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Title: The Chain of Life in Geological Time - A Sketch of the Origin and Succession of Animals and Plants
Author: Dawson, Sir J. William
Language: English
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[Illustration: LIFE IN THE SILURIAN AGE.]
THE CHAIN OF LIFE
IN
GEOLOGICAL TIME
_A SKETCH OF THE ORIGIN AND SUCCESSION OF
ANIMALS AND PLANTS_
BY
SIR J. WILLIAM DAWSON
C.M.G., LL.D., F.R.S., F.G.S., ETC.
AUTHOR OF
“ACADIAN GEOLOGY,” “THE STORY OF THE EARTH,” “EGYPT AND SYRIA; THEIR
PHYSICAL FEATURES IN RELATION TO BIBLE HISTORY,” ETC.
_THIRD AND REVISED EDITION_
WITH NUMEROUS ILLUSTRATIONS
THE RELIGIOUS TRACT SOCIETY,
56 PATERNOSTER ROW; 65 ST. PAUL’S CHURCHYARD;
AND 164 PICCADILLY
1888
RICHARD CLAY AND SONS.
LONDON AND BUNGAY.
PREFACE.
Questions as to the origin and history of life are not at the present
time answered by mere philosophical speculation and poetical imagining.
Such solutions of these questions as science can profess to have
obtained are based on vast accumulations of facts respecting the remains
of animals and plants preserved in the rocky beds of the earth’s crust,
which have been successively accumulated in the course of its long
geological history. These facts undoubtedly afford the means of
attaining to very certain conclusions on many points relating to the
history of life on the earth. But, on the other hand, they have
furnished the material for hypotheses which, though confidently affirmed
to be indisputable, have no real foundation in nature, and are
indirectly subversive of some of the most sacred beliefs of mankind.
In these circumstances it is most desirable that those who are not
specialists in such matters should be in a position to judge for
themselves; and it does not appear impossible in the actual state of
knowledge, to present, in terms intelligible to the general reader, such
a view of the ascertained sequence of the forms of life as may serve at
once to give exalted and elevating views of the great plan of creation,
and to prevent the deceptions of pseudo-scientists from doing their evil
work. Difficulties, no doubt, attend the attempt. They arise from the
number and variety of the facts, from the uncertainties attending many
important points, from the new views constantly opening up in the
progress of discovery, and from the difficulty of presenting in an
intelligible form the preliminary data in biology and geology necessary
for the understanding of the questions in hand. In order, as far as
possible, to obviate these difficulties, the plan adopted in this work
has been to note the first known appearance of each leading type of
life, and to follow its progress down to the present time or until it
became extinct. This method is at least natural and historical, and has
commended itself to the writer as giving a very clear comprehension of
the actual state of our knowledge, and as presenting some aspects of the
subject which may be novel and suggestive even to those who have studied
it most deeply.
In selecting examples and illustrations, the writer has endeavoured to
avoid, as far as possible, those already familiar to the general reader.
He has carefully sought for the latest facts, while rejecting as
unproved many things that are confidently asserted; and has endeavoured
to avoid all that is irrelevant to the subject in hand, and to abstain
from all technical terms not absolutely essential. In a work at once so
wide in its scope, so popular in its character, and so limited in its
dimensions, a certain amount of hostile criticism on the part of
specialists is to be expected, some portion of it perhaps just, other
portions arising from narrow prejudices due to limited lines of study.
The writer is willing to receive such comments with attention and
gratitude, but he would deprecate the misuse of them in the interest of
those coteries which are at present engaged in the effort to torture
nature into a confession of belief in the doctrines of a materialistic
or agnostic philosophy.
The title of the work was suggested by that of Gaudry’s recent
attractive book, _Les Enchaînements du Monde animal_. It seemed well
fitted to express the connection and succession of forms of life,
without implying their derivation from one another, while it reminds us
that nature is not a fortuitously tangled skein, and that the links
which connect man himself with the lowest and oldest creatures bind him
also to the throne of the Eternal.
In the few years that have elapsed since the publication of the first
edition of this work, great additions have been made to our knowledge of
fossil animals and plants. Many new species have been described, and
many new facts have been discovered, respecting species previously
known. This rapid progress of discovery has, however, invalidated few of
the statements made in the first edition, and has certainly established
nothing against the general laws of the succession of life as stated in
this work.
Perhaps the most interesting phase of recent discovery is the tracing
back of certain forms of life to earlier periods of the earth’s
geological history. Some of the most recent facts of this kind are the
finding, by M. Charles Brongniart, of a fossil insect, allied to the
_Blattae_ or cockroaches, in the Silurian of Spain, that of true
Scorpions in the Upper Silurian of Sweden by Lindström, and in the Upper
Silurian of Scotland by Peach, who has also described fossil Millipedes
from the Lower Devonian. The tendency of such discoveries is to carry
farther back the origin of highly specialised forms of life, and thus to
render less probable their origin by any process of gradual derivation.
Other discoveries serve to fill up blanks in our knowledge, and thus to
render the geological record less imperfect. Of this kind is the close
approximation now worked out in Western America between the end of the
reign of the great Mesozoïc reptiles and the beginning of that of the
mammals of the Tertiary—a great and abrupt revolution, effected
apparently by a _coup de main_. I have myself had opportunity to show
that a similarly sharp line separates that quaint old Mesozoïc flora of
pines, cycads and ferns, which extends upward into the Lower Cretaceous,
from the rich and luxuriant assemblage of broad-leaved trees of modern
aspect, which takes its place in the middle part of the same formation.
It is not too much to say that these and similar discoveries, while they
serve to bridge over gaps in the succession of organic beings, do not
favour the theory of slow modification of types. They rather point to a
law of rapid development of new forms under special conditions as yet
unknown to science, and this accompanied with the extinction of older
species. Recent discoveries also present many remarkable instances of
the early introduction of highly specialised types, of higher forms
preceding those that are lower in the same class, and of the persistence
of certain types throughout geological time without any important
change.
J. W. D.
MCGILL COLLEGE.
CONTENTS.
CHAP. PAGE
I. PRELIMINARY CONSIDERATIONS AS TO THE EXTENT AND
SOURCES OF OUR KNOWLEDGE 1
II. THE BEGINNING OF LIFE ON THE EARTH 21
III. THE AGE OF INVERTEBRATES OF THE SEA 45
IV. THE ORIGIN OF PLANT LIFE ON THE LAND 89
V. THE APPEARANCE OF VERTEBRATE ANIMALS 117
VI. THE FIRST AIR-BREATHERS 137
VII. THE EMPIRE OF THE GREAT REPTILES 165
VIII. THE FIRST FORESTS OF MODERN TYPE 185
IX. THE REIGN OF MAMMALS 207
X. THE ADVENT OF MAN 233
XI. REVIEW OF THE HISTORY OF LIFE 253
LIST OF ILLUSTRATIONS.
FRONTISPIECE.—Life in the Silurian Age _To face Title._
FIG. PAGE
1. Bank of stream or coast, showing stratification 4
2. Section at Niagara Falls 4
3. Section obtained by boring, near Goderich, Ontario 5
4. Inclined beds, holding fossil plants 6
5. Ideal section of the Apalachian Mountains 7
6. Generalised section across England from Menai Straits to
the Valley of the Thames 9
7. Generalised section from the Laurentian of Canada to the
coal-field of Michigan 9
8. Unconformable superposition of Devonian Conglomerate on
Silurian slates, at St. Abb’s Head, Berwickshire 10
9. Section of Trenton limestone, Montreal 14
10. Diagram showing different state of fossilisation of a
cell of a Tabulate Coral 15
11. Cast of erect tree (_Sigillaria_) in Sandstone 16
12. _Protichnites septem-notatus_ 17
12_a_. Footprints of modern _Limulus_, or king-crab 18
13. Current markings on shale, resembling a fossil plant 18
_Frontispiece._ Magnified and restored section of a portion
of _Eozoon canadense_ 20
14. Ideal section, showing the relations of the Laurentian and
Huronian 24
15. Small weathered specimen of _Eozoon_ 28
16. Nature-printed specimen of _Eozoon_ slightly etched with acid 29
17. Magnified group of canals in supplemental skeleton of
_Eozoon_ 31
18. Portion of _Eozoon_ magnified 100 diameters 31
19. Magnified portion of shell of _Calcarina_ 32
20. _Amœba_, a fresh-water naked Rhizopod; and _Actinophrys_,
a fresh-water Protozoon 34
21. _Nonionina_, a modern marine Foraminifer 34
22. _Stromatopora concentrica_ 35
23. _Caunopora planulata_ 36
24. _Archæocyathus minganensis_. A Primordial Protozoon 37
25. Receptaculites. Restored 38
26. Section of _Loftusia Persica_. An Eocene Foraminifer 39
27. Foraminiferal Rock Builders, in the Cretaceous and Eocene 41
_Frontispiece._ _Paradoxides Regina_ (Matthew) 44
28. Group of Cambrian Animals 46
29. Portion of skeleton of Hexactinellid Sponge (_Cœloptychium_) 49
30. _Protospongia fenestrata_ (Salter) 50
31. _Astylospongia præmorsa_ (Roemer) 51
32. Spicules of Lithistid Sponge (_Trichospongia_, Billings) 51
33. _Oldhamia antiqua_ (Forbes) 52
34. _Dictyonema sociale._ Enlarged 52
35. _Dictyonema Websteri_ (Dn.) 53
36. Group of modern Hydroids allied to Graptolites 54
37. Silurian Graptolitidæ 55
38. Central portion of Graptolite, with membrane, or float
(_Dichograpsus octobrachiatus_, Hall) 55
39. _Ptilodictya acuta_ (Hall). Bryozoan 55
39_a_. _Fenestella Lyelli_ (Dn.). A Carboniferous Bryozoan 56
40. _Chaetetes fibrosa._ A Tabulate Coral with microscopic
cells 56
41. _a_, _Stenopora exilis_ (Dn.). _b_, _Chaetetes tumidus_
(Edwards and Haine) 57
42. Living Anthozoan Coral (_Astræa_) 58
43. Tabulate Corals (_Halisites_ and _Favosites_) 59
44. Rugose Coral (_Heliophyllum Halli_) 59
44_a_. _Zaphrentis prolifica_ (Billings) 60
45. Rugose Corals (_Zaphrentis Minas_, Dn., and _Cyathophyllum_
_Billingsi_, Dn.) 60
46. Modern Crinoid (_Rhizocrinus Lofotensis_) 61
47. _Palæaster Niagarensis_ (Hall) 62
48. _Palæchinus ellipticus_ (McCoy) 62
49. _Pleurocystites squamosus_ 63
50. _Heterocrinus simplex_ (Meek) 63
51. Body of _Glyptocrinus_ 63
52. _Extracrinus Briareus_ 64
53. _Pentacrinus caput-medusæ_ 64
54. _Lingula anatina_ 65
55. Cambrian and Silurian Lingulæ 65
56. _Terebratula sacculus_ (Martin) 66
57. Brachiopods; genus _Orthis_ 66
58. _Rhynchonella increbrescens_ (Hall) 66
59. _Spirifer mucronatus_ (Conrad) 67
59_a_. _Athyris subtilita_ (Hall) 67
60. _Productus cora_ (D’Orbigny) 68
61. Group of Older Palæozoic Lamellibranchs 69
62. _Conularia planicostata_ (Dn.). A Carboniferous Pteropod 70
63. Silurian Sea-snails 70
64. Squid (_Loligo_) 72
65. Pearly Nautilus (_Nautilus pompilius_) 72
66. _Orthoceras_ 73
67. _Gomphoceras_ 73
68. _Lituites_ 73
69. _Nautilus Avonensis_ (Dn.) 74
70. _Goniatites crenistria_ (Philips) 74
71. _Ceratites nodosus_ (Schloth) 75
72. _Ammonites Jason_ (Reinecke) 76
72_a_. Suture of _Ammonites componens_ (Meek) 76
73. Cretaceous Ammonitidæ 77
74. _Belemnite_ 78
74_a_. _Belemnoteuthis antiquus_ 78
75. Cambrian Trilobites 79
76. Transverse section of _Calymene_. A Silurian Trilobite 80
76_a_. Burrows of Trilobite and of modern King-crab 81
77. Silurian Trilobites 82
78. Devonian and Carboniferous Trilobites 83
79. Palæozoic Ostracod Crustaceans 83
80. _Pterygotus anglicus_ 84
81. _Amphipeltis paradoxus_ (Salter) 85
82. _Anthropalæmon Hilliana_ (Dn.) 85
_Frontispiece._ _Cordaites_, of the group of _Dory-Cordaites_ 88
83. _Protannularia Harknessii_ (Nicholson) 91
84. American Lower Silurian Plants 92
86. Fragment of outer surface of _Glyptodendron_ of Claypole 93
87. _Psilophyton princeps_ (Dn.) 95
88. Trunk of a Devonian Tree-fern (_Caulopteris Lockwoodi_, Dn.) 97
89. Frond of _Archæopteris Jacksoni_ (Dn.) 98
90. Portion of a branch of _Leptophleum rhombicum_ (Dn.) 98
91. _Calamites radiatus_ (Brongniart) 99
92. A Devonian Taxine Conifer (_Dadoxylon ouangondianum_, Dn.) 100
93. Group of Devonian fruits, &c. 101
94. Structures of the oldest-known Angiospermous Exogen
(_Syringoxylon mirabile_, Dn.) 102
95. _Asterophyllites parvula_ (Dn.) and _Sphenophyllum
antiquum_ (Dn.) 103
96. _Calamites_ 104
97. Carboniferous Ferns 105
98. Carboniferous Tree-ferns 107
99. _Lepidodendron corrugatum_ (Dn.) 108
100. _Sigillariæ_ of the Carboniferous 109
101. _Trigonocarpum Hookeri_ (Dn.) 111
_Frontispiece._ Pteraspis. Restored 116
102. Siluro-Cambrian Conodonts 118
103. Lower Carboniferous Conodont 119
104. _a_, Head-shield of an Upper Silurian Fish (_Cyathaspis_);
_b_, Spine of a Silurian Shark (_Onchus tenui-striatus_,
Agass.); _c_, _d_, Scales of _Thecodus_ 121
105. _Cephalaspis Dawsoni_ (Lankester) 122
106. Devonian Placoganoid Fishes (_Pterichthys cornutus_,
_Cephalaspis Lyelli_) 123
107. Devonian Lepidoganoid Fishes (_Diplacanthus_ and
_Osteolepis_) 124
108. Modern Dipnoi (_Ceratodus Fosteri_ and _Lepidosiren
annectus_) 124
109. Anterior part of the palate of _Dipterus_ 125
110. Dental plate of _Conchodus plicatus_ (Dn.) 126
111. Dental plate of _Ceratodus Barrandii_ 126
112. Dental plate of _Ceratodus serratus_ 127
113. Jaws of _Dinichthys Hertzeri_ (Newberry) 127
114. Lower Jaw of _Dinichthys Hertzeri_ 128
115. Jaws of _Lepidosiren_ 128
116. A small Carboniferous Ganoid (_Palæoniscus_
(_Rhadinichthys_) _Modulus_, Dn.) 129
117. Teeth and Spines of Carboniferous Sharks 130
118. Teeth of Cretaceous Sharks (_Otodus_ and _Ptychodus_) 131
119. Tooth of a Tertiary Shark (_Carcharodon_) 132
120. A Liassic Ganoid (_Dapedius_) 132
121. Cretaceous Fishes of the modern or Teleostian type
(_Beryx Lewesiensis_ and _Portheus molossus_, Cope) 133
122. Modern Ganoids (_Polypterus_ and _Lepidosteus_) 134
_Frontispiece._ A Microsaurian of the Carboniferous Period
(_Hylonomus Lyelli_) 136
123. Wings of Devonian Insects 140
124. Land-snail (_Pupa vetusta_, Dn.) 143
125. Land-snail (_Zonites_ (_Conulus_) _priscus_, Carpenter) 143
126. Millipedes (_Xylobius sigillariæ_, Dn.; _Archiulus
Xylobioides_, Scudder; _X. farctus_, Scudder) 145
127. Wings of Cockroaches 146
128. Wing of May-fly (_Haplophlebium Barnesii_, Scudder) 147
129. A Jurassic Sphinx-moth (_Sphinx Snelleri_, Weyenburgh) 148
130. An Eocene Butterfly (_Prodryas persephone_, Scudder) 149
131. Abdominal part of a Carboniferous Scorpion 150
132. Carboniferous Scorpion (_Eoscorpius carbonarius_,
Meek and Worthen) 151
133. Footprints of one of the oldest known Batrachians,
probably a species of _Dendrerpeton_ 152
134. _Archegosaurus Decheni_ 154
135. _Ptyonius_ 154
136. A large Carboniferous Labyrinthodont (_Baphetes
planiceps_, Owen) 155
137. _Baphetes planiceps_ (Owen) 156
138. A lizard-like Amphibian (_Hylonomus aciedentatus_) 157
139. _Stelliosaurus longicostatus_ (Fritsch) 158
140. Section showing the position of an erect _Sigillaria_,
containing remains of land animals 160
140_a_. Section of base of erect _Sigillaria_, containing
remains of land animals 161
_Frontispiece._ Inhabitants of the English Seas in the Age of
Reptiles 164
141. Arm of _Proterosaurus Speneri_ 166
142. Skeleton of _Ichthyosaurus_ 167
142_a_. Head of _Pliosaurus_ 168
142_b_. Paddle of _Plesiosaurus Oxoniensis_ 168
143. Skeleton of _Clidastes_ 170
144. An Anomodont Reptile of the Trias (_Dicynodon
lacerticeps_, Owen) 170
145. A Theriodont Reptile of the Trias (_Lycosaurus_) 170
146. Skeleton of _Pterodochylus crassirostris_ 170
147. Restoration of _Rhamphorhyncus Bucklandi_ 171
148. A Jurassic bird (_Archæopteryx macroura_) 172
149. Jaw of a Cretaceous Toothed Bird (_Ichthyornis dispar_) 173
150. Jaw of _Bathygnathus borealis_ (Leidy) 174
151. _Hadrosaurus Foulkii_ (Cope) 175
152. Jaws of _Megalosaurus_ 176
153. Tooth of _Megalosaurus_ 177
154. _Compsognathus_ 179
_Frontispiece._ Lower Cretaceous Leaves 184
155. _Sassafras cretaceum_ (Newberry) 190
156. _Liriodendron primævum_ (Newberry) 191
157. _Onoclea sensibilis_ 191
158. _Davallia tenuifolia_ 192
159. Eocene Leaves 194
160. An Ancient Clover (_Trifolium palæogæum_, Saporta) 195
161. An Eocene Maple (_Acer sextianus_, Saporta) 195
162. A European _Magnolia_ of the Eocene (_M. dianæ_, Saporta) 195
163. Flower and Leaf of _Bombax sepultiflorum_ 196
164. Branch and Fruit of _Sequoia Couttsiæ_ (Heer) 197
165. _Cinnamomum Scheuchzeri_ (Heer) 198
_Frontispiece._ _Sivatherium giganteum_ 206
166. Jaw of _Dromatherium sylvestre_ (Emmons) 209
167. _Myrmecobius fasciatus_ 209
168. Jaw and Molar of _Phascolotherium Bucklandi_ 210
169. Jaw and Pre-molar of _Plagiaulax Becklesii_ 210
170. Restoration of _Palæotherium magnum_ 211
171. Skull of a Lower Eocene Perissodactyl (_Coryphodon
Hamatus_) 214
172. Fore-foot of _Coryphodon_ 215
173. Skull of Upper Eocene Perissodactyl (_Dinoceras
mirabilis_) 216
174. Fore-foot of _Dinoceras_ 217
175. Skull of Miocene Perissodactyl (_Brontotherium ingens_,
Marsh) 217
176. Series of Equine feet 218
177. Skull of generalised Miocene Ruminant (_Oreodon major_) 221
178. Lower Jaw of _Megatherium_ 222
179. Ungual Phalanx and Claw-core of _Megatherium_ 222
180. Tooth of Eocene Whale (_Zeuglodon cetioides_) 223
181. _Mastodon ohioticus_ 225
182. Head of _Dinotherium giganteum_ 226
183. Wing of Eocene Bat (_Vespertilio aquensis_) 226
184. Skull of a Cymetar-toothed Tiger (_Machairodus
cultridens_) 228
185. Lower Jaw of _Dryopithecus Fontani_ 229
_Frontispiece._ Contemporaries of Post-Glacial Man 232
186. _Elephas primigenius_ 241
187. Tooth of _Elasmotherium_ 242
188. Engis Skull 243
189. Outlines of Three Prehistoric European Skulls compared
with an American Skull 244
190. Flint Implement found in Kent’s Cavern, Torquay 245
191. Bone Harpoon (Palæocosmic) 246
192. Sketch of a Mammoth carved on a portion of a Tusk of the
same Animal 249
Tabular View of Geological Periods and of Life-Epochs.
+--------------------------------------+---------------+--------------+
| GEOLOGICAL PERIODS. | ANIMAL LIFE. | VEGETABLE |
| | | LIFE. |
+--------------------------------------+---------------+--------------+
| | | |
|C {_Post- {Modern. | Age of _Man_ | |
|A N {Tertiary_ or {Post-Glacial. | and _modern | |
|I E {_Quaternary_. | Mammals_. | Age of |
|N o O { | | _Angiosperms_|
|O r Z {_Tertiary_ {Pleistocene or |Age of _Extinct| and _Palms_. |
|Z O { {Glacial. | Mammals_. | |
|O I { {Pliocene. | (Earliest | |
|I C.{ {Miocene. | Placental | |
|C { {Eocene. | Mammals.) | |
| | | |
| ----------------------------+---------------+--------------+
| | | |
| { {Upper, | | |
| M {_Cretaceous_ {Lower, or | | |
| E { {Neocomian. | | |
| S { | Age of | |
| O {_Jurassic_ {Oolite. | _Reptiles_ and| (Earliest |
| Z { {Lias. | _Birds_. |Modern Trees.)|
| O { | | Age of |
| I { | | _Cycads_ and |
| C. { {Upper, | (Earliest | _Pines_. |
| { {Middle, or | Marsupial | |
| {_Triassic_ {Muschelkalk. | Mammals.) | |
| { {Lower | | |
| | | |
| --------------------------------+---------------+--------------+
| | | |
| {Upper, | | |
| {_Permian_ {Middle, or | | |
| { {Magnesian | (Earliest | |
| { { Limestone. | true | |
| { {Lower. | Reptiles.) | |
| { | | |
| { {Upper | | |
| { { Coal-Formation.| | |
| {_Carbon- {Coal-Formation | | |
| { iferous_ {Carboniferous | | |
| { { Limestone. | | |
| { {Lower | | |
| P { { Coal-Formation.| | |
| A { | | |
| L { {Upper. | Age of | Age of |
| Æ {_Devonian_ {Middle. | _Amphibians_ |_Acrogens_ and|
| O { {Lower. | and _Fishes_.|_Gymnosperms_.|
| Z { | | (Earliest |
| O {_Silurian_ {Upper. | |Land Plants.) |
| I { {Lower. | | Age of |
| C. { | | _Algæ_. |
| {_Siluro-Cam- | Age of | |
| { brian_ or {Upper. | _Mollusks_, | |
| {_Ordovician_ {Lower. | _Corals_, and | |
| { | _Crustaceans_.| |
| { {Upper. | | |
| {_Cambrian_ {Middle. | | |
| {Lower | | |
| | | |
| --------------------------------+---------------+--------------+
| | | |
| {_Huronian_ {Upper. | | |
| { {Lower. | | |
| E { | Age of | |
| O { | _Protozoa_. | Indications |
| Z { | (First animal | Plants |
| O { {Upper. | remains.) | not |
| I {_Laurentian_ {Middle, | |determinable. |
| C. {Lower, or | | |
| {Bojian. | | |
| | | |
+--------------------------------------+---------------+--------------+
THE CHAIN OF LIFE.
CHAPTER I.
PRELIMINARY CONSIDERATIONS AS TO THE EXTENT AND SOURCES OF OUR
KNOWLEDGE.
It is of the nature of true science to take nothing on trust or on
authority. Every fact must be established by accurate observation,
experiment, or calculation. Every law and principle must rest on
inductive argument. The apostolic motto, “Prove all things, hold fast
that which is good,” is thoroughly scientific. It is true that the mere
reader of popular science must often be content to take that on
testimony which he cannot personally verify; but it is desirable that
even the most cursory reader should fully comprehend the modes in which
facts are ascertained and the reasons on which conclusions are based.
Failing this, he loses all the benefit of his reading in so far as
training is concerned, and cannot have full assurance of that which he
believes. When, therefore, we speak of life-epochs, or of links in a
chain of living beings, the question is at once raised—What evidence
have we of the succession of such epochs? This question, with some
accessory points, must engage our attention in the present chapter.
Geology as a practical science consists of three leading parts. The
first and most elementary of these is the study of the different kinds
of rocks which enter into the composition of those parts of the earth
which are accessible to us, and which we are in the habit of calling the
crust of the earth. This is the subject of _Lithology_, which is based
on the knowledge of minerals, and has recently become a much more
precise department of science than heretofore, owing to the successful
employment of the microscope in the investigation of the minute
structure and composition of rocks. The second is the study of the
arrangement of the materials of the earth on the large scale, as beds,
veins, and irregular masses; and inasmuch as the greater part of the
rocks known to us in the earth’s crust are arranged in beds or strata,
this department may be named _Stratigraphy_. A more general name
sometimes employed is that of _Petrography_. The third division of
geology relates to the remains of animals and plants buried in the rocks
of the earth, and which have lived at the time when those rocks were in
process of formation. These fossil remains introduce us to the history
of life on the earth, and constitute the subject of _Palæontology_.
It is plain that in considering what may be learned as to epochs in the
history of life we are chiefly concerned with the last of these
divisions. The second may also be important as a means of determining
the relative ages of the fossils. With the first we have comparatively
little to do.
Previous to observation and inquiry, we might suppose that the kinds of
animals and plants which now inhabit the earth are those which have
always peopled it; but a very little study of fossils suffices to
convince us that vast numbers of creatures once inhabitants of this
world have become extinct, and can be known to us only by their remains
buried in the earth. When we place this in connection with
stratigraphical facts, we further find that these extinct species have
succeeded each other at different times, so as to constitute successive
dynasties of life. On the one hand, when we know the successive ages of
fossil forms, these become to us, like medals or coins to the historian,
evidences of periods in the earth’s history. On the other hand, we are
obliged in the first instance to ascertain the ages of the medals
themselves by their position in the successive strata which have been
accumulated on the surface. The series of layers which explorers like
Schliemann find on the site of an ancient city, and which hold the works
of successive peoples who have inhabited the place, thus present on a
small scale a faithful picture of the succession of beds and of forms of
life on the great earth itself.
Our leading criterion for estimating the relative ages of rocks is the
superposition of their beds on each other. The beds of sandstone, shale,
limestone, and other rocks which constitute the earth’s crust have
nearly all been deposited thereon by water, and originally in attitudes
approaching to horizontality. Hence the bed that is the lower is the
older of any two beds. Hence also, when any cutting or section reveals
to us the succession of several beds, we know that fossil remains
contained in the lower beds must be of older date.
We can scarcely walk by the side of a stream which has been cutting into
its banks, or at the foot of a sea-cliff, or through a road-cutting,
without observing illustrations of this. For instance, in the section
represented in Fig. 1, we see at the surface the vegetable soil, below
this layers of gravel and sand, below this a bed of clay, and below this
hard limestone. Of these beds _a_ is the newest, _d_ the oldest; and if,
for example, we should find some marine shells in _d_, some fresh-water
shells in _c_, bones of land animals and flint arrowheads in _b_, and
fragments of modern pottery in _a_, we should be able at once to assign
their relative ages to these fossils, and to form some idea of the
succession of conditions and of life which had occurred in the locality.
On a somewhat larger scale, we have in Fig. 2 a section of the beds cut
through by the great Fall of Niagara. All of these except that marked
_a_ are very ancient marine rocks, holding fossil shells and corals, but
now forming part of the interior of a continent, and cut through by a
fresh-water river.
[Illustration: FIG. 1.—Bank of stream or coast, showing stratification.
_a_, Vegetable soil.
_b_, Gravel and sand.
_c_, Clays.
_d_, Limestone rock, slightly inclined.]
[Illustration: FIG. 2.—Section at Niagara Falls, showing the strata cut
through by the action of the Fall. Thickness of beds about 250 feet.
_a_, Boulder clay and gravel—Post-pliocene.
_b_, Niagara limestone } Upper Silurian, with
_c_, Niagara shale } marine shells and
_d_, Clinton limestone } corals.
_e_, Medina sandstone }]
In deep mines and borings still more profound sections may be laid open,
as in Fig. 3, which represents the sequence of beds ascertained by
boring with the diamond drill in search of rock salt near Goderich in
Canada. Here we have a succession of 1,500 feet of beds, some of which
must have been formed under very peculiar and exceptional conditions.
The beds of rock salt and gypsum must have been formed by the drying up
of sea-water in limited basins. Those of Dolomite imply precipitation
of carbonate of lime and magnesia in the sea-bottom. The marls must have
been formed largely by the driftage of sand and clay, while some of the
limestone was produced by accumulation of corals and shells. Such
deposits must not only have been successive, but must have required a
long time for their formation.
[Illustration: FIG. 3.—Section obtained by boring with the diamond
drill, near Goderich, Ontario, Canada, in the Salina series of the Upper
Silurian. From a memoir by Dr. Hunt in the Report of the Geological
Survey of Canada for 1876-7.
No. 1, Clay, gravel, and boulders—Post-pliocene.
Nos. 2, 4, 7, 9, 13, Dol omite or magnesian limestone, with layers
of marl, limestone, and gypsum.
No. 3, Limestone with corals—_Favosites_, etc.
Nos. 5, 11, 15, 17, Marls with layers of Dolomite and anhydrous
gypsum.
Nos. 6, 8, 10, 12, 14, 16, Rock salt.]
[Illustration: FIG. 4.—Inclined beds, holding fossil plants.
Carboniferous. South Joggins, Nova Scotia.
1. Shale and sandstone. Plants with _Spirorbis_ attached;
rain marks (?).
2. Sandstone and shale, 8 feet. Erect
_Calamites_. } An erect coniferous (?) tree, rooted
3. Gray sandstone, 7 feet. } on the shale, passes up through 15
4. Gray shale, 4 feet. } feet of the sandstones and shale.
5. Gray sandstone, 4 feet.
6. Gray shale, 6 inches. Prostrate and erect trees, with rootlets,
leaves, _Naiadites_, and _Spirorbis_ on the plants.
7. Main coal-seam, 5 feet coal in two beds.
8. Underclay, with rootlets.]
In Fig. 4 we have a bed of coal and its accompaniments. The coal itself
was produced by the slow accumulation of vegetable matter on a
water-soaked soil, and this was buried under successive beds of sand and
clay, now hardened into sandstone and shale, some of the beds holding
trees and reed-like plants, which still stand on the soils on which
they grew, and which must have been buried in sediment deposited in
inundations or after subsidence of the land. In this section we may also
observe that the beds are somewhat inclined; and that this is not their
original position is shown by the posture of the stems of trees, once
erect, but now inclined with the beds. This leads to a consideration
very important with reference to our present subject; namely, that as
our continents are mostly made up of beds deposited under water and
afterwards elevated, these beds have in this process experienced such
disturbances that they rarely retain their horizontal position, but are
tilted at various angles. When we follow such inclined strata over large
areas, we find that they undulate in great waves or folds, forming what
are called anticlinal and synclinal lines, and that the irregularities
of the surface of the land depend to a great extent on these
undulations, along with the projection of hard beds whose edges protrude
at the surface. In point of fact, as shown in Fig. 5, mountain ranges
depend on these crumplings of the earth’s crust; and the primary cause
of these is probably the shrinkage of the mass of the earth owing to
contraction in cooling. When the disturbances of beds are extreme, they
often cause intricacies of structure difficult to unravel; but when of
moderate extent they very much aid us in penetrating below the surface,
for we can often see a great thickness of beds rising one from beneath
another, and can thus know by mere superficial examination the structure
of the earth to a great depth. It thus happens that geologists reckon
the thickness of the stratified deposits of the crust of the earth at
more than 70,000 feet, though they cannot penetrate it perpendicularly
to more than a fraction of that depth. The two sections, Figs. 6 and 7,
showing the sequence of beds in England and in the northern part of
North America, will serve, if studied by the reader, to show how, by
merely travelling over the surface and measuring the upturned edges of
beds, many thousands of feet of deposits may be observed, and their
relative ages distinctly ascertained.
[Illustration: FIG. 5.—Ideal section of the Apalachian Mountains
showing folding of the earth’s crust.
_a_, Anticlinal axes.
_b_, Overturned strata.
_c_, Synclinals.
_d_, Unconformable beds.]
In studying any extensive section of rock we find that its members may
more or less readily be separated into distinct groups. Sometimes these
are distinguished by what is termed unconformability, that is, the lower
series has been disturbed or inclined before the upper has been
deposited upon it. This is seen on a grand scale in the section Fig. 7,
in the case of the Laurentian and Cambrian formations, and on a smaller
scale in Fig. 8 in the unconformable superposition of Devonian
conglomerate on Silurian slates at St. Abb’s Head. In the last section
it is quite evident that the beds of the lower series have been bent
into abrupt folds and worn away to a considerable extent before the
deposition of the overlying series. In such a case we know not merely
that the upper series is newer than the lower, but that some
considerable time must have elapsed after the deposition of the one
before the other was laid down; and we are not surprised to find that
the fossils in the groups thus unconformable to each other are very
different.
But even when the beds are conformable, they can usually be separated
into groups, depending upon differences of mineral character, or changes
which have occurred in the mode of deposition. One group of beds, for
example, may be largely composed of limestone, another of sandstone or
shale. One group may be distinguished by containing some special
mineral, as, for example, rock salt or coal, while others may be
destitute of such special minerals. One group may show by its fossils
that it was deposited in the sea, others may be estuarine or
lacustrine. Thus we obtain the means of dividing the rocks of the earth
into groups of different ages, known as “Formations,” and marking
particular periods of geological time. By tracing these formations from
one district or region to another, we learn the further truth that the
succession is not merely local, but that, though liable to variation in
detail, its larger subdivisions hold so extensively that they may be
regarded as world-wide in their distribution.
[Illustration: FIG. 6. Generalised section across England from Menai
Straits to the Valley of the Thames.—After Ramsay.
0 Huronian? or Laurentian?
1 Cambrian and Lower Silurian.
2 Upper Silurian.
3 Devonian.
6, 7, 8 Trias and lias.
9 and 10 Jurassic.
11 Cretaceous.
12 Eocene.]
[Illustration: FIG. 7.—Generalised section from the Laurentian of
Canada to the coal-field of Michigan.
0 Laurentian (the Huronian is absent in the line of this section).
1 Cambrian.
2 Lower Silurian.
3 Upper Silurian.
4 Devonian.
5 Carboniferous.]
[Illustration: FIG. 8.—Unconformable superposition of Devonian
conglomerate on Silurian slates, at St. Abb’s Head, Berwickshire.—After
Lyell.]
Putting together the facts thus obtained, we can frame a tabular
arrangement of the earth’s strata, as in the table prefixed to this
chapter; and when we add the further discovery, very early made by
geologists, that the successive formations differ from each other in
their fossil remains, we have the means of recognising any particular
formation by its fossils, even when the stratigraphical evidence may be
obscure or wanting. Thus our knowledge of Epochs of Life, and indeed of
the whole geological history of the earth, is based on the superposition
of beds in the earth’s crust, and on the diversity of fossil remains in
the successive beds so superimposed on each other; and it is on these
grounds that we are enabled to construct a Table of Geological
Formations representing the whole series of beds as far as known, with
the characteristic groups of fossils of each period. Here I might close
these preliminary considerations, but there are a few accessory
questions, important to our clear comprehension of the subject, which
may profitably occupy our attention for a short time.
One of these relates to the absolute duration of the time represented by
the geological history of the earth. Such estimates as our present
knowledge enables us to form are very indefinite. Whether we seek for
astronomical or geological data, we find great uncertainty. To such an
extent is this the case, that current estimates of the time necessary to
bring the earth from a state of primitive incandescence to its present
condition have varied from fifteen millions of years to five hundred
millions. Of the various modes proposed, perhaps the most satisfactory
as well as instructive is that based on the rate of denudation of our
present continents, as indicated by the amount of sediment carried down
by great rivers. The Mississippi, draining a vast and varied area in
temperate latitudes, is washing away the American land at the rate of
one foot in 6,000 years. The Ganges, in a tropical climate and draining
many mountain valleys, works at the rate of one foot in 2,358 years. The
mean of these two great rivers would give one foot in 4,179 years, at
which rate our continents would be levelled with the waters in about six
millions of years. But the land has been in process of renewal as well
as of waste in geological time; and a better measure will be afforded by
the amount of beds actually deposited. The entire thickness of all the
stratified rocks of Great Britain has been calculated by Ramsay at
72,000 feet. Now, if we suppose the waste in all geological time to have
been on the average the same as at present, and that this material has
been deposited to the thickness of 72,000 feet on a belt of sea margin
100 miles in width, we shall have about 86 millions of years as the time
required.[1] This has the merit of approximating to Sir William
Thomson’s calculation, based on the rate of cooling of the earth, that a
minimum of 100 millions of years may represent the time since a solid
crust first began to form. As it is more likely that the rate of
denudation has on the average been greater in former geological periods
than at present, we may perhaps estimate fifty or sixty millions of
years as the time required for the accumulation of all our formations.
Some geologists object to this as too little, but in this some of them
are influenced by the exigencies of theories of evolution, and others
appear to have no adequate conception of the vast lapse of time
represented by such numbers, in its relation to the actual rates of
denudation and deposition.
It should be mentioned here, however, that, on certain theories now
somewhat generally accepted, respecting the nature and source of solar
heat, the absolute duration of geological time would be much reduced
below the estimate of Sir Wm. Thomson. Prof. Tait has based on such data
an estimate of fifteen millions of years. Prof. Simon Newcomb says that
“on the only hypothesis science will now allow us to make respecting the
source of the solar heat” (the gravitation hypothesis of Helmholtz) “the
earth was, twenty millions of years ago, enveloped in the fiery
atmosphere of the sun.” Dr. Kirkwood has called attention to these
results in connection with the planetary hypothesis of La Place, in the
_Proceedings of the American Philosophical Society_.[2] Should such
views prove to be well-founded, geological calculations as to the time
required for the successive formations may have to be revised.
If now we attempt to divide this time among the formations known to us,
according to their relative thicknesses, we have, according to an
elaborate estimate of Professor Dana, the time ratios of 12, 3, and 1
for the Palæozoic, Mesozoic, and Cainozoic periods respectively. Taking
the whole time since the beginning of the Cambrian as forty-eight
millions of years, we should thus have for the Palæozoic thirty-six
millions, for the Mesozoic nine, and for the Tertiary three. Another
calculation, recently made by Professors Hull and Haughton, gives the
following ratios:—
Azoic 34·3 per cent.
Palæozoic 42·5 ”
Mesozoic and Cainozoic 23·2 ”
This calculation is, however, based on the absolute thickness of the
several series as ascertained in Great Britain, without reference to the
nature of the beds, as indicating different rates of accumulation. Under
either estimate it will be seen that the Palæozoic time greatly exceeds
the Mesozoic and Cainozoic together, and consequently that changes of
life seem to have proceeded at an accelerated rate as time wore on.
Another inquiry of some importance relates to the manner of preservation
of fossils, and the extent to which they constitute the material of
rocks. This inquiry is doubly important, as it bears on the genuineness
of fossil remains, and on the means we have of understanding their
nature.
Some rocks are entirely made up of matter that once was alive, or formed
part of living organisms. This is the case with some limestones, which
consist of microscopic shells, or of larger shells, corals, and similar
calcareous organisms, either entire or broken into fragments and
cemented together with pasty or crystalline limestone filling their
interstices. This may be seen in Fig. 9, which represents a magnified
slice of a Silurian limestone. Coal in like manner consists of
carbonised vegetable matter, retaining more or less perfectly its
organic structure, and sometimes even the external forms of its
constituent parts. More frequently, fossils are dispersed more or less
sparsely through the substance of beds composed of earthy matter; and
they have usually been more or less affected by chemical changes, or by
mechanical pressure, or are mineralised by different substances which
have either filled their pores by infiltration or have more or less
completely replaced their substance. Of course, as a rule, the softer
and more putrescible organic matters have perished by decay, and it is
only the harder and more resisting parts that remain. Even these have
often yielded to the enormous pressure to which they have been
subjected, and if at all porous, have been changed by the slow action of
percolating water charged with various kinds of mineral matter in
solution.
[Illustration: FIG. 9.—Section of Trenton limestone, magnified, showing
that it is composed of fragments of corals, crinoids, and shells.
Montreal.]
[Illustration: FIG. 10.—Diagram showing different state of
fossilisation of a cell of a tabulate coral (Dawson’s _Dawn of Life_).
_a_ Natural condition, wall calcite cell empty.
_b_ Wall calcite, cells filled with the same.
_c_ Walls calcite, cells filled with silica or a silicate.
_d_ Wall silicified, cells filled with calcite.
_e_ Wall silicified, cell filled with silica.]
It thus happens that many fossils are infiltrated with mineral matter.
Wood, for example, may have the cavities of its cells and vessels filled
with silica or silicates, with sulphide or carbonate of iron, or with
limestone, while the woody walls of the cells may remain either as coaly
matter or charcoal. I have often seen the microscopic cells of fossil
wood not only filled in this way, but presenting under a high power
successive coats of deposit, like the banded structure of an agate.
In some cases not only are the pores filled with mineral matter, but
the solid parts themselves have been replaced, and the whole mass has
actually become stone, while still retaining its original structure.
Thus silicified wood is often as hard and solid as agate, and under the
microscope we see that the wood has entirely perished, and is
represented by silica or flint, differing merely in colour from that
which fills the cavities. In this case we may imagine the wood to have
been acted on by water holding in solution silica, combined with soda or
potash, in the manner of what is termed soluble glass. The wood, in
decay, would be converted into carbon dioxide, and this as formed would
seize on the potash or soda, leaving the silica in an insoluble state,
to be deposited instead of the carbon. Thus each particle of the carbon
of the wood, as removed by decay, would be replaced by a particle of
silica, till the whole became stone. By similar chemical changes corals
and shells are often represented by silica, or by pyrite, which has
taken the place of the original calcareous matter; and still more
remarkable changes sometimes occur, as when the siliceous spicules of
sponges have been replaced by carbonate of lime. The organic matter
present in the fossils greatly promotes these changes, by the substances
produced in its decay, and thus it often happens that the shells,
corals, etc., contained in limestone have been replaced by flint, while
the inclosing limestone is unchanged. Fig. 10 shows the various
conditions which a coral may assume under these different modes of
treatment.
[Illustration: FIG. 11.—Cast of erect tree (_Sigillaria_) in sandstone,
standing on a small bed of coal, South Joggins, Nova Scotia (Dawson’s
_Acadian Geology_).]
The substance of a fossil may be entirely removed by decay or solution,
leaving a mere mould representing its external form, and this may
subsequently be filled with mineral matter, so as to produce a natural
cast of the object. This is very common in the case of fossil plants;
and large trunks of trees may sometimes be found represented, as seen in
Fig. 11, by stony pillars retaining nothing of the original wood except
perhaps a portion of the bark in the state of coal. It sometimes happens
that the substance of fossils has been removed, leaving mere empty
cavities, sometimes containing stony cores representing the internal
chambers of the fossils. Again, calcareous fossils imbedded in hard
rocks are often removed by weathering, leaving very perfect impressions
of their forms. For this reason the fossil remains contained in some
hard resisting rocks can be best seen as impressed moulds on the
weathered surfaces.
[Illustration: FIG. 12.—_Protichnites septem-notatus._ A supposed
series of crustacean footprints made in sand, now hardened into
sandstone. Cambrian.—After Logan.]
Lastly, we sometimes have impressions or footprints representing the
locomotion of fossil animals, rather than the fossils themselves. In
this way some extinct creatures are known to us only by their footsteps
on sand or clay, once soft, but now hardened into stone; and in the
case of some of the lower animals the trails thus made are often not
easily interpreted (Figs. 12, 12_a_). It has been found that even
sea-weeds drifted by the tide make impressions of this kind, which, when
they occur in old rocks, are very mysterious. Even rain-drops are
capable of being permanently impressed on rocks, and constitute a kind
of fossils. Besides these we have many kinds of imitative markings which
simulate fossils, as those of concretions or nodules, which are often
very fantastic in shape, those of dendritic crystallisation giving
moss-like forms, and the complicated tracery produced on muddy shores
by the little rills of water which follow the receding tide (Fig. 13).
Such things are often mistaken by the ignorant for fossil remains, but
are easily distinguished by a practised eye.
[Illustration: FIG. 12_a_.—Footprints of modern _Limulus_, or
king-crab, in the sand, which enable us to interpret those in Fig. 12.]
The reader who has followed these, perhaps somewhat dry, details, will
be rewarded for his patience by having some conception of the conditions
in which we find fossil remains, and of the evidence by which we can
refer these to different periods in the history of the earth.
[Illustration: FIG. 13.—Current markings on shale, resembling a fossil
plant. Reduced from a photograph (Dawson’s _Acadian Geology_).]
Carrying this knowledge with us, and at the same time glancing at the
table of successive formations prefixed to this chapter, we shall be
prepared, without any additional geological study, to understand the
statements to be made in the following chapters, and to appreciate the
actual nature of the succession of life in so far as it is at present
known.
[Illustration: MAGNIFIED AND RESTORED SECTION OF A PORTION OF EOZOON
CANADENSE.
The shaded portions show the animal matter of the Chambers, Tubuli,
Canals, and Pseudopodia; the unshaded portions the calcareous
skeleton.]
CHAPTER II.
THE BEGINNING OF LIFE ON THE EARTH.
The day must have been when the first living being appeared for the
first time on our planet. Was it plant or animal? or a generalised
organism uniting in some mysterious way the properties and powers of two
kingdoms of nature, now so distinct, and even contrary to each other in
their manifestations? Did it appear suddenly, or was it slowly evolved
from dead matter by some process in which the albuminous or protoplasmic
matter, which we know forms the basal substance of living beings, was
first produced and then endowed with life? Did the first living being
appear in a mature state, or was it merely a germ from which the mature
individual could be produced? These are questions which science in its
present state has no means of answering. We do not know any process by
which the ingredients of protoplasm can be combined so as to produce
that substance without a previous living being. We do not know what
molecular differences may exist between dead albumen and that which we
see growing and moving and instinct with life; still less do we know how
to set up or establish these differences. We do not know the precise
nature or relation to other forces of the energy which actuates living
organisms. In our experience the simplest creatures that have life
spring from previous germs, themselves the products of previous
generations of living beings. Thus we are in the presence of great
mysteries which it might be impossible for us to solve, even if we were
permitted to visit some new planet on which the dawn of life was
breaking.
Some things, however, we can infer as to the conditions of the
introduction of life.
First, there is every reason to believe that the earth we inhabit was
once a glowing, incandescent mass, condensing from a vaporous condition,
and quite unfit for the abode of living beings, and which, even if in
some previous state its materials had constituted the mass of an
inhabited world, must have lost every trace of any living germ in the
fervent heat to which it had been subjected. There must, therefore, have
been in some way an absolute creation or origination of life and
organisation.
Secondly, we may infer that in the earlier stages of the earth, when it
was perhaps wholly or almost entirely covered with the waters, when it
was still uniformly warmed with its own internal heat, when it was
surrounded with a pall of dense vapours preventing radiation, and
nursing its heat within itself, though in a condition entirely unsuited
to the higher forms of life, it may have presented circumstances more
favourable to the origination and multiplication of living beings of low
organisation than at any subsequent time. This incubation of creative
power in the vaporous mantle over the primæval ocean was a favourite
imagination of old thinkers, and is not obscurely hinted at in the Book
of Genesis. It has been revived and much insisted on by evolutionists in
our own time, though it has no certain foundation in scientific
observation or experiment.
Thirdly, from the fact that plant-life alone has the power of subsisting
on inorganic matter, and that plants furnish all the nourishment of
animals, we may fairly infer that the life of the plant preceded that of
the animal. It has, indeed, been suggested that some of the humbler
forms of life may combine in a rude and simple way enough of the powers
of the plant and the animal to enable them to bridge over the double
gap between the animal and the plant, and the animal and the mineral, or
that such creatures may in their early stages carry on vegetable
functions, and in their later those of the animal. It is theoretically
possible that life may have begun with such creatures, which some of the
results of microscopical research would lead us to believe still exist.
It is, however, on the whole more probable that simple plants first
existed, and furnished pabulum to animals of low grade introduced almost
contemporaneously.
Fourthly, all our knowledge of the succession of life leads us to
believe that it was not the higher plants and animals that first sprang
into existence from the teeming earth, but creatures of low and humble
organisation, suited to the then immature and unfinished condition of
the planet. It is also in accordance with the amazing fecundity of the
seas in all geological periods in these lower forms of life, to suppose
that the earliest living things originated in the waters, and that the
plants and animals of the land are of later date.
Do we know anything from actual observation of this earliest population
of the world? Such knowledge we can hope to acquire only by studying the
oldest formations known to us; and these, it must be confessed, exist in
a state so highly crystalline, and so much affected by internal heat, by
mechanical pressure, and by movement, as to render it little likely that
organic remains should be preserved in them in a state fit for
recognition.
In many parts of the world, and notably in Canada and Scandinavia, as
well as in Wales, Scotland, and Bavaria, the older Palæozoic rocks, the
lowest containing plants in great abundance, rest on still older
crystalline beds, which have become hard and crystalline in
pre-Palæozoic times, and have contributed sand and pebbles to the
succeeding very ancient deposits. These old rocks—the Eozoic series of
our table—may be grouped in two great systems, the Laurentian and
Huronian (Fig. 14). The former may be conveniently divided into three
members: First, the Bojian, or Ottawa gneiss, consisting of stratified
granite rocks, usually of a red colour, and of very great thickness.
This contains, so far as known, no limestone, and has afforded as yet no
trace of fossils. Secondly, the Middle Laurentian, the greater part of
which consists of gneiss, but containing important beds of other rocks,
as quartzite, iron ore, and limestone. It is in this series that we have
the first evidence of life, and it is here also that we find the
greatest abundance of carbon, in the form of graphite or plumbago, and
also large quantities of calcium phosphate, or bone earth. Thirdly, the
Upper Laurentian or Norian series. This consists in great part of
Labadorite, or lime feldspar, but has also beds of ordinary gneiss,
limestone, and iron ore.
[Illustration: FIG. 14.—Ideal section, showing the relations of the
Laurentian and Huronian.
_a_, Lower Laurentian.
_b_, Middle Laurentian.
_c_, Upper Laurentian.
_d_, Huronian.
_e_, Cambrian and Silurian.]
The latter, the Huronian, is much less crystalline, and is divisible
into two series—the Lower Huronian, which includes many beds of
volcanic origin, and the Upper Huronian, which has afforded some obscure
fossils. The Huronian was first recognised by Sir W. E. Logan in Canada,
but corresponding rocks exist in Europe. The Pebidian series of Hicks in
Wales is probably of this age.
It is likely that much of the present appearance and condition of the
most ancient rocks may be attributed to metamorphism, that is, to the
slow baking under the influence of heat, heated water, and pressure, to
which they have been subjected in the lower parts of the earth’s crust,
when buried deeply under newer deposits. It is also true, however, as
Dr. Sterry Hunt has pointed out in detail, that they present mineral
characters which show a mode of deposition different from that which has
prevailed subsequently, and probably indicating great ejections of
heated mineral matter into the primitive ocean, and comparatively little
of that deposit therein of mere sand and clay which has prevailed in
subsequent geological periods. In short, these rocks have an
unmistakably primitive aspect, distinguishing them from those of later
times, and conveying the impression that they approach at least to the
records of that time when a heated ocean first rested on the thin and
recently solidified crust of our planet. If this is really the case,
then our Lower Laurentian—hard, compact, destitute of limestone, and
composed of material which may be little else than the _débris_ of
products of internal heat merely spread out into bedded forms by
water—may represent a time when no living thing as yet tenanted the
waters; and the dawn of life may have appeared in that period when the
Middle Laurentian beds were laid down. Here at least we find two kinds
of evidence pointing to the existence of certain forms of life in the
waters.
The first depends on the mineral character of the beds themselves. This
formation holds several very thick beds of limestone. Now although this
kind of rock may, under certain circumstances, be deposited directly
from solution in water, it is not ordinarily so deposited, but more
usually through the agency of living beings inhabiting the waters, and
forming their skeletons or hard parts of limestone derived from the
water, usually through the medium of humble forms of plant life. In this
way are formed reefs of coral and beds of shells and of chalky ooze, all
composed of material once constituting the skeletons of animals. The
study of limestones of all geological ages shows that this has been the
usual mode of their formation. If the Laurentian limestones had a
similar origin, the seas of that period must have swarmed with animals
having calcareous coverings; and the study of more modern limestones
which have become highly crystalline shows that it is quite possible
that the forms and structures of these organisms may have been
obliterated.
Again, the Middle Laurentian abounds in carbon or coaly matter. True,
this is in the form of graphite or plumbago, but this condition may be a
result of metamorphism; and we know that the carbon of coal-beds and
bituminous shales of much more modern times has been altered into
graphite. Further, the graphite occurs in the way in which we should
expect it to occur if of organic origin. It is found disseminated in the
limestone, just as bituminous matter is found in unaltered rocks of this
kind. It is found interlaminated with gneiss, as carbonaceous and
bituminous matters are found in the shales of the ordinary fossiliferous
rocks, where these substances are known to be of organic origin. The
graphite also occurs in a very pure form in irregular veins, just as in
some bituminous formations the rock oil, oozing into fissures, has been
hardened into asphalt or coaly matter.[3]
To these facts may be added the presence of thick beds and veins of iron
ore and of apatite or calcium phosphate (bone earth). Both of these
substances occur in a disseminated state in nearly all rocks, but they
are concentrated into definite deposits by the action of life. Iron is
usually dissolved out and redeposited by acids produced in the decay of
vegetable matter, as we see in the clay ironstones of the coal formation
and in bog-iron ores. Calcic phosphate is taken up by many animals, and
forms their shells or skeletons, and on their death is deposited in beds
on the sea-bottom, sometimes to a very considerable extent.
The concurrence of all these phenomena in the Middle Laurentian may be
held to afford a strong presumption that, could we discover these rocks
in an unaltered state, we should find the limestones filled with marine
fossils and the graphite showing the forms or structure of plants. The
only startling feature in this conclusion is, that if we admit it, we
must also admit that life was developed in the Laurentian time in an
exuberance not surpassed, if equalled, in any subsequent period. Still,
there is nothing incredible in this, for if the forms of life were few
and low, their increase may have been rapid, because unchecked; and they
no doubt found in the ancient seas a surplusage of material on which to
feed and with which to construct their skeletons. Dr. Hunt has estimated
that the amount of carbon now sealed up as coaly matter would, if
diffused in the atmosphere as carbon dioxide, afford 600 times the
quantity of that gas at present floating in the air. A still more vast
amount is sealed up in the limestone of the several geological
formations. The same chemist has shown that the quantity of lime held in
solution in the ocean must have been much greater in Laurentian times
than at present. These facts at least allow us to suppose that in the
Eozoic times there were great supplies of carbon and of lime available
to such creatures of low organisation as were capable of profiting by
them; and we have no reason to doubt that there may have been plants and
animals so constituted as to flourish in conditions of this kind, in
which perhaps scarcely any modern species could exist.
These probabilities have caused geologists anxiously to search for any
traces of fossil organic remains in the old Laurentian rocks; and they
have been rewarded by the discovery of one species, _Eozoon Canadense_,
still often referred to as only a problematical fossil; but this arises
to a large extent from the prevalent want of knowledge sufficient to
appreciate the evidence for its organic character. This being once
admitted, we have in the existence of _Eozoon_ alone a sufficient cause
for the accumulation of much of the Laurentian limestone, though there
is reason to believe that it was not the only inhabitant of those
ancient seas.
[Illustration: FIG. 15 (Nos. 1 to 4).—Small weathered specimen of
_Eozoon_. From Petite Nation.
1, Natural size; showing general form, and acervuline portion above and
laminated portion below. 2, Enlarged casts of cells from upper part. 3,
Enlarged casts of cells from the lower part of the acervuline portion.
4, Enlarged casts of sarcode layers from the laminated part.]
The best specimens of _Eozoon_ occur as rounded, flattened, or more or
less irregular lumps or masses in certain layers of the Laurentian
limestone. When weathered on the surface of the rock, these lumps show a
regular concentric lamination, caused by thin fibres of limestone,
alternating with other mineral substances, filling up the spaces between
them. When these intervening layers are composed of such minerals as
Serpentine, Loganite, Pyroxene, or Dolomite, which are more resisting
than the limestone, they project when weathered, or when the limestone
is etched by an acid, so as to show the lamination very distinctly. At
the lower surface of the masses the layers are seen to be thicker than
they are above, and in perfect specimens they are seen toward the
surface to break up into small rounded vesicles of calcite, like little
bubbles, which constitute the so-called acervuline condition of _Eozoon_
(Fig. 15, No. 2). Slices of the fossil etched with an acid show these
appearances very perfectly, and can even be printed from, so as to
present perfect nature-prints of the structure (Fig. 16).
FIG. 16.—Nature-printed specimen of _Eozoon_ slightly etched with acid.
It shows the lamination, and at one side fragmental _Eozoon_ (_Life’s Dawn
on Earth_).
On etching a small fragment or slice with very dilute acid, so as to
dissolve away the calcite slowly, if the specimen be well preserved, we
find that the calcite layers have a very curious structure. This is
indicated by the appearance of little white or transparent threads of
Serpentine, Dolomite, or Pyroxene, which ramify throughout the substance
of the limestone layers, and are left intact when they have been
dissolved. These little processes must originally have been pores in the
limestone layers, which have been filled with the substance which
constitutes the alternate laminæ. In addition to this, if we use a
somewhat high microscopic power, and especially if we study the
structures as seen in thin transparent slices, we can perceive a still
finer tubulation along the sides of the calcite layers, represented by
extremely minute parallel rods of mineral matter (Figs. 17, 18).
Now if we regard these structures as those of an infiltrated fossil, as
described in last chapter, their interpretation will not be difficult.
The original organism was composed of calcareous matter in thin
concentric laminæ, connected with each other by pillars and plates of
similar material. Between these laminæ was lodged the soft, jelly-like
substance of a marine animal, growing by the addition of successive
layers, each protected by a thin calcareous crust. The layers were
originally traversed by very numerous parallel tubuli, permitting the
soft protoplasm to penetrate them; and when, in the progress of growth,
it was necessary to strengthen these layers, they were thickened by a
supplemental deposit traversed by larger and ramifying canals. When the
animal was dead, and its soft parts removed by decay, the chambers
between the laminæ, as well as the minute canals and tubuli, became
infiltrated with mineral matter, in the manner described in the last
chapter, and when so preserved became absolutely imperishable under any
circumstances short of absolute fusion.
[Illustration: FIG. 17.—Magnified group of canals in supplemental
skeleton of _Eozoon_.
Taken from the specimen in which they were first recognised (_Life’s
Dawn on Earth_).]
[Illustration: FIG. 18.—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. A. _b_, _c_, Intermediate skeleton, with canals.]
This interpretation leads to the conclusion, at which I arrived from the
study of the first well-preserved specimen ever submitted to microscopic
examination, that the animal which produced the calcareous skeleton of
_Eozoon_ was a member of that lowest grade of Protozoa known as
Foraminifera; and which, after living through the whole of geological
time, still abound in the sea. The main differences are, that _Eozoon_
presents a somewhat generalised structure, intermediate between two
modern types, and that it attained to a gigantic size compared with most
of these organisms in later periods. How near it approaches in structure
to some modern forms may be seen by comparison of the recent species
represented in Fig. 19, in which the parts corresponding to the
chambers, laminæ, tubuli, and canals of _Eozoon_ can be readily
distinguished.
[Illustration: FIG. 19.—Magnified portion of shell of _Calcarina_.—After
Carpenter.
_a_, Cells.
_b_, Original cell-wall with tubuli.
_c_, Supplementary skeleton with canals.]
The modern animals of this group are wholly composed of soft gelatinous
protoplasm or sarcode, the outer layer of which is usually somewhat
denser than the inner portion; but both are structureless, except that
the inner layer may present a more or less distinct granular
appearance. Many of them show a distinct spot or cell, called the
nucleus, and some have minute transparent vesicles, which contract and
expand alternately, and appear to be of the nature of circulatory or
excretory organs. They have no proper alimentary canal, but receive
their food into the general mass and digest it in temporary cavities.
Their means of locomotion and prehension are soft thread-like or
finger-like processes, extended at will from the surface of any part of
the body, and known as false feet (pseudopodia). From these processes
the whole group has obtained the name of Rhizopods, or rootfooted
animals. They may be regarded as constituting the simplest and humblest
form of animal life certainly known to us.
The very numerous species of these creatures existing in the waters of
the modern world may be arranged under three principal groups. The first
and highest includes those which have lobate or finger-like pseudopods,
and a well-developed nucleus and pulsating vesicle (Fig. 20, _a_). They
are mostly inhabitants of fresh water, and destitute of a hard crust or
shell. A second group, including many inhabitants of the sea as well as
of fresh waters, has thread-like radiating pseudopodia[4] (Fig. 20 _b_).
Some of these form beautiful silicious skeletons. A third group,
essentially marine, consists of those with reticulated pseudopodia, and
usually destitute of distinct nucleus and pulsating vesicle (Fig. 21).
They produce beautiful calcareous skeletons, often very complex, or
sometimes are content to cover themselves with a crust of agglutinated
grains of sand. It is to this last group that _Eozoon_ belongs, and to the
highest division of it—that which has the shell perforated with minute
pores, often of two kinds. It is curious that just as we have the
chambers and pores of _Eozoon_ filled with serpentine, so in all
geological formations and in the modern seas it is not uncommon to find
Foraminifera having their cavities filled with glauconite and other
hydrous silicates allied to serpentine.
[Illustration: FIG. 20.—_a_, _Amœba_, a fresh-water naked Rhizopod; and
_b_, _Actinophrys_, a fresh-water Protozoon of the group Radiolaria,
with thread-like pseudopodia.]
[Illustration: FIG. 21.—_Nonionina_, a modern marine Foraminifer.
Showing its chambered shell and netted pseudopodia.—After Carpenter.]
If we attempt to trace the Rhizopods onward from the Middle Laurentian,
we are met with a great hiatus in the Upper Laurentian. The species
_Eozoon Bavaricum_ has, however, been found in rocks apparently of
Huronian age; but this is the last known appearance of _Eozoon_, properly
so-called. In the Cambrian or Siluro-Cambrian, however, we meet with
many gigantic Protozoa, more especially those known as _Stromatopora_,
_Archæocyathus_, _Receptaculites_, and _Cryptozoon_.
[Illustration: FIG. 22.—_Stromatopora concentrica._—After Hall.
_a_, Section of the same, magnified.
_b_, Small portion highly magnified, showing laminæ and pillars.]
The typical Stromatoporæ, or Layer-corals, consist, like _Eozoon_, of
concentric layers, connected by numerous pillars, which are often,
though not always, more definite and regular than in the Laurentian
fossil. The laminæ are perforated, but more coarsely than in _Eozoon_, and
they are often thickened with supplemental deposit which, in some of the
forms, presents canals radiating from vertical tubes or bundles of tubes
penetrating the mass (Figs. 22, 23). The mode of growth of _Stromatopora_
must have closely resembled that of _Eozoon_, and the forms produced are
so similar that it is often quite impossible to distinguish them by the
naked eye. Like _Eozoon_, they form the substance of important limestones,
and single masses are sometimes found as much as three feet in diameter.
The Stromatoporæ extend from the Upper Cambrian to the Devonian
inclusive. In the Carboniferous they are continued by smaller and more
regular organisms of the genus _Loftusia_,[5] and this genus seems to
extend without marked change up to the Eocene Tertiary. Recent students
of the Stromatoporæ seem disposed to promote them from the province of
Protozoa to that of the Hydroids.[6] The reasons for this seem cogent in
the case of some of the forms, but in my judgment fail in others, more
especially in the older forms. It may ultimately be found that the group
as now held includes very different types of structure. In modern times
I know of no nearer representative than the animal whose skeleton often
adheres in red encrusting patches to our specimens of corals, and which
is known as _Polytrema_. In general structure it is not very far from
being a very degenerate kind of _Stromatopora_.
[Illustration: FIG. 23.—_Caunopora planulata._ Showing the radiating
canals on a weathered surface. Devonian.—After Hall.]
It is curious that in the line of succession above stated, the beautiful
tubulated cell-wall of _Eozoon_ disappears; and this structure seems,
after the Laurentian, to be for ever divorced from the great laminated
Protozoans. It reappears in the Carboniferous, in certain smaller
organisms of the type of the _Nummulites_, or Money-stone Foraminifers,
and is continued in this group of smaller and free animals down to the
present time. In the Cretaceous and early Tertiary periods, the
Foraminifera of different types have been nearly as great rock-builders
as they were in the Laurentian. Some of these later rock-builders,
however, have belonged to the lower or imperforate group; others to the
higher or Rotaline and Nummuline groups; and, as a whole, they have been
individually small, making up in numbers what they lacked in size.
Probably the conditions for enabling animals of this type rapidly, and
on a large scale, to collect calcareous matter, were more favourable in
the Laurentian than they have ever been since.
[Illustration: FIG. 24.—_Archæocyathus minganensis._ A Primordial
Protozoon.—After Billings.
_a_, Pores of the inner wall.]
In the Siluro-Cambrian age two other forms of gigantic Foraminiferal
Protozoans were introduced, widely different from _Eozoon_, and destined
apparently not to survive the period in which they appeared. These were
_Archæocyathus_, the ancient Cup-corals, and Receptaculites, which may
perhaps be called the Sack-corals. Both are quite remote from _Eozoon_ in
structure, wanting its complexity in the matter of minute tubules, and
having greater regularity and complication on the large scale.
_Archæocyathus_ had the form of a hollow inverted cone with double
perforated walls, connected by radiating irregular plates, also
perforated (Fig. 24). It has been regarded as a sponge, and some species
are certainly accompanied with spicules; but these I have ascertained to
be merely accidental, and will be referred to in the next chapter. The
true structure of _Archæocyathus_ consists of radiating calcareous plates
enclosing chambers connected by pores. Archæocyathus came in with the
Later Cambrian, and seems to have died out in the Siluro-Cambrian. The
only more modern things which at all resemble it are the Foraminifera
called _Dactylopora_, which belong to the Tertiary period.
[Illustration: FIG. 25.—Receptaculites. Restored.—After Billings.
_a_, Aperture.
_b_, Inner wall.
_c_, Outer wall.
_n_, Nucleus, or primary chamber.
_v_, Internal cavity.]
Receptaculites is a still more complex organism. It has a sack-like
form, often attaining a large size, and the double walls are composed of
square or rhombic plates, connected with each other by hollow tubes from
which proceed canals perforating the plates (Fig. 25). This curious
structure is confined to the Siluro-Cambrian, and is so dissimilar from
modern forms that its affinities have been subject to grave doubts.
[Illustration: FIG. 26.—Section of _Loftusia Persica_. An Eocene
Foraminifer. Magnified five diameters.—After Carpenter and Brady.]
We thus have presented to us the remarkable fact that in the Palæozoic
age we have no precise representative of _Eozoon_, but instead three
divergent types, differing from it and from each other, all apparently
specialised to particular uses, all temporary in their duration; while
in later times nature seems to have returned nearer to the type of
_Eozoon_, though on a smaller scale, and separating some characters
conjoined in it. Some portion of this curious result may be due to our
ignorance; and it would be interesting to know, what we may know some
day, how this type of life was represented in the long interval between
the Huronian and the Upper Cambrian, when perhaps there may have been
forms that would at least enable us to connect _Eozoon_ and _Stromatopora_.
Another link in the chain of being remains to be noticed here. In the
Laurentian limestones we meet with numerous minute spherical bodies and
groups of spheres with calcareous tubulated tests.[7] These may either
be small Foraminiferæ, distinct from _Eozoon_, or may be germs or detached
cells from its surface. Similar bodies are found in the lower part of
the Siluro-Cambrian, in the Quebec group at Point Levis; and there they
are filled with a species of glauconite constituting a sort of greensand
rock. Still higher, in the Carboniferous, there are very numerous
species of Foraminifera, presenting forms very similar to those in the
modern seas, so that in the smaller shells of this group we seem to have
evidence of a continuous series all the way from the Laurentian to the
present time. The greater laminated forms co-exist with these up to the
Eocene Tertiary. Throughout the whole of geological time—from the
formation of the Laurentian limestones to that of the chalky ooze
accumulating in the modern ocean—these humble creatures have been among
the chief instruments in seizing on the calcareous matter of the waters
and depositing it in the form of limestone.
[Illustration: FIG. 27.—Foraminiferal Rock Builders, in the Cretaceous
and Eocene.
_a_, _Nummulites lævigata_—Eocene. _b_, The same, showing chambered
interior. _c_, Milioline limestone, magnified—Eocene, Paris. _d_, Hard
Chalk, section magnified—Cretaceous.]
I have said nothing of the development of higher forms of animal life
from _Eozoon_, simply because I know nothing of it. We shall see in the
next chapter that these are introduced seemingly in an independent
manner. We may be content to trace foraminiferal life along its own line
of development, waxing and waning, but ever confined within the same
general boundaries, from the Laurentian to the present time. It is
likely that if, in any of the ages constituting this vast lapse of time,
a dredge had been dropped into the depths of ocean, it would have
brought up Foraminifera not essentially different in form and structure.
If any one asks to what extent the successive species constituting this
almost endless chain may be descendants one of the other, we have no
absolutely certain information to give. On the one hand, it is not
inconceivable that such forms as _Stromatopora_ or _Nummulina_ may have
descended from _Eozoon_. On the other hand, it is equally conceivable that
the same power which produced _Eozoon_ at first, whether from dead matter
or from some unknown lower form of life, may have repeated the process
in later times with modifications. In any case it is probable that the
Foraminifera have experienced alternations of expansion and shrinkage,
of elevation and decadence, in the lapse of geological time. There were
times in which many new forms swarmed into existence, and times in which
old forms were becoming extinct without being replaced by others. In so
far as the areas of the continents and the adjacent waters are
concerned, those periods when the land was subsiding under the ocean
must have been their times of prosperity, those in which the crust of
the earth shrunk and raised up large areas of land must have been their
times of decay. Still this lowest form of animal life has never
perished, but has always found abundant place for itself, however
pressed by physical change and by the introduction of higher beings.
[Illustration: _Paradoxides Regina_ (Matthews). Lower Cambrian of New
Brunswick.
1/6th Nat. Size.]
CHAPTER III.
THE AGE OF INVERTEBRATES OF THE SEA.
If the middle portion of the Laurentian age was really a time of
exuberant and abounding life, either this met with strange reverses in
succeeding periods, or the conditions of preservation have been such as
to prevent us from tracing its onward history. Certain it is, that
according to present appearances we have a new beginning in the
Cambrian, which introduces the great Palæozoic age, and few links of
connection are known between this and the previous Eozoic.
At the beginning of the Palæozoic we have reason to believe that our
continents were slowly subsiding under the sea, after a period of
general continental elevation which was consequent on the crumbling of
the earth’s crust at the close of the Eozoic; and on the new sea-bottoms
formed by this subsidence came in, slowly at first, but in
ever-increasing swarms, the abundant and varied life of the early
Palæozoic.
In the oldest portion of the Cambrian series in Wales, Hicks has
catalogued species of no less than seventeen genera, embracing
Crustaceans, the representatives of our crabs and lobsters, bivalve and
univalve shell-fishes of different types, worms, sea-stars, zoophytes,
and sponges. If we could have walked on the shores of the old Cambrian
sea, or cast our dredge or trawl into its depths, we should have found
representatives of most of the humbler forms of sea life still extant,
though of specific forms strange to us. Perhaps the nearest approach to
such experience which we can make is to examine the group of Cambrian
animals delineated in Fig. 28, and to notice, under the guidance of the
geologist above named, the sections seen at St. David’s, in South Wales.
[Illustration: FIG. 28.—Group of Cambrian Animals (from Nicholson).
_a_, _Arenicolites didymus_, worm tubes. _b_, _Lingulella ferruginea_.
_c_, _Theca Davidii_. _d_, _Modiolopsis solvensis_. _e_, _Orthis
Hicksii_. _f_, _Obolella sagittalis_. _g_, _Hymenocaris vermicauda_.
_h_, Trilobite, _Olenus micrurus_.]
Here we find a nucleus of ancient rocks supposed to be Laurentian,
though in mineral character more nearly akin to the Huronian, but which
have hitherto afforded no trace of fossils. Resting unconformably on
these is a series of partially altered rocks, regarded as Lower
Cambrian, and also destitute of organic remains. These have a thickness
of almost 1,000 feet, and they are succeeded by 3,000 feet more of
similar rocks, still classed as Lower Cambrian, but which have afforded
fossils. The lowest bed which contains indications of life is a red
shale, perhaps a deep-sea bed, and possibly itself partly of organic
origin, by that strange process of decomposition or dissolution of
foraminiferal ooze and volcanic fragments, going on in the depths of the
modern ocean, and described by Dr. Wyville Thomson as occurring over
large areas in the South Pacific. The species are two _Lingulellæ_, a
_Discina_ and a _Leperditia_. Supposing these to be all, it is
remarkable that we have no Protozoa or Corals or Echinoderms, and that
the types of Brachiopods and Crustaceans are of comparatively modern
affinities. Passing upward through another 1,000 feet of barren
sandstone, we reach a zone in which no less than five genera of
Trilobites are found, along with Pteropods and a sponge. Thus it is that
life comes in at the base of the Cambrian in Wales, and it may be
regarded as a fair specimen of the facts as they appear in the earlier
fossiliferous beds succeeding the Laurentian. Taking the first of these
groups of fossils, we may recognise in the _Leperditia_ a two-valved
Crustacean closely allied to forms still living in the seas and fresh
waters. The Lingulellæ, whether we regard them as molluscoids, or, with
Professor Morse, as singularly specialised worms, represent a peculiar
and distinct type, handed down, through all the vicissitudes of the
geological ages, to the present day. The Pteropods and the sponge are
very similar to forms now living. The Trilobites are an extinct group,
but closely allied to some modern Crustaceans. Had the primordial life
begun with species altogether inscrutable and unexampled in succeeding
ages, this would no doubt have been mysterious; but next to this is the
mystery of the oldest forms of life being also among the newest.
Whatever the origin of these creatures, they represent families which
have endured till now in the struggle for existence without either
elevation or degradation. Yet, though thus vast in their duration, they
seem to have swarmed in together and in great numbers, in the Cambrian,
without any previous preparation. From the Cambrian onward, throughout
the whole Palæozoic, there is no decided break in the continuity of
marine life; and already in the Silurian period the sea was tenanted
with all the forms of invertebrate life it yet presents, and these in a
teeming abundance not surpassed in any succeeding age. Let us now, in
accordance with our plan, select some of these ancient inhabitants of
the waters and trace their subsequent history.
Remains of sea-weeds are undoubtedly present in the Cambrian rocks. One
of the lowest beds in Sweden has been named from their abundance the
Fucoidal Sandstone; and wherever fossiliferous Cambrian rocks occur,
some traces, more or less obscure, of these plants may be found. Nearly
all that we can say of them, however, is, that, in so far as their
remains give any information, they are very like the plants of the same
group that now abound in our seas. In the fucoidal sandstone of Sweden
certain striated or ribbed bodies have been found, which have even been
regarded as land plants;[8] but they seem rather to be trails or marks
left by sea-weeds dragged by currents over a muddy bottom. The plants of
the sea thus precede those of the land, and they begin on the same level
as to structure that they have since maintained. I agree with Nathorst,
however, in holding that the Bilobites and many other forms believed by
some to be sea-weeds, are really trails and tracks of animals.[9]
The Foraminifera of the Palæozoic we have noticed in the last chapter;
but we now find a new type of Protozoan—that of the Sponge. Sponges as
they exist at present may be defined to be composite animals, made up of
a great number of one-celled or gelatinous zoids, provided with
vibrating threads or cilia, and so arranged that currents of water are
driven through passages or canals in the mass, by the action of the
cilia, bringing food and aerated water for respiration. To support these
soft sarcodic sponge-masses, they secrete fibres of horny matter and
needles (spiculæ) of flint or of limestone, forming complicated fibrous
and spicular skeletons, often of great beauty. They abound in all seas,
and some species are found in fresh waters.
[Illustration: FIG. 29.—Portion of skeleton of Hexactinellid Sponge
(_Cœloptychium_). Magnified. After Zittel.]
With the exception of a very few species destitute of skeleton, and
which we cannot expect to find in a fossil state, the sponges may be
roughly divided into three groups: 1, those with corneous or horny
skeleton, like our common washing sponges; 2, those with skeletons
composed of silicious needles of various forms and arrangement; 3, those
with calcareous spicules. Of these, the second or silicious group has
precedence in point of time, beginning in the Early Cambrian, and
continuing to the present. Two of its subdivisions are especially
interesting in their range. The first is that of the Lattice-sponges
(_Hexactinellidæ_), in which the spicules have six rays placed at right
angles, and are attached to each other by their points, so as to form a
very regular network (Fig. 29). The second is that of the Stone-sponges
(_Lithistidæ_), in which the spicules are four-rayed or irregular, and
are united by the branching root-like ends of the rays. The most
beautiful of all sponges, the Venus Flower-basket (_Euplectella_), is a
modern Hexactinellid, and the wonderful weaving of its spicules is as
marvellous a triumph of constructive skill as its general form is
graceful. The Lithistids are less beautiful, but are the densest and
most compact of sponges, and are represented by several species in the
modern seas. Both of these types go back to the Early Cambrian, and have
continued side by side to the present day, as representatives of two
distinct geometrical methods for the construction of a spicular
skeleton.
[Illustration: FIG. 30.—_Protospongia fenestrata_ (Salter). Menevian
group.
_a_, Fragment showing the spicules partially displaced. _b_, Portion
enlarged.]
[Illustration: FIG. 31.—_Astylospongia præmorsa_ (Roemer). Niagara
group.—After Hall.
_a_, Spicules magnified.]
[Illustration: FIG. 32.—Spicules of Lithistid sponge (_Trichospongia_
of Billings). From the Cambrian of Labrador.]
Many years ago the keen eye of the late lamented Salter detected in a
stain on the surface of a slab of Cambrian slate the remains of a
sponge; and minute examination showed that its spicules crossed each
other, and formed lattice-work on the hexactinellid plan. Salter boldly
named it _Protospongia_ (the first sponge), and it is still the earliest
that we know (Fig. 30). Thus the type whose skeleton is the most perfect
in a mechanical point of view takes the lead. It is continued in the
Silurian in many curious forms, of which the stalkless sponges
(_Astylospongia_) are the most common (Fig. 31). It perhaps attains its
maximum in the Cretaceous, from which the beautiful example in Fig. 29
is taken, and it still flourishes, giving us the most beautiful of all
recent forms. Before the close of the Cambrian there were other sponges
of the Lithistid type. Fig. 32 represents a group of spicules from the
Calciferous (Lowest Silurian or Upper Cambrian) of Mingan,[10] and which
probably belong to a large Lithistid sponge of that early time. The
Lithistids have been recognised in the Upper Silurian and Carboniferous,
and continuing upward to the Cretaceous, there become vastly numerous,
while their modern representatives are by no means few. The silicious
sponges with simple spicules appear to have existed as far back as the
Siluro-Cambrian, and there is believed to be almost as early evidence of
horny or corneous sponges. The calcareous sponges have been recognised
as far back as the Silurian.[11] Thus from the close of the Palæozoic
all the types of sponges seem to have existed side by side; and in the
Cretaceous period, when such large areas of our continents were deeply
submerged, they attained a wonderful development, perhaps not equalled
in any other era of the earth’s history.
[Illustration: FIG. 33.—_Oldhamia antiqua_ (Forbes).]
[Illustration: FIG. 34.—_Dictyonema sociale_. Enlarged. _Lingula_
flags.—After Salter.]
Sponges may be regarded as the highest or most complex of the Protozoa
or the lowest of the Coelenterates. We have no links wherewith to
connect them with the lower Protozoa of the Eozoic period; and through
their long history, though very numerous in genera and species, they
show no closer relationship with the Foraminifera below, and the Corals
above, than do their successors in the modern seas. They thus stand very
much apart; and modern studies of their development and minute
structures do not seem to remove them from this isolation. Though we are
treating here of inhabitants of the sea, it may be proper to mention
that Geinitz has described two species from the Permian which he
believed to be early precursors of the Spongillæ, or fresh-water
sponges; but more recently he seems to regard them as probably Algæ.
Young has, however, recently found true spicules of _Spongilla_ in the
Purbeck beds.[12]
[Illustration: FIG. 35.—_Dictyonema Websteri_ (Dn). Niagara formation.
_a_, Enlarged portion (_Acadian Geology_).]
[Illustration: FIG. 36.—Group of modern Hydroids allied to Graptolites.
Magnified, and natural size.
_a_, _Sertularia_. _b_, _Tubularia_. _c_, _Campanularia._]
[Illustration: FIG. 37.—Silurian Graptolitidæ.
_a_, _Graptolithus_. _b_, _Diplograpsus_. _c_, _Phyllograpsus_. _d_,
_Tetragrapsus_. _e_, _Didymograpsus_.]
[Illustration: FIG. 38.—Central portion of Graptolite, with membrane,
or float (_Dichograpsus octobrachiatus_, Hall).]
[Illustration: FIG. 39—_Ptilodictya acuta_ (Hall). Bryozoan.
Siluro-Cambrian.]
A stage higher than the sponges are those little polyp-like animals with
sac-like bodies and radiating arms or tentacles, which form minute horny
or calcareous cells, and bud out into branching communities, looking to
untrained eyes like delicate sea-weeds—the sea-firs and sea-mosses of
our coasts (Fig. 36). These belong to a very old group, for in the
oldest Cambrian we have a form referred to this type (Fig. 33), and in
the Upper Cambrian another still more decided example (Fig. 34).[13]
This style of life, once introduced, must have increased in variety and
extended itself with amazing rapidity, for in the Siluro-Cambrian age we
find it already as characteristic as in our modern seas, and so abundant
that vast thicknesses of shale are filled and blackened with the
_débris_ of forms allied to the sea-firs, and masses of limestone
largely made up of the more calcareous forms of the sea-mosses. As
examples of the former we may take the _Graptolites_, so named from
their resemblance to lines of writing, and of which several forms are
represented in Fig. 37. The little teeth on the sides of these were
cells, inhabited probably by polyps, like those represented in the
modern _Sertularia_ in Fig. 36. Some of them were probably attached to
the bottom. In others the branches radiated from a central film which
may have been a hollow vesicle or float, enabling them to live at the
surface of the water (Fig. 38). These Graptolites are specially
characteristic of the Upper Cambrian and Lower Silurian. The netted ones
(_Dictyonema_), as may be seen from Figs. 34 and 35, came in before the
close of the Cambrian, and continue unchanged to the Silurian, where
they disappear. The branching forms, seen in Fig. 37, have scarcely so
great a range. They thus form most certain marks of the period to which
they belong, and being oceanic and probably floaters, they diffused
themselves so rapidly that they appear to indicate the same geological
time in countries so widely separated as Europe, North America, and
Australia. It is curious, too, that while the Graptolites thus mark a
definite geological time, and seem to disappear abruptly and without
apparent cause, they are the first link in the long chain of the
Hydroids, which, though under different family forms, continue to this
day, apparently neither better nor worse than their perished Palæozoic
relatives. There is a group of little Stony Corals (_Monticuliporidæ_),
which were possibly also the cells of Hydroids, that have a similar
history. They are the only known Corals that date so far back as the
Upper Cambrian; and they continue under very similar forms all through
the Palæozic, and are represented by the millepore corals of the present
day. Fig. 40 represents a form found at the base of the Siluro-Cambrian,
and Fig. 41 shows forms characteristic of the Carboniferous Limestone.
[Illustration: FIG. 39_a_.—_Fenestella Lyelli_ (Dawson). A
Carboniferous Bryozoan.]
[Illustration: FIG. 40.—_Chaetetes fibrosa_. A tubulate coral with
microscopic cells. Siluro-Cambrian.]
If we turn now to the sea-mosses (Bryozoa), we have a group of minute
polyp-like animals inhabiting cells not unlike those of the Hydroids,
and which form plant-like aggregates. But the animals themselves are so
different in structure that they are considered to be nearer allies of
the bivalve shell-fishes than of the Corals. They are, in short, so
different, that the most ardent evolutionist would scarcely hold a
community of origin between them and such creatures as the Graptolites
and Millepores, though an ordinary observer might readily confound the
one with the other. These animals appear at the beginning of the
Siluro-Cambrian, and such forms as that represented in Fig. 39, very
closely allied to some now living, are large constituents of some of the
limestones of that period. Other forms, like that represented in Fig.
39_a_, are very characteristic of the Carboniferous. These animals,
individually small, though complicated in structure and branching into
communities, scarcely ever of any great magnitude, humble creatures
which have never played any great part in the world, have, nevertheless,
been so persistent that, though specific and generic forms have been
changed, the group may be said to be in the modern seas exactly what it
was in those of the early Palæozoic, nor can it be affirmed to have
originated in anything different, or to have produced anything.
[Illustration: FIG. 41.—_a_, _Stenopora exilis_ (Dawson). _b_,
_Chaetetes tumidus_ (Edwards and Haine). Carboniferous.]
The true Stony Corals (_Anthozoa_) are as yet unknown in the Cambrian.
They entered on the stage in immense abundance in the Siluro-Cambrian,
where considerable limestones are largely composed of their remains,
mixed, however, and sometimes overpowered with those of Bryozoa and
Hydroids. An ordinary coral, such as those of which coral reefs are
built—the red coral, used for ornament is not quite similar—is the
skeleton of an animal constructed on the plan of a sea anemone; with a
central stomach surrounded by radiating chambers, and having above a
crown of tentacles. The stony coral surrounds and protects the soft body
of the animal, and may either be a single cell, for one animal, or an
aggregation of such cells, constituting a rounded or branching mass.
The modern star coral, represented in Fig. 42, is an instance of the
latter condition. It shows nineteen or twenty animals, each with a
central mouth and fringe of short tentacles, aggregated together, and
two of them showing the spontaneous division by which the number of
animals in the mass is progressively increased. The living coral shows
only the soft animals and the animal matter connecting them; but if dead
there would be a white stony mass with a star-like cell or depression
corresponding to each animal.
[Illustration: FIG. 42.—Living Anthozoan Coral (_Astræa_).]
In their general plan, the oldest Corals were precisely of this
character, but they presented some differences in detail, which have
caused them to be divided into two groups, which are eminently
characteristic of the Palæozoic age—the tabulate or floored corals, and
the rugose or wrinkled corals. In the former (Fig. 43) the cells are
usually small and thin-walled, often hexagonal, like a honeycomb, and
are floored across at intervals with tabulæ or horizontal plates. A few
modern corals present a similar arrangement,[14] but this kind of
structure was far more prevalent in the Palæozoic. In the second type
the animals are usually larger and often solitary, the cell has strongly
marked radiating plates, while the horizontal floors are absent or
subordinate, and there is usually a thick external rind or outer coat
(Figs. 44, 45). In general plan, these rugose corals closely resemble
those of our modern reefs; but they differ in their details of
structure, and only a very few modern forms from the deep sea are
regarded as actual modern representatives.[15] One curious point of
difference is that their radiating laminæ begin with four, and increase
by multiples of that number, while in modern corals the numbers are six
and multiples of six; a change of mathematical relation not easily
accounted for, and which assimilates them to Hydroids on the one hand,
and to a higher group, the Alcyonids, on the other, both of which prefer
four and eight to six, or have had these numbers chosen for them. In the
Mesozoic period the tabulate and rugose corals were replaced by others,
the porous and solid corals of the modern seas; but, in so far as we
know, the animals producing these, though differing in some details,
were neither more nor less elevated than their predecessors, and they
took up precisely the same rôle as reef-builders in the sea, though with
probably more tendency to the accumulation of great masses of coral
limestone in particular spots.
[Illustration: FIG. 43.—Tabulate Corals.
_a_, _Halisites_, and _b_, _Favosites_. Upper Silurian.]
[Illustration: FIG. 44.—Rugose Coral (_Heliophyllum Halli_). Devonian.]
[Illustration: FIG. 44_a_.—_Zaphrentis prolifica_ (Billings). Devonian.]
[Illustration: FIG. 45.—Rugose Corals.
_a_, _Zaphrentis Minas_ (Dn.), and _b_, _Cyathophyllum Billingsi_ (Dn.).
Carboniferous.]
Leaving the corals, we may turn to the sea-stars and sea-urchins. These
merely put in an appearance in the Early Cambrian, but become vastly
multiplied in the Silurian, where the stalked feather stars (Crinoids)
(Fig. 46) seem to have covered great areas of sea-bottom, and multiplied
so rapidly that thick sheets of limestone are largely made up of the
fragments of their skeletons. The ordinary star-fishes appear first in
the Silurian (Fig. 47). The sea-urchins begin in the Upper Silurian, the
early species having numerous and loosely attached plates, like some of
those now found in the deep sea[16] (Fig. 48).
[Illustration: FIG. 46.—Modern Crinoid (_Rhisocrinus Lofotensis_).—After
Sars.]
[Illustration: FIG. 47.—_Palæaster Niagarensis_ (Hall). One of the
oldest star fishes.]
[Illustration: FIG. 48.—_Palæchinus ellipticus_ (McCoy). One of the
oldest types of sea-urchins.]
The most curious history in this group is that of the feather-stars. In
the Early Cambrian they are represented by a few species known to us
only in fragments, and these belong to a humble group (Cystideans)
resembling the larval or immature condition of the higher Crinoids. Fig.
49 shows one of these animals of somewhat later age. They have few or
rudimentary arms and short stalks, and want the beautiful radial
symmetry of the typical star-fishes. In the Silurian these creatures are
reinforced by a vast number of beautiful and perfect feather-stars
(Figs. 50, 51). These continue to increase in number and beauty, and
apparently culminate in the Mesozoic, where gigantic forms exist, some
of them probably having more complicated skeletons, in so far as number
of distinct parts is concerned, than any other animals. Buckland has
calculated that in a crinoid similar to that in Fig. 52 there are no
less than 150,000 little bones, and 300,000 contractile bundles of
fibres to move them. In the modern seas the feather-stars have somewhat
dwindled both in numbers and complexity, and are mostly confined to the
depths of the ocean. On the other hand, the various types of ordinary
star-fishes and sea-urchins have increased in number and importance. We
thus find in this group a certain advance and improvement from the
Cystideans of the Early Palæozoic to the sea-urchins and their allies.
This advance is not, however, along one line for the Cystideans
continue unimproved to the end. The Crinoids culminate in the Mesozoic,
and are not known to give origin to anything higher. The star-fishes and
sea-urchins commence independently, before the culmination of the
Crinoids, and, though greatly increased in number and variety, still
adhere very closely to their original types.
[Illustration: FIG. 49.—_Pleurocystites squamosus_. Siluro-Cambrian.
After Billings.]
[Illustration: FIG. 50.—_Heterocrinus simplex_ (Meek). One of the least
complex crinoids of that period. Siluro-Cambrian.]
[Illustration: FIG. 51.—Body of _Glyptocrinus_. Siluro-Cambrian.]
The great sub-kingdom of the Mollusca, including the bivalve and
univalve shell-fishes, makes its first appearance in the Cambrian, where
its earliest representatives belong to a group, the Arm-bearers or Lamp
shells (Brachiopods), held by some to be allied to worms as much as to
mollusks. The oldest of all these shells are allies of the modern
_Lingulæ_ (Fig. 54), some of the earliest of which are shown in Fig.
55. The modern _Lingula_ is protected by a delicate two-valved shell,
composed, unlike that of most other mollusks, of phosphate of lime or
bone earth. It lives on sand-banks, attached by its long flexible stalk,
which it buries like a root in the bottom. Its food consists of
microscopic organisms, drifted to its mouth by cilia placed on two
arm-like processes, from which the group derives its name. In the modern
world about one hundred species of Brachiopods are known, belonging to
about twenty genera, some of which differ considerably from the Lingulæ.
The genus _Terebratula_, represented at Fig. 56, is one of the most
common modern as well as fossil forms, and has the valves unequal, with
a round opening in one of them for the stalk, which is attached to some
hard object, and there is an internal shelly loop for supporting the
arms.
[Illustration: FIG. 52.—_Extracrinus Briareus_. Reduced. Jurassic.]
[Illustration: FIG. 53.—_Pentacrinus caput-medusæ_. Reduced. Modern.]
[Illustration: FIG. 54.—_Lingula anatina_. With flexible muscular
stalk. Modern.]
[Illustration: FIG. 55.—Cambrian and Silurian Lingulæ.
_a_, _Lingulella Matthewi_ (Hartt). Acadian group. _b_, _Lingula
quadrata_ (Hall). Siluro-Cambrian. _c_, _Lingulella prima_ (Hall).
Potsdam. _d_, _Lingulella antiqua_ (Hall). Potsdam.]
These curious, and in the modern seas, exceptional shells, were dominant
in the Palæozoic period. Upwards of three thousand fossil species are
known, of which a large proportion belong to the Cambrian and Silurian,
nine genera appearing in the Cambrian, and no less than fifty-two in the
Silurian. The history of these creatures is very remarkable. The
Lingulæ, which are the first to appear, continue unchanged and with the
same phosphatic shells to the present day. Morse, who has carefully
studied an American species, remarks in illustration of this, that it is
exceedingly tenacious of life, bearing much change of depth,
temperature, etc., without being destroyed. The genus _Discina_, which
is nearly as old, also continues throughout geological time. The genus
_Orthis_ (Fig. 57), which appears at the same time with the last,
becomes vastly abundant in Silurian times, but dies out altogether
before the end of the Palæozoic. _Rhynchonella_ (Fig. 58), which comes
in a little later, near the beginning of the Siluro-Cambrian, continues
to this day. _Spirifer_ and _Productus_ (Figs. 59 and 60) appear later, and
die out at the close of the Palæozoic. So strange and inscrutable are
the fortunes of these animals, which on the whole have lost in the
battle of life, that their place in nature is vastly less important than
it was. It has been suggested that if any group of creatures could throw
light upon the theory of descent with modification, it would be these;
but Davidson, who has perhaps studied them more thoroughly than any
other naturalist, found them as silent on the subject as the sponges or
the corals. In a series of papers published in the _Geological
Magazine_, a short time before his death, he remarked as follows:
[Illustration: FIG. 56.—_Terebratula sacculus_ (Martin).
Carboniferous.]
[Illustration: FIG. 57.—Brachiopods; genus _Orthis_.
_a_, _O. Billingsi_ (Hartt). Lower Cambrian. _b_, _O. pectinella_
(Hall). Siluro-Cambrian. _c_, _O. lynx_ (Eichwald). Siluro-Cambrian.]
[Illustration: FIG. 58.—_Rhynchonella increbrescens_ (Hall).
Siluro-Cambrian.]
[Illustration: FIG. 59.—_Spirifer mucronatus_ (Conrad). Devonian.]
[Illustration: FIG. 59_a_.—_Athyris subtilita_ (Hall). Carboniferous.
_a_, _b_, Exteriors. _c_, Interior, showing spirals.]
“We find that the large number of genera made their first appearance
during the Palæozoic periods, and since they have been decreasing in
number to the present period. We will leave out of question the species,
for they vary so little that it is often very difficult to trace really
good distinctive characters between them; it is different with the
genera, as they are, or should be, founded on much greater and more
permanent distinctions. Thus, for example, the family _Spiriferidæ_
includes genera which are all characterised by a calcified spiral lamina
for the support of the brachial appendages; and, however varied these
may be, they always retain the distinctive characters of the group from
their first appearance to their extinction. The Brachiopodist labours
under the difficulties of not being able to determine what are the
simplest, or which are the highest families into which either of the two
great groups of his favourite class is divided; so far, then, he is
unable to point out any evidence favouring progressive development in
it. But, confining himself to species, he sees often before him great
varietal changes, so much so as to make it difficult for him to define
the species; and it leads him to the belief that such groups were not of
independent origin, as was universally thought before Darwin published
his great work on the _Origin of Species_. But in this respect the
Brachiopoda reveal nothing more than other groups of the organic
kingdoms.
[Illustration: FIG. 60.—_Productus cora_ (D’Orbigny). Carboniferous.]
“Now, although certain genera, such as _Terebratula_, _Rhynchonella_,
_Crania_, and _Discina_, have enjoyed a very considerable geological
existence, there are genera, such as _Stringocephalus_, _Uncites_,
_Porambonites_, _Koninckina_, and several others, which made their
appearance very suddenly and without any warning; after a while they
disappeared in a similar abrupt manner, having enjoyed a comparatively
short existence. They are all possessed of such marked and distinctive
internal characters that we cannot trace between them and associated or
synchronous genera any evidence of their being either modifications of
one or the other, or of being the result of descent with modification.
Therefore, although far from denying the possibility or probability of
the correctness of the Darwinian theory, I could not conscientiously
affirm that the Brachiopoda, as far as I am at present acquainted with
them, would be of much service in proving it. The subject is worthy of
the continued and serious attention of every well-informed man of
science. The sublime Creator of the universe has bestowed on him a
thinking mind; therefore all that can be discovered is legitimate.
Science has this advantage, that it is continually on the advance, and
is ever ready to correct its errors when fresh light or new discoveries
make such necessary.” The late Joachim Barrande, the great
palæontologist of Bohemia, bears similar testimony.
[Illustration: FIG. 61.—Group of Older Palæozoic Lamellibranchs.—After
Billings.
1, _Cucullea opima_. 2, _Nucula oblonga_. 3, _Nucula lineata_. 4,
_Cypricardia truncata_. 5, _Tellina ovata_. 6, _Nucula bellatula_. 7,
_Modiola concentrica_.]
The ordinary bivalves, like the mussels and cockles, now so very
plentiful on our coasts, are rare in the Cambrian and Silurian, and for
the first time make a somewhat conspicuous appearance in the Upper
Silurian and Devonian. But from the first they resemble very closely
their modern successors, though on the whole neither so large nor so
ornate (Fig. 61). Their fortunes have thus been precisely the opposite
of those of the Brachiopods, though in neither case is there very
marked elevation or deterioration in the individual animals. A very
similar statement may be made as to the sea-snails, whether the curious
winged snails (Pteropods) or the ordinary crawlers (Gastropods). The
former come in early, and are represented by Palæozoic forms finer than
any now extant. The genus _Conularia_ (Fig. 62) presents some Silurian
species six inches or more in length, which are giants in comparison
with any now living. The forms of more ordinary Gastropods from the
Silurian represented in Fig. 63 will suffice to show that their styles
are not very dissimilar from those still extant.[17] As in the case of
the ordinary bivalves, however, the modern Gastropods much exceed in
numbers and magnitude those of the Palæozoic.
[Illustration: FIG. 62.—_Conularia planicostata_ (Dn.). A Carboniferous
Pteropod.]
[Illustration: FIG. 63.—Silurian Sea-snails. Canada.
_a_, _Murchisonia bicincta_ (Hall). _b_, _Pleurotomaria umbilicatula_
(Hall). _c_, _Murchisonia gracilis_ (Hall). _d_, _Bellerophon
sulcatinus_ (Billings).]
The highest group of Mollusks, represented in the modern ocean by the
Nautili and Cuttle-fishes, has a history so strange and eventful, and so
different from what might have been anticipated, that it perhaps
deserves a more detailed notice, more especially as Barrande has
recently directed marked attention to it in his magnificent work on the
Palæontology of Bohemia.
The Cuttle-fishes and Squids and their allies are, in the modern seas, a
most important group (Fig. 64). The great numbers in which the smaller
species appear on many coasts, and the immense size and formidable
character of others; their singular apparatus of arms, bearing suckers,
their strange forms, and the inky secretion with which they can darken
the water, have at all times attracted popular attention. The great
complexity of their structures, and the fact that in many points they
stand quite at the head of the invertebrates of the sea, and approach
most nearly to the elevation of the true fishes, have secured to them
the attention of naturalists. Some of these animals have shelly internal
supports, and one genus, that of the Argonauts, or Paper Nautili, has an
external protective shell. Allied, though more distantly, to the
Cuttle-fishes, are the true Nautili, represented in the modern sea
principally by the Pearly Nautilus, though there are two other species,
both of them very rare. The modern pearly nautilus (Fig. 65) may be
regarded as a peculiar kind of cuttle-fish provided with a discoidal
shell for protection, and also for floatage. The shell is divided into a
number of chambers by partitions. Of these the animal inhabits the last
and largest. The others are empty, and are connected with the body of
the animal only by a pipe, or siphuncle, with membranous walls and
filled with fluid. Thus provided, the nautilus, when in the water, has
practically no weight, and can move up or down in the sea with the
greatest facility, using its sucker-bearing arms and horny beak to seize
and devour the animals on which it preys. The buoyancy of the shell
seems exactly adapted to the weight of the animal; and this proportion
is kept up by the addition of new air-chambers as the body increases in
size. In the modern seas this singular little group stands entirely
isolated, and its individuals are so rare that it is difficult to
procure perfect specimens for collections, though its mechanical
structure and advantages for the struggle for existence seem of the
highest order. But in the old world of past geological time the case was
altogether different.
[Illustration: FIG. 64.—Squid (_Loligo_).]
[Illustration: FIG. 65.—Pearly Nautilus (_Nautilus pompilius_).
_a_, Mantle. _b_, Its dorsal fold. _c_, Hood. _o_, Eye. _t_, Tentacles.
_f_, Funnel. _g_, Air chambers. _h_, Siphuncle.]
The Nautiloid shell-fishes burst suddenly upon us in the beginning of
the Siluro-Cambrian, or Lower Silurian, Barrande’s second fauna; and
this applies to all the countries where they have been studied. In this
formation alone about 450 species are known, and in the Silurian these
increase to 1,200; and here the group culminates. It returns in the
Devonian to about the same number with the Lower Silurian, diminishes in
the Carboniferous to 350, and in the Mesozoic, where the Nautiloid forms
are replaced by others of the type of the Ammonites, becomes largely
reduced. In the Tertiary there are but nineteen species, and, as already
stated, in the modern world _three_. These statements do not, however,
represent the whole truth. In the Palæozoic, in addition to the genus
_Nautilus_, we have a great number of other genera, some with perfectly
straight shells, like _Orthoceras_ (Fig. 66), others bent
(_Cyrtoceras_), others differing in the style of siphuncle, or aperture,
or chambers (_Endoceras_, _Gomphoceras_, _Lituites_, Figs. 67 to 69), or
inflated into sac-like forms (_Ascoceras_). There is, besides, the
family of the _Goniatidæ_ (Fig. 70), with the chambers thrown into
angular folds and the siphuncle at the back. Further, some of the early
forms, as the Orthoceratidæ, attain to gigantic dimensions, being six
feet or more in length, and nearly a foot in diameter. Thus the idea
that we should naturally form from the study of the Nautilus, that it
represents a type suited for much more varied and important adaptations
than those that we now see, is more than realised in those Palæozoic
ages when these animals seem to have been the lords of the seas.
[Illustration: FIG. 66.—_Orthoceras_. Siluro-Cambrian. The dotted line
shows the position of the siphuncle.]
[Illustration: FIG. 67.—_Gomphoceras._]
[Illustration: FIG. 68.—_Lituites._]
[Illustration: FIG. 69.—_Nautilus Avonensis_ (Dn.). Carboniferous.
_a_, Shell, reduced. _b_, Section, showing siphuncle.]
[Illustration: FIG. 70.—_Goniatites crenistria_ (Philips).
Carboniferous.]
[Illustration: FIG. 71.—_Ceratites nodosus_ (Schloth). Triassic.]
When we leave the Palæozoic and enter the Mesozoic, though the Nautiloid
shells still abound, we find them superseded, in great part, by a nobler
form, that of the _Ammonitidæ_ (Figs. 71, 72). These are remarkable for
the ornate markings on the surfaces of their shells, and for the
beautifully waved edges of the partitions (Fig. 72_a_), which, by giving
a much more complete support to the sides of the shell, must have
contributed greatly to the union of lightness and strength so important
to the utility of the shell as a float. This type admits of all the same
variety of straight, bent, and curled forms with the simpler Nautiloid
type, and some of the species are of great size, Ammonites being known
three feet or more in diameter. These animals, unknown in the Palæozoic,
appear in numerous species in the Early Mesozoic, culminate in hundreds
of beautiful species in the middle of that era, and disappear for ever
at its close, leaving no modern successors. Many and beautiful species
of Ammonites and their allies have been obtained from the Mesozoic rocks
of British Columbia and other parts of the west coast of North America,
perfectly representing this group as it occurs at the same period in
Europe, and closely resembling the Mesozoic Ammonites of India. These
animals have all perished, yet the Atlantic and the Pacific roll
between, apparently with conditions as favourable for their comfortable
existence as those of any previous time. They perished long ago, at the
dawn of the Tertiary; yet the genus Nautilus, one of the oldest and
least improved of the whole, survived, and still testifies to the
wonderful contrivance embodied in these animals.
[Illustration: FIG. 72.—_Ammonites Jason_ (Reinecke). Jurassic.]
[Illustration: FIG. 72_a_.—Suture of _Ammonites componens_ (Meek), of
British Columbia. Showing the complicated folding of the edges of the
chambers to give strength to the shell. Cretaceous.]
[Illustration: FIG. 73.—Cretaceous Ammonitidæ.
_a_, _Baculites_. _b_, _Ancyloceras_. _c_, _Crioceras_. _d_,
_Turrilites_.]
These are merely general considerations, but Barrande, in his _Études
Générales_, goes much farther. He sums up all the known facts in the
most elaborate manner, considering first the embryonic characters of the
shell in the different genera, then their distribution in space and
time, then all the different parts and characters of the shells in the
different groups—the whole with reference to any possible derivation of
the species; and he finds that all leads to the result that in every
respect these shells seem to have been so introduced as to make any
theory of evolution with respect to them altogether untenable. In his
concluding sentence this greatest of Palæozoic palæontologists affirms
that, “The theoretical evolution of the Cephalopods is, like that of the
Trilobites, a mere figment of imagination, without any foundation in
fact.”[18]
[Illustration: FIG. 74.—_Belemnite._—After Philips.]
[Illustration: FIG. 74_a_.—_Belemnoteuthis antiquus._ Supposed to be a
Belemnite, with soft parts preserved.—Jurassic.—After Mantell.]
I have reserved no space to notice the geological history of the other
and higher group of Cephalopods, including the true Cuttles and Squids.
This is perhaps less to be regretted, as, from the absence of external
shells, they are likely to be much less perfectly known as fossils. So
far as known, they are vastly younger than the Nautiloids, for no
examples whatever have been found in the Palæozoic. They appear
abundantly in the Mesozoic, but are there represented principally by an
extinct group of squids (Belemnites and their allies, Figs. 74, 74_a_),
remarkable for the great and complicated development of their internal
support, which has a chambered float as well as a solid sheath. This
family becomes extinct at the close of the Mesozoic, though the cuttles
as a whole perhaps culminate in the modern.
[Illustration: FIG. 75.—Cambrian Trilobites.
_a_, _Paradoxides_. _b_, _Dikellocephalus_. _c_, _Conocoryphe_ (head).
_d_, _Agnostus_ (head and tail).]
The remarkable group of the Trilobites had precedence in order of time
of the Nautiloid shell-fishes. No animal structures can well be more
dissimilar than those of the two great groups of aquatic animals which
popular speech confounds under the name of “shell-fishes.” Take a whelk
and a crab, for example, and compare their general forms, the structure
of their shells, and their organs of motion, and it is scarcely possible
to imagine any two animals more unlike; and when we examine their
anatomy in detail this difference does not diminish. They have, it is
true, corresponding parts, and these parts serve similar uses, but in
plan of structure they are wholly different. Yet both animals may live
in the same pool, and may subsist on nearly the same food. If we attempt
to find some common type which both resemble, we may trace the structure
of the crab back to those of some of the marine worms with which it has
some affinity, and those of the whelk to such creatures as the
_Lingula_, which are supposed to have a resemblance to the worms. But
still the two types, that of the Mollusk and the Articulate, are
distinct even from their first appearance in the egg, nor have either
any close affinities with the Protozoa, the Hydroids, or the Corals.
[Illustration: FIG. 76.—Transverse section of _Calymene_. A Silurian
Trilobite.—After Wolcott.
_a_, Dorsal shell. _b_, Visceral cavity. _c_, Legs. _d_,
Epipodite—gill-cleaner or palp. _e_, Spiral gills.]
Both types meet us in the Early Cambrian, but while the Mollusk is there
represented only by low forms, the Articulate is then not only in the
humble guise of the worm, but in the complex and highly organised form
of the Trilobite (Figs. 28 and 75). What older phases they may have
passed through we know not; but in the Lower Cambrian we have various
forms of these animals, including some of the largest known as well as
some of the smallest; some of the most complex in number of parts as
well as some of the simplest. These animals, in short, seem to have
appeared at once all over the world fully formed, and in a variety of
generic and specific forms; and nothing short of a very large faith in
the imperfection of the geological record can suffice to account for
their evolution.
[Illustration: FIG. 76_a_.—Burrows of Trilobite and of modern
King-crab. The Trilobite burrow is known as Ruschinites, and has been
supposed to be a sea-weed of the kind called _Bilobites_.]
A Trilobite is a creature in whose structure the number three is
dominant. Seen from above, it presents three divisions from front to
rear:—first, a cephalic shield or head-piece; secondly, a thorax,
divided into several segments movable upon each other; and thirdly, a
tail-piece or pygidium, which, when brought against the head by the
rolling up of the body segments, effectually covers the lower parts.
This lower portion was until lately little known; but the discoveries of
Billings and of Wolcott have enabled us to restore the jaws under the
head, the jointed legs and spiral gills under the thorax, and thus to
complete the structure of the animal, and understand better its
relations to modern crabs and shrimps (Fig. 76). Of these it certainly
comes nearest to the King-crabs and Horseshoe-crabs, a somewhat limited
group at present, and one which reaches back in geological time only to
the Upper Silurian, when the Trilobites had perhaps already passed their
culmination.
Constructed as above described, the Trilobite could swim, as is
supposed, usually on its back or side. It could crawl on the bottom.
Using its snout as a shovel, it could burrow like a modern King-crab
(Fig. 76_a_); and when pressed by danger some species could roll
themselves into balls and defy their enemies.
[Illustration: FIG. 77.—Silurian Trilobites.
_a_, _Isotelus_. _b_, _Homalonotus_. _c_, _Calymene_.]
This type of animal, entering on the stage in full force in the Older
Cambrian, continues under many forms through the whole Palæozoic age,
dying out finally in the Carboniferous. Figs. 77 and 78 show a few of
the forms of the Silurian, Devonian, and Carboniferous.
Contemporaneously with the dawn of the Trilobite group, appear some
small shrimp-like forms (Fig. 28),[19] and others with bivalve shells
(Fig. 79), which are closely allied to modern forms,[20] and, like the
_Lingulæ_, persist through the succeeding formations with little more
than specific change—presenting in this a strange contrast to the
Trilobites. While the latter were still flourishing, about the close of
the Lower Silurian, a remarkable group of large and highly-developed
creatures, allied to the Trilobites, but suited for rapid swimming
rather than creeping, was introduced; and in the Upper Silurian and
Devonian these creatures[21] attained to gigantic sizes, exceeding,
probably, any modern Crustaceans, and were tyrants of the seas.
_Pterygotus anglicus_ (Fig. 80) is supposed to have attained the length
of six feet. Yet these noble representatives of the Crustaceans became
extinct in the Carboniferous. On the other hand, a few small king-crabs
appear in the Upper Silurian, and this type still continues, and seems
to culminate as to size in modern times; so diverse have been the
fortunes of these various groups.
[Illustration: FIG. 78.—Devonian and Carboniferous Trilobites.
_a_, _Phaceps latifrons_ (Bronn). _b_, _Philipsia Howi_ (Billings)
(tail).]
[Illustration: FIG. 79.—Palæozoic Ostracod Crustaceans. Magnified.
_a_, _Bairdia_. _b_, _Cytherella inflata_ (Jones). _c_, _Cythere_.
Carboniferous. _d_, _Beyrichia Jonesii_ (Dn.). Carboniferous. _e_,
_Beyrichia pustulosa_ (Hall). Silurian.]
The higher, or decapod Crustaceans, now familiar to us in the modern
crabs and lobsters, are first found in a few small species in the
Devonian[22] and Carboniferous, and they are accompanied in the Devonian
by at least one species of the allied group of the Stomapods (Figs. 81,
82).
[Illustration: FIG. 80.—_Pterygotus anglicus_. Reduced.—After Page and
Woodward.]
[Illustration: FIG. 81.—_Amphipeltis paradoxus_ (Salter). A Devonian
Stomapod from New Brunswick.]
[Illustration: FIG. 82.—_Anthropalæmon Hilliana_ (Dn). A Carboniferous
Decapod from Nova Scotia. The carapace only.]
The Palæozoic age of geology is thus emphatically an age of
invertebrates of the sea. In this period they were dominant in the
waters, and until toward its close almost without rivals. We shall find,
however, that in the Upper Silurian, fishes made their appearance, and
in the Carboniferous amphibian reptiles, and that, before the close of
the Palæozoic, vertebrate life in these forms had become predominant.
We shall also see that just as the leading groups of Mollusks and
Crustaceans seem to have had no ancestors, so it is with the groups of
Vertebrates which take their places. It is also interesting to observe
that already in the Palæozoic all the types of invertebrate marine life
were as fully represented as at present, and that this swarming marine
life breaks upon us in successive waves as we proceed upward from the
Cambrian. Thus the progress of life is not gradual, but intermittent,
and consists in the sudden and rapid influx of new forms destined to
increase and multiply in the place of those which are becoming effete
and ready to vanish away or to sink to a lower place. Farther, since the
great waves of aquatic life roll in with each great subsidence of the
land, a fact which coincides with their appearance in the limestones of
the successive periods, it follows that it is not struggle for
existence, but expansion under favourable circumstances and the opening
up of new fields of migration that is favourable to the introduction of
new species. The testimony of palæontology on this point, which I have
elsewhere adduced at length,[23] in my judgment altogether subverts the
prevalent theory of “survival of the fittest,” and shows that the
struggle for existence, so far from being a cause of development and
improvement, has led only to decay and extinction, whereas the advent of
new and favourable conditions, and the removal of severe competition,
are the circumstances favourable to introduction of new and advanced
species. This testimony of the invertebrates of the sea we shall find is
confirmed by other groups of living beings, to be noticed in the
sequel.[24]
* * * * *
NOTE.—The term “Siluro-Cambrian,” as used in this and the next chapter,
is synonymous with “Ordovician” of Lapworth, which is now coming into
somewhat general use.
[Illustration: CORDAITES, OF THE GROUP OF DORY-CORDAITES. BRANCH
RESTORED.—After Grand’ Eury.]
CHAPTER IV.
THE ORIGIN OF PLANT LIFE ON THE LAND.
If the graphite of the Laurentian rocks was derived from vegetable
matter, the further question arises, Was this vegetation of the land, or
of the sea? and something may be said on both sides of this question. If
there were land plants in the Laurentian period, they must have grown
either on rocks older than the Laurentian itself, or on such portions of
the beds of the latter as had been raised out of the sea, forming
perhaps swampy flats of newly-made soil. But we know no rocks older than
the Laurentian, and there is no positive evidence that any of the beds
of that formation were other than marine. Still it is not impossible
that some of the beds which are now graphitic gneisses may originally
have been similar to the bituminous shales, coals, or under-clays of the
coal formation. The graphite occurring in veins, if of vegetable origin,
must have been derived from liquid bitumen oozing into fissures; and
veins of this kind occur in later formations, both in marine and
fresh-water beds. The only other positive argument which has been
adduced in favour of the existence of abundant land plants in the
Laurentian is that of Dr. Sterry Hunt, derived from the great beds of
iron ore, which it is difficult to account for chemically except on the
hypothesis of the decay in the air of great quantities of vegetable
matter. The question must remain in doubt till some one is fortunate
enough to find portions of the Laurentian carbon retaining traces of
organic structure. My own observations, though somewhat numerous, allow
me only to say that the graphite sometimes presents fibrous forms, that
it occasionally appears as vermicular threads—which, however, I suppose
to be fillings of canals of _Eozoon_—and that in the graphitic beds there
are occasionally slender root-like bodies of a lighter colour than the
mass; but none of these indications are sufficient to determine anything
as to its vegetable origin, or the nature of the plants from which it
may have been derived.
In any case, the quantity of carbon which has been accumulated in the
Laurentian rocks is very great. I have measured one bed at Buckingham,
on the Ottawa, estimated to contain 20 per cent. of carbon, and which is
at least eight feet in thickness. Sir William Logan has described
another similar bed from ten to twelve feet thick, and more recent
reports of the Geological Survey of Canada mention a bed supposed to be
twenty-five feet thick, in which Mr. Hoffman finds 30 per cent. of
carbon. On the whole the quantity of carbon in the graphitic zone of the
Laurentian is comparable with that in certain productive coal-fields,
and we certainly have in the subsequent geological history no examples
of such accumulations except from remains of the luxuriant vegetation of
swampy flats.
The Upper Laurentian and Huronian have as yet afforded no evidence of
land vegetation. The Cambrian, as already stated, abounds in remains of
sea-weeds; but though the forms which have been named _Eophyton_ have
been regarded as land plants, this claim is, to say the least, very
doubtful; and I have as yet seen nothing of this kind which did not
appear to me to be merely markings made by objects drifted over the
bottom or remains of marine plants. Yet in the Upper Cambrian there are
wide surfaces of littoral sandstone often containing minute carbonised
fragments, and which might be expected to afford indications of land
vegetation, had such existed. I have myself devoted many days of
fruitless labour to the examination of the large areas of Potsdam
sandstone exposed in some parts of Canada. But as these rocks were
evidently formed along the borders of a Laurentian continent capable of
supporting vegetation, we may still hope for some discovery of this
kind, more especially if we could find the point where some fresh-water
stream ran into the Cambrian sea.
[Illustration: FIG. 83.—_Protannularia Harknessii_ (Nicholson). A
Siluro-Cambrian Plant, from the Skiddaw series.]
The oldest plants, probably higher than Algæ, known to me by their
external forms, are those described by Nicholson[25] from the
Siluro-Cambrian Skiddaw slates of the north of England (Fig. 83). Their
discoverer has named them _Buthotrephis Harknessii_ and _B.
radiata_,[26] stating, however, that these two species are not
improbably portions of the same plant, and that its form is rather that
of a land plant than of an Alga. The specimens of these plants which I
have seen appear to me to support the conclusion that they represent one
species, and this allied to the _Annulariæ_ of the Devonian and
Carboniferous periods, which probably grew in shallow water with only
their upper parts in the air, and bore whorls or verticles of narrow
leaves. They were either relatives of the Mare’s-tails, or of the
Rhosocarps, of our modern swamps and ponds.
[Illustration: FIG. 84.—American Lower Silurian Plants.—After
Lesquereux.
_a_, _Sphenophyllum primævum_. _b_, _Protostigma sigillarioides_.]
Somewhat higher up in the Lower Silurian, in the Cincinnati group of
America, Lesquereux finds objects which he refers to the genus
_Sphenophyllum_, which is closely allied to _Annularia_ (Fig. 84, _a_),
and also a plant which he terms _Protostigma_ (Fig. 84, _b_), and
believes to be the stem of a tree allied to the club-mosses.[27] He also
finds minute branching stems, which he refers to the genus
_Psilophyton_, to be mentioned in the sequel; but as to these I have
some doubts whether they may not be Zoophytes allied to the Graptolites,
rather than plants of that genus. These discoveries tend to show the
probable existence in the Siluro-Cambrian of plants representing two of
the three leading families of the higher cryptogams or flowerless
plants, namely, the Club-mosses and the Mare’s-tails. Thus land
vegetation begins with the highest members of the lower of the two great
series into which botanists divide the vegetable kingdom.
[Illustration: FIG. 86.—Fragment of outer surface of _Glyptodendron_ of
Claypole. A Silurian Tree.]
If we now turn to the Silurian, further evidence of land vegetation
presents itself. Near the base of this great series, the club-moss
family is represented by a plant discovered by Claypole in the Clinton
group, and referred to a new genus (_Glyptodendron_, Fig. 86). Plants of
this family have also been noticed by Barrande in Bohemia, and by page
in Scotland; and a humble but interesting member of the family,
connecting it with the pillworts, _Psilophyton_ (Fig. 87), though more
characteristic of the Devonian, has been found in the Upper Silurian
both in Canada and the United States. No Ferns or Equiseta have as yet
been found in the Silurian; but in 1870 I recognised in some fragments
of wood from the Ludlow bone-bed, in the Museum of the Geological Survey
of Great Britain, the structure of that curious prototypal tree, to
which I have given the name _Nematophyton_, and which was first
recognised in the Devonian of Gaspé. Since that time I have found in the
Upper Silurian beds of Cape Bon Ami, in New Brunswick, similar fragments
of fossil wood, associated with round seed-like bodies, having a central
nucleus and a thick wall or test of radiating fibres. These bodies show
a structure similar to that of those found in the Upper Ludlow of
England, and described by Hooker under the name _Pachytheca_. In my
judgment they are certainly true seeds.[28] Seeds of this kind have also
been found by Hicks in the still older Denbighshire grits of North
Wales, along with fragments of the wood of _Nematophyton_, and with
remains of branching stems which have been described under the name
_Berwynia_, though it is not unlikely that they represent the branches
of _Nematophyton_. It is proper to add that these ancient vegetable
fossils are regarded by some English botanists as gigantic algæ or
sea-weeds, but I confess I am unable to adopt this view of their nature.
The supposed fern of the Upper Silurian, figured in the first edition of
this work, has proved on further examination to be merely an imitative
form produced by crystallisation. On the other hand, the recent
discovery of a cockroach and two species of Scorpion in the Silurian,
proves the existence of land animals as well as plants at this period.
[Illustration: FIG. 87.—_Psilophyton princeps_ (Dn.) Silurian and
Devonian. Restored.
_a_, Fruit, natural size. _b_, Stem, natural size. _c_, Scalariform
tissue of the axis, highly magnified. In the restoration one side is
represented in vernation, and the other in fruit.]
It is probable that these discoveries represent merely a small
proportion of the plants actually existing in the Silurian period. All
the deposits of this age at present known to us are marine; and most of
them were probably formed at a distance from land, so that it is little
likely that land plants could find their way into them. At any time the
discovery of an estuarine or lacustrine deposit of Silurian age might
wonderfully extend our knowledge of this ancient flora.
The Devonian or Erian age, that of the classic Old Red Sandstone of
Scotland, is that in which we find the first great and complete land
flora; and though this is inferior in number of species to that of the
succeeding Carboniferous, and greatly less important with reference to
its practical bearing on our welfare, it is in some respects superior in
that variety which depends on diversity of soil and of station. To
appreciate this, it will be necessary to glance at the range and
subdivisions of the modern flora.
In the modern world we divide all vegetation into two great series, that
of the Flowering Plants (_Phænogams_), which also produce true fruits
and seeds, and that of the Flowerless Plants (_Cryptogams_), which
produce minute spores instead of seeds. The latter is in every respect
the lower group. This lower series is again divisible into three
classes—first and lowest, that of the Seaweeds, Moulds, and Lichens
(Thallophytes). Secondly, that of the Mosses and their allies
(Anophytes). Thirdly, that of the Ferns, Equisetums and Club-mosses
(Acrogens). In like manner the second, or higher series is divisible
into three classes: that of the Pines and Cycads (Gymnosperms), having
naked seeds not covered by true fruits, and woody tissue of simple
structure; that of the Palms and Grasses and their allies (Endogens);
and last and highest, that of the ordinary timber trees and other plants
allied to them, with exogenous stems, netted-veined leaves, and a
two-leaved embryo (Exogens). These last are in every respect the
dominant plants on our present continents. Carrying with us this twofold
division of the vegetable kingdom and its subdivisions, we shall be
prepared to understand the relation of the more ancient floras to that
now living.
[Illustration: FIG. 88.—Trunk of a Devonian Tree-fern (_Caulopteris
Lockwoodi_, Dn.). Gilboa, New York. One-third natural size.]
[Illustration: FIG. 89.—Frond of _Archæopteris Jacksoni_ (Dn.).
Devonian, of Maine.]
[Illustration: FIG. 90.—Portion of a branch of _Leptophleum rhombicum_
(Dn.). A Lycopodiaceous tree of the Devonian of Maine. Natural size.]
[Illustration: FIG. 91.—_Calamites radiatus_ (Brongniart). Middle
Devonian of N. Brunswick.]
In the Devonian age we meet with no land plants of the two lower
classes of the Cryptogams, and with scarcely any that can be referred to
the two higher classes of Phænogams, so that the vegetation of this
period presents a remarkable character of mediocrity, being composed
almost entirely of the highest class of the flowerless plants and the
lowest class of those that flower. Of the former there are Tree-ferns
and vast numbers of herbaceous forms (Figs. 88, 89), great
Lycopodiaceous plants, immensely better developed than those now
existing (Fig. 90), and gigantic _Calamites_, allied to the Mares’-tails
(Fig. 91), along with humbler members of the same group (Fig. 95). Of
the latter there were Pines of great stature, known to us at present
only by their wood (Fig. 92); and that other allied trees existed we
have evidence in numerous seeds which must have belonged to this class
(Fig. 93), and in long flag-like leaves[29] which modern discoveries
would refer to the same group. As yet we know no Devonian Palms or
Grasses; and only a single specimen has been found indicating the
existence of a plant of the highest vegetable class, that of the true
exogens. This unique specimen, found by Hall in the Devonian of the
shores of Lake Erie, is a fragment of mineralised wood, the structures
of which are represented in Fig. 94. The large ducts seen in cross
section in Nos. 1, 2, and 3, and in longitudinal section in Nos. 4 and
5, and the medullary rays, seen in Nos. 1, 4, and 6, testify to the fact
that this chip of wood must have belonged to a tree of the same type
which contains our oaks, maples, and poplars; a type which does not
appear to have become dominant till near the close of the Mesozoic, but
which already existed, though perhaps only in few species, and only in
upland and inland positions, as far back as the Middle Devonian. Perhaps
one of the most interesting discoveries in the Erian or Devonian rocks
has been that of the immense abundance of spores of those humble plants
the Rhizocarps, represented in modern times by the Pillworts and
Salviniæ, &c. To these it is believed that _Sphenophyllum_ and
_Psilophyton_ were allied; but in addition to this there are thick and
vastly extended beds of bituminous shale which owe their inflammable
properties to countless multitudes of Macrospores (_Sporangites_) of the
genus _Protosalvinia_.[30] In Ohio there are beds of this kind 350 feet
thick, and extending across the State. They occur also in Canada, where
these forms were first recognised by the writer in the bituminous shale
of Kettle Point, Lake Huron.
[Illustration: FIG. 92.—A Devonian Taxine Conifer (_Dadoxylon
ouangondianum_, Dn.). St. John, New Brunswick.
A, Fragment showing _Sternbergia_ pith and wood; _a_, Medullary sheath;
_b_, Pith; _c_, Wood; _d_, Section of pith.
B, Wood cell _a_, and hexagonal areole and pore _b_.
C, Longitudinal section of wood, showing _a_, Areolation, and _b_,
Medullary rays.
D, Transverse section showing _a_, Wood-cells, and _b_, Limit of layer
of growth.]
[Illustration: FIG. 93.—Group of Devonian Fruits, &c. Middle Devonian,
New Brunswick.
A, _Cardiocarpum cornutum_.
B, _Cardiocarpum acutum_.
C, _Cardiocarpum Crampii_.
D, _Cardiocarpum Baileyi_.
E, _Trigonocarpum racemosum_.
E¹, E², Fruits enlarged.
F, _Antholithes Devonicus_.
F¹, Fruit of the same.
G, _Annularia acuminata_.
H, _Asterophyllites acicularis_.
H¹, Leaf.
K, _Cardiocarpum_. (? young of A.)
L, _Pinnularia dispalans_.
From _Acadian Geology_. ]
[Illustration: FIG. 94.—Structures of the oldest-known Angiospermous
Exogen (_Syringoxylon mirabile_, Dn.). From Eighteen-mile Creek, Lake
Erie.
1, Transverse section x 100.
2 and 3, Portions of the same x 300.
4, Longitudinal section x 300.
5, Fragment of duct from the same x 600.
6, Wood cells and medullary ray x 600.]
The Devonian flora seems to have been introduced in the northern parts
of the American continent at a time of warm and equable climate, and of
elevation of new land out of the Silurian sea. It spread itself to the
southward, and was finally destroyed in the great subsidences and
disturbances which closed the Devonian age, and which were probably
accompanied with refrigeration of climate. It was succeeded by the more
massive and richer, but more monotonous flora of the Carboniferous, a
period in which large areas of our continents were in the state of
swampy and often submerged flats, and in which the climate was again
warm and uniform.
[Illustration: FIG. 95.—_Asterophyllites parvula_ (Dn.), and
_Sphenophyllum antiquum_ (Dn.). Middle Devonian, New Brunswick.]
The Carboniferous age was, even more emphatically than the Devonian, an
age of Acrogens and Conifers. A few Carboniferous Fungi have recently
been discovered, but there are no known Lichens or Mosses. There seem to
be a few Endogens, but no true Exogens. The great bulk of the plants
consists of Acrogens and Gymnosperms, as in the previous period. As this
flora is so very important and so much better known than any other of
those belonging to the infancy of the vegetable kingdom, we may notice a
little in detail some of its leading forms.
[Illustration: FIG. 96.—_Calamites._ Carboniferous.
A, _C. Suckovii_. B, _C. Cistii_ (Bt.). C, Base of _Calamites_. D, E,
Structures.
From _Acadian Geology_.]
[Illustration: FIG. 97.—Carboniferous Ferns.
A, _Odontopteris subcuneata_ (Bunbury).
B, _Neuropteris cordata_ (Brongniart).
C, _Alethopteris tonchitica_ (Brongniart).]
Beginning with the Mares’-tails, we find these represented in the
Carboniferous by many gigantic species, attaining to almost tree-like
dimensions (Fig. 96). These are the _Calamites_, which formed dense brakes
and jungles on the margins of the great swampy flats of this period.
Their tall stems, ribbed and jointed, bore whorls of leaves or
branchlets. Sending out horizontal root-stocks and budding out from the
base, they grew in great clumps, and had the capacity to resist the
effects of accumulating sediment by constantly sending out new stems at
higher and higher levels. The larger species assumed a complexity in the
structure of their stems unknown in their modern congeners, and enabling
them to grow to a great height;[31] but their foliage and fructification
were not correspondingly advanced. Thus the family of the Equisetaceæ
culminated in the Carboniferous, and thenceforth descended gradually in
the succeeding ages, leaving the comparatively humble Mares’-tails and
Scouring Rushes as its present representatives.
The Ferns of the Carboniferous, like those of the Devonian, presented
both gigantic forms like those of the tree-ferns of the modern tropics,
and delicate herbaceous species, and these in great profusion. On the
whole, they do not strike the observer as very dissimilar from those of
modern times. A more critical examination, however, shows that the bulk
of the tree-ferns of the Devonian and Carboniferous are allied not to
the Polypod type, which is the most common at present, but to certain
comparatively rare southern ferns, the _Marattias_ and their allies,
characterised by a peculiar style of fructification, perhaps adapting
them to a moist and warm atmosphere (Fig. 97).[32] Thus the ferns, while
a wonderfully persistent type, were in their grander forms far more
widely distributed in the Carboniferous than at present; and genera now
comparatively rare, and limited to warm and moist climates, were then
abundant, and ranged over those temperate and boreal regions of the
Northern Hemisphere where only a few humble and hardy species can now
subsist. There were also some remarkable and anomalous tree-ferns, of
which that represented in Fig. 98 is an example.
[Illustration: FIG. 98.—Carboniferous Tree-ferns.
A, _Megaphyton magnificum_ (Dn.).
C, _Palæopteris Hartii_ (Dn.).
D, _P. Acadica_ (Dn.).]
The family of the Club-mosses, already, even in the Devonian, in advance
of its modern development, experiences in the Carboniferous a remarkable
and portentous extension into great trees of several genera and many
species, constituting apparently extensive forests, and having the woody
tissues of their stems developed to a degree unheard of in their present
representatives (Fig. 99). Further, they become closely linked, in
external form at least, with another and more advanced type, that of the
_Sigillariæ_. These remarkable trees were the most abundant of all in
the swamps of the coal-formation, and probably those which most
contributed to the accumulation of coal. They presented tall pillar-like
trunks, often ribbed longitudinally, and with perpendicular rows of
scars of fallen leaves. Dividing at top into a few thick branches, they
were covered with long rigid grass-like foliage. Their fruit was borne
in rings or whorls of spikes surrounding the branches at intervals (Fig.
100). Their roots were strangely symmetrical, spreading out like
underground branches into the soft soil by a regular process of
bifurcation, and were covered with rootlets diverging in every
direction, and so jointed to the main root that when broken off they
left round marks regularly arranged. These roots are the so-called
_Stigmariæ_, so abundant in every coal-field, and especially filling the
“under-clays” of the coal-beds, which are the soils on which the plants
forming these beds were supported. The true botanical position of the
_Sigillariæ_ has been a matter of much controversy. Some of them
undoubtedly have structures akin to those of the tree-like Club-mosses,
as Williamson has well shown, and may have been cryptogamous. Others
have structures of higher character, akin to those of the modern Cycads,
and seem to have borne nutlets allied to those of these plants. Yet the
external forms of these diverse sorts are so similar that no definite
separation of them has yet been made. Either these anomalous trees
constitute a link connecting the two great series of the vegetable
kingdom, or we have been confounding two distinct groups, owing to
imperfect information.
[Illustration: FIG. 99.—_Lepidodendron corrugatum_ (Dn.). A
characteristic Lycopod of the Lower Carboniferous of America.
A, Restoration.
B, Leaf, natural size.
C, Cone. D, Leafy branch.
E, Forms of leaf-bases.
F, Sporangium.
I, L, M, N, O, Markings on stem and branches, in various states.]
[Illustration: FIG. 100.—_Sigillariæ_ of the Carboniferous.
A, _Sigillaria Brownii_ (Dn.).
B, _S. elegans_ (Brongniart).
B¹, &c. Leaf and Leaf-scars.]
Another curious, and till recently little understood, group of
Carboniferous trees is that known as _Cordaites_, which existed already
in some of its species in the Devonian. Their leaves are long, and often
broad as well, and with numerous delicate parallel veins, resembling in
this the leaves of grasses. Corda long ago showed that one species at
least has a stem allied to the Club-mosses. More recently Grand’ Eury
has found in the South of France admirably preserved specimens, which
show that others more resembled in their structure the Pines and Yews,
and were probably Gymnosperms, approaching to the Pines, but with very
peculiar and exceptional foliage, of which the only modern examples are
the broad-leaved Pines of the genus _Dammara_ (Frontispiece to Chapter).
Here again we have either two very distinct groups, combined through our
ignorance, or a connecting link between the Lycopods and the Pines.
[Illustration: FIG. 101.—_Trigonocarpum Hookeri_ (Dn.). A Gymnospermous
seed.
_a_, Testa. _b_, Tegmen. _c_, Nucleus. _d_, Embryo.]
The Yews and their allies among modern trees, while members of the great
Cone-bearing order, bear nut-like seeds in fleshy envelopes, sometimes,
as in the Gínkgo of Japan, constituting edible fruits. Seeds of this
type seem to have been extremely abundant in the Carboniferous age in
all parts of the world, and were probably produced by trees of several
genera (_Dadoxylon_, _Sigillaria_, _Cordaites_, etc.) (Fig. 101).
Charles Brongniart has recently described no less than seventeen genera
of these seeds from the coal-field of St. Étienne alone, and it would be
a low estimate to say that we probably know as many as sixty or seventy
species in all, while the trunks of great coniferous trees allied to
Taxineæ, and showing well-preserved structure, are by no means uncommon
in the Devonian and Carboniferous. Had these great Yews appeared for the
first time in the Coal-formation, we might have supposed that they had
been developed from such Lycopods as _Lepidodendra_, and that the
_Cordaites_ are the intermediate forms; but unfortunately the Pines go
almost as far back in geological time as the Lycopods, and it does not
help us, when in search of evidence of evolution, to find the link which
is missing or imperfect in the Early Devonian supplied in the
Coal-formation, where, for this purpose at least, it is no longer
needed.
We have said something of what was in the Palæozoic flora; but what of
that which was not? We may answer:—Nearly all that is characteristic of
our modern forests, whether in the ordinary Exogens, which predominate
so greatly in the trees and shrubs of temperate climates, or in the
Palms and their allies, which figure so conspicuously within the
tropics. The few rare, and to some extent doubtful, representatives of
these types scarcely deserve to be noted as exceptions. Had a botanist
searched the Palæozoic forests for precursors of the future, he would
probably have found only a few rare species, while he would have seen
all around him the giant forms and peculiar and monotonous foliage of
tribes now degraded in magnitude and structure, and of small account in
the system of nature.
It must not be supposed that the Palæozoic flora remained in undisturbed
possession of the continents during the whole of that long period. In
the successive subsidences of the continental plateaux, in which the
marine limestones were deposited, it was to a great extent swept away,
or was restricted to limited insular areas, and these more especially in
the far north, so that on re-elevation of the land it was always peopled
with northern plants. Thus there were alternate restrictions and
expansions of vegetation, and the latter were always signalised by the
introduction of new species, for here, as elsewhere, it was not
struggle, but opportunity, that favoured improvement.
In the Lower Silurian such plants as existed must have experienced great
restriction at the age of the Niagara or Wenlock limestone. Those of the
Upper Silurian suffered a similar reverse at the time of the Lower
Helderberg or Ludlow limestones. This recurred at the close of the
Devonian and in the time of the Lower Carboniferous limestone; and
finally the Palæozoic flora disappeared altogether in the Permian, to be
replaced by new types in the Mesozoic. While, therefore, there is a
great general similarity in the successive Palæozoic floras, there are
minor differences, so that the Devonian plants are for the most part
distinct specifically from those of the Lower Carboniferous, those of
the Lower Carboniferous from those of the Coal-formation, and those of
the latter from those of the Permian.
With all these vicissitudes it is to be observed that there is no
apparent elevation of type in all the long ages from the Devonian to the
Permian, that the Acrogens and Gymnosperms of these periods are in some
respects superior, in all respects equal, to their modern successors,
and that their history shows a decadence toward the modern period; that
intermediate forms arrive too late to form connecting links in time,
that several distinct types appear together at the beginning, and that
all utterly and apparently simultaneously perish at the end of the
Palæozoic, to make way for the entirely new vegetation of the succeeding
age. Theories of evolution receive no support from facts like these,
though their practical significance, as parts of the one great uniform
scheme of nature, is sufficiently manifest.
Of what use then were these old floras? To the naturalist, vegetable
life, with regard to its modern uses, is the great accumulator of
pabulum for the sustenance of the higher forms of vital energy
manifested in the animal. In the Palæozoic this consideration sinks in
importance. In the Coal period we know few land animals, and these not
vegetable feeders, with the exception of some insects, millipedes, and
snails. But the Carboniferous forests did not live in vain, if their
only use was to store up the light and heat of those old summers in the
form of coal, and to remove the excess of carbonic acid from the
atmosphere. In the Devonian period even these utilities fail, for coal
does not seem to have been accumulated to any great extent, and the
petroleum of the Devonian appears to have been produced from aquatic
vegetation. Even with reference to theories of evolution, there seems no
necessity for the long continuance and frequent changes of species of
acrogenous plants without any perceptible elevation. We may have much
yet to learn of the life of the Devonian; but for the present the great
plan of vegetable nature goes beyond our measures of utility; and there
remains only what is perhaps the most wonderful and suggestive
correlation of all, namely, that our minds, made in the image of the
Creator, are able to trace in these perished organisms structures
similar to those of modern plants, and thus to reproduce in imagination
the forms and habits of growth of living things which so long preceded
us on the earth. We may indeed proceed a step further, and hold that,
independently of human appreciation, these primitive plants commended
themselves to the approval of their Maker, and perhaps of higher
intelligences unknown to us; and that in the last resort it was for His
pleasure that they were created.
[Illustration: PTERASPIS. RESTORED.—AFTER LANKESTER.]
CHAPTER V.
THE APPEARANCE OF VERTEBRATE ANIMALS.
Confessedly the highest style of animal is that which possesses a skull
and backbone, with brain and nerve system to match, and which embodies
the general plan of structure employed in man himself. Yet among the
fishes, which constitute the lowest manifestation of this type, are some
so rudimentary that the brain is scarcely developed, and the skeleton is
merely a cord of gristle. These are represented in the modern world only
by the Lancelot,[33] a creature which has sometimes been mistaken for a
worm, and by a slightly more advanced type, that of the Lampreys.[34] In
these animals the Vertebrates make the nearest approach to the lower
domains of the animal kingdom, collectively known as Invertebrates. We
should naturally expect that since the vertebrates succeed the inferior
animals in time, their lower types should appear first, and that these
should be aquatic rather than terrestrial. On the other hand, as the
oldest fishes that are certainly known are strongly protected with bony
armour, and had to contend against formidable Crustaceans and Cuttles,
we might suppose that the Lancelot and the Lampreys are rather degraded
types belonging to the modern period, than the true precursors of the
other fishes.
[Illustration: FIG. 102.—Siluro-Cambrian Conodonts. Magnified.—After
Pander.]
But if fishes like the Lancelot preceded all others, we may never find
in a fossil state any traces of their soft and perishable bodies; and
even the Lampreys have no hard parts except small horny teeth, which
might easily escape observation. But palæontologists have sharp eyes,
and it has not escaped them that certain microscopic tooth-like bodies
are somewhat widely distributed in the older rocks. In Russia, Pander
has found in the Upper Cambrian and Lower Silurian, and also in the
Devonian and Carboniferous, minute conical and comb-like teeth, to which
he has given the name of _Conodonts_ (Fig. 102), and which he supposes
to be the teeth of ancient Lampreys. Similar teeth have been found by
Moore and others in the Carboniferous of England, and by Newberry in
Carboniferous shales in Ohio. In point of form, these bodies certainly
resemble the teeth of the humble fishes to which they have been
referred. In the case of the Carboniferous specimens from Ohio—the only
ones I have had an opportunity to examinethe material is calcium
phosphate, and the structures are more like those of teeth of Sharks
than of Lampreys, so that there can be no doubt that they are really
teeth of fishes, and probably of fishes of somewhat higher grade than
the Lampreys.[35] The Cambrian and Silurian specimens are said to be
composed of calcium carbonate, which would render it more probable that,
as has been suggested by Prof. Owen, they may have been teeth of some
species of Sea-snail destitute of shell. It is, however, possible that
they may have originally been horny, and that the animal matter has been
replaced by carbonate of lime. Rohon and Zittel have recently shown that
many of these are more allied to the teeth of worms than of any other
animals.[36]
[Illustration: FIG. 103.—Lower Carboniferous Conodont.
Magnified.—After Newberry.]
If these older Conodonts were really teeth of fishes, they carry the
introduction of these nearly as far back as that of the Mollusks and
Crustaceans. If they were not, then the earliest known representatives
of this class belong to a much later age, that of the Silurian. Here we
have undoubted remains of fishes belonging to two of the higher orders
of the class; and in the succeeding Devonian these became multiplied and
extended exceedingly.
Besides the inferior tribes already referred to, the modern seas and
rivers present four leading types of fishes:—first, the ordinary bony
fishes (Teleostians), such as the Cod, Salmon, and Herring; secondly,
the Ganoid fishes, protected with bony plates on the skin, as the
Bony-pike[37] and Sturgeon; thirdly, the Sharks and their allies, the
Dog-fishes and Rays; fourthly, the peculiar and at present rare group of
semi-reptilian fishes to which the name of _Dipnoi_ has been given, on
account of their capacity for breathing both in air and in water.
Of these four types the first is altogether modern, and includes the
great majority of our present fishes. It does not make its appearance
till the Cretaceous age, and then is at once represented by at least
three of the modern families, those of the Salmon, Herring, and Perch.
The history of the other three groups is precisely the opposite of this.
They abound exceedingly at an early period, and dwindle to a much
smaller number in the modern time. This is especially the case with the
Ganoids and the Dipnoi. It is also remarkable that these groups of
old-fashioned fishes[38] are in some respects the highest members of the
class, approaching the nearest to the reptiles; but this accords with a
well-known palæontological law, namely, that the higher members of low
groups give way on the introduction of more elevated types, while the
lower members may continue. Thus the decadence of these higher fish
begins with the incoming of the reptiles, just as the decadence of the
higher Mollusks and predaceous Crustaceans began with the incoming of
the fishes. Further, the modern Ganoids and Dipnoi are mostly
fresh-water animals, though the Sharks are largely pelagic. In the
Palæozoic there seem to have been abundance of marine species of all
these types; but though marine, they probably flourished most in bays
and estuaries and on shallow banks; and the existence of these implies
continental masses of land. This explains the curious coincidence that
the introduction of fishes and of an abundant land flora synchronise,
and that the ocean was still dominated by Invertebrates long after the
fishes had become supreme in bays, estuaries, and rivers.
[Illustration: FIG. 104.—_a_, Head-shield of an Upper Silurian fish
(_Cyathaspis_). _b_, Spine of a Silurian Shark (_Onchus tenui-striatus_,
Agass.). _c_, _d_, Scales of _Thecodus_, enlarged.]
The first fishes that we certainly know are the Ganoids and Sharks,
which appear near the close of the Upper Silurian, in the English Ludlow
for example (Fig. 104). The Ganoids found here all belong to an extinct
group, characterised by the covering of the head and anterior part of
the body with large bony plates. They are mostly small fishes, and
probably fed at the bottom, and used their long or rounded bony snouts
for grubbing in the mud for food. In this respect they present a
singular resemblance to the Trilobites, so that we seem to have here
animals of an entirely new type, the Vertebrate, and with bony instead
of shelly coverings, taking up the _rôle_ and, to some extent, the
external form of a group about to pass away. Yet I presume that no
derivationist would be hardy enough to affirm that the Trilobites could
have been the ancestors of these fishes. Nor indeed is any ancestry even
hypothetically known for them, for the doubtful Lampreys of the Cambrian
Silurian are too remote and uncertain to be used in that way. The
head-shield copied in outline in Fig. 104, and the restoration after
Lankester in the frontispiece to this chapter, may serve to represent
these curious primitive Ganoids, which are continued in the Devonian
fishes represented in Figs. 105, 106.
[Illustration: FIG. 105.—_Cephalaspis Dawsoni_ (Lankester). Lower
Devonian of Gaspé.]
Along with these, and not improbably their enemies, were certain Sharks
(Fig. 104), known to us only by the spines which were attached to their
fins as weapons of defence, and by detached bony tubercles which
protected their skin. These remains are chiefly interesting as
indications that two of the great leading divisions of the class of
fishes originated together.
In the Devonian age the Ganoids and Sharks, thus introduced in the
Silurian, may be said to culminate. The former, more especially, are
represented by a great variety of species, some of them nearly allied to
their Silurian predecessors (Fig. 106), others of forms and structure
not dissimilar to those of the few surviving representatives of the
order, or altogether peculiar to the Devonian (Fig. 107). So numerous
are these fishes, and of so many genera and species—and this not merely
in one region, but in widely separated parts of the world—that the
Devonian has not inaptly been called the reign of Ganoids. As an
illustration at once of the very peculiar forms of some of these fishes
and of their wide distribution, I figure here along with the British
species a _Cephalaspis_ (Fig. 105) found in the Lower Devonian of Gaspé,
in the same beds with some of the antique Devonian plants described in
the last chapter.
[Illustration: FIG. 106.—Devonian Placoganoid Fishes (_Pterichthys
cornutus_, _Cephalaspis Lyelli_), from Scotland.]
[Illustration: FIG. 107.—Devonian Lepidoganoid Fishes (_Diplacanthus_
and _Osteolepis_). After Page and Nicholson.]
[Illustration: FIG. 108.—Modern Dipnoi.
_a_, _Ceratodus Fosteri_. Australia. _b_, _Lepidosiren annectus_.
Africa.]
A new and interesting light has recently been cast upon some of the most
anomalous of the ancient fishes by the study of the now rare and
peculiar species of the group of Dipnoi. Two of these, belonging to the
genus _Lepidosiren_, are the “Mud-fishes” of the rivers of tropical
Africa and America (Fig. 108, _b._) These creatures have an elongated
and elegant form, and the body is covered with overlapping horny scales
like those of ordinary fishes; but the pectoral and ventral fins are
rod-like, and are supported by simple cartilaginous rays, while the
tailfin forms a fringe around the posterior part of the body. Unlike
ordinary fishes, they have lungs as well as gills, and their mouths are
armed with sharp, bony, beak-like teeth (Fig. 115), with which they can
inflict terrible bites on the small fishes and frogs which furnish them
with food. Their most remarkable habit is that of burying themselves in
the mud of dried-up ponds, thus forming a sort of water-chamber or
“cocoon,” in which they remain in a torpid state until the return of the
rainy season sets them free.
Another example of these Dipnoi is the Barramunda, or _Ceratodus_ of the
Australian rivers (Fig. 108_a_). This fish resembles the _Lepidosiren_ in
many essential points of structure; but its fins have lateral rays, and
are consequently of some breadth, though of peculiar form, and its mouth
is armed with flat, pavement-like teeth, wherewith it browses on aquatic
grasses.
[Illustration: FIG. 109.—Anterior part of the palate of _Dipterus_.
Showing the dental plates at _a_, Devonian.—After Traquair.]
These modern fishes have enabled us to understand several mysterious
forms met with in the older rocks. In the first place, they show the
meaning of certain flat-toothed fishes, like _Dipterus_ of the Devonian
(Fig. 109), _Conchodus_ of the Carboniferous (Fig. 110), and _Ceratodus_
of the Carboniferous and Trias (Figs. 111, 112), previously of very
doubtful character. These must all have been of similar structure and
habits with the Barramunda, which is thus the sole survivor, perhaps
itself verging on extinction, of a group of herbivorous fishes
introduced, it may be, contemporaneously with the first stream affording
the requisite vegetable food, and which have continued almost without
improvement or deterioration to the present time. These fishes are,
however, very closely connected with the Ganoids, and there are some of
these, with fringed fins and overlapping scales, which, while regarded
as true Ganoids, resemble the Dipnoi very closely.
[Illustration: FIG. 110.—Dental plate of _Conchodus plicatus_ (Dn.).
Coal-formation of Nova Scotia. _Acadian Geology_.]
[Illustration: FIG. 111.—Dental plate of _Ceratodus Barrandii_.
Coal-formation of Bohemia. After Fritsch.]
[Illustration: FIG. 112.—Dental plate of _Ceratodus serratus_. From the
Trias.]
[Illustration: FIG. 113.—Jaws of _Dinichthys Hertzeri_ (Newberry).
Laterally compressed; one-sixth natural size.]
Again, certain huge fishes, whose remains are found in the Devonian of
Ohio,[39] had jaws on the same plan with those of _Lepidosiren_, but of
enormous size and strength (Figs. 113, 114, 115), so that in this and
some other points of structure they may be regarded as colossal
Mud-fishes, and they must have had the same destructive powers, but on a
far grander scale. They were besides clothed with heavy armour of bony
scales, having some resemblance to that of those mailed fishes of
smaller size already referred to, and indicating that, huge though they
were, and formidable in destructive power, they also had enemies to be
dreaded. These plates serve to ally them with the Ganoids, as their jaws
do with _Lepidosiren_.
[Illustration: FIG. 114.—Lower Jaw of _Dinichthys Hertzeri_. One-sixth
natural size.]
[Illustration: FIG. 115.—Jaws of _Lepidosiren_. Natural size.—After
Newberry.]
We are thus enabled to see in the streams, lakes, and bays of the
Palæozoic, harmless fishes, of the type of _Ceratodus_, feeding on plants,
and huge precursors of the Mud-fishes darting from the depths, and
provided with a dental apparatus more formidable than that of any modern
fish, sufficient to pierce the strongest armour of the Ganoids, and to
destroy and devour the largest aquatic animals. These huge fishes, armed
with shears two or three feet in length, and capable of cutting asunder
scale, flesh, and bone, are the _beau idéal_ of destructive monsters of
the deep, far surpassing our modern Sharks; and if, by means of
supplementary lungs, they could breathe in air as well as in water, they
would on that account be all the more vigorous and voracious.
Newberry has well remarked that while in the Devonian the Ganoids and
Dipnoi were the real tyrants of the sea, as well as of the streams, in
the Carboniferous they already diminish in size, though still abundant
as to numbers, and are more limited to estuaries and fresh waters. Thus
their departure from power had already begun, and went on until in
modern times the proportion of Ganoids to ordinary fishes is, according
to Günther, nine out of 9,000. The Carboniferous, indeed, very specially
abounds in small Ganoids, though there are many large and formidable
species. One of these smaller species, a very beautiful little fish, of
fresh-water ponds and streams in the older part of the Carboniferous
age, is represented of the natural size in Fig. 116, and is not a
restoration, being found preserved entire, though flattened, in a fine
bituminous shale, which has perfectly preserved even the most delicate
sculpturing of its bony scales.
[Illustration: FIG. 116.—A small Carboniferous Ganoid (_Palæoniscus
(Rhadinichthys) Modulus_ Dn.). Lower Carboniferous, New Brunswick.
_a_, Outline. _b_, _c_, _d_, Sculpture of scales magnified.]
[Illustration: FIG. 117.—Teeth and Spines of Carboniferous Sharks. Nova
Scotia.
_a_, _Diplodus penetrans_. _b_, _Psammodus_. _c_, _Ctenoptychius
cristatus_. _d_, Spine, _Gyracanthus magnificus_. One-eighth natural
size.—_Acadian Geology._]
The Sharks in the Carboniferous increase in number and importance. Fig.
117 shows a few examples of their teeth and spines. In the
Carboniferous, however, there is a great preponderance of those species
with flat, crushing teeth fitted for grinding shells,[40] which in
diminishing numbers continue up to the present time, when they are
represented by the Port Jackson Shark and a few other species. The
increase toward the modern time of the true Sharks[41] with sharp
cutting teeth, is obviously related to the increase of the ordinary
fishes which furnish them with food. Another curious difference,
connected probably with the same circumstance, is the fact that in the
sharp toothed Sharks of the Carboniferous the two side fangs of each
tooth are the largest, or are exclusively developed (Fig. 117, _a_),
while in later periods the central point becomes dominant, or is
developed to the exclusion of the others (Figs. 118, 119).
[Illustration: FIG. 118.—Teeth of Cretaceous Sharks (_Otodus_ and
_Ptychodus_).—After Leidy.]
[Illustration: FIG. 119.—Tooth of a Tertiary Shark (_Carcharodon_).]
[Illustration: FIG. 120.—A Liassic Ganoid (_Dapedius_).
Restored.—After Nicholson.]
The Ganoids and Dipnoi still, however, occupy a very important place
through the Mesozoic ages (Fig. 120), and it is only at the close of the
Cretaceous that they finally give place to the Teleosts, or common
fishes, which, though perhaps more fully specialised in purely ichthyic
features, have dropped the reptilian characteristics of their
predecessors (Fig. 121). It is interesting to observe that these
old-fashioned fishes had culminated before the advent of air-breathing
Vertebrates, which appear for the first time in the Carboniferous. It is
further to be observed that groups of fishes furnished with means of
aiding their gills by rudimentary lungs were especially suited to waters
more charged with carbonic acid, and less with free oxygen, than those
of more recent times. This remark especially applies to the mephitic and
sluggish streams and lagoons of the Carboniferous swamps, where, in the
midst of a rank vegetation and reeking masses of decaying organic
matter, the half air-breathing fishes and the amphibious reptilian
animals met with each other and found equally congenial abodes. Thus,
independently of the fact that some of these fishes were probably
vegetable feeders, it is not altogether an accident, but a wise
adaptation, that caused the culmination of the reptilian fishes and
batrachian reptiles to coincide with the enormous development of the
lower forms of land-plants in the Devonian and Carboniferous. Another
curious illustration of the diminishing necessity for air-breathing to
the fishes, is the change of the tail from the unequally-lobed or
heterocercal form, which prevailed in the Palæozoic, to the more modern
equally-lobed (homocercal) style in the Mesozoic. The former is better
suited to animals which have to rise rapidly to the surface for air, and
is still continued in some modern fishes, which for other reasons need
to ascend and descend, or to turn themselves in the water; but the
homocercal form is best suited to the ordinary fish, whether Ganoids or
Teleosts (Fig. 122). It is curious also to find the beginning of the
dominancy of the ordinary fish to coincide with that of the broad-leaved
exogenous trees in the later Cretaceous, and to precede immediately the
appearance of the mammals on the land; all these changes being related
to the purer air, the clearer waters, and the more varied continental
profiles of the later geological periods. Thus physical improvement and
the changes of animal and vegetable life are linked together by
correlations which imply not only design, but prescience, whether we
attribute these qualities to a spiritual Creator or to mere atoms and
forces.
[Illustration: FIG. 121.—Cretaceous Fishes of the modern or Teleostian
type.
_a_, _Beryx Lewesiensis_. English chalk. _b_, _Portheus molossus_
(Cope). A large fish from the American Cretaceous. One twenty-eighth
natural size.]
The history of fishes extends further through geological time than that
of any other Vertebrates, and is perhaps more completely known to us, in
consequence of the greater facilities for the preservation of their
remains in aqueous deposits. If we receive Pander’s Conodonts as
indicating a low type of cartilaginous fishes, these must have
continued for vast ages without any elevation, and struggling for a bare
existence amidst formidable Cuttle-fishes and Crustaceans, before, under
more favourable conditions, they suddenly expanded into the high and
perfect types of Ganoids and Sharks. If we reject the early Conodonts,
then the two last-mentioned types spring together and suddenly into
existence, like the armed men from the dragon’s teeth of Cadmus. They
rapidly attain to numbers and grandeur unexampled in later times, and
become the lords of the waters at the time when there was probably no
Vertebrate life on the land. As the reptiles establish themselves on the
land and in the waters, the Ganoids diminish, but the Sharks hold their
own. At length the reign of reptiles is over, but the Ganoids, instead
of resuming their pristine numbers, give place to the Teleosts, and
become reduced to insignificance; while the Sharks, profiting by the
decadence of the great marine reptiles, remain the tyrants of the seas.
This history is strangely unlike a continuous evolution; but we are
anticipating facts which will fall to be discussed in a subsequent
chapter.
[Illustration: FIG. 122.—Modern Ganoids (_Polypterus._ Africa.
_Lepidosteus._ America).]
[Illustration: A MICROSAURIAN OF THE CARBONIFEROUS PERIOD (_Hylonomus
Lyelli_). RESTORED FROM THE SKELETON AND DERMAL APPENDAGES FOUND IN AN
ERECT SIGILLARIA. HALF NATURAL SIZE.]
CHAPTER VI.
THE FIRST AIR-BREATHERS.
Were our experience limited to the animals whose remains are found in
the earlier Palæozoic rocks, we might be unable to conceive the
possibility of an animal capable of living and breathing in the thin and
apparently uncongenial medium of air. More especially would this appear
doubtful if our experience of the atmosphere presented it to us as
loaded with carbonic acid, and less rich in vital air than it is at
present. Even the mechanical difficulties of the case might strike us as
considerable, in our ignorance of the capabilities of limbs. Still, as
time wore on, we should find this problem worked out along three
distinct lines of advancement—those of the Mollusk, the Arthropod, and
the Vertebrate, and in each of these with different machinery, related
to the previous locomotive and water-breathing apparatus of the type.
Respiration under water depends, not on the water itself, but on the
small percentage of free oxygen which it contains, and this is utilised
for the aëration of the blood of animals, by that wonderful and often
extremely beautiful apparatus of delicate fibres or laminæ penetrated
with blood-vessels, which we call a gill. Except those lowest creatures
which aërate their blood merely at the general surface of the body, all
animals capable of respiration in water are provided with gills in some
form, though in many of the humbler types, like that of the familiar
Oyster, the gills are used for the double purpose of aërating the blood
and, by their minute vibrating threads or cilia, drifting food to the
mouth.
In the great group of radiated animals, the _Protozoa_, _Cœlenterata_,
and _Echinodermata_, no air-breathing creature exists, or, in so far as
is known, has existed, so that this vast group of animals is limited
altogether to the waters; and this is undoubtedly one mark of its
inferiority.
In the sub-kingdom of the Mollusks the highest class, that of the
Cuttle-fishes and Nautili, has been, singularly enough, rejected as
unfit for this promotion, though it was early introduced, and attains to
a high development of muscular energy and nervous power. The group next
in order, that of the Snails and their allies, alone ventures in some of
its families to assume the _rôle_ of air-breathing. As might be
expected, in creatures of this stamp the simplest means are employed to
effect the result. In the sub-aquatic species the gills are contained in
a chamber, where they are protected and kept supplied with water. In the
air-breathing species, this gill-chamber is merely emptied of its
contents and converted into an air-sac or functional lung. Thus a rude
and imperfect method of air-breathing is contrived, which scarcely
separates the animals that possess it from their aquatic relatives, but
which nevertheless gives to us the beautiful and varied groups of the
Land-snails and of the air-breathing fresh-water Snails.
In the worms and Crustaceans the gills are placed at the sides of the
body, and connected with its several segments. But the Crustaceans, like
the Cuttle-fishes, though the highest aquatic type, never become
air-breathers. It is true some of them, like the Land-crabs, live in the
air; but they retain their gills, and have to carry with them a supply
of water to keep these moist.
But in order to elevate the Annulose type to the true dignity of air
breathing, three new classes had to be introduced, differing altogether
in their details of structure; and all three seem to have been placed on
the earth about the same time. They are: First, the Myriapods, or
Gallyworms and Centipedes; secondly, the Insects; and thirdly, the
Arachnidans, or Spiders and Scorpions.
In the Myriapods a system of air-tubes, kept open by elastic spiral
fibres, penetrates the body by lateral pores, thus retaining the
resemblance to the lateral respiration of the Crustaceans and worms. In
the Insects, where this type of structure rises to its highest
mechanical perfection, and where the animal is enabled to be not merely
an air-breather, but a flier, the same system of lateral pores and
internal air-tubes is adopted, and is so extended and ramified as to
give a very perfect respiration. In the Spiders and Scorpions the system
is the same, except that in the latter and a part of the former the
whole or a part of the tracheal system becomes expanded into
air-chambers simulating true lungs.
Among the Vertebrates, the fishes are breathers by gills attached to
arches at the sides of the neck. But already in the Devonian we have
reason to believe that there were fishes having the swimming-bladder
opening into the back of the mouth to receive air, and divided into
chambers, so as to constitute an imperfect lung. And here we have not,
as in the lower types, an adaptation of the old water-breathing organs,
but an entirely new apparatus. In the next grade of Vertebrates we find,
as in the Frogs, Water-lizards, etc., that the young are aquatic and
breathe by gills, while the adults acquire lungs, sometimes retaining
their gills also, but in the higher forms parting with them. Thus in the
vertebrates alone we have true lungs, distinct structurally from gills;
and these lungs attain to their highest perfection in the birds and
mammals.
[Illustration: FIG. 123.—Wings of Devonian Insects. Middle Devonian of
New Brunswick.
_a_, _Platephemera antiqua_ (Scudder).
_b_, _Homothetus fossilis_ (Scudder).
_c_, _Lithentomum Harttii_ (Scudder).
_d_, _Xenoneura antiquorum_ (Scudder).]
The oldest air breathers at present known are Scorpions and insects
allied to the modern May-flies, which have been found in the Silurian.
Next to these, and more important in number and variety, are the
insects of the Erian plant beds of New Brunswick. They were discovered
by the late lamented Prof. C. F. Hartt in the plant-bearing shales of
the Middle Devonian (Fig. 123). The beds containing them hold also a
species of _Eurypterus_, an obscure Trilobite, and a Crustacean allied
to the modern Stomapods,[42] besides a shell which may possibly be that
of a Land-snail, to be mentioned in the sequel. They are also
exceedingly rich in beautifully-preserved remains of Devonian plants.
The collection made by Prof. Hartt is limited to a few fragments of
wings; but these, in the skilful hands of Mr. Scudder, have proved to be
rich in geological interest. One is a gigantic _Ephemera_ or May-fly,
which must have been five inches in the expanse of the wings, which are
more complex in their venation than those of its modern allies (Fig.
123, _a_). Another presents peculiarities between those of the May-flies
and Dragon-flies (Fig. 123, _b_). A third is a Neuropter, not belonging
to any known family, but allied to some in the Coal-formation (Fig. 123,
_c_). A fourth (Fig. 123, _d_) is a small and delicate wing, supposed
to have belonged to an animal having some points of resemblance to the
modern crickets. Two others are represented by mere fragments of wings,
insufficient to determine their affinities with certainty. No other
insects of this age have been discovered elsewhere; but it is to be
borne in mind that no other locality rich in Devonian plants has
probably been so thoroughly explored. The hard slaty ridges containing
these fossils are well exposed on the coast near the city of St. John,
and Messrs. Hartt and Matthew of that city, acting, I believe, in
concert with and aided by the Natural History Society of the place, not
only searched superficially, but removed by blasting large portions of
the richest beds, and examined every fragment with the greatest care.
Their primary object was fossil plants, of which they obtained
magnificent collections; and it is scarcely possible that the insects
could have been found but for the exhaustive methods of exploration
employed.
It is interesting to observe, respecting these oldest insects, that they
all belong to those families which have jaws, and not suctorial
apparatus, that they are not of those which undergo a complete
metamorphosis, and that their modern congeners pass their larval stage
in the water. Thus the waters gave birth to the first insects, and their
earliest families were not of those which suck honied juices or the
blood of animals, or which pass through a worm-like infancy. These
groups belong apparently to much later times.
On one of the specimens collected by Messrs. Hartt and Matthew, and
placed by them in my hands, is a spiral form which in every particular
of external marking resembles a genus of modern West Indian
Land-snails.[43] I have hesitated to describe it, as the structure is
lost and the form imperfect; but I cannot help regarding it as an
indication that this group of land animals also will be traced back to
the Devonian age.
Ascending from the Devonian to the Carboniferous, we at once find
ourselves in the midst of air-breathers of various types. Here are
Myriapods, insects of several orders, Spiders, Scorpions, Land-snails,
and Batrachian reptiles, and these of many species, and found in many
localities widely separated. We can thus people those dark, luxuriant
forests, to which we owe our most valuable beds of coal, with many forms
of life; and as most of these belong to tribes likely to multiply
abundantly where food was plentiful, we can imagine multitudes of Snails
and Millepedes feeding on succulent or decaying vegetable matter, swarms
of insects flitting through the air in the sunnier spots, while their
larvæ luxuriated in decaying masses of leaves or wood, or peopled the
pools and streams. In like manner, in imagination we can render these
old woods vocal with the trill of crickets and with the piping or
booming of smaller and larger Batrachians. Let us now, in accordance
with our plan, inquire as to the nature of these early air-breathers and
the fortunes of their families in the geological history.
[Illustration: FIG. 124.—Land-snail (_Pupa vetusta_, Dawson). From the
Coal-formation.
_a_, Natural size. _b_, Magnified. _c_, Apex. _d_, Sculpture. Enlarged.]
[Illustration: FIG. 125.—Land-snail (_Zonites (Conulus) priscus_,
Carpenter). From the Coal-formation.
_a_, Shell. Enlarged; the line below shows the natural size. _b_,
Sculpture. Enlarged.]
The Land-snails known as yet in the Carboniferous are limited to five or
six species, belonging to four genera, all American and related to
existing American forms. The two earliest known are represented in Figs.
124 and 125.[44] One of them is a _Pupa_, or elongated Land-snail, so
similar to modern forms that it does not merit a generic distinction,
and is indeed very near to some existing West Indian species. The other
is in like manner a member of the modern genus _Zonites_. These are from
the Coal-formation of Nova Scotia, and the Pupa must have been very
abundant, as it has been found in considerable numbers in a layer of
shale, and in the stumps of erect trees, in beds separated from each
other by a thickness of 2,000 feet of strata. The _Zonites_ is much more
rare. A second Pupa is found in Nova Scotia, and two species occur in
the Coal-field of Illinois. One of these is a Pupa still smaller than
_P. vetusta_, and, like some modern species, with a tooth-like process
on the inner lip. The other has been placed in a new genus,[45] but is
very near to some of the smaller American Snails still living. Its most
special character is a plate extending from the inner lip over half the
aperture, a contrivance for protection still seen in some modern forms.
Thus the Land-snails come on the stage in at least three generic forms,
similar to those which still live, but all of small size, indicating
perhaps that the conditions were less favourable for such creatures than
those of the temperate and warmer climates at present. It may seem a
small step in advance for Sea-snails to lose their gills and to become
Land-snails, and this without any elevation of their general structure;
but it must be borne in mind that we have here not only the dropping of
the gills for an air-sac, but profound changes in teeth, mucous glands,
shell, and other particulars, to fit them for new food and new habits.
It is also singular that the Land-snails at once appear instead of the
intermediate forms of the air-breathing fresh-water snails. These last
may, however, yet be found.
The Millepedes, like the Land-snails, were first found in the
Coal-formation of Nova Scotia, but species have since been discovered
not only in Illinois, but also in Great Britain and in Bohemia. In Nova
Scotia alone two genera and five distinct species have been found, all
in the interior of erect trees, to which these creatures probably
resorted for food and shelter (Fig. 126). All the species yet known are
allied to the modern Gallyworms, though presenting special features
which seem to separate them as a distinct family,[46] and were probably
vegetable-feeders. Some of the species have the peculiarity, unknown
among their modern successors, of being armed with long spines.[47] The
moist, equable climate and exuberant vegetation of the Coal-period would
naturally be very favourable to Millepedes, and it is likely that the
discoveries made as yet give but a faint idea of their actual abundance.
It is not improbable that they subsequently declined, as we know of none
between the Carboniferous and the Jurassic, and they do not seem to have
improved up to the modern period. The Carnivorous Myriapods, however, or
Centipedes proper, a higher and essentially distinct type, are not known
until much more recent times.
[Illustration: FIG. 126.—Millepedes. From the Coal-formation.
_a_, _Xylobius sigillariæ_ (Dawson). _b_, _Archiulus xylobioides_
(Scudder). Anterior segments. Enlarged, _c_, _X. farctus_ (Scudder).
Caudal portion. Enlarged.]
The insects of the Carboniferous as yet known, belong to three out of
the ten or more orders into which the class is divided. One of these is
represented by a number of species of Cockroach, another by May-flies
and a Dragon-fly, and another by some weevil-like Beetles. The Cockroach
is characterised by Huxley as one of the “oldest, least modified, and in
many ways most instructive forms of insects;” and both he and Rolleston
take its anatomy as typical of that of the class. That these creatures
should have abounded in the Coal-period we need not wonder, when we
consider the habits of those that infest our houses, and when we further
bear in mind the number of species, some of them two inches in length,
that exist in tropical climates. So many species of this family have
been found in the Coal-formation on both sides of the Atlantic,[48] that
we may fairly regard them as constituting one of its most characteristic
features, and as probably the oldest representatives of the order to
which they belong[49] (Fig. 127). There were also in the Coal-period
insects allied to the Locusts and to the Mantids, a carnivorous group.
One of the latter (_Lithomantis_), described by Woodward, is a
magnificent insect, not unlike some modern tropical species. It was
found in the Coal-formation of Scotland. A still larger species,
probably the largest insect known, has been described by Brongniart. The
May-flies (_Ephemeridæ_) are represented in the Carboniferous by several
very large species. That of which the wing is shown in Fig. 128 must
have been seven inches in expanse of wings. The habits of the modern
May-flies show us how animals of this group, living as larvæ in the
streams and lakes, must have afforded large supplies of food to fishes,
and when mature must have emerged from the waters in countless myriads,
filling the air for the brief term of their existence in the perfect
state. The May-flies represent another insect order.[50] The
Coal-measures of Saarbruck have afforded several species allied to the
white ants (_Termites_), insects which must have found abundant scope
for their activity in the dead trees of the carboniferous forests. The
occurrence of beetles,[51] especially of the weevil family, which have
as yet been found only in Europe, might have been expected, considering
the habits and modern distribution of this group. It has been asserted
that moths[52] have been found in the Carboniferous; but the proof of
this, so far as known to me, is the occurrence of leaves, noticed by
Sternberg, with markings similar to those made by the larvæ of minute
leaf-mining moths. This, however, is uncertain evidence. If we consider
the orders of insects not found in the Coal-formation, we can perceive
good reasons for the absence of some of them. Those containing the lice
and fleas, and other minute and parasitic insects, we can scarcely
expect to find. The bees and wasps, and the butterflies and moths, are
little likely to have been present where there were scarcely any
flowering plants; but such groups as those of the two-winged flies, the
plant-bugs and the ants, we might have expected, but for the fact of
their being highly specialised forms, and for that reason likely to have
appeared later.[53] There are, indeed, as yet no haustellate or
suctorial insects known in this early period. Plausible theories of the
phylogeny of insects are not wanting; but they do not well suit the
known facts as to their first appearance; and perhaps we may venture
without much blame to apply to the insects of the Coal-period the remark
made by Wollaston with reference to the rich insect fauna of the
isolated rock of St. Helena: “To a mind which, like my own, can accept
the doctrine of creative acts as not necessarily ‘unphilosophical,’ the
mysteries [of the existence of these species in an island so remote from
other lands], however great, become at least conceivable; but those
which are not able to do this may, perhaps, succeed in elaborating some
special theory of their own, which, even if it does not satisfy all the
requirements of the problem, may at least prove convincing to
themselves.”
[Illustration: FIG. 127.—Wings of Cockroaches. From the Coal-formation.
_a_, _Archimulacris Acadicus_ (Scudder). _b_, _Blattina Bretonensis_
(Scudder). _c_, _B. Hesri_ (Scudder).]
[Illustration: FIG. 128.—Wing of May-fly (_Haplophlebium Barnesii_,
Scudder). From the Coal-formation.]
[Illustration: FIG. 129.—A Jurassic Sphinx-moth (_Sphinx Snelleri_,
Weyenburgh).]
[Illustration: FIG. 130.—An Eocene Butterfly (_Prodryas persephone_,
Scudder). From Colorado.]
The suctorial insects make their first certain appearance in the
Jurassic; and the magnificent Sphinx Moth in Fig. 129 is an example of
the magnitude and perfection to which that tribe attained in the age of
the Solenhofen slate; though Weyenburgh, who describes it, fancies that
he sees evidence that it may, unlike any modern moths, have been
provided with a sting. The most perfect and beautiful fossil butterfly
known to me is that represented in Fig. 130, from a photograph kindly
given to me by Mr. Scudder. It is from the Tertiary rocks of Western
America, and is laid out in stone as neatly as if prepared by an
entomologist, while its preservation is so perfect that even the
microscopic scales on the wings can be made out. It belongs to one of
the highest types of modern butterflies, that to which the _Vanessæ_
belong, but with some points of structure pointing to the lower group of
the “Skippers” (_Hesperiadæ_). Scudder remarks that while the fore-wings
resemble those of the former group, the hind-wings look more like those
of the latter; and this seems to be a common character of two or three
others of the few fossil species known, none of which are older than the
Tertiary.
[Illustration: FIG. 131.—Abdominal part of a Carboniferous
Scorpion.[54]]
We know too little of the spiders and scorpions of the Carboniferous to
say more than that they closely resemble modern forms. Two of the
scorpions are represented in Figs. 131 and 132; and the only spider
certainly known, which is from Silesia, is said to belong to the group
of the hunting or trap-door spiders (_Lycosa_).[55]
The Batrachians of the Coal are its most characteristic and remarkable
air-breathers,—especially so as the precursors of the reptiles of the
Mesozoic age. Cope in a recent summary enumerates no less than
thirty-nine genera and about one hundred species; and to these have to
be added at least a dozen more recently discovered in Europe; though it
was only in 1841 that the first indications of such creatures were
found, and were then regarded by geologists with the same scepticism
which some of them still apply to _Eozoon_. The first trace ever observed
of batrachians in the Carboniferous consisted of a series of small but
well-marked footprints found by the late Sir W. E. Logan in the Lower
Carboniferous shales of Horton Bluff, in Nova Scotia. In that year this
painstaking geologist had examined the coal-fields of Pennsylvania and
Nova Scotia, with the view of following up his important discovery of
the _Stigmariæ_, or roots of _Sigillaria_, as accompaniments of the
coal-underclays. On his return he read a paper, detailing his
observations, before the Geological Society of London. In this he
mentioned the footprints in question; but the paper was published only
in abstract, and the importance of the discovery was overlooked for a
time, the anatomists evidently being shy to acknowledge the validity of
the evidence for a fact so unexpected. Fig. 133 is a representation of
another slab subsequently found in beds of the same age in Nova Scotia,
and which may serve to indicate the nature of Sir William’s discovery.
In consequence of the neglect of this first hint by the London
geologists, the discovery of bones of a batrachian by von Dechen at
Saarbruck in 1844, and that of footprints by King in Pennsylvania in the
same year, are usually represented as the first facts of this kind. My
own earliest discovery of reptilian bones in Nova Scotia was made in
1844, though not published till some time afterward, and was followed
up by further collections in company with Sir Charles Lyell in 1851, at
which time also the earliest land-snail was found, and in the following
year the first millepede. Since that time the progress of discovery has
been astonishingly rapid, and has extended over most of the principal
coal-areas on both sides of the Atlantic.
[Illustration: FIG. 132.—Carboniferous Scorpion (_Eoscorpius
carbonarius_, Meek and Worthen). Illinois.]
[Illustration: FIG. 133.—Footprints of one of the oldest known
Batrachians, probably a species of _Dendrerpeton_. From the Lower
Carboniferous of Parrsboro’, Nova Scotia. Upper figure natural size.]
We may, for convenience, call these animals reptiles, but they are
regarded as belonging to that lower grade of reptilian animals, the
Amphibians or Batrachians, which includes the modern frogs and newts and
water-lizards.[56] Still it would be doing great injustice to the
carboniferous reptiles not to say, that while related to this low type,
they presented a much greater range of organisation than it shows at
present, evincing a capability to fill most of the places now occupied
by the true reptiles. Some of them were aquatic, and with limbs
rudimentary or little developed, but many of them walked on the land,
and were powerful and predaceous creatures. They had large and complex
teeth, they were protected by external bony plates, and some of them had
in addition a beautiful covering of horny plates and spines, and
ornamental lappets. Many had well-developed ribs, indicating a condition
of respiration much in advance of that in the ribless batrachians. Some
of them attained to size and strength rivalling those of the modern
alligators, while some of the smallest species exhibit characters
approaching in some respects to the lizards.
Perhaps the most fish-like of these animals are those first discovered
by von Dechen (_Archegosaurus_, Fig. 134). Their long heads, short
necks, supports for gills, feeble limbs and long flat tail, show that
they were aquatic creatures presenting many points of resemblance to the
Ganoid fishes which must have been their companions. Yet they show what
no fish can exhibit, fore and hind limbs with proper toes, and the
complete series of bones that appear in our own arms and legs, while
they must have had true lungs and breathed through nostrils. So
different are they from the fish in details, that a single limb bone, a
vertebra, a rib, or a fragment of a skull bone, suffices to distinguish
them. Much has been said recently of the genesis of limbs; and here, as
far as now known, we have the first true limbs; but it is scarcely too
much to say that the feet of _Archegosaurus_ differ more from the fins
of any carboniferous fish than they do from the human hand; while it is
certain that the feet which made the impressions represented in Fig.
133, on the lowest beds of the Carboniferous, or that from the upper
coal-formation represented in Fig. 139, were not less typical or
perfectly formed feet than those of modern lizards.
Leaving these fish-like forms, we find the remainder of the
carboniferous reptiles to diverge from them along three lines.
[Illustration: FIG. 134.—_Archegosaurus Decheni._ Head and anterior
limb reduced. Coal-field of Saarbruck.]
[Illustration: FIG. 135.—_Ptyonius._ A Snake-like Amphibian.
Coal-measures of Ohio.—After Cope.]
The first leads to snake-like creatures, destitute of limbs, and which
must have been functionally the representatives of the serpents in the
Palæozoic, though batrachian in their affinities (Fig. 135). They are
found both in Europe and America; and Huxley describes one from Ireland
more than twenty-one inches long, and with over one hundred
vertebræ.[57] Some extraordinary traces are found on the sandstones of
the coal-formation,[58] which appear to indicate that there may have
been species of this type much larger than any represented by
skeletons, and with bodies perhaps six inches in diameter. It is not
unlikely that they had the habits of the modern water snakes.
[Illustration: FIG. 136.—A large Carboniferous Labyrinthodont
(_Baphetes planiceps_, Owen).
_a_, Anterior part of the skull, viewed from beneath. One-sixth natural
size, _b_, One of the largest teeth, natural size.]
A second line leads upward to large crocodile-like creatures, with
formidable teeth, strong bony armour, and well-developed limbs
(_Labyrinthodontia_, Figs. 136, 137). Some of them must have attained a
length of ten feet. They were lizard-like in form, could walk well, as
is seen from the footprints of some of the species which present a
considerable stride, and moved over mud without the belly touching the
ground. Their tails were long, and probably useful in swimming. Their
heads were flat and massive, and their teeth were strengthened by a
remarkable folding inward of the outer plate of enamel (Fig. 137 _b_).
The belly was protected by bony plates and closely imbricated scales. In
some of the species at least the upper parts were clothed with horny
scales, and the throat and sides were ornamented with pendent scaly
fringes or lappets.[59] Their general aspect and mode of life must have
resembled those of modern alligators; and in the vast swamps of the
Coal-period, full of ponds and sluggish streams swarming with fish, they
must have found a most suitable abode. While rigid anatomy may ally
these animals rather with the batrachians than the true reptiles, it is
evident that their great size, their capacity for walking with the body
borne well above the ground, their bony and scaly armour, their powerful
teeth and their capacious chests, with well-developed ribs, indicate
conditions of respiration and general vitality quite comparable with
those of the highest modern members of the class Reptilia.
[Illustration: FIG. 137.—_Baphetes planiceps_ (Owen).
_a_, Fragment of maxillary bone showing sculpture, four outer teeth, and
one inner tooth. Natural size. _b_, Section of inner tooth. Magnified,
_c_, Dermal scale. Natural size.]
The third line of progress leads to some slender and beautiful creatures
(_Microsauria_), chiefly known to us by remains found in erect trees,
and which resembled in form and habits the smaller modern lizards. They
have simple teeth, a well-developed brain-case, limbs of some length,
and bony and scaly armour, the latter in some cases highly ornate.[60]
They were probably the most thoroughly terrestrial, and the most active
of the coal batrachians, if indeed they were not strictly intermediate
between them and the lizards proper. Fig. 138 shows some fragments of
one of these animals; and the animal represented in Fig. 139, recently
figured by Fritsch, probably belongs to this group.
[Illustration: FIG. 138.—A lizard-like Amphibian (_Hylonomus
aciedentatus_).
_a_, Maxillary bone; enlarged.
_b_, Mandible; enlarged.
_c_, Teeth; magnified, showing front and side view of
ordinary tooth and grooved anterior tooth.
_d_, Section of tooth; magnified.
_e_, Scale; natural size and magnified.
_f_, Pelvic bone (?); natural size.
_g_, Rib; natural size.
_h_, Scapular bone (?); natural size.
_i_, Palate; natural size.]
[Illustration: FIG. 139.—_Stelliosaurus longicostatus_ (Fritsch). Upper
Coal-formation of Bohemia.]
The Labyrinthodonts of the Carboniferous continue upward into the
Permian, where they meet with the true reptiles; and in the earlier
Mesozoic some of the largest and most typical examples are found.[61]
But here their reign ceases, and they give place to reptiles of more
elevated type, whose history we must consider in the next chapter.
Nothing can be more remarkable than the apparently sudden and
simultaneous incoming of the batrachian reptiles in the Coal-formation.
As if at a given signal, they came up like the frogs of Egypt everywhere
and in all varieties of form. If, as evolutionists suppose, they were
developed from fishes, this must have been by some sudden change,
occurring at once all over the world, unless indeed some great and
unknown gap separates the Devonian from the Carboniferous—a supposition
which seems quite contrary to fact—or unless in some region yet
unexplored this change was proceeding, and at a particular time its
products spread themselves over the world—a supposition equally
improbable. In short, the hypothesis of evolution, as applied to these
animals, is surrounded with geological improbabilities.
A remarkable picture of the conditions of Palæozoic land life is
presented by the occurrence of remains of reptiles, millepedes and
land-snails in such erect trees as that represented in Fig. 140. In the
now celebrated section of the South Joggins in Nova Scotia, trees of
this kind occur at more than sixty different levels; but only in one of
these have they as yet been found to be rich in animal remains.
Fortunately this bed is so well exposed and so abundant in trees, that I
have myself, within a few years, removed from it about twenty of them,
the greater number affording remains of land animals.
[Illustration: FIG. 140.—Section showing the position of an erect
_Sigillaria_, containing remains of land animals.
1. Underclay, with rootlets of _Stigmaria_, resting on gray shale,
with two thin coaly seams.
2. Gray sandstone, with erect trees, _Calamites_, and other stems:
9 feet.
3. Coal, with erect tree on its surface: 6 inches.
4. Underclay with _Stigmaria_ rootlets.
_a_, _Calamites_.
_b_, Stem of plant undetermined.
_c_, _Stigmaria_ roots.
_d_, Erect trunk, 9 feet high.]
The history of one of these trees may be shortly stated thus. It was a
_Sigillaria_, perhaps two feet in diameter, and its stem had a dense and
imperishable outer bark, a soft cellular inner bark liable to rapid
decay, and a slender woody axis not very durable. It grew on the surface
of a swamp, now represented by a bed of coal. By inundations and by
subsidence, this swamp was exposed to the invasion of muddy and sandy
sediment, and this went on accumulating until the stem of the tree was
buried to the height of about nine feet, before which time it was no
doubt killed. After a time the top decayed and fell, leaving the buried
stump imbedded in the sandy soil, which had now become dry, or nearly
so. The trunk decayed, its inner bark and axis rotting away and falling
in shreds into the bottom of the cylindrical hole, about nine feet deep,
once occupied by the stem, and now kept open like a shaft or well by the
hard resisting outer bank. The ground around this opening became clothed
with ferns and reed-like _Calamites_, partly masking and concealing it.
And now millepedes and land snails made the buried trunk a home, or fell
into it in their wanderings; and small reptiles sporting around, in
pursuit of prey, or themselves pursued, stumbled into the open pitfall,
and were unable to extricate themselves, though I have found in some of
the layers in these trees trails which show that these imprisoned
reptiles had wearily wandered round and round, in the vain search for
means of exit, till they died of exhaustion and famine. The bones of
these dead reptiles, shells of land-snails and crusts of millepedes,
accumulated in these natural coffins, and became mixed with vegetable
debris falling into them, and with thin layers of mud washed in by the
rains; and this process continued so long that a layer of six inches to
a foot in thickness, full of bones, was sometimes produced. At length a
new change supervened, the area was again inundated and drifted over
with sand, and the hollow trunk was filled to the top and buried under
many feet of sediment, never to be re-opened till, after the whole had
been hardened into sandstone and elevated to form a part of the modern
coast, when the old tree and its forest companions which had shared the
same fate with it, are made to yield up their treasures to the
geologist. This history is no fancy picture. It represents the results
of long and careful study of the beds holding these erect trees, and of
the laborious extraction of great numbers of them, and the breaking-up
of their contents into thin flakes, to be carefully examined with the
lens under a bright light in search of the relics they contained. Fig.
11 in Chap. I. represents the extraction of one of these trees, which
happened to be partially exposed by the wasting of the cliff; but many
others had to be laboriously mined out of the rock by blasting with
gunpowder.
[Illustration: FIG. 140_a_.—Section of base of erect _Sigillaria_,
containing remains of land animals.
_a_, Mineral charcoal. _b_, Dark-coloured sandstone, with plants, bones,
&c. _c_, Gray sandstone, with Calamites and Cordaites.]
It is evident that the combination of circumstances referred to above
could not often occur; and it is therefore not wonderful that only in
one place and one bed has evidence of it been found, and that even in
this some of the trees have been filled up at once by sand and clay, or
so crushed by falling in or lateral pressure, that they could receive no
animal remains. In one respect this is a striking evidence of the
imperfection of the geological record, since, but for what may be called
a fortunate accident, many of the most interesting inhabitants of the
coal forests might have been altogether unknown to us. On the other
hand, it shows how strange and unexpected are the ways in which the
relics of the old world have been preserved for our inspection, and that
there is probably scarcely any animal or plant that has ever lived of
which some fragment does not exist, did we know where to look for it.
It may be well to remark, in closing this chapter, how many new forms of
life, air-breathing and otherwise, make their first appearance in the
Carboniferous, and have continued to prevail until now. Here we find the
first specimens of Amphibians, Spiders, Myriapods, Orthopterous and
Coleopterous Insects, and of the Crabs among ten-footed Crustaceans. In
the latter group Woodward has recently described the oldest known crab,
from the Coal-formation of Belgium.
[Illustration: INHABITANTS OF THE ENGLISH SEAS IN THE AGE OF REPTILES.
_Pliosaurus_, _Ichthyosaurus_, _Plesiosaurus_, _Mososaurus_, and
_Teleosaurus_.]
CHAPTER VII.
THE EMPIRE OF THE GREAT REPTILES.
Had we lived in the Carboniferous period, we might have supposed that
the line of the great Labyrinthodont Batrachians would have been
continued onward and elevated, perhaps, in the direction of the
Mammalia, to which some features of their structure point. But we should
have been mistaken in this. The Labyrinthodonts, it is true, extend into
the Trias; but there is perhaps a sign of their coming degradation in
the appearance in the Permian of the first known mud-eel, a humble
Batrachian form allied to the Newts and Water-lizards.[62] Their special
peculiarities are dropped in the Mesozoic in favour of those of certain
small and feeble lizard-like animals, appearing first in the
Carboniferous, and more manifestly in the Permian, and which are the
true forerunners, though they can scarcely be the ancestors, of the
magnificent reptilian species of the Mesozoic, which have caused this
period to be called “the age of reptiles.”
The leading reptilian animal from the European Permian has long been the
_Proterosaurus_, from the copper slates of Thuringia (Fig. 141), a
reptile of lizard-like form, with well-developed limbs, and attaining a
length of three or four feet. It resembles more nearly those large
modern lizards known as “Monitors,” than any other existing form. The
fore-limb represented in the figure foreshadows very closely the bones
of the human arm and hand. Besides this we find in the Permian certain
lizards (_Theriodonts_ of Owen) which present the remarkable and
advanced peculiarity already predicted by some Carboniferous
Microsauria,[63] of having distinct canine teeth, producing a division
into incisors, canines, and molars, in the manner of the Carnivorous
quadrupeds, which they seem also to have resembled in some other parts
of their skeletons. It is not impossible that the footprints in the
Permian sandstones of Scotland, which have been referred to tortoises,
were those of animals of this type. Cope has recently described from the
Permian of Texas a number of reptiles which have the complex dentition
of the Theriodonts, and others which simulate that of Herbivorous
mammals, by the possession of flat grinding teeth supposed to be adapted
to vegetable food.[64] The teeth of all these Permian reptiles were set
in sockets, also an advanced peculiarity. Thus already in the Permian,
before the final decadence of the Carboniferous flora, and while the
Palæozoic invertebrates still lingered in the sea, the age of reptiles
dawned, and gave promise of its future greatness by the assumption on
the part of reptilian species of structures now limited to the Mammalia.
[Illustration: FIG. 141.—Arm of _Proterosaurus Speneri_. Reduced.
Permian.]
But the great Mesozoic reptiles were not fully enthroned, till the
Permian, an unsettled and disturbed age, characterised by great earth
movements, had passed away, and until that period of continental
elevation, with local deserts and desiccation, and much volcanic action,
which we call the Trias, had also passed.
Then in the Jurassic and early Cretaceous the reptiles culminated, and
presented features of magnitude and structural complexity unrivalled in
later times. At the same time the Labyrinthodonts disappear, or are
degraded into the humble stations which the modern Batrachians now
occupy.
To understand the reptiles of this age, it will be necessary to notice
the subdivisions of their modern representatives. The true reptiles now
existing constitute the following orders:—1, the Turtles and Tortoises
(_Chelonia_); 2, the Snakes (_Ophidia_); 3, the Lizards (_Lacertilia_);
4, the Crocodiles and Alligators (_Crocodilia_). All of these, except
the snakes, are well represented among Mesozoic fossils; but we have in
this middle age of the earth’s geological history to add to them from
five to seven orders now altogether extinct, and these not of low and
inferior organisation, but including species far in advance of any now
existing both in elevation and magnitude, and constituting the veritable
aristocracy of the reptile race. It will best serve our purpose here to
consider chiefly these perished orders and their history, and then to
notice very shortly those that now survive.
[Illustration: FIG. 142.—Skeleton of _Ichthyosaurus_. Lias. England.]
The first of the extinct orders is that of the great Sea-lizards,[65] of
which the now familiar _Ichthyosaurus_ and _Plesiosaurus_ of the English
seas, to be seen in all museums and text-books, are the types (Figs.
142, 142_a_ and 142_b_). These were marine animals of large size, but
not fishes or amphibians. They were true air-breathing reptiles, but
with paddles for swimming instead of feet, and some of them with long
flattened tails for steering and propulsion. They bore, in short,
precisely the same relation to the other members of the class Reptilia
which the Whales and Porpoises bear to the ordinary quadrupeds. Some of
these animals are believed to have been fifty or sixty feet in length,
thus rivalling the Whales, while others were of smaller dimensions, like
the Porpoises and Dolphins. Some, like the _Ichthyosaurus_ and
_Pliosaurus_ (Fig. 142_a_), were strongly built and powerful swimmers,
and able to destroy the largest fishes, while others, like
_Plesiosaurus_, had the body short and compact, the head small, and the
neck long and flexible, and probably preyed on small animals near the
borders of the waters. Catalogues of British fossils alone include about
thirty species of Enaliosaurs, which haunted the coasts of Mesozoic
Europe, a wonderful fact, when we consider the absence of these
creatures from the modern seas, and the probability that only a fraction
of the species are yet known to us.
[Illustration: FIG. 142_a_.—Head of _Pliosaurus_. Jurassic. Much
reduced.]
[Illustration: FIG. 142_b_.—Paddle of _Plesiosaurus Oxoniensis_.
Jurassic.—After Phillips. One-tenth natural size.]
Another remarkable group is that to which Cope has given the name of
_Pythonomorpha_, and which he regards as allied to the serpents, or as
gigantic sea-serpents provided with swimming paddles, but which Owen
considers more nearly connected with the lizards. In either case they
constitute a group by themselves, remarkable not only on account of
their anatomical affinities with animals so unlike them in general port,
but also for their enormously extended length and formidable dentition
(Fig. 143). Such animals as the _Mososaurus_ of Maestricht and
_Clidastes_ of Western America may have exceeded in length the largest
Ichthyosaurs and the most bulky of living Cetaceans, though their
slender forms and numerous vertebræ remind one of the semi-fabulous
sea-serpent, rather than of any known animal of our modern age. They
were characteristic of the Later Mesozoic, more especially of the
Cretaceous period, and must have been formidable enemies to the fishes
of their time.
Owen has formed two orders[66] for the reception of some remarkable
extinct reptiles of this age, found especially in South Africa and
India, but also in Europe and America. The first includes large
lizard-like animals having horny jaws like those of turtles, and in some
of the species with great defensive tusks (Fig. 144). Their mode of life
is not well known, but they may have been peaceable and harmless
vegetable feeders. The second has been already referred to, in
connection with the Permian, where it first appears, though it is
continued in the Trias (Fig. 145). The resemblance of the skulls of
these creatures to those of Carnivorous mammals is very striking, and
nothing can be more singular than their early appearance and their
decadence before the advent of those Tertiary mammals which in more
modern times occupy their place.
[Illustration: FIG. 143.—Skeleton of _Clidastes_. A great Mososauroid
Sea Reptile of the Cretaceous.—After Cope, much reduced.]
[Illustration: FIG. 144.—An Anomodont Reptile of the Trias (_Dicynodon
lacerticeps_, Owen). Reduced.]
[Illustration: FIG. 145.—A Theriodont Reptile of the Trias
(_Lycosaurus_).—After Owen. Reduced.]
[Illustration: FIG. 146.—Skeleton of _Pterodochylus crassirostris_.
Jurassic of Solenhofen. Reduced.]
[Illustration: FIG. 147.—Restoration of _Rhamphorhyncus Bucklandi_.
Jurassic of England.—After Phillips.
_a_, One of the teeth. Natural size.]
Perhaps the most extraordinary of all the Mesozoic modifications of the
reptilian type was that of the flying reptiles, or _Pterodactyls_.
These were, in short, lizards modified for flight, somewhat in the same
manner with the bats among the mammals. If the bat may be likened to a
flying shrew-mouse, a Pterodactyl may in like manner be compared to a
flying lizard; but the modification in the latter case is by much the
more remarkable, inasmuch as the lizard is a cold-blooded animal, and
far less likely to be endowed with the active circulation and muscular
power necessary to flight than is the mouse. In point of fact, there can
be no doubt that the Pterodactyls must have been provided with some
approach to a mammalian or ornithic heart, as they certainly were with
great breast-muscles attached to a keel in the breast-bone for working
their large membranous wings. These wings were also somewhat original in
their construction. They were not furnished with pinions, like those of
the bird, but with a membrane like that of the bat, and this, instead of
being stretched over four enormously lengthened fingers, as in that
quadruped, was supported on a single elongated finger, corresponding,
singularly enough, to the little finger, which usually inconspicuous
member constituted in some of these strange creatures a limb longer than
the whole body (Figs. 146, 147.) The other fingers of the hand were left
free for walking or grasping. They are thus believed to have been able
to walk as well as to fly, and even in case of need, to swim; while
they could probably perch like birds on rocks and trees. Their heads,
though very lightly framed, were large and reptilian in aspect, and
furnished with sharp teeth, and sometimes probably with a beak as well.
Few creatures of the old world are of more hideous and sinister aspect.
Yet some of them must have been as light and graceful on the wing as
swallows or sea-gulls. There are many species, most of them small, but
some of those in the later Mesozoic attained to so great a size that the
expanse of their wings must have exceeded twenty feet, making them
veritable flying dragons, probably formidable to all the smaller animals
of their time. Though these animals were strictly reptiles, they
combined in their structures contrivances for aërial locomotion now
distributed between the bats and the birds. They had bat-like wings and
bird-like chests. Some had horny beaks. All had hollow limb bones, and
air cavities to give lightness to the skull. Their brains approach to
those of birds, and, as already stated, their respiration and
circulation must have been of a high order. These facts are very
suggestive, and perhaps in no point is the imagination or the faith of
the devout evolutionist more severely tested than in realising the
spontaneous assumption of these characters by reptiles, and their
subsequent distribution between the very dissimilar types in which they
are now continued.
[Illustration: FIG. 148.—A Jurassic Bird (_Archæopteryx
macroura_).—After Owen.]
[Illustration: FIG. 149.—Jaw of a Cretaceous Toothed Bird (_Ichthyornis
dispar_).—After Marsh. Natural size.]
The approximation of the winged reptiles to the birds is further
increased by the facts that in the Jurassic and Cretaceous periods there
were birds having reptilian tails and probably toothed jaws
(_Archæopteryx macroura_, Fig. 148). The species just named, while in
its limbs, trunk, and feathers a veritable perching bird, resembles a
reptile in its head and tail. In the Cretaceous of Western America,
Marsh has recently discovered two distinct types of toothed birds, one
having the teeth in regular sockets, the other having them implanted in
a groove in the jaw. One of these birds (_Ichthyornis dispar_, Fig. 149)
was larger than a pigeon, with powerful wings constructed like those of
ordinary birds. It had also the curious and old-fashioned peculiarity of
biconcave vertebræ, like those of fishes and some reptiles. Another
(_Hesperornis regalis_) stood five or six feet high, and had rudimentary
wings like those of the Penguins. These toothed birds extend into the
Eocene Tertiary, where the _Odontopteryx_ of Owen has been known for
some time. In the Eocene, however, this toothed bird is associated with
others of ordinary types, allied closely to the Ostriches, the Pelicans,
the Ibis, the Woodpeckers, the Hawks, the Owls, the Vultures, and the
ordinary perching birds. In the Later Mesozoic, indeed, some reptiles
became so bird-like that they nearly approached the earliest birds; but
this was a final and futile effort of the reptile to obtain in the air
that supremacy which it had long enjoyed in earth and water; and its
failure was immediately succeeded in the Eocene by the appearance of a
cloud of true birds, representing all the existing orders of the class.
[Illustration: FIG. 150.—Jaw of _Bathygnathus borealis_ (Leidy). A
Triassic Dinosaur from Prince Edward Island.
_a_, Cross section of second tooth, natural size. _b_, Fifth tooth,
natural size.]
We may close our notice of the winged reptiles of the Mesozoic by
quoting from Phillips his summary of the characters of _Rhamphorhyncus_
(Fig. 147)[67]: “Gifted with ample means of flight, able at least to
perch on rocks and scuffle along the shore, perhaps competent to dive,
though not so well as a palmiped bird, many fishes must have yielded to
the cruel beak and sharp teeth of the _Rhamphorhyncus_. If we ask to which
of the many families of birds the analogy of structure and probable way
of life would lead us to assimilate _Rhamphorhyncus_, the answer must
point to the swimming races, with long wings, clawed feet, hooked beak,
and habits of violence and voracity; and for preference, the shortness
of the legs and other circumstances may be held to claim for the
Stonesfield fossil a more than fanciful similitude to the groups of
Cormorants and other marine divers which constitute an effective part of
the picturesque army of robbers of the sea.”
[Illustration: FIG. 151.—_Hadrosaurus Foulkii_ (Cope). An Herbivorous
Dinosaur, 28 feet long.—After Hawkins’s restoration.]
Lastly, the reptiles, in this age of their imperial sway, culminated in
the _Dinosaurians_, animals far above any modern Reptilia in the
perfection of their organisation, and many of them of gigantic size.
Just as the Pterosaurs filled the place now occupied by the birds, so
the Dinosaurs filled that represented by the mammals, or rather they
took up a place holding some close relations with both the birds and the
mammals. There were thus reptilian animals which on the one hand were
the elephants and lions of their time, and on the other bore a grotesque
resemblance to creatures so unlike these as the Ostriches, in so far as
their anatomical structure was concerned; while it is evident that their
whole organisation places them in the highest position possible within
the reptilian class. Some of them must have been herbivorous, and
probably slow in movement and quiet in nature. Others were carnivorous
and of terrible energy, while furnished with the most destructive
weapons (Figs. 152, 153). Many had the power of erecting themselves on
their hind-feet and walking as bipeds; and to adapt them to this end
their hinder limbs were very large and strong, and they had long
pillar-like tails, while their fore-feet were comparatively small, and
used perhaps mainly for prehension (Figs. 151, 154).
[Illustration: FIG. 152.—Jaws of _Megalosaurus_.—After Phillips.
One-tenth natural size.]
The size of some of these creatures was stupendous. The _Hadrosaurus_ of
New Jersey, an Herbivorous species (Fig. 151), when erected on its hind
limbs and tail, must have stood more than twenty feet in height.
_Megalosaurus_ and _Iguanodon_, of the English Jurassic and Wealden,
must have been of still more gigantic size. The former was a carnivorous
animal, its head (Fig. 152) four or five feet in length, armed with
teeth, sabre-shaped, sharp and crenate on the edges (Fig. 153), its hind
limbs of enormous power, so that if our imagination does not fail us in
the attempt to realise such a wonder, we may even suppose this huge
animal, much larger than the largest elephant, springing like a tiger on
its prey, a miracle of terrible strength and ferocity, before which no
living thing could stand. Its companion, _Iguanodon_, was, on the
contrary, a harmless herbivorous creature, using its great strength and
stature as a means of obtaining leaves and fruits for food, and perhaps
falling a prey to the larger Carnivorous Dinosaurs its contemporaries. A
still more bulky animal was the _Ceteosaurus_, so admirably described by
Phillips. Its thigh-bone measures more than five feet in length and a
foot in diameter; and it must have stood ten feet high when on all
fours, while its length must have reached forty or fifty feet. It seems
from the forms of its bones to have been able to walk on land, but
probably spent most of its time in the water, where it may be compared
to a huge reptilian hippopotamus. Very recently some bones found in
rocks, possibly of Wealden age, in Western America, and described by
Cope and by Marsh, indicate that even _Ceteosaurus_ had not attained to
the maximum of Dinosaurian dimensions. These new animals have vertebræ
twenty inches in length and from twelve inches to thirteen inches in the
diameter of their bodies, while their lateral processes stretched three
and a half feet. The shoulder-blade of one species is five feet in
length, and its thigh-bone is six feet long. From these measurements
Cope concludes that, unlike most other Dinosaurs, it had the fore-feet
larger in proportion than the hind-feet, so as to have somewhat the
appearance of a large giraffe. The bones of the back have a remarkable
cavernous structure, which Cope interprets as indicating air cavities,
to give lightness, as in the case of the bones of birds; but Owen
suggests that the cavities were filled with cartilage, and that the
animals were aquatic in their habits. Evidently in point of size the
Dinosaurs had a better claim than even Behemoth to be called the “chief
of the ways of God.” Some of them, however, were of small size, and
probably active and bird-like in their movements. One of these is the
animal represented in Fig. 154, a species from the lithographic
limestone of Solenhofen.[68]
[Illustration: FIG. 153.—Tooth of _Megalosaurus_. Natural size.
_a_, Cross section. _b_, Crenellation of edges. Enlarged.]
Nothing in the life of the Mesozoic has so seized on the imagination of
evolutionists as the links of connection between birds and reptiles,
which has even been introduced by Huxley into the classification of
animals, by his grouping these heretofore very distinct classes in one
gigantic and comprehensive class of _Sauropsida_. It is necessary,
therefore, to glance at these connections, and if possible to arrive at
some conception of their true value. The links which connect the
reptiles and the birds are twofold. First, that between the Dinosaurs
and the ostrich tribe,[69] and, secondly, that between the Pterodactyls
and their allies, and the peculiar Mesozoic birds, such as
_Archæopteryx_. The first would serve to account for the few exceptional
Struthious birds of the modern world. The second would account for the
Passerine and other more ordinary birds; and thus, according to
evolution, the now somewhat homogeneous class of birds would have a
double, or more probably multiple, origin from several lines of
reptilian ancestors. This, no doubt, greatly complicates the links of
connection, whether these be supposed to indicate derivation or not.
[Illustration: FIG. 154.—_Compsognathus._ One of the smaller
Dinosaurs.—After Wagner.]
If we inquire as to the first connection above stated, we may define it
briefly in the words of Prof. Phillips, with reference to
_Megalosaurus_, which “was not a ground-crawler, like the alligator, but
moving with free steps, chiefly, if not solely, on the hind limbs, and
claiming a curious analogy, if not some degree of affinity, with the
ostrich.”[70] But the question arises, Was this resemblance merely that
of two oviparous bipeds, or anything more? and when we set off, against
the resemblance in haunch bones and hind limbs, the entire dissimilarity
in head, in fore limbs, in vertebræ, in tail, and probably in external
covering, we are disposed to agree with Huxley in his statement, with
respect to the Struthious birds, that their “total amount of
approximation to the reptilian type is but small; and the gap between
reptiles and birds is but very slightly narrowed by their existence.”
There is therefore here a great gap, even in the linking together of the
types, independently of any question of derivation.
The second line of connection appears at first sight more promising.
_Archæopteryx_ has a reptilian tail, and claws on the wing; and, as it had
toothed jaws, like some of the birds in the Cretaceous, must have
altogether made a much nearer approach to a reptile than any modern bird
does. The remarkable “fish-bird” (_Ichthyornis_) of Marsh is also very
reptilian in some of its characters. But when we compare these reptilian
birds with the Pterodactyls and their allies, a vast gap at once becomes
apparent. Disregarding the external clothing, we find the wing in the
two groups entirely dissimilar in details of construction, and this
dissimilarity extends to the hind limbs as well, so that the
Pterodactyls resemble bats rather than birds.
Without committing ourselves to any doctrine of development, we might
have rejoiced if our geological discoveries had established a continuous
chain, or two continuous chains, of being between the reptiles and the
birds; but this end is evidently still far from being attained, though
some approximation has undoubtedly been made. To quote again the
admission of Huxley: “Birds are no more modified reptiles than reptiles
are modified birds, the reptilian and ornithic types being both in
reality somewhat different superstructures, raised upon one and the same
ground-plan”—that ground-plan being the idea of the air-breathing
oviparous vertebrate, and the reptile representing the less specialized
and less ornate building. As yet the origin of that idea, and the mode
of carrying it out to completion, remain unknown, except to the
Architect and Builder, who may reveal them to earnest seekers for truth
in His own good time.
As to links of connection with the Mammalia, these are still more
obscure. In the Mesozoic the mammals are represented as yet only by a
few small species allied to the pouched (Marsupial) and insectivorous
quadrupeds of Australia, and these are closely linked with some of the
smaller carnivorous Mammalia of the early Tertiary; but neither approach
very closely to any known reptilian types. Nor have we yet any
connecting links between the great marine reptiles and the Cetaceans and
Sirenians which in the Tertiary take their place in the sea.
It is an interesting fact, to come before us in our next chapter, that
the great land reptiles of the Mesozoic survived long enough to become
contemporary with the introduction and first luxuriance of the modern
types of vegetation in the later Cretaceous. It would be natural to
suppose that access to these great supplies of better food would have
stimulated the increase and development of the herbivorous species, and
would have indirectly had the same effect on those that were
carnivorous; but the opposite result seems to have followed, and in the
next period the reptiles altogether gave place to the mammals, unless,
indeed, they were themselves by some mysterious and comparatively rapid
process transformed into Mammalia, to suit them to the better conditions
of an improved world.
So far as yet known, the reign of reptiles was world-wide in its time;
and the imagination is taxed to conceive of a state of things in which
the seas swarmed with great reptiles on every coast, when the land was
trodden by colossal reptilian bipeds and quadrupeds, in comparison with
some of which our elephants are pygmies, and when the air was filled
with the grotesque and formidable Pterodactyls. Yet this is no fancy
picture. It represents a time which actually existed, when that
comparatively low, brutal, and insensate type of existence represented
by the modern crocodiles and alligators was supreme in the world. The
duration of these creatures was long, and in watching the progress of
creation, they would have seemed the permanent inhabitants of the earth.
Yet all have perished, and their modern successors, except a few large
species existing in the warmer climates, have become subject to the more
recently introduced Mammalia.
How did the ancient reptile aristocracy perish? We are ignorant of the
details of the catastrophe, but their final disappearance and
replacement by the more modern fauna was connected with a great
continental subsidence in the Cretaceous age, and with changes of
climate and conditions preceding and subsequent to it. Yet the struggle
for continued dominion was hard and protracted; and toward its close
some of the champions of the reign of reptiles were the greatest and
most magnificent examples of the type; as if they had risen in their
might to defy approaching ruin. Thus some of the most stupendous forms
appear in the later Cretaceous, after the great subsidence had made
progress and almost attained its consummation. Like the antediluvian
giants, they were undismayed even when the land began to sink beneath
their feet; and for them there was no ark of deliverance.
[Illustration: LOWER CRETACEOUS LEAVES. REDUCED IN SIZE.—After
Lesquereux.
_a_, _Aralia Saporteana_. _b_, _Sassafras araliopsis_. _c_, _Quercus
primordialis_. _d_, _Fagus polyclada_. _e_, _Salix proteæfolia_. _f_,
_Laurus proteæfolia_.]
CHAPTER VIII.
THE FIRST FORESTS OF MODERN TYPE.
For a long time it was believed by geologists that a great and
mysterious gap separated the Upper Cretaceous from the oldest Tertiary
formations; and in Western Europe, in so far as physical conditions and
animal life are concerned, the severance seemed nearly complete. Oceanic
deposits, like the Upper Chalk, are succeeded by beds of littoral and
estuarine characters. The last and some of the greatest of the Mesozoic
Saurians have their burial-places in the Upper Cretaceous, and appear no
more on earth. The wonderful shell-fishes of the Ammonite group, and the
cuttle-fishes of the Belemnite type, share the same fate. With the
earliest deposits of the Eocene Tertiary came in multitudes of large
Mammalia heretofore unknown, and the Cetaceans appear in the sea instead
of the great marine lizards; while shells, corals, and crustaceans of
modern types swarm in the waters. Thus it is true that a great and
apparently somewhat abrupt change takes place at the close of the
Cretaceous, and terminates for ever the reptilian age. Even in regions
like Western America, where physically the later Cretaceous shades
gradually into the earlier Tertiary, so that there have been doubts as
to the limits of these several periods, the same great change in animal
life occurs.
But a link of connection has at length been found in the history of the
vegetable kingdom. The modern flora came in with its full force in the
later Cretaceous, before the end of the reptilian age, and continued
onward to the present time. Thus the plant takes precedence of the
animal, and the preparation was made for the mammalian life of the
Eocene by the introduction of the modern flora in the Cretaceous period.
In like manner it is possible that the great graphite deposits of the
Laurentian indicate a vegetation which preceded the swarming marine life
of the Cambrian; and it is not improbable that the Palæozoic land flora
existed long before the first land animals. Thus the plant, as in the
old Mosaic record, ever appears on the day before the animal, in each
stage of the development of the world.
In Chapter IV. we traced the history of the old and rich vegetation of
the Coal period. But this vegetation consisted principally of cryptogams
and those lowest phænogams, of the pine and cycad groups, which have
naked seeds. In the modern flora we may arrange the several groups of
plants, somewhat naturally, as follows:—
_Series I._, CRYPTOGAMS:—
Class 1, _Thallophytes_, sea-weeds, lichens, fungi.
” 2, _Anophytes_, mosses, &c.
” 3, _Acrogens_, ferns, lycopods, horsetails.
_Series II._, PHÆNOGAMS:—
Class 4, _Gymnosperms_, pines, cycads, &c.
” 5, _Endogens_, palms, grasses, &c.
” 6, _Exogens_, oaks, maples, &c.
With reference to the history of these groups the record stands as
follows:—In the Palæozoic age classes 3 and 4 culminated, and
constituted the great mass of the arboreal vegetation. On entering the
Mesozoic, No. 3 becomes somewhat diminished, but No. 4 continues with
unabated prevalence, so that the Mesozoic has sometimes been
characterized as emphatically the age of Gymnosperms. With these appear
some Endogens, allied to the modern Yuccas and Screw pines and Arums.
But in the lower Mesozoic rocks we have no representatives of the
broad-leaved Exogens (Angiosperms), which constitute the great mass of
ordinary forest vegetation; and it is only in the Cretaceous that we
find them appearing in force, and that the monotonous vegetation of the
older style was replaced by the more beautiful and varied forms of our
modern woods.
In Europe, in the lower part of the Upper Cretaceous of Bohemia
(_Cenomanian_), have been found some leaves which indicate the beginning
of this change. These have been referred to Cæsalpinias or Brasilettos,
pod-bearing trees of India and tropical America, _Aralias_ or Ginsengs,
_Magnolias_, Laurels, an Ivy, and a peculiar and uncertain genus
(_Credneria_). With these are noble palms, both of the types with
pinnate and palmate leaves, and trees allied to the Giant _Sequoias_ of
California, and to the Araucarian pines of the southern hemisphere. (See
Frontispiece to this Chapter.) These ancient Cretaceous forests of
Eastern Europe are compared by Saporta with those which now live in the
warmer portions of China or in South America—truly a marvellous change
from the sombre and uniform vegetation by which they seem to have been
immediately preceded. A still further development of modern vegetation
takes place in the next or highest member of the Cretaceous, the
Maestricht beds (_Senonian_), where we find a crowd of modern types. On
this great change Count Saporta remarks with truth that there seem to
have been periods of pause and of activity in the introduction of
plants. The Jurassic period was one of inactivity; and a new and
vigorous evolution, as he regards it, is introduced in the middle of the
Cretaceous.
This new and grand elevation of the vegetable kingdom in the Cretaceous
age was not local merely. In Moravia, in the Hartz, in Belgium and
France, even in Greenland, the same great renewing of the face of the
earth was in progress. In America it was proceeding on a grand scale,
and seems to have set in earlier than in Europe.[71] In the Dakota group
of the West, one of the lower members of the Cretaceous, and covering a
vast area, a rich angiospermous flora has been discovered by Hayden, and
described by Lesquereux and Newberry, and beds of coal have been formed
from its remains. In Vancouver’s Island in British Columbia, Cretaceous
coal measures occur, comparable in value and in the excellence of the
fuel they afford with those of the true coal formation. Some of the beds
of coal are eight feet in thickness, and the shales associated with them
abound in leaves of exogenous trees generally similar to those still
living in America. In these beds are also found mineralized trunks,
which present under the microscope the familiar structures of our oaks,
birches, and other modern trees. Thus all over the northern hemisphere
the elevation of the land out of the waters of the great Cretaceous
subsidence was signalized by a development of noble and exuberant forest
vegetation, of the types still extant. The following list of families
found in the Cretaceous, after Saporta, will show the botanist how fully
our modern Exogens are represented:—
APETALÆ.
_Myricaceæ._
_Cupuliferæ._
_Betulaceæ._
_Salicaceæ._
_Moreæ._
_Proteaceæ._
_Lauraceæ._
GAMOPETALÆ.
_Apocynaceæ._
_Ericaceæ._
_Ebenaceæ._
_Myrsineæ._
POLYPETALÆ.
_Araliaceæ._
_Hamameliaceæ._
_Helleborineæ._
_Magnoliaceæ._
_Tiliaceæ._
_Celastraceæ._
_Anacardiaceæ._
_Myrtaceæ._
Of the plants in this list, some, like the oaks, birches, willows, and
heaths, are common and familiar members of the flora of the northern
hemisphere to-day, and even of the European flora. Some, like the
_Magnolias_, _Myricas_, and witch-hazels, are characteristically American,
and a few, like the Proteaceæ, are now confined to the southern
hemisphere. Some of these families have dwindled since the Cretaceous
time, so as to be represented by very few species, or at least have not
advanced, while others have multiplied and prospered; and on the whole
the flora of the northern hemisphere seems to have been as rich in this
early beginning of our modern forests as it is at the present day.
Lesquereux’s results, with reference to the American flora of the Dakota
group, are very similar, and present some surprising features of
resemblance to modern American forests, though he remarks that these
Cretaceous trees are generally characterized by the even or unserrated
edges of their leaves; and the same remark seems to apply to the oldest
Cretaceous leaves of Europe.
A very singular feature of the Cretaceous flora is the number of species
of some genera now represented by few or even a single species; and this
is the more remarkable when we consider how few species, comparatively,
of the older flora, are known to us. For example, Lesquereux, though
aware of the great variability of the modern _Sassafras_ of America,
recognizes eight species of this genus in the Dakota Cretaceous, one of
which seems to be that still living in America, so that it has continued
unchanged, while the others have perished (Fig. 155). Thus this genus
culminates at once in the Cretaceous, but continues still in one of its
species. Again, the tulip-tree, _Liriodendron_, one of the most
beautiful, unique, and invariable of American trees, is represented by
one sole species in the present world. There seem to be no less than
four in the Dakota beds, besides others in the Cretaceous of New Jersey,
and one species is found in the Tertiary of Greenland as well as in that
of Europe (Fig. 156). There are probably four or five species of
plane-tree (_Platanus_) now extant, of which but one occurs in America,
unless _P. Mexicana_, the Mexican plane-tree, is a good species as
distinct from the ordinary, more northern, form. There are seven
species, according to Lesquereux, in the Cretaceous of Dakota alone.
This sort of evolution backward, or from many species to few, would
probably be greatly increased, had we fuller knowledge of the Cretaceous
flora, as there are several genera already represented by as many
species as they can boast in modern times. We have already seen that
this abrupt and sudden culmination of genera and families, and their
subsequent decadence, is no rare thing in geology, and it connects
itself with that idea of periods of creative activity which we have
already had occasion to notice.
[Illustration: FIG. 155.—_Sassafras cretaceum_ (Newberry).]
[Illustration: FIG. 156.—_Liriodendron primævum_ (Newberry). A
Cretaceous Tulip-tree.]
[Illustration: FIG. 157.—_Onoclea sensibilis._ Eocene.—After
Newberry.]
[Illustration: FIG. 158.—_Davallia tenuifolia._ Eocene.—After Dawson.
Natural size and enlarged.]
I have dwelt principally on the phænogamous plants of the Cretaceous, as
presenting the most noteworthy and new features of the time; but we must
not forget that though cryptogams were deposed from the high position
they held in the Palæozoic, they still existed; and there are more
especially many interesting species of ferns and equisetums in the
Cretaceous and Eocene rocks. These are, however, of modern types; and
it is remarkable that some of them appear to have continued without even
specific change from the later Cretaceous up to the present time. A
striking illustration of this is afforded by two ferns discovered side
by side in the oldest Eocene beds[72] of the plains west of Red River,
and described in Dr. G. M. Dawson’s report on the 49th parallel. One of
these is the well-known and very common _Onoclea sensibilis_ (Fig. 157),
or sensitive fern of Eastern America.[73] This species came into
existence at latest at the close of the Cretaceous, and has apparently
been continued in America up to the present time. In Europe, where it
does not now live, it occurs as a fossil in Eocene beds in the Isle of
Mull. The other is _Davallia tenuifolia_ (Fig. 158), a delicate little
plant belonging to a genus not now represented in America, and to a
species at present found only in Asia. Yet this species also lived in
America in early Eocene times, but has since been banished, though its
former companion, the _Onoclea_, still holds its ground. Such cases of
specific persistence along with great changes of habitat are very
instructive as to the permanence of species.
Count Saporta, whose just remarks on the marvellously sudden incoming of
the Cretaceous flora we have already referred to, also notices the fact
that the families and genera represented in this flora are a most
miscellaneous and unconnected assemblage, showing either the
simultaneous appearance of many dissimilar types, or requiring us to
believe in the existence of these and of intermediate forms for a very
long period before that in which they are first found. This may,
however, be placed in connection with the appearance of an exogenous
tree (_Syringoxylon_) in the Devonian, referred to in a previous
chapter. It would be a strange and now little suspected case of
imperfection of the record, if it should be found that trees of this
type were lurking in exceptional corners through all the vast periods
between the Devonian and the Cretaceous, to burst forth in unwonted
variety and luxuriance in the latter period.
The new Cretaceous flora appears first in beds which had been recently
elevated from the ocean of the great Cretaceous subsidence; and when it
first flourished, in temperate regions at least, the continents were of
small dimensions, and broken up into groups of islands. Farther, America
would seem to have had precedence of the Eastern Continent, and the
Arctic of the Temperate regions. Thus on the elevation of the later
Cretaceous land, plants previously established in the far north spread
themselves southward, over newly-raised lands, radiating from the polar
regions into Europe, Asia, and America. This seems the only way of
accounting for the similarity of the plants in these distant countries.
The new flora of the Upper Cretaceous in its journey southward met with
a climate probably warmer than the present, yet not so warm as to
prevent trees similar to those now living in the same latitudes from
flourishing.
Let us now trace this flora through the succeeding ages, in which I
shall follow pretty closely some general statements made by Count De
Saporta in memoirs recently published.
[Illustration: FIG. 159.—Eocene Leaves. From Aix.
_a_, _Quercus antecedens_ (Saporta). _b_, _Diospyros pyrifolia_
(Saporta). _c_, _Myrica Mathesonii_ (Saporta).]
At the beginning of the Eocene we find a humid and warm climate in
Europe, with great forests of oaks, chestnuts, laurels, giant pines, and
other genera, some of them still European, others Asiatic or American,
and many of them survivors of the Cretaceous (Figs. 159 to 162); and at
the same period similar forests overspread those great plains of North
America which were rising from out the Cretaceous sea, and there vast
swampy beds were formed of vegetable _débris_, giving origin to beds of
brown coal, some of them eighteen feet in thickness. Then came in Europe
and Asia that great subsidence under the sea, during which the Nummuline
limestones were deposited, and when the old continent was resolved again
into an archipelago of islands, perhaps closely connected with more
southern lands. This led to a great increase of southern forms of
plants, which does not seem to have occurred to the same extent in
America, where the flora is more continuous, though showing a warmer
climate in the older than in the newer Eocene. At this period Palms,
Screw pines, Proteaceous shrubs, Myrtles, _Acacias_, and other plants of
the character of those of more southern climates were dominant in Europe
(Fig. 163). The well-known beds of Bournemouth, in the south of
England,[74] contain a rich flora of the Eocene age, perhaps of its
middle period, and reminding us of the forests of sub-tropical India or
Australia.
[Illustration: FIG. 160.—An Ancient Clover (_Trifolium palæogæum_,
Saporta). Eocene. Aix.]
[Illustration: FIG. 161.—An Eocene Maple (_Acer sextianus_, Saporta).
Aix.]
[Illustration: FIG. 162.—A European Magnolia of the Eocene (_M. dianæ_,
Saporta). Aix.]
[Illustration: FIG. 163.—Flower and Leaf of _Bombax sepultiflorum_.
Eocene of Aix.—After Saporta.
A European representative of the Silk-cotton-tree of the East Indies and
Tropical America.]
Gradual elevation of the land favoured for a time the extension of these
plants, and the warmth of the climate allowed them to extend even into
Arctic latitudes. But in the middle of the Eocene another subsidence
occurred, which exterminated much of the Eocene flora, and was perhaps
accompanied with a reduction of temperature, in which the more northern
lands became covered with great forests of trees allied to the Pines. In
England a remarkable deposit of this age is that of Bovey Tracey, in
Devonshire, where beds of clay and brown coal have afforded a rich flora
of American and southern types. The _Sequoia_ shown in Fig. 164 abounds
at this place, and is a near relation to the celebrated “big trees” of
California; the _Cinnamomum_ in Fig. 165 is a type equally foreign from
modern England. It is a curious feature of the Bovey deposit that
immediately above these Eocene beds, holding a rich flora of warm
temperate character, are glacial clays with leaves of Arctic willows and
of the dwarf birch, indicating a climate much more severe than that of
the British Islands at present.[75]
[Illustration: FIG. 164.—Branch and Fruit of _Sequoia Couttsiæ_ (Heer).
Eocene. England.]
In the Miocene period the land again rose, and the northern flora spread
itself southward equally over Europe, Asia, and America, so that the
Miocene flora of all these regions is very similar; and this Miocene
flora continues substantially to this day in Eastern America and Eastern
Asia, except that it has been greatly reduced in number of species by
the intervention of the cold glacial period; but in Europe and Western
America it has been largely replaced by other apparently more modern
species.
[Illustration: FIG. 165.—_Cinnamomum Scheuchzeri_ (Heer). Eocene.
England.]
A striking result of recent discoveries is the fact that in Cretaceous
and Eocene times a very warm climate prevailed in the extreme Arctic
regions, and trees of temperate latitudes grew there freely. In the
recent Arctic expedition, Captain Fielden found in latitude 81° 40’,
within 600 miles of the Pole, a bed of lignite, from twenty-five to
thirty feet in thickness, associated with remains of plants such as now
grow only in temperate latitudes.
“From the character of the plant-remains, Dr. Heer infers that the
lignite of this locality represents an ancient peat-moss, which must
have been of wide extent, with reeds, sedges, birches, poplar, and
certain conifers growing on its banks; while the higher and drier ground
in the neighbourhood probably supported a growth of pines and firs, with
elms and hazel-bushes. The remains of water-lilies suggest the existence
of a fresh-water lake in the old peat-moss, which must have remained
unfrozen during a great part of the year.”
It is to be observed with reference to the age of these beds, that as
the Later Cretaceous and Eocene flora of Europe and America migrated
from the north, the plants found in the beds of that age in the
temperate latitudes may really be somewhat older in the Arctic regions,
a fact which produces some uncertainty as to their actual age.
The warmth required for the growth of luxuriant forests near the Pole
might be secured by a different distribution of land and water, and of
the oceanic currents, but the requirements of plants as to light seem
more difficult to meet, and it has been doubted whether species similar
to those which are accustomed in modern times to regular alternations of
day and night could submit to the long Arctic winter darkness. It is
known, however, that in conservatories in Northern Russia plants
supplied with heat and moisture can endure in winter great deprivation
of light, and at Disco, in Greenland, roses and fuchsias flourish as
house plants.[76] These facts show that if there were sufficient light
and heat in summer, a great number of the plants of temperate latitudes
could endure extreme cold and much deprivation of light in winter.
It may be well here to inform the reader that some confusion as to the
succession of the Cretaceous and Tertiary floras in America has arisen
from the fact that the plants which are evidently Eocene in Greenland
and America have been until lately incorrectly regarded as Miocene in
Europe. In the Western States, the Dakota group of Lesquereux is
overlain by 2000 feet of Cretaceous beds, containing the marine shells
characteristic of that age, but no plants. But in Vancouver’s Island
these same Upper Cretaceous beds contain an abundant flora, which some
botanists have called Tertiary for the reason already mentioned. Above
the 2000 feet of marine beds overlying the Dakota group is the Lower
Lignite group of Lesquereux, holding many fossil plants, including Palms
and other evidences of a warmer climate than that of the Cretaceous, and
which constitute a Lower Eocene flora corresponding in some respects to
that of Europe. This is succeeded by an Upper Lignite group, also
Eocene, but representing a more temperate climate, and therefore
resembling more nearly the Cretaceous flora. This is nearly identical
with the so-called Miocene of Greenland, Alaska, and Mackenzie River,
which the facts collected by the Canadian geologists have shown to be
really Eocene.[77] But the Canadian reports containing these facts are
comparatively little known in Europe, hence incorrect ideas as to the
succession of these floras have been handed from one writer to another.
To those who adopt extreme views as to the refrigeration of the northern
hemisphere in so-called glacial times, there is great difficulty in
accounting for the continued existence of the early Tertiary flora; but
if we adopt moderate views as to this, and demand merely a great
subsidence, with much reduction of mean temperature, we may suppose that
the plants previously existing were preserved on insular spots, whence
they were ready to recolonize the land on its emergence from the sea. It
seems certain, however, that our continents never regained, after the
Glacial period, the exuberance of plant life which they presented in the
Miocene and earlier Pliocene; and we shall find that this statement
applies to the world of animals as well as to that of plants. This
reduction was more extreme in Europe than in Eastern Asia and Eastern
America, and the fact is thus accounted for in a recent lecture by Prof.
Asa Gray:—
“I conceive that three things have conspired to this loss. First,
Europe, hardly extending south of latitude 40°, is all within the limits
generally assigned to severe glacial action. Second, its mountains trend
east and west, from the Pyrenees to the Carpathians and the Caucasus
beyond, near its southern border; and they had glaciers of their own,
which must have begun their operations, and poured down the northward
flanks, while the plains were still covered with forest, on the retreat
from the great ice-wave coming from the north. Attacked both on front
and rear, much of the forest must have perished then and there. Third,
across the line of retreat of those which may have flanked the
mountain-ranges, or were stationed south of them, stretched the
Mediterranean, an impassable barrier. Some hardy trees may have eked out
their existence on the northern shore of the Mediterranean and the
Atlantic coast. But we doubt not, _Taxodium_ and _Sequoias_, _Magnolias_
and _Liquidambars_, and even Hickories and the like, were among the
missing. Escape by the east, and rehabilitation from that quarter until
a very late period, were apparently prevented by the prolongation of the
Mediterranean to the Caspian, and thence to the Siberian ocean. If we
accept the supposition of Nordenskiöld, that, anterior to the Glacial
period, Europe was ‘bounded on the south by an ocean extending from the
Atlantic over the present deserts of Sahara and Central Asia to the
Pacific,’ all chance of these American types having escaped from or
re-entered Europe from the south and east is excluded. Europe may thus
be conceived to have been for a time somewhat in the condition in which
Greenland is now, and indeed to have been connected with Greenland in
this or in earlier times.[78] Such a junction, cutting off access of the
Gulf Stream to the Polar Sea, would, as some think, other things
remaining as they are, almost of itself give glaciation to Europe.
Greenland may be referred to, by way of comparison, as a country which,
having undergone extreme glaciation, bears the marks of it in the
extreme poverty of its flora, and in the absence of the plants to which
its southern portion, extending six degrees below the Arctic Circle,
might be entitled. It ought to have trees, and might support them. But
since destruction by glaciation no way has been opened for their return.
Europe fared much better, but suffered in its degree in a similar way.
“Turning for a moment to the American continent for a contrast, we find
the land unbroken and open down to the tropic, and the mountains running
north and south. The trees, when touched on the north by the on-coming
refrigeration, had only to move their southern border southward, along
an open way, as far as the exigency required; and there was no
impediment to their due return. Then the more southern latitude of the
United States gave great advantage over Europe. On the Atlantic border,
proper glaciation was felt only in the northern part, down to about
latitude 40°. In the interior of the country, owing doubtless to greater
dryness and summer heat, the limit receded greatly northward in the
Mississippi Valley, and gave only local glaciers to the Rocky Mountains;
and no volcanic outbreaks or violent changes of any kind have here
occurred since the types of our present vegetation came to the land. So
our lines have been cast in pleasant places, and the goodly heritage of
forest-trees is one of the consequences.
“The still greater richness of North-east Asia in arboreal vegetation
may find explanation in the prevalence of particularly favourable
conditions, both ante-glacial and recent. The trees of the Miocene
circumpolar forest appear to have found there a secure home; and the
Japanese islands, to which most of these trees belong, must be
remarkably adapted to them. The situation of these islands—analogous to
that of Great Britain, but with the advantage of lower latitude and
greater sunshinetheir ample extent north and south, their diversified
configuration, their proximity to the great Pacific gulf-stream, by
which a vast body of warm water sweeps along their accentuated shores,
and the comparatively equable diffusion of rain throughout the year, all
probably conspire to the preservation and development of an originally
ample inheritance.”
The comparative paucity in species of the west coast of America, though
the _Sequoias_ and some other forms which have perished elsewhere are
retained there, is admitted to be exceptional, and not easily explained,
except by the supposition of peculiar local conditions affecting the
comparatively narrow strip of land between the Rocky Mountains and coast
ranges, and the Pacific.
To such widely-distributed and varied and complex phenomena as those
which have been discussed in the present chapter, it is impossible to do
justice in the space at our command. Details in relation to them will be
found in the publications of Heer, of Saporta, and of Lesquereux, and
are well worthy of study by botanists, to whom alone they can be made
fully intelligible. In general, with reference to now prevalent theories
of derivation, they present two very dissimilar aspects. No difficulty
can be greater to the evolutionist than to account for the simultaneous
appearance of so many modern generic forms in the Cretaceous; and the
fact of many of the genera presenting more and more species the farther
we trace them back is a strange anomaly of evolution. On the other hand,
the number of species continuing unchanged from the Eocene to the
Modern, the others only slightly modified, and the representative
species occurring in the floras of the old and new continents, appear to
many to give great support to the doctrine of gradual transformation of
species. Farther facts and farther comprehension of the difference
between species and races will be necessary to the settlement of these
questions. In the meantime it would appear that the Jurassic flora
rapidly gave place, at a particular point of geological time, to that
of the modern world, and this not merely in one locality, but over the
whole northern hemisphere; and there are apparently similar facts in the
southern hemisphere as well. It farther appears that each genus was at
first represented by many species, and that as time went on these were
gradually reduced to a few best suited to survive; and that the changes
of climate and level which occurred distributed these over different
parts of the continents in a way at first sight very anomalous, but
which Prof. Gray somewhat quaintly represents as follows:—
“It is as if Nature, when she had enough species of a genus to go round
the four floral regions (Europe, East Asia, West America, and East
America), dealt them fairly one at least to each quarter of our zone;
but when she had only two of some peculiar kind, gave one to us, and the
other to Japan, Mantchuria, or the Himalayas; and when she had only one,
divided it between the two partners on the opposite sides of the table.”
Lastly, it seems very probable that many so-called species are nothing
more than varietal forms, which may very well be modified descendants of
Miocene or Eocene plants now figuring in our lists under different
names.
[Illustration: SIVATHERIUM GIGANTEUM.
A Great Ruminant of the Miocene of India.
Copied by special permission of James Murie, M.D., F.G.S., &c.]
CHAPTER IX.
THE REIGN OF MAMMALS.
The incoming of that highest order of animals in which man himself, in
so far as his physical nature is concerned, takes his place, presents
some features which, though not unparalleled in the history of other
forms of life, are still very striking. The modern Mammalia are somewhat
sharply divided into three very unequal groups. First, those which
present in their full perfection the property of producing fully
developed young, which is one of the distinctive characters of the
class. These are the Placental Mammals. Secondly, those in which the
young are produced in a very imperfect condition, and are usually
nourished for a time in a marsupium or pouch. These are hence called
Marsupials. They are for the most part confined to Australasia, though a
few occur in America; and are decidedly inferior in rank to the ordinary
mammals. Thirdly, those in which there is a bird-like bill, and also
certain bird-like or reptilian peculiarities of skeleton and of the
alimentary canal. These are the Monotremes, represented by a very few
species in Australia and New Guinea.
In geological history, so far as the facts are at present known, the
second group, that of the Marsupials, antedated the others by a vast
lapse of time. The Marsupials appear in the Trias, near the beginning of
the Mesozoic period. The Placentals are not found until we reach the
beginning of the Tertiary. The Monotremes would seem to be a
comparatively modern degraded type. Thus the Marsupials existed
throughout the reptilian age, and this in those countries of the
northern hemisphere in which they are not now found. The Mesozoic
Marsupials were, it is true, of small size, but there were probably
numerous species, and though unable to cope with the great reptiles that
swarmed by the shores and on the plains, they may have found abundant
scope in the upland and interior regions of the continents.
The Upper Trias of Germany has afforded to Professor Pleininger two
teeth of a small mammal, to which the name of _Microlestes antiquus_ has
been given, under the impression that it was carnivorous, though it now
seems more likely that it was a vegetable feeder. In rocks of nearly the
same age in America, Emmons found a jaw-bone of another species
(_Dromatherium sylvestre_), which has been supposed to be a near ally of
the existing _Myrmecobius fasciatus_ of Australia (Figs. 166, 167). In
the Stonesfield slate, a member of the English Jurassic, several other
species have been found (Fig. 168), and a still larger number in the
fresh-water beds of the Upper Purbeck. Marsh has obtained many others
from the Jurassic of America. None appear to have yet been found in the
Cretaceous, but they reappear in the Eocene Tertiary, and continue to
the modern time. Their absence in the Cretaceous is probably a mere
accident, and they present an illustration of a very permanent type
little changed since its first introduction. Lyell enumerates in all
thirty-three species from the Mesozoic, all of them of small size, and
all more or less nearly related to existing Australian Marsupials,
though differing much among themselves, and including both carnivorous
and herbivorous forms (Fig. 169). Marsh has recently suggested a
somewhat new interpretation of these interesting mammalian remains.[79]
He considers them divisible into two groups, one allied to the modern
Insectivora (Moles, Shrews, Hedgehogs, &c.), but of generalized forms.
For these he constitutes a new order (_Pantotheria_, Marsh). The other
group is less numerous and is Marsupial (_Allotheria_, Marsh). The jaws
in Figs. 166 and 168 belong to the former group, that in Fig. 169 to the
latter. We should thus have both placental and Marsupial mammals in the
Mesozoic. Marsh remarks that the descent of these different types from a
common ancestry would require us to trace mammals back into the
Palæozoic, that is, on the doctrine of gradual evolution.
[Illustration: FIG. 166.—Jaw of _Dromatherium sylvestre_ (Emmons). From
the Trias of North Carolina.]
[Illustration: FIG. 167.—_Myrmecobius fasciatus._ A modern Australian
marsupial, allied to Mesozoic species.]
So soon as the palæontologist passes from the Upper Cretaceous to the
Eocene, he finds himself in the domain of the placental mammals, which
appear in numerous and large species, and this, not merely in one
region, but in every part of the world in which these deposits are known
to exist.
[Illustration: FIG. 168.—Jaw, and enlarged molar of _Phascolotherium
Bucklandi_. Stonesfield slate. England.—After Phillips.]
[Illustration: FIG. 169.—_Plagiaulax Becklesii._ Jaw, and pre-molar
enlarged, showing flat surface, with ridges.—Purbeck.]
Indeed, the recent discoveries in America and in the east of Europe have
almost thrown into the shade those researches of Cuvier in the Paris
basin which first brought this important fact to light. The Eocene
mammals, like the Carboniferous amphibians, the Mesozoic reptiles, and
the Cretaceous forests, appear to spring full-grown from the earth, and
this at nearly the same time in every part of the northern hemisphere.
It has been suggested that they may have come in gradually without our
knowledge in the Cretaceous period; but if so, we should have found some
of their remains along with those of the Upper Cretaceous plants. But
the prevalence of the great reptiles up to the close of the Cretaceous
would seem to render the co-existence of large mammals unlikely. It has
further been supposed that geological changes in the southern and
northern hemispheres may have alternated with each other, so that there
may be in the former Cretaceous beds in which the remains of ancestors
of the Eocene mammals may be found. But we do not as yet know of such
deposits. We may be content, therefore, to suppose that at the close of
the Cretaceous there was established somewhere a sort of Eden for the
first placental mammals, in which they were introduced and could live
unharmed by the decaying monsters of the reptilian age, until the time
came when they could increase and multiply and replenish the earth. The
nearest approach to such a centre of mammalian life is perhaps to be
found in those great American lake basins embedded in the mountains of
the West, which have been so well described by Hayden and Newberry, and
which have yielded so many animal remains to the researches of Leidy,
Marsh, and Cope.
[Illustration: FIG. 170.—Restoration of _Palæotherium magnum_.
Eocene.—After Cuvier and Owen.]
The typical deposits of the Early Eocene have long been those of the
Basin of Paris, where thick and highly fossiliferous deposits of this
age rest on the more or less denuded surface of the Upper Chalk, and
have afforded a rich harvest of remains of about fifty species of
placental quadrupeds, whose bones have been found in the gypsum quarries
of Montmartre. The great majority belong to the Ungulates, or hoofed
animals, and the most abundant genera are those called by Cuvier
_Palæotherium_ (Fig. 170) and _Anoplotherium_, of which there are
several species, and which have affinities with the modern Tapirs on the
one hand, and with the Horse on the other. Of the Unguiculate or clawed
orders there are carnivorous forms allied to the Hyæna and the Fox, a
Bat and a Squirrel; and the Marsupials are represented by an Opossum.
Lyell describes a bed of clay associated with the gypsum, in which are
numerous footprints, probably produced on the margin of a lake. Many of
these might be referred to the Palæothere and its allies; but there are
others belonging to quadrupeds yet unknown, and there are also tracks of
tortoises, crocodiles, and lizards, and of a large wading bird. Such a
bed, perhaps deposited on the margin of a salt lake, resorted to as a
“lick” by herbivorous animals, and by the carnivorous species which
preyed on them, is well fitted, by the thronging life which it
indicates, to teach how little we can know of the actual number and
variety of the old inhabitants of the earth.
In England, Eocene beds of the age of those of Paris, occupy the valley
of the Thames and the Isle of Wight and neighbouring parts of Hants.
They have afforded mammalian fossils similar to those of Paris, though
less abundantly, but they are rich in remains of marine animals and of
land plants.
Instead of describing the well-known animals of the French and English
Tertiaries, from these Eocene deposits upwards, I shall shortly sketch
the succession in America, as worked out by Marsh and Cope, with the aid
of the admirable summary given by Gaudry of the present state of
knowledge with reference to the sequence of mammalian life from its
appearance in the Early Eocene up to the present time.[80]
Eocene mammals, especially those gigantic whale-like creatures called
_Zeuglodon_ (Fig. 180), have been found in Eastern North America, but
the most remarkable discoveries have been made in the Western
Territories, where vast numbers of bones are imbedded in certain ancient
and wide-spread lacustrine beds. It may be well to premise here that
though the division into Eocene, Miocene, and Pliocene is recognised in
America as well as in Europe, the limits of these groups may not
precisely correspond with those in the Old World. Still we have this
certain point of departure, that the Eocene begins where the peculiar
animals of the Cretaceous end, and that the drying up of the later
Cretaceous sea and the establishment of the Eocene land were probably
nearly contemporaneous in both continents. It is true, however, in
animals as in plants, that in the successive periods of the Tertiary,
America presents an older aspect than Europe, just as its modern fauna
still contains such old forms as the opossum.
It would seem that as the mountain-ranges and table-lands of Western
America emerged from the Cretaceous waters, they became clothed with
Eocene forests and inhabited by Eocene mammals. But the waters, dammed
up by surrounding ridges, formed large lake basins, which were drained
only by the slow excavation of “cañons” as the land rose still higher.
In the successive deposits formed in these lakes both by ordinary
deposition of silt and by paroxysmal showers of volcanic ashes were
entombed great numbers of the animals which fed on their banks. It
appears that these deposits, which in some places are estimated at not
less than 8000 feet in thickness, hold the remains of three successive
faunas, differing materially from each other, and representing the
Lower, Middle, and Upper Eocene. On the flanks of the elevated region
supporting the beds formed in the Eocene lakes, are other later lake
basins of Miocene age, also abounding in animal remains. East of the
Rocky Mountains, and also on the Pacific coast, are still later Pliocene
deposits holding other and more modern Mammalia. The vast area of these
formations and the complete sequence which they show are scarcely
equalled elsewhere.
[Illustration: FIG. 171.—_Coryphodon Hamatus._ A Lower Eocene
Perissodactyl skull, greatly reduced, showing small size of brain,
_a_.—After Marsh.]
As in the Paris basin, the large Ungulates constitute the most
conspicuous feature. The great group is now usually divided into those
that are odd-toed (Perissodactyl) and those that are even-toed
(Artiodactyl). Though these are apparently arbitrary characters, they
correspond with other more fundamental differences. The first includes
such modern animals as the Rhinoceros, Tapir, and Horse. The second
includes two somewhat distinct assemblages—that with mammillated teeth,
of which the Hog and Hippopotamus are types (Bunodonts), and that with
crescental plates of enamel in the teeth, of which the Ruminants like
the Deer, Ox and Camel, are examples (Selenodonts).
[Illustration: FIG. 172.—Fore-foot of _Coryphodon_. Greatly
reduced.—After Marsh.]
The most characteristic animals of the lowest Eocene belong to the genus
_Coryphodon_ (Figs. 171, 172), which so abounded in Eocene America that
bones of about 150 individuals were found by the Wheeler Expedition in
one year in the Eocene beds of New Mexico. These animals in their
dentition approached the American tapirs, except that they had great
canines like the bear, while their feet resembled those of the elephant,
and some of them attained the dimensions of the ox. _Coryphodon_ is
thus, as might be expected in a primal placental mammal, a creature of
somewhat generalised type. Another point in which it resembles some at
least of its early Tertiary contemporaries is the small size of the
brain, especially in those parts of it supposed to minister to the
intelligence and higher instincts (Fig. 171, _a_). It is certainly
remarkable that as Tertiary time went on the successive groups of
mammals were gifted with brains of larger and larger size, fitting them
for higher functions; and ultimately for associating with man. Animals
thus low in development of brain were probably slow and sluggish and
stubbornly ferocious, and dependent on brute force for subsistence and
defence; and they would have been altogether unsuitable for
domestication had they lived to the present time.
[Illustration: FIG. 173.—Skull of an Upper Eocene Perissodactyl
(_Dinoceras mirabilis_), showing three pairs of horn-bases. Greatly
reduced.—After Marsh.]
In the Middle Eocene, the place of _Coryphodon_ was taken by _Dinoceras_
and allied forms. Some of the species nearly equalled the elephant in
size, but had shorter and stouter limbs, each supported on five great
toes—the most perfect possible sort of pedestal foot (Figs. 172, 174).
They were heavily armed with immense canines on the upper jaws, and two
or even three pairs of horns or hard protuberances on the head (Fig.
173). Creatures so supported and so armed, and living where food was
plentiful, might well dispense with any great degree of intelligence,
and their development of brain is consequently little better than that
of _Coryphodon_. These great and characteristic Eocene families have no
known successors; and in the Miocene age their place is taken by a very
different group, that of which _Brontotherium_ is the type (Fig. 175).
They are creatures of huge size, with a pair of horn-cores on the nose,
and feet with four toes in front and three behind, resembling in form
those of the rhinoceros.
[Illustration: FIG. 174.—Fore-foot of _Dinoceras_. Greatly
reduced.—After Marsh.]
[Illustration: FIG. 175.—Skull of _Brontotherium ingens_ (Marsh).
Greatly reduced. A Miocene Perissodactyl.]
[Illustration: FIG. 176.—Series of Equine Feet.—After Marsh.
_a_, _Orohippus_, Eocene. _b_, _Miohippus_, Miocene. _c_, _Protohippus_,
Lower Pliocene. _d_, _Pliohippus_, Upper Pliocene. _e_, _Equus_,
Post-Pliocene and Modern.]
While these gigantic Perissodactyles have no successors as yet known to
us, another and less conspicuous Eocene type can be traced onward to
modern times by a chain of successors which the imagination of
evolutionists has converted into a veritable genetic series, to which
they appeal as a “demonstration” of the process of descent with specific
modifications. In the Lower Eocene are found the remains of a diminutive
ungulate (_Eohippus_), of the stature of a moderately-sized dog. It has
four toes and a rudiment of a fifth in front, and three toes behind; and
has teeth slightly resembling those of the horse, but more simple and
shorter in the crown. In this creature it has been supposed that we have
a direct ancestor of the modern horse. A very similar genus
(_Orohippus_), lacking only the fifth rudimentary toe, replaces
_Eohippus_ in the Middle Eocene. _Mesohippus_ of the Lower Miocene is as
large as a sheep, and has only three toes on the fore-foot and a splint
bone, while its teeth assume a more equine character (Fig. 176). In the
Upper Miocene _Miohippus_ continues the line, while _Protohippus_ of the
Lower Pliocene is still more equine and as large as an ass, and
corresponds with the European _Hipparion_ in having the middle toe of
each foot alone long enough to reach the ground. In the Upper Pliocene
true horses appear with only a single toe, and splint bones instead of
the others. In America, though the horse was unknown at the time of the
discovery of the continent, several species occur in the Tertiary and
Post-Pliocene, showing that the genus existed there up to a
comparatively late period; and when re-introduced it has thriven and run
wild in the more temperate regions. What cause could have led to its
extinction in Post-Glacial times is as yet a mystery. This genealogy of
the horse, independently of its evolutionist application, is very
interesting. It shows that some Eocene types were suited to continuance,
and even adapted for extension, while others were destined to become
altogether extinct at an early date. It shows farther that the power of
continuance resided not so much in the gigantic and prominent species as
in smaller forms. It is to be observed, however, that Gaudry and other
orthodox evolutionists in Europe deduce the horse, not from _Eohippus_,
but from _Palæotherium_, and that it is equally impossible to verify
either phylogeny, since the mere sequence of more or less closely allied
species in time does not prove continuous derivation. Nor indeed are we
certain that one-toed horses like those now living did not exist on the
dry plains in Eocene times, since the inhabitants of these plains are
probably unknown to us. An amusing illustration of the probable reason
of the disappearance of the missing links has recently been given by a
writer not very favourable to the new philosophy. The several
consecutive species may be represented by coins. We may suppose, for
example, sixpences to have been coined first, then sevenpenny and
eightpenny pieces, and so on up to a shilling, then pieces representing
thirteen, fourteen and fifteen pence, and so on up to a half-crown or
crown; but all the intervening denominations between the sixpence and
the shilling, and between the shilling and the half-crown, were found
practically of little use. Hence few were coined, and they soon became
obsolete. Thus the antiquary would find only a few denominations, and
those connecting them would be seldom or never found. It is plain that
if we could suppose that nations constructed their coinage after this
unthinking and empirical fashion, and that if we were justified in
ascribing a similar procedure to the Creator, it might help to account
for the facts as we find them, otherwise we should rather suppose that
in both cases something like plan and calculation determined the
selection of the species produced, whether of coins or animals. But
Chance is a blind goddess, and if we instal her as creator, we must
expect the work to proceed by a series of abortive experiments.
The Perissodactyls are not numerous at present. The three groups
represented by the Horse, Rhinoceros, and Tapir constitute the whole;
and the two latter forms can be traced back to predecessors in Eocene
times, even more closely resembling them than those supposed to be
ancestors of the horse resemble that animal. But the few species now
living have thus a vast surplusage of possible ancestors. Many species
and genera are dropped without any modern representatives, so that the
tendency has been to a gradual elimination of surplus types, until only
a few isolated and somewhat specialised forms remain at present. Yet
this process of elimination is not necessarily an evolution or survival
of the fittest, in the sense of modern derivationists. It rather implies
that in certain past states of the earth the conditions of life afforded
scope for many forms not now required, or replaced by other types more
suited to the advanced and specialised nature of the world.
On the other hand, the Artiodactyls have gained in numbers and
importance, in comparison with their odd-toed comrades; and this, though
an odd number, namely five, was the typical number with which the
earliest quadrupedal forms began life far back in the Palæozoic. The
typical Artiodactyls are those that cleave the hoof, and many of which
also chew the cud; and they are of all others, the horse perhaps
excepted, those that are most valuable to man. The lower type
(Bunodont), to which the hog belongs, is the older; and many hog-like
animals occur from the earlier Tertiary upwards. In the Upper Eocene,
even-toed species appear with an approach at least to the
crescent-shaped teeth of the modern deer and oxen. Some of the species
are obviously forerunners of the modern antelopes and deer, though as
yet destitute of horns or antlers. Others, like _Oreodon_, are of more
hog-like aspect, though believed to have been ruminants (Fig. 177).
These are characteristic of the Middle Miocene, at which stage true deer
appear in Europe (_Dicroceras_), though they are not known in America
until the Pliocene period. The earliest deer have small and simple
antlers, these ornaments becoming larger and more elaborate in
approaching the modern era. The hollow-horned ruminants appear for the
first time in America in the Lower Pliocene; and no ancestry has so far
been attempted to be traced for them. The antelopes of this group, as
well as the gigantic _Sivatherium_ of India,[81] allied to the modern
prong-horned antelope of North America, were prominent in the Old World
in the Miocene.
[Illustration: FIG. 177.—_Oreodon major._ A generalised Miocene
ruminant, with affinities to the Deer, Camel, and Hog. Greatly
reduced.—After Leidy.]
[Illustration: FIG. 178.—Lower Jaw of _Megatherium_. Greatly reduced.
Post-Pliocene of South America.—After Owen.]
[Illustration: FIG. 179.—Ungual Phalanx and Claw-core of
_Megatherium_. Greatly reduced.]
A very noteworthy and specially American group of mammals is that of the
_Edentates_, the Sloths and Ant-eaters, a group which _à priori_ we
should have supposed would have been one of the earliest in time. They
appear, however, first in the Miocene, without even any suggested
ancestry, and are represented from the first by large species, though
they attain their grandest stature in the _Megatherium_ and _Mylodon_ of
the Post-Pliocene (Figs. 178, 179), which were sloths of so gigantic
size that they must have pulled down trees to feed on their leaves,
unless, indeed, there were trees equally colossal for them to climb. But
before the modern time, like the American horses, the larger herbivorous
forms suddenly disappear, and are now represented only by a few
diminutive South American species, which can scarcely, by any stretch of
imagination, be supposed to be descendants of their gigantic
predecessors. The history of these animals, like those of the great
Tertiary marsupials of Australia and the many Miocene elephants of
India, affords a remarkable illustration of the persistence of similar
groups of creatures in successive ages in the same region, along with
diminution in magnitude and number of species toward the modern times.
[Illustration: FIG. 180.—Tooth of Eocene Whale (_Zeuglodon cetioides_).
One-half natural size.]
The Whale-tribe (Cetaceans) at once in the earliest Eocene takes the
place of the great Sea-lizards of the Cretaceous; and the oldest of the
whales are in their dentition more perfect than any of their successors,
since their teeth are each implanted by two roots, and have serrated
crowns, like those of the Seals. The great Eocene whales of the Southern
Atlantic (_Zeuglodon_) (Fig. 180), which have these characters, attained
the length of seventy feet, and are undoubtedly the first of the whales
in rank as well as in time. This is perhaps one of the most difficult
facts to be explained on the theory of evolution. Allied to the whales
is the small and peculiar group of the Sea-cows or Dugongs
(_Sirenians_). These creatures, highly specialised and very distinct
from all others, appear in the Early Tertiary in forms very similar to
those which now exist, and probably in much more numerous species, and
they pursue the even tenor of their way down to modern times without
perceptible elevation or degradation. “We have questioned,” says Gaudry,
when speaking of the Tertiary Cetaceans, “these strange and gigantic
sovereigns of the Tertiary oceans as to their progenitors—they leave us
without reply.” Their silence is the more significant as one can
scarcely suppose these animals to have been nurtured in any limited or
secluded space in the early stages of their development. The true Seals,
which are more elevated than the Whales, and very different in type,
appear much later, and without any probable ancestry.
The Elephants, two or three species of which constitute in the modern
world the sole representatives of an order, are a remnant of an ancient
race once vastly more numerous. They appear in Europe and Asia in the
Miocene, when they were represented by three distinct genera (_Elephas_,
_Mastodon_, and _Dinotherium_). The second genus (Fig. 181) differs from
the proper Elephants in having tuberculated teeth, indicating a more
swinish habit, and probably a more fierce disposition. The third (Fig.
182) is remarkable for the immense size of some of its species, far
exceeding the modern Elephants, and has the farther peculiarity of a
pair of descending tusks on the lower jaw, constituting a strong and
heavy grubbing-hoe, with which it could probably dig deeply for roots.
So important was the group in Miocene times that seven elephants are
already known from this formation in India alone, besides three species
of Mastodon. Four or five Miocene Mastodons are known in Europe, besides
two _Dinotheria_; and the true Elephants appear there in the Pliocene,
and continue to the beginning of the Modern. The elephantine animals are
not known in America till the Pliocene, but in that and the Pleistocene,
and perhaps up to the human period, the western continent, now
altogether destitute of elephants, possessed several species both of
_Elephas_ and _Mastodon_, which extended, as in Siberia, even into the
Arctic regions; and, as we know from specimens preserved in a frozen
state in the latter region, some of the species were so protected by
dense fur as to be able to endure extreme cold. The candid Gaudry closes
his summary of the history and affinities of the elephantine animals
with the words: “However, the sum of the differences compared with that
of the resemblances is too great to permit us to indicate any relation
of descent between the proboscidians and the animals of other orders
known to us at present.” So these greatest of all the animals of the
land, with their strangely specialised forms and almost human sagacity,
stand alone, without father or mother, without descent.
[Illustration: FIG. 181.—_Mastodon ohioticus._ An American Elephant.
Post-Glacial.]
[Illustration: FIG. 182.—Head of _Dinotherium giganteum_. Greatly
reduced. Miocene of Europe.]
[Illustration: FIG. 183.—Wing of _Vespertilio aquensis_. An Eocene Bat.
After Gaudry.]
The Rodents, or gnawing animals, appear in the Early Eocene on both
continents in familiar forms allied to our Squirrels and Rats.
Porcupines and Beavers are added in the Miocene. This group seems thus
to have continued much as it was; and it is still perhaps represented by
as many species as at any previous time. Many of the ancient forms were,
however, much larger than any modern species, and some of these larger
forms[82] present singular points of approach to very distinct types,
as, for example, to that of the Bears; but these large and composite
species are long since extinct. The insectivorous mammals have much the
same history with the Rodents. Such highly specialised and abnormal
forms as the Bats might be supposed to be modern. But, strange to say,
they appear with fully developed wings both in Europe and America in the
Eocene (Fig. 183). Gaudry thinks that it is “natural to suppose” that
there must have been species existing previously with shorter fingers
and rudimentary wings; but there are no facts to support this
supposition, which is the more questionable since the supposed
rudimentary wings would be useless, and perhaps harmful to their
possessors. Besides, if from the Eocene to the present the Bats have
remained the same, how long would it take to develop an animal with
ordinary feet, like those of a shrew, into a bat?
The Early Eocene was not altogether a time of peace in the animal world.
The old carnivorous Saurians were dead and buried, but their place was
taken by carnivorous mammals, allied to our modern Tigers, Hyænas,
Foxes, and Weasels. The Carnivora, however, were subordinate in the
Eocene, and, as already remarked, some of them appear to be intermediate
between marsupial and placental forms—a fact which evolutionists have
noticed with much satisfaction. They appear to attain to their
culmination in the Miocene, when their powers seem to be proportionate
to those of the great and well-armed quadrupeds they had to deal with.
To this age belongs the introduction of the terrible “Cymetar-toothed
Tiger” (_Machairodus_, Fig. 184). Its huge tusk-like canines and
powerful limbs seem to fit it more than any other of the cat family for
destructive efficiency. Yet ordinary cat-like animals were contemporary
with it, and have survived it, since _Machairodus_ disappears in the
Post-Pliocene, though in previous periods it had been very widely
distributed on both continents. It is a curious fact, perhaps of more
significance in various ways than we yet understand, that the Dog-bear
(_Arctocyon_), of the oldest French Eocene, believed to be the oldest
placental mammal known, though technically placed among the Carnivora,
has a kind of dentition indicating that, like the modern Bears, it was
really omnivorous; and its skull shows some peculiarities tending to
those of the Marsupials.
[Illustration: FIG. 184.—Skull of a Cymetar-toothed Tiger (_Machairodus
cultridens_). Pliocene, France. Reduced.]
[Illustration: FIG. 185.—Lower Jaw of _Dryopithecus Fontani_. An
Anthropoid Ape of the Middle Miocene of France. Natural size.]
Much interest attaches to the first appearance of the order of Apes
(_Quadrumana_), or, if we take the somewhat deceptive classification
favoured by some modern zoologists, the _Primates_, including the apes
and man. They begin in the Eocene, both in Europe and America, with the
lowest tribe, that of the Lemurs, now confined to the island of
Madagascar and parts of Africa and Southern Asia, and which may, Gaudry
thinks, be modified Marsupials, though he admits that this is hard to
understand. He mentions the resemblance of the teeth of monkeys to those
of some hog-like animals, a resemblance, however, merely marking a
similarity of food, and suggests on this ground that some of the
primitive ancestors of the hog may have also given rise to the Monkeys.
In the Miocene of Europe and Asia we have true Apes; and one of these,
which rivals man in stature (_Dryopithecus_), belongs to the group of
the gibbons, or long-armed apes, one of the higher families of the
modern _Quadrumana_ (Fig. 185). This animal presents, indeed, the
nearest approach to man made by any Tertiary mammal. Still the
differences are great, as, for instance, in the much larger size of the
canines and premolars. Yet so much confidence has Gaudry in the
resemblances, that he even ventures to suggest that certain flint chips
found in the Miocene of Thenay, and which have been supposed to indicate
human workmanship, may have been chipped by the hands of _Dryopithecus_.
Should this view be adopted by evolutionists, it will at least have the
effect of preventing flint chips from being received as evidences of the
antiquity of man.
It is scarcely necessary to sum up this review of the history of the
Tertiary mammals. Much that has been said may be modified or changed by
future discoveries; but the great facts of the late appearance of the
placental mammals, of their rapid introduction, with their ordinal
differentiation nearly complete over all the continents, of the speedy
culmination and early decadence of many types, and of the unchanged
permanence of others, must in the main be sustained. It is not too much
to say that to account for these facts the evolutionist must abandon the
idea of gradual change, and adopt that of “critical periods” when sudden
changes occurred. The history becomes inexplicable, unless with Mivart,
Le Conte, and Saporta, we admit “periods of rapid evolution” alternating
with others of stagnation or retrogression; and if we admit these, we
practically fall back on the old idea of creation; only it may perhaps
be “Creation by Law.”
[Illustration: CONTEMPORARIES OF POST-GLACIAL MAN. From a painting by
Waterhouse Hawkins.]
CHAPTER X.
THE ADVENT OF MAN.
Hitherto we have met with no trace of man or of his works. Yet there
have been in our upward progress from the dawn of life mute prophecies
of his advent. Man is in his bodily frame a vertebrate animal and a
mammal; and when first the Amphibians were introduced in the Palæozoic,
the framework of man’s body was already sketched out and its principles
settled. Those great reptilian lords, the biped Saurians of the
Mesozoic, already foreshadowed his erect posture, though their limbs may
have been more ornithic than mammalian. The gradual advance in the
brain-development of the Tertiary mammals presaged a coming time when
mind would obtain the mastery over claw and tooth and horn; and in the
Miocene ages there was already some hint of the precise style of
structure in which this new creative idea would be realised. Yet it
might have been impossible to imagine beforehand the vast changes which
this new idea would inaugurate. In the lower animals such intelligence
as they possess is so tied to the physical organisation that it
manifests itself as a mechanical unvarying instinct. Man bursts this
bond, and in doing so revolutionises the whole scheme of nature. Old
things are now put to new uses, the face of nature is changed, varied
arts are introduced, and thought enters into the domain of general and
abstract truth. Objects are arranged, classified, understood, and while
in some respects the whole creation is made to groan under the tyrannous
inventions of man, yet these are the inventions of imagination and
design. They are the triumph, not of brute force, but of will and
intelligence.
That man was not in all the earlier ages of the world, except in these
prophecies of his coming, geology assures us. That he is, we know. How
he came to be, is, independently of Divine revelation, an impenetrable
mystery—one which it is doubtful if in all its bearings science will
ever be competent to solve. Yet there are legitimate scientific
questions of great interest relating to the time and manner of his
appearance, and to the condition of his earlier existence and subsequent
history, which belong to geology, and in which so great stores of
material have been accumulated that a treatise rather than a chapter
would be required for their discussion. We may endeavour to select a few
of the more important points.
One of the first questions meeting us is that which relates to the point
in geological time signalised by the advent of our species. In the
Eocene period our continents were being gradually raised out of the
ocean, and were still in great part under the waters, which several
times returned upon the land, and seemed ready again to engulf it. In
this period not only have we no traces of man, but all the higher
animals of that age are now extinct. In the later Eocene and Miocene the
extent of land became greater, but it was so disposed as to allow the
influx into the Arctic Sea of vast volumes of heated water from the
equatorial regions; and there may have been also astronomical causes at
work to increase this influx of warm water, and so to raise the
temperature of the Arctic regions still higher.[83] The middle period of
the Tertiary was undoubtedly a time very favourable to the wide
distribution of the higher forms of life both animal and vegetable. But
we cannot trace man or any of the contemporary mammals back to the
Miocene. In the Pliocene the continents had attained to their present
elevations, and climates were not dissimilar from those prevailing at
present; but still we have no certain indication of the presence of man;
and if other modern mammals extend back to this period their number is
very small. In this age also the greater part of the continents must
have been covered with a great thickness of soil and disintegrated rock
favourable to vegetation, and there seemed nothing to preclude the
introduction of man. But a new and at first sight most unfavourable
change was to intervene. Whether through internal changes affecting the
distribution of land and water, or through astronomical vicissitudes,
the northern hemisphere, and possibly the whole world, entered on an era
of refrigeration, the so-called “Glacial Age” of the Post-Pliocene or
Pleistocene period. That in this period our continents as far south as
the latitude of 40° were overwhelmed with ice or ice-laden seas is
rendered evident by the fact that the whole surface up to several
thousands of feet above the sea-level has been bared of its accumulated
_débris_ and polished and grooved by ice, and laden with boulders and
other glacial deposits, while in many places at heights of even 1,000 or
1,200 feet these deposits contain sea-shells of species now living in
the colder parts of the ocean. These phenomena do not exist in the
tropical regions, except in the vicinity of high mountains, but they
recur in the southern hemisphere. It is still uncertain whether the
period of greatest cold in the two hemispheres was at the same time or
in successive ages. Geologically, however, they are approximately
contemporaneous, both occurring between the end of the Pliocene and the
modern period; but nevertheless they may not have coincided in absolute
date.
Very different views have been held as to the precise condition of the
continents in the Glacial Age, though all agree in the prevalence of
cold and the action of ice, and in the fact of a great submergence at
one or more stages of the period. My own conclusions, which I have
advocated elsewhere,[84] and which are based on extensive study of the
northern parts of America, where the deposits of this age are more
widely developed than elsewhere, are that there was one great
subsidence, leading to a condition in which the lower levels of the
continents were covered with ice-laden water and the higher regions were
occupied with permanent snow and glaciers. This submergence went on till
even high mountains 4,000 feet or more in elevation were under water.
Then there was a gradual though intermittent elevation, during which the
climate became ameliorated, and lastly there was a condition in which
the land of the northern hemisphere stood higher than at present, and
which immediately preceded the modern period. As these conditions have
great significance in relation to the appearance of man, I have
tabulated them for reference as they occur in Scandinavia, Great
Britain, and North America. The so-called “Interglacial Periods” of some
geologists are in reality local results of the stages of intermittent
elevation in which were deposited beds which in some cases, as in
Scotland, Sweden, and Eastern Canada, hold sea-shells, and in others, as
in the central areas of North America, contain remains of plants of
northern species.
We shall name, for convenience, the parts of this Pleistocene revolution
which include the great subsidence and glaciation, the _Glacial_ Age,
that extending from the re-elevation to the modern the _Post-glacial_.
The Glacial Age proved fatal to a large proportion of the land life of
the previous periods. According to Professor Boyd Dawkins, out of
fifty-three species known in Britain in the Post-glacial, only twelve
are survivors of the Pliocene; and probably the proportions would not be
greater in any part of the northern hemisphere. Some, however, did
survive, either by migrating southward or by being inhabitants of places
less severely affected than most by the general cold and submergence.
There was thus no absolute break in the chain of life effected by the
Glacial Age.
TABLE OF PLEISTOCENE DEPOSITS IN SCANDINAVIA, ENGLAND, AND AMERICA.
(Order descending.)
+---------------------+--------------------+--------------------------+
| SCANDINAVIA. | GREAT BRITAIN. | NORTH AMERICA. |
| (Torell.) | (Lyell, &c.) | |
+---------------------+--------------------+--------------------------+
| | | |
| Valley-clays and | Hoxne Deposits and | Terrace Gravels |
| Heath-sands of | Upper Terrace | and Loess |
| Sweden. (No | Gravels. | Deposits. |
| fossils.) | Palæolithic | |
| | Implements. | |
| | | Placer Gravels of West. |
| Terrace-gravels of | Upper Glacial Beds.| |
| Norway and Sweden.| Bridlington Beds.| Do. Sand and Gravel, |
| (No fossils.) | Upper Boulder | Newer Boulder Drift. |
| | Beds. | |
| | | So-called Interglacial |
| Dryas-clay with | So-called | Beds, with Plants, &c. |
| Fossil plants of | "Interglacial" | |
| northern species. | Deposits. | Loess Deposits of |
| | | Mississippi. |
| | | |
| Uddevalla beds with | Clyde Beds and | Upper Leda Clay and |
| Boreal Marine | Marine Clays. | Champlain Clay, with |
| shells. | | Boreal Shells. |
| | | |
| | | White Silts of British |
| | | Columbia. |
| | | |
| | Mid-Glacial Sands. | Erie Clays and similar |
| | | Beds of West. |
| | | |
| Yoldia Clay and | | Lower Leda Clay, with |
| Sand. Arctic | | Arctic Shells. |
| Marine Shells. | | |
| | | Port Hudson Deposit of |
| | | Mississippi. |
| Yellow Stony Clay | | |
| and Sand, and | | "Syrtensian" Beds of |
| Gravel of Scania. | | New Brunswick. |
| | | |
| | | Orange Sand of |
| | | Mississippi. |
| | | |
| "Moraines de Fond," | Till, or Older | Boulder Clays, with |
| or Boulder Clay | Boulder Clay. | Local and some |
| proper. | | Travelled Boulders. |
| | | |
| | | Old Land Surfaces--Peat |
| Ancient Diluvial | Pebbly Beds and | under Boulder Clay, |
| Sand. | Weyburne Sands, | Local Gravels and |
| | Lignitic Forest | Sands. |
| | Beds. | |
| | | Pre-glacial Gravels of |
| | | British Columbia. |
+---------------------+--------------------+--------------------------+
In what part of this sequence did man appear? In answer to this, I think
it is now generally admitted that he is not certainly known earlier than
the Post-glacial period. Various supposed indications of his presence in
“Interglacial” Glacial, Pliocene, and even Miocene deposits have proved
on examination to be unreliable. America has recently put forth claims
to have been inhabited by man in the Pliocene, on the faith of remains
found in auriferous gravels in the West. But the facts that the
implements and bones found are modern in type, that the gravels were
deeply mined by the Indians, and that the objects found, as mortars for
dressing gravel, etc., are in many cases such as they would be likely to
leave in their excavations, have discredited these supposed discoveries.
Still more recently, chipped flints found in gravels in New Jersey, by
Abbott, have been supposed to carry back the Indians of the East coast
to the Glacial period. It is evident, however, from the description of
these deposits by the late Mr. Belt and by Professor Cook, director of
the Survey of New Jersey, that they are really Post-glacial, that their
age must be estimated by study of the local conditions, and that there
is no good ground for correlating them with the upper members of the
true Glacial drift to the northwards, with which they had been somewhat
rashly identified. Irrespective of the doubtful character of many if not
all of the so-called implements, the deposits in which they are found is
confessedly not a product of the ice of the Glacial period proper,
whether that was, as some maintain, a period of land glaciation as far
south as New Jersey or not. It belongs to a time of denudation by water,
aided perhaps by floating ice, and is not necessarily older than the
river gravels of the Somme, which, like it, contain boulders and imply
conditions of torrential action and climate which have long since passed
away. If, however, these implements are genuine, they would imply the
presence of Palæocosmic or Antediluvian man in America. This would in
itself be an important discovery.
For the present, therefore, man is geologically a Post-glacial species,
and there is nothing unreasonable in supposing that he dates no farther
back, since several animals his contemporaries are in the same case; and
by supposing him to have originated after the Glacial age we avoid the
difficulties attendant on his survival of that great revolution. The
only necessity for supposing an earlier appearance arises from the
requirements of the hypothesis of evolution. Those, however, who hold
this theory, may with Haeckel take refuge in that shadowy continent
supposed to have extended from Africa to Australia,[85] and to have
sheltered man in his transition from the ape to humanity, in the
Tertiary period. The name Lemuria is taken from the Lemurs, supposed
ancestors of the Apes, which still haunt the margin of the Indian Ocean;
but it may be taken also in its old Latin sense of ghosts of the evil
dead; and as we are not likely to obtain any more tangible evidence of
the old natives of Lemuria, perhaps we may hope that some spiritualist
may succeed in charming them from the vasty deep for our enlightenment.
Should this be so, it is to be hoped that no “drum ecclesiastic” will be
beaten to drive them away till they have revealed all they can tell.
It may be well to add that, in addition to the negative evidence, there
is at least one positive evidence of the recent origin of man which has
been well urged by Le Conte. It is this: animals have continued long in
geological time in the inverse ratio of their rank. Some Mesozoic
protozoa still survive. So do many early Tertiary mollusks. But the
mammals are of much less duration. No living species goes back farther
than the Pliocene. Few extend farther than the Glacial age. On the same
principle it is not to be expected that man, the highest of all animals,
should extend far back in geological time.
Accepting the Post-glacial age as that of the advent of man, it may be
interesting to ask what we know of the condition of our continents when
he appeared. In Western Asia, in Europe, except in its more northern
portions, and it would now seem also in America, man had been introduced
at a time closely following the emergence of the land from the Glacial
sea. At this time the land area of both continents was larger than it is
at present, and the character of the fauna shows that much of the
surface was occupied with great steppes or prairies, over which
migration would be easy; while there were probably connections by land
or chains of islands between the continents of the northern hemisphere.
The land animals of the continents were more numerous and of greater
stature than at present. Several species of elephants (Fig. 186) and a
rhinoceros roamed over the plains. The formidable _Elasmotherium_ (Fig.
187),[86] an animal allied to the rhinoceros, but more fleet and active,
and of immense size, inhabited Asia and Europe. Hippopotami, wild
horses, the gigantic Irish stag, several species of wild cattle, and
bisons of greater size than their successors, haunted the streams and
steppes. The cave bear, the cave lion, the spotted hyæna, and possibly
the _Machairodus_, were among the beasts of prey even in the temperate
latitudes. The climate must have been a continental one, ranging through
considerable extremes; but the conditions favoured migration of animals
on the great scale, so as to avoid these extremes, and hence species of
types now comparatively restricted enjoyed a wide distribution.
[Illustration: FIG. 186.—_Elephas primigenius._ Post-glacial.]
To establish themselves in such a world, the primitive men must have
been no puny race, either in mind or body, and they must have been
sheltered in some Eden of plenty and comparative safety till, by
increase of numbers, invention of weapons and implements, and
domestication of useful animals, they became able to cope with the
monarchs of the waste. But this position once attained in the original
seats of the species, the wide continents presented great facilities for
their movements, and there were ample stores of food for wandering
tribes subsisting by the chase.
[Illustration: FIG. 187.—Tooth of _Elasmotherium_. Grinding surface,
natural size. Siberia. From _Nature_.]
With such views the skeletons of the most ancient known men[87] fully
accord. They indicate a people of great stature, of powerful muscular
development, especially in the lower limbs, of large brain, indicating
great capacity and resources (Fig. 188), but of coarse Turanian
features, like those of the tribes that now roam over the plains of
Northern Asia (Fig. 189). They used flint and bone implements, which
they manufactured with much skill (Figs. 190, 191). They were probably
clothed in dressed skins, ornamented with embroidery, in the manner of
the North American Indians. They used shells and carved bones as
ornaments. Recent discoveries at Soloutre, in France, render it probable
that some of the tribes had tamed the horse, and resided in fortified
villages. They buried their dead with offerings, indicating a belief in
immortality. These Post-glacial men are certainly known as yet only in
Europe and Western Asia; and we cannot therefore determine if they
represent the average man of the period. There were in Belgium and other
parts of Europe, men of smaller stature and of lower cranial type,
contemporary or nearly so with the higher race. There may have been
fruit-eating or agricultural peoples in the more genial and fertile
lands of the east and south. The conditions above sketched are, I think,
fairly deducible from the facts stated by Christy and Lartet, Dupont,
Rivière, Dawkins, and others, who have studied the remains of these
early men, the Palæolithic men of some writers, or the men of the
Mammoth age, and whom I have elsewhere named Palæocosmic men, as a term
less objectionable than those founded on implements not confined to any
age, or animals which may have long antedated man. Recent discoveries in
the caves of Spy in Belgium,[88] taken in connection with the previous
discoveries of Schmerling and Dupont, seem to show the existence in that
country of men of the low-browed Neanderthal or Canstadt type (Fig. 189
third outline), perhaps locally preceding but perhaps contemporaneous
with, the larger and better developed men of the Cro-Magnon type (Fig.
189 first outline). These two types are, however, allied, and there are
intermediate forms, so that they are to be regarded as two races of
Palæocosmic men not more dissimilar than we find in cognate rude races
at present.
[Illustration: FIG. 188.—Engis Skull. Reduced.—After Lyell. The Skull
of one of the Men of the Mammoth age.]
[Illustration: FIG. 189.—Outlines of Three Prehistoric European Skulls
compared with an American Skull from Hochelaga.
Outer outline, Cro-Magnon Skull. Second outline, Engis Skull. Third
outline (dotted), Neanderthal Skull. Inner figure, Hochelagan Skull on a
smaller scale.]
They were succeeded in Western Europe by a smaller and less elevated
race, identical apparently with the modern Lapps and Basques, and in
whose time the mammoth and many large animals had disappeared, Europe
had become clad with dense forests, and the reindeer had extended his
range far to the south, while the land of our continents had become
narrowed to its present limits, or even less. The cause of these changes
must have been physical, and to some extent cataclysmal; and its
wide-spread and effectual character is shown by the fact that it
exterminated so many animals of both continents which had survived the
Glacial age. Similar testimony is borne by the occurrence of the
implements and remains of Palæocosmic men in gravels and in diluvial
clays in caverns, and by the changes of level and deep erosions of
valleys that are referable to the close of the Palæocosmic age. The most
probable agencies in this revolution were subsidences of the land,
accompanied with climatal changes; but the precise nature and extent of
these is still unknown; and the prevalent tendency on the part of
geologists to stretch the doctrine of uniformity, so valuable within
proper limits, to the absurd extreme of excluding all changes not
exemplified even in amount in the modern period, will probably for some
time prevent any adequate conception of them.
It would be premature to correlate what is yet known of the Palæocosmic
age with historical periods; but the tendency of the facts accumulated
is, I think, toward the identification of the Palæocosmic men with the
Antediluvians; and their Neocosmic successors, whether of the reindeer
age, of the Danish shell-mounds, or the Swiss lake habitations, with
Postdiluvian and still existing tribes.
[Illustration: FIG. 190.—Flint Implement found in Kent’s Cavern,
Torquay, under four feet of cave mud and one foot of stalagmite.—After
Pengelly.]
After what has been already said, it will be unnecessary to dwell upon
the characteristics of the first race of men known to us. They were rude
and uncivilised, in so far as outward appliances are concerned; but they
are confessedly altogether men, and in no respect akin to apes, and
their volume of brain is rather greater than that of the average
European of to-day; so that they must have had quite as much natural
sagacity and capacity for culture, and, like the modern and historic
Turanian nations, they were probably superior to the average European in
the instinct for art and construction. Thus if we suppose these men
derived from apes by any process of gradual change, we must look for
their brute ancestors, not in the Pliocene or Miocene, but in the Eocene
itself. This causes us to recur to the doctrine of critical periods,
when many species were introduced together, alternating with periods of
decay and extinction. Post-glacial man appears at the end of a time of
sifting and trial, a time in which a vast number of species succumbed to
great physical reverses. No very great number of species came in with
him, and in the early period of his history there was a decadence or
destruction either by the diluvial cataclysm or gradually. Out of
ninety-eight species of mammals contemporary with early man in Europe,
forty-one are wholly or locally extinct, and none have been introduced
except those brought by man himself. Thus man stands alone, the grand
product of his period and a lord of creation, for whom great preparatory
changes were made, and multitudes of lower animals swept away to make
room for him. According to our sacred Scriptures, this change is still
imperfect, and great additional ameliorations would have taken place but
for a moral catastrophe not within the domain of geology—the fall of
man. If we identify the Palæocosmic men with the Antediluvians of the
same venerable record, the roving tribes whose remains are known to us
represent that part of the race of Cain of whom Jubal was the father,
the nomads dwelling in tents, as distinguished from the settled
agricultural peoples. In this case, also, the catastrophe which
destroyed these rude and lawless men was that which culminated in the
deluge of Noah, which may represent the extinction of the last great
body of this primitive race, whose arts, handed down to the physically
inferior men of Postdiluvian times, astonish us by their early
development in Chaldæa and in Egypt.
[Illustration: FIG. 191.—Bone Harpoon (Palæocosmic), from Périgord
Cavern.]
If man is so recent geologically, he may still be very old historically;
and the question remains, Have we any facts bearing on the absolute
antiquity of man? For the properly historical aspect of this question,
I may refer to the excellent work of Canon Rawlinson on the _Origin of
Nations_,[89] which shows conclusively that the historic origin of all
the great nations of antiquity extends backward less than 4,400 years
from our time. Beyond this we have, however, the Palæocosmic or
Antediluvian men; and their extension backward seems limited
geologically only by the close of the Glacial period, while many hold
that the Genealogy in Genesis does not require us to limit very narrowly
their antiquity. The date of the Glacial period is, however, at present
very uncertain. On the one hand, some geologists, like Lyell, have
supposed it may be as far back as 200,000 years ago. Others, like Croll,
are contented with the more moderate estimate of 80,000 years. On the
other hand, the calculations of Andrews, based on the recession of the
American lakes, those of Winchell on the recession of the Falls of St.
Anthony, and the recent surveys of the recession of the Falls of
Niagara, reduce the time to from 7,000 to 10,000 years. It is impossible
in the present state of knowledge to settle these disputes; but one may
refer in the sequel to some of the evidences which have been adduced in
favour of great antiquity. Since the publication of the second edition
of this work Prof. Prestwich, in a paper read before the Geological
Society,[90] has brought forward other reasons which induce him to
conclude that the close of the Glacial epoch occurred “from 8,000 to
10,000 years since.” It is true, he admits, on geological evidence still
in dispute, that man may have existed in Europe before that time, and he
also admits, on historical, not geological evidence, the existence of
“Neolithic” man in Asia, “at an earlier date than 4,000 B.C.” Still the
repudiation, by so good an authority, of the exaggerated antiquity which
it has been the fashion, since the rise of Darwinian evolution, to
assign to man, contrary to the geological evidence, is a satisfactory
indication of a return to more rational views; and when geologists get
rid of the fiction of a continental ice-sheet, still farther progress
in this direction may be expected.
We may, I think, at once take it for granted, that none of the Neocosmic
races date farther back than the origin of the great eastern nations.
There are certainly no geological evidences requiring a greater
antiquity, for in their time the land had attained to its present
configuration, and the changes which have occurred in the succession of
forests and the growth of peat are such as our experience in America
shows to be possibly quite modern. There is besides no doubt that these
people, from the Reindeer men of France and Belgium to the people of the
Swiss lakes, are modern races, whose descendants still live in Europe.
We can thus limit our inquiry to the Palæocosmic men; and with respect
to them we know only what may be gathered from a consideration of the
physical changes which have occurred since they lived.
In Europe a great number of considerations have been adduced as evidence
of their high antiquity; and these deserve careful attention, though I
think it will be found that they are all liable to serious objections or
great abatements on geological grounds.
(1) The occurrence of human remains with those of animals now extinct
affords no certain evidence of antiquity. Admitting that human remains
are found along with those of the mammoth in Europe, and with those of
the mastodon in America, the question remains, How late did these
species survive? In Europe we know that several large animals now
extinct existed up to comparatively modern times. This is the case with
the Irish deer (_Megaceros_), the urus, the aurochs, and the reindeer,
in temperate Europe. How long previously the mammoth or the hairy
rhinoceros disappeared we do not know, but need not suppose the time
very long.
(2) The accumulation of sediment or of stalagmite over human remains in
caverns is not necessarily indicative of very great antiquity. We know
that in favourable circumstances mud, sand, and gravel may be rapidly
deposited in caves by land floods or river inundations, and that
_débris_ of various sorts accumulates in such places from decay of rock
and vegetable and animal agencies. The deposition of stalagmite is also
very variable in its rate; and the fact that it is being very slowly
deposited in any cave now does not prove that more rapid deposition may
not have taken place formerly. Dawkins and others have ascertained a
rate of a quarter of an inch per annum in some caverns; and this would
allow the stalagmite crust of Kent’s cave, for which an antiquity of
half a million of years has been claimed, to have been formed in a
thousand years.
[Illustration: FIG. 192.—Sketch of a Mammoth, carved on a portion of a
Tusk of the same Animal (Lartet).]
(3) The erosion of river valleys to great depths since the Glacial
period fails to establish the great antiquity of the caves left on their
sides or the high level gravels of their banks. Throughout the northern
hemisphere, the river valleys are of old date, and were merely filled
with loose detritus in the Glacial age. The sweeping out of this
_débris_ would be a rapid process, more especially when changes of level
were occurring, and when the rainfall was greater than at present.
Besides, as Croll has well remarked, the actual configuration of our
continents, the amount of drift still remaining, and the imperfect
manner in which the river valleys have been cleared out, all testify to
the comparative recency of the Glacial period.[91] These considerations
would, indeed, materially reduce the antiquity which he claims on
astronomical grounds for the ice age.
(4) The growth of peat and the deposition of silt are very deceptive as
indications of great antiquity. For instance, accurate observations made
by a French engineer in the construction of docks at St. Nazaire,[92]
show that in 1,600 years the Loire had deposited over Gallo-Roman
remains six metres of mud. Relics of the Bronze age occur below these at
a depth indicating 500 years previously as their date; and the beginning
of the modern deposit of the Loire would, on the same evidence, be only
6,000 years ago. Hilgard’s observations on the delta of the Mississippi
in like manner tend greatly to reduce our estimates of the time occupied
in the deposit of the modern silt of that river. The peat deposit at
Abbeville, at the mouth of the Somme, has been supposed to have required
30,000 years for its formation. But this estimate was based upon the
present rate of growth; and, as Andrews has shown, the fact admitted by
Boucher de Perthes, that birch stems three feet high stand in this peat,
implies a much more rapid rate, which is also proved by the depth at
which Roman remains have been found. In like manner the Scandinavian
peats, to which a fabulous antiquity has been ascribed, have been proved
to be comparatively modern by the depths at which metallic works of art
are found in them.
(5) The paucity of remains of Palæocosmic men in Europe, with their wide
distribution, indicate that their sojourn was not long, or that the
population was very small and much scattered. Even in a few thousands of
years, an active and vigorous people, living in a country well supplied
with food, must have multiplied greatly, and must have left considerable
remains. On the theory that these men inhabited Europe even for 2,000
years, we have to suppose that the greater part of their remains have
been swept away, or remain under the waters, or buried out of sight in
diluvial sediments.
(6) Much importance has been attached to the early works and high
culture of Egypt and Chaldæa, as evidence of vast time during which arts
were growing from a supposed rude stone age. But it must be observed
that no such period is known to antedate civilisation in the East, and
that if the early empires were established by survivors of the Deluge,
they must have brought with them the culture of Antediluvian times.
Farther, the notion of men emerging from a half-brutal state, and from
the use of the rudest implements, is purely conjectural and not
supported by facts. In America, where the semi-civilised agricultural
races are unquestionably the oldest, the rudest possible implements were
used by these partially civilised agricultural people along with
polished stone and metal; and Schliemann has shown that a rude stone age
succeeded the civilisation of Troy, and this at a time when Phœnicia and
Egypt were at the height of their civilisation. Such facts, which might
fill volumes, show how little value is to be attached to supposed ages
of rough and polished stone.
(7) The difficulties attending the establishment of geological dates for
deposits like those containing the remains of men are very great. They
are altogether superficial and local, not wide-spread marine beds in
which a distinct order of superposition can be clearly traced. They are
not easily separated from the glacial beds below, or from those above
which have been modified by human agency, by land-floods, or by
landslips. Thus the application of geological criteria of age to them is
very difficult and uncertain. Evidence of this could easily be given, in
the many errors which have been promulgated, and which have had to be
retracted by their authors, or have been disproved by the observations
of others. For example, no country was at one time richer in supposed
evidences of the antiquity of man than Scandinavia; but Professor
Torell, the director of the Geological Survey of Sweden, has recently
made a careful re-examination of the facts, and has found that there is
no evidence whatever of the existence of man in Scandinavia before the
Neolithic or polished stone age. There are, however, evidences of
considerable changes of level since that time, and it would seem even
since the twelfth century of our era. The remarkable and seemingly
inexcusable errors of observation referred to in Professor Torell’s
memoir, should enforce a caution on geologists as to the uncertainties
of such evidence. Lyell sifted the testimony bearing on this subject
with great care in the first edition of his _Antiquity of Man_. In later
editions he had to make large abatements, and now much of the evidence
in the latest edition would have to be withdrawn or otherwise applied.
From all these considerations the conclusion is obvious that while we
have no certain data for assigning a definite number of years to the
residence of man on the earth, we have no geological evidence for the
rash assertion often made that in comparison with historical periods the
date of the earliest races of men recedes into a dim, mysterious, and
measureless antiquity. On the basis of that Lyellian principle of the
application of modern causes to explain past changes, which is the
stable foundation of modern geology, we fail to erect any such edifice
as the indefinite antiquity of man, or to extend this comparatively
insignificant interval to an equality with the long æons of the
preceding Tertiary. The demand for such indefinite extension of the
history of man rests not on geological facts, but on the necessities of
hypotheses which, whatever their foundation, have no basis in the
discoveries of that science, and are not required to account for the
sequence which it discloses.
CHAPTER XI.
REVIEW OF THE HISTORY OF LIFE.
What general conclusions can we reach as to this long and strange
history of the progress of life on our planet? Perhaps the most
comprehensive of these is that the links in the chain of life, or rather
in its many chains, are not scattered and disunited things, but members
of a great and complex plan; and that when we discern their combinations
and their pattern, we find them not only orderly and symmetrical, but
all tending to one point and bound to one central object, even the
throne of the Eternal. It must also appear evident that the original
plan of nature, both in the animal and vegetable worlds, was too vast to
be realised at one time on a globe so limited as ours, but had to be
distributed in time as well as in space, thus realising the idea of
time-worlds: successive æons in which, one after the other, the work of
creation could rise to successive stages of perfection and completeness
till it culminated in man. All this is sufficiently plain on the
theistic view of nature, and may suffice for those who reverently regard
the God of nature as the Father of their own spirits. But there are
others who ask further questions. Do we know anything of the secondary
causes and origin of life, of the manner of its introduction and
advance, of the laws of its succession?
As to the first of these questions, it is certain that, up to this time,
the origination of the living being from the non-living is an
inscrutable mystery. No one has witnessed this change, or has been able
to effect it experimentally. Nor have we any direct evidence of the
origination of one specific type from another. Such reasonings as assume
the possibility of these things, or on analogical grounds assert their
probability, belong rather to the domain of philosophical speculation
than to science. As to the laws of the succession of life, however, it
is possible to learn something from the sequence of facts as already
ascertained; and though much remains to be discovered, there are a few
leading statements on this subject which can already be made with
safety.
Unity and uniformity, within the limits imposed by progress and
increasing complexity, can be affirmed of the whole process. From the
dawn of life to the present time the great laws of physical nature which
operate on animals and plants have been uniform. These stable laws have
regulated the action of the outer world on organisms. The plans of
structure of these organisms laid down at the first have been followed
throughout. Thus the succession of life presents nothing fortuitous or
arbitrary, but a continuous plan carried out uniformly in time and
space, with certain materials of fixed properties, and with certain
structures predetermined from the first. There is, for example, a great
sameness of plan throughout the whole history of the marine invertebrate
life of the Palæozoic. If we turn over the pages of an illustrated
text-book of geology, or examine the cases or drawers of a collection of
fossils, we shall find extending through every succeeding formation,
representative forms of Crustaceans, Mollusks, and Corals, in such a
manner as to indicate that in each successive period there has been a
reproduction of the same type with modifications; and if the series is
not continuous, this appears to be due to lack of specimens, or to
abrupt physical changes; since sometimes, where two formations pass into
each other, we find a gradual change in the fossils by the dropping out
and introduction of species one by one. Thus in the whole of the great
Palæozoic period, both in its fauna and flora, we have a continuity and
similarity of a most marked character.
There is, indeed, nothing to preclude the supposition that many forms
reckoned as species are really only race modifications. My own
provisional conclusion, based on the study of Palæozoic plants,
published many years ago,[93] is that the general law will be found to
be the existence of distinct specific types independent of each other,
but liable in geological time to minor modifications, which have often
been regarded as distinct species.
While this unity of successive faunæ at first sight presents an
appearance of hereditary succession, it loses much of this character
when we consider the number of new types introduced without apparent
predecessors, or ceasing without successors, and the almost changeless
persistence of other types; the necessity that there should be
similarity of type in successive faunæ on any hypothesis of a continuous
plan; and, above all, the fact that the recurrence of representative
species or races in large proportion marks times of decadence rather
than of expansion in the types to which they belong. To return to a
later period, this is very manifest in that singular resemblance which
obtains between the modern mammals of South America and Australia and
their immediate fossil predecessors—the phenomenon being here
manifestly that of decadence of large and abundant species into a few
depauperated representatives. This will be found to be a very general
law, elevation being accompanied by the abrupt appearance of new types,
and decadence by the apparent continuation of old species, or
modifications of them.
This resemblance with difference in successive faunæ also connects
itself very directly with the successive elevations and depressions of
our continental plateaus in geological time.
Every great Palæozoic limestone, for example, indicates a depression
with succeeding elevation. On each elevation marine animals were driven
back into the ocean, and on each depression swarmed in over the land,
reinforced by new species, either then introduced or derived by
migration from other localities. In like manner on every depression,
land plants and animals were driven in upon insular areas, and on
re-elevation again spread themselves widely. Now I think it will be
found to be a law here that periods of expansion were eminently those of
introduction of new specific types, and periods of contraction those of
extinction, and also of continuance of old types under new varietal
forms. It must also be borne in mind that all the leading types of
invertebrate life were early introduced, that change within these was
necessarily limited, and that elevation could take place mainly by the
introduction of the vertebrate orders. So in plants, Cryptogams early
attained their maximum as well as Gymnosperms, and elevation occurred in
the introduction of Phænogams.
Another allied fact is the simultaneous appearance of like types of life
in one and the same geological period, over widely separated regions of
the earth’s surface. This strikes us especially in the comparatively
simple and homogeneous life-dynasties of the Palæozoic, when for example
we find the same types of Silurian Graptolites, Trilobites and
Brachiopods appearing simultaneously in Australia, America, and Europe.
Perhaps in no department is it more impressive than in the introduction
in the Devonian and Carboniferous ages of that grand cryptogamous and
gymnospermous flora which ranges from Brazil to Spitzbergen, and from
Australia to Scotland, accompanied in all by the same groups of marine
invertebrates; or in the like wholesale production of modern types of
trees in the Cretaceous. Such facts may depend either on that long life
of specific types which gives them ample time to spread to all possible
habitats, before their extinction; or on some general law whereby the
conditions suitable to similar types of life emerge at one time in all
parts of the world. Both causes may be influential, as the one does not
exclude the other, and there is reason to believe that both are natural
facts. Should it be ultimately proved that species allied and
representative, but distinct in origin, come into being simultaneously
everywhere, we shall arrive at one of the laws of creation, and one
probably connected with the gradual change of the physical conditions of
the world.
A closely related truth is the periodicity of introduction of species.
They come in by bursts or flood-tides at particular points of time,
while these great life-waves are followed and preceded by times of ebb
in which little that is new is being produced. We labour in our
investigation of this matter under the disadvantage that the modern
period is evidently one of the times of pause in the creative work. Had
our time been that of the early Tertiary or early Mesozoic, our views as
to the question of origin of species might have been very different. It
is a striking fact, in illustration of this, that since the Glacial age
no new species of mammal can be proved to have originated on our
continents, while a great number of large and conspicuous forms have
disappeared. It is possible that the proximate or secondary causes of
the ebb and flow of life-production may be in part at least physical;
but other and more important efficient causes may be behind these. In
any case these undulations in the history of life are in harmony with
much that we see in other departments of nature.
It results from the above and the immediately preceding statement that
specific and generic types enter on the stage in great force, and
gradually taper off toward extinction. They should so appear in the
geological diagrams made to illustrate the succession of life. This
applies even to those forms of life which come in with fewest species
and under the most humble guise. What a remarkable swarming, for
example, there must have been of Marsupial Mammals in the early
Mesozoic; and in the Coal formation the only known Pulmonates, four or
five in number, belong to as many generic types.
I have already referred to the permanence of certain species in
geological time. I may now place this in connection with the law of
origination and more or less continuous transmission of varietal forms.
I may, perhaps, best illustrate this in connection with a group of
species with which I am very familiar, that which came into our seas at
the beginning of the Glacial age, and still exists. With regard to their
permanence, it can be affirmed that the shells now elevated in Wales to
1,200 and in Canada to 600 feet above the sea, and which lived before
the last great revolution of our continents, a period vastly remote as
compared with human history, differ in no tittle from their modern
successors after thousands or tens of thousands of generations. It can
also be affirmed that the more variable species appear under precisely
the same varietal forms then as now, though these varieties have changed
much in their local distribution. The real import of these statements,
which might also be made with regard to other groups well known to
palæontologists, is of so great significance that it can be realised
only after we have thought of the vast time and numerous changes through
which these humble creatures have survived. I may call in evidence here
a familiar British and American animal, the common sand clam, _Mya
arenaria_, and its relative, _Mya truncata_, which now inhabit together
all the northern seas; for the Pacific specimens, from Japan and
California, though differently named, are undoubtedly the same. _Mya
truncata_ appears in Europe in the older Pliocene, and was followed by
_M. arenaria_ a little later. Both shells occur in the Pleistocene of
America, and their several varietal forms had then already developed
themselves, and remain the same to-day; so that these humble mollusks,
littoral in their habits, and subjected to a great variety of
conditions, have continued, perhaps for one or two thousand centuries,
to construct their shells precisely as at present. Nor are there any
indications of a transition between the two species. Similar statements
may be made with regard to other mollusks of the Pliocene and Modern
periods, and there are even species which extend unchanged from the
early Eocene. Nor is it impossible that some modern bivalves of the
Brachiopod group may be scarcely modified descendants even of Palæozoic
species.
Perhaps some of the most remarkable facts in connection with the
permanence of species and varietal forms are those furnished by that
magnificent flora which burst in all its majesty on the American
continent in the Cretaceous period, and still survives among us even in
some of its specific types, I say survives; for we have but a remnant of
its forms living, and comparatively little that is new has probably been
added since. Take, for example, the facts stated in Chapter VIII. as to
the continuance to the present time of species of plants introduced in
the Cretaceous and Eocene, and which thus came in at the very time when
the great Mesozoic reptiles were decaying or had just disappeared, and
when the placental mammals were being introduced. Some of these plants
must have propagated themselves unchanged for half a million of years.
Plants and the lower tribes of animals are, however, more permanent than
the higher animals; and a strange contrast is afforded to the foregoing
examples of persistence by the repeated revolutions that have affected
vertebrate life since the Mesozoic age. Yet even in the case of
vertebrates there seems to have been little change, except in the
extinction of species, since the Pliocene period.
In conclusion of this review, can we formulate a few of the general
laws, or perhaps I had better call them the general conclusions
respecting life, in which all palæontologists may agree? Perhaps it is
not possible to do this at present satisfactorily, but the attempt may
do no harm. We may, then, I think, make the following affirmations:—
(1) The existence of life and organisation on the earth is not eternal,
or even coeval with the beginning of the physical universe, but may
possibly date from Laurentian or immediately pre-Laurentian times.
(2) The introduction of new species of animals and plants has been a
continuous process, not necessarily in the sense of derivation of one
species from another, but in the higher sense of the continued operation
of the cause or causes which introduced life at first. This, as already
stated, I take to be the true theological or Scriptural as well as
scientific idea of what we ordinarily and somewhat loosely term
creation.
(3) Though thus continuous, the process has not been uniform; but
periods of rapid production of species have alternated with others in
which many disappeared and few were introduced. This may have been an
effect of physical cycles reacting on the progress of life.
(4) Species, like individuals, have greater energy and vitality in their
younger stages, and rapidly assume all their varietal forms, and extend
themselves as widely as external circumstances will permit. Like
individuals, also, they have their periods of old age and decay, though
the life of some species has been of enormous duration in comparison
with that of others; the difference appearing to be connected with
degrees of adaptation to different conditions of life.
(5) Many allied species, constituting groups of animals and plants, have
made their appearance at once in various parts of the earth, and these
groups have obeyed the same laws with the individual and the species in
culminating rapidly, and then slowly diminishing, though a large group
once introduced has rarely disappeared altogether.
(6) Groups of species, as genera and orders, do not usually begin with
their highest or lowest forms, but with intermediate and generalised
types, and they show a capacity for both elevation and degradation in
their subsequent history.
(7) The history of life presents a progress from the lower to the
higher, and from the simpler to the more complex, and from the more
generalised to the more specialised. In this progress new types are
introduced, and take the place of the older ones, which sink to a
relatively subordinate place, and become thus degraded. But the physical
and organic changes have been so correlated and adjusted that life has
not only always maintained its existence, but has been enabled to assume
more complex forms, and that older forms have been made to prepare the
way for newer, so that there has been on the whole a steady elevation
culminating in man himself. Elevation and specialisation have, however,
been secured at the expense of vital energy and range of adaptation,
until the new element of a rational and inventive nature was introduced
in the case of man.
(8) In regard to the larger and more distinct types, we cannot find
evidence that they have, in their introduction, been preceded by similar
forms connecting them with previous groups; but there is reason to
believe that many supposed representative species in successive
formations are really only races or varieties.
(9) In so far as we can trace their history, specific types are
permanent in their characters from their introduction to their
extinction, and their earlier varietal forms are similar to their later
ones.
(10) Palæontology furnishes no direct evidence, perhaps never can
furnish any, as to the actual transformation of one species into
another, or as to the actual circumstances of creation of a species, but
the drift of its testimony is to show that species come in _per saltum_,
rather than by any slow and gradual process.
(11) The origin and history of life cannot, any more than the origin and
determination of matter and force, be explained on purely material
grounds, but involve the consideration of power referable to the unseen
and spiritual world.
Different minds may state these principles in different ways, but I
believe that in so far as palæontology is concerned, in substance they
must hold good, at least as steps to higher truths. And now I may be
permitted to add that we should be thankful that it is given to us to
deal with so great questions, and that in doing so deep humility,
earnest seeking for truth, patient collection of all facts, self-denying
abstinence from hasty generalisations, forbearance and generous
estimation with regard to our fellow-labourers, and reliance on that
Divine Spirit which has breathed into us our intelligent life, and is
the source of all true wisdom, are the qualities which best become us.
As we have traced onward the succession of life, reference has been made
here and there to the defects of those bold theories of descent with
modification which are held forth in our time as the true bond of the
links of the chain of life. It must have been apparent that these
theories, however specious when placed in connection with a limited
induction of facts selected for the purpose of illustrating them, are
very far from affording a satisfactory solution of all difficulties.
They cannot perhaps be expected to take us back to the origin of living
beings; but they also fail to explain why so vast numbers of highly
organised species struggle into existence simultaneously in one age and
disappear in another, why no continuous chain of succession in time can
be found gradually blending species into each other, and why in the
natural succession of things degradation under the influence of external
conditions and final extinction seem to be laws of organic existence. It
is useless here to appeal to the imperfection of the record or to the
movements or migrations of species. The record is now in many important
parts too complete, and the simultaneousness of the entrance of the
faunas and floras too certainly established, while the moving of species
from place to place only evades the difficulty. The truth is that such
hypotheses are at present premature, and that we require to have larger
collections of facts. Independently of this, however, it would seem that
from a philosophical point of view all theories of evolution, as at
present applied to life, are fundamentally defective in being too
partial in their character; and this applies more particularly to those
which are “monstic” or “agnostic,” and thus endeavour to dispense with a
Creative Will behind nature. It may be instructive to illustrate from
the facts developed in preceding chapters this feature of most of the
attempts at generalisation on this subject.
First, then, these hypotheses are too partial, in their tendency to
refer numerous and complex phenomena to one cause, or to a few causes
only, when all trustworthy analogy would indicate that they must result
from many concurrent forces and determinations of force. We have of late
been very familiar with those ingenious, not to say amusing,
speculations in which some entomologists and botanists have indulged
with reference to the mutual relations of flowers and haustellate
insects. Geologically the facts oblige us to begin with Cryptogamous
plants and mandibulate insects; and out of the desire of insects for
non-existent honey, and the adaptations of plants to the requirements of
non-existent suctorial apparatus, we have to evolve the marvellous
complexity of floral form and colouring, and the exquisitely delicate
apparatus of the mouths of haustellate insects. Now when it is borne in
mind that this theory implies a mental confusion on our part precisely
similar to that which in the department of mechanics actuates the
seekers for perpetual motion, that we have not the smallest tittle of
evidence that the changes required have actually occurred in any one
case, and that the thousands of other structures and relations of the
plant and the insect have to be worked out by a series of concurrent
evolutions so complex and absolutely incalculable in the aggregate that
the cycles and epicycles of the Ptolemaic astronomy were child’s play in
comparison, we need not wonder that the common sense of mankind revolts
against such fancies, and that we are accused of attempting to construct
the universe by methods that would baffle Omnipotence itself, because
they are simply absurd. In this aspect of them, indeed, such
speculations are necessarily futile, because no mind can grasp all the
complexities of even any one case, and it is useless to follow out an
imaginary line of development which unexplained facts must contradict at
every step. This is also no doubt the reason why all recent attempts at
constructing “Phylogenies” are so changeable, and why no two experts can
agree about almost any of them.
A second aspect in which such speculations are too partial is in the
unwarranted use which they make of analogy. It is not unusual to find
such analogies as that between the embryonic development of the
individual animal and the succession of animals in geological time
placed on a level with that reasoning from analogy by which geologists
apply modern causes to explain geological formations. No claim could be
more unfounded. When the geologist studies ancient limestones built up
of the remains of corals, and then applies the phenomena of modern coral
reefs to explain their origin, he brings the latter to bear on the
former by an analogy which includes not merely the apparent results but
the causes at work, and the conditions of their action; and it is on
this that the validity of his comparison depends, in so far as it
relates to similarity of mode of formation. But when we compare the
development of an animal from an embryo cell with the progress of
animals in time, though we have a curious analogy as to the steps of the
process, the conditions and agents at work are known to be altogether
dissimilar, and therefore we have no evidence whatever as to identity of
cause, and our reasoning becomes at once the most transparent of
fallacies. Farther, we have no right here to overlook the fact that the
conditions of the embryo are determined by those of a previous adult,
and that no sooner does this hereditary potentiality produce a new adult
animal than the terrible external agencies of the physical world, in
presence of which all life exists, begin to tell on the organism, and
after a struggle of longer or shorter duration it succumbs to death, and
its substance returns into inorganic nature, a law from which even the
longer life of the species does not seem to exempt it. All this is so
plain and manifest that it is extraordinary that evolutionists will
continue to use such partial and imperfect arguments. Another example
may be taken from that application of the doctrine of natural selection
to explain the introduction of species in geological time which is so
elaborately discussed by Sir C. Lyell in the last edition of his
_Principles of Geology_. The great geologist evidently leans strongly to
the theory, and claims for it the “highest degree of probability,” yet
he perceives that there is a serious gap in it; since no modern fact has
ever proved the origin of a new species by modification. Such a gap, if
it existed in those grand analogies by which we explain geological
formations through modern causes, would be admitted to be fatal.
A third illustration of the partial character of these hypotheses may be
taken from the use made of the theory deduced from modern physical
discoveries, that life must be merely a product of the continuous
operation of physical laws. The assumption, for it is nothing more, that
the phenomena of life are produced merely by some arrangement of
physical forces, even if it be admitted to be true, gives only a partial
explanation of the possible origin of life. It does not account for the
fact that life as a force or combination of forces is set in antagonism
to all other forces. It does not account for the marvellous connection
of life with organisation. It does not account for the determination and
arrangement of forces implied in life. A very simple illustration may
make this plain. If the problem to be solved were the origin of the
mariner’s compass, one might assert that it is wholly a physical
arrangement both as to matter and force. Another might assert that it
involves mind and intelligence in addition. In some sense both would be
right. The properties of magnetic force and of iron or steel are purely
physical, and it might even be within the bounds of possibility that
somewhere in the universe a mass of natural loadstone may have been so
balanced as to swing in harmony with the earth’s magnetism. Yet we
should surely be regarded as very credulous if we could be induced to
believe that the mariner’s compass has originated in that way. This
argument applies with a thousandfold greater force to the origin of
life, which involves even in its simplest forms so many more adjustments
of force and so much more complex machinery.
Fourthly, these hypotheses are partial, inasmuch as they fail to account
for the vastly varied and correlated interdependencies of natural things
and forces, and for the unity of plan which pervades the whole. These
can be explained only by taking into the account another element from
without. Even when it professes to admit the existence of a God, the
evolutionist reasoning of our day limits itself practically to the
physical or visible universe, and leaves entirely out of sight the power
of the unseen and spiritual, as if this were something with which
science has nothing to do, but which belongs only to imagination or
sentiment. So much has this been the case that when recently a few
physicists and naturalists have turned to this aspect of the subject,
they have seemed to be teaching new and startling truths, though only
reviving some of the oldest and most permanent ideas of our race. From
the dawn of human thought it has been the conclusion alike of
philosophers, theologians, and the common sense of mankind, that the
seen can be explained only by reference to the unseen, and that any
merely physical theory of the world is necessarily partial. This, too,
is the position of our sacred Scriptures, and is broadly stated in their
opening verse; and indeed it lies alike at the basis of all true
religion and all sound philosophy, for it must necessarily be that “the
things that are seen are temporal, the things that are unseen, eternal.”
With reference to the primal aggregation of energy in the visible
universe, with reference to the introduction of life, with reference to
the soul of man, with reference to the heavenly gifts of genius and
prophecy, with reference to the introduction of the Saviour Himself into
the world, and with reference to the spiritual gifts and graces of God’s
people, all these spring not from sporadic acts of intervention, but
from the continuous action of God and the unseen world; and this, we
must never forget, is the true ideal of creation in Scripture and in
sound theology. Only in such exceptional and little influential
philosophies as that of Democritus, and in the speculations of a few men
carried off their balance by the brilliant physical discoveries of our
age, has this necessarily partial and imperfect view been adopted. Never
indeed was its imperfection more clear than in the light of modern
science.
Geology, by tracing back all present things to their origin, was the
first science to establish on a basis of observed facts the necessity of
a beginning and end of the world. But even physical science now teaches
us that the visible universe is a vast machine for the dissipation of
energy; that the processes going on in it must have had a beginning in
time, and that all things tend to a final and helpless equilibrium. This
necessity implies an unseen power, an invisible universe, in which the
visible universe must have originated, and to which its energy is ever
returning. The hiatus between the seen and the unseen may be bridged
over by the conceptions of atomic vortices of force, and by the
universal and continuous ether; but whether or not, it has become clear
that the conception of the unseen as existing has become necessary to
our belief in the possible existence of the physical universe itself,
even without taking life into the account.
It is in the domain of life, however, that this necessity becomes most
apparent; and it is in the plant that we first clearly perceive a
visible testimony to that unseen which is the counterpart of the seen.
Life in the plant opposes the outward rush of force in our system,
arrests a part of it on its way, fixes it as potential energy, and
thus, forming a mere eddy, so to speak, in the process of dissipation of
energy, it accumulates that on which animal life and man himself may
subsist, and assert for a time supremacy over the seen and temporal on
behalf of the unseen and eternal. I say, for a time, because life is, in
the visible universe, as at present constituted, but a temporary
exception, introduced from that unseen world where it is no longer the
exception but the eternal rule. In a still higher sense, then, than that
in which matter and force testify to a Creator, organisation and life,
whether in the plant, the animal, or man, bear the same testimony, and
exist as outposts put forth in the succession of ages from that higher
heaven that surrounds the visible universe. In them, as in dead matter,
Almighty power is no doubt conditioned by law, yet they bear more
distinctly upon them the impress of their Maker, and while all
explanations of the physical universe which refuse to recognise its
spiritual and unseen origin must necessarily be partial and in the end
incomprehensible, this destiny falls more quickly and surely on the
attempt to account for life and its succession on merely materialistic
principles.
Here, however, we must remember that creation, as maintained against
such materialistic evolution, whether by theology, philosophy, or Holy
Scripture, is necessarily a continuous, nay, an eternal influence, not
an intervention of disconnected acts. It is the true continuity, which
includes and binds together all other continuity.
It is here that natural science meets with theology, not as an
antagonist, but as a friend and ally in its time of greatest need; and I
must here record my belief that neither men of science nor theologians
have a right to separate what God in Holy Scripture has joined together,
or to build up a wall between nature and religion, and write upon it “no
thoroughfare.” The science that does this must be impotent to explain
nature and without hold on the higher sentiments of man. The theology
that does this must sink into mere superstition.
In the light of all these considerations, whether bearing on our
knowledge or our ignorance, a higher and deeper question presents
itself, namely, that as to the relation of nature and of man to a
Personal Creator. To this it seems to me that the study of the
succession of life yields no uncertain reply. Call the progress of life
an evolution if you will; trace it back to primæval Protozoa, or to a
congeries of atoms: still the truth remains that nothing can be evolved
out of these primitive materials except what they originally contained.
Now we find in the existence of man, and in the tendency of the scheme
of nature towards his introduction, evidence that at least all that is
involved in the reasoning and moral nature of man must have existed
potentially before atoms began to shape themselves into crystals or into
organic forms. Nay, more than this is implied, for we do not know that
man and what he has hitherto been and done constitute the ultimate
perfection of nature, and we must suspect that something much more than
what we see in man must be required for the origination of the chain of
life. What does this prove, in any sense in which human reason can
understand it? Nothing less, it seems to me, than that doctrine of the
Almighty Divine Logos, or Creative Reason, as the cause of all things,
asserted in our sacred Scriptures, and held in one form or another by
all the greatest thinkers who have attempted to deal with the question
of origins. Falling back on this great truth, whether presented to us in
the simple “God said” of Genesis, or in the more definite form of the
New Testament, “The Word was with God, and the Word was God,” we find
ourselves in the presence of a Divine plan pervading all the ages of the
earth’s history and culminating in man, who presents for the first time
the image and likeness of the Divine Maker; and this forms the true
nexus of all the separate chains of life. Had man never existed, such
reasoning might have been speculative merely, but the existence of man,
taken in connection with the progress of the plan which has terminated
in his advent, proves the existence of God.
Divine revelation carries us a step farther, and teaches us to recognise
in Jesus of Nazareth God manifest in the flesh, the Divine Logos
dwelling among men. But though this is a doctrine of revelation and not
of science, it is in perfect harmony with the plan of progress which we
have been sketching. It is the natural outcome of a process leading to
the introduction of a rational and accountable being, understanding
something of the works and ways of God, that to him God should reveal
Himself, and that the Divine Logos, by whom were “constituted the
ages”[94] of the world’s geological history, should preside also over
its future consummation, when all the degradation that has sprung from
the aberrations of fallen and imperfect humanity shall be removed, and
man himself shall become fully a partaker of the Divine nature.
The world we live in is thus not necessarily a finished world, and it is
now marred by the sins of man. What it may be in the future, we can
perhaps as little guess as an intelligence studying the Palæozoic world
could have understood that of the present time. But it is a glorious
truth to know that our Maker has revealed Himself to us also as a
Saviour, and that as individuals we shall not perish, to be replaced by
an improved species in the future, but that we ourselves, as sons of
God, may enter into and possess the new earth and new heavens of future
æons of the universe. Thus it would seem that the Gospel of Jesus Christ
is that which was wanting to complete and justify the history of nature
by bringing to light the final “restitution of all things,” and our own
union to God in a happy immortality.
FOOTNOTES:
[1] Croll has elaborated this calculation in his work, _Climate and
Time_.
[2] Sept. 1879.
[3] Analyses recently made by Mr. C. Hoffman, of the Geological Survey
of Canada, show that beds of graphitic gneiss, some of them 8 feet in
thickness, contain as much as 25·5 to 30 per cent. of carbon, the
remaining earthy matter consisting principally of silica, alumina, and
lime. The graphite from veins was nearly pure carbon, containing from
97·6 to 99·8 per cent. of that substance.
[4] Sometimes separated as a distinct order under the name of
_Radiolaria_.
[5] _Loftusia Columbiana_, Dawson, from British Columbia, is the only
Carboniferous species yet known.
[6] See Nicholson in the _Memoirs_ of the Palæontographical Society.
[7] _Archæospherinæ_ of the author.
[8] _Eophyton Linnæanum_ (Torrell).
[9] See Paper on “Footprints and Impressions of Animals,” _Am. Journal
of Science_, 1873.
[10] They probably belong to a large sponge named by Billings
_Trichospongia sericea_.
[11] _Amphispongia._
[12] _Geological Magazine_, May, 1878.
[13] It is regarded as somewhat doubtful whether these are Hydroids or
Bryozoa.
[14] _Heliopora_, an Alcyonarian; _Pocillopora_, an Anthozoan.
[15] _Haplophyllia_, _Guynia_, _Duncania_, of Pourtales.
[16] _Palæchinus._
[17] Some of the earliest appear to be allies of the modern limpets.
[18] “Un produit de l’imagination, sans aucun fondement dans la
réalité.”
[19] _Hymenocaris_.
[20] Phyllopods and Ostracods.
[21] _Pterygotus, Eurypterus_, &c.
[22] Whitfield, _Am. Journ. of Sci._, 1880.
[23] _Report on Devonian Fossil Plants of Canada_, 1871. _Story of the
Earth and Man_, 1873. _Address to American Association_, 1875.
[24] See the important memoir of Barrande on the Silurian Brachiopods,
in which, as the result of the most elaborate and detailed comparisons,
he concludes that in the case of these shells, as in that of the
Cephalopods and Trilobites, the introduction of species in geological
time has not occurred by modification, but must have depended on a
creative process. It is such painstaking researches as those of the
great Bohemian palæontologist which must finally settle these questions,
in so far as geology is concerned.
[25] _Geological Magazine_, November, 1869.
[26] The genus _Buthotrephis_ includes supposed branching sea-weeds of
the Silurian. For this reason I would propose the name _Protannularia_
for these plants.
[27] _Lycopodiaceæ._
[28] Allied to those named by Brongniart _Aetheotesta_.
[29] _Cordaites._
[30] Paper by Sir W. Dawson in _Chicago Academy’s Bulletin_, 1886.
[31] _Calamodendron_ and _Arthropitys_ are forms of this kind.
[32] Grand’ Eury and Williamson have directed attention to this in the
case of those of France and England.
[33] _Amphioxus._
[34] _Petromyzon_, &c.
[35] Dr. Newberry has kindly furnished me with specimens, and Dr.
Harrington has submitted to analysis portions of shale filled with these
little teeth, the result giving 2·58 of calcium phosphate for the whole,
which indicates that the Conodonts are really bone. Their microscopic
structure approaches to that of the dentine of such Carboniferous fishes
as _Diplodus_. Hinde has described Conodonts from the Silurian of
Canada.
[36] _Ueber Conodonten_: Munich, 1886.
[37] _Lepidosteus._
[38] _Palæichthyes_ of Günther.
[39] _Dinichthys Terrelli_ and _D. Hertzeri_ (Newberry).
[40] Cestracionts.
[41] Selachians.
[42] _Amphipeltis paradoxus_ of Salter.
[43] Genus _Strophia_. I have provisionally named the St. John species
_Strophites erianus_.
[44] The enlarged figure of _Pupa vetusta_ is too much elongated, and
the aperture is somewhat conjectural, as it is usually crushed.
[45] _Dawsonella_ of Bradley.
[46] _Archiulidæ_ of Scudder.
[47] _Euphobesia armigera_ (Meek and Worthen), from Illinois.
[48] About fifty in all, as I learn from Mr. Scudder.
[49] _Orthoptera._
[50] _Neuroptera._
[51] _Coleoptera._
[52] _Tincæ._
[53] One highly specialised Carboniferous insect recently found is the
_Protophasma_ of Brongniart, a relative of the modern “Walking-sticks.”
[54] This was first described as part of the larva of a Dragon-fly. It
is now recognised as belonging to a Scorpion.
[55] _Protolycosa_ (Roemer).
[56] _Menopoma_, _Menobranchus_, &c.
[57] _Ophiderpeton Brownriggii._
[58] _Diplichnites._
[59] These are known in some of the smaller species, but not as yet in
the larger.
[60] _Hylonomus._ See Fig. facing this chapter.
[61] _Mastodonsaurus_ or _Labyrinthodon_.
[62] _Palæosiren Beinertii_ of Geinitz.
[63] _Hyleopeton._
[64] _Diadictes_ and _Bolasaurus_ (Cope).
[65] _Enaliosauria_, including _Ichthyopterygia_ and _Sauropterygia_.
[66] _Anomodontia_ and _Theriodontia_.
[67] _Geology of Oxford_, p. 227.
[68] Cope has proposed the names _Camerosaurus_, _Amphicœlias_, &c., for
these problematical animals. Marsh names them _Titanosaurus_,
_Atlantosaurus_, &c., while Owen holds that some of them at least are
identical with his genus _Chondrosteosaurus_. Seeley and Hulke adopt the
name _Ornithopsis_, and support Cope’s view of their nature.
[69] _Ratitæ._
[70] Woodward in a recent paper refers to a still more curious
resemblance of the Dinosaurs to the biped lizard of Australia
(_Chlamydosaurus_), which runs on its hind limbs, and even perches on
trees.
[71] A poplar occurs in Greenland, in beds held to be Lower Cretaceous.
[72] By some regarded as Upper Cretaceous.
[73] First recognized in American Eocene by Newberry.
[74] Described by La Harpe and Gaudin, and recently by Gardner.
[75] Recent discoveries have since the publication of the first edition
removed the Bovey Tracey beds from the Miocene to the Eocene. See
Reports of Mr. Starkie Gardner to the British Association.
[76] Lyell, _Principles_; Brown, _Florula Discoana_.
[77] G. M. Dawson, _Report on 49th Parallel_; _Reports on British
Columbia_.
[78] Gray’s reasoning is based on the extreme view of the Glacial period
now prevalent in America, contrary, as it appears to me, to the actual
facts; but with limitations it holds good on more moderate views as
well.
[79] _Geological Magazine_, July, 1887.
[80] _Les Enchainements du Monde Animal._
[81] See Frontispiece to this Chapter.
[82] For example, _Tillotherium_ of the American Eocene, which was as
large as a tapir, and in form resembled a bear.
[83] Croll, _Climate and Time_.
[84] Notes on Post-Pliocene of Canada; _Acadian Geology_, 3rd edition.
[85] The actual reason for belief in the past existence of land in the
basin of the Indian Ocean is found in the close relationship of forms of
life found in Madagascar, Southern Asia, and Australia.
[86] Traditions of this animal, a veritable primæval unicorn, are said
still to exist in Siberia.
[87] As, for instance, those of Cro-Magnon, and Mentone, and Engis.
[88] De Puyot and Lohert, Namur, 1887.
[89] Religious Tract Society, 1878.
[90] May, 1887.
[91] _Climate and Time_, a work in which these and other matters
relating to the Glacial period are very well discussed.
[92] Kimber, quoted by Southall.
[93] _Report on Devonian Plants of Canada_, 1871.
[94] The true meaning of Hebrews i. 2 and xi. 3.
INDEX.
(_Principally to Forms of Life noticed or illustrated._)
Agnostus, 79
Alethopteris, 105
Ammonites, 76
_Amphibians_, 152
Amphipeltis, 85
Ancyloceras, 77
Antholithes, 101
Anthozoa, 57
_Angiosperms_, 187
Anthropalæmon, 85
_Antiquity of Man_, 247
_Apes_, 228
Arachnida, 150
Archæocyathus, 38
Archæopteryx, 172
Archegosaurus, 153
Archimulacris, 146
Arctocyon, 228
Asterophyllites, 103
Astylospongia, 51
Athyris, 67
Baculites, 77
Baphetes, 155
Bathygnathus, 174
_Batrachians_, 152
_Bats_, 226
_Beetles_, 145
_Beginning of Life_, 23
Belemnites, 78
Beryx, 133
Beyrichia, 83
_Birds_, 172
_Bivalve shells_, 69
Blattina, 146
_Brachiopods_, 63
Brontotherium, 217
Buthotrephis, 92
_Butterflies_, 150
Calamites, 99, 105
Calymene, 80, 82
Campsognathus, 179
Carcharodon, 132
Cardiocarpum, 101
Cephalaspis, 122
_Cephalopods_, 71
Ceratites, 75
Ceratodus, 126
Ceteosaurus, 178
Cinnamomum, 198
Clidastes, 169
_Cockroaches_, 146
Conocephalites, 79
_Conodonts_, 118
_Corals_, 55
Cordaites, 110
Coryphodon, 215
_Crinoids_, 61
Crioceras, 77
Crustacea, 79
_Cuttle-fishes_, 71
Cyathaspis, 121
Cyathophyllum, 60
_Cystideans_, 62
Cythere, 83
Dadoxylon, 100
Dapedius, 132
Davallia, 192
Dictyonema, 53
Dikellocephalus, 79
Dinichthys, 127
Dinoceras, 216
_Dinosaurs_, 174
Dipnoi, 123
Discina, 66
_Dragon-fly_, 148
Dromatherium, 209
Dryopithecus, 229
Echinoderms, 61
Elasmotherium, 242
Elephants, 224
Eocene age, 213
Eopteris, 93
Eoscorpius, 151
Eozoon, 27
_Equine feet_, 218
Equisetaceæ, 97
Extracrinus, 64
Favosites, 59
_Ferns of Palæozoic_, 106
_Ferns, Tree_, 97
_Fishes_, 120
_Floras, distribution of_, 201
_Footprints_, 152
Foraminifera, 32
_Fruits of Devonian_, 101
_Ganoids_, 120
_Gastropods_, 70
_Glacial age_, 233
Glyptocrinus, 63
Glyptodendron, 94
Gomphoceras, 73
Graptolites, 53
Halisites, 59
Heliophyllum, 59
Heterocrinus, 63
_Horse_, 218
_Huronian age_, 24
Hydrozoa, 54
Hylonomus, 157
Ichthyosaurus, 167
Implements, 245
Insects, 139
Isotelus, 82
_Labyrinthodonts_, 155
Lamellibranchiata, 69
_Lampreys_, 117
_Land-snails_, 142
_Laurentian age_, 24
Lepidodendron, 108
Lepidosiren, 124
Leptophleum, 98
Libellula, 148
Lingula, 65
Liriodendron, 191
Lituites, 73
Loligo, 72
Machairodus, 227
_Mammals_, 207
_Mammoth_, 240
Man, advent of, 233
_Mantids_, 146
_Mares-tails_, 97
_Marsupials_, 207
Mastodon, 224
May-flies, 146
Megalosaurus, 1
Megaphyton, 107
Megatherium, 222
Microlestes, 208
Microsauria, 156
_Millepedes_, 145
_Modern forests_, 186
Monotremes, 208
Mososaurus, 169
Moths, 148
Murchisonia, 70
Myrica, 194
Nautilus, 71
Neuropteris, 105
Oldhamia, 52
Onchus, 121
Onoclea, 191
Oreodon, 221
_Origin of Life_, 23
Orthis, 66
Orthoceras, 73
Osteolepis, 124
_Ostracods_, 83
Otodus, 131
Palæaster, 62
Palæchinus, 62
Palæoniscus, 129
Palæotherium, 212
Paradoxides, 79
Pentacrinus, 64
Phaceps, 83
Phascolotherium, 210
Pinnularia, 101
Plagiaulax, 210
_Plants, earliest_, 89
_Pleistocene_, 240
Plesiosaurus, 167
Pleurocystites, 63
Pleurotomaria, 70
Pliosaurus, 168
Polyzoa, 59
Post-glacial, 236
Prodryas, 150
Productus, 68
Protannularia, 91
Protosalvinia, 101
Proterosaurus, 166
Protostigma, 92
Protozoa, 27
Psilophyton, 95
Pterichthys, 123
_Pterodactyls_, 171
Pteropods, 70
Pterygotus, 84
Ptilodictya, 55
Ptyonius, 154
Quadrumana, 228
Quercus, 194
Receptaculites, 38
_Reptiles_, 165
Rhamphorhyncus, 171
_Rhizopods_, 34
Ruschinites, 81
Sassafras, 190
_Scorpions_, 151
_Sea-lizards_, 167
Selachians, 130
Sequoia, 197
_Sharks_, 120
Sigillaria, 109
Sphenophyllum, 92, 103
Sphinx-moth, 149
Spirifer, 67
Sponges, 48
_Squids_, 72
Stelliosaurus, 158
Stenopora, 57
Stromatopora, 36
Syringoxylon, 102
Tabulata, 59
_Teliosts_, 120
Terebratula, 66
Trichospongia, 51
Trigonocarpum, 101
Trilobites, 78
Turrilites, 77
Xylobius, 145
Zaphrentis, 60
Zonites, 143
RICHARD CLAY AND SONS, LONDON AND BUNGAY.
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