
may be allied to the last, and may be named variety "_minor_."
[Footnote AF: _Proceedings of Geological Society_, 1875.]
[Illustration: Fig. 31. _Acervuline Variety of Eozoon, St. Pierre._
(_a._) General form, half natural size. (_b._) Portion of cellular
interior, magnified, showing the course of the tubuli.]
All this, however, has nothing to do with the layers of fragments of
Eozoon which are scattered through the Laurentian limestones. In these
the fossil is sometimes preserved in the ordinary manner, with its
cavities filled with serpentine, and the thicker parts of the skeleton
having their canals filled with this substance. In this case the
chambers may have been occupied with serpentine before it was broken
up. At St. Pierre there are distinct layers of this kind, from half an
inch to several inches in thickness, regularly interstratified with
the ordinary limestone. In other layers no serpentine occurs, but the
interstices of the fragments are filled with crystalline dolomite or
magnesian limestone, which has also penetrated the canals; and there
are indications, though less manifest, that some at least of the layers
of pure limestone are composed of fragmental Eozoon. In the Laurentian
limestone of Wentworth, belonging apparently to the same band with
that of St. Pierre, there are many small rounded pieces of limestone,
evidently the debris of some older rock, broken up and rounded by
attrition. In some of these fragments the structure of Eozoon may be
plainly perceived. This shows that still older limestones composed of
Eozoon were at that time undergoing waste, and carries our view of the
existence of this fossil back to the very beginning of the Laurentian.
With respect to organic fragments not showing the structure of Eozoon,
I have not as yet been able to refer these to any definite origin. Some
of them may be simply thick portions of the shell of Eozoon with their
pores filled with calcite, so as to present a homogeneous appearance.
Others have much the appearance of fragments of such Primordial forms
as _Archæocyathus_, to be described in the sequel; but after much
careful search, I have thus far been unable to say more than I could
say in 1865.
[Illustration: Fig. 32. _Archæospherinæ from St. Pierre._
(_a._) Specimens dissolved out by acid. The lower one showing interior
septa. (_b._) Specimens seen in section.]
[Illustration: Fig. 33. _Archæospherinæ from Burgess Eozoon._
Magnified.]
[Illustration: Fig. 34. _Archæospherinæ from Wentworth Limestone._
Magnified.]
It is different, however, with the round cells infiltrated with
serpentine and with the silicious grains included in the loganite. I
have already referred to and figured (fig. 18) the remarkable rounded
bodies occurring at Long Lake. I now figure similar bodies found mixed
with fragmental Eozoon and in separate thin layers at St. Pierre (fig.
32), also some of the singular grains found in the loganite occupying
the chambers of Eozoon from Burgess (fig. 33), and a beaded body set
free by acid, with others of irregular forms, from the limestone of
Wentworth (fig. 34). All these I think are essentially of the same
nature, namely, chambers originally invested with a tubulated wall
like Eozoon, and aggregated in groups, sometimes in a linear manner,
sometimes spirally, like those Globigerinæ which constitute the mass
of modern deep-sea dredgings and also of the chalk. These bodies occur
dispersed in the limestone, arranged in thin layers parallel to the
bedding or sometimes in the large chamber-cavities of Eozoon. They
are so variable in size and form that it is not unlikely they may be
of different origins. The most probable of these may be thus stated.
First, they may in some cases be the looser superficial parts of the
surface of Eozoon broken up into little groups of cells. Secondly,
they may be few-celled germs or buds given off from Eozoon. Thirdly,
they may be smaller Foraminifera, structurally allied to Eozoon, but
in habit of growth resembling those little globe-shaped forms which,
as already stated, abound in chalk and in the modern ocean. The latter
view I should regard as highly probable in the case of many of them;
and I have proposed for them, in consequence, and as a convenient name,
_Archæospherinæ_, or ancient spherical animals.
Carbonaceous matter is rare in the true Eozoon limestones, and, as
already stated, I would refer the Laurentian graphite or plumbago
mainly to plants. With regard to the worm-burrows referred to in 1865,
there can be no doubt of their nature, but there is some doubt as to
whether the beds that contain them are really Lower Laurentian. They
may be Upper Laurentian or Huronian. I give here figures of these
burrows as published in 1866[AG] (fig. 35). The rocks which contain
them hold also fragments of Eozoon, and are not known to contain other
fossils.
[Footnote AG: _Journal of Geological Society._]
[Illustration: Fig. 35. _Annelid Burrows, Laurentian or Huronian._
Fig 1. _Transverse section of Worm-burrow_--magnified, as a transparent
object. (_a._) Calcareo-silicious rock. (_b._) Space filled with
calcareous spar. (_c._) Sand agglutinated and stained black. (_d._)
Sand less agglutinated and uncoloured. Fig. 2. _Transverse section of
Worm-burrow on weathered surface_, natural size. Fig. 3. _The same_,
magnified.]
If we now turn to other countries in search of contemporaries of
Eozoon, I may refer first to some specimens found by my friend Dr.
Honeyman at Arisaig, in Nova Scotia, in beds underlying the Silurian
rocks of that locality, but otherwise of uncertain age. I do not vouch
for them as Laurentian, and if of that age they seem to indicate a
species distinct from that of Canada proper. They differ in coarser
tubulation, and in their canals being large and beaded, and less
divergent. I proposed for these specimens, in some notes contributed to
the survey of Canada, the name _Eozoon Acadianum_.
Dr. Gümbel, the Director of the Geological Survey of Bavaria, is
one of the most active and widely informed of European geologists,
combining European knowledge with an extensive acquaintance with the
larger and in some respects more typical areas of the older rocks in
America, and stratigraphical geology with enthusiastic interest in the
microscopic structures of fossils. He at once and in a most able manner
took up the question of the application of the discoveries in Canada
to the rocks of Bavaria. The spirit in which he did so may be inferred
from the following extract:--
"The discovery of organic remains in the crystalline limestones of the
ancient gneiss of Canada, for which we are indebted to the researches
of Sir William Logan and his colleagues, and to the careful microscopic
investigations of Drs. Dawson and Carpenter, must be regarded as
opening a new era in geological science.
"This discovery overturns at once the notions hitherto commonly
entertained with regard to the origin of the stratified primary
limestones, and their accompanying gneissic and quartzose strata,
included under the general name of primitive crystalline schists. It
shows us that these crystalline stratified rocks, of the so-called
primary system, are only a backward prolongation of the chain of
fossiliferous strata; the elements of which were deposited as oceanic
sediment, like the clay-slates, limestones, and sandstones of the
palæozoic formations, and under similar conditions, though at a time
far more remote, and more favourable to the generation of crystalline
mineral compounds.
"In this discovery of organic remains in the primary rocks, we hail
with joy the dawn of a new epoch in the critical history of these
earlier formations. Already in its light, the primeval geological time
is seen to be everywhere animated, and peopled with new animal forms
of whose very existence we had previously no suspicion. Life, which
had hitherto been supposed to have first appeared in the Primordial
division of the Silurian period, is now seen to be immeasurably
lengthened beyond its former limit, and to embrace in its domain the
most ancient known portions of the earth's crust. It would almost
seem as if organic life had been awakened simultaneously with the
solidification of the earth's crust.
"The great importance of this discovery cannot be clearly understood,
unless we first consider the various and conflicting opinions
and theories which had hitherto been maintained concerning the
origin of these primary rocks. Thus some, who consider them as the
first-formed crust of a previously molten globe, regard their apparent
stratification as a kind of concentric parallel structure, developed
in the progressive cooling of the mass from without. Others, while
admitting a similar origin of these rocks, suppose their division
into parallel layers to be due, like the lamination of clay-slates,
to lateral pressure. If we admit such views, the igneous origin of
schistose rocks becomes conceivable, and is in fact maintained by many.
"On the other hand, we have the school which, while recognising the
sedimentary origin of these crystalline schists, supposes them to
have been metamorphosed at a later period; either by the internal
heat, acting in the deeply buried strata; by the proximity of eruptive
rocks; or finally, through the agency of permeating waters charged with
certain mineral salts.
"A few geologists only have hitherto inclined to the opinion that
these crystalline schists, while possessing real stratification,
and sedimentary in their origin, were formed at a period when the
conditions were more favourable to the production of crystalline
materials than at present. According to this view, the crystalline
structure of these rocks is an original condition, and not one
superinduced at a later period by metamorphosis. In order, however,
to arrange and classify these ancient crystalline rocks, it becomes
necessary to establish by superposition, or by other evidence,
differences in age, such as are recognised in the more recent
stratified deposits. The discovery of similar organic remains,
occupying a determinate position in the stratification, in different
and remote portions of these primitive rocks, furnishes a powerful
argument in favour of the latter view, as opposed to the notion which
maintains the metamorphic origin of the various minerals and rocks of
these ancient formations; so that we may regard the direct formation of
these mineral elements, at least so far as these fossiliferous primary
limestones are concerned, as an established fact."
His first discovery is thus recorded, in terms which show the very
close resemblance of the Bavarian and Canadian Eozoic.
"My discovery of similar organic remains in the serpentine-limestone
from near Passau was made in 1865, when I had returned from my
geological labours of the summer, and received the recently published
descriptions of Messrs. Logan, Dawson, etc. Small portions of this
rock, gathered in the progress of the Geological Survey in 1854,
and ever since preserved in my collection, having been submitted
to microscopic examination, confirmed in the most brilliant manner
the acute judgment of the Canadian geologists, and furnished
palæontological evidence that, notwithstanding the great distance which
separates Canada from Bavaria, the equivalent primitive rocks of the
two regions are characterized by similar organic remains; showing at
the same time that the law governing the definite succession of organic
life on the earth is maintained even in these most ancient formations.
The fragments of serpentine-limestone, or ophicalcite, in which I first
detected the existence of Eozoon, were like those described in Canada,
in which the lamellar structure is wanting, and offer only what Dr.
Carpenter has called an acervuline structure. For further confirmation
of my observations, I deemed it advisable, through the kindness of
Sir Charles Lyell, to submit specimens of the Bavarian rock to the
examination of that eminent authority, Dr. Carpenter, who, without any
hesitation, declared them to contain Eozoon.
"This fact being established, I procured from the quarries near Passau
as many specimens of the limestone as the advanced season of the year
would permit; and, aided by my diligent and skillful assistants,
Messrs. Reber and Schwager, examined them by the methods indicated by
Messrs. Dawson and Carpenter. In this way I soon convinced myself of
the general similarity of our organic remains with those of Canada.
Our examinations were made on polished sections and in portions etched
with dilute nitric acid, or, better, with warm acetic acid. The most
beautiful results were however obtained by etching moderately thin
sections, so that the specimens may be examined at will either by
reflected or transmitted light.
"The specimens in which I first detected Eozoon came from a quarry
at Steinhag, near Obernzell, on the Danube, not far from Passau. The
crystalline limestone here forms a mass from fifty to seventy feet
thick, divided into several beds, included in the gneiss, whose general
strike in this region is N.W., with a dip of 40°-60° N.E. The limestone
strata of Steinhag have a dip of 45° N.E. The gneiss of this vicinity
is chiefly grey, and very silicious, containing dichroite, and of
the variety known as dichroite-gneiss; and I conceive it to belong,
like the gneiss of Bodenmais and Arber, to that younger division of
the primitive gneiss system which I have designated as the Hercynian
gneiss formation; which, both to the north, between Tischenreuth and
Mahring, and to the south on the north-west of the mountains of Ossa,
is immediately overlaid by the mica-slate formation. Lithologically,
this newer division of the gneiss is characterized by the predominance
of a grey variety, rich in quartz, with black magnesian-mica and
orthoclase, besides which a small quantity of oligoclase is never
wanting. A further characteristic of this Hercynian gneiss is the
frequent intercalation of beds of rocks rich in hornblende, such as
hornblende-schist, amphibolite, diorite, syenite, and syenitic granite,
and also of serpentine and granulite. Beds of granular limestone,
or of calcareous schists are also never altogether wanting; while
iron pyrites and graphite, in lenticular masses, or in local beds
conformable to the great mass of the gneiss strata, are very generally
present.
"In the large quarry of Steinhag, from which I first obtained the
Eozoon, the enclosing rock is a grey hornblendic gneiss, which
sometimes passes into a hornblende-slate. The limestone is in many
places overlaid by a bed of hornblende-schist, sometimes five feet
in thickness, which separates it from the normal gneiss. In many
localities, a bed of serpentine, three or four feet thick, is
interposed between the limestone and the hornblende-schist; and in
some cases a zone, consisting chiefly of scapolite, crystalline and
almost compact, with an admixture however of hornblende and chlorite.
Below the serpentine band, the crystalline limestone appears divided
into distinct beds, and encloses various accidental minerals, among
which are reddish-white mica, chlorite, hornblende, tremolite,
chondrodite, rosellan, garnet, and scapolite, arranged in bands.
In several places the lime is mingled with serpentine, grains or
portions of which, often of the size of peas, are scattered through
the limestone with apparent irregularity, giving rise to a beautiful
variety of ophicalcite or serpentine-marble. These portions, which are
enclosed in the limestone destitute of serpentine, always present a
rounded outline. In one instance there appears, in a high naked wall
of limestone without serpentine, the outline of a mass of ophicalcite,
about sixteen feet long and twenty-five feet high, which, rising from
a broad base, ends in a point, and is separated from the enclosing
limestone by an undulating but clearly defined margin, as already well
described by Wineberger. This mass of ophicalcite recalls vividly a
reef-like structure. Within this and similar masses of ophicalcite in
the crystalline limestone, there are, so far as my observations in 1854
extend, no continuous lines or concentric layers of serpentine to be
observed, this mineral being always distributed in small grains and
patches. The few apparently regular layers which may be observed are
soon interrupted, and the whole aggregation is irregular."
It will be observed that this acervuline Eozoon of Steinhag appears to
exist in large reefs, and that in its want of lamination it differs
from the Canadian examples. In fossils of low organization, like
Foraminifera, such differences are often accidental and compatible with
specific unity, but yet there may be a difference specifically in the
Bavarian Eozoon as compared with the Canadian.
Gümbel also found in the Finnish and Bavarian limestones knotted
chambers, like those of Wentworth above mentioned (fig. 36), which he
regards as belonging to some other organism than Eozoon; and flocculi
having tubes, pores, and reticulations which would seem to point to the
presence of structures akin to sponges or possibly remains of seaweeds.
These observations Gümbel has extended into other localities in Bavaria
and Bohemia, and also in Silesia and Sweden, establishing the existence
of Eozoon fossils in all the Laurentian limestones of the middle and
north of Europe.
[Illustration: Fig. 36. _Archæospherinæ from Pargas in Finland._
(_After Gümbel._)
Magnified.]
Gümbel has further found in beds overlying the older Eozoic series,
and probably of the same age with the Canadian Huronian, a different
species of Eozoon, with smaller and more contracted chambers, and
still finer and more crowded canals. This, which is to be regarded as
a distinct species, or at least a well-marked varietal form, he has
named _Eozoon Bavaricum_ (fig. 37). Thus this early introduction of
life is not peculiar to that old continent which we sometimes call the
New World, but applies to Europe as well, and Europe has furnished a
successor to Eozoon in the later Eozoic or Huronian period. In rocks of
this age in America, after long search and much slicing of limestones,
I have hitherto failed to find any decided organic remains other than
the Tudor and Madoc specimens of Eozoon. If these are really Huronian
and not Laurentian, the Eozoon from this horizon does not sensibly
differ from that of the Lower Laurentian. The curious limpet-like
objects from Newfoundland, discovered by Murray, and described by
Billings,[AH] under the name _Aspidella_, are believed to be Huronian,
but they have no connection with Eozoon, and therefore need not detain
us here.
[Footnote AH: _Canadian Naturalist_, 1871.]
[Illustration: Fig. 37. _Section of Eozoon Bavaricum, with Serpentine,
from the Crystalline Limestone of the Hercynian primitive Clay-state
Formation at Hohenberg; 25 diameters._
(_a._) Sparry carbonate of lime. (_b._) Cellular carbonate of lime.
(_c._) System of tubuli. (_d._) Serpentine replacing the coarser
ordinary variety. (_e._) Serpentine and hornblende replacing the finer
variety, in the very much contorted portions.]
Leaving the Eozoic age, we find ourselves next in the Primordial or
Cambrian, and here we discover the sea already tenanted by many
kinds of crustaceans and shell-fishes, which have been collected and
described by palæontologists in Bohemia, Scandinavia, Wales, and North
America;[AI] curiously enough, however, the rocks of this age are
not so rich in Foraminifera as those of some succeeding periods. Had
this primitive type played out its part in the Eozoic and exhausted
its energies, and did it remain in abeyance in the Primordial age to
resume its activity in the succeeding times? It is not necessary to
believe this. The geologist is familiar with the fact, that in one
formation he may have before him chiefly oceanic and deep-sea deposits,
and in another those of the shallower waters, and that alternations
of these may, in the same age or immediately succeeding ages, present
very different groups of fossils. Now the rocks and fossils of the
Laurentian seem to be oceanic in character, while the Huronian and
early Primordial rocks evidence great disturbances, and much coarse
and muddy sediment, such as that found in shallows or near the land.
They abound in coarse conglomerates, sandstones and thick beds of slate
or shale, but are not rich in limestones, which do not in the parts
of the world yet explored regain their importance till the succeeding
Siluro-Cambrian age. No doubt there were, in the Primordial, deep-sea
areas swarming with Foraminifera, the successors of Eozoon; but these
are as yet unknown or little known, and our known Primordial fauna is
chiefly that of the shallows. Enlarged knowledge may thus bridge over
much of the apparent gap in the life of these two great periods.
[Footnote AI: Barrande, Angelin, Hicks, Hall, Billings, etc.]
Only as yet on the coast of Labrador and neighbouring parts of North
America, and in rocks that were formed in seas that washed the old
Laurentian rocks, in which Eozoon was already as fully sealed up as
it is at this moment, do we find Protozoa which can claim any near
kinship to the proto-foraminifer. These are the fossils of the genus
_Archæocyathus_--"ancient cup-sponges, or cup-foraminifers," which
have been described in much detail by Mr. Billings in the reports of
the Canadian Survey. Mr. Billings regards them as possibly sponges,
or as intermediate between these and Foraminifera, and the silicious
spicules found in some of them justify this view, unless indeed, as
partly suspected by Mr. Billings, these belong to true sponges which
may have grown along with Archæocyathus or attached to it. Certain
it is, however, that if allied to sponges, they are allied also to
Foraminifera, and that some of them deviate altogether from the sponge
type and become calcareous chambered bodies, the animals of which can
have differed very little from those of the Laurentian Eozoon. It is
to these calcareous Foraminiferal species that I shall at present
restrict my attention. I give a few figures, for which I am indebted to
Mr. Billings, of three of his species (figs. 38 to 40), with enlarged
drawings of the structures of one of them which has the most decidedly
foraminiferal characters.
[Illustration: Fig. 38. _Archæocyathus Minganensis--a Primordial
Protozoon._ (_After Billings._)
(_a._) Pores of the inner wall.]
[Illustration: Fig. 39. _Archæocyathus profundus--showing the base of
attachment and radiating chambers._ (_After Billings._)]
[Illustration: Fig. 40. _Archæocyathus Atlanticus--showing outer
surface and longitudinal and transverse sections._ (_After Billings._)]
[Illustration: Fig. 41. _Structures of Archæocyathus Profundus._
(_a._) Lower acervuline portion. (_b._) Upper portion, with three of
the radiating laminæ. (_c._) Portion of lamina with pores and thickened
part with canals. In figs. _a_ and _b_ the calcareous part is unshaded.]
To understand Archæocyathus, let us imagine an inverted cone of
carbonate of lime from an inch or two to a foot in length, and with
its point buried in the mud at the bottom of the sea, while its open
cup extends upward into the water. The lower part buried in the soil
is composed of an irregular acervuline network of thick calcareous
plates, enclosing chambers communicating with one another (figs. 40
and 41 A). Above this where the cup expands, its walls are composed
of thin outer and inner plates, perforated with innumerable holes,
and connected with each other by vertical plates, which are also
perforated with round pores, establishing a communication between the
radiating chambers into which they divide the thickness of the wall
(figs. 38, 39, and 41 B). In such a structure the chambers in the wall
of the cup and the irregular chambers of the base would be filled with
gelatinous animal matter, and the pseudopods would project from the
numerous pores in the inner and outer wall. In the older parts of the
skeleton, the structure is further complicated by the formation of
thin transverse plates, irregular in distribution, and where greater
strength is required a calcareous thickening is added, which in some
places shows a canal system like that of Eozoon (fig. 41, B, C).[AJ]
As compared with Eozoon, the fossils want its fine perforated wall,
but have a more regular plan of growth. There are fragments in the
Eozoon limestones which may have belonged to structures like these;
and when we know more of the deep sea of the Primordial, we may
recover true species of Eozoon from it, or may find forms intermediate
between it and Archæocyathus. In the meantime I know no nearer bond of
connection between Eozoon and the Primordial age than that furnished
by the ancient cup Zoophytes of Labrador, though I have searched very
carefully in the fossiliferous conglomerates of Cambrian age on the
Lower St. Lawrence, which contain rocks of all the formations from the
Laurentian upwards, often with characteristic fossils. I have also made
sections of many of the fossiliferous pebbles in these conglomerates
without finding any certain remains of such organisms, though the
fragments of the crusts of some of the Primordial tribolites, when
their tubuli are infiltrated with dark carbonaceous matter, are so like
the supplemental skeleton of Eozoon, that but for their forms they
might readily be mistaken for it; and associated with them are broken
pieces of other porous organisms which may belong to Protozoa, though
this is not yet certain.
[Footnote AJ: On the whole these curious fossils, if regarded as
Foraminifera, are most nearly allied to the Orbitolites and Dactyloporæ
of the Early Tertiary period, as described by Carpenter.]
Of all the fossils of the Silurian rocks those which most resemble
Eozoon are the _Stromatoporæ_, or "layer-corals," whose resemblance
to the old Laurentian fossil at once struck Sir William Logan; and
these occur in the earliest great oceanic limestones which succeed the
Primordial period, those of the Trenton group, in the Siluro-Cambrian.
From this they extend upward as far as the Devonian, appearing
everywhere in the limestones, and themselves often constituting large
masses of calcareous rock. Our figure (fig. 42) shows a small example
of one of these fossils; and when sawn asunder or broken across and
weathered, they precisely resemble Eozoon in general appearance,
especially when, as sometimes happens, their cell-walls have been
silicified.
[Illustration: Fig. 42. _Stromatopora rugosa, Hall--Lower Silurian,
Canada._ (_After Billings._)
The specimen is of smaller size than usual, and is silicified. It is
probably inverted in position, and the concentric marks on the outer
surface are due to concretions of silica.]
There are, however, different types of these fossils. The most common,
the Stromatoporæ properly so called, consist of concentric layers of
calcareous matter attached to each other by pillar-like processes,
which, as well as the layers, are made up of little threads of
limestone netted together, or radiating from the tops and bottoms of
the pillars, and forming a very porous substance. Though they have
been regarded as corals by some, they are more generally believed
to be Protozoa; but whether more nearly allied to sponges or to
Foraminifera may admit of doubt. Some of the more porous kinds are
not very dissimilar from calcareous sponges, but they generally want
true oscula and pores, and seem better adapted to shield the gelatinous
body of a Foraminifer projecting pseudopods in search of food, than
that of a sponge, living by the introduction of currents of water. Many
of the denser kinds, however, have their calcareous floors so solid
that they must be regarded as much more nearly akin to Foraminifers,
and some of them have the same irregular inosculation of these floors
observed in Eozoon. Figs. 43, A to D, show portions of species of
this description, in which the resemblance to Eozoon in structure and
arrangement of parts is not remote.
[Illustration: Fig. 43. _Structures of Stromatopora._
(_a._) Portion of an oblique section magnified, showing laminæ and
columns. (_b._) Portion of wall with pores, and crusted on both sides
with quartz crystals. (_c._) Thickened portion of wall with canals.
(_d._) Portion of another specimen, showing irregular laminæ and
pillars.]
These fossils, however, show no very distinct canal system or
supplemental skeleton, but this also appears in those forms which have
been called Caunopora or Cœnostroma. In these the plates are traversed
by tubes, or groups of tubes, which in each successive floor give out
radiating and branching canals exactly like those of Eozoon, though
more regularly arranged; and if we had specimens with the canals
infiltrated with glauconite or serpentine, the resemblance would be
perfect. When, as in figs. 44 and 45 A, these canals are seen on the
abraded surface, they appear as little grooves arranged in stars,
which resemble the radiating plates of corals, but this resemblance
is altogether superficial, and I have no doubt that they are really
foraminiferal organisms. This will appear more distinctly from the
sections in fig. 45 B, C, which represents an undescribed species
recently found by Mr. Weston, in the Upper Silurian limestone of
Ontario.
[Illustration: Fig. 44. _Caunopora planulata, Hall--Devonian; showing
the radiating canals on a weathered surface._ (_After Hall._)]
[Illustration: Fig. 45. _Cœnostroma--Guelph Limestone, Upper Silurian,
from a specimen collected by Mr. Weston, showing the canals._
(_a._) Surface with canals, natural size. (_b._) Vertical section,
natural size. (_c._) The same magnified, showing canals and laminæ.]
There are probably many species of these curious fossils, but their
discrimination is difficult, and their nomenclature confused, so that
it would not be profitable to engage the attention of the reader
with it except in a note. Their state of preservation, however, is
so highly illustrative of that of Eozoon that a word as to this
will not be out of place. They are sometimes preserved merely by
infiltration with calcite or dolomite, and in this case it is most
difficult to make out their minute structures. Often they appear
merely as concentrically laminated masses which, but for their mode
of occurrence, might be regarded as mere concretions. In other cases
the cell-walls and pillars are perfectly silicified, and then they
form beautiful microscopic objects, especially when decalcified with
an acid. In still other cases, they are preserved like Eozoon, the
walls being calcareous and the chambers filled with silica. In this
state when weathered or decalcified they are remarkably like Eozoon,
but I have not met with any having their minute pores and tubes so
well preserved as in some of the Laurentian fossils. In many of them,
however, the growth and overlapping of the successive amœba-like coats
of sarcode can be beautifully seen, exactly as on the surface of a
decalcified piece of Eozoon. Those in my collection which most nearly
resemble the Laurentian specimens are from the older part of the Lower
Silurian series; but unfortunately their minute structures are not well
preserved.
In the Silurian and Devonian ages, these Stromatoporæ evidently carried
out the same function as the Eozoon in the Laurentian. Winchell tells
us that in Michigan and Ohio single specimens can be found several feet
in diameter, and that they constitute the mass of considerable beds of
limestone. I have myself seen in Canada specimens a foot in diameter,
with a great number of laminæ. Lindberg[AK] has given a most vivid
account of their occurrence in the Isle of Gothland. He says that they
form beds of large irregular discs and balls, attaining a thickness of
five Swedish feet, and traceable for miles along the coast, and the
individual balls are sometimes a yard in diameter. In some of them the
structure is beautifully preserved. In others, or in parts of them,
it is reduced to a mass of crystalline limestone. This species is of
the Cœnostroma type, and is regarded by Lindberg as a coral, though
he admits its low type and resemblance to Protozoa. Its continuous
calcareous skeleton he rightly regards as fatal to its claim to be a
true sponge. Such a fossil, differing as it does in minute points of
structure from Eozoon, is nevertheless probably allied to it in no very
distant way, and a successor to its limestone-making function. Those
which most nearly approach to Foraminifera are those with thick and
solid calcareous laminæ, and with a radiating canal system; and one
of the most Eozoon-like I have seen, is a specimen of the undescribed
species already mentioned from the Guelph (Upper Silurian) limestone
of Ontario, collected by Mr. Weston, and now in the Museum of the
Geological Survey. I have attempted to represent its structures in fig.
44.
[Footnote AK: _Transactions of Swedish Academy_, 1870.]
[Illustration: Fig. 46. _Receptaculites, restored._ (_After Billings._)
(_a._) Aperture. (_b._) Inner wall. (_c._) Outer wall. (_n._) Nucleus,
or primary chamber. (_v._) Internal cavity.]
[Illustration: Fig. 47. _Diagram of Wall and Tubes of Receptaculites._
(_After Billings._)
(_b._) Inner wall. (_c._) Outer wall. (_d._) Section of plates. (_e._)
Pore of inner wall. (_f._) Canal of inner wall. (_g._) Radial stolon.
(_h._) Cyclical stolon. (_k._) Suture of plates of outer wall.]
[Illustration: Fig. 48. _Receptaculites, Inner Surface of Outer Wall
with the Stolons remaining on its Surface._ (_After Billings._)]
In the rocks extending from the Lower Silurian and perhaps from the
Upper Cambrian to the Devonian inclusive, the type and function of
Eozoon are continued by the Stromatoporæ, and in the earlier part of
this time these are accompanied by the Archæocyathids, and by another
curious form, more nearly allied to the latter than to Eozoon, the
_Receptaculites_. These curious and beautiful fossils, which sometimes
are a foot in diameter, consist, like Archæocyathus, of an outer and
inner coat enclosing a cavity; but these coats are composed of square
plates with pores at the corners, and they are connected by hollow
pillars passing in a regular manner from the outer to the inner coat.
They have been regarded by Salter as Foraminifers, while Billings
considers their nearest analogues to be the seed-like germs of some
modern silicious sponges. On the whole, if not Foraminifera, they must
have been organisms intermediate between these and sponges, and they
certainly constitute one of the most beautiful and complex types of
the ancient Protozoa, showing the wonderful perfection to which these
creatures attained at a very early period. (Figs. 46, 47, 48.)
I might trace these ancient forms of foraminiferal life further up in
the geological series, and show how in the Carboniferous there are
nummulitic shells conforming to the general type of Eozoon, and in some
cases making up the mass of great limestones.[AL] Further, in the great
chalk series and its allied beds, and in the Lower Tertiary, there are
not only vast foraminiferal limestones, but gigantic species reminding
us of Stromatopora and Eozoon.[AM] Lastly, more diminutive species are
doing similar work on a great scale in the modern ocean. Thus we may
gather up the broken links of the chain of foraminiferal life, and
affirm that Eozoon has never wanted some representative to uphold its
family and function throughout all the vast lapse of geological time.
[Footnote AL: _Fusulina_, as recently described by Carpenter,
_Archæodiscus_ of Brady, and the Nummulite recently found in the
Carboniferous of Belgium.]
[Footnote AM: _Parkeria_ and _Loftusia_ of Carpenter.]
NOTES TO CHAPTER VI.
(A.) Stromatoporidæ, Etc.
For the best description of Archæocyathus, I may refer to _The
Palæozoic Fossils of Canada_, by Mr. Billings, vol. i. There also,
and in Mr. Salter's memoir in _The Decades of the Canadian Survey_,
will be found all that is known of the structure of Receptaculites.
For the American Stromatoporæ I may refer to Winchell's paper in the
_Proceedings of the American Association_, 1866; to Professor Hall's
Descriptions of New Species of Fossils from Iowa, _Report of the
State Cabinet, Albany_, 1872; and to the Descriptions of Canadian
Species by Dr. Nicholson, in his _Report on the Palæontology of
Ontario_, 1874.
The genus Stromatopora of Goldfuss was defined by him as consisting
of laminæ of a solid and porous character, alternating and
contiguous, and constituting a hemispherical or sub-globose mass.
In this definition, the porous strata are really those of the
fossil, the alternating solid strata being the stony filling of the
chambers; and the descriptions of subsequent authors have varied
according as, from the state of preservation of the specimens or
other circumstances, the original laminæ or the filling of the spaces
attracted their attention. In the former case the fossil could be
described as consisting of laminæ made up of interlaced fibrils of
calcite, radiating from vertical pillars which connect the laminæ.
In the latter case, the laminæ, appear as solid plates, separated
by very narrow spaces, and perforated with round vertical holes
representing the connecting pillars. These Stromatoporæ range from
the Lower Silurian to the Devonian, inclusive, and many species have
been described; but their limits are not very definite, though there
are undoubtedly remarkable differences in the distances of the laminæ
and in their texture, and in the smooth or mammillated character
of the masses. Hall's genus Stromatocerium belongs to these forms,
and D'Orbigny's genus Sparsispongia refers to mammillated species,
sometimes with apparent oscula.
Phillip's genus Caunopora was formed to receive specimens with
concentric cellular layers traversed by "long vermiform cylindrical
canals;" while Winchell's genus Cœnostroma includes species with
these vermiform canals arranged in a radiate manner, diverging from
little eminences in the concentric laminæ. The distinction between
these last genera does not seem to be very clear, and may depend
on the state of preservation of the specimens. A more important
distinction appears to exist between those that have a single
vertical canal from which the subordinate canals diverge, and those
that have groups of such canals.
Some species of the Cœnostroma group have very dense calcareous
laminæ traversed by the canals; but it does not seem that any
distinction has yet been made between the proper wall and the
intermediate skeleton; and most observers have been prevented from
attending to such structures by the prevailing idea that these
fossils are either corals or sponges, while the state of preservation
of the more delicate tissues is often very imperfect.
(B.) Localities of Eozoon, or of Limestones supposed to contain it.
In Canada the principal localities of Eozoon Canadense are at
Grenville, Petite Nation, the Calumets Rapids, Burgess, Tudor, and
Madoc. At the two last places the fossil occurs in beds which may be
on a somewhat higher horizon than the others. Mr. Vennor has recently
found specimens which have the general form of Eozoon, though the
minute structure is not preserved, at Dalhousie, in Lanark Co.,
Ontario. One specimen from this place is remarkable from having been
mineralized in part by a talcose mineral associated with serpentine.
I have examined specimens from Chelmsford, in Massachusetts, and from
Amity and Warren County, New York, the latter from the collection of
Professor D. S. Martin, which show the canals of Eozoon in a fair
state of preservation, though the specimens are fragmental, and do
not show the laminated structure.
In European specimens of limestones of Laurentian age, from Tunaberg
and Fahlun in Sweden, and from the Western Islands of Scotland, I
have hitherto failed to recognise the characteristic structure of
the fossil. Connemara specimens have also failed to afford me any
satisfactory results, and specimens of a serpentine limestone from
the Alps, collected by M. Favre, and communicated to me by Dr. Hunt,
though in general texture they much resemble acervuline Eozoon, do
not show its minute structures.
[Illustration:
Plate VII.
_Untouched nature-print of part of a large specimen of Eozoon, from
Petite Nation._
The lighter portions are less perfect than in the original, owing to
the finer laminæ of serpentine giving way. The dark band at one side is
one of the deep lacunæ or oscula.]
CHAPTER VII.
OPPONENTS AND OBJECTIONS.
The active objectors to the animal nature of Eozoon have been few,
though some of them have returned to the attack with a pertinacity and
determination which would lead one to believe that they think the most
sacred interests of science to be dependent on the annihilation of this
proto-foraminifer. I do not propose here to treat of the objections in
detail. I have presented the case of Eozoon on its own merits, and on
these it must stand. I may merely state that the objectors strive to
account for the existence of Eozoon by purely mineral deposition, and
that the complicated changes which they require to suppose are perhaps
the strongest indirect evidence for the necessity of regarding the
structures as organic. The reader who desires to appreciate this may
consult the notes to this chapter.[AN]
[Footnote AN: Also Rowney and King's papers in _Journal Geological
Society_, August, 1866; and _Proceedings Irish Academy_, 1870 and 1871.]
I confess that I feel disposed to treat very tenderly the position of
objectors. The facts I have stated make large demands on the faith
of the greater part even of naturalists. Very few geologists or
naturalists have much knowledge of the structure of foraminiferal
shells, or would be able under the microscope to recognise them with
certainty. Nor have they any distinct ideas of the appearances of such
structures under different kinds of preservation and mineralisation.
Further, they have long been accustomed to regard the so-called Azoic
rocks as not only destitute of organic remains, but as being in such
a state of metamorphism that these could not have been preserved had
they existed. Few, therefore, are able intelligently to decide for
themselves, and so they are called on to trust to the investigations
of others, and on their testimony to modify in a marked degree their
previous beliefs as to the duration of life on our planet. In these
circumstances it is rather wonderful that the researches made with
reference to Eozoon have met with so general acceptance, and that the
resurrection of this ancient inhabitant of the earth has not aroused
more of the sceptical tendency of our age.
It must not be lost sight of, however, that in such cases there may
exist a large amount of undeveloped and even unconscious scepticism,
which shows itself not in active opposition, but merely in quietly
ignoring this great discovery, or regarding it with doubt, as an
uncertain or unestablished point in science. Such scepticism may best
be met by the plain and simple statements in the foregoing chapters,
and by the illustrations accompanying them. It may nevertheless be
profitable to review some of the points referred to, and to present
some considerations making the existence of Laurentian life less
anomalous than may at first sight be supposed. One of these is the
fact that the discovery of Eozoon brings the rocks of the Laurentian
system into more full harmony with the other geological formations. It
explains the origin of the Laurentian limestones in consistency with
that of similar rocks in the later periods, and in like manner it helps
us to account for the graphite and sulphides and iron ores of these old
rocks. It shows us that no time was lost in the introduction of life
on the earth. Otherwise there would have been a vast lapse of time in
which, while the conditions suitable to life were probably present, no
living thing existed to take advantage of these conditions. Further, it
gives a more simple beginning of life than that afforded by the more
complex fauna of the Primordial age; and this is more in accordance
with what we know of the slow and gradual introduction of new forms of
living things during the vast periods of Palæozoic time. In connection
with this it opens a new and promising field of observation in the
older rocks, and if this should prove fertile, its exploration may
afford a vast harvest of new forms to the geologists of the present and
coming time. This result will be in entire accordance with what has
taken place before in the history of geological discovery. It is not
very long since the old and semi-metamorphic sediments constituting the
great Silurian and Cambrian systems were massed together in geological
classifications as primitive or primary rocks, destitute or nearly
destitute of organic remains. The brilliant discoveries of Sedgwick,
Murchison, Barrande, and a host of others, have peopled these once
barren regions; and they now stretch before our wondering gaze in
the long vistas of early Palæozoic life. So we now look out from the
Cambrian shore upon the vast ocean of the Huronian and Laurentian,
all to us yet tenantless, except for the few organisms, which, like
stray shells cast upon the beach, or a far-off land dimly seen in the
distance, incite to further researches, and to the exploration of the
unknown treasures that still lie undiscovered. It would be a suitable
culmination of the geological work of the last half-century, and one
within reach at least of our immediate successors, to fill up this
great blank, and to trace back the Primordial life to the stage of
Eozoon, and perhaps even beyond this, to predecessors which may have
existed at the beginning of the Lower Laurentian, when the earliest
sediments of that great formation were laid down. Vast unexplored areas
of Laurentian and Huronian rocks exist in the Old World and the New.
The most ample facilities for microscopic examination of rocks may
now be obtained; and I could wish that one result of the publication
of these pages may be to direct the attention of some of the younger
and more active geologists to these fields of investigation. It is to
be observed also that such regions are among the richest in useful
minerals, and there is no reason why search for these fossils should
not be connected with other and more practically useful researches. On
this subject it will not be out of place to quote the remarks which I
made in one of my earlier papers on the Laurentian fossils:--
"This subject opens up several interesting fields of chemical,
physiological, and geological inquiry. One of these relates to the
conclusions stated by Dr. Hunt as to the probable existence of a
large amount of carbonic acid in the Laurentian atmosphere, and of
much carbonate of lime in the seas of that period, and the possible
relation of this to the abundance of certain low forms of plants and
animals. Another is the comparison already instituted by Professor
Huxley and Dr. Carpenter, between the conditions of the Laurentian and
those of the deeper parts of the modern ocean. Another is the possible
occurrence of other forms of animal life than Eozoon and Annelids,
which I have stated in my paper of 1864, after extensive microscopic
study of the Laurentian limestones, to be indicated by the occurrence
of calcareous fragments, differing in structure from Eozoon, but at
present of unknown nature. Another is the effort to bridge over, by
further discoveries similar to that of the _Eozoon Bavaricum_ of
Gümbel, the gap now existing between the life of the Lower Laurentian
and that of the Primordial Silurian or Cambrian period. It is scarcely
too much to say that these inquiries open up a new world of thought and
investigation, and hold out the hope of bringing us into the presence
of the actual origin of organic life on our planet, though this may
perhaps be found to have been Prelaurentian. I would here take the
opportunity of stating that, in proposing the name Eozoon for the
first fossil of the Laurentian, and in suggesting for the period the
name "Eozoic," I have by no means desired to exclude the possibility
of forms of life which may have been precursors of what is now to us
the dawn of organic existence. Should remains of still older organisms
be found in those rocks now known to us only by pebbles in the
Laurentian, these names will at least serve to mark an important stage
in geological investigation."
But what if the result of such investigations should be to produce
more sceptics, or to bring to light mineral structures so resembling
Eozoon as to throw doubt upon the whole of the results detailed in
these chapters? I can fancy that this might be the first consequence,
more especially if the investigations were in the hands of persons
more conversant with minerals than with fossils; but I see no reason
to fear the ultimate results. In any case, no doubt, the value of the
researches hitherto made may be diminished. It is always the fate of
discoverers in Natural Science, either to be followed by opponents who
temporarily or permanently impugn or destroy the value of their new
facts, or by other investigators who push on the knowledge of facts and
principles so far beyond their standpoint that the original discoveries
are cast into the shade. This is a fatality incident to the progress of
scientific work, from which no man can be free; and in so far as such
matters are concerned, we must all be content to share the fate of the
old fossils whose history we investigate, and, having served our day
and generation to give place to others. If any part of our work should
stand the fire of discussion let us be thankful. One thing at least is
certain, that such careful surveys as those in the Laurentian rocks
of Canada which led to the discovery of Eozoon, and such microscopic
examinations as those by which it has been worked up and presented to
the public, cannot fail to yield good results of one kind or another.
Already the attention excited by the controversies about Eozoon, by
attracting investigators to the study of various microscopic and
imitative forms in rocks, has promoted the advancement of knowledge,
and must do so still more. For my own part, though I am not content to
base all my reputation on such work as I have done with respect to this
old fossil, I am willing at least to take the responsibility of the
results I have announced, whatever conclusions may be finally reached;
and in the consciousness of an honest effort to extend the knowledge
of nature, to look forward to a better fame than any that could result
from the most successful and permanent vindication of every detail
of our scientific discoveries, even if they could be pushed to a
point which no subsequent investigation in the same difficult line of
research would be able to overpass.
Contenting myself with these general remarks, I shall, for the benefit
of those who relish geological controversy, append to this chapter a
summary of the objections urged by the most active opponents of the
animal nature of Eozoon, with the replies that may be or have been
given; and I now merely add (in fig. 49) a magnified camera tracing of
a portion of a lamina of Eozoon with its canals and tubuli, to show
more fully the nature of the structures in controversy.
[Illustration: Fig. 49. _Portion of a thin Transverse Slice of a Lamina
of Eozoon, magnified, showing its structure, as traced with the camera._
(_a._) Nummuline wall of under side. (_b._) Intermediate skeleton with
canals. (_a´._) Nummuline wall of upper side. The two lower figures
show the lower and upper sides more highly magnified. The specimen is
one in which the canals are unusually well seen.]
It may be well, however, to sum up the evidence as it has been
presented by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and the author,
in a short and intelligible form; and I shall do so under a few brief
heads, with some explanatory remarks:--
1. The Lower Laurentian of Canada, a rock formation whose
distribution, age, and structure have been thoroughly worked out by
the Canadian Survey, is found to contain thick and widely distributed
beds of limestone, related to the other beds in the same way in which
limestones occur in the sediments of other geological formations. There
also occur in the same formation, graphite, iron ores, and metallic
sulphides, in such relations as to suggest the idea that the limestones
as well as these other minerals are of organic origin.
2. In the limestones are found laminated bodies of definite form and
structure, composed of calcite alternating with serpentine and other
minerals. The forms of these bodies suggested a resemblance to the
Silurian Stromatoporæ, and the different mineral substances associated
with the calcite in the production of similar forms, showed that these
were not accidental or concretionary.
3. On microscopic examination, it proved that the calcareous laminæ
of these forms were similar in structure to the shells of modern
and fossil Foraminifera, more especially those of the Rotaline and
Nummuline types, and that the finer structures, though usually filled
with serpentine and other hydrous silicates, were sometimes occupied
with calcite, pyroxene, or dolomite, showing that they must when recent
have been empty canals and tubes.
4. The mode of filling thus suggested for the chambers and tubes of
Eozoon, is precisely that which takes place in modern Foraminifera
filled with glauconite, and in Palæozoic crinoids and corals filled
with other hydrous silicates.
5. The type of growth and structure predicated of Eozoon from the
observed appearances, in its great size, its laminated and acervuline
forms, and in its canal system and tubulation, are not only in
conformity with those of other Foraminifera, but such as might be
expected in a very ancient form of that group.
6. Indications exist of other organic bodies in the limestones
containing Eozoon, and also of the Eozoon being preserved not only in
reefs but in drifted fragmental beds as in the case of modern corals.
7. Similar organic structures have been found in the Laurentian
limestones of Massachusetts and New York, and also in those of various
parts of Europe, and Dr. Gümbel has found an additional species in
rocks succeeding the Laurentian in age.
8. The manner in which the structures of Eozoon are affected by the
faulting, development of crystals, mineral veins, and other effects of
disturbance and metamorphism in the containing rocks, is precisely that
which might be expected on the supposition that it is of organic origin.
9. The exertions of several active and able opponents have failed to
show how, otherwise than by organic agency, such structures as those
of Eozoon can be formed, except on the supposition of pseudomorphism
and replacement, which must be regarded as chemically extravagant, and
which would equally impugn the validity of all fossils determined
by microscopic structure. In like manner all comparisons of these
structures with dendritic and other imitative forms have signally
failed, in the opinion of those best qualified to judge.
Another and perhaps simpler way of putting the case is the
following:--Only three general modes of accounting for the existence
of Eozoon have been proposed. The first is that of Professors King and
Rowney, who regard the chambers and canals filled with serpentine as
arising from the erosion or partial dissolving away of serpentine and
its replacement by calcite. The objections to this are conclusive.
It does not explain the nummuline wall, which has to be separately
accounted for by confounding it, contrary to the observed facts,
with the veins of fibrous serpentine which actually pass through
cracks in the fossil. Such replacement is in the highest degree
unlikely on chemical grounds, and there is no evidence of it in the
numerous serpentine grains, nodules, and bands in the Laurentian
limestones. On the other hand, the opposite replacement, that of
limestone by serpentine, seems to have occurred. The mechanical
difficulties in accounting for the delicate canals on this theory are
also insurmountable. Finally, it does not account for the specimens
preserved in pyroxene and other silicates, and in dolomite and calcite.
A second mode of accounting for the facts is that the Eozoon forms are
merely peculiar concretions. But this fails to account for their great
difference from the other serpentine concretions in the same beds, and
for their regularity of plan and the delicacy of their structure, and
also for minerals of different kinds entering into their composition,
and still presenting precisely the same forms and structures. The only
remaining theory is that of the filling of cavities by infiltration
with serpentine. This accords with the fact that such infiltration by
minerals akin to serpentine exists in fossils in later rocks. It also
accords with the known aqueous origin of the serpentine nodules and
bands, the veins of fibrous serpentine, and the other minerals found
filling the cavities of Eozoon. Even the pyroxene has been shown by
Hunt to exist in the Laurentian in veins of aqueous origin. The only
difficulty existing on this view is how a calcite skeleton with such
chambers, canals, and tubuli could be formed; and this is solved by the
discovery that all these facts correspond precisely with those to be
found in the shells of modern oceanic Foraminifera. The existence then
of Eozoon, its structure, and its relations to the containing rocks and
minerals being admitted, no rational explanation of its origin seems at
present possible other than that advocated in the preceding pages.
If the reader will now turn to Plate VIII., page 207, he will find some
interesting illustrations of several very important facts bearing on
the above arguments. Fig. 1 represents a portion of a very thin slice
of a specimen traversed by veins of fibrous serpentine or chrysotile,
and having the calcite of the walls more broken by cleavage planes
than usual. The portion selected shows a part of one of the chambers
filled with serpentine, which presents the usual curdled aspect
almost impossible to represent in a drawing (_s_). It is traversed
by a branching vein of chrysotile (_s_´), which, where cut precisely
parallel to its fibres, shows clear fine cross lines, indicating the
sides of its constituent prisms, and where the plane of section has
passed obliquely to its fibres, has a curiously stippled or frowsy
appearance. On either side of the serpentine band is the nummuline
or proper wall, showing under a low power a milky appearance, which,
with a higher power, becomes resolved into a tissue of the most
beautiful parallel threads, representing the filling of its tubuli.
Nothing can be more distinct than the appearances presented by this
wall and the chrysotile vein, under every variety of magnifying power
and illumination; and all who have had an opportunity of examining my
specimens have expressed astonishment that appearances so dissimilar
should have been confounded with each other. On the lower side two
indentations are seen in the proper wall (_c_). These are connected
with the openings into small subordinate chamberlets, one of which is
in part included in the thickness of the slice. At the upper and lower
parts of the figure are seen portions of the intermediate skeleton
traversed by canals, which in the lower part are very large, though
from the analogy of other specimens it is probable that they have in
their interstices minute canaliculi not visible in this slice. Fig.
2, from the same specimen, shows the termination of one of the canals
against the proper wall, its end expanding into a wide disc of sarcode
on the surface of the wall, as may be seen in similar structures in
modern Foraminifera. In this specimen the canals are beautifully smooth
and cylindrical, but they sometimes present a knotted or jointed
appearance, especially in specimens decalcified by acids, in which
perhaps some erosion has taken place. They are also occasionally
fringed with minute crystals, especially in those specimens in which
the calcite has been partially replaced with other minerals. Fig. 3
shows an example of faulting of the proper wall, an appearance not
infrequently observed; and it also shows a vein chrysotile crossing the
line of fault, and not itself affected by it--a clear evidence of its
posterior origin. Figs. 4 and 5 are examples of specimens having the
canals filled with dolomite, and showing extremely fine canals in the
interstices of the others: an appearance observed only in the thicker
parts of the skeleton, and when these are very well preserved. These
dolomitized portions require some precautions for their observation,
either in slices or decalcified specimens, but when properly managed
they show the structures in very great perfection. The specimen in fig.
5 is from an abnormally thick portion of intermediate skeleton, having
unusually thick canals, and referred to in a previous chapter.
One object which I have in view in thus minutely directing attention
to these illustrations, is to show the nature of the misapprehensions
which may occur in examining specimens of this kind, and at the same
time the certainty which may be attained when proper precautions are
taken. I may add that such structures as those referred to are best
seen in extremely thin slices, and that the observer must not expect
that every specimen will exhibit them equally well. It is only by
preparing and examining many specimens that the best results can be
obtained. It often happens that one specimen is required to show well
one part of the structures, and a different one to show another; and
previous to actual trial, it is not easy to say which portion of
the structures any particular fragment will show most clearly. This
renders it somewhat difficult to supply one's friends with specimens.
Really good slices can be prepared only from the best material and by
skilled manipulators; imperfect slices may only mislead; and rough
specimens may not be properly prepared by persons unaccustomed to the
work, or if so prepared may not turn out satisfactory, or may not be
skilfully examined. These difficulties, however, Eozoon shares with
other specimens in micro-geology, and I have experienced similar
disappointments in the case of fossil wood.
In conclusion of this part of the subject, and referring to the notes
appended to this chapter for further details, I would express the hope
that those who have hitherto opposed the interpretation of Eozoon as
organic, and to whose ability and honesty of purpose I willingly bear
testimony, will find themselves enabled to acknowledge at least the
reasonable probability of that interpretation of these remarkable forms
and structures.
NOTES TO CHAPTER VII.
(A.) Objections of Profs. King and Rowney.
_Trans. Royal Irish Academy, July, 1869._[AO]
[Footnote AO: Reprinted in the _Annals and Magazine of Natural
History_, May, 1874.]
The following summary, given by these authors, may be taken as
including the substance of their objections to the animal nature of
Eozoon. I shall give them in their words and follow them with short
answers to each.
"1st. The serpentine in ophitic rocks has been shown to present
appearances which can only be explained on the view that it undergoes
structural and chemical changes, causing it to pass into variously
subdivided states, and etching out the resulting portions into a
variety of forms--grains and plates, with lobulated or segmented
surfaces--fibres and aciculi--simple and branching configurations.
Crystals of malacolite, often associated with the serpentine,
manifest some of these changes in a remarkable degree.
"2nd. The 'intermediate skeleton' of Eozoon (which we hold to be
the calcareous matrix of the above lobulated grains, etc.) is
completely paralleled in various crystalline rocks--notably marble
containing grains of coccolite (Aker and Tyree), pargasite (Finland),
chondrodite (New Jersey, etc.)
"3rd. The 'chamber casts' in the acervuline variety of Eozoon are
more or less paralleled by the grains of the mineral silicates in the
pre-cited marbles.
"4th. The 'chamber casts' being composed occasionally of loganite and
malacolite, besides serpentine, is a fact which, instead of favouring
their organic origin, as supposed, must be held as a proof of their
having been produced by mineral agencies; inasmuch as these three
silicates have a close pseudomorphic relationship, and may therefore
replace one another in their naturally prescribed order.
"5th. Dr. Gümbel, observing rounded, cylindrical, or tuberculated
grains of coccolite and pargasite in crystalline calcareous marbles,
considered them to be 'chamber casts,' or of organic origin. We have
shown that such grains often present crystalline planes, angles, and
edges; a fact clearly proving that they were originally simple or
compound crystals that have undergone external decretion by chemical
or solvent action.
"6th. We have adduced evidences to show that the 'nummuline layer' in
its typical condition--that is, consisting of cylindrical aciculi,
separated by interspaces filled with calcite--has originated directly
from closely packed fibres; these from chrysotile or asbestiform
serpentine; this from incipiently fibrous serpentine; and the latter
from the same mineral in its amorphous or structureless condition.
"7th. The 'nummuline layer,' in its typical condition, unmistakably
occurs in cracks or fissures, both in Canadian and Connemara ophite.
"8th. The 'nummuline layer' is paralleled by the fibrous coat which
is occasionally present on the surface of grains of chondrodite.
"9th. We have shown that the relative position of two superposed
asbestiform layers (an _upper_ and an _under_ 'proper wall'), and the
admitted fact of their component aciculi often passing continuously
and without interruption from one 'chamber cast' to another, to the
exclusion of the 'intermediate skeleton,' are totally incompatible
with the idea of the 'nummuline layer' having resulted from
pseudopodial tubulation.
"10th. The so-called 'stolons' and 'passages of communication
exactly corresponding with those described in _Cycloclypeus_,'
have been shown to be tabular crystals and variously formed bodies,
belonging to different minerals, wedged crossways or obliquely in the
calcareous interspaces between the grains and plates of serpentine.
"11th. The 'canal system' is composed of serpentine, or malacolite.
Its typical kinds in the first of these minerals may be traced in
all stages of formation out of plates, prisms, and other solids,
undergoing a process of superficial decretion. Those in malacolite
are made up of crystals--single, or aggregated together--that have
had their planes, angles, and edges rounded off; or have become
further reduced by some solvent.
"12th. The 'canal system' in its remarkable branching varieties is
completely paralleled by crystalline configurations in the coccolite
marble of Aker, in Sweden; and in the crevices of a crystal of spinel
imbedded in a calcitic matrix from Amity, New York.
"13th. The _configurations_, presumed to represent the 'canal
systems,' are _totally without any regularity_ of form, of relative
size, or of arrangement; and they occur independently of and apart
from other 'eozoonal features' (Amity, Boden, etc.); facts not only
demonstrating them to be purely mineral products, but which strike at
the root of the idea that they are of organic origin.
"14th. In answer to the argument that as all the foregoing 'eozoonal
features' are occasionally found together in ophite, the combination
must be considered a conclusive evidence of their organic origin,
we have shown, from the composition, physical characters, and
circumstances of occurrence and association of their component
serpentine, that they represent the structural and chemical changes
which are eminently and peculiarly characteristic of this mineral.
It has also been shown that the combination is paralleled to a
remarkable extent in chondrodite and its calcitic matrix.
"15th. The 'regular alternation of lamellæ of calcareous and
silicious minerals' (respectively representing the 'intermediate
skeleton' and 'chamber casts') occasionally seen in ophite, and
considered to be a 'fundamental fact' evidencing an organic
arrangement, is proved to be a _mineralogical_ phenomenon by the
fact that a similar alternation occurs in amphiboline-calcitic
marbles, and gneissose rocks.
"16th. In order to account for certain _untoward_ difficulties
presented by the configurations forming the 'canal system,' and
the aciculi of the 'nummuline layer'--that is, when they occur as
'_solid bundles_'--or are '_closely packed_'--or '_appear to be
glued together_'--Dr. Carpenter has proposed the theory that the
sarcodic extensions which they are presumed to represent have been
'turned into stone' (a 'silicious mineral') 'by Nature's cunning'
('just as the sarcodic layer on the surface of the shell of living
Foraminifers is formed by the spreading out of _coalesced_ bundles
of the pseudopodia that have emerged from the chamber wall')--'by
a process of chemical substitution _before_ their destruction by
ordinary decomposition.' We showed this quasi-alchymical theory to be
altogether unscientific.
"17th. The 'silicious mineral' (serpentine) has been analogued with
those forming the variously-formed casts (in 'glauconite,' etc.)
of recent and fossil Foraminifers. We have shown that the mineral
silicates of Eozoon have no relation whatever to the substances
composing such casts.
"18th. Dr. Hunt, in order to account for the serpentine, loganite,
and malacolite, being the presumed in-filling substances of Eozoon,
has conceived the 'novel doctrine,' that such minerals were
_directly_ deposited in the ocean waters in which this 'fossil'
lived. We have gone over all his evidences and arguments without
finding _one_ to be substantiated.
"19th. Having investigated the alleged cases of 'chambers' and
'tubes' occurring 'filled with calcite,' and presumed to be 'a
conclusive answer to' our 'objections,' we have shown that there are
the strongest grounds for removing them from the category of reliable
evidences on the side of the organic doctrine. The Tudor specimen has
been shown to be equally unavailable.
"20th. The occurrence of the best preserved specimens of Eozoon
Canadense in rocks that are in a '_highly crystalline condition_'
(Dawson) must be accepted as a fact utterly fatal to its organic
origin.
"21st. The occurrence of 'eozoonal features' _solely_ in crystalline
or metamorphosed rocks, belonging to the Laurentian, the Lower
Silurian, and the Liassic systems--never in ordinary unaltered
deposits of these and the intermediate systems--must be assumed as
completely demonstrating their purely mineral origin."
The answers already given to these objections may be summed up
severally as follows:--
1st. This is a mere hypothesis to account for the forms presented by
serpentine grains and by Eozoon. Hunt has shown that it is untenable
chemically, and has completely exploded it in his recent papers on
Chemistry and Geology.[AP] My own observations show that it does not
accord with the mode of occurrence of serpentine in the Laurentian
limestones of Canada.
[Footnote AP: Boston, 1874.]
2nd. Some of the things stated to parallel the intermediate skeleton
of Eozoon, are probably themselves examples of that skeleton. Others
have been shown to have no resemblance to it.
3rd. The words "more or less" indicate the precise value of this
statement, in a question of comparison between mineral and organic
structures. So the prismatic structure of satin-spar may be said
"more or less" to resemble that of a shell, or of the cells of a
Stenopora.
4th. This overlooks the filling of chamber casts with pyroxene,
dolomite, or limestone. Even in the case of loganite this objection
is of no value unless it can be applied equally to the similar
silicates which fill cavities of fossils[AQ] in the Silurian
limestones and in the green-sand.
[Footnote AQ: See for a full discussion of this subject Dr. Hunt's
"Papers" above referred to.]
5th. Dr. Gümbel's observations are those of a highly skilled and
accurate observer. Even if crystalline forms appear in "chamber
casts," this is as likely to be a result of the injury of organic
structures by crystallization, as of the partial effacement of
crystals by other actions. Crystalline faces occur abundantly in many
undoubted fossil woods and corals; and crystals not unfrequently
cross and interfere with the structures in such specimens.
6th. On the contrary, the Canadian specimens prove clearly that the
veins of chrysotile have been filled subsequently to the existence of
Eozoon in its present state, and that there is no connection whatever
between them and the Nummuline wall.
7th. This I have never seen in all my examinations of Eozoon. The
writers must have mistaken veins of fibrous serpentine for the
nummuline wall.
8th. Only if such grains of chondrodite are themselves casts of
foraminiferal chambers. But Messrs. King and Rowney have repeatedly
figured mere groups of crystals as examples of the nummuline wall.
9th. Dr. Carpenter has shown that this objection depends on a
misconception of the structure of modern Foraminifera, which show
similar appearances.
10th. That disseminated crystals occur in the Eozoon limestones is a
familiar fact, and one paralleled in many other more or less altered
organic limestones. Foreign bodies also occur in the chambers filled
with loganite and other minerals; but these need not any more be
confounded with the pillars and walls connecting the laminæ than
the sand filling a dead coral with its lamellæ. Further, it is well
known that foreign bodies are often contained both in the testa and
chambers even of recent Foraminifera.
11th. The canal system is not always filled with serpentine or
malacolite; and when filled with pyroxene, dolomite, or calcite, the
forms are the same. The irregularities spoken of are perhaps more
manifest in the serpentine specimens, because this mineral has in
places encroached on or partially replaced the calcite walls.
12th. If this is true of the Aker marble, then it must contain
Eozoon; and specimens of the Amity limestone which I have examined,
certainly contain large fragments of Eozoon.
13th. The configuration of the canal system is quite definite,
though varying in coarseness and fineness. It is not known to occur
independently of the forms of Eozoon except in fragmental deposits.
14th. The argument is not that they are "occasionally found together
in ophite," but that they are found together in specimens preserved
by different minerals, and in such a way as to show that all these
minerals have filled chambers, canals, and tubuli, previously
existing in a skeleton of limestone.
15th. The lamination of Eozoon is not like that of any rock, but
a strictly limited and definite form, comparable with that of
Stromatopora.
16th. This I pass over, as a mere captious criticism of modes of
expression used by Dr. Carpenter.
17th. Dr. Hunt, whose knowledge of chemical geology should give
the greatest weight to his judgment, maintains the deposition of
serpentine and loganite to have taken place in a manner similar to
that of jollyte and glauconite in undoubted fossils: and this would
seem to be a clear deduction from the facts he has stated, and from
the chemical character of the substances. My own observations of the
mode of occurrence of serpentine in the Eozoon limestones lead me to
the same result.
18th. Dr. Hunt's arguments on the subject, as recently presented
in his _Papers on Chemistry and Geology_, need only be studied by
any candid and competent chemist or mineralogist to lead to a very
different conclusion from that of the objectors.
19th. This is a mere statement of opinion. The fact remains that the
chambers and canals are sometimes filled with calcite.
20th. That the occurrence of Eozoon in crystalline limestones is
"utterly fatal" to its claims to organic origin can be held only by
those who are utterly ignorant of the frequency with which organic
remains are preserved in highly crystalline limestones of all ages.
In addition to other examples mentioned above, I may state that the
curious specimen of Cœnostroma from the Guelph limestone figured
in Chapter VI., has been converted into a perfectly crystalline
dolomite, while its canals and cavities have been filled with
calcite, since weathered out.
21st. This limited occurrence is an assumption contrary to facts.
It leaves out of account the Tudor specimens, and also the abundant
occurrence of the Stromatoporoid successors of Eozoon in the
Silurian and Devonian. Further, even if the Eozoon were limited to
the Laurentian, this would not be remarkable; and since all the
Laurentian rocks known to us are more or less altered, it could not
in that case occur in unaltered rocks.
I have gone over these objections seriatim, because, though
individually weak, they have an imposing appearance in the aggregate,
and have been paraded as a conclusive settlement of the questions
at issue. They have even been reprinted in the year just past in an
English journal of some standing, which professes to accept only
original contributions to science, but has deviated from its rule in
their favour. I may be excused for adding a portion of my original
argument in opposition to these objections, as given more at length
in the _Transactions of the Irish Academy_.
1. I object to the authors' mode of stating the question at issue,
whereby they convey to the reader the impression that this is merely
to account for the occurrence of certain peculiar forms in ophite.
With reference to this, it is to be observed that the attention of
Sir William Logan, and of the writer, was first called to Eozoon
by the occurrence in Laurentian rocks of definite forms resembling
the Silurian _Stromatoporæ_, and dissimilar from any concretions or
crystalline structures found in these rocks. With his usual sagacity,
Sir William added to these facts the consideration that the mineral
substances occurring is these forms were so dissimilar as to suggest
that the forms themselves must be due to some extraneous cause rather
than to any crystalline or segregative tendency of their constituent
minerals. These specimens, which were exhibited by Sir William as
probably fossils, at the meeting of the American Association in
1859, and noticed with figures in the Report of the Canadian Survey
for 1863, showed under the microscope no minute structures. The
writer, who had at the time an opportunity of examining them, stated
his belief that if fossils, they would prove to be not Corals but
Protozoa.
In 1864, additional specimens having been obtained by the Survey,
slices were submitted to the writer, in which he at once detected
a well-marked canal-system, and stated, decidedly, his belief that
the forms were organic and foraminiferal. The announcement of this
discovery was first made by Sir W. E. Logan, in _Silliman's Journal_
for 1864. So far, the facts obtained and stated related to definite
forms mineralised by loganite, serpentine, pyroxene, dolomite, and
calcite. But before publishing these facts in detail, extensive
series of sections of all the Laurentian limestones, and of those
of the altered Quebec group of the Green Mountain range, were made,
under the direction of Sir W. E. Logan and Dr. Hunt, and examined
microscopically. Specimens were also decalcified by acids, and
subjected to chemical examination by Dr. Sterry Hunt. The result was
the conviction that the definite laminated forms must be organic,
and further, that there exist in the Laurentian limestones fragments
of such forms retaining their structure, and also other fragments,
probably organic, but distinct from Eozoon. These conclusions were
submitted to the Geological Society of London, in 1864, after the
specimens on which they were based had been shown to Dr. Carpenter
and Professor T. R. Jones, the former of whom detected in some of
the specimens an additional foraminiferal structure--that of the
tubulation of the proper wall, which I had not been able to make out.
Subsequently, in rocks at Tudor, of somewhat later age than those
of the Lower Laurentian at Grenville, similar structures were found
in limestones not more metamorphic than many of those which retain
fossils in the Silurian system. I make this historical statement in
order to place the question in its true light, and to show that it
relates to the organic origin of certain definite mineral masses,
exhibiting, not only the external forms of fossils, but also their
internal structure.
In opposition to these facts, and to the careful deductions drawn
from them, the authors of the paper under consideration maintain that
the structures are mineral and crystalline. I believe that in the
present state of science such an attempt to return to the doctrine
of "plastic-force" as a mode of accounting for fossils would not
be tolerated for a moment, were it not for the great antiquity and
highly crystalline condition of the rocks in which the structures
are found, which naturally create a prejudice against the idea of
their being fossiliferous. That the authors themselves feel this is
apparent from the slight manner in which they state the leading facts
above given, and from their evident anxiety to restrict the question
to the mode of occurrence of serpentine in limestone, and to ignore
the specimens of Eozoon preserved under different mineral conditions.
2. With reference to the general form of Eozoon and its structure
on the large scale, I would call attention to two admissions of
the authors of the paper, which appear to me to be fatal to their
case:--First, they admit, at page 533 [_Proceedings_, vol. x.],
their "inability to explain satisfactorily" the alternating layers
of carbonate of lime and other minerals in the typical specimens of
Canadian Eozoon. They make a feeble attempt to establish an analogy
between this and certain concentric concretionary layers; but the
cases are clearly not parallel, and the laminæ of the Canadian
Eozoon present connecting plates and columns not explicable on any
concretionary hypothesis. If, however, they are unable to explain the
lamellar structure alone, as it appeared to Logan in 1859, is it not
rash to attempt to explain it away now, when certain minute internal
structures, corresponding to what might have been expected on the
hypothesis of its organic origin, are added to it? If I affirm that
a certain mass is the trunk of a fossil tree, and another asserts
that it is a concretion, but professes to be unable to account for
its form and its rings of growth, surely his case becomes very weak
after I have made a slice of it, and have shown that it retains the
structure of wood.
Next, they appear to admit that if specimens occur wholly composed
of carbonate of lime, their theory will fall to the ground. Now such
specimens do exist. They treat the Tudor specimen with scepticism as
probably "strings of segregated calcite." Since the account of that
specimen was published, additional fragments have been collected, so
that new slices have been prepared. I have examined these with care,
and am prepared to affirm that the chambers in these specimens are
filled with a dark-coloured limestone not more crystalline than is
usual in the Silurian rocks, and that the chamber walls are composed
of carbonate of lime, with the canals filled with the same material,
except where the limestone filling the chambers has penetrated into
parts of the larger ones. I should add that the stratigraphical
researches of Mr. Vennor, of the Canadian Survey, have rendered it
probable that the beds containing these fossils, though unconformably
underlying the Lower Silurian, overlie the Lower Laurentian of the
locality, and are, therefore, probably Upper Laurentian, or perhaps
Huronian, so that the Tudor specimens may approach in age to Gümbel's
Eozoon Bavaricum.[AR]
[Footnote AR: I may now refer in addition to the canals filled with
calcite and dolomite, detected by Dr. Carpenter and myself in specimens
from Petite Nation, and mentioned in a previous chapter. See also Plate
VIII.]
Further, the authors of the paper have no right to object to our
regarding the laminated specimen as "typical" Eozoon. If the question
were as to _typical ophite_ the case would be different; but the
question actually is as to certain well-defined forms which we regard
as fossils, and allege to have organic structure on the small scale,
as well as lamination on the large scale. We profess to account for
the acervuline forms by the irregular growth at the surface of the
organisms, and by the breaking of them into fragments confusedly
intermingled in great thicknesses of limestone, just as fragments of
corals occur in Palæozoic limestones; but we are under no obligation
to accept irregular or disintegrated specimens as typical; and when
objectors reason from these fragments, we have a right to point to
the more perfect examples. It would be easy to explain the loose
cells of _Tetradium_ which characterize the bird's-eye limestone
of the Lower Silurian of America, as crystalline structures; but
a comparison with the unbroken masses of the same coral, shows
their true nature. I have for some time made the minute structure
of Palæozoic limestones a special study, and have described some
of them from the Silurian formations of Canada.[AS] I possess now
many additional examples, showing fragments of various kinds of
fossils preserved in these limestones, and recognisable only by the
infiltration of their pores with different silicious minerals. It can
also be shown that in many cases the crystallization of the carbonate
of lime, both of the fossils themselves and of their matrix, has
not interfered with the perfection of the most minute of these
structures.
[Footnote AS: In the _Canadian Naturalist_.]
The fact that the chambers are usually filled with silicates is
strangely regarded by the authors as an argument against the organic
nature of Eozoon. One would think that the extreme frequency of
silicious fillings of the cavities of fossils, and even of silicious
replacement of their tissues, should have prevented the use of such
an argument, without taking into account the opposite conclusions to
be drawn from the various kinds of silicates found in the specimens,
and from the modern filling of Foraminifera by hydrous silicates, as
shown by Ehrenberg, Mantell, Carpenter, Bailey, and Pourtales.[AT]
Further, I have elsewhere shown that the loganite is proved by its
texture to have been a fragmental substance, or at least filled
with loose _debris_; that the Tudor specimens have the cavities
filled with a sedimentary limestone, and that several fragmental
specimens from Madoc are actually wholly calcareous. It is to be
observed, however, that the wholly calcareous specimens present
great difficulties to an observer; and I have no doubt that they are
usually overlooked by collectors in consequence of their not being
developed by weathering, or showing any obvious structure in fresh
fractures.
[Footnote AT: _Quarterly Journal Geol. Society_, 1864.]
3. With regard to the canal system, the authors persist in
confusing the casts of it which occur in serpentine with "metaxite"
concretions, and in likening them to dendritic crystallizations of
silver, etc., and coralloidal forms of carbonate of lime. In answer
to this, I think it quite sufficient to say that I fail to perceive
the resemblance as other than very imperfectly imitative. I may add,
that the case is one of the occurrence of a canal structure in forms
which on other grounds appear to be organic, while the concretionary
forms referred to are produced under diverse conditions, none of
them similar to those of which evidence appears in the specimens of
Eozoon. With the singular theory of pseudomorphism, by means of which
the authors now supplement their previous objections, I leave Dr.
Hunt to deal.
4. With respect to the proper wall and its minute tubulation, the
essential error of the authors consists in confounding it with
fibrous and acicular crystals, and in maintaining that because the
tubuli are sometimes apparently confused and confluent they must
be inorganic. With regard to the first of these positions, I may
repeat what I have stated in former papers--that the true cell-wall
presents minute cylindrical processes traversing carbonate of lime,
and usually nearly parallel to each other, and often slightly
bulbose at the extremity. Fibrous serpentine, on the other hand,
appears as angular crystals, closely packed together, while the
numerous spicular crystals of silicious minerals which often appear
in metamorphic limestones, and may be developed by decalcification,
appear as sharp angular needles usually radiating from centres or
irregularly disposed. Their own plate (Ophite from Skye, King and
Rowney's Paper, _Proc. R. I. A._, vol. x.), is an eminent example
of this; and whatever the nature of the crystals represented, they
have no appearance of being true tubuli of Eozoon. I have very often
shown microscopists and geologists the cell-wall along with veins of
chrysotile and coatings of acicular crystals occurring in the same or
similar limestones, and they have never failed at once to recognise
the difference, especially under high powers.
I do not deny that the tubulation is often imperfectly preserved,
and that in such cases the casts of the tubuli may appear to be
glued together by concretions of mineral matter, or to be broken
or imperfect. But this occurs in all fossils, and is familiar to
any microscopist examining them. How difficult is it in many cases
to detect the minute structure of Nummulites and other fossil
Foraminifera? How often does a specimen of fossil wood present in one
part distorted and confused fibres or mere crystals, with the remains
of the wood forming phragmata between them, when in other parts it
may show the most minute structures in perfect preservation? But
who would use the disintegrated portions to invalidate the evidence
of the parts better preserved? Yet this is precisely the argument
of Professors King and Rowney, and which they have not hesitated
in using in the case of a fossil so old as Eozoon, and so often
compressed, crushed, and partly destroyed by mineralization.
I have in the above remarks confined myself to what I regard as
absolutely essential by way of explanation and defence of the
organic nature of Eozoon. It would be unprofitable to enter into the
multitude of subordinate points raised by the authors, and their
theory of mineral pseudomorphism is discussed by my friend Dr. Hunt;
but I must say here that this theory ought, in my opinion, to afford
to any chemist a strong presumption against the validity of their
objections, especially since it confessedly does not account for all
the facts, while requiring a most complicated series of unproved and
improbable suppositions.
The only other new features in the communication to which this note
refers are contained in the "supplementary note." The first of
these relates to the grains of coccolite in the limestone of Aker,
in Sweden. Whether or not these are organic, they are apparently
different from _Eozoon Canadense_. They, no doubt, resemble the
grains referred to by Gümbel as possibly organic, and also similar
granular objects with projections which, in a previous paper, I have
described from Laurentian limestones in Canada. These objects are of
doubtful nature; but if organic, they are distinct from Eozoon. The
second relates to the supposed crystals of malacolite from the same
place. Admitting the interpretation given of these to be correct,
they are no more related to Eozoon than are the curious vermicular
crystals of a micaceous mineral which I have noticed in the Canadian
limestones.
The third and still more remarkable case is that of a spinel from
Amity, New York, containing calcite in its crevices, including a
perfect canal system preserved in malacolite. With reference to
this, as spinels of large size occur in veins in the Laurentian
rocks, I am not prepared to say that it is absolutely impossible that
fragments of limestone containing Eozoon may not be occasionally
associated with them in their matrix. I confess, however, that
until I can examine such specimens, which I have not yet met with,
I cannot, after my experience of the tendencies of Messrs. Rowney
and King to confound other forms with those of Eozoon, accept their
determinations in a matter so critical and in a case so unlikely.[AU]
[Footnote AU: I have since ascertained that Laurentian limestone found
at Amity, New York, and containing spinels, does hold fragments of the
intermediate skeleton of Eozoon. The limestone may have been originally
a mass of fragments of this kind with the aluminous and magnesian
material of the spinel in their interstices.]
If all specimens of Eozoon were of the acervuline character, the
comparison of the chamber-casts with concretionary granules might
have some plausibility. But it is to be observed that the laminated
arrangement is the typical one; and the study of the larger
specimens, cut under the direction of Sir W. E. Logan, shows that
these laminated forms must have grown on certain strata-planes before
the deposition of the overlying beds, and that the beds are, in part,
composed of the broken fragments of similar laminated structures.
Further, much of the apparently acervuline Eozoon rock is composed
of such broken fragments, the interstices between which should not
be confounded with the chambers: while the fact that the serpentine
fills such interstices as well as the chambers shows that its
arrangement is not concretionary. Again, these chambers are filled in
different specimens with serpentine, pyroxene, loganite, calcareous
spar, chondrodite, or even with arenaceous limestone. It is also to
be observed that the examination of a number of limestones, other
than Canadian, by Messrs. King and Rowney, has obliged them to admit
that the laminated forms in combination with the canal-system are
"essentially Canadian," and that the only instances of structures
clearly resembling the Canadian specimens are afforded by limestones
Laurentian in age, and in some of which (as, for instance, in those
of Bavaria and Scandinavia) Carpenter and Gümbel have actually found
the structure of Eozoon. The other serpentine-limestones examined
(for example, that of Skye) are admitted to fail in essential points
of structure; and the only serpentine believed to be of eruptive
origin examined by them is confessedly destitute of all semblance
of Eozoon. Similar results have been attained by the more careful
researches of Prof. Gümbel, whose paper is well deserving of study by
all who have any doubts on this subject.
(B.) Reply by Dr. Hunt to Chemical Objections--(_Ibid._).
"In the _Proceedings of the Royal Irish Academy_, for July 12,
1869, Messrs. King and Rowney have given us at length their latest
corrected views on various questions connected with Eozoon Canadense.
Leaving to my friend, Dr. Dawson, the discussion of the zoological
aspects of the question, I cannot forbear making a few criticisms
on the chemical and mineralogical views of the authors. The problem
which they had before them was to explain the occurrence of certain
forms which, to skilled observers, like Carpenter, Dawson, and
Rupert Jones, appear to possess all the structural character of the
calcareous skeleton of a foraminiferal organism, and moreover to
show how it happens that these forms of crystalline carbonate of
lime are associated with serpentine in such a way as to lead these
observers to conclude that this hydrous silicate of magnesia filled
and enveloped the calcareous skeleton, replacing the perishable
sarcode. The hypothesis now put forward by Messrs. King and Rowney
to explain the appearances in question, is, that all this curiously
arranged serpentine, which appears to be a cast of the interior of a
complex foraminiferal organism, has been shaped or sculptured out of
plates, prisms, and other solids of serpentine, by "the erosion and
incomplete waste of the latter, _the definite shapes_ being residual
portions of the solid that have not completely disappeared." The
calcite which limits these definite shapes, or, in other words, what
is regarded as the calcareous skeleton of Eozoon, is a 'replacement
pseudomorph' of calcite taking the place of the wasted and eroded
serpentine. It was not a calcareous fossil, filled and surrounded
by the serpentine, but was formed in the midst of the serpentine
itself, by a mysterious agency which dissolved away this mineral to
form a mould, in which the calcite was cast. This marvellous process
can only be paralleled by the operations of that plastic force in
virtue of which sea-shells were supposed by some old naturalists
to be generated in the midst of rocky strata. Such equivocally
formed fossils, whether oysters or Foraminifers, may well be termed
_pseudomorphs_, but we are at a loss to see with what propriety the
authors of this singular hypothesis invoke the doctrines of mineral
pseudomorphism, as taught by Rose, Blum, Bischof, and Dana. In
replacement pseudomorphs, as understood by these authors, a mineral
species disappears and is replaced by another which retains the
external form of the first. Could it be shown that the calcite of the
cell-wall of Eozoon was once serpentine, this portion of carbonate
of lime would be a replacement pseudomorph after serpentine; but why
the portions of this mineral, which on the hypothesis of Messrs. King
and Rowney have been thus replaced, should assume the forms of a
foraminiferal skeleton, is precisely what our authors fail to show,
and, as all must see, is the gist of the whole matter.
"Messrs. King and Rowney, it will be observed, assume the existence
of calcite as a replacement pseudomorph after serpentine, but give
no evidence of the possibility of such pseudomorphs. Both Rose and
Bischof regard serpentine itself as in all cases, of pseudomorphous
origin, and as the last result of the changes of a number of mineral
species, but give us no example of the pseudomorphous alteration of
serpentine itself. It is, according to Bischof, the very insolubility
and unalterability of serpentine which cause it to appear as the
final result of the change of so many mineral species. Delesse,
moreover, in his carefully prepared table of pseudomorphous minerals,
in which he has resumed the results of his own and all preceding
observers, does not admit the pseudomorphic replacement of serpentine
by calcite, nor indeed by any other species.[AV] If, then, such
pseudomorphs exist, it appears to be a fact hitherto unobserved,
and our authors should at least have given us some evidence of this
remarkable case of pseudomorphism by which they seek to support their
singular hypothesis.
[Footnote AV: _Annales des Mines_, 5, xvi., 317.]
"I hasten to say, however, that I reject with Scheerer, Delesse
and Naumann, a great part of the supposed cases of mineral
pseudomorphism, and do not even admit the pseudomorphous origin of
serpentine itself, but believe that this, with many other related
silicates, has been formed by direct chemical precipitation. This
view, which our authors do me the honour to criticise, was set
forth by me in 1860 and 1861,[AW] and will be found noticed more
in detail in the _Geological Report of Canada_, for 1866, p. 229.
I have there and elsewhere maintained that 'steatite, serpentine,
pyroxene, hornblende, and in many cases garnet, epidote, and other
silicated minerals, are formed by a crystallization and molecular
re-arrangement of silicates, generated by chemical processes in
waters at the earth's surface.'[AX]
[Footnote AW: _Amer. Journ. Science_ (2), xxix., 284; xxxii., 286.]
[Footnote AX: _Ibid._, xxxvii., 266; xxxviii., 183.]
"This view, which at once explains the origin of all these bedded
rocks, and the fact that their constituent mineral species, like
silica and carbonate of lime, replace the perishable matter of
organic forms, is designated by Messrs. King and Rowney 'as so
completely destitute of the characters of a scientific hypothesis
as to be wholly unworthy of consideration,' and they speak of my
attempt to maintain this hypothesis as 'a total collapse.' How far
this statement is from the truth my readers shall judge. My views
as to the origin of serpentine and other silicated minerals were
set forth by me as above in 1860-1864, before anything was known
of the mineralogy of Eozoon, and were forced upon me by my studies
of the older crystalline schists of North America. Naumann had
already pointed out the necessity of some such hypothesis when he
protested against the extravagances of the pseudomorphist school,
and maintained that the beds of various silicates found in the
crystalline schists are original deposits, and not formed by an
epigenic process (_Geognosie_, ii., 65, 154, and _Bull. Soc. Geol.
de France_, 2, xviii., 678). This conclusion of Naumann's I have
attempted to explain and support by numerous facts and observations,
which have led me to the hypothesis in question. Gümbel, who accepts
Naumann's view, sustains my hypothesis of the origin of these rocks
in a most emphatic manner,[AY] and Credner, in discussing the genesis
of the Eozoic rocks, has most ably defended it.[AZ] So much for my
theoretical views so contemptuously denounced by Messrs. King and
Rowney, which are nevertheless unhesitatingly adopted by the two
geologists of the time who have made the most special studies of the
rocks in question,--Gümbel in Germany, and Credner in North America.
[Footnote AY: _Proc. Royal Bavarian Acad._ for 1866, translated in
_Can. Naturalist_, iii., 81.]
[Footnote AZ: _Die Gliederung der Eozoischen Formations gruppe
Nord.-Amerikas,--a Thesis defended before the University of Leipzig,
March 15, 1869_, by Dr. Hermann Credner. Halle, 1869, p. 53.]
"It would be a thankless task to follow Messrs. King and Rowney
through their long paper, which abounds in statements as unsound as
those I have just exposed, but I cannot conclude without calling
attention to one misconception of theirs as to my view of the origin
of limestones. They quote Professor Hull's remark to the effect that
the researches of the Canadian geologists and others have shown that
the oldest known limestones of the world owe their origin to Eozoon,
and remark that the existence of great limestone beds in the Eozoic
rocks seems to have influenced Lyell, Ramsay, and others in admitting
the received view of Eozoon. Were there no other conceivable source
of limestones than Eozoon or similar calcareous skeletons, one might
suppose that the presence of such rocks in the Laurentian system
could have thus influenced these distinguished geologists, but
there are found beneath the Eozoon horizon two great formations of
limestone in which this fossil has never been detected. When found,
indeed, it owes its conservation in a readily recognisable form to
the fact, that it was preserved by the introduction of serpentine
at the time of its growth. Above the unbroken Eozoon reefs are
limestones made up apparently of the debris of Eozoon thus preserved
by serpentine, and there is no doubt that this calcareous rhizopod,
growing in water where serpentine was not in process of formation,
might, and probably did, build up pure limestone beds like those
formed in later times from the ruins of corals and crinoids. Nor
is there anything inconsistent in this with the assertion which
Messrs. King and Rowney quote from me, viz., that the popular notion
that _all limestone formations_ owe their origin to organic life is
based upon a fallacy. The idea that marine organisms originate the
carbonate of lime of their skeletons, in a manner somewhat similar to
that in which plants generate the organic matter of theirs, appears
to be commonly held among certain geologists. It cannot, however,
be too often repeated that animals only appropriate the carbonate
of lime which is furnished them by chemical reaction. Were there
no animals present to make use of it, the carbonate of lime would
accumulate in natural waters till these became saturated, and would
then be deposited in an insoluble form; and although thousands of
feet of limestone have been formed from the calcareous skeletons
of marine animals, it is not less true that great beds of ancient
marble, like many modern travertines and tufas, have been deposited
without the intervention of life, and even in waters from which
living organisms were probably absent. To illustrate this with the
parallel case of silicious deposits, there are great beds made
up of silicious shields of diatoms. These during their lifetime
extracted from the waters the dissolved silica, which, but for their
intervention, might have accumulated till it was at length deposited
in the form of schist or of crystalline quartz. In either case the
function of the coral, the rhizopod, or the diatom is limited to
assimilating the carbonate of lime or the silica from its solution,
and the organised form thus given to these substances is purely
accidental. It is characteristic of our authors, that, rather than
admit the limestone beds of the Eozoon rocks to have been formed like
beds of coralline limestone, or deposited as chemical precipitates
like travertine, they prefer, as they assure us, to regard them as
the results of that hitherto unheard-of process, the pseudomorphism
of serpentine; as if the deposition of the carbonate of lime in
the place of dissolved serpentine were a simpler process than its
direct deposition in one or the other of the ways which all the world
understands!"
(C.) Dr. Carpenter on the Foraminiferal Relations of Eozoon.
In the _Annals of Natural History_, for June, 1874, Dr. Carpenter
has given a crushing reply to some objections raised in that journal
by Mr. Carter. He first shows, contrary to the statement of Mr.
Carter, that the fine nummuline tubulation corresponds precisely in
its direction with reference to the chambers, with that observed in
Nummulites and Orbitoides. In the second place, he shows by clear
descriptions and figures, that the relation of the canal system to
the fine tubulation is precisely that which he had demonstrated in
more recent nummuline and rotaline Foraminifera. In the third place
he adduces additional facts to show that in some specimens of Eozoon
the calcareous skeleton has been filled with calcite before the
introduction of any foreign mineral matter. He concludes the argument
in the following words:--
"I have thus shown:--(1) that the 'utter incompatibility' asserted
by my opponents to exist between the arrangement of the supposed
'nummuline tubulation' of Eozoon and true Nummuline structure, so far
from having any real existence, really furnishes an additional point
of conformity; and (2) that three most striking and complete points
of conformity exist between the structure of the best-preserved
specimens of Eozoon, and that of the Nummulites whose tubulation I
described in 1849, and of the Calcarina whose tubulation and canal
system I described in 1860.
"That I have not troubled myself to reply to the reiterated arguments
in favour of the doctrine [of mineral origin] advanced by Professors
King and Rowney on the strength of the occurrence of undoubted
results of mineralization in the Canadian Ophite, and of still more
marked evidences of the same action in other Ophites, has been
simply because these arguments appeared to me, as I thought they
must also appear to others, entirely destitute of logical force.
Every scientific palæontologist I have ever been acquainted with has
taken the _best_ preserved specimens, not the _worst_, as the basis
of his reconstructions; and if he should meet with distinct evidence
of characteristic organic structure in even a very small fragment
of a doubtful form, he would consider the organic origin of that
form to be thereby substantiated, whatever might be the evidence of
purely mineral arrangement which the greater part of his specimen
may present,--since he would regard that arrangement as a probable
result of _subsequent_ mineralization, by which the original organic
structure has been more or less obscured. If this is _not_ to be our
rule of interpretation, a large part of the palæontological work
of our time must be thrown aside as worthless. If, for example,
Professors King and Rowney were to begin their study of Nummulites
by the examination of their most mineralized forms, they would deem
themselves justified (according to their canons of interpretation)
in denying the existence of the tubulation and canalization which I
described (in 1849) in the N. lævigata preserved almost unaltered in
the London Clay of Bracklesham Bay.
"My own notions of Eozoic structure have been formed on the
examination of the Canadian specimens selected by the experienced
discrimination of Sir William Logan, as those in which there was
_least_ appearance of metamorphism; and having found in these what I
regarded as unmistakable evidence of an organic structure conformable
to the foraminiferal type, I cannot regard it as any disproof of
that conformity, either to show that the true Eozoic structure has
been frequently altered by mineral metamorphism, or to adduce the
occurrence of Ophites more or less resembling the Eozoon of the
Canadian Laurentians at various subsequent geological epochs. The
existence of any number or variety of _purely mineral_ Ophites would
not disprove the organic origin of the Canadian Eozoon--unless
it could be shown that some wonderful process of mineralization
is competent to construct not only its multiplied alternating
lamellæ of calcite and serpentine, the dendritic extensions of the
latter into the former, and the 'acicular layer' of decalcified
specimens, but (1) the _pre-existing canalization_ of the calcareous
lamellæ, (2) the _unfilled nummuline tubulation_ of the proper
wall of the chambers, and (3) the peculiar _calcarine_ relation of
the canalization and tubulation, here described and figured from
specimens in the highest state of preservation, showing the _least_
evidence of any mineral change.
"On the other hand, Professors King and Rowney began their studies of
Eozoic structure upon the Galway Ophite--a rock which Sir Roderick
Murchison described to me at the time as having been so much 'tumbled
about,' that he was not at all sure of its geological position, and
which exhibits such obvious evidences of mineralization, with such
an entire absence of any vestige of organic structure, that I should
never for a moment have thought of crediting it with an organic
origin, but for the general resemblance of its serpentine-grains
to those of the 'acervuline' portion of the Canadian Eozoon. They
pronounced with the most positive certainty upon the mineral origin
of the Canadian Eozoon, before they had subjected transparent
sections of it to any of that careful comparison with similar
sections of recent Foraminifera, which had been the basis of
Dr. Dawson's original determination, and of my own subsequent
confirmation, of its organic structure.
[Illustration:
Plate VIII.
_Eozoon and Chrysotile Veins, etc._
Fig. 1.--Portion of two laminæ and intervening serpentine,
with chrysotile vein. (_a._) Proper wall tubulated. (_b._)
Intermediate skeleton, with large canals. (_c._) Openings of
small chamberlets filled with serpentine. (_s._) Serpentine
filling chamber. (_s^1._) Vein of chrysotile, showing its
difference from the proper wall.
Fig. 2.--Junction of a canal and the proper wall. Lettering as in
Fig. 1.
Fig. 3.--Proper wall shifted by a fault, and more recent chrysotile
vein not faulted. Lettering as in Fig. 1.
Fig. 4.--Large and small canals filled with dolomite.
Fig. 5.--Abnormally thick portion of intermediate skeleton, with
large tubes and small canals filled with dolomite.]
CHAPTER VIII.
THE DAWN-ANIMAL AS A TEACHER IN SCIENCE.
The thoughts suggested to the philosophical naturalist by the
contemplation of the dawn of life on our planet are necessarily many
and exciting, and the subject has in it the materials for enabling the
general reader better to judge of some of the theories of the origin of
life agitated in our time. In this respect our dawn-animal has scarcely
yet had justice; and we may not be able to render this in these pages.
Let us put it into the witness-box, however, and try to elicit its
testimony as to the beginnings of life.
Looking down from the elevation of our physiological and mental
superiority, it is difficult to realize the exact conditions in which
life exists in creatures so simple as the Protozoa. There may perhaps
be higher intelligences that find it equally difficult to realize how
life and reason can manifest themselves in such poor houses of clay
as those we inhabit. But placing ourselves near to these creatures,
and entering as it were into sympathy with them, we can understand
something of their powers and feelings. In the first place it is plain
that they can vigorously, if roughly, exercise those mechanical,
chemical, and vegetative powers of life which are characteristic of
the animal. They can seize, swallow, digest, and assimilate food; and,
employing its albuminous parts in nourishing their tissues, can burn
away the rest in processes akin to our respiration, or reject it from
their system. Like us, they can subsist only on food which the plant
has previously produced; for in this world, from the beginning of time,
the plant has been the only organism which could use the solar light
and heat as forces to enable it to turn the dead elements of matter
into living, growing tissues, and into organic compounds capable of
nourishing the animal. Like us, the Protozoa expend the food which
they have assimilated in the production of animal force, and in doing
so cause it to be oxidized, or burnt away, and resolved again into
dead matter. It is true that we have much more complicated apparatus
for performing these functions, but it does not follow that this gives
us much real superiority, except relatively to the more difficult
conditions of our existence. The gourmand who enjoys his dinner may
have no more pleasure in the act than the Amœba which swallows a
Diatom; and for all that the man knows of the subsequent processes to
which the food is subjected, his interior might be a mass of jelly,
with extemporised vacuoles, like that of his humble fellow-animal. The
workman or the athlete has bones and muscles of vastly complicated
structure, but to him the muscular act is as simple and unconscious a
process as the sending out of a pseudopod to a Protozoon. The clay is
after all the same, and there may be as much credit to the artist in
making a simple organism with varied powers, as a more complex frame
for doing nicer work. It is a weakness of humanity to plume itself on
advantages not of its own making, and to treat its superior gifts as
if they were the result of its own endeavours. The truculent traveller
who illustrated his boast of superiority over the Indian by comparing
his rifle with the bow and arrows of the savage, was well answered by
the question, "Can you make a rifle?" and when he had to answer, "No,"
by the rejoinder, "Then I am at least better than you, for I can make
my bow and arrows." The Amœba or the Eozoon is probably no more than we
its own creator; but if it could produce itself out of vegetable matter
or out of inorganic substances, it might claim in so far a higher
place in the scale of being than we; and as it is, it can assert equal
powers of digestion, assimilation, and motion, with much less of bodily
mechanism.
In order that we may feel, a complicated apparatus of nerves and
brain-cells has to be constructed and set to work; but the Protozoon,
without any distinct brain, is all brain, and its sensation is simply
direct. Thus vision in these creatures is probably performed in a rough
way by any part of their transparent bodies, and taste and smell are no
doubt in the same case. Whether they have any perception of sound as
distinct from the mere vibrations ascertained by touch, we do not know.
Here also we are not far removed above the Protozoa, especially those
of us to whom touch, seeing, and hearing are mere feelings, without
thought or knowledge of the apparatus employed. We might so far as
well be Amœbas. As we rise higher we meet with more differences. Yet
it is evident that our gelatinous fellow-being can feel pain, dread
danger, desire possessions, enjoy pleasure, and in a simple unconscious
way entertain many of the appetites and passions that affect ourselves.
The wonder is that with so little of organization it can do so much.
Yet, perhaps, life can manifest itself in a broader and more intense
way where there is little organization; and a highly strung and
complex organism is not so much a necessary condition of a higher life
as a mere means of better adapting it to its present surroundings.
Those philosophies which identify the thinking mind with the material
organism, must seem outrageous blunders to an Amœba on the one hand, or
to an angel on the other, could either be enabled to understand them;
which, however, is not very probable, as they are too intimately bound
up with the mere prejudices incident to the present condition of our
humanity. In any case the Protozoa teach us how much of animal function
may be fulfilled by a very simple organism, and warn us against the
fallacy that creatures of this simple structure are necessarily nearer
to inorganic matter, and more easily developed from it than beings of
more complex mould.
A similar lesson is taught by the complexity of their skeletons.
We speak in a crude unscientific way of these animals accumulating
calcareous matter, and building up reefs of limestone. We must,
however, bear in mind that they are as dependent on their food for
the materials of their skeletons as we are, and that their crusts
grow in the interior of the sarcode just as our bones do within our
bodies. The provision even for nourishing the interior of the skeleton
by tubuli and canals is in principle similar to that involved in the
Haversian canals, cells, and canalicules of bone. The Amœba of course
knows neither more nor less of this than the average Englishman.
It is altogether a matter of unconscious growth. The process in
the Protozoa strikes some minds, however, as the more wonderful of
the two. It is, says an eminent modern physiologist, a matter of
"profound significance" that this "particle of jelly [the sarcode
of a Foraminifer] is capable of guiding physical forces in such a
manner as to give rise to these exquisite and almost mathematically
arranged structures." Respecting the structures themselves there is no
exaggeration in this. No arch or dome framed by human skill is more
perfect in beauty or in the realization of mechanical ideas than the
tests of some Foraminifera, and none is so complete and wonderful in
its internal structure. The particle of jelly, however, is a figure of
speech. The body of the humblest Foraminifer is much more than this.
It is an organism with divers parts, as we have already seen in a
previous chapter, and it is endowed with the mysterious forces of life
which in it guide the physical forces, just as they do in building
up phosphate of lime in our bones, or indeed just as the will of the
architect does in building a palace. The profound significance which
this has, reaches beyond the domain of the physical and vital, even to
the spiritual. It clings to all our conceptions of living things: quite
as much, for example, to the evolution of an animal with all its parts
from a one-celled germ, or to the connection of brain-cells with the
manifestations of intelligence. Viewed in this way, we may share with
the author of the sentence I have quoted his feeling of veneration in
the presence of this great wonder of animal life, "burning, and not
consumed," nay, building up, and that in many and beautiful forms. We
may realize it most of all in the presence of the organism which was
perhaps the first to manifest on our planet these marvellous powers.
We must, however, here also, beware of that credulity which makes too
many thinkers limit their conceptions altogether to physical force
in matters of this kind. The merely materialistic physiologist is
really in no better position than the savage who quails before the
thunderstorm, or rejoices in the solar warmth, and seeing no force or
power beyond, fancies himself in the immediate presence of his God. In
Eozoon we must discern not only a mass of jelly, but a being endowed
with that higher vital force which surpasses vegetable life and also
physical and chemical forces; and in this animal energy we must see an
emanation from a Will higher than our own, ruling vitality itself; and
this not merely to the end of constructing the skeleton of a Protozoon,
but of elaborating all the wonderful developments of life that were to
follow in succeeding ages, and with reference to which the production
and growth of this creature were initial steps. It is this mystery of
design which really constitutes the "profound significance" of the
foraminiferal skeleton.
Another phenomenon of animality forced upon our notice by the Protozoa
is that of the conditions of life in animals not individual, as we
are, but aggregative and cumulative in indefinite masses. What, for
instance, the relations to each other of the Polyps, growing together
in a coral mass, of the separate parts of a Sponge, or the separate
cells of a Foraminifer, or of the sarcode mass of an indefinitely
spread out Stromatopora or Bathybius. In the case of the Polyps, we
may believe that there is special sensation in the tentacles and
oral opening of each individual, and that each may experience hunger
when in want, or satisfaction when it is filled with food, and that
injuries to one part of the mass may indirectly affect other parts,
but that the nutrition of the whole mass may be as much unfelt by the
individual Polyps as the processes going on in our own bones are by
us. So in the case of a large Sponge or Foraminifer, there may be some
special sensation in individual cells, pseudopods, or segments, and
the general sensation may be very limited, while unconscious living
powers pervade the whole. In this matter of aggregation of animals we
have thus various grades. The Foraminifers and Sponges present us with
the simplest of all, and that which most resembles the aggregation of
buds in the plant. The Polyps and complex Bryozoons present a higher
and more specialised type; and though the bilateral symmetry which
obtains in the higher animals is of a different nature, it still at
least reminds us of that multiplication of similar parts which we see
in the lower grades of being. It is worthy of notice here that the
lower animals which show aggregative tendencies present but imperfect
indications, or none at all, of bilateral symmetry. Their bodies, like
those of plants, are for the most part built up around a central axis,
or they show tendencies to spiral modes of growth.
It is this composite sort of life which is connected with the main
geological function of the Foraminifer. While active sensation,
appetite, and enjoyment pervade the pseudopods and external sarcode
of the mass, the hard skeleton common to the whole is growing within;
and in this way the calcareous matter is gradually removed from
the sea water, and built up in solid reefs, or in piles of loose
foraminiferal shells. Thus it is the aggregative or common life,
alike in Foraminifers as in Corals, that tends most powerfully to the
accumulation of calcareous matter; and those creatures whose life is
of this complex character are best suited to be world-builders, since
the result of their growth is not merely a cemetery of their osseous
remains, but a huge communistic edifice, to which multitudes of lives
have contributed, and in which successive generations take up their
abode on the remains of their ancestors. This process, so potent in
the progress of the earth's geological history, began, as far as we
know, with Eozoon.
Whether, then, in questioning our proto-foraminifer, we have reference
to the vital functions of its gelatinous sarcode, to the complexity and
beauty of its calcareous test, or to its capacity for effecting great
material results through the union of individuals, we perceive that we
have to do, not with a low condition of those powers which we designate
life, but with the manifestation of those powers through the means of a
simple organism; and this in a degree of perfection which we, from our
point of view, would have in the first instance supposed impossible.
If we imagine a world altogether destitute of life, we still might
have geological formations in progress. Not only would volcanoes belch
forth their liquid lavas and their stones and ashes, but the waves and
currents of the ocean and the rains and streams on the land, with the
ceaseless decomposing action of the carbonic acid of the atmosphere,
would be piling up mud, sand, and pebbles in the sea. There might even
be some formation of limestone taking place where springs charged
with bicarbonate of lime were oozing out on the land or the bottom of
the waters. But in such a world all the carbon would be in the state
of carbonic acid, and all the limestone would either be diffused in
small quantities through various rocks or in limited local beds, or
in solution, perhaps as chloride of calcium, in the sea. Dr. Hunt has
given chemical grounds for supposing that the most ancient seas were
largely supplied with this very soluble salt, instead of the chloride
of sodium, or common salt, which now prevails in the sea-water.
Where in such a world would life be introduced? on the land or in the
waters? All scientific probability would say in the latter. The ocean
is now vastly more populous than the land. The waters alone afford
the conditions necessary at once for the most minute and the grandest
organisms, at once for the simplest and for others of the most complex
character. Especially do they afford the best conditions for those
animals which subsist in complex communities, and which aggregate large
quantities of mineral matter in their skeletons. So true is this that
up to the present time all the species of Protozoa and of the animals
most nearly allied to them are aquatic. Even in the waters, however,
plant life, though possibly in very simple forms, must precede the
animal.
Let humble plants, then, be introduced in the waters, and they would
at once begin to use the solar light for the purpose of decomposing
carbonic acid, and forming carbon compounds which had not before
existed, and which independently of vegetable life would never have
existed. At the same time lime and other mineral substances present in
the sea-water would be fixed in the tissues of these plants, either in
a minute state of division, as little grains or Coccoliths, or in more
solid masses like those of the Corallines and Nullipores. In this way
a beginning of limestone formation might be made, and quantities of
carbonaceous and bituminous matter, resulting from the decay of marine
plants might accumulate in the sea-bottom. Now arises the opportunity
for animal life. The plants have collected stores of organic matter,
and their minute germs, along with microscopic species, are floating
everywhere in the sea. Nay, there may be abundant examples of those
Amœba-like germs of aquatic plants, simulating for a time the life
of the animal, and then returning into the circle of vegetable life.
In these some might see precursors of the Protozoa, though they are
probably rather prophetic analogues than blood relations. The plant
has fulfilled its function as far as the waters are concerned, and now
arises the opportunity for the animal. In what form shall it appear?
Many of its higher forms, those which depend upon animal food or on the
more complex plants for subsistence, would obviously be unsuitable.
Further, the sea-water is still too much saturated with saline matter
to be fit for the higher animals of the waters. Still further, there
may be a residue of internal heat forbidding coolness, and that
solution of free oxygen which is an essential condition of existence to
most of the modern animals. Something must be found suitable for this
saline, imperfectly oxygenated, tepid sea. Something too is wanted that
can aid in introducing conditions more favourable to higher life in
the future. Our experience of the modern world shows us that all these
conditions can be better fulfilled by the Protozoa than by any other
creatures. They can live now equally in those great depths of ocean
where the conditions are most unfavourable to other forms of life, and
in tepid unhealthy pools overstocked with vegetable matter in a state
of putridity. They form a most suitable basis for higher forms of life.
They have remarkable powers of removing mineral matters from the waters
and of fixing them in solid forms. So in the fitness of things Eozoon
is just what we need, and after it has spread itself over the mud and
rock of the primeval seas, and built up extensive reefs therein, other
animals may be introduced capable of feeding on it, or of sheltering
themselves in its stony masses, and thus we have the appropriate dawn
of animal life.
But what are we to say of the cause of this new series of facts, so
wonderfully superimposed upon the merely vegetable and mineral? Must
it remain to us as an act of creation, or was it derived from some
pre-existing matter in which it had been potentially present? Science
fails to inform us, but conjectural "phylogeny" steps in and takes its
place. Haeckel, the prophet of this new philosophy, waves his magic
wand, and simple masses of sarcode spring from inorganic matter, and
form diffused sheets of sea-slime, from which are in time separated
distinct Amœboid and Foraminiferal forms. Experience, however, gives us
no facts whereon to build this supposition, and it remains neither more
nor less scientific or certain than that old fancy of the Egyptians,
which derived animals from the fertile mud of the Nile.
If we fail to learn anything of the origin of Eozoon, and if its
life-processes are just as inscrutable as those of higher creatures,
we can at least inquire as to its history in geological time. In this
respect we find in the first place that the Protozoa have not had
a monopoly in their profession of accumulators of calcareous rock.
Originated by Eozoon in the old Laurentian time, this process has
been proceeding throughout the geological ages; and while Protozoa,
equally simple with the great prototype of the race, have been and
are continuing its function, and producing new limestones in every
geological period, and so adding to the volume of the successive
formations, new workers of higher grades have been introduced, capable
of enjoying higher forms of animal activity, and equally of labouring
at the great task of continent-building; of existing, too, in seas
less rich in mineral substances than those of the Eozoic time, and for
that very reason better suited to higher and more skilled artists. It
is to be observed in connection with this, that as the work of the
Foraminifers has thus been assumed by others, their size and importance
have diminished, and the grander forms of more recent times have some
of them been fain to build up their hard parts of cemented sand instead
of limestone.
But we further find that, while the first though not the only organic
gatherers of limestone from the ocean waters, they have had to do, not
merely with the formation of calcareous sediments, but also with that
of silicious deposits. The greenish silicate called glauconite, or
green-sand, is found to be associated with much of the foraminiferal
slime now accumulating in the ocean, and also with the older deposits
of this kind now consolidated in chalks and similar rocks. This name
glauconite is, as Dr. Hunt has shown, employed to designate not only
the hydrous silicate of iron and potash, which perhaps has the best
right to it, but also compounds which contain in addition large
percentages of alumina, or magnesia, or both; and one glauconite from
the Tertiary limestones near Paris, is said to be a true serpentine,
or hydrous silicate of magnesia.[BA] Now the association of such
substances with Foraminifera is not purely accidental. Just as a
fragment of decaying wood, imbedded in sediment, has the power of
decomposing soluble silicates carried to it by water, and parting with
its carbon in the form of carbonic acid, in exchange for the silica,
and thus replacing, particle by particle, the carbon of the wood
with silicon, so that at length it becomes petrified into a flinty
mass, so the sarcode of a Foraminifer, which is a more dense kind of
animal matter than is usually supposed, can in like manner abstract
silica from the surrounding water or water-soaked sediment. From some
peculiarity in the conditions of the case, however, our Protozoon
usually becomes petrified with a hydrous silicate instead of with pure
silica. The favourable conditions presented by the deep sea for the
combination of silica with bases, may perhaps account in part for
this. But whatever the cause, it is usual to find fossil Foraminifera
with their sarcode replaced by such material. We also find beds of
glauconite retaining the forms of Foraminifera, while the calcareous
tests of these have been removed, apparently by acid waters.
[Footnote BA: Berthier, quoted by Hunt.]
One consideration which, though conjectural, deserves notice, is
connected with the food of these humble animals. They are known to feed
to a large extent on minute plants, the Diatoms, and other organisms
having silica in their skeletons or cell-walls, and consequently
soluble silicates in their juices. The silicious matter contained
in these organisms is not wanted by the Foraminifera for their own
skeletons, and will therefore be voided by them as an excrementitious
matter. In this way, where Foraminifera greatly abound, there may be a
large production of soluble silica and silicates, in a condition ready
to enter into new and insoluble compounds, and to fill the cavities
and pores of dead shells. Thus glauconite and even serpentine may,
in a certain sense, be a sort of foraminiferal coprolitic matter or
excrement. Of course it is not necessary to suppose that this is the
only source of such materials. They may be formed in other ways; but I
suggest this as at least a possible link of connection.
Whether or not the conjecture last mentioned has any validity, there
is another and most curious bond of connection between oceanic
Protozoa and silicious deposits. Professor Wyville Thompson reports
from the _Challenger_ soundings, that in certain areas of the South
Pacific the ordinary foraminiferal ooze is replaced by a peculiar red
clay, which he attributes to the action of water laden with carbonic
acid, in removing all the lime, and leaving this red mud as a sort
of ash, composed of silica, alumina, and iron oxide. Now this is in
all probability a product of the decomposition and oxidation of the
glauconitic matter contained in the ooze. Thus we learn that when areas
on which calcareous deposits have been accumulated by Protozoa, are
invaded by cold arctic or antarctic waters charged with carbonic acid,
the carbonate of lime may be removed, and the glauconite left, or even
the latter may be decomposed, leaving silicious, aluminous, and other
deposits, which may be quite destitute of any organic structures, or
retain only such remnants of them as have been accidentally or by
their more resisting character protected from destruction.[BB] In this
way it may be possible that many silicious rocks of the Laurentian
and Primordial ages, which now show no trace of organization, may be
indirectly products of the action of life. When the recent deposits
discovered by the _Challenger_ dredgings shall have been more fully
examined, we may perhaps have the means of distinguishing such rocks,
and thus of still further enlarging our conceptions of the part played
by Protozoa in the drama of the earth's history. In any case it seems
plain that beds of green-sand and similar hydrous silicates may be the
residue of thick deposits of foraminiferal limestone or chalky matter,
and that these silicates may in their turn be oxidised and decomposed,
leaving beds of apparently inorganic clay. Such beds may finally be
consolidated and rendered crystalline by metamorphism, and thus a
great variety of silicated rocks may result, retaining little or no
indication of any connection with the agency of life. We can scarcely
yet conjecture the amount of light which these new facts may eventually
throw on the serpentine and other rocks of the Eozoic age. In the
meantime they open up a noble field to chemists and microscopists.
[Footnote BB: The "red chalk" of Antrim, and that of Speeton, contain
arenaceous Foraminifera and silicious casts of their shells, apparently
different from typical glauconite, and the extremely fine ferruginous
and argillaceous sediment of these chalks may well be decomposed
glauconitic matter like that of the South Pacific. I have found these
beds, the hard limestones of the French Neocomian, and the altered
green-sands of the Alps, very instructive for comparison with the
Laurentian limestones; and they well deserve study by all interested in
such subjects.]
When the marvellous results of recent deep-sea dredgings were first
made known, and it was found that chalky foraminiferal earth is yet
accumulating in the Atlantic, with sponges and sea urchins resembling
in many respects those whose remains exist in the chalk, the fact was
expressed by the statement that we still live in the chalk period. Thus
stated the conclusion is scarcely correct. We do not live in the chalk
period, but the conditions of the chalk period still exist in the
deep sea. We may say more than this. To some extent the conditions of
the Laurentian period still exist in the sea, except in so far as they
have been removed by the action of the Foraminifera and other limestone
builders. To those who can realize the enormous lapse of time involved
in the geological history of the earth, this conveys an impression
almost of eternity in the existence of this oldest of all the families
of the animal kingdom.
We are still more deeply impressed with this when we bring into view
the great physical changes which have occurred since the dawn of life.
When we consider that the skeletons of Eozoon contribute to form the
oldest hills of our continents; that they have been sealed up in solid
marble, and that they are associated with hard crystalline rocks
contorted in the most fantastic manner; that these rocks have almost
from the beginning of geological time been undergoing waste to supply
the material of new formations; that they have witnessed innumerable
subsidences and elevations of the continents; and that the greatest
mountain chains of the earth have been built up from the sea since
Eozoon began to exist,--we acquire a most profound impression of the
persistence of the lower forms of animal life, and know that mountains
may be removed and continents swept away and replaced, before the least
of the humble gelatinous Protozoa can finally perish. Life may be a
fleeting thing in the individual, but as handed down through successive
generations of beings, and as a constant animating power in successive
organisms, it appears, like its Creator, eternal.
This leads to another and very serious question. How long did lineal
descendants of Eozoon exist, and do they still exist? We may for the
present consider this question apart from ideas of derivation and
elevation into higher planes of existence. Eozoon as a species and
even as a genus may cease to exist with the Eozoic age, and we have no
evidence whatever that Archæocyathus, Stromatopora, or Receptaculites
are its modified descendants. As far as their structures inform us,
they may as much claim to be original creations as Eozoon itself.
Still descendants of Eozoon may have continued to exist, though we
have not yet met with them. I should not be surprised to hear of a
veritable specimen being some day dredged alive in the Atlantic or
the Pacific. It is also to be observed that in animals so simple as
Eozoon many varieties may appear, widely different from the original.
In these the general form and habit of life are the most likely things
to change, the minute structures much less so. We need not, therefore,
be surprised to find its descendants diminishing in size or altering
in general form, while the characters of the fine tubulation and of
the canal system would remain. We need not wonder if any sessile
Foraminifer of the Nummuline group should prove to be a descendant
of Eozoon. It would be less likely that a Sponge or a Foraminifer of
the Rotaline type should originate from it. If one could only secure
a succession of deep-sea limestones with Foraminifers, extending all
the way from the Laurentian to the present time, I can imagine nothing
more interesting than to compare the whole series, with the view of
ascertaining the limits of descent with variation, and the points where
new forms are introduced. We have not yet such a series, but it may be
obtained; and as Foraminifera are eminently cosmopolitan, occurring
over vastly wide areas of sea-bottom, and are very variable, they would
afford a better test of theories of derivation than any that can be
obtained from the more locally distributed and less variable animals
of higher grade. I was much struck with this recently, in examining a
series of Foraminifera from the Cretaceous of Manitoba, and comparing
them with the varietal forms of the same species in the interior of
Nebraska, 500 miles to the south, and with those of the English chalk
and of the modern seas. In all these different times and places we had
the same species. In all they existed under so many varietal forms
passing into each other, that in former times every species had been
multiplied into several. Yet in all, the identical varietal forms
were repeated with the most minute markings alike. Here were at once
constancy the most remarkable and variations the most extensive. If we
dwell on the one to the exclusion of the other, we reach only one-sided
conclusions, imperfect and unsatisfactory. By taking both in connection
we can alone realize the full significance of the facts. We cannot
yet obtain such series for all geological time; but it may even now
be worth while to inquire, What do we know as to any modification in
the case of the primeval Foraminifers, whether with reference to the
derivation from them of other Protozoa or of higher forms of life?
There is no link whatever in geological fact to connect Eozoon with any
of the Mollusks, Radiates, or Crustaceans of the succeeding Primordial.
What may be discovered in the future we cannot conjecture; but at
present these stand before us as distinct creations. It would of course
be more probable that Eozoon should be the ancestor of some of the
Foraminifera of the Primordial age, but strangely enough it is very
dissimilar from all these except Stromatopora; and here, as already
stated, the evidence of minute structure fails to a great extent, and
Eozoon Bavaricum of the Huronian age scarcely helps to bridge over the
gap which yawns in our imperfect geological record. Of actual facts,
therefore, we have none; and those evolutionists who have regarded the
dawn-animal as an evidence in their favour, have been obliged to have
recourse to supposition and assumption.
Taking the ground of the derivationist, it is convenient to assume
(1) that Eozoon was either the first or nearly the first of animals,
and that, being a Protozoan of simple structure, it constitutes an
appropriate beginning of life; (2) that it originated from some
unexplained change in the protoplasmic or albuminous matter of some
humble plant, or directly from inorganic matter, or at least was
descended from some creature only a little more simple which had
being in this way; (3) that it had in itself unlimited capacities
for variation and also for extension in time; (4) that it tended to
multiply rapidly, and at last so to occupy the ocean that a struggle
for existence arose; (5) that though at first, from the very nature
of its origin, adapted to the conditions of the world, yet as these
conditions became altered by physical changes, it was induced to
accommodate itself to them, and so to pass into new species and genera,
until at last it appeared in entirely new types in the Primordial fauna.
These assumptions are, with the exception of the first two, merely
the application to Eozoon of what have been called the Darwinian laws
of multiplication, of limited population, of variation, of change of
physical conditions, and of equilibrium of nature. If otherwise proved,
and shown to be applicable to creatures like Eozoon, of course we must
apply them to it; but in so far as that creature itself is concerned
they are incapable of proof, and some of them contrary to such evidence
as we have. We have, for example, no connecting link between Eozoon and
any form of vegetable life. Its structures are such as to enable us at
once to assign it to the animal kingdom, and if we seek for connecting
links between the lower animals and plants we have to look for them
in the modern waters. We have no reason to conclude that Eozoon could
multiply so rapidly as to fill all the stations suitable for it, and to
commence a struggle for existence. On the contrary, after the lapse of
untold ages the conditions for the life of Foraminifers still exist
over two-thirds of the surface of the earth. In regard to variation, we
have, it is true, evidence of the wide range of varieties of species
in Protozoa, within the limits of the group, but none whatever of any
tendency to pass into other groups. Nor can it be proved that the
conditions of the ocean were so different in Cambrian or Silurian times
as to preclude the continued and comfortable existence of Eozoon.
New creatures came in which superseded it, and new conditions more
favourable in proportion to these new creatures, but neither the new
creatures nor the new conditions were necessarily or probably connected
with Eozoon, any farther than that it may have served newer tribes of
animals for food, and may have rid the sea of some of its superfluous
lime in their interest. In short, the hypothesis of evolution will
explain the derivation of other animals from Eozoon if we adopt its
assumptions, just as it will in that case explain anything else, but
the assumptions are improbable, and contrary to such facts as we know.
Eozoon itself, however, bears some negative though damaging testimony
against evolution, and its argument may be thus stated in what we may
imagine to be its own expressions:--"I, Eozoon Canadense, being a
creature of low organization and intelligence, and of practical turn,
am no theorist, but have a lively appreciation of such facts as I am
able to perceive. I found myself growing upon the sea-bottom, and know
not whence I came. I grew and flourished for ages, and found no let or
hindrance to my expansion, and abundance of food was always floated
to me without my having to go in search of it. At length a change
came. Certain creatures with hard snouts and jaws began to prey on
me. Whence they came I know not; I cannot think that they came from
the germs which I had dispersed so abundantly throughout the ocean.
Unfortunately, just at the same time lime became a little less abundant
in the waters, perhaps because of the great demands I myself had made,
and thus it was not so easy as before to produce a thick supplemental
skeleton for defence. So I had to give way. I have done my best to
avoid extinction; but it is clear that I must at length be overcome,
and must either disappear or subside into a humbler condition, and that
other creatures better provided for the new conditions of the world
must take my place." In such terms we may suppose that this patriarch
of the seas might tell his history, and mourn his destiny, though he
might also congratulate himself on having in an honest way done his
duty and fulfilled his function in the world, leaving it to other and
perhaps wiser creatures to dispute as to his origin and fate, while
much less perfectly fulfilling the ends of their own existence.
Thus our dawn-animal has positively no story to tell as to his own
introduction or his transmutation into other forms of existence.
He leaves the mystery of creation where it was; but in connection
with the subsequent history of life we can learn from him a little
as to the laws which have governed the succession of animals in
geological time. First, we may learn that the plan of creation has been
progressive, that there has been an advance from the few, low, and
generalized types of the primæval ocean to the more numerous, higher,
and more specialized types of more recent times. Secondly, we learn
that the lower types, when first introduced, and before they were
subordinated to higher forms of life, existed in some of their grandest
modifications as to form and complexity, and that in succeeding ages,
when higher types were replacing them, they were subjected to decay and
degeneracy. Thirdly, we learn that while the species has a limited term
of existence in geological time, any grand type of animal existence,
like that of the Foraminifera or Sponges, for example, once introduced,
continues and finds throughout all the vicissitudes of the earth some
appropriate residence. Fourthly, as to the mode of introduction of new
types, or whether such creatures as Eozoon had any direct connection
with the subsequent introduction of mollusks, worms, or crustaceans, it
is altogether silent, nor can it predict anything as to the order or
manner of their introduction.
Had we been permitted to visit the Laurentian seas, and to study Eozoon
and its contemporary Protozoa when alive, it is plain that we could not
have foreseen or predicted from the consideration of such organisms
the future development of life. No amount of study of the prototypal
Foraminifer could have led us distinctly to the conception of even
a Sponge or a Polyp, much less of any of the higher animals. Why is
this? The answer is that the improvement into such higher types does
not take place by any change of the elementary sarcode, either in those
chemical, mechanical, or vital properties which we can study, but in
the adding to it of new structures. In the Sponge, which is perhaps
the nearest type of all, we have the movable pulsating cilium and true
animal cellular tissue, and along with this the spicular or fibrous
skeleton, these structures leading to an entire change in the mode of
life and subsistence. In the higher types of animals it is the same.
Even in the highest we have white blood-corpuscles and germinal matter,
which, in so far as we know, carry on no higher forms of life than
those of an Amœba; but they are now made subordinate to other kinds of
tissue, of great variety and complexity, which never have been observed
to arise out of the growth of any Protozoon. There would be only a very
few conceivable inferences which the highest finite intelligence could
deduce as to the development of future and higher animals. He might
infer that the foraminiferal sarcode, once introduced, might be the
substratum or foundation of other but unknown tissues in the higher
animals, and that the Protozoan type might continue to subsist side
by side with higher forms of living things as they were successively
introduced. He might also infer that the elevation of the animal
kingdom would take place with reference to those new properties of
sensation and voluntary motion in which the humblest animals diverge
from the life of the plant.
It is important that these points should be clearly before our minds,
because there has been current of late among naturalists a loose way
of writing with reference to them, which seems to have imposed on many
who are not naturalists. It has been said, for example, that such an
organism as Eozoon may include potentially all the structures and
functions of the higher animals, and that it is possible that we might
be able to infer or calculate all these with as much certainty as we
can calculate an eclipse or any other physical phenomenon. Now, there
is not only no foundation in fact for these assertions, but it is from
our present standpoint not conceivable that they can ever be realized.
The laws of inorganic matter give no data whence any _à priori_
deductions or calculations could be made as to the structure and
vital forces of the plant. The plant gives no data from which we can
calculate the functions of the animal. The Protozoon gives no data from
which we can calculate the specialties of the Mollusc, the Articulate,
or the Vertebrate. Nor unhappily do the present conditions of life of
themselves give us any sure grounds for predicting the new creations
that may be in store for our old planet. Those who think to build a
philosophy and even a religion on such data are mere dreamers, and have
no scientific basis for their dogmas. They are more blind guides than
our primæval Protozoon himself would be, in matters whose real solution
lies in the harmony of our own higher and immaterial nature with the
Being who is the author of all life--the Father "from whom every
family in heaven and earth is named."
While this work was going through the press, Lyell, the greatest
geological thinker of our time, passed away. In the preceding pages I
have refrained from quoting the many able geologists and biologists who
have publicly accepted the evidence of the animal nature of Eozoon as
sufficient, preferring to rest my case on its own merits rather than on
authority; but it is due to the great man whose loss we now mourn, to
say that, before the discovery of Eozoon, he had expressed on general
grounds his anticipation that fossils would be found in the rocks older
than the so-called Primordial Series, and that he at once admitted the
organic nature of Eozoon, and introduced it, as a fossil, into the
edition of his Elements of Geology published in the same year in which
it was described.
APPENDIX.
CHARACTERS OF LAURENTIAN AND HURONIAN PROTOZOA.
It may be useful to students to state the technical characters of
Eozoon, in addition to the more popular and general descriptions in the
preceding pages.
_Genus_ EOZOON.
Foraminiferal skeletons, with irregular and often confluent cells,
arranged in concentric and horizontal laminæ, or sometimes piled in an
acervuline manner. Septal orifices irregularly disposed. Proper wall
finely tubulated. Intermediate skeleton with branching canals.
Eozoon Canadense, _Dawson_.
In rounded masses or thick encrusting sheets, frequently of large
dimensions. Typical structure stromatoporoid, or with concentric
calcareous walls, frequently uniting with each other, and separating
flat chambers, more or less mammillated, and spreading into horizontal
lobes and small chamberlets; chambers often confluent and crossed by
irregular calcareous pillars connecting the opposite walls. Upper
part often composed of acervuline chambers of rounded forms. Proper
wall tubulated very finely. Intermediate skeleton largely developed,
especially at the lower part, and traversed by large canals, often
with smaller canals in their interstices. Lower laminæ and chambers
often three millimetres in thickness. Upper laminæ and chambers one
millimetre or less. Age Laurentian and perhaps Huronian.
_Var._ MINOR.--Supplemental skeleton wanting, except near the base, and
with very fine canals. Laminæ of sarcode much mammillated, thin, and
separated by very thin walls. Probably a depauperated variety.
_Var._ ACERVULINA.--In oval or rounded masses, wholly acervuline. Cells
rounded; intermediate skeleton absent or much reduced; cell-walls
tubulated. This may be a distinct species, but it closely resembles the
acervuline parts of the ordinary form.
Eozoon Bavaricum, _Gümbel_.
Composed of small acervuline chambers, separated by contorted walls,
and associated with broad plate-like chambers below. Large canals
in the thicker parts of the intermediate skeleton. Differs from _E.
Canadense_ in its smaller and more contorted chambers. Age probably
Huronian.
_Genus_ ARCHÆOSPHERINA.
A provisional genus, to include rounded solitary chambers, or
globigerine assemblages of such chambers, with the cell-wall
surrounding them tubulated as in Eozoon. They may be distinct
organisms, or gemmæ or detached fragments of Eozoon. Some of them
much resemble the bodies figured by Dr. Carpenter, as gemmæ or ova
and primitive chambers of Orbitolites. They are very abundant on some
of the strata surfaces of the limestone at Côte St. Pierre. Age Lower
Laurentian.
SYSTEMATIC POSITION OF EOZOON.
The unsettled condition of the classification of the Protozoa, and our
absolute ignorance of the animal matter of Eozoon, render it difficult
to make any statement on this subject more definite than the somewhat
vague intimations given in the text. My own views at present, based on
the study of recent and fossil forms, and of the writings of Carpenter,
Max Schultze, Carter, Wallich, Haeckel, and Clarepede, may be stated,
though with some diffidence, as follows:--
I. The class _Rhizopoda_ includes all the sarcodous animals whose only
external organs are pseudopodia, and is the lowest class in the animal
kingdom. Immediately above it are the classes of the Sponges and of the
flagellate and ciliate Infusoria, which rise from it like two diverging
branches.
II. The group of Rhizopods, as thus defined, includes three leading
_orders_, which, in descending grade, are as follows:--
(_a_) _Lobosa_, or Amœboid Rhizopods, including those with
distinct nucleus and pulsating vesicle, and thick lobulate
pseudopodia--naked, or in membranous coverings.
(_b_) _Radiolaria_, or Polycistius and their allies, including
those with thread-like pseudopodia, with or without a
nucleus, and with the skeleton, when present, silicious.
(_c_) _Reticularia_, or Foraminifera and their allies, including
those with thread-like and reticulating pseudopodia, with
granular matter instead of a nucleus, and with calcareous,
membranous, or arenaceous skeletons.
The place of _Eozoon_ will be in the lowest order, _Reticularia_.
III. The order _Reticularia_ may be farther divided into two
_sub-orders_, as follows:--
(_a_) _Perforata_--having calcareous skeletons penetrated with
pores.
(_b_) _Imperforata_--having calcareous, membranous, or arenaceous
skeletons, without pores.
The place of Eozoon will be in the higher sub-order, _Perforata_.
IV. The sub-order _Perforata_ includes three _families_--the
_Nummulinidæ_, _Globigerinidæ_, and _Lagemdæ_. Of these Carpenter
regards the Nummulinidæ as the highest in rank.
The place of Eozoon will be in the family _Nummulinidæ_, or between
this and the next family. This oldest known Protozoon would thus belong
to the highest family in the highest sub-order of the lowest class of
animals.
THE LATE SIR WILLIAM E. LOGAN.
When writing the dedication of this work, I little thought that the
eminent geologist and valued friend to whom it gave me so much pleasure
to tender this tribute of respect, would have passed away before its
publication. But so it is, and we have now to mourn, not only Lyell,
who so frankly accepted the evidence in favour of Eozoon, but Logan,
who so boldly from the first maintained its true nature as a fossil.
This boldness on his part is the more remarkable and impressive, from
the extreme caution by which he was characterized, and which induced
him to take the most scrupulous pains to verify every new fact before
committing himself to it. Though Sir William's early work in the Welsh
coal-fields, his organization and management of the Survey of Canada,
and his reducing to order for the first time all the widely extended
Palæozoic formations of that great country, must always constitute
leading elements in his reputation, I think that in nothing does he
deserve greater credit than in the skill and genius with which he
attacked the difficult problem of the Laurentian rocks, unravelled
their intricacies, and ascertained their true nature as sediments, and
the leading facts of their arrangement and distribution. The discovery
of Eozoon was one of the results of this great work; and it was the
firm conviction to which Sir William had attained of the sedimentary
character of the rocks, which rendered his mind open to the evidence of
these contained fossils, and induced him even to expect the discovery
of them.
This would not be the proper place to dwell on the general character
and work of Sir William Logan, but I cannot close without referring to
his untiring industry, his enthusiasm in the investigation of nature,
his cheerful and single-hearted disposition, his earnest public spirit
and patriotism--qualities which won for him the regard even of those
who could little appreciate the details of his work, and which did much
to enable him to attain to the success which he achieved.
INDEX.
Acervuline explained, 66.
Acervuline Variety of Eozoon, 135.
Aggregative Growth of Animals, 213.
Aker Limestone, 197.
Amity Limestone, 197.
Amœba described, 59.
Annelid Burrows, 133, 139.
Archæospherinæ, 137, 148.
Archæocyathus, 151.
Arisaig, Supposed Eozoon of, 140.
Bathybius, 65.
Bavaria, Eozoon of, 148.
Beginning of Life, 215.
Billings, Mr.,--referred to, 41;
on Archæocyathus, 151;
on Receptaculites, 163.
Calumet, Eozoon of, 38.
Calcarina, 74.
Calcite filling Tubes of Eozoon, 98.
Canal System of Eozoon, 40, 66, 107, 176, 181.
Carpenter--referred to, 41;
on Eozoon, 82;
Reply to Carter, 204.
Caunopora, 158.
Chrysotile Veins, 107, 180.
Chemistry of Eozoon, 199.
Coccoliths, 70.
Cœnostroma, 158.
Contemporaries of Eozoon, 127.
Côte St. Pierre, 20.
Derivation applied to Eozoon, 225.
Discovery of Eozoon, 35.
Eozoic Time, 7.
Eozoon,--Discovery of, 35;
Structure of, 65;
Growth of, 70;
Fragments of, 74;
Description of, 65, 77 (also Appendix);
Note on by Dr. Carpenter, 82;
Thickened Walls of, 66;
Preservation of, 100;
Pores filled with Calcite, 97, 109;
with Pyroxene, 108;
with Serpentine, 101;
with Dolomite, 109;
in Limestone, 110;
Defective Specimens of, 113;
how Mineralized, 102, 116;
its Contemporaries, 127;
Acervuline Variety of, 135;
Variety _Minor_ of, 135;
Acadianum, 140;
Bavaricum, 148;
Localities of, 166;
Harmony of with other Fossils, 171;
Summary of evidence relating to, 176.
Faulted Eozoon, 182.
Foraminifera, Notice of, 61.
Fossils, how Mineralized, 93.
Fusulina, 74.
Glauconite, 100, 125, 220.
Graphite of Laurentian, 18, 27.
Green-sand, 99.
Grenville, Eozoon of, 38.
Gümbel on Laurentian Fossils, 124;
on Eozoon Bavaricum, 141.
Hastings, Rocks of, 57.
History of Discovery of Eozoon, 35.
Honeyman, Dr., referred to, 140.
Hunt, Dr. Sterry, referred to, 35;
on Mineralization of Eozoon, 115;
on Silurian Fossils infiltrated with Silicates, 121;
on Minerals of the Laurentian, 123;
on Laurentian Life, 27;
his Reply to Objections, 199.
Huronian Rocks, 9.
Intermediate Skeleton, 64.
Iron Ores of Laurentian, 19.
Jones, Prof. T. Rupert, on Eozoon, 42.
King, Prof., his Objections, 184.
Labrador Feldspar, 13.
Laurentian Rocks, 7;
Fossils of, 130;
Graphite of, 18, 27;
Iron Ores of, 19;
Limestones of, 17.
Limestones, Laurentian, 17;
Silurian, 98.
Localities of Eozoon, 166.
Loftusia, 164.
Logan, Sir Wm., referred to, 36;
on Laurentian, 24;
on Nature of Eozoon, 37;
Geological Relations of Eozoon, 48;
on Additional Specimens of Eozoon, 52.
Loganite in Eozoon, 36, 102.
Lowe, Mr., referred to, 38.
Long Lake, Specimens from, 91.
Lyell, Sir C., on Eozoon, 234.
Madoc, Specimens from, 132.
Maps of Laurentian, 7, 16.
MacMullen, Mr., referred to, 37.
Metamorphism of Rocks, 13, 34.
Mineralization of Eozoon, 101;
of Fossils, 93;
Hunt on, 115.
Nicholson on Stromatopora, 165.
Nummulites, 73.
Nummuline Wall, 43, 65, 106, 176, 181.
Objections answered, 169, 188.
Parkeria, 164.
Petite Nation, 20, 43.
Pole Hill, Specimens from, 121.
Proper Wall, 43, 65, 106, 176, 181.
Preservation of Eozoon, 93.
Protozoa, their Nature, 59, 207.
Pseudomorphism, 200.
Pyroxene filling Eozoon, 108.
Red Clay of Pacific, 222.
Red Chalk, 222.
Reply to Objections, 167, 188.
Receptaculites, 162.
Robb, Mr., referred to, 120.
Rowney, Prof., Objections of, 184.
Serpentine mineralizing Eozoon, 102.
Silicates mineralizing Fossils, 100, 103, 121, 220.
Silurian Fossils infiltrated with Silicates, 121.
Steinhag, Eozoon of, 146.
Stromatopora, 37, 156.
Stromatoporidæ, 165.
Supplemental Skeleton, 64.
Table of Formations, 6.
Trinity Cape, 10.
Tubuli Explained, 66, 106.
Varieties of Eozoon, 135, 236.
Vennor, Mr., referred to, 46, 57.
Wentworth Specimens, 91.
Weston, Mr., referred to, 20, 40, 162.
Wilson, Dr., referred to, 36.
Worm-burrows in the Laurentian, 133, 139.
Butler & Tanner. The Selwood Printing Works. Frome, and London.
* * * * *
Transcriber Notes
The label Plate II was added to the illustration's page. The "NOTES"
sections were standardized to say "NOTES TO CHAPTER ..." and the
sections labeled as (A.), (B.), etc.
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