BERKELEY
LIBRARY
UNIVERSITY OF
CALIFORNIA
EARTH
SCIENCES
LIBRARY
THE LIBRARY
OF
THE UNIVERSITY
OF CALIFORNIA
PRESENTED BY
PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID
CLASS-BOOK OF GEOLOGY
CLASS-BOOK
GEOLOGY
BY
SIR ARCHIBALD GEIKIE, F.R.S.
D.C.L. OXF.; D.SC. CAMR., DUEL.; LL.D. ST. AND., EDIN., GLASG. J
FOREIGN MEMBER OF THE R. ACAD. LINCEI ROME J
CORRESPONDENT OF THE INSTITUTE OF FRANCE, ETC.;
LATE DIRECTOR-GENERAL OF THE GEOLOGICAL SURVEY OF THE UNITED
KINGDOM, AND FORMERLY MURCHISON PROFESSOR OF GEOLOGY
AND MINERALOGY IN THE UNIVERSITY OF EDINBURGH
FO UR TH EDI TION
ILLUSTRATED WITH WOODCUTS
Honton
MACMILLAN AND CO., LIMITED
NEW YORK : THE MACMILLAN COMPANY
1902
A II rights reserved
First Edition, 1886. Second Edition, 1890. Reprinted 1891. Third Edition, 1892.
Reprinted 1893, 1894 March and September, 1896, 1897, 1859, 1900.
Fourth Edition, 1902.
EARTH
SCIENCES
LIBRARY
PREFACE
TO THE FIRST EDITION (1886)
THE present volume completes a series of educational works on
Physical Geography and Geology, projected by me many years
ago. In the Primers^ published in 1873, tne most elementary
facts and principles were presented in such a way as I thought
most likely to attract the learner, by stimulating at once his
faculties of observation and reflection. The continued sale of
large editions of these little books in this country and in
America, and the translation of them into most European
languages, leads me to believe that the practical methods of
instruction adopted in them have been found useful. They
were followed in 1877 by my Class-Book of Physical Geography ',
in which, upon as far as possible the same line of treatment,
the subject was developed with greater breadth and fulness.
This volume was meant to be immediately succeeded by a
corresponding one on Geology, but pressure of other engage-
ments has delayed till now the completion of this plan.
So many introductory works on Geology have been written
that some apology or explanation seems required from an
author who adds to their number. Experience of the practical
work of teaching science long ago convinced me that what the
tti
vi PREFACE
young learner primarily needs is a class-book which will awaken
his curiosity and interest. There should be enough of detail
to enable him to understand how conclusions are arrived at.
All through its chapters he should see how observation,
generalisation, and induction go hand in hand in the progress
of scientific research. But it should not be overloaded with
technical details which, though of the highest importance,
cannot be adequately understood until considerable advance
has been made in the study. It ought to present a broad,
luminous picture of each branch of the subject, necessarily, of
course, incomplete, but perfectly correct and intelligible as far
as it goes. This picture should be amplified in detail by a
skilful teacher. It may, however, so arrest the attention of the
learner himself as to lead him to seek, of his own accord, in
larger treatises, fuller sources of information. To this ideal
standard of a class-book I have striven in some measure to
approach.
Originally, I purposed that this present volume should be
uniform in size with the Class-Book of PJiysical Geography.
But, as the illustrations were in progress, the advantage of
adopting a larger page became evident, and with this greater
scope and my own enthusiasm for the subject the book has
gradually grown into what it now is. With few exceptions, the
woodcuts have been drawn and engraved expressly for this
volume. Mr. Sharman has kindly made for me most of the
drawings of the fossils. The landscape sketches are chiefly
from my own note-books. I have to thank Messrs. J. D.
Cooper and M. Lacour for the skill with which they have given
in wood-engraving the expression of the originals.
PREFACE vii
In preparing a Fourth Edition of this Class-Book I have
endeavoured to keep it abreast of the continued advance of
Geology. Some parts of it have been re-arranged and to some
extent re-written, and considerable additions have been made
throughout the volume. In compliance with frequent repre-
sentations made to me by friends in the United States, I have
inserted fuller references to North American Geology, and in
illustration of them have been favoured by my friend Mr.
C. D. Walcott, the Director of the United States Geological
Survey, with the use of a series of photographs taken by him-
self and members of his staff, which were selected for me by
his eminent coadjutor Mr. G. K. Gilbert, and from which a
number of fresh cuts have been prepared. I am much indebted
also to my colleague Dr. F. L. Kitchin for his valuable assist-
ance in reading the proofs of Part IV., and for supplying a
thorough revision of the Table of the Vegetable and Animal
Kingdoms in the Appendix.
li f A November 1901.
CONTENTS
CHAPTER I
i
INTRODUCTORY
PART I
THE MATERIALS FOR THE HISTORY OF THE
EARTH
CHAPTER II
THE INFLUENCE OF THE ATMOSPHERE IN THE CHANGES
OF THE EARTH'S SURFACE 10
CHAPTER III
THE INFLUENCE OF RUNNING WATER IN GEOLOGICAL
CHANGES, AND HOW IT IS RECORDED . . . 26
CHAPTER IV
THE MEMORIALS LEFT BY LAKES .... .48
CONTENTS
CHAPTER V
PAGE
HOW SPRINGS LEAVE THEIR MARK IN GEOLOGICAL HIS-
TORY . 57
CHAPTER VI
ICE -RECORDS ........ 69
CHAPTER VII
THE MEMORIALS OF THE PRESENCE OF THE SEA . . 80
CHAPTER VIII
HOW PLANTS AND ANIMALS INSCRIBE THEIR RECORDS
IN GEOLOGICAL HISTORY 91
CHAPTER IX
THE RECORDS LEFT BY VOLCANOES AND EARTHQUAKES 103
PART II
ROCKS, AND HOW THEY TELL THE HISTORY
OF THE EARTH
CHAPTER X
THE MORE IMPORTANT ELEMENTS AND MINERALS OF
THE EARTH'S CRUST . . , 127
CONTENTS
- CHAPTER XI
PAGE
THE MORE IMPORTANT ROCKS OF THE EARTH'S CRUST 154
PART III
THE STRUCTURE OF THE CRUST OF THE EARTH
CHAPTER XII
SEDIMENTARY ROCKS THEIR ORIGINAL STRUCTURES . I 92
CHAPTER XIII
SEDIMENTARY ROCKS STRUCTURE SUPERINDUCED IN
THEM AFTER THEIR FORMATION . . . 2OJ
CHAPTER XIV
ERUPTIVE ROCKS AND MINERAL VEINS IN THE ARCHI-
TECTURE OF THE EARTH'S CRUST . . . 224
CHAPTER XV
HOW FOSSILS HAVE BEEN ENTOMBED AND PRESERVED,
AND HOW THEY ARE USED IN INVESTIGATING THE
STRUCTURE OF THE EARTH'S CRUST, AND IN STUDY-
ING GEOLOGICAL HISTORY ... . ......... _ , ... 237
xii CONTENTS
PART IV
THE GEOLOGICAL RECORD OF THE HISTORY
OF THE EARTH
CHAPTER XVI
PAGE
THE EARLIEST CONDITIONS OF THE GLOBE -- THE
ARCHAEAN PERIODS . . . . . .251
CHAPTER XVII
THE PALEOZOIC PERIODS CAMBRIAN .... 264
CHAPTER XVIII
SILURIAN . 276
CHAPTER XIX
DEVONIAN AND OLD RED SANDSTONE . . . .287
CHAPTER XX
CARBONIFEROUS
CHAPTER XXI
PERMIAN . . . . . . . . .3M
CHAPTER XXII
THE MESOZOIC PERIODS TRIASSIC . . . . 323
CONTENTS xin
CHAPTER XXIII
PAGE
JURASSIC . . 33 2
CHAPTER XXIV
CRETACEOUS . 34$
CHAPTER XXV
TERTIARY OR CAINOZOIC EOCENE OLIGOCENE . .365
CHAPTER XXVI
MIOCENE PLIOCENE 380
CHAPTER XXVII
POST-TERTIARY OR QUATERNARY PERIODS PLEISTO-
CENE OR POST-PLIOCENE RECENT . . . 394
APPENDIX . . . . . . . . . 413
INDEX 429
LIST OF ILLUSTRATIONS
FIG. I'AGE
1. Weathering of rock, as shown by old masonry. (The "false-
bedding " and other original structures of the stone are revealed
by weathering) .".'"..'..'.' ... I2
2. Passage of sandstone upwards into soil ...'.' . . ' . . 1$
3. Passage of granite upwards into soil . . .. . . . i6
4. Talus-slopes at the foot of a line of cliffs ...*'., . . . 20
5. Section of rain- wash or brick-earth . . '. . . .. . .20
' 6. Sand-dunes . ' . . ' . . ' '. . . .'. . _aa
7. "Jail and Court-house Rocks" typical outliers or " buttes "
of soft sandstone, developed by atmospheric denudation in a
semi-arid region ; Platte River, Western Nebraska . . 23
8. Erosion of limestone by the solvent action of a peaty stream,
Durness, Sutherlandshire ' . . '.".'." ."".' . 28
9. Pot-holes worn out by the gyration of stones in the bed of a
stream . .' ''.* . . ' ." ^ " '. " ~. : ''" "" ..'" "" . 33
10. Windings of the Mississippi river ...... 34
11. Windings of the gorge of the Moselle above Cochem . . . ' 35
12. Section at the Horse-Shoe Fall, Niagara . . . . . " '36
13. Grand Canon of the Colorado . . ^. . . . . . '$f
14. Gullies torn out of the side of a mountain by descending torrents,
with cones of detritus at their base ...... 40
15. Flat stones in a bank of river-shingle, showing the direction of the
current that transported and left them . . . . .41
16. Section of alluvium showing direction of currents . . .42
17. River-terraces . . . '. . . . . .43
18. Section of river-terraces ... . . . . . 44
19. Alluvial terraces on the side of an emptied reservoir ... 49
20. Parallel roads of Glen Roy . . '. ' . '. . . 50
21. Stages in the filling up of a lake .-..'. . . 51
22. Well-worn shingle on the shore of a large lake (Lake Ontario) . 52
23. Piece of shell-marl containing shells of Limn&a peregra . . 53
b
xvi LIST OF ILLUSTRATIONS
FIG. 1'AGE
24. View of Axmouth landslip (as it appeared in April 1885) . . 59
25. Section of cavern with stalactites and stalagmite ... 62
26. Section showing successive layers of growth in a stalactite . . 64
27. Travertine with impressions of leaves . ". , . . 66
28. Glacier with medial and lateral moraines . . . . . 71
29. Perched blocks scattered over ice- worn surface of rock . . 72
30. Glacier-borne block of granite resting on red sandstone, Corrie,
Isle of Arran, Scotland . . . . . . . -73
31. Front of Muir Glacier, Alaska, in June 1899, the L-e-cliff is from
200 to 300 feet high ........ 74
32. Stone from the Boulder-clay of Central Scotland, which has been
smoothed and striated under an ice-sheet . . . . 75
33. Ice-striation on the floor and side of a valley . . . . .76
34. ' ' Moulin pot-holes " in granite, High Sierra, California . . 78
35. Buller of Buchan a caldron-shaped cavity or blow-hole worn out
of granite by the sea on the coast of Aberdeenshire . . .81
36. The Stacks of Duncansby, Caithness, a wave-beaten coast-line . 83
37. Section of submarine plain . . . . .84
38. Storm-beach ponding back a stream and forming a lake ; west
coast of Sutherlandshire . . . . . . . . 87 ,
39* Section of a peat-bog . . .... . . . 93
40. Diatom-earth from floor of Antarctic Ocean, magnified 300
diameters . . . . . . ...... . . 94
41. Recent limestone (cockle, etc.) . . . . . . -95
42. Globigerina ooze magnified . . . , ...... . . 96
43. Section of a coral-reef . ; . ... . . . 97
44. Cellular Lava with a few of the cells filled up with infiltrated
mineral matter (Amygdales) . . , , . . . 107
45. Section of a lava-current . . .... . . . 108
46. Elongation of cells in direction of flow of a lava-s'ream . .109
47. Volcanic block ejected during the deposition of strata in water . 112
48. Volcanoes on lines of fissure . . * , "., . . . 114
49. Volcanic Necks, Texas . . , , . : . , . . 116
50. Outline of a Volcanic Neck . . ,'j ... . . .117
51. Ground-plan of the structure of the Neck shown in Fig. 50 .117
52. Section through the same Neck as in Figs. 50 and 51 . 118
53. Volcanic dykes rising through the bedded tuff of a crater . . 119
54. Raised marine terraces, or Strand-lines, Alten Fjord, Norway . 124
55. Group of Quartz-crystals (Rock-crystal) . . ,. . . 131
56. Calcite (Iceland spar), showing its characteristic rhombohedral
cleavage .......... 138
57. Cube, octahedron, dodecahedron . . . . . -139
58. Tetragonal prism and pyramid , , . . . .139
LIST OF ILLUSTRATIONS xvil
FIG. PAGE
59. Orthorhombic prism . . . . . . . . 139
60. Hexagonal prism, rhombohedron, and scalenohedron . . . 140
6:. Monoclinic prism. Crystal of Augite . . . , '-.'. . 140
62. Triclinic prism. Crystal of Albite felspar . . ... . 140
63. Section of a pebble of Chalcedony . . . . .'. . 142
64. Piece of Haematite, showing the nodular external form and the
internal crystalline structure . . . ... .... 143
65. Octahedral crystals of Magnetite in chlorite-schist . . * 144
66. Dendritic markings due to arborescent deposit of earthy manganese
oxide . . . . . . . . . ,.145
67. Cavity in a lava, filled with zeolite which has crystallised in long
slender needles . . . . ... . 147
68. Hornblende crystal ......... 148
69. Magnified section of an Olivine crystal . . . . . .148
70. Calcite in the form of " nail-head spar" . . . - . .149
71. Calcite in the form of dog-tooth spar ..... 150
72. Sphaerosiderite or Clay-ironstone concretion enclosing portion of a
fern . . . . . . . . . . . 1 5 1
73. Gypsum crystals . . . . . . . . .152
74. Group of fluor-spar crystals . . . . y . 153
75. Concretions . . . . . . . . . -155
76. Section of a Septarian nodule, with coprolite of a fish as a nucleus 156
77. Piece of Oolite ... . . . . ... .157
78. Piece of Pisolite . . . . . .... . 157
79. Cavities in quartz containing liquids (magnified) .... 158
80. Various forms of Crystallites (highly magnified) .... 159
81. Porphyritic structure . ... . . . . . 160
82. Spherulitic and fluxion-structure ...... 161
83. Schistose structure . . . . . . . . 162
84. Brecciated structure volcanic breccia, a rock composed of angular
fragments of lava, in a paste of finer volcanic debris . . .165
85. Conglomerate . . . . . ... . .166
86. Concretionary forms assumed by Dolomite, Magnesian Limestone,
Durham . . . . . '........ .,.-.. 172
87. Weathered surface of a limestone composed of the broken stems of
encrinites . . . . ... . . . 175
08. Group of crystals of felspar, quartz, and mica, from a cavity in the
Mourne Mountain granite . . . . .178
89. Columnar basalts of the Isle of Staffa, resting upon tuff (to the
right is Fingal's Cave) . . . . ... . .185
90. Section of stratified rocks . . . . . . . .193
91. Section showing alternation of beds ...... 195
92. False-bedded sandstone . . . . . . . .196
xviil LIST OF ILLUSTRATIONS
FIG. PAGE
93. Ripple-marked surface of sandstone . . . . . .197
94. Cast of sun-cracked surface preserved in the next succeeding layer
of sediment . . . . ' . .' . . . . 198
95. Rain-prints on fine mud . . . . . . . 199
96. Regular alternation of limestone and shale, Greenhorn formation
(Cretaceous), Colorado . . . ... . . 200
97. Vertical trees (Sigillaria] in sandstone, Swansea (Logan) . . 202
98. Hills formed out of horizontal sedimentary rocks . ... 203
99. Section of Overlap . . . . . . ... 204
100. Unconformability . - .'*'.' . . ' 1 ' . " . . 204
101. Joints in a stratified rock . . . . . . ''" . . 208
102. Dip and Strike . . . . , . . . . 210
103. Clinometer . . . .'.'-.. . . .210
104. Dip, Strike, and Outcrop . . . . . . . .211
105. Inclined strata shown to be parts of curves . . . . 212
106. Curved strata (Anticlinal fold), near St. Abb's Head . '.- . 213
107. Curved strata (Synclinal fold) near Banff .' / . . . 214
108. Anticlines and Synclines .*" . . . . . . .215
109. Section of folded and crumpled strata forming the Grosse Windgalle
(10,482 feet), Canton Uri, Switzerland, showing crumpled and
inverted strata (after Heim) . ..-.-. . . 215
no. Distortion of fossils by the shearing of rocks . -. ' . . . 216
in. Curved and cleaved rocks. Coast of Wigtonshire . . . 217
112. Examples of normal Faults . . . . . . .218
113. Sections to show the relations of Plications to reversed Faults . 219
114. Throw of a Fault . ... V ... . 219
115. Section showing Thrust-planes, Loch Maree, Scotland . . 220
116. Ordinary unaltered red sandstone, Keeshorn, Ross-shire (magni-
fied) . . . ' . . . . . . . . 222
117. Sheared red sandstone forming now a micaceous schist, Keeshorn,
Ross-shire (magnified) . . . .' ... . 222
118. Outline and section of a Boss traversing stratified rocks . . 226
119. Ground-plan of Granite-boss with ring of Contact-Metamorphism 227
1 20. Sill or Intrusive Sheet . .-.'." . ' . . . 228
121. Interstratified or Contemporaneous Sheets ..... 229
122. Section to illustrate evidence of contemporaneous volcanic action 229
123. Succession of lava-sheets and volcanic conglomerates, Canon of
Yellowstone River, Yellowstone Natural Park . . . . 231
124. Map of Dykes near Muirkirk, Ayrshire . . . . . 233
125. Section of a Volcanic neck . .' . ... . 233
126. Section of a Mineral vein . .' ... . i . 235
127. Common Cockle (Cardium edule] . . ' . - . . . 241
128. Fragment of crumpled Schist . . . . . . . 259
LIST OF ILLUSTRATIONS xix
FIG. * PAGE
129. Fucoid-like impression (Eophyton Linneanuin} from Cambrian
rocks (|) . . . . . . . , . 269
130. Oldhamia radiata (natural size), Ireland . . -" . . 270
131. Hydrozoon from the Cambrian rocks . . . . . 270
132. Cambrian Trilobites . . . ... , . . 272
133. Cambrian Brachiopod (Li?igulella Davisii], natural size . . 273
134. An Upper Silurian sea- weed (Chondrites verisimilis), natural size 277
135. Graptolites from Silurian rocks . . ... .278
136. Silurian Corals . . . . . . . . . 279
137. Silurian Echinoderms . . . . . . . . 280
138. Filled-up Burrows or Trails left by a sea-worm on the bed of the
Silurian sea (Ltimbricaria antiqua, J) . . . ' , . 281
139. Lower and Upper Silurian Trilobites . . ... 282
140. Silurian Phyllocarid Crustacean . . . . . 283
141. Silurian Brachiopods . . . ... . . . 283
142. Silurian Lamellibranch ........ 284
143. Silurian Gasteropod ........ 284
144. Silurian Cephalopods . . . . . ... 285
145. Plants of the Devonian period . . . . . . 288
146. Overlapping scales of an Old Red Sandstone fish ... ..--, 290
147. Scale-covered Old Red Sandstone fishes . . ... 290
148. Old Red Sandstone Placoderms . . . . . . . 291
149. Devonian Eurypterid Crustacean . . . . 292
150. Devonian Trilobites ........ 292
151. Devonian Corals . . . . . . ... 293
152. Devonian Brachiopods . . . . . . . . 294
153. Devonian Lamellibranch and Cephalopod . . * . 294
154. Section of part of the Cape Breton coal-field, showing a succession
of buried trees and land-surfaces . . . . . 299
155. Carboniferous Ferns . . . ... . . . 300
156. Carboniferous Lycopod . . . . ... . 301
157. Carboniferous Equisetaceous Plants . . . . . . 302
158. Sigillaria with Stigmaria roots . . ... . . . 302
159. Cordaites alloidius . . . . . . . . . 303
1 60. Carboniferous Scorpion . . .... . . 304
161. Carboniferous Foraminifer . . . . . . . 306
162. Carboniferous Rugose Corals . . . . ... 306
163. Carboniferous Sea-Urchin . . . . . 307
164. Carboniferous Crinoid . . - . . . . . 307
165. Carboniferous Blastoid . . . . . ... . . 307
166. Carboniferous Trilobite . . . , . . .-.: J >< . 507
167. Carboniferous Polyzoon . . ... . . . . v- . 308
1 68. Carboniferous Brachiopods . . . . . . . 309
XX LIST OF ILLUSTRATIONS
FIG - PAC'.E
169. Carboniferous Laniellibranchs . . . . . . . 309
170. Carboniferous Gasteropods . . . . . . .310
171. Carboniferous Pteropod . . . . . . . -310
172. Carboniferous Cephalopods . . . . . . -310
173. Carboniferous Fishes . . . . . . . .311
174. Permian Plants . . . . . . . . . 317
175. Permian Brachiopods . . .... .318
176. Permian Laniellibranchs . . .... . - 319
177. Permian Ganoid Fish . . . . . . . 319
178. Permian Labyrinthodont . . . . ... . . 320
179. Triassic Plants . . . . . . . . 32^
1 80. Triassic Crinoid ......... 326
181. Triassic Laniellibranchs . . . . . . . -327
182. Triassic Cephalopods ........ 327
183. Triassic Lizard ......... 328
184. Triassic Crocodile (Scutes) ....... 328
185. Triassic Marsupial Teeth ........ 328
186. Jurassic Cycad ......... 333
187. Jurassic reef-building Coral ....... 333
188. Jurassic Crinoid ......... 334
189. Jurassic Sea-urchin . . . . . . . . -334
190. Jurassic Laniellibranchs ........ 335
191. Jurassic Ammonites ......... 336
192. Jurassic Belemnite ......... 336
193. Jurassic Crustacean ......... 337
194. Jurassic Fish .......... 338
195. Jurassic Sea-lizard ......... 338
196. Jurassic Pterosaur ......... 339
197. Jurassic Bird .......... 340
198. Jurassic Marsupial . . . . . . . . .341
199. Cretaceous Plants . . . . . . . . -35
200. Cretaceous Foraminifera . . . . . . . -351
201. Cretaceous Sponge . . . . . . . . 351
202. Cretaceous Sea-urchins ........ 352
203. Cretaceous Lamellibranchs ....... 353
204. Cretaceous Lamellibranchs . . . . . . -353
205. Cretaceous Cephalopods . . . . . . . . 354
206. Cretaceous Fish ......... 355
207. Cretaceous Deinosaur . 356
208. Eocene Plant . . . ' . . . . . . . 369
. 209. Eocene Molluscs . . . . . . . . 369
210. Eocene Mammal .... . 370
211. Skull of Uintatherium ingens . .'.*' . . . . 371
LIST OF ILLUSTRATIONS xxi
FIG. 1>AGE
212. Typical "Bad Lands," carved by denudation out of Tertiary
strata at the base of Scott's BluiT, Western Nebraska . . 375
213. Oligocene Molluscs . . . . . . . . 377
214. Miocene Plants . . . . . . . . .381
215. Mastodon angustidens . . . . . . . .382
216. Skull of Deinotherium giganteum . . . . . -383
217. Pliocene Plants ......... 388
218. Pliocene Marine Shells ........ 389
219. Helladotherium Duvernoyi a gigantic animal belonging to the
same family as the living giraffe, Pikermi, Attica . . . 392
220. Pleistocene or Glacial Shells ....... 399
221. Mammoth, from the skeleton in the Muse"e Royal, Brussels . . 400
222. Back view of skull of musk-sheep, Brick-earth, Crayford, Kent . 400
223. Palaeolithic Implements ........ 406
224. Antler of Reindeer found at Bilney Moor, East Dereham, Norfolk 408
225. Neolithic Implements . . . . . . . .' 410
CHAPTER I
INTRODUCTORY
THE main features of the dry land on which we live seem to
remain unchanged from year to year. The valleys and plains
familiar to our forefathers are still familiar to us, bearing the same
meadows and woodlands, the same hamlets and villages, though
generation after generation of men has meanwhile passed away.
The hills and mountains now rise along the sky-line as they did
long centuries ago, catching as of old the fresh rains of heaven
and gathering them into the brooks and rivers which, through
unknown ages, have never ceased to flow seawards. So stead-
fast do these features appear to stand, and so strong a contrast
do they offer to the shortness and changeableness of human life,
that they have become typical in our minds of all that is ancient
and durable. We speak of the firrn, earth, of the everlasting hills,
of the imperishable mountains, as if, where all else is fleeting and
mutable, these forms at least remain unchanged.
And yet attentive observation of what takes place from day to
day around us shows that the surface of a country is not now
exactly as it used to be. We notice various changes of its topo-
graphy going on now, which have doubtless been in progress for
a long time, and the accumulated effect of which may ultimately
transform altogether the character of a landscape. A strong gale,
for instance, will level thousands of trees in its pathway, turning
a tract of forest or woodland into a bare space, which may become
a quaking morass, until perhaps changed into arable ground by
the fanner. A flooded river will in a few hours cut away large
slices from its banks, and spreading over field and meadows, will
bury many acres of fertile land under a covering of barren sand
and shingle. A long-continued, heavy rain, by loosening masses
IE B
2 INTRODUCTORY CHAP.
of earth or rock on steep slopes, causes destructive landslips. A
hard frost splinters the naked fronts of crags and cliffs, and breaks
up bare soil. In short, every shower of rain and gust of wind, if
we could only watch them narrowly enough, would be found to
have done something towards modifying the surface of the land.
Along the sea-margin, too, how ceaseless is the progress of change !
In most places, the waves are cutting away the land, sometimes
even at so fast a rate as two or three feet in a year. Here and
there, on the other hand, they cast sand and silt ^ashore so as to
increase the breadth of the dry land.
These are ordinary everyday causes of alteration, and though
singly insignificant enough, their united effect after long centuries
cannot but be great. From time to time, however, other less
frequent but more powerful influences come into play. In most
large regions of the globe, the ground is often convulsed by earth-
quakes, many of which leave permanent scars upon the surface of
the land. Volcanoes, too, in many countries pour forth streams
of molten rock and showers of dust and cinders that bury the
surrounding districts and greatly alter their appearance.
Turning to the pages of human history, we find there the
records of similar changes in bygone times. Lakes, on which
our rude forefathers paddled their canoes and built their wattled
island-dwellings, have wholly disappeared. Bogs, over whose
treacherous surface these early hunters could not follow the chase
of deer or elk or bison, have become meadows and fields. Forests,
where they hunted the wild boar, have been turned into grassy
pastures. Cities have been entirely destroyed by earthquakes or
have been entombed under the piles of ashes discharged from a
burning mountain. So great have been the inroads of the sea
that, in some instances, the sites of what a few hundred years ago
were farms and hamlets, now lie under the sea half a mile or
more from the modern* shore. Elsewhere the land has gained
upon the sea, and the harbours of an earlier time are now, several
miles distant from the coast-line.
But man has naturally kept note only of the more impressive
changes ; in other words, of those which have had most influence
upon his own doings. We may be certain, however, that there have
been innumerable minor alterations of the surface of the land
within human history, of which no chronicler has made mention,
either because they seemed too trivial, or because they took place
so imperceptibly as never to be noticed. Fortunately, in many
cases, these mutations of the land have written their own memorials,
i GEOLOGICAL CHANGES WITNESSED BY MAN 3
which can be as satisfactorily interpreted as the ancient manu-
scripts from which our early national history is compiled.
In illustration of the character of these natural chronicles, let us
for a moment consider the subsoil beneath cities that have been
inhabited for many centuries. In London, for example, when
excavations are made for drainage, building, or other purposes,
there are sometimes found, many feet below the level of the present
streets, mosaic pavements and foundations, together with earthen
vessels, bronze implements, ornaments, coins, and other relics of
Roman time. Now, if we knew nothing, from actual authentic
history, of the existence of such a people as the Romans, or of
their former presence in England, these discoveries, deep beneath
the surface of modern London, would prove that long before the
present streets were built, the site of the city was occupied by a
civilised race which employed bronze and iron for the useful pur-
poses of life, had a metal coinage, and showed not a little artistic
skill in its pottery, glass, and sculpture. But down beneath the
rubbish wherein the Roman remains are embedded, lie gravels and
sands from which rudely-fashioned human implements of flint have
been obtained. Whence we further learn that, before the civilised
metal-using people appeared, an earlier race had been there,
which employed weapons and instruments of roughly chipped
flint.
That this was the order of appearance of the successive peoples
that have inhabited the site of London is, of course, obvious.
But let us ask ourselves why it is obvious. We observe that there
are, broadly speaking, three layers or deposits from which the
evidence is derived. The upper layer is that which contains the
foundations and rubbish of modern London. Next comes that
which encloses the relics of the Roman occupation. At the
bottom lies the layer that preserves the scanty traces of the early
flint-folk. The upper deposit is necessarily the newest, for it could
not be laid down until after the accumulation of those below it,
which must, of course, be progressively older, as they are traced
deeper from the surface. By the mere fact that the layers lie one
above another, we are furnished with a simple clue which enables
us to determine their relative time of formation. We may know
nothing whatever as to how old they are, measured by years or
centuries. But we can be absolutely certain of what is termed
their " order of superposition," or chronological sequence ; in other
words, we can be confident that the bottom layer came first and
the top layer last.
4 INTRODUCTORY CHAP.
This kind of observation and reasoning will enable us to detect
almost everywhere proofs that the surface of the land has not
always been what it is to-day. In some districts, for example,
when the dark layer of vegetable soil is turned up which supports
the plants that keep the land so green, there may be found below
it sand and gravel, full of smooth well-rounded 'stones. Such
materials are to be seen in the course of formation where water
keeps them moving to and fro, as on the beds of rivers, the
margins of lakes, or the shores of the sea. Wherever smoothed
rolled pebbles occur, they point to the influence of moving water ;
so that we conclude, even though the site is now dry land, that
the sand and gravel underneath it prove it to have been formerly
under water. Again, below the soil in other regions, lie layers of
oysters and other sea- shells. These remains, spread out like
similar shells on the beach or bed of the sea at the present day,
enable us to infer that where they lie the sea once rolled.
Pits, quarries, or other excavations that lay open still deeper
layers of material, bring before us interesting and impressive
testimony regarding the ancient mutations of the land. Suppose,
by way of further illustration, that underneath a bed of sand full
of oyster -shells, there lies a dark brown band of peat. This
substance, composed of mosses and other water-loving plants, is
formed in boggy places by the growth of marshy vegetation.
Below the peat there might occur a layer of soft white marl full of
lake-shells, such as may be observed on the bottoms of many lakes
at the present time (compare Fig. 39). These three layers oyster-
bed, peat, and marl would present a perfectly clear and intelli-
gible record of a curious series of changes in the site of the
locality. The bottom layer of white marl with its peculiar shells
would show that at one time the place was occupied by a lake.
The next layer of peat would indicate that, by the growth of
marshy vegetation, the lake was gradually changed into a morass.
The upper layer of oyster-shells would prove that the ground was
then submerged beneath the sea. The present condition of the
ground shows that subsequently the sea retired and the locality
passed into dry land as it is to-day.
It is evident that by this method of examination information
may be gathered regarding early conditions of the earth's surface,
long before the authentic dates of human history. Such inquiries
form the subject of -Geology, which is the science that investigates
the History of the Earth. The records in which this history is
chronicled are the soils and rocks under our feet. It is the task
I GEOLOGICAL METHODS 5
of the geologist so to arrange and interpret these records as to
show through what successive changes the globe has passed, and
how the dry land has come to wear the aspect which it presents
at the present time.
Just as the historian would be wholly unable to decipher the
inscriptions of an ancient race of people unless a key had first
been discovered to the language in which they are written, so the
geologist would find himself baffled in his efforts to trace backward
the history of the earth if he were not provided with a clue to the
interpretation of the records in which that history is contained.
Such a clue is furnished to him by a study of the operations of
nature now in progress upon the earth's surface. Only in so far
as he makes himself acquainted with these modern changes, can
he hope to follow intelligently and successfully the story of earlier
phases in the earth's progress. It will be seen that this truth has
already been illustrated in the instances above given of the
evidence that the surface of the land has not been always as it is
now. The beds of sand and gravel, of oyster-shells, of peat and
of marl, would have told us nothing as to ancient geography had
we not been able to ascertain their origin and history by finding
corresponding materials now in course of accumulation. To one
ignorant of the peculiarities of fresh-water shells, the layer of marl
would have conveyed no intelligible meaning. But knowing and
recognising these peculiarities, we feel sure that the marl marks
the site of a former lake. Thus the study of the Present supplies
a key that unlocks the secrets of the Past.
In order, therefore, to trace back the history of the Earth, the
geologist must begin by carefully watching the changes that now
take place, and by observing how nature elaborates the materials
that preserve more or less completely the record of these changes.
In the following pages, I propose to follow this method of inquiry,
and, as far as the subject will permit, to start with no assumptions
which the learner cannot easily verify for himself. We shall begin
with the familiar everyday ^operations of the air, rain, frost, and
other natural agents. As these have been fully described in my
Elementary Lessons in Physical Geography^ it will not be needful
here to consider them again in detail. We shall rather pass on to
inquire in what various ways they are engaged in contributing to
the formation of new mineral accumulations, and in thereby
providing fresh materials for the preservation of the facts on which
geological history is founded. Having thus traced how new rocks
are formed, we may then proceed to arrange the similar rocks of
6 INTRODUCTORY CHAP.
older time, marking what are the peculiarities of each and how
they may best be classified.
If the labours of the geologist were concerned merely with the
former mutations of the earth's surface, how sea and land have
changed places, how rivers have altered their courses, how lakes
have been filled up, how valleys have been excavated, how
mountains, peaks, and precipices have been carved, how plains
have been spread out, and how the story of these revolutions has
been written in enduring characters upon the very framework of
the land, he would feel the want of one of the great sources of
interest in the study of the present face of nature. We naturally
connect all modern changes of the earth's surface with the life of
the plants and animals that flourish there, and more especially
with their influence on the progress of Man himself. If there
were no similar connection of the ancient changes with once living
things if the history of the earth were merely one of dead inert
matter it would lose much of its interest for us. But happily
that history includes the records of successive generations of
plants and animals which, from early times, have peopled land
and sea. The remains of these organisms have been preserved
in the deposits of different ages, and can be compared and con-
trasted with those of the modern world.
To realise how such preservation has been possible, and how
far the forms so retained afford an adequate picture of the life of
the time to which they belonged, we must turn once more to
watch how nature deals with this matter at the present time. Of
the millions of flowers, shrubs, and trees which year after year
clothe the land with beauty, how many relics are preserved? Where
are the successive generations of insect, bird, and beast which
have appeared in this country since man first set foot upon its
soil ? They have utterly vanished. If all their living descendants
could suddenly be swept away, how could we tell that such plants
and animals ever lived at all ? It must be confessed that the vast
majority of them leave no trace behind. Nevertheless we should
be able to recover relics of some of them by searching in the
comparatively few places where, at the present day, dead plants
and animals are entombed and preserved. From the alluvial
terraces of rivers, from the silt of lake-bottoms, from the depths of
peat-mosses, from the floors of subterranean caverns, from the
incrustations left by springs, we might recover traces of some at
least of the living things that people the land. And from these
fragmentary and incomplete records we might conjecture what
i GEOLOGICAL RECORDS 7
may have been the general character of the life of the time. By
searching the similar records of earlier ages, the geologist has
brought to light many profoundly interesting vestiges of vegetation
and of animal life belonging to types that have long since passed
away.
It must be evident, however, that were we to confine our inquiries
merely to the Earth's surface, we should necessarily gain only an
imperfect view of the general history of our globe. Beneath that
surface, as volcanoes show, there lies a hot interior, which must
have profoundly influenced the changes of the outer parts or crust
of the planet. The study of volcanoes enables us to penetrate, as
it were, a little way into that interior, and to understand some of
the processes in progress there. But our knowledge of the inside
of the Earth can obviously be based only to a very limited extent
on direct observation, for man cannot penetrate far below the
surface. The deepest mines do not go deep enough to reach
materials differing in any essential respect from those visible above
ground. Nevertheless, by inference from such observations as
can be made, and by repeated and varied experiments in labora-
tories, imitating as closely as can be devised what may be sup-
posed to be the conditions that exist deep within the globe, some
probable conclusions can be drawn even as to the changes that
take place in those deeper recesses that lie for ever concealed
from our eyes. These conclusions will be stated in later chapters
of this book, and the rocks will be described, on the origin of
which they appear to throw light.
I have compared the soils and rocks with which geology deals
to the records out of which the historian writes the chronicles of
a nation. We might vary the simile by likening them to the
materials employed in the construction of a great building. It
is of course interesting enough to know what kinds of marble,
granite, mortar, wood, brass, or iron have been chosen by an
architect. But much more important is it to inquire how these
various substances have been grouped together so as to form such
a building. In like manner, besides the nature and mode of
origin of the various rocks of which the visible and accessible
part of the earth consists, we ought to know how these varied
substances have been arranged so as to build up what we can see
of the outer part or crust of our globe. In short, we should try
to trace what may be called the architecture of the planet, noting
how each variety of rock occupies its own characteristic place, and
how they are all grouped and braced together in the solid framework
8 INTRODUCTORY CHAP.
of the land. This then will be the next subject for consideration
in this volume.
But in a great historical edifice, like one of the Gothic minsters
of Europe, for example, there are often several different styles.
A student of architecture can detect these distinctions, and by
their means can show that a cathedral has not been completed in
one age ; that it may even have been partially destroyed and re-
built during successive centuries, only finally taking its present form
after many political vicissitudes and many changes of architectural
taste. Each edifice has thus a separate history, which is recorded
by the way the materials have been shaped and put together in
the various parts of the masonry. So it is with the architecture
of the Earth. We have evidence of many demolitions and rebuild-
ings, and the story of their general progress can still be deciphered
among the rocks. It is the business of Geology to trace out that
story, to put all the scattered materials together, and to make
known through what a long succession of changes the Earth has
reached its present state. An outline of what science has accom-
plished in this task will form the last and concluding part of this
book.
In the following chapters I wish two principles to be kept
steadily in view. In the first place, looking upon Geology as the
study of the Earth's history, we need not at first concern ourselves
with any details, save those that may be needed to enable us
clearly to understand what the general character and progress of
this history have been. In a science which embraces so vast a
range as Geology, the multiplicity of facts to be examined and
remembered may seem at first to be almost overwhelming. But
a selection of the essential facts is sufficient to give the learner a
clear view of the general principles and conclusions of the science,
and to enable him to enter with intelligence and interest into
more detailed treatises. In the second place, Geology is essentially
a science of observation. The facts with which it deals should, as
far as possible, be verified by our own personal examination. We
should lose no opportunity of seeing with our own eyes the actual
progress of the changes which it investigates, and the proofs
which it adduces of similar changes in the far past. To do this
will lead us into the fields and hills, to the banks of rivers and
lakes, and to the shores of the sea. We can hardly take any
country walk, indeed, in which with duly observant eye we may
not detect either some geological operation in actual progress, or
the evidence of one which was completed long ago. Having
i INTEREST OF GEOLOGY 9
learnt what to look for and how to interpret it when seen, we are
as it were gifted with a new sense. Every landscape comes to
possess a fresh interest and charm, for we carry aboftt with us
everywhere an added power of enjoyment, whether the scenery
has long been familiar or presents itself for the first time. I
would therefore seek at the outset to impress upon those who
propose to read the following pages, that one of the main objects
with which this book is written is to foster a habit of observation,
and to serve as a guide to what they are themselves to look for,
rather than merely to relate what has been seen and determined
by others. If they will so learn these lessons, I feel sure that
they will never regret the time and labour they may spend over
the task.
PART I
THE MATERIALS FOR THE HISTORY OF
THE EARTH
CHAPTER II
THE INFLUENCE OF THE ATMOSPHERE IN THE CHANGES OF
THE EARTH'S SURFACE
IN the history of mankind no sharp line can be drawn between
the events that are happening now or have happened within the
last few generations, and those that took place long ago, and which
are sometimes, though inaccurately, spoken of as historical. Every
people is enacting its history to-day just as fully as it did many
centuries ago. The historian recognises this continuity in human
progress. He knows that the feelings and aspirations which
guided mankind in old times were essentially the same influences
that impel them now, and therefore that the wider his knowledge
of his fellovvmen of the present day, the broader will be his grasp
in dealing with the transactions of former generations. So too is
it with the history of the Earth. That history is in progress now
as really as it has ever been, and its events are being recorded in
the same way and by the same agents as in the far past. Its con-
tinuity has never been broken. Obviously, therefore, if we would
explore its records "in the dark backward and abysm of time,"
we should first make ourselves familiar with the manner in which
these records are being written from day to day before our eyes.
In this first Part, attention will accordingly be given to the
changes in progress upon the Earth at the present time, and to the
various ways in which the passing of these changes is chronicled
CHAP, ii WEATHERING 11
in natural records. We shall watch the actual transaction of
geological history, and mark in what way its incidents inscribe
themselves on the page of the earth's surface. 1 Every day and
hour witness the enacting of some geological event, trifling and
transient or stupendous and durable. Sometimes the event leaves
behind it only an imperceptible trace of its passage, at other times
it graves itself almost imperishably in the annals of the globe. In
tracing the origin and development of these geological annals of
the present time, we shall best qualify ourselves for deciphering
the records of the early revolutions of the planet. We are thereby
led to study the various chronicles compiled respectively by the
air, rain, rivers, springs, glaciers, the sea, plants and animals,
volcanoes and earthquakes in other words, all the deposits left
by the operations of these agents, the scars or other features made
by them upon the earth's surface, and all other memorials of
geological change. Having learnt how modern deposits are pro-
duced, and how they preserve the story of their origin, we shall
then be able to group with them the corresponding deposits of
earlier times, and to embrace all the geological records,, ancient as
well as modern, in one general scheme of classification. Such a
scheme will enable us to see the continuity of the materials of
geological history, and will fix definitely for us the character and
relative position of all the chief rocks out of which the visible part
of the globe is composed.
"Weathering. The gradual change that overtakes everything
on the face of the earth is expressed in all languages by familiar
phrases which imply that the mere passing of time is the cause of
the change. As Sir Thomas Browne quaintly said more than two
hundred years ago, " time antiquates antiquities, and hath an art
to make dust of all things." We speak of the dust of antiquity
and the gnawing tooth of time. We say that things are time-
eaten, worn with age, crumbling under a weight of years.
Nothing suggests such epithets so strikingly as an old building.
We know that the masonry at first was smooth and fresh ; but
now we describe it as weather-beaten, decayed, corroded. So
distinctive is this appearance that it is always looked for in an
ancient piece of stone-work ; and if not seen, its absence at once
suggests a doubt whether the masonry can really be old. No
1 For descriptions of the ordinary operations of geological agents the reader
is referred to my Elementary Lessons in Physical Geography. My object now
is to direct attention to what is most enduring in these operations, and in what
various ways they form permanent geological records.
12 GEOLOGICAL WORK OF THE AIR CHAP.
matter of what varieties of stone the edifice may have been built,
a few generations may be enough to give them this look of
venerable antiquity. The surface that was left smoothly polished
by the ' builders grows rough and uneven, with scars and holes
eaten into it (Fig. i). Portions of the original polish that may
here and there have escaped, serve as a measure of how much has
actually been removed from the rest of the surface.
Now, if in the lapse of time, stone which has been artificially
dressed is wasted away, we may be quite certain that the same
stone in its natural position on
the slope of a hill or valley, or
by the edge of a river or of the
sea, must decay in a similar way.
Indeed, an examination of any
crumbling building will show that,
in proportion as the chiselled
surface disappears, the stone puts
on the ordinary look which it
wears where it has never been
cut by man, and where only the
finger of time has touched it.
Could we remove some of the
FIG. i. Weathering of rock, as shown by decayed stones from the building
old masonry (The" false-bedding " and and insert them j nt() R natural
other original structures of the stone are . . _ . .
revealed by weathering.) cra g r dlff f the Same kmd of
stone, their peculiar time-worn
aspect would be found to be so exactly that of the rest of the
cliff that probably no one would ever suspect that a mason's tools
had once been upon them.
From this identity of surface between the time-worn stones of
an old building and the stone of a cliff we may confidently infer
that the decay so characteristic of ancient masonry is as marked
upon natural faces of rock. The gradual disappearance of the
artificial smoothness given by the mason, and its replacement by
the ordinary natural rough surface of the stone, shows that this
natural surface must also be the result of decay. And as the
peculiar crumbling character is universal, we may be sure that
the decay with which it is connected must be general over the
globe.
But the mere passing of time obviously cannot change anything,
and to say that it does is only a convenient figure of speech. It
is not time, but the natural processes which require time for their
n CAUSES OF WEATHERING 13
work, that produce the widespread decay over the surface of the
earth. Of these natural processes, there are four that specially
deserve consideration changes of temperature, saturation and
desiccation^ frost, and rain.
(1) Changes of Temperature. In countries where the
days are excessively hot, with nights correspondingly cool, the
surfaces of rocks heated sometimes, as in parts of Africa, up
to more than 130 Fahr. by a tropical sun, undergo considerable
expansion in consequence of this increase of temperature. At
night, on the other hand, the rapid radiation quickly chills the
stone and causes it to contract. Hence the superficial parts,
being in a perpetual state of strain, from time to time suddenly
split open, or gradually peel off. The face of a cliff is thus
worn slowly backward, and the prostrate blocks that fall from it
are reduced to smaller fragments and finally to dust. Where, as
in Europe and the settled parts of North America, the con-
trasts of temperature are not so marked, the same kind of
waste takes place in a less striking manner.
(2) Saturation and Desiccation. Another cause of the
decay of the exposed surfaces of rocks is to be sought in the
alternate soaking of them with rain and drying of them in
sunshine, whereby the component particles of the stone are
loosened and fall to powder. Some kinds of stone freshly
quarried and left to this kind of action are rapidly disintegrated.
The rock called shale (see p. 168) is peculiarly liable to decay
from this cause. The cliffs into which it sometimes rises show
at their base long trails of rubbish entirely derived from its
waste.
(3) Frost. A third and familiar source of decay in stone
exposed to the atmosphere is to be found in the action of Frost.
The water that falls from the air upon the surface of the land
soaks into the soil and into the pores of rocks. When the
temperature of the air falls below the freezing point, the im-
prisoned moisture expands as it passes into ice, and in expanding
pushes aside the particles between which it is entangled. Where
this takes place in soil, the pebbles and the grains of sand and
earth are separated from each other by the ice that shoots
between them. They are all frozen into a solid mass that rings
like stone under our feet ; but, as soon as a thaw sets in, the ice
that formed the binding cement passes into water which converts
the soil into soft earth or mud. This process, repeated winter
after winter, breaks up the materials of the soil, and enables
U GEOLOGICAL WORK OF THE AIR CHAP.
them to be more easily made use of by plants, and more readily
blown away by wind or washed off by rain. Where the action of
frost affects the surface of a rock, the particles separated from
each other are eventually blown or washed away, or the rock
peels off in thin crusts or breaks up into angular pieces, which
are gradually disintegrated and removed.
(4) .Rain. One further cause of decay may be sought in the
remarkable power possessed by Rain of chemically corroding
stones. In falling through the atmosphere, rain absorbs the
gases of the air, and with their aid attacks surfaces of rock.
With the oxygen thus acquired, it oxidises those substances
which can still take more of this gas, causing them to rust
(pp. 130, 132). As a consequence of this alteration, the
cohesion of the particles is usually weakened, and the stone
crumbles down. With the aid of its carbon-dioxide, or carbonic
acid, rain-water dissolves and removes some of the more soluble in-
gredients in the form of carbonates, thereby also usually loosening
the component particles of the stone. In general, the influence of
rain is to cause the exposed parts of rocks to rot from the
surface inward. Where the ground is protected with vegetation,
the decay is no doubt retarded ; but in the absence of vegetation,
the outer crust of the decayed layer is apt to be washed off by
rain, or when dried to powder may be blown away and scattered
by wind. As fast as it is removed from the surface, however, it
is renewed underneath by the continued soaking of rain into the
stone.
In bare limestone districts, the solvent action of rain-water
gives rise to some singular forms of ground. Pure limestone
being wholly soluble, its surface is dissolved without leaving any
residue from which soil could be formed, so that in many places
wide spaces of bare verdureless stone are exposed. On these the
rain, acting with special vigour along the numerous lines of
division or "joints" by which the rock is traversed, hollows out
such an intricate assemblage of furrows, channels, clefts, fissures,
and gullies, that the surface becomes in places hardly passable.
Some of these gullies descend to a great depth underground,
where they join the system of subterranean tunnels and caverns
described in Chapter V. (p. 61), where this subject is more fully
explained.
Hence one of the first lessons to be learnt when from the
common evidence that lies around us we seek to know what has
been the history of the ground on which we live is one of
EFFECTS OF WEATHERING
ceaseless decay. All over the land, in all kinds of climates, and
from various causes, bare surfaces of soil and rock yield to the
influences of the atmosphere or weather. The decay thus set
in motion is commonly called " weathering." That it may
often be comparatively rapid is familiarly and instructively shown
in buildings or open-air monuments of which the dates are pre-
cisely known. Marble tombstones in the graveyards of large
towns, for example, hardly keep their inscriptions legible for even
so long as a century. Before that time, the surface of the
stone has crumbled away into a kind of sand. Everywhere
over the land, the weather -eaten surfaces, the crumbling crust
of decayed stone, and the scattered blocks and trains of rubbish,
tell their tale of universal waste.
It is well to take numerous opportunities of observing the
progress of this decay in different situations and on various kinds
of materials. We can thus best realise the important part which
weathering must play in the changes of the earth's surface, and
we prepare ourselves for the consideration of the next question
that arises, What becomes of all the rotted material ? a question
to answer which leads us into the very
foundations of geological history.
Openings from the soil down into
the rock underneath often afford in-
structive lessons regarding the decay of
the surface of the land. Fig. 2, for
instance, is a drawing of one of these
sections, in which a gradual passage
may be traced from solid sandstone (a)
underneath up into broken-up sandstone
(b), and thence into the earthy layer
(<:) that supports the vegetation of the
surface. Traced from below upwards,
the rock is found to become more and
more broken and crumbling, with an
increasing number of rootlets that strike
freely through it in all directions, until it passes insensibly into
the uppermost dark layer of vegetable soil or humus. This
dark layer owes its characteristic brown or black colour mainly to
the decaying remains of vegetation diffused through it. Again,
granite in its unweathered state is a hard, compact, crystalline
rock that may be quarried out in large solid blocks (a in Fig. 3),
yet when traced upward to within a few feet from the surface it
FIG. 2. Passage of sandstone
upwards into soil.
i6
GEOLOGICAL WORK OF THE AIR
may be seen to have been split by innumerable rents into frag-
ments which are nevertheless still lying in their original position.
As these fragments are attacked by percolating moisture, their
surfaces decay, leaving the still unweathered parts as rounded
blocks (^), which might at first
be mistaken for transported
boulders. They are, however,
parts of the rock broken up in
place, and not fragments that
have been carried from a
distance. The little quartz-veins
that traverse the solid granite
can be recognised running
through the decayed and fresh
parts alike. But, besides being
broken into pieces, the granite,
owing to the solution and re-
moval of some part of its sub-
stance, rots away and loses its
FIG. 3.-Passage of granite upwards cohesion. ' Some of the smaller
into soil. . , , , , ,
pieces can be crumbled down
between the fingers, and this decay increases upwards, until
the rock becomes a mere sand or sandy clay in which a few
harder kernels are still left. Into this soft layer roots may
descend from the surface, and, like the sandstone, the granite
merges above into the overlying soil (c).
Soil and Subsoil. In such sections as the foregoing, three
distinct layers can be recognised which pass into each other.
At the bottom lies the rock, either undecayed or at least still fresh
enough to show its true nature. Next comes the broken-up
crumbling layer through which stray roots descend, and which is
known as the subsoil. At the top lies the dark band, crowded
with rootlets and forming the true soil. These three layers
obviously represent successive stages in the decay of the surface
of the land. The soil is the layer of most complete decay. The
subsoil is an intermediate band where the progress of decomposi-
tion has not advanced so far, while the shattered rock underneath
shows the earlier stages of disintegration. Vegetation sends its
roots and rootlets through the rotted rock. As the plants die,
they are succeeded by others, and the rotted remains of their
successive generations gradually darken the uppermost decom-
posed layer. Worms, insects, and larger animals that may die
ii SOIL SUBSOIL 17
on the surface, likewise add their mouldering remains to this
uppermost deposit. And thus from animals and plants there is
furnished to the soil that organic matte?' on which its fertility so
much depends.
The very decay of the vegetation helps to promote that of the
underlying rock, for it supplies various organic acids ready to be
absorbed by percolating rain-water, the power of which to decom-
pose rocks is thereby increased. A complete series of chemical
changes is thus set on foot. The organic matter in its decay
abstracts oxygen from the air and from surrounding objects.
Rocks and minerals have their insoluble peroxides reduced to
protoxides which, in combination with organic acids or with
carbonic acid, are removed in solution. By this abstraction, red
rocks and soils are bleached, and the coherence of even compact
stones is weakened, until they crumble down into soil. The
carbonates, such for instance as the carbonate of iron, are sparingly
soluble in water containing carbonic acid, but some of them are
then liable to oxidation, when they become insoluble, and are
precipitated to the bottom. Hence ferruginous minerals are decom-
posed by decaying organic matter, and their iron, removed first as
protoxide, is deposited elsewhere as peroxide. In this way beds
of haematite and limonite (p. 143) may be formed.
It is obvious, then, that in answer to the question, What
becomes of the rotted material produced by weathering ? we may
confidently assert that, over surfaces of land protected by a cover
of vegetation, this material in large measure accumulates where it
is formed. Such accumulation will naturally take place chiefly on
flat or gently inclined ground. Where the slope is steep, the
decomposed layer will tend to travel down-hill by mere gravitation,
and to be further impelled downward by descending rain-water.
If there is so intimate a connection between the soil at the
surface and the rock underneath, we can readily understand that
soils should vary from one district to another, according to the
nature of the underlying rocks. Clays will produce clayey soil,
sandstones, sandy soil, or, where these two kinds of rock occur
together, they may give rise to sandy clay or loam. Hence,
knowing what the underlying rock is, we may usually infer what
must be the character of the overlying soil, or, from the nature of
the soil, we may form an opinion respecting the quality of the
rock that lies below.
But it will probably occur to the thoughtful observer that when
once a covering of soil and subsoil has been formed over a level
C
i8 GEOLOGICAL WORK OF THE AIR CHAP.
piece of ground, especially where there is also an overlying carpet
of verdure, the process of decay should cease the very layer of
rotted material coming eventually to protect the rock from further
disintegration. Undoubtedly, under these circumstances, weather-
ing is reduced to its feeblest condition. But that it still continues
will be evident from some considerations, the force of which will
be better understood a few pages further on. If the process were
wholly arrested, then in course of time plants growing on the
surface would extract from the soil all the nutriment they could
get out of it, and with the increasing impoverishment of the soil,
they would dwindle away and finally die out, until perhaps only
the simpler forms of vegetation would grow on the site. Some-
thing of this kind not improbably takes place where forests decay
and are replaced by scrub and grass. But the long-continued
vigorous growth of the same kind of plants upon a tract of land
doubtless indicates that in some way the process of weathering is
not entirely arrested, but that, as generation succeeds generation,
the plants are still able to draw nutriment from fresh portions of
decomposed rock. A cutting made through the soil and subsoil
shows that roots force their way downward into the rock, which
splits up and allows percolating water to soak downwards through
it. The subsoil thus gradually eats its way into the solid rock
below. Influences are at work also, whereby there is an imper-
ceptible removal of material from the surface of the soil. Notable
among these influences are Rain, Wind, and Earthworms.
Wherever soil is bare of vegetation it is directly exposed to
removal by Rain. Ground is seldom so flat that rain may not
flow a little way along the surface before sinking -underneath. In
its flow, it carries off the finer particles of the soil. These may
travel each time only a short way, but as the operation is
repeated, they are in the course of years gradually moved down to
lower ground or to some runnel or brook that sweeps them away
seaward. Both on gentle and on steep slopes, this transporting
power of rain is continually removing the upper layer of bared
soil.
Where soil is exposed to the sun, it is liable to be dried into
mere dust, which is borne off by Wind. How readily this may
happen is often strikingly seen after dry weather in spring-time.
The earth of ploughed fields becomes loose and powdery, and
clouds of its finer particles are carried up into the air and trans-
ported to other farms, as gusts of wind sweep across. " March
dust," which is a proverbial expression, may be remembered as an
ii TALUS-SLOPES 19
illustration of one way in which the upper parts of the soil are
removed (see p. 21).
Even where a grassy turf protects the general surface, bare
places may always be found whence this covering has been
removed. Rabbits, moles, and other animals throw out soil from
their burrows. Mice sometimes lay it bare by eating the pasture
down to the roots. The common Earthworms bring up to day-
light in the course of a year an almost incredible quantity of it
in their castings. Mr. Darwin estimated that this quantity is in
some places not less than 10 tons per annum over an acre of
ground. Only the finest particles of mould are swallowed by
worms and conveyed by them to the surface, and it is precisely
these which are most apt to be washed off by rain or to be dried
and blown away as dust by the wind. Where it remains on the
ground, the soil brought up by worms covers over stones and
other objects lying there, which consequently seem to sink into
the earth. The operation of these animals causes the materials
of the soil to be thoroughly mixed. In tropical countries, the
termite or " white ant " conveys a prodigious amount of fine earth
up into the open air. With this material it builds hills sometimes
60 feet high and visible for a distance of several miles ; likewise
tunnels and chambers, which it plasters all over the stems and
branches of trees, often so continuously that hardly any bark can
be seen. The fine soil thus exposed is liable to be blown away
by the wind or washed off by the fierce tropical rains.
Although, therefore, the layer of vegetable soil which covers
the land appears to be a permanent protection, it does not really
prevent a large amount of material from being removed even from
grassy ground. It forms the record of the slow and almost
imperceptible geological changes that affect the regions where it
accumulates, the quiet fall of rain, the gradual rotting away of
the upper part of the underlying rock, the growth. and decay of a
long succession of generations of plants, the ceaseless labours of
the earthworm, the scarcely appreciable removal of material from
the surface by the action of rain and wind, and the equally
insensible descent of the crumbling subsoil farther and farther
into the solid stone below. Having learnt how all this is told by
the soil beneath our feet, we should be ready to recognise in the
soil of former ages a similar chronicle of quiet atmospheric dis-
integration.
Talus. Besides soil and subsoil, there are other forms in
which decomposed rock accumulates on the surface of the land.
GEOLOGICAL WORK OF THE AIR
Where a large mass of bare rock rises up as a steep bank or cliff,
it is liable to constant degradation, and the materials detached
from its. surface accumulate down the slopes, forming what is
known as a Talus (Fig. 4). In mountainous or hilly regions,
FIG. 4. Talus-slopes at the foot of a line of cliffs.
where rocky precipices rise high into the air, there gather at their
feet and down their clefts long trails or screes of loose blocks that
have been split off from them by the weather. Such slopes,
especially where they are not too steep, and where the rubbish
that forms them is not too coarse, may be more or less covered with
vegetation, which in some measure arrests the descent of the
debris. But from time to time, during heavy rains, deep gullies
are torn out of them by rapidly formed
torrents, which sweep down their materials
to lower levels (Fig. 14). The sections
laid bare in these gullies show that the
rubbish is arranged in more or less distinct
layers which lie generally parallel with
the surface of the slope ; in other words,
it is rudely stratified, and its layers or
strata are inclined at the angle of the
declivity which seldom exceeds 35.
Rain-wash, Brick-earth. On more
^ slopes, even where no bare rock
- . -
projects into the air, the fall of ram gradu-
FIG s.-Section of rain-wash
or bnck-earth. 7. Vegetable
soil. 6. Brick-earth. 5 . Whit
sand. 4. Brick-earth. 3. ally washes down the upper parts of the
White sand. 2. Brick-earth. so ji to lower levels. Hence arise thick
i. Gravel with seams of sand. accumulations Q f what is known as rain .
wash -soil mixed often with angular fragments of still undecom-
posed rock, and not infrequently forming a kind of brick -earth
n SAND-DUNES 21
(Fig. 5). Deposits of this nature are still gathering now, though
their lower portions may be of great antiquity. In the south-east
of England, for instance, the brick-earths contain the bones of
animals that have long since passed away.
Dust. By the action of wind, above referred to, a vast
amount of fine dust and sand is carried up into the air and strewn
far and wide over the land. In dry countries, such as large tracts
of Central Asia, the air is often thick with a fine yellow dust
which may entirely obscure the sun at mid-day, and which settles
over everything. After many centuries, a deposit, which may be
hundreds of feet deep, is thus accumulated on the surface of the
land. Some of the ancient cities of the Old World, Nineveh and
Babylon for example, after being long abandoned by man, have
gradually been buried under the fine soil drifted over them by the
wind and intercepted and protected by the weeds that grew up
over the ruins. Even in regions where, as in Britain, there is a
large annual rainfall, seasons of drought occur, during which
there may be a considerable drifting of the finer particles of soil
by the wind. We probably hardly realise how much the soil
may be removed here and heightened there from this cause.
Sand-dunes. Some of the most striking and familiar examples
of the accumulation of loose deposits by the wind are those to which
the name of Dunes is given (Fig. 6). On sandy shores, exposed
to winds that blow landwards, the sand is dried and then carried
away from the beach, gathering into long mounds or ridges which
run parallel to the coast-line. These ridges are often 50 or 60
feet, sometimes even more than 250 feet high, with deep troughs
and irregular circular hollows between them, and they occasionally
form a strip several miles broad, bordering the sea. The particles
of sand are driven inland by the wind, and the dunes gradually
bury fields, roads, and villages, unless their progress is arrested
by the growth of vegetation over their shifting- surfaces. On
many parts of the west coast of Europe, the dunes are marching
into the interior at the rate of 20 feet in a year. Hence large
tracts of land have within historic times been entirely lost under
them. In the north of Scotland, for example, an ancient and
extensive barony, so noted for its fertility that it was called " the
granary of Moray," was devastated about the middle of the seven-
teenth century by the moving sands, which now rise in barren
ridges more than 100 feet above the site of the buried land. In
the interior of continents also, where with great dryness of climate
there is a continual disintegration of the surface of rocks, wide
GEOLOGICAL \VORK OF THE AIR
CHAP. II
wastes of sand accumulate, as in the deserts of Libya, Arabia,
and Gobi, in the heart of Australia, and in many of the western
parts of the United States.
There can be no doubt, however, that though the layer of
vegetable soil, the heaps of rubbish that gather on slopes and at
the base of rocky banks and precipices, and the widespread
drifting of dust and sand over the land, afford evidence that much
of the material arising from the general decay of the surface of
the land accumulates under various forms upon that surface,
nevertheless its stay there is not permanent. Wind and rain are
continually removing it, sometimes in vast quantities, into the sea.
FIG. 6. Sand-dunes.
Every brook, made muddy by heavy rain, is an example of this
transport, for the mud that discolours the water is simply the finer
material of the soil washed off by rain. When we reflect upon
the multitude of streams, large and small, in all parts of the globe,
and consider that they are all busy carrying their freights of mud
to the sea, we can in some measure appreciate how great must be
the total annual amount of material so removed. What becomes
of this material will form the subject of succeeding chapters.
Results of Weathering. In the course of time the opera-
tion of the different atmospheric agents which have been described
in this chapter brings out the most astonishing changes in the
topography of the land. The softer rocks are worn down and
O _;
f J
c/5
I*
M
12 ^
2 c
A M
3 t)
24 GEOLOGICAL WORK OF THE AIR CHAP.
the harder masses are left projecting. Thus hills and valleys may
be carved out of a surface which at first, when the process began,
may have been nearly flat. It is hardly possible to exaggerate
the importance of the part taken by these destructive agents in
producing the present topography of the dry land. In regions
where the climate is dry and the rocks at the surface consist of
horizontal stratified formations, the reality and results of atmo-
spheric erosion are most impressively displayed. No part of the
world has furnished more admirable illustrations of this depart-
ment of geology than the Western States of the American Union.
As shown in Fig. 7, some of the most abrupt and singular rock-
scenery may be traced entirely to this kind of slow, long continued
sculpture, by air, temperature, rain, frost, and the other agents
above enumerated. The " Bad Lands " of these regions (Fig. 2 1 2)
are marvellous examples of the same processes.
Summary. The first lesson to be learnt from an examination
of the surface of the land is, that everywhere decay is in progress
upon it. Wherever the solid rock rises into the air, it breaks up
and crumbles away under the various influences combined in the
process of Weathering. The wasted materials caused by this
universal disintegration partly accumulate where they are formed,
and make soil. But in large measure, also, they are blown away
by wind and washed off by rain. Even where they appear to be
securely protected by a covering of vegetation, the common earth-
worm brings the finer parts of them up to the surface, where they
come within reach of rain and wind, so that on tracts permanently
grassed over, there may be a continuous and not inconsiderable
removal of fine soil from the surface. In proportion as the upper
layers of soil are removed, roots and percolating water are enabled
to reach down farther into the solid rock, which is broken up into
subsoil, and thus the general surface of the land is insensibly
lowered.
Besides accumulating in situ as subsoil and soil, the debris of
decomposed rock forms talus -slopes and screes at the foot of
crags, and a layer of rain-wash or brick-earth over gentler slopes.
Where the action of wind comes markedly into play, tracts of
sand-dunes may be piled up along the borders of the sea and of
lakes, or in the arid interior of continents ; and wide regions have
been in course of time buried under the fine dust which is some-
times so thick in the air as to obscure the noonday sun. But in
none of these forms can the accumulation of decomposed material
be regarded as permanent. So long as it is exposed to the
ir SUMMARY 25
influences of the atmosphere, this material is still liable to be
swept away from the surface of the land and borne outwards into
the sea.
One of the prominent results of this universal waste of the
surface has been the gradual carving out of the surface of the
land into heights and hollows. In general, the harder materials
better resist the processes of destruction and are allowed to
project in hills and ridges, while the softer rocks are worn away
into valleys and plains. As will be afterwards shown, original
hollows on the surface of a newly upheaved tract of land would,
from the first, guide the descent of the drainage towards the sea,
and after long ages of ceaseless erosion (p. 32) might be carved
into valleys, glens, and ravines, while the intervening ground, even
though formed of as destructible materials, being less rapidly worn
down, would be left as ridges and hills. Hence the existing
scenery of the land has in large measure been produced by the
sculpturing action of the different agents of atmospheric disin-
tegration.
CHAPTER III
THE INFLUENCE OF RUNNING WATER IN GEOLOGICAL
CHANGES, AND HOW IT IS RECORDED
IT appears, then, that from various causes all over the globe, there
is a continual decay of the surface of the land ; that the decom-
posed material partly accumulates as soil, subsoil, and sheets or
heaps of loose earth or sand, but that much of it is washed off the
land by rain or blown into the rivers or into the sea by wind.
We have now to consider the part taken by Running Water in
this transport. From the single rain-drop up to the mighty river,
every portion of the water that flows over the land is busy with
its own share of the work. When we reflect on the amount of
rain that falls annually over the land, and on the number of
streams, large and small, that are ceaselessly at work, we realise
how difficult it must be to form any fit notion of the entire amount
of change which, even in a single year, these agents work upon
the surface of the earth.
The influence of rain in the decay of the surface of the land
was briefly alluded to in the last chapter. As soon as a drop of
rain reaches the ground, it begins its appointed geological task,
dissolving what it can carry off in solution, and pushing forward
and downward whatever it has power to move. As the rain-drops
gather into runnels, the same duty, but on a greater scale, is
performed by them ; and as the runnels unite into larger streams,
and these into yet mightier rivers, the operations, though becoming
colossal in magnitude, remain essentially the same in kind. In
the operations of the nearest brook, we see before us in miniature
a sample of the changes produced by the thousands of rivers which,
in all quarters of the globe, are flowing from the mountains to the
sea. Watching these operations from day to day, we discover
that they may all be classed under two heads. In the first place,
26
CHAP, in CHEMICAL ACTION OF RUNNING WATER 27
the brook hollows out the channel in which it flows and thus aids
in the general waste of the surface of the land ; and in the second
place, it carries away fine silt and other material resulting from
that waste, and either deposits it again on the land or carries it
out to sea. Rivers are thus at once agents that themselves
directly degrade the land, and that sweep the loosened detritus
towards the ocean. An acquaintance with each of these kinds of
work is needful to enable us to understand the nature of the
records which river-action leaves behind it.
i. EROSIVE AND TRANSPORTING POWER OF RUNNING WATER
Chemical Action. We have seen that rain in its descent from
the clouds absorbs air, and that with the oxygen and carbonic acid
which it thus obtains it proceeds to corrode the surfaces of rock
on which it falls. When it reaches the ground and absorbs the
acids termed " humous," which are supplied by the decomposing
vegetation of the soil, it acquires increased power of eating into the
stones over which it flows. When it rolls along as a runnel, brook,
or river, it no doubt still attacks chemically the rocks of its channel,
though its action in this respect is not so easily detected. In
some circumstances, however, the solvent influence of river-water
upon solid rocks is strikingly displayed. Where the water contains
a large proportion of the acids of the soil, and flows over a kind
of rock specially liable to be eaten away by these acids, the most
favourable conditions are presented for observing the change.
Thus, a stream which issues from a peat-bog is usually dark brown
in colour, from the vegetable solutions which it extracts from the
moss. Among these solutions are some of the organic acids
referred to, ready to eat into the surface of the rocks or loose
stones which the stream may encounter in its descent No kind
of rock is more liable than limestone to corrosion under such
circumstances. Peaty water flowing over it eats it away with
comparative rapidity, while those portions of the rock that rise
above the stream escape solution, except in so far as they are
attacked by rain. Hence arise some curious features in the
scenery of limestone districts. The walls of limestone above
the water, being attacked only by the atmosphere, are not eaten
away so fast as their base, over which the stream flows. They are
consequently undermined, and are sometimes cut into dark tunnels
and passages (Fig. 8). Even where the solvent action of the
28 RECORDS OF RUNNING WATER CHAP.
water of rivers is otherwise inappreciable, it can be detected by
means of chemical analysis. Thus rivers, partly by the action of
their water upon the loose stones and solid rocks of their channels,
and partly by the contributions they receive from Springs (which
will be afterwards described), convey a vast amount of dissolved
material into the sea. The mineral substance thus invisibly
transported consists of various salts. One of the most abundant
of these carbonate of lime is the substance that forms lime-
stone, and furnishes the mineral matter required for the hard parts
of a large proportion of the lower animals. It is a matter of some
FIG. 8. Erosion of limestone by the solvent action of a peaty stream,
Durness, Sutherlandshire.
interest to know that this substance, so indispensable for the
formation of the shells of so great a number of sea-creatures,
is constantly supplied to the sea by the streams that flow into it. 1
The rivers of Western Europe, for instance, have been ascertained
to convey about i part of dissolved mineral matter in every 5000
parts of water, and of this mineral matter about a half consists
of carbonate of lime. It has been estimated that the Rhine bears
enough carbonate of lime into the sea every year to make three
hundred and thirty-two thousand millions of oysters of the usual
1 There is now reason, however, to suspect that the carbonate of lime in
marine organisms is not derived so much from the comparatively minute
proportion of that substance present in solution in sea-water, as from the
much more abundant sulphate of lime which undergoes apparently a process
of chemical transformation into carbonate within the living animals.
in MECHANICAL ACTION 29
size. Another abundant ingredient of river-water is gypsum or
sulphate of lime, of which the Thames is computed to carry
annually past London not less than 180,000 tons.
It would be difficult to determine what proportion of mineral
matter annually transported by rivers to the sea is supplied to
them by springs, and how much is due to their own chemical
action and to that of the rain and brooks which flow into them.
But, obviously, whether removed from the rocks at the surface
or from those underground, this chemically dissolved mineral
matter represents so much loss from the solid land. Its amount
can be approximately estimated by ascertaining the average
proportion of dissolved substances in the river-waters of a
country and the amount of water discharged into the sea. When
this calculation is made we learn what an important element in
the degradation of the land is the solvent action of rain, springs,
and streams. It has been computed, for instance, that more than
eight millions of tons of dissolved mineral matter are removed
from the rocks of England and Wales in a single year, which is
equivalent to a general lowering of the surface of the country, by
chemical solution alone, at a rate of .0077 of a foot in a century
or one foot in about 1 3,000 years.
Mechanical Action ( i)Transport. The dissolved material,
large though its total amount is thus seen to be, forms but a
small proportion of the total quantity of mineral substances con-
veyed by rivers from land to sea. A single shower of rain washes
off fine dust and soil from the surface of the ground into the
nearest brook, which then rolls along with a discoloured current.
An increase in the volume of the water enables a stream to sweep
along sand, gravel, and blocks of stone lying in its channel, and
to keep these materials moving until, as the declivity lessens and
the rain ceases, the current becomes too feeble to do more than
lazily carry onward the fine silt that discolours it. Every stream,
large or small, is ceaselessly busy transporting mud, sand, or
gravel. And as the ultimate destination of all this sediment is
the bottom of the sea, it is evident that if there be no compensat-
ing influences at work to repair the constant loss, the land must
in the end be all worn away.
Some of the most instructive lessons regarding the work of
running water on land are afforded by the beds of mountain-
torrents. Huge blocks, detached from the crags and cliffs on
either side, may there be seen cumbering the pathway of the
water, which seems quite powerless to move such masses and can
3 o RECORDS OF RUNNING WATER CHAP.
only sweep round them or find a passage beneath them. But
visit such a torrent when it is swollen with heavy rains or rapidly
melted snow, and you will hear the stones knocking against each
. other or on the rocky bottom, as they are driven downwards by
the flood. When the stream is at its lowest, in dry summer
weather, follow its course a little way down hill, and you will see
that by degrees the blocks, losing their sharp edges, have become
rounded boulders, and that these are gradually replaced by coarse
shingle, and then by finer gravel. In the quieter reaches of
the water, sheets of sand begin to make their appearance,
and at last when the stream reaches the plains, no sediment
of coarser grain than mere silt may be seen in its channel.
It is thus obvious that in the constant transport maintained
by watercourses, the carried materials, by being rolled along
rocky channels and continually ground against each other, diminish
in size as they descend. A river flowing from a range of
mountains to the distant ocean may be likened to a mill, into
which large angular masses of rock are cast at the upper end,
and out of which only fine sand and silt are discharged at the
lower.
Partly, therefore, owing to the fine dust and soil swept into
them by wind and rain from the slowly decomposing surface of
the land, and partly to the friction of the detritus which they
sweep along their channels, rivers always contain more or less
mineral matter suspended in their water or travelling with the
current on the bottom. The amount of material thus transported
varies greatly in different rivers, and at successive seasons even in
the same river. In some cases, the rainfall is spread so equably
through the year that the rivers flow onward with a quiet monotony,
never rising much above nor sinking much below their average
level. In such circumstances, the amount of sediment they carry
downward is proportionately small. On the other hand, where
either from heavy periodical rains or from rapid melting of snow,
rivers are liable to floods, they acquire an enormously increased
power of transport, and their burden of sediment is proportion-
ately augmented. In a few days or weeks of high water, they
may convey to the sea a hundredfold the amount of mineral
matter which they could carry in a whole year of their quieter
mood.
Measurements have been made of the proportions of sediment
in the waters of different rivers at various seasons of the year.
The results, as might be expected, show great variations. Thus
in MECHANICAL ACTION 31
the Garonne, rising among the higher peaks of the Pyrenees,
drains a large area of the south of France, and is subject to floods
by which an enormous quantity of sediment is swept down from
the mountains to the plains. Its proportion of mud has been
estimated to be as much as I part in 100 parts of water. The
Durance, which takes its source high on the western flank of the
Cottian Alps, is one of the rapidest and muddiest rivers in Europe.
Its angle of slope varies from I in 208 to I in 467, the average
declivity of the great rivers of the globe being probably not more
than i in 2600, while that of a navigable stream ought not to
exceed 10 inches per mile or i in 6336. The Durance is, there-
fore, rather a torrent than a river. With this rapidity of descent
is conjoined an excessive capacity for transporting sediment. In
floods of exceptional severity, the proportion of mud in that stream
has been estimated at one-tenth by weight of the water, while the
average proportion for nine years from 1867 to 1875 was about
T i^. Probably the best general average is to be obtained from a
river which drains a wide region exhibiting considerable diversities
of climate, topography, rocks, and soils. The Mississippi presents
a good illustration of these diversities, and has accordingly been
taken as a kind of typical river, furnishing, so to speak, a standard
by which the operations of other rivers may be compared, and
which may perhaps be assumed as a fair average for all the rivers
of the globe. Numerous measurements have been made of the
proportion of sediment carried into the Gulf of Mexico by this
vast river, with the result of showing that the average amount of
sediment is by weight i part in every 1500 parts of water, or
little more than one-third of the proportion in the water of the
Durance.
If now we assume that, all over the world, the general average
proportion of sediment floating in the water of rivers is i part in
every 1500 of water, we can readily understand how seriously in
the course of time must the land be lowered by the constant
removal of so much decomposed rock from its surface. Knowing
the area of the basin drained by a river, and also the proportion
of sediment in its water, we can easily calculate the general loss
from the surface of the basin. The ratio of the weight or
specific gravity of the silt to that of solid rock may be taken to
be as 19 is to 25. Accordingly the Mississippi conveys annually
from its drainage basin an amount of sediment equivalent to the
removal of g-^y-y- part of a foot of rock from the general surface of
the basin. At this rate, one foot of rock will be worn away every
32 RECORDS OF RUNNING WATER CHAP.
6000 years. If we take the general height of the land of the
whole globe to be 2100 feet, and suppose it to be continuously
wasted at the same rate at which the Mississippi basin is now
suffering, then the whole dry land would be carried into the sea
in 12,600,000 years. Or if we assume the mean height of
Europe to be 940 feet and that this continent is degraded at the
Mississippi rate of waste until the last vestige of it disappears, the
process of destruction would be completed in 5,640,000 years.
Such estimates are not intended to be close approximations to the
truth. As the land is lowered, the rate of decay will gradually
diminish, so that the later stages of decay will be enormously
protracted. But by taking the rate of operation now ascertained
to be in progress in such a river basin as the Mississippi, we
obtain a valuable standard of comparison, and learn that the
degradation of the land is much more rapid than might have been
supposed.
(2) Erosion. But rivers are not merely carriers of the mud,
sand, and gravel swept into their channels by other agencies. By
keeping these materials in motion, the currents reduce them in
size, and at the same time employ them to hollow out the channels
wherein they move. The mutual friction that grinds down large
blocks of rock into sand and mud, tells also upon the rocky
beds along which the material is driven. The most solid rocks
are worn down ; deep long gorges are dug out, and the water-
courses, when they have once chosen their sites, remain on them
and sink gradually deeper and deeper beneath the general level
of the country. The surfaces of stone exposed to this attrition
assume the familiar smoothed and rounded appearance which is
known as water-worn. The loose stones lying in the channel of
a stream, and the solid rocks as high up as floods can scour them,
present this characteristic aspect. Here and there, where a few
stones have been caught in an eddy of the current, and are kept
in constant gyration, they reduce each other in dimensions, and
at the same time grind out a hollow in the underlying rock. The
sand and mud produced by the friction are swept off by the
current, and the stones when sufficiently reduced in size are also
carried away. But their places are eventually taken by" other
blocks brought down by floods, so that the supply of grinding
material to the whirling eddy is kept up until the original hollow
is enlarged into a wide deep caldron, at the bottom of which the
stones can only be stirred by the heaviest floods. Cavities of this
kind, known as pot-holes, are of frequent occurrence in rocky
EROSION
33
watercourses as well as on rocky shores, in short, wherever eddies
of water can keep shingle rotating upon solid rock. As they
often coalesce by the wearing away of the intervening wall of
rock, they greatly aid in the deepening of a watercourse. In
most rocky gorges, a succession of old pot-holes may be traced
far above the present level of the stream (Fig. 9).
That it is by means of the gravel and other detritus pushed
FIG. 9. Pot-holes worn out by the gyration of stones in the bed of a stream.
along the bottom by the current, rather than by the mere friction
of the water on its bed, that a river excavates its channel, is most
strikingly shown immediately below a lake. In traversing a lake,
the tributary streams deposit their sediment on its bottom, because
the still water checks their current and, by depriving the water of
its more rapid movement, compels it to drop its burden of gravel,
sand, and silt (see p. 48). Filtered in this way, the water of the
various streams that unite in the lake escapes at the lower end as
a clear transparent river. The Rhone, for instance, flows into the
D
RECORDS OF RUNNING WATER
CHAP.
Lake of Geneva as a turbid stream ; it issues from that great
reservoir at Geneva as a rushing current of the bluest, most trans-
lucent water which, though it sweeps over ledges of rock, has
not yet been able to grind them down into a deep channel.
The Niagara, also, filtered by Lake Erie, has not acquired
sediment enough to enable it to cut deeply into the rocks
over which it foams in its rapids before throwing itself over the
great Falls.
One of the most characteristic features of streams is the
singularly sinuous courses which they follow. As a rule, too, the
flatter the ground over which they flow, the more do they wind. Not
uncommonly they form loops, the
nearest bends of which in the end
unite, and as the current passes
along the now straightened chan-
nel, the old one is left to become
by degrees a lake or pond of
stagnant water, then a marsh, and
lastly, dry ground (Fig. 10). We
might suppose that in flowing off
the land, water would take the
shortest and most direct road to
the sea. But this is far from
being the case. The slightest in-
equalities of level have originally
determined sinuosities of the
channels, while trifling differences
in the hardness of the banks, in
the accumulation of sediment, and
in the direction of the currents
and eddies, have been enough to
turn a stream now to one side now
to another, until it has assumed
its present meandering course,
of the Mississippi HOW easily this may be done can
be instructively observed on a
roadway or other bare surface of
FIG. io. Windin
river. The shaded part marks the
alluvial plain.
ground. When quite dry and smooth, hardly any depressions in
which water would flow may be detected on such a surface. But
after a heavy shower of rain, runnels of muddy water will be seen
coursing down the slope in serpentine channels that at once recall
the winding rivers of a great drainage-system. The slightest
Ill
EROSION OF RIVER-CHANNELS
35
differences of level have been enough to turn the water from
side to side. A mere pebble or projecting heap of earth or
tuft of grass has sufficed to cause a bend. The water,
though always descending, can only reach the bottom by
keeping the lowest levels, and turning from right to left as these
guide it
When a river has once taken its course and has begun to ex-
cavate its channel, only some great disturbance, such as a landslip,
an earthquake, or a volcanic
eruption, can turn it out of that
course. If its original pathway
has been a winding one, it goes
on digging out its bed which,
with all its bends, gradually sinks
below the level of the surround-
ing country. The deep and
picturesque gorge (Fig. 11) in
which the Moselle winds from
Treves to Coblenz has in this
way been slowly eroded out
of the undulating tableland
across which the river originally
flowed.
In another and most char-
acteristic way, the shape of the
ground and the nature and
arrangement of the rocks over
which they flow, materially
influence rivers in the forms
into which they carve their
channels. The Rhone and the
Niagara, for instance, though
filtered by the lakes through
which they flow, do not run far
before plunging into deep
ravines. Obviously such ravines
cannot have been dug out by
the same process of mechanical
attrition whereby river-channels in general are eroded. Yet the
frequency of gorges in river scenery shows that they cannot
be due to any exceptional operation. They may generally be
accounted for by some arrangement of rocks wherein a bed of
FIG. ii. Windings of the gorge of the
Moselle above Cochem.
RECORDS OF RUNNING WATER
CHAP. Ill
harder material is underlain by one more easily removable.
Where a stream, after flowing over the upper bed, encounters the
decomposable bed below, it eats away the latter more rapidly.
The overlying hard rock is thus undermined, and, as its support
is destroyed, slice after slice is cut away from it. The waterfall
which this kind of structure produces continues to eat its way
backward or up the course of the stream, so long as the necessary
conditions are maintained of hard rocks lying upon soft. Any
change of structure which would bring the hard rocks down to
the bed of the channel, and remove the soft rocks from the action
of the current and the dash of the spray, would gradually destroy
the waterfall. . It is obvious that, by cutting its way backward, a
waterfall excavates a ravine.
The renowned Falls of Niagara supply a striking illustration of
the process now described. The vast body of water which issues
from Lake Erie, after flowing through a level country for a few
miles, rushes down its rapids and then plunges over a precipice
of flat limestone. Beneath this
hard rock lie comparatively easily
eroded shales and sandstones
(Fig. 12). As the water loosens
and removes the lower rock, large
portions of the face of the
precipice behind the Falls are
from time to time precipitated into
the boiling flood below. The
waterfall is thus slowly prolong-
ing the ravine below the Falls.
The magnificent gorge in which
FIG. 12. Section at the Horse-Shoe Fall, & r
the Niagara, after its tumultuous
descent, flows sullenly to Lake
Ontario is not less than 7 miles
^ dg wid
J .
and fr m 2O tO ^O feet deep.
There is no reason to doubt that
this chasm has been entirely dug out by the gradual recession of
the Falls from the cliffs at Queenstown, over which the river at
first poured. We may form some conception of the amount of
rock thus removed from the estimate that it would make a rampart
about 12 feet high and 6 feet thick extending right round the
whole globe at the equator. Still more gigantic are the gorges
or canons of the Colorado and its tributaries in Western America.
Niagara.
, Medina Sandstone, 300 feet ; b, Clinton
Limestone and Shale, 30 feet; c, Nia-
gara Shale, 80 feet; d, Niagara Lime- ^ from 2OQ
stone, 16.5 feet, of which 85 feet are
seen at the Fall.
38 RECORDS OF RUNNING WATER CHAP.
The Grand Canon of the Colorado is 300 miles long, and in
some places more than 6000 feet deep (Fig. 13). The country
traversed by it is a network of profound ravines, at the bottom
of which the streams flow that have eroded them out of the
table-land.
It is obvious that eventually there must be a limit to the
deepening of a river-channel, when the slope of the bed has been
so reduced that the current can only flow along languidly, without
possessing any longer the velocity necessary for sweeping along
the coarser detritus by which the channel is worn away. When
this condition has been reached the river is said to have arrived
at a base-level of erosion. We see this result most conspicuously
in broad alluvial plains across which the streams that traverse
them no longer deepen their channels, but rather tend to raise
them by allowing more of the transported sediment to settle
down upon them.
ii. DEPOSITION OF MATERIALS BY RUNNING WATER
Permanent Records of River-Action. If, then, all the
streams on the surface of the globe are engaged in the double task
of digging out their channels and carrying away the loose materials
that arise from the decomposition of the surface of the land, let
us ask ourselves what memorials of these operations they leave
behind them. In what form do the running waters of the land
inscribe their annals in geological history ? If these waters could
suddenly be dried up all over the earth, how could we tell what
changes they had once worked upon the surface of the land ?
Can we detect the traces of ancient rivers where there are no
rivers now ?
From what has been said in this lesson it will be evident that
in answer to such questions as these, we may affirm that one un-
mistakable evidence of the former presence of rivers is to be found
in the channels which they have eroded. The gorges, rocky
defiles, pot-holes, and water-worn rocks which mark the pathway
of a stream would long remain as striking memorials of the work
of running water. In districts, now dry and barren, such as large
regions in the Levant, there are abundant channels (wadies) now
seldom or never occupied by a stream, but which were evidently
at one time the beds of active torrents.
Alluvium. But more universal testimony to the work of
in ALLUVIAL DEPOSITS 39
running water is to be found in the deposits which it has accumu-
lated. To these deposits the general name of alluvium has been
given. Spreading out on either side, sometimes far beyond the
limits of the ordinary or modern channels, these deposits, even
when worn into fragmentary patches, retain their clear record of
the operations of rivers.
The power possessed by running water to carry forward sedi-
ment depends mainly upon the velocity of the current. The more
rapidly a stream flows, the more sediment can it transport, and
the larger are the blocks which it can move. The velocity is
regulated chiefly by the angle of slope ; the greater the declivity,
the higher the velocity and the larger the capacity of the stream
to carry down debris. Any cause, therefore, which lessens the
velocity of a current diminishes its carrying power. If water,
bearing along gravel, sand, or mud, is checked in its flow, some
of these materials will drop and remain at rest on the bottom.
In the course of every stream, various conditions arise whereby
the velocity of the current is reduced. One of the most obvious
of these is a diminution in the slope of the channel, either existing
in the original form of the ground or effected by the stream itself,
as where it reaches a base-level of erosion. Another is the union
of a rapid tributary with a more gently flowing stream. A third
is the junction of a stream with the still waters of a lake (see
p. 48) or with the sea. In these circumstances, the flow of the
water being checked, the sediment at once begins to fall to the
bottom.
Let us in imagination follow the course of a river from the
mountains to the sea, marking as we go the circumstances under
which the accumulation of sediment takes place, and noting illus-
trations of this law of deposition. We find that among the
mountains where the river takes its rise, the torrents that rush
down the declivities have torn out of them such -vast quantities
of soil and rock as to seam them with deep clefts and gullies.
Where each of these rapid streamlets reaches the valley below,
its rapidity of motion is at once lessened, and with this slackening
of speed and consequent loss of carrying power, there is an
accompanying deposit of detritus. Blocks of rock, angular rubbish,
rounded shingle, sand, and earth are thrown down in the form of
a cone, of which the apex starts from the bottom of the gully and
the base spreads out over the plain (Fig. 14). Such cones vary
in dimensions according to the size of the torrent and the com-
parative ease with which the rocks of the mountain-side can be
RECORDS OF RUNNING WATER
CHAP.
loosened and removed. Some of them, thrown down by the transient
runnels of the last sudden rain-storm, may not be more than a few
cubic yards in bulk. But on the skirts of mountainous regions
they may grow into masses hundreds of feet thick and many miles
in diameter. The valleys in a range of mountains afford many
striking examples of these alluvial cones OY fans, as they are called.
FIG. 14. Gullies torn out of the side of a mountain by descending torrents, with
cones of detritus at their base.
Where the tributary torrents are numerous, a succession of such
cones or fans, nearly or quite touching each other, spreads over the
floor of a valley. From this cause, so large an amount of detritus
has within historic times been swept down into some of the valleys
of the Tyrol that churches and other buildings are now half-buried
in the accumulation.
Looking more closely at the materials brought down by the
in ARRANGEMENT OF ALLUVIUM 41
torrents, we find them arranged in rude irregular layers, sloping
downwards into the plain, the coarsest and most angular detritus
lying nearest to the mountains, while more rounded and water-
worn shingle or sand extends to the lower margin of the cone.
This grouping of irregular layers of angular and half-rounded
detritus is characteristic of the action of torrents. Hence, where
it occurs, even though no water may run there at the present day,
it may be regarded as indicating that at some former time a torrent
swept down detritus over that site.
Quitting the more abrupt declivities, and augmented by
numerous tributaries from either side, the stream whose course
we are tracing loses the character of a torrent and assumes that
of a river. It still flows with velocity enough to carry along not
only mud and sand, but even somewhat coarse gravel. The large
angular blocks of the torrential part of its course, however, are no
longer to be seen, and all the detritus becomes more and more
rounded and smoothed as we follow it towards the plains. At
many places, deposits of gravel or sand take place, more especi-
ally at the inner side of the curves which the stream makes as it
winds down the valley. Sweeping with a more rapid flow round
the outer side of each curve, the current lingers in eddies on the
inner side and drops there a quantity of sediment. When the
water is low, strips of bare sand and shingle on the concave side
of each bend of the stream form a distinctive feature in river
scenery. It is interesting to walk along one of these strips and
to mark how the current has left its record there. The stones
are well smoothed and rounded, showing that they have been
rolled far enough along the bottom of the channel to lose their
original sharp edges, and to pass from the state of rough angular
detritus into that of thoroughly water -worn gravel. Further,
they will be found not to lie entirely at random, as might at first
sight be imagined. A little examination will show that, where
the stones are oblong, they are generally placed with their longer
axis pointing across
the stream. This
would naturally be
the position which FlG - iS--Flat stones in a bank of river-shingle showing
, , the direction of the current (indicated by the arrow)
they would assume that transported and left them.
where the current
kept rolling them forward along the channel. Those which are flat
in shape will be observed usually to slope up stream. That the
sloping face must look in the direction from which the current
RECORDS OF RUNNING WATER
CHAP.
moves will be evident from Fig. i 5, where a current, moving in
the direction of the arrow and gradually diminishing in force,
would no longer be able to overturn the stones which it had so
placed as to offer the least obstacle to its passage. Had the
current flowed from the opposite quarter, it would have found the
upturned edges of the stones exposed to it, and would have
readily overturned them until they found a position in which
they again presented least resistance to the water. In a section
of gravel, it is thus often quite possible to tell from what quarter
the current flowed that deposited the pebbles.
Yet another feature in the arrangement of the materials is well
seen where a digging has been made in one of the alluvial banks,
but better still in a section of one of the terraces to be immedi-
ately referred to. The layers of gravel or sand in some bands
may be observed to be inclined at a steeper angle than in others,
as shown in the accompanying figure (Fig. 16). In such cases,
it will be noticed that the
slope O f the more inclined
layers is down the stream,
and hence that their direc-
tion gives a clue to that of
the current which arranged
them. We may watch
similar layers in the act of
deposition among shallow
pools into which currents
are discharging sediment.
The gravel or sand may be
observed moving along the
bottom, and then falling over
the edge of a bank into the bottom of the pool. As the sediment
advances by successive additions to its steep slope in front, it
gradually fills the pool up. Its progress may be compared to
that of a railway embankment formed by the discharge of
waggon-loads of rubbish down its end. A section through such
an embankment would reveal a series of bands of variously
coloured materials inclined steeply towards the direction in which
the waggon-loads were thrown down. Yet the top of the em-
bankment may be kept quite level for the permanent way. The
nearly level bands (^, c) in Fig. 16 represent the general bottom
on which the sediment accumulated, while the steeper lines in the
lower gravel (a) point to the existence and direction of the
FIG. 16. Section of alluvium showing
direction of currents.
Ill
ORIGIN OF RIVER TERRACES
43
currents by which sediment was pushed forward along that
bottom. (Compare pp. 195, 196.)
As the river flows onward through a gradually expanding
valley, another characteristic feature becomes prominent. Flank-
ing each side of the flat land through which the stream pursues
its winding course, there runs a steep slope or bank a few feet or
yards in height, terminating above in a second or higher plain,
which again may be bordered with another similar bank, above
which there may lie a third plain. These slopes and plains form
a group of terraces, rising step by step above and away from the
river, sometimes to a height of several hundred feet, and occasion-
ally to the number of 6 or 8 or even more (Figs. 1 7 and 1 8).
FIG. 17. River-terraces.
Here and there, by the narrowing of the intervening strip of
plain, two terraces merge into one, and at some places the river
in winding down the valley has cut away great slices from one or
more of the terraces, perhaps even entirely removing some of
them from one or both sides and eating back into the rock
out of which the valley has been excavated. Even when
the floor of a river has been reduced to a base-level of erosion,
the stream in flood may undermine banks of soft material, and
thus widen and alter its channel, though no longer capable of
deepening it. Sections are thus exposed showing a succession
of gravels, sands, and loams like those of the present river.
From the line of the uppermost terrace down to the spits of
shingle now forming in the channel, we have evidently a chrono-
logically arranged' series of river-deposits, the oldest being at
the top and the youngest at the bottom. But how could the
44 RECORDS OF RUNNING WATER CHAP.
river have flowed at the level of these high gravels, so far
above its present limits ? An examination of the behaviour of
the stream during floods will help towards an answer to this
question.
When from heavy rains or melted snows the river overflows
its banks, it spreads out over the level ground on either side.
The tract liable to be thus submerged during inundations is
called the flood-plain. As the river rises in flood, it becomes
more and more turbid from the quantity of mud and silt poured
into it by its tributaries on either side. Its increase in volume like-
wise augments its velocity, and consequently its power of trans-
porting the coarser detritus resting on its bed. Large quantities
of shingle may thus be swept out of the ordinary channel and
be strewn across the nearer parts of the flood-plain. As the
current spreads over this plain, its velocity and transporting
FIG. 18. Section of river-terraces.
capacity diminish, ana consequently sediment begins to be thrown
down. Grass, bushes, and trees, growing on the flood -plain,
filter some of the sediment out of the water. Fine mud and
sand, for instance, adhere to the leaves and stems, whence they
are eventually washed off by rain into the soil underneath. In this
way, the flood-plain is gradually heightened by the river itself.
At the same time, before a base-level of excavation is reached, the
bed of the river is deepened by the scour of the current, until, in
the end, even the highest floods are no longer able to inundate
the flood-plain. The difference of level between that plain and
the surface of the river gradually increases ; by degrees the
river begins to cut away the edges of the terrace which it cannot
now overflow, and to form a new flood-plain at a lower level. In
this manner, it slowly lowers its bed, and leaves on either side a
set of alluvial terraces to mark successive stages in the process of
excavation. If, during this process, the level of the land should
be raised, the slope of the rivers, and consequently their scour,
would be augmented, and they would thereby acquire greater
capacity for eroding their channels and leaving terraces above
in ORIGIN OF RIVER TERRACES 45
them. Even those which had brought down their floors to
a level below which they could no longer erode them, might
thus recommence the process of erosion. There is reason to
believe that this cause has acted both in Europe and North
America.
While it is obvious that the highest terraces must be the
oldest, and that the series is progressively younger down to the
terrace that is being formed at the present time, nevertheless, in
the materials comprising any one terrace, those lying at the top
must be the youngest. This apparent contradiction arises from
the double action of the river in eroding its bed and depositing its
sediment. If there were no lowering of the channel, then the
deposits would follow the usual order of sequence, the oldest being
below and the youngest above. This order is maintained in the
constituents of each single terrace, for the lowermost layers of
grave) must evidently have been accumulated before the deposit
of those that overlie them. But when the level of the water is
lowered, the next set of deposits must, though younger, lie on a
lower platform than those that preceded them. In no case,
however, will the older beds, though higher in position, be found
really to overlie the younger. They have been formed at
different levels.
The gravel, sand, and loam laid down by a river are marked,
as we have seen, by an arrangement in layers, beds, or strata
lying one upon another. This stratified disposition, indeed, is
characteristic of all sedimentary accumulations, and is best
developed where currents have been most active in transporting
and assorting the materials (p. 193). It is the feature that first
catches the eye in any river-bank, where a section of the older
deposits or alluvium is exposed. Beds of coarser and finer
detritus alternate with each other, but the coarsest are generally
to be observed below and the finest above. The " deltas " accu-
mulated by rivers in lakes and in the sea will be noticed in
Chapters IV. and VII.
But besides the inorganic detritus carried forward by a river,
we have also to consider the fate of the remains of plants and the
carcases of animals that are swept down, especially during floods.
Swollen by sudden and heavy rains, a river will rise above its
ordinary level and uproot trees and shrubs. On such occasions,
too, moles and rabbits are drowned and buried in their burrows
on the alluvial flood-plain. Birds, insects, and even some of the
larger mammals are from time to time drowned, swept away by
46 RECORDS OF RUNNING WATER CHAP.
floods and buried in the sediment, and their remains, where of a
durable kind or where sufficiently covered over, may be preserved
for an indefinite period. The shells and fishes living in the river
itself may also be killed during the flood, and may be entombed
with the other organisms in the sediment.
Summary. The material produced by the universal decay of
the surface of the land is washed off by rain and swept seawards
by brooks and rivers. The rate at which the general level of the
land is being lowered by the operation of running water may be
approximately ascertained by measuring or estimating the amount
of mineral matter carried seaward every year from a definite
region, such as a river-basin. Taking merely the matter in
mechanical suspension, and assuming that the proportion of
it transported annually in the water of the Mississippi may be
regarded as an average proportion for the rivers of Europe,
we find that this continent, at the Mississippi rate of degradation,
might be reduced to the sea-level in rather less than 6,000,000
years.
In pursuing their course over the land, running waters gradu-
ally deepen and widen the channels m which they flow, partly
by chemically dissolving the rocks and partly by rubbing them
down by the friction of the transported sand, gravel, and stones.
When they have once chosen their channels, they usually keep to
them, and the sinuous windings, at first determined by trifling
inequalities on the surface of country across which the streams
first began to flow, are gradually deepened into picturesque gorges.
In the excavation of such ravines, waterfalls play an important
part by gradually receding up stream. River-channels, especially
if cut deeply into the solid rock, remain as enduring monuments
of the work of running water. The process of erosion goes on
until the slope of a river-bed has been so lowered that the
current can no longer drive along the sediment that is employed
in excavating its channel. When a base-level of erosion is thus
reached only the finer silt and sand are borne along or are allowed
to sink to the bottom.
But still more important as geological records, because more
frequent and covering a larger area, are the deposits which rivers
leave as their memorials. Whatever checks the velocity of a
current weakens its transporting power, and causes it to drop
some of its sediment to the bottom. Accordingly, accumulations
of sediment occur at the foot of torrent slopes, along the lower
and more level ground, especially on the inner or concave side of
in SUMMARY 47
the loops, over the flood-plains, and finally in the deltas formed
where rivers enter lakes or the sea. In these various situations,
thick stratified beds of silt, sand, and gravel may be formed,
enclosing the remains of the plants and animals living on the land
at the time. As a river deepens its channel, it leaves on either
side alluvial terraces that mark successive flood-plains over which
it has flowed.
CHAPTER IV
THE MEMORIALS LEFT BY LAKES
Fresh -Water Lakes. According to the law stated in last
chapter, that when water is checked in its flow, it must drop
some of its sediment, lakes are pre-eminently places for the
deposition and accumulation of mineral matter. In their quiet
depths, the debris worn away from the surface of the land is
filtered out of the water and allowed to gather undisturbed upon
the bottom. The tributary streams may enter a large lake swollen
and muddy, but the escaping river is transparent. It is evident,
therefore, that lakes must be continually silting up, and that when
this process is complete, the site of a lake will be occupied by a
series of deposits comprising a record of how the water was made
to disappear.
To those who know the aspect of lakes only in fine weather,
they may seem places where geological operations are at their very
minimum of activity. The placid surface of the water ripples upon
beaches of gravel or spits of sand ; reeds and marshy plants grow
out into the shallows ; the few streamlets that tumble down from
the surrounding hills furnish perhaps the only sounds that break
the stillness, but their music and motion are at once hushed when
they lose themselves in the lake. The scene might serve as the
very emblem of perfectly undisturbed conditions of repose. But
come back to this same scene during an autumn storm, when the
mists have gathered all round the hills, and the rain, after pouring
down for hours, has turned every gully into the track of a roaring
torrent. Each tributary brook, hardly visible perhaps in drought,
now rushes foaming and muddy from its dell and sweeps out into
the lake. The large streams bear along on their swift brown
currents trunks of trees, leaves, twigs, with now and then the
carcase of some animal that has been drowned by the rising
48
CHAP. IV
SILTING UP OF LAKES
49
flood. Hour after hour, from every side, these innumerable
swollen waters bear their freights of gravel, sand, and mud into
the lake. Hundreds or thousands of tons of sediment must thus be
swept down during a single storm. When we multiply this result
by the number of storms in a year and by the number of years in
an ordinary human life, we need not be surprised to be told that
even within the memory of the present generation, and still more
within historic times, conspicuous changes have taken place in
many lakes.
Filling up of Lakes. In the Lake of Lucerne, for example,
the River Reuss, which bears down the drainage of the huge
mountains round the St. Gothard, deposits about 7,000,000 cubic
feet of sediment every year. Since the year 1714 the Kander,
FIG. 19. Alluvial terraces on the side of an emptied reservoir.
which drains the northern flanks of the centre of the Bernese
Oberland, is said to have thrown into the lower end of the Lake
of Thun such an amount of sediment as to form an area of 230
acres, now partly woodland, partly meadow and marsh. Since
the time of the Romans, the Rhone has filled up the upper end
of the Lake of Geneva to such an extent that a Roman harbour,
still called Port Valais, is now nearly two miles from the edge of
the lake, the intervening ground having been converted first into
marshes and then into meadows and farms.
It is at the mouths of streams pouring into a lake that the
process of filling up is most rapid and striking. But it may be
detected at many other places round the margin. Instructive
lessons on this subject may be learned at a reservoir formed by
damming back the waters of a steep-sided valley, and liable to
be sometimes nearly dry (Fig. 19). In such a situation, when
the water is low, it may be noticed that a series of parallel lines
runs all round the sides of the reservoir, and that these lines
E
RECORDS OF LAKES
CHAP.
consist of gravel, sand, or earth. Each of them marks a former
level of the water, and they show that the reservoir was not drained
off at once but intermittently, each pause in the diminution of
level being marked by a notch or platform in the slope of sediment.
It is easy to watch how these lines are formed along the present
margin of the water. The loose debris from the bare slope above,
partly by its own gravitation, partly by the wash of rain, slides
down into the water. But as soon as it gets there, its further
FIG. 20. Parallel roads of Glen Roy.
downward movement is checked. By the ripple of the water it
is gently moved up and down, but keeps on the whole just below
the line to which the water reaches. So long as it is concealed
under the water, its position and extent can hardly be realised.
But as soon as the level of the reservoir sinks, the sediment is
left as a marked shelf or terrace. In natural lakes, the same
process is going on, though, in like manner, scarcely recognisable,
because hidden under the water. But if by any means a lake
could be rapidly emptied, its former level would be marked by
a shelf or alluvial terrace. In some cases, the barrier of a lake
has been removed, and the sinking of the water has revealed
the terrace. The famous " parallel roads " of Glen Roy, in the
IV
SILTING UP OF LAKES
west of Scotland, are notable examples (Fig. 20). The valleys
in that region were anciently dammed up by large glaciers. The
drainage accumulated behind the ice, filled up the valleys, and
converted them into a series of lakes or fresh-water "fjords."
The former levels of these sheets of water and the successive
stages of their diminution and disappearance are shown by the
series of alluvial shelves known as "parallel roads." The highest
of these is 1155 feet, the middle 1077 feet, and the lowest 862
feet above the level of the sea.
Thus, partly by the washing of detritus down from the adjoin-
ing slopes by rain, partly by the sediment carried into them by
streams, and partly by the growth of marshy vegetation along
their margins, lakes are visibly diminishing in size. In mountain-
ous countries, every stage of this appearance may be observed
FIG. 21. Stages in the filling up of a lake. In A two streamlets are represented as
pouring their "deltas " into a lake. In B they have filled the lake up, converting it
into a meadow across which they wind on their way down the valley.
(Fig. 2 i). Where the lakes are deep, the tongues of sediment or
" deltas " which the streams push in front of them have not yet
been able to advance far from the shore. Where, on the other
hand, the water is shallow, every tributary has built up an alluvial
plain which grows outwards and along the coast, until it unites
with those of its neighbours to form a nearly continuous belt of
flat meadow and marsh round the lake. By degrees, as this belt
increases in width, the lake narrows, until the whole tract is
finally converted into an alluvial plain, through which the river
and its tributaries wind on their way to lower levels. The
successive flat meadow-like expansions, so abundant in the valleys
of hilly and mountainous regions, were probably in many cases
originally lakes which have in this manner been gradually filled
up.
Lake Deposits. On large sheets of fresh water many of
the phenomena of waves and of erosion and deposition may be
RECORDS OF LAKES
CHAP.
witnessed on a great scale. The shingle that gathers on their
shores rivals, in coarseness and in its rolled water-worn character,
the accumulations of an exposed sea-coast (Fig. 22). Much fine
sediment is produced by the trituration of these beach stones, and
is swept by the wind-driven currents out into deeper water. Thus
by the action of the waters of the lakes themselves great abrasion
FIG. 22. Well-worn shingle on the shore of a large lake (Lake Ontario),
by Mr. G. K. Gilbert, U.S. Geol. Survey.
Photograph
may take place, and a good deal of detritus may be deposited on
the lake-floors. But in general, the deposits in lakes are due
rather to materials brought into them by rivers than to the opera-
tion of the lake-waters.
The bottoms of lakes must evidently contain many interesting
relics. Dispersed through the shingle, sand, and mud that
gather there, are the remains of plants and animals that lived
on the surrounding land. Leaves, fruits, twigs, branches, and
trunks embedded in the silt may preserve for an indefinite
period their record of the vegetation of the time. The wings
LACUSTRINE DEPOSITS
53
or wing-cases of insects, the shells of land-snails, the bones of
birds and mammals, carried down into the depths of a lake and
entombed in the silt there, will remain as a chronicle of the kind
of animals that haunted the surrounding hills and valleys.
The layers of gravel, sand, and silt laid down on the floor of a
lake differ in some respects from those deposited in the terraces
of a river, being generally finer in grain, and including a larger
proportion of silt, mud, or clay among them, especially away from
the margin of the lake. They are, no doubt, further distinguished
by the greater abundance of the remains of plants and animals
preserved in them.
But lakes likewise serve as receptacles for a series of deposits
which are peculiar to them, and which consequently have much
interest and importance, inasmuch as they furnish a ready means
of detecting the sites of lakes that have long disappeared. The
molluscs that live in lacustrine waters are distinct from the snails
of the adjoining shores. Their dead shells gather on the bottoms
of some lakes in such numbers as to form there a deposit of the
white crumbling marl, already referred to on p. 4. In course of
time this deposit may grow to be many feet or yards in thickness.
The shells in the upper parts may be quite fresh, some of the
animals having only recently died ; but they become more and more
decayed below until,
towards the bottom of
the deposit, the marl
passes into a more
compact chalk - like
substance in which
few or no shells may
be recognisable (Fig.
23). On the sites of
lakes that have been
naturally filled up or
artificially drained,
such marl has been
extensively dug as a
manure for land. Besides the shells from the decay of which it
is chiefly formed, it sometimes yields the bones of deer, oxen, and
other animals, whose carcases must originally have sunk to the
bottom of the lake and been there gradually covered up in the
growing mass of marl. Many examples of these marl-deposits are
to be found among the drained lakes of Scotland and Ireland.
FIG. 23. Piece of shell-marl containing shells of
L imtuea peregra.
54 RECORDS OF LAKES CHAP.
Yet another peculiar accumulation is met with on the bottom
of some lakes, particularly in Sweden. In the neighbourhood of
banks of reeds and on the sloping shallows of the larger lakes, a
deposit of hydrated peroxide of iron takes place, in the form of
concretions varying in size from small grains like gunpowder up
to cakes measuring six inches across. The iron is no doubt dis-
solved out of the rocks of the neighbourhood by water containing
organic acids or carbonic acid. In this condition, it is liable to
be oxidised on exposure. As after oxidation it can no longer be
retained in solution, it is precipitated to the bottom where it
collects in grains which by successive additions to their surface
become pellets, balls, or cakes. Possibly some of the microscopic
plants (diatoms) which abound on the bottoms of the lakes may
facilitate the accumulation of the iron by abstracting this substance
from the water and depositing it inside their siliceous coverings.
Beds of concretionary brown ironstone are formed in Sweden
from ten to 200 yards long, 5 to 1 5 yards broad, and from 8 to
30 inches thick. During winter when the lakes are frozen over,
the iron is raked up from the bottom through holes made for the
purpose in the ice, and is largely used for the manufacture of iron
in the Swedish furnaces. When the iron has been removed, it
begins to form again, and instances are known where, after the
supply had been completely exhausted, beds several inches in
thickness were deposited in twenty-six years.
Among the rocks which form the dry land of the globe there
occur masses of limestone, sandstone, marl, and other materials
which can be proved to have been deposited in lakes, because they
contain a type of plant and animal remains similar to that found
in modern lakes. From evidence of this nature the existence and
wide extent of ancient and long-vanished lakes have been deter-
mined in Europe and North America. Their deposits have
yielded an extraordinary number and variety of extinct land-
animals, as will be more fully stated in Chapter XXV. Hence a
careful study of existing lakes enables us to follow with more
interest and success the history of the terrestrial waters of former
ages.
Salt-Lakes. The salt-lakes of desert regions present a wholly
peculiar series of deposits. These sheets of water have no outlet ;
yet there is reason to believe that most of them were at first fresh,
and discharged their outflow like ordinary lakes. Owing to
geological changes of level and of climate, they have long ceased
to overflow. The water that runs into them, instead of escaping
iv SUMMARY 45
by a river, is evaporated back into the air. But the various
mineral salts carried by it in solution from rocks and soils are not
evaporated also. They remain behind in the lakes, which are
consequently becoming gradually salter. Among the salts thus
introduced, common salt (sodium-chloride) and gypsum (calcium-
sulphate) are two of the most important. These substances, as the
water evaporates in the shallows, bays, and pools, are precipitated to
the bottom where they form solid layers of salt and gypsum. The
latter substance begins to be thrown down when 37 per cent of
the water containing it has been evaporated. The sodium-chloride
does not appear until 93 per cent of the water has disappeared.
In the order of deposit, -therefore, gypsum comes before the salt
(see p. 150). Some bitter lakes contain sodium-carbonate, in
others magnesium- chloride is abundant. The Dead Sea, the
Great Salt Lake of Utah, and many other salt-lakes and inland
seas furnish interesting evidence of the way in which they have
gradually changed. In the upper terraces of the Great Salt
Lake, 1000 feet or more above the present level of the water,
fresh-water shells occur, showing that the basin was at first fresh.
The valley-bottoms around saline lakes are now crusted with
gypsum, salt, or other efflorescence, and their waters are almost
wholly devoid of life. Such conditions as these help us to
understand how great deposits of gypsum and rock-salt were
formed in England, Germany, and many other regions where
the climate would not now permit of any such condensation of
the water (Chapter XXII.).
Summary. The records inscribed by lakes in geological
history consist of layers of various kinds of sediment. These
deposits may form mere shelves or terraces along the margin of
the water which, if drained off, will leave them as evidence of its
former levels. Partly by the erosive action of the shore-waters of
the lakes themselves when agitated by the winds, but chiefly
by the long -continued operations of rain, brooks, and rivers,
continually bringing down sediment, lakes are gradually filled up
with alluvium, and finally become flat meadow-land with tributary
streams running through it. The deposits that thus replace
the lacustrine water consist mainly of sand or gravel near shore,
while finer silt occupies the site of the deeper water. They
may also include beds of marl formed of fresh-water shells, and
sheets of brown iron ore. Throughout them all, remains of the
plants and animals of the surrounding land are likely to be
entombed and preserved.
56 RECORDS OF LAKES CHAP, iv
Salt lakes leave, as their enduring memorial, beds of rock-salt
and gypsum, sometimes carbonate of soda and other salts. Many
of them were at first fresh, as is shown by the presence of ordinary
fresh-water shells in their upper terraces. But by change of
climate and long-continued excess of evaporation over precipitation,
the water has gradually become more and more saline, and has
sometimes disappeared altogether, leaving behind it deposits of
common salt, gypsum, and other chemical precipitates.
CHAPTER V
HOW SPRINGS LEAVE THEIR MARK IN GEOLOGICAL HISTORY
THE changes made by running water upon the land are not con-
fined to that portion of the rainfall which courses along the surface.
Even when it sinks underground and seems to have passed out of
the general circulation, the subterranean moisture does not remain
inactive. After travelling for a longer or shorter distance through
the pores of rocks, or along their joints and other divisional planes,
it finds its way once more to daylight and reappears in Springs^
In this underground journey, it corrodes rocks, somewhat in the
same way as rain attacks those that are exposed to the outer
air, and it works some curious changes upon the face of the
land. Subterranean water thus leaves distinct and characteristic
memorials as its contribution to geological history.
There are two aspects in which the work of underground water
may be considered here. In the first place, portions of the sub-
stance of subterranean rocks are removed by the percolating water
and in large measure carried up above ground ; in the second
place, some of these materials are laid down again in a new form
and take a conspicuous place among the geological monuments of
their time.
In the removal of mineral substance, water percolating
through rocks acts in two distinct ways, mechanical and' chemical,
each of which shows itself in its own peculiar effects upon the
surface.
(i) Mechanical Action. While slowly filtering through
porous materials, water tends to remove loose particles and thus
to lessen the support of overlying rocks. But even where there
is no transport, the water itself, by saturating a porous layer that
rests upon a more or less impervious one, loosens the cohesion of
1 Physical Geography Class-Book, p. 240.
57
5 8 RECORDS LEFT BY SPRINGS CHAP, v
that porous layer. The overlying mass of rock is thus made to
rest upon a watery and weakened platform, and if from its position
it should have a tendency to gravitate in any given direction, it
may at last yield to this tendency and slide downwards. Along
the sides of sea-cliffs, on the precipitous slopes of valleys or river-
gorges, or on the declivities of hills and mountains, the conditions
are often extremely favourable for the descent of large masses of
rock from higher to lower levels.
Remarkable illustrations of such Landslips, as they are called,
from time to time take place on coast-lines and on the sides of
ravines and hills. Where porous sandy rocks rest upon more or
less impervious clays, the percolating water is arrested in its
descent, and thrown out along the base of the slopes. After much
wet weather, the upper surface of the clays becomes, as it were,
lubricated by the accumulation of water, and large slices of the
overlying rocks, having their support thereby weakened, break off
from the solid ground behind and slide downwards. A memorable
example of this process occurred at Christmas time, in the year
1 839, on the south coast of England, not far from Axmouth. At that
locality, the chalk-downs end off in a line of broken cliff some 500
feet above the sea. From the edge of the downs flanked by this
cliff, a tract about 800 yards long, containing not less than 30 acres
of arable land, sank down with all its fields, hedgerows, and path-
ways. This sunken mass, where it broke away from the upland,
left behind it a new cliff, showing along the crest the truncated
ends of the fields, of which the continuation was to be found in a
chasm more than 200 feet deep. While the ground sank into this
defile and was tilted steeply towards the base of the cliff, it was
torn up by a long rent running on the whole in the line of the
cliff, and by many parallel and transverse fissures. Although
more than half a century has passed since this landslip occurred,
the cliff remains much as it was at first, and the sunken fields
with their bits of hedgerow still slope steeply down to the bottom
of the declivity (Fig. 24). But the lapse of time has allowed the
influence of the atmosphere to come into play. The outstanding
dislocated fragments with their vertical walls and flat tops, show-
ing segments of fields, have been gradually worn into tower-like
masses with sloping declivities of debris. The long parallel rent
has been widened by rain into a defile with shelving sides. Every-
where the rawness of the original fissures has been softened by
the rich tapestry of verdure which the genial climate of that
southern coast fosters in every sheltered nook. But the scars
60 RECORDS LEFT BY SPRINGS CHAP.
have not been healed, and they will no doubt remain still visible
for many a year to come.
Landslips, of which there is no historical record, have produced
some of the most picturesque scenery along the south coast of
England. Masses that have slipped away from the main cliff
have so grouped themselves down the slopes that hillocks and
hollows succeed each other in endless confusion, as in the well-
known Undercliff of the Isle of Wight. Some of the tumbled
rocks are still fresh enough to show that they have fallen at no
very remote period, or even that the slipping still continues ;
others, again, have yielded so much to the weather that their
date doubtless goes far back into the past, and some of them are
crowned with what are now venerable ruins.
The most stupendous landslips on record have occurred in
mountainous countries. Upwards of 150 destructive examples
have been chronicled in Switzerland. Of these, one of the most
memorable was that of the Rossberg, a mountain lying behind
the Rigi, and composed of thick masses of hard red sandstone
and conglomerate, so arranged as to slope down into the valley
of Goldau. The summer of the year 1 806 having been particu-
larly wet, so large an amount of water had collected in the more
porous layers of rock as to weaken the support of the overlying
mass ; consequently a large part of the side of the mountain
suddenly gave way and rushed down into the valley, burying
under the debris about a square German mile of fertile land, four
villages containing 330 cottages and outhouses, and 457 inhabit-
ants. To this day, huge angular blocks of sandstone lying on
the farther side of the valley bear witness to the destruction
caused by this landslip, and the scar on the mountain-slope whence
the fallen masses descended is still fresh.
(2) Chemical Action (a) Solution. But it is by its
chemical action on the rocks through which it flows that sub-
terranean water removes by far the largest amount of mineral
matter, and produces the greatest geological change. Even pure
water will dissolve a minute quantity of the substance of many
rocks. But rain is far from being chemically pure water. In
previous chapters it has been described as taking oxygen and
carbonic acid out of the air in its descent, and abstracting organic
acids and carbonic acid from the soil through which it sinks.
By help of these ingredients, the water is enabled to attack even
the most durable rocks, and to carry some of their dissolved
substance up to the surface of the ground.
v CHEMICAL ACTION .OF SPRINGS 61
One of the substances most readily attacked and removed, even
by pure water, is the mineral known as carbonate of lime. Among
other impurities, natural waters generally contain carbonic acid,
which may be derived from the air or from the soil ; occasionally
from some deeper subterranean source. The presence of this acid
gives the water greatly increased solvent power, enabling it readily
to attack carbonate of lime, whether in the form of limestone,
or diffused through rocks composed mainly of other substances.
Even lime, which is not in the form of carbonate, but is united
with silica in various crystalline minerals (silicates, p. 145), may
by this means be decomposed and combined with carbonic acid.
It is then removed in solution as carbonate. So long as the
water retains enough of free carbonic acid, it can keep the
carbonate of lime in solution and carry it onward.
Limestone is a rock almost entirely composed of carbonate of
lime. It occurs in most parts of the world, covering sometimes
tracts of hundreds or thousands of square miles, and often rising
into groups of hills, or even into ranges of mountains (see
pp. 170, 174). The remarkable solvent action of rain-water on
exposed surfaces of limestone has been already referred to in
Chapter II. The abundance of this rock affords ample opportunity
for the display of similar action on the part of subterranean water.
Continuing the same process of solution which we have seen to
work such changes at the surface, the water trickles down the
vertical joints and along the planes between the limestone beds.
As it flows on, it dissolves and removes the stone, until in the
course of centuries these passages are gradually enlarged into
clefts, tunnels, and caverns. The ground becomes honeycombed
with openings into dark subterranean chambers, and running
streams fall into these openings and continue their course
underground.
Every country which possesses large limestone tracts furnishes
examples of the way in which such labyrinthine tunnels and
systems of caverns are excavated. In England, for example, the
Peak Cavern of Derbyshire is believed to be 2300 feet long, and
in some places 120 feet high. On a much more magnificent
scale are the caverns of Adelsberg near Trieste, which have been
explored to a distance of between four and five miles, but are
probably still more extensive. The river Poik has broken into
one part of the labyrinth of chambers, through which it rushes
before emerging again to the light. Narrow tunnels expand into
spacious halls, beyond which egress is again afforded by low
62
RECORDS LEFT BY SPRINGS
CHAP.
passages into other lofty recesses. The most stupendous chamber
measures 669 feet in length, 630 feet in breadth, and 1 1 1 feet in
height. From the roofs hang pendent white stalactites (p. 64),
which, uniting with the floor, form pillars showing endless varieties
of form and size (Fig. 25). Still more gigantic is the system of
subterranean passages in the Mammoth Cave of Kentucky, the
accessible parts of which are believed to have a combined length
of about 150 miles. The largest cavern in this vast labyrinth
has an area of two acres, and is covered by a vault 125 feet high.
Of the mineral matter dissolved by permeating water out of
the rocks ' underground, by far the larger part is discharged by
springs into rivers, and ultimately finds its way to the sea. The
MSW^^FwRi
FIG. 25. Section of cavern with stalactites and stalagmite.
total amount of material thus supplied to the sea every year must
be enormous. Much of it, indeed, is abstracted from ocean-water
by the numerous tribes of marine plants and animals. In par-
ticular, the lime, silica, and organic matter are readily seized
upon to build up the framework and furnish the food of these
creatures. But probably more mineral matter is supplied in
solution than is required by the organisms of the sea, in which
case the water of the sea must be gradually growing heavier and
'salter.
(b) Deposition. But it is the smaller proportion of the
material not conveyed into the sea that specially demands attention.
Every spring, even the purest and most transparent, contains
mineral solutions in sufficient quantity to be detected by chemical
analysis. Hence all plants and animals that drink the water of
springs and rivers necessarily imbibe these solutions which,
indeed, supply some of the mineral salts whereof the harder
v CALCAREOUS SPRINGS 63
parts both of plants and animals are constructed. Many springs,
however, contain so large a proportion of mineral matter, that
when they reach the surface and begin to evaporate, they drop
their solutions as a precipitate, which settles down upon the
bottom or on objects within reach of the water. After years of
undisturbed continuance, extensive sheets of mineral material
may in this manner be accumulated, which remain as enduring
monuments of the work of underground water, even long after
the springs that formed them may have ceased to flow.
Calcareous Springs. Among the accumulations of this nature
by far the most frequent and important are those formed by what
are called Calcareous Springs. In regions abounding in lime-
stone or rocks containing much carbonate of lime, the subterranean
waters which, as we have seen, gradually erode such vast systems
of tunnels, clefts, and caverns, carry away the dissolved rock, and
retain it in solution only so long as they can keep their carbonic
acid. As soon as they begin to evaporate and to lose some of
this acid, they lose also the power of retaining so much carbonate
of lime in solution. This substance is accordingly dropped as a
fine white precipitate, which gathers on the surfaces over which
the water trickles or flows.
The most familiar example of this process is to be seen under
the arches of bridges and vaults. Long pendent white stalks or
stalactites hang from between the joints of the masonry, while
wavy ribs of the same substance run down the piers or walls, and
even collect upon the ground (stalagmite). A few years may
suffice to drape an archway with a kind of fringe of these pencil-
like icicles of stone. Percolating from above through the joints
between the stones of the masonry, the rain-water, armed with its
minute proportion of carbonic acid at once attacks the lime of
the mortar and forms carbonate of lime, which is carried down-
ward in solution. Arriving at the surface of the -arch, the water
gathers into a drop, which remains hanging there for a brief
interval before it falls to the ground. That interval suffices to
allow some of the carbonic acid to escape, and some of the water
to evaporate. Consequently, round the outer rim of the drop a
slight precipitation of white chalky carbonate of lime takes place.
This circular pellicle, after the drop falls, is increased by a similar
deposit from the next drop, and thus drop by drop the original
rim or ring is gradually lengthened into a tube which may
eventually be filled up inside, and may be thickened irregularly
outside by the trickle of calcareous water (Fig. 26). But the
6 4
RECORDS LEFT BY SPRINGS
CHAP.
deposition on the roof does not exhaust the stock of dissolved
carbonate. When the drops reach the ground the same process
of evaporation and precipitation continues. Little mounds of the
same white substance are built up on the floor, and, if the place
remain undisturbed, may grow until they unite
with the stalactites from the roof, forming
white pillars that reach from floor to ceiling
(Fig. 25, and p. 170).
It is in limestone caverns that stalactitic
growth is seen on the most colossal scale.
These quiet recesses having remained undis-
turbed for many ages, the process of solu-
tion and precipitation has advanced without
interruption until, in many cases, vast caverns
have been transformed into grottoes of the
most marvellous beauty. White glistening
fringes and curtains of crystalline carbonate
of lime, or spar, as it is popularly called,
hang in endless variety and beauty of form
from the roof. Pillars of every dimension,
from slender wands up to thick-ribbed
columns like those of a cathedral, connect
the roof and the pavement. The walls, pro-
jecting in massive buttresses and retiring into
alcoves, are everywhere festooned with a
grotesque drapery of stone. The floor is
crowded with mounds and bosses of strangely
imitative forms which recall some of the
FIG. 2 6.-Section show- oddest shapes above -ground. Wandering
ing successive layers of
growth in a stalactite, through such a scene, the visitor somehow
feels himself to be in another world, where
much of the architecture and ornament belongs to styles utterly
unlike those which can be seen anywhere else.
The material composing stalactite and stalagmite is at first, as
already stated, a fine white chalky pulp-like substance which dries
into a white powder. But as the deposition continues, the older
layers, being impregnated with calcareous water, receive a
precipitation of carbonate of lime between their minute pores and
crevices, and assume a crystalline structure. Solidifying and
hardening by degrees, they end by becoming a compact crystalline
stone (spar) which rings under the hammer.
The numerous caverns of limestone districts have offered
v CALCAREOUS DEPOSITS 65
ready shelter to various kinds of wild animals and to man himself.
Some of them {Bone-Caves} have been hyaena-dens, and from
under their hard floor of stalagmite the bones of hyaenas and
of the creatures they fed upon are disinterred in abundance.
Rude human implements have likewise been obtained from the
same deposits, showing that man was contemporary with animals
which have long been extinct. The solvent action of underground
water has thus been of the utmost service in geological history,
first, in forming caverns that could be used as retreats, and then
in providing a hard incrustation which should effectually seal up
and preserve the relics of the denizens left upon the cavern-floors.
Calcareous springs, issuing from limestone or other rock
abounding in lime, deposit carbonate of lime as a white pre-
cipitate. So large is the proportion of mineral contained by
some waters that thick and extensive accumulations of it have
been formed. The substance thus deposited is known by the
name of Calcareous Tufa^ Calc-sinter, or Travertine. It varies
in texture, some kinds being loose and crumbling, others hard and
crystalline. In many places it is composed of thin layers or
laminae, of which sixty may be counted in the thickness of an
inch, but bound together into a solid stone. These laminae mark
the successive layers of deposit. They are formed parallel to the
surface over which the water flows or trickles, hence they may be
observed not only on the flat bottoms of the pools, but irregularly
enveloping the walls of the channel as far up as the dash of water
or spray can reach. Rounded bosses may thus be formed above
the level of the stream, and the recesses may be hung with
stalactites.
The calcareous springs of Northern and Central Italy have
long been noted for the large amount of their dissolved lime, the
rapidity with which it is deposited, and the extensive masses in
which it has accumulated. Thus at San Filippo in Tuscany, it is
deposited in places at the rate of one foot in four months, and it
has been piled up to a depth of at least 250 feet, forming a hill a
mile and a quarter long, and a third of a mile broad. So com-
pact are many of the Italian travertines that they have from time
immemorial been extensively used as a building stone, which can
be dressed and is remarkably durable. Many of the finest build-
ings of ancient and modern Rome have been constructed of
travertine.
A familiar feature of many calcareous springs deserves notice
here. The precipitation of calc-sinter is not always due merely
F
66 RECORDS LEFT BY SPRINGS CHAP.
to evaporation. In many cases, where the proportion of carbonate
of lime in solution is so small that under ordinary circumstances
no precipitation of it would take place, large masses of it have
been deposited in a peculiar fibrous form. On examination, this
precipitation will be found to be caused by the action of plants,
particularly bog-mosses which, decomposing the carbonic acid in
the water, cause the lime-carbonate to be deposited along their
stems and leaflets. The plants are thus incrusted with sinter
which, preserving their forms, looks as if it were composed of
heaps of moss turned into stone. Hence the name of petrifying
springs often given to waters where this process is to be seen.
FIG. 27. Travertine with impressions of leaves.
There is, however, no true petrifaction or conversion of the actual
substance of the plants into stone. The fibres are merely
incrusted with travertine, inside of which they eventually die and
decay. But as the plants continue to grow outward, they increase
the sinter by fresh layers, while the inner and dead parts of the
mass are filled up and solidified by the deposit of the precipitate
within their cavities.
A growing accumulation of travertine presents a special
interest to the geologist from the fact that it offers exceptional
facilities for the preservation of remains of the plants and animals
of the neighbourhood. Leaves from the surrounding trees and
shrubs are blown into pools or fall upon moist surfaces where the
v CHALYBEATE AND SILICEOUS SPRINGS 67
precipitation of lime is actively going on (Fig. 27). Dead insects,
snail-shells, birds, small mammals, and other denizens of the dis-
trict may fall or be carried into similar positions. These remains
may be rapidly enclosed within the stony substance before they
have time to decay, and even if they should afterwards moulder
into dust, the sinter enclosing them retains the mould of their
forms, and thus preserves for an indefinite period the record of
their former existence.
Chalybeate Springs. A second but less abundant deposit from
springs is found in regions where the rocks below-ground contain
decomposing sulphide of iron (p. i 5 3). Water percolating through
such rocks and oxidising the sulphur of that mineral, forms sulphate
of iron (ferrous sulphate), which it removes in solution. The
presence of any notable quantity of this sulphate is at once
revealed by the marked inky taste of the water and by the
yellowish-brown precipitate of ochre on the sides and bottom of the
channel. Such water is termed Chalybeate. When it mixes with
other water containing dissolved carbonates (which are so generally
present in running water), the sulphate is decomposed, the
sulphuric acid passing over to the lime or alkali of the carbonate,
while the iron takes up oxygen and falls to the bottom as a
yellowish-brown precipitate (limonite, p. 143). This interchange
of combinations, with the consequent precipitation of iron-oxide,
may continue for a considerable distance from the outflow of the
chalybeate water. Nearest the source the deposit of hydrated
ferric oxide or ochre is thickest. It encloses leaves, stems, and
other organic remains, and preserves moulds or casts of their
forms. It also cements the loose sand and shingle of a river-
bottom into solid rock.
Siliceous Springs. One other deposit from spring- water may
be enumerated here. In volcanic regions, hot springs (geysers)
rise to the surface which, besides other mineral ingredients, con-
tain a considerable proportion of silica (p. 130). This substance
is deposited as Siliceous Sinter round the vents whence the water
is discharged, where it forms a white stone rising into mounds
and terraces with fringes and bunches of coral-lihe growth.
Where many springs have risen in the same district, their respect-
ive sheets of sinter may unite, and thus extensive tracts are buried
under the deposit. In Iceland, for example, one of the sheets is
said to be two leagues long, a quarter of a league wide, and a
hundred feet thick. In the Yellowstone Park of North America,
many valleys are floored over with heaps of sinter, and in New
68 RECORDS LEFT BY SPRINGS CHAP, v
Zealand other extensive accumulations of the same material have
been formed. It is obvious that, like travertine, siliceous sinter
may readily entomb and preserve a record of the plants and
animals that lived at the time of its deposition.
Summary. The underground circulation of water produces
changes that leave durable records in geological history. These
changes are of two kinds, (i) Landslips are caused, by which
the forms of cliffs, hills, and mountains are permanently altered.
Vast labyrinths of subterranean tunnels, galleries, and caverns are
dissolved out of calcareous rocks, and openings are made from
these passages up to the surface, whereby rivers are engulfed.
Many of the caves thus hollowed out have served as dens of wild
beasts, and dwelling-places for man, and the relics of these inhabit-
ants have been preserved under the stalagmite of the floors. (2)
An enormous quantity of mineral matter is brought up to the
surface by springs. Most of the solutions are conveyed ulti-
mately to the sea, where they partly supply the substances required
by the teeming population of marine plants and animals. But,
under favourable circumstances, considerable deposits of mineral
matter are made by springs, more especially in the form of traver-
tine, siliceous sinter, and ochre. In these deposits the remains
of terrestrial vegetation, also of insects, birds, mammals, and
other animals, are not infrequently preserved, and remain as per-
manent memorials of the life of the time when they flourished.
CHAPTER VI
ICE-RECORDS
ICE in various ways alters the surface of the land. By disinte-
grating and eroding even the most durable rocks, and by removing
loose materials and piling them up elsewhere, it greatly modifies
the details of a landscape. As it assumes various forms, so it
accomplishes its work with considerable diversity. The action of
frost upon soil and bare surfaces of rock has already (p. 13) been
described. We have now to consider the action of frozen rivers
and lakes, snow and glaciers, which have each their own char-
acteristic style of operation, and leave behind them their distinctive
contribution to the geological history of the earth.
Frozen Rivers and Lakes. In countries with a severe winter
climate, the rivers and lakes are frozen over, and the cake of ice
that covers them may be more than two feet thick. When this cake
is broken up in early summer, large masses of it are driven ashore,
tearing up the littoral boulders, gravel, sand, or mud, and pushing
them to a height of many feet above the ordinary level of the water.
When the ice melts, huge heaps of detritus are found to have been
piled up by it x which may long remain as monuments of its power.
Not only so, but large fragments of the ice that has been formed
along shore and has enclosed blocks of stone, gravel, and sand,
are driven away and may travel many miles before they melt and
drop their freight of stones. On the St. Lawrence and on the
coast of Labrador, there is a constant transportation of boulders
by this means. Further, besides freezing over the surface, the
water not infrequently forms a loose spongy kind of ice on the
bottom (Anchor-ice, Ground-ice) which encloses stones and gravel,
and carries them up to the surface where it joins the cake of ice
there. This bottom-ice is formed abundantly on some parts of
the Canadian rivers. Swept down by the current, it accumulates
69
70 ICE-RECORDS CHAP.
against the bars or banks, or is pushed over the upper ice, and
from time to time gathers into temporary barriers, the bursting of
which may cause destructive floods. In the river St. Lawrence,
banks and islets have been to a large extent worn down by the
grating of successive ice-rafts upon them.
Snow. On level or gently inclined ground, whence snow dis-
appears merely by melting or evaporation, it exercises, while it
remains, a protective influence upon the soil and vegetation,
shielding them from the action of frost. On slopes of suffi-
cient declivity, however, the sheet of snow acquires a tendency to
descend by gravitation, as we may often see on house-roofs in winter.
In many cases, it creeps or slides down the sides of a hill or valley,
and in so doing pushes forward any loose material that may lie on
the surface. By this means, in exposed situations, vegetation, soil,
subsoil, stones, and loose objects are gradually thrust down-hill, so
as to bare the rock for further disintegration. But where the
declivities are steep enough to allow the snow to break off in
large sheets and to rush rapidly down, the most striking changes
are observable. Such descending masses are known as Ava-
lanches. Varying from 10 to 50 feet or more in thickness and
several hundred yards broad and long, they sweep down the
mountain sides with terrific force, carrying away trees, soil, houses,
and even large blocks of rock. The winter of 1884-85 was
especially remarkable for the number of avalanches in the valleys
of the Alps, and for the enormous loss of life and property which
they caused. In such mountain ground, not only are declivities
bared of their trees, soil, and boulders, but huge mounds of debris
are piled up in the valleys below. Frequently, also, such a
quantity of snow, ice, and rubbish is thrown across the course of
a stream as to dam back the water, which accumulates until it
overflows or sweeps away the barrier. In another but indirect
way, snow may powerfully affect the surface of a district where,
by rapid melting, it so swells the rivers as to give rise to destruc-
tive floods.
While, therefore, the influence of snow is on the whole to
protect the surface of the land, it shows itself in mountainous
regions singularly destructive, and leaves, as chief memorials of
this destructiveness, the mounds and rough heaps of earth and
stones that mark where the down-rushing avalanches have come
to rest.
Glaciers and Ice-Sheets leave their record in characters so
distinct as not to be easily confounded with those of any other
vi TRANSPORT BY GLACIERS 71
kind of geological agent. The changes which they produce
on the surface of the land may be divided into two parts : (i) the
transport of materials from high ground to lower levels, and (2)
the erosion of their beds.
(i) Transport. As a glacier descends its valley, it receives
upon its surface the earth, sand, mud, gravel, boulders, and masses
of rock that roll or are washed down from the slopes on either
side. Most of this rubbish accumulates on the edges of the
glacier, where it is slowly borne to lower levels as the ice creeps
downwards. But some of it falls into the crevasses or rents by
FIG. 28. Glacier with medial and lateral moraines.
which the ice is split, and may either be imprisoned within the
glacier, or may reach the rocky floor over which the ice is sliding.
The rubbish borne onward upon the surface of the glacier is known
as moraine-stuff ($'vg. 28). The mounds of it running along each
side of the glacier form lateral moraines, those on the right-hand
side as we look down the length of the valley being the right latera^
moraine, those on the other side the left lateral moraine. Where
two glaciers unite, the left lateral moraine of the one joins the
right lateral moraine of the other, forming what is called a medial
moraine that runs down the middle of the united glacier. Where
a glacier has many tributaries bearing much moraine- stuff, its
72 ICE-RECORDS CHAP.
surface may be like a bare plain covered with earth and stones,
so that, except where a yawning crevasse reveals the clear blue
gleam of the ice below, nothing but earth and stones meets the
eye. When the glacier melts, the detritus is thrown in heaps upon
the valley, forming there the terminal moraine.
Glaciers, like rivers, are subject to variations of level. Even
from year to year they slowly sink below their previous limit or
rise above it. The glacier of La Brenva, for example, on the
Italian side of Mont Blanc, subsided no less than 300 feet in the
first half of the nineteenth century. One notable consequence of
such diminution is that the blocks of rock lying on the edges of a
glacier are stranded on the side of the valley, as the ice shrinks
FIG. 29. Perched blocks scattered over ice-worn surface of rock.
away from them. Such Perched Blocks or Erratics (Figs. 29, 30),
as they are called, afford an excellent means of noting how much
higher and longer a glacier has once been than it is now. Their
great size (some of them are as large as good-sized cottages) and
their peculiar positions make it quite certain that they could not
have been transported by any current of water. They are often
poised on the tops of crags, on the very edges of precipices, or
on steep slopes where they could never have been left by any
flood, even had the flood been capable of moving them. The
agent that deposited them in such positions must have been one
that acted very quietly and slowly, letting the blocks gently sink
into the sites they now occupy. The only agent known to us
that could have done this is glacier-ice. We can actually see
similar blocks on the glaciers now, and others which have only
VI
ERRATIC BLOCKS
73
recently been stranded on the side of a valley from which the ice
has sunk. In the Swiss valleys, the scattered ice-borne boulders
may be observed by hundreds, far above the existing level of the
glaciers and many miles beyond where these now end. If the
origin of the dispersed erratics is self-evident in a valley where a
glacier is still busy transporting them, those that occur in valleys
which are now destitute of glaciers can offer no difficulty ; they
1 ^^^a
FIG. 30. Glacier-borne block of granite resting on red sandstone,
(^nrrif T1*a of Arran ^^rvl-lonrl
Corrie, Isle of Arran, Scotland.
become, indeed, striking monuments that glaciers once existed
there.
Scattered erratic blocks offer much interesting evidence of the
movements of the ice by which they were transported. In a
glacier-valley, the blocks that fall upon the ice remain on the side
from which they have descended. Hence, if there is any notable
difference between the rocks of the two sides, this difference will
be recognisable in the composition of the moraines, and will
remain distinct even to the end of the glacier. If, therefore, in a
district from which the glaciers have disappeared, we can trace
74
ICE-RECORDS
CHAP.
up the scattered blocks to their sources among the mountains, we
thereby obtain evidence of the actual track followed by the vanished
glaciers. The limits to which these blocks are traceable do not,
of course, absolutely fix the limits of the ice that transported them.
They prove, however, that the ice extended at least as far as they
occur, but it may obviously have risen higher and advanced farther
than the space within which the blocks are now confined. In
Europe, some striking examples occur of the use of this kind of
evidence. Thus the peculiar blocks of the Valais can be traced
all the way to the site of the modern city of Lyons. There can
therefore be no doubt that the glacier of the Rhone once extended
FIG. 31. Front of Muir Glacier, Alaska, in June 1899, *hc ice-cliff is from 200 to 300 feet
high. Photograph by Mr. G. K. Gilbert, U.S. Geol. Survey.
over all that intervening country and reached at least as far as
Lyons, a distance of not less than 170 miles from where it now
ends. Again, from the occurrence of blocks of some of the char-
acteristic rocks of Southern Scandinavia, in Northern Germany,
Belgium, and the east of England, we learn that a great sheet ot
ice once filled up the bed of the Baltic and the North Sea, carrying
with it immense numbers of northern erratics. In Britain, where
there are now neither glaciers nor snow-fields, the abundant dis-
persion of boulders from the chief tracts of high ground shows
that this country was once in large part buried under ice. In
the northern United States and in Canada, similar proofs remain
of the former extension of great sheets of ice that moved south-
ward beyond where the city of New York now stands. The
aspect of these regions must have closely resembled that of Alaska
vi ROCK-STRIATION BY ICE 75
and Greenland at the present time (Fig. 31). The evidence for
these statements will be more fully given in* a later part of this
Volume (Chapter XXVI I.).
Besides the moraine-stuff carried along on the surface, abundant
loose detritus and blocks of rock are pushed onwards under the
ice, and sometimes enclosed within its mass. The great Green-
land glaciers or ice-sheet include much detritus in their lower
portions. When a glacier retires, this earthy and stony debris,
where not swept away by the escaping -river, is left on the floor of
the valley. One remarkable feature of the stones in it is that a
large proportion of them are smoothed, polished, and covered
FIG. 32. Stone from the Boulder-clay of Central Scotland, which has been
smoothed and striated under an ice-sheet.
with fine scratches or ruts, such as would be made by hard sharp-
pointed fragments of stone or grains of sand. These markings
run for the most part along the length of each oblong stone, but
not infrequently cross each other, and sometimes an older may be
noticed partially effaced by a newer set. This peculiar striation
is a most characteristic mark of the action of glaciers. The
stones under the ice are fixed in the line of least resistance that
is, end on. In this position, under the weight of hundreds of feet
of ice, they are pressed upon the floor over which the glacier is
travelling. Every sharp edge of stone or grain of sand, driven
along the surface of a block, or over which the block itself is
slowly drawn, engraves a fine scratch or a deeper rut (Fig. 32).
As the block moves onward, it is more and more scratched,
losing its corners and edges, and becoming smaller and smoother
till, if it travel far enough, it may be entirely ground into sand
or mud.
7 6
ICE-RECORDS
CHAP.
(2) Erosion. The same process of erosion is carried on
upon the solid rocks over which the ice moves. These are
smoothed, striated, and polished by the friction of the grains of
sand, pebbles, and blocks of stone crushed against them by the
slowly creeping mass of ice. Every boss of rock that looks toward
the quarter from which the overlying ice is moving is ground
away, while those that face to the opposite side, being more or
less protected, remain comparatively sharp and unworn. The
FIG. 33. Ice-striation on the floor and side of a valley.
polish and striation are especially noteworthy. From the fine
scratches, such as are made by grains of sand, up to deep flutings
or ruts like those of cart-wheels in unmended roadways, or to still
wider and deeper hollows, all the friction-markings run on smoothed
and polished surfaces, in a general uniform direction, which is
that of the motion of the glacier. The degree of polish of the
surface and the delicacy of the striae and flutings depend in great
measure upon the texture of the stone over which the ice has
moved. Hard close-grained rocks like limestone have received
and retained their ice-worn surface with such perfection that they
sometimes look like sheets of artificially polished marble. Such
vi ROCK-STRIATION BY ICE 77
striated surfaces could only be produced by some agent possessing
rigidity enough to hold the sand-grains and stones in position, and
press them steadily onward upon the rocks. A river polishes the
rocks of its channel by driving shingle and sand across them ;
but the currents are perpetually tossing these materials now to
one side, now to another, so that smoothed and polished surfaces
are produced, but with nothing at all resembling striation. A
glacier, however, by keeping its grinding materials fixed in the
bottom of the ice, engraves its characteristic parallel striae and
groovings, as it slowly creeps down the valley. All the surfaces
of rock within reach of the ice are smoothed, polished, and
striated. Such surfaces present the most unmistakable evidence
of glacier-action, for they can be produced by no other known
natural agency. Hence, where they occur in glacier valleys, far
above and beyond the present limits of the ice, they prove how
greatly the ice has sunk. In regions also where there are now
no glaciers, these rock-markings remain as almost imperishable
witnesses that glaciers once existed. By means of their evidence,
for example, we can trace the march of great ice-sheets which
once enveloped the whole of Scandinavia, lay deep upon nearly
the whole of Britain, and moved across thousands of square miles
in North America.
The river that escapes from the end of a glacier is always
milky or muddy. The fine sand and mud that discolour the
water are not supplied by the thawing of the clear ice, nor by the
sparkling brooks that gush out of the mountain-slopes, nor by the
melting of the snows among the peaks that rise on either side.
This material can only come from the rocky floor of the glacier
itself. It is the fine sediment ground away from the rocks and
loose stones by their mutual friction under the pressure of the
overlying ice. This " flour of rocks " serves thus as. a kind of index
or measure of the amount of material worn off the rocky bed by
the grinding action of the glacier. We can readily see that as
this erosion and transport are continually in progress, the amount
of material removed in the course of time must be very great. It
has been estimated, for example, that the Justedal glacier in
Norway removes annually from its bed 2,427,000 cubic feet of
sediment. At this rate the amount removed in a century would be
enough to fill up a valley or ravine 10 miles long, 100 feet broad,
and 40 feet deep.
Reference may here be made to an interesting form of erosion
which takes place on the rocky floor of a glacier, not by the action
78 ICE-RECORDS CHAP.
of the ice but by that of running water. The surface of a glacier
thaws under the sun's rays, and streams of water are consequently
produced, which course over the ice and often fall down crevasses,
bearing with them the sand, gravel, and stones which they have
swept off the moraine-loaded ice. When one of these cascades
falls for a time on a particular part of the floor it uses the
detritus to excavate a pot-hole in the rock. Such excavations
are not infrequent in glaciated countries which have long been
free from ice. They are known as "giants' kettles" and "moulin
pot-holes" (Fig. 34).
In arctic and antarctic latitudes, where the land is buried under
FIG. 34. " Moulin pot-holes" in granite, High Sierra, California. Photograph by
Mr. H. W. Turner, U.S. Geol. Survey.
a vast ice-sheet, which is continually creeping seaward and break-
ing off into huge masses that float away as icebergs, there must
be a constant erosion of the terrestrial surface. Were the ice to
retire from these regions, the ground would be found to wear
a glaciated surface (Figs. 29, 32, 33) ; that is to say, all the bare-
rocks would present a characteristic ice-worn aspect, rising into
smooth rounded bosses like dolphins' backs (roches moutonnees),
and sinking into hollows that would become lake-basins. Every-
where these bare rocks would show the striae and groovings graven
upon them by the ice, radiating generally from the central high
grounds, and thus indicating the direction of flow of the main
streams of the ice-sheet. Piles of earth, ice-polished stones, and
blocks of rock would be found strewn over the country, especially
in the valleys and over the plains. These materials would still
vi SUMMARY 79
further illustrate the movements of the ice, for they would be
found to be singularly local in character^ each district having
supplied its own contribution of detritus. Thus from a region of
red sandstone, the rubbish would be red and sandy ; from one of
black slate, it would be black and clayey (see Chapter XXVI.).
Summary. In this chapter we have seen that Ice in various
ways affects the surface of the land and leaves its mark there.
Frost, as already explained in Chapter II., pulverises soil, dis-
integrates exposed surfaces of stone, and splits open bare rocks
along their lines of natural joint. On frozen rivers and lakes, the
disrupted ice wears down banks and pushes up mounds of sand,
gravel, and boulders along the shores. Snow lying on the surface
of the land protects that surface from the action of frost and air.
In the condition of avalanches, snow causes large quantities of
earth, soil, and blocks of rock to be removed from the mountain-
slopes and piled up on the valleys. In the form of glaciers, ice
transports the debris of the mountains to lower levels, bearing
along and sometimes stranding masses of rock as large as
cottages, which no other known natural agent could transport.
Moving down a valley, a glacier wears away the rocks, giving
them a peculiar smoothed and striated surface which is thoroughly
characteristic. By this grinding action, it erodes its bed and
produces a large amount of fine sediment, which is carried away
by the river that escapes at the end of the ice-stream. Land-ice
thus leaves thoroughly distinctive and enduring memorials of its
presence in polished and grooved rocks, in masses of earth, clay,
or gravel, with striated stones, and in the dispersal of erratic
blocks from the principal masses of high ground. These memorials
may remain for ages after the ice itself has vanished. By their
evidence we know that the present glaciers of the Alps are only a
shrunk remnant of the great ice-fields which once covered that
region ; that the Scandinavian glaciers swept across what is now
the bed of the North Sea as far as the mouth of the Thames ;
that Scotland, Ireland, Wales, and the greater part of England
were buried under great sheets of ice which crept downwards
into the North Sea on the one side, and into the Atlantic on the
other, and that Canada and the northern United States were over-
spread with ice as far south as Pennsylvania (Chapter XXVII.).
CHAPTER VII
THE MEMORIALS OF THE PRESENCE OF THE SEA
WE have now to inquire how the work of the Sea is registered in
geological history. This work is broadly of two kinds. In the
first place, the sea is engaged in wearing away the edges of the
land, and in the second place, being the great receptacle into which
all the materials, worn away from the land, are transported, it
arranges these materials over its floor, ready to be raised again
into land at some future time.
i. Demolition of the Land. In its work of destruction along
the coasts of the land, the sea acts to some extent (though we do
not yet know how far) by chemically dissolving the rocks and
sediments which it covers. Cast-iron bars, for example, have been
found to be so corroded by sea-water as to lose nearly half their
strength in fifty years. Doubtless many minerals and rocks are
liable to similar attacks.
But it is by its mechanical effects that the sea accomplishes
most of its erosion. The mere weight with which ocean-waves
fall upon exposed coasts breaks off fragments of rock from cliffs.
Masses, 1 3 tons in weight, have been known to be quarried out of
the solid rock by the force of the breakers in Shetland, at a height
of 70 feet above sea-level. As a wave may fall with a blow equal
to a pressure of 3 tons on the square foot, it compresses the air in
every cleft and cranny of a cliff, and when it drops it allows the
air instantly to expand again. By this alternate compression and
expansion, portions of the cliff are loosened and removed. Where
there is any weaker part in the rock, a long tunnel may be exca-
vated, which may even be drilled through to the daylight above,
forming an opening at some distance inland from the edge of the
cliff. During storms, the breakers rush through such a tunnel, and
spout forth from the opening (or blow-hole) in clouds of spray
(Fig. 35).
80
CHAP, vii ACTION OF BREAKERS 81
Probably the most effective part of the destructive action of the
sea is to be found in the battery of gravel, shingle, and loose blocks
of stone which the waves discharge against cliffs exposed to their
fury. These loose materials, caught up by the advancing breakers
and thrown with great force upon the rocks of a coast-line, are
dragged back in the recoil of the water, but only to be again lifted
and swung forward. In this loud turmoil, the loose stones are
reduced in size and are ground smooth by friction against each
FIG. 35. Buller of Buchan a caldron-shaped cavity or blow-hole worn out of granite
by the sea on the coast of Aberdeenshire.
other and upon the solid cliff. The well-rounded and polished
aspect of the gravel on such storm-beaten shores is an eloquent
testimony to the work of the waves. But still more striking,
because more measurable, is the proof that the very cliffs them-
selves cannot resist the blows dealt upon them by the wave-borne
stones. Above the ordinary limit reached by the tides, the rocks
rise with a rough ragged face, bearing the scars inflicted on it by
the ceaseless attacks of the air, rain, frost, and' the other agencies
that waste the surface of the land. But all along the base of the
cliff, within reach of the waves, the rocks have been smoothed and
G
82 MEMORIALS LEFT BY THE SEA CHAP, vn
polished by the ceaseless grinding of the shingle upon them, while
arches, tunnels, solitary pillars, half-tide skerries, creeks, and caves
attest the steady advance of the sea and the gradual demolition of
the shore.
Every rocky coast -line exposed to a tempestuous sea affords
illustrations of these features of the work of waves. Even where
the recks are of the most durable kind, they cannot resist the
ceaseless artillery of the ocean. They are slowly battered down,
and every stage in their demolition may be witnessed, from the
sunken reef, which at some distance from the shore marks where
the coast-line once ran, up to the tunnelled cliff from which a huge
mass was detached during the storms of last winter (Fig. 36). But
where the materials composing the cliffs are more easily removed,
the progress of the waves may be comparatively rapid. Thus on
the east coast of Yorkshire, between Spurn Point and Flamborough
Head, the cliffs consist of boulder-clay, and vary up to more than
100 feet in height. At high water, the tide rises against the base
of these cliffs, and easily scours away the loose debris which would
otherwise gather there and protect them. Hence, within historic
times, a large tract of land, with its parishes, farms, villages, and sea-
ports, has been washed away, the rate of loss being estimated at not
less than 2 \ yards in a year. Since the Roman occupation a strip of
land between 2 and 3 miles broad is believed to have disappeared.
It is evident that to carry on effectively this mechanical erosion,
the sea-water must be in rapid motion. But in the deeper recesses
of the ocean, where there is probably no appreciable movement of
the water, there can hardly be any sensible erosion. In truth, it
is only in the upper parts of the sea which are liable to be affected
by wind, that the conditions for marine erosion can be said to
exist. The space within which these conditions are to be looked
for is that comprised between the lowest depth to which the
influence of waves and marine currents extends, and the greatest
height to which breakers are thrown upon the land. These limits,
no doubt, vary considerably in different regions. In some parts
of the open sea, as off the coast of Florida, the disturbing action
of the waves has been supposed to reach to a depth of 600 feet,
though the average limit is probably greatly less. On exposed
promontories in stormy seas, such as those of the north of Scot-
land, breakers have been known to hurl up stones to a height of
300 feet above sea-level. But probably the zone, within which
the erosive work of the sea is mainly carried on, does not as a
rule exceed 300 feet in vertical range.
84 MEMORIALS LEFT BY THE SEA CHAP.
Within some such limits as these, the sea is engaged in gnaw-
ing away the edges of the land. A little reflection will show us
that, if no counteracting operation should come into play, the pro-
longed erosive action of the waves would reduce the land below
the sea-level. If we suppose the average rate of demolition to be
10 feet in a century, then it would take not less than 52,800 years
to cut away a strip one mile broad from the edge of the land. But
while the sea is slowly eating away the coast-line, the whole surface
of the land is at the same time crumbling down, and the wasted
materials are being carried away by rivers into the sea at such a
rate that, long before the sea could pare away more than a mere
narrow selvage, the whole land might be worn down to the sea-
level by air, rain, and rivers (p. 31).
But there are counteracting influences in nature that would
probably prevent the complete demolition of the land. What
these influences are will be more fully considered in a later chapter.
In the meantime, it will be enough to bear in mind that while the
land is constantly worn down by the forces that are acting upon
FIG. 37. Section of submarine plain. /, Land cut into caves, tunnels, sea-stacks, reefs,
and skerries by the waves, and reduced to a platform below the level of the sea (.$ s) on
which the gravel, sand, and mud (d) produced by the waste of the coast may accumu-
late.
its surface, it is liable from time to time to be uplifted by other
forces acting from below. And the existing relation between the
amount and height of land, and the extent of sea, on the face of
the globe, must be looked upon as the balance between the work-
ing of both these antagonistic classes of agencies.
But without considering for the present whether the results of
the erosion performed by the sea will be interrupted or arrested,
we can readily perceive that their tendency is toward the reduc-
tion of the level of the land to a submarine plain (Fig. 37). As
the waves cut away slice after slice from a coast-line, the portion
of land which they thus overflow, and over which they drive the
shingle to and fro, is worn down until it comes below the lower
limit of breaker-action, where it may be covered up with sand or
vii MARINE DEPOSITS 85
mud. When the abraded land has been reduced to this level, it
reaches a limit where erosion ceases, and where the sea, no longer
able to wear it down further, protects it from injury by other agents
of demolition. This lower limit of destruction on the surface
of the earth has been already referred to as a base-level of erosion.
We see, then, that the goal toward which all the wear and tear
of a coast-line tends, is the formation of a more or less level plat-
form cut out of the land. Yet an attentive study of the process
will convince us that in the production of such a platform the sea
has really had less to do than the atmospheric agents of destruc-
tion. An ordinary sea-cliff is not a vertical wall. In the great
majority of cases it slopes seaward at a steep angle ; but if it had
been formed, and were now being cut away, mainly by the sea,
it ought obviously to have receded fastest where the waves attack
it that is, at its base. In other words, if sea-cliffs retired chiefly
because they are demolished by the sea, they ought to be most
eroded at the bottom, and should therefore be usually overhanging
precipices. That this is not the case shows that some other
agency is concerned, which makes the higher parts of a cliff to
recede faster than those below. This agency can be no other
than that of the atmospheric forces air, frost, rain, and springs.
These cause the face of the cliff to crumble down, detaching mass
after mass, which, piled up below, serve as a breakwater, and
must be broken up and removed by the waves before the solid
cliff behind them can be attacked.
ii. Accumulations formed by the Sea. It is not its erosive
action that constitutes the most important claim of the sea to the
careful study of the geologist. After all, the mere marginal belt
or fringe within which this action is confined forms such a small
fraction of the whole terrestrial area of the globe, that its import-
ance dwindles down when we compare it with the enormously
vaster surface over which the operations of the air, rain, rivers,
springs, and glaciers are displayed. But when we regard the sea
as the receptacle into which all the materials worn off the land
ultimately find their way, we see what a large part it must play in
geological history.
During the second half of the nineteenth century great additions
have been made to our knowledge of the sea-bottom all over the
world. Portions of the deposits accumulating there have been
dredged up even from the deepest abysses, so that it is now
possible to construct charts, showing the general distribution of
materials over the floor of the ocean.
86 MEMORIALS LEFT BY THE SEA CHAP.
Beginning at the shore, let us trace the various types of marine
deposits outward to the floors of the great ocean-abysses. In
many places, the sea is more or less barred back by the accumu-
lation of sediment worn away from the land. In estuaries, for
example, there is often such an amount of mud in the water that
the bottom on either side is gradually raised above the level of tide-
mark, and forms eventually a series of meadows which the sea
can no longer overflow. At the mouths of rivers with a consider-
able current, a check is given to the flow of the water when it
reaches the sea, and "there is a consequent arrest of its detritus.
Hence a bar is formed across the outflow of a river, which during
floods is swept seawards, and during on-shore gales is driven again
inland. Even where there is no large river, the smaller streams
flowing off the surface of a country may carry down sediment
enough to be arrested by the sea, and to be thrown up as a long
bank or bar running parallel with the coast. Behind this bar, the
drainage of the interior accumulates in long lagoons, which find
an outflow through some breach in the bar, or by soaking through
the porous materials of the bar itself. A large part of the eastern
coast of the United States is fringed with such bars and lagoons.
A space several hundred miles long on the east coast of India is
similarly bordered.
But the most remarkable kind of accumulation of terrestrial
detritus in the sea is undoubtedly that of river-deltas. Where the
tidal scour is not too great, the sediment brought down by a large
river into a marine bay or gulf gradually sinks to the bottom, as
the fresh spreads over and mingles with the salt water. During
floods, coarse sediment is swept along, while during low states of
the river nothing but fine mud may be transported. Alternating
sheets of different kinds of sediment are thus laid down one upon
another on the sea-floor, until by degrees they reach the surface,
and thus gradually increase the breadth of the land. Some deltas
are of enormous size and depth. That of the Ganges and Brah-
maputra covers an area of between 50,000 and 60,000 square
miles that is, about as large as England and Wales. It has
been bored through to a depth of 481 feet, and has been found to
consist of numerous alternations of fine clays, marls, and sands or
sandstones, with occasional layers of gravel. In all this great
thickness of sediment, no trace of marine organisms was found,
but land-plants and bones of terrestrial and fluviatile animals
occurred. Lower Egypt has been formed by the growth of the
delta of the Nile, whereby a wide tract of alluvial land has not only
vrr STORM-BEACHES 87
filled up the bottom of the valley, but has advanced into the
Mediterranean.
Turning now to the deposits that are more distinctively those
of the sea itself, we find that ridges of coarse shingle, gravel, and
sand are piled up along the extreme upper limit reached by the
waves. The coarsest materials are for the most part thrown
highest, especially in bays and narrow creeks where the breakers
are confined within converging shores. In such situations, during
heavy gales, storm-beaches of coarse rounded shingle are formed,
sometimes several yards above ordinary high-tide mark (Fig. 38).
FIG. 38. Storm-beach ponding back a stream and forming a lake ; west coast of
Sutherlandshire.
Where a barrier of this kind is thrown across the mouth of a
brook, the fresh water may be ponded back to form a small lake,
of which the outflow usually escapes by percolation through the
shingle. In sheltered bays, behind headlands, or on parts of a
coast-line where tidal currents meet, detritus may accumulate in
spits or bars. Islands have in this way been gradually united to
each other or to the mainland, while the mainland itself has
gained considerably in breadth. At Romney Marsh, on the
south-east coast of England, for instance, a tract of more than 80
square miles, which in Roman times was in great part covered by
the sea at high water, is now dry land, having been gained partly
by the natural increase of shingle thrown up by the waves, and
partly by the barriers artificially erected to exclude the sea.
88 MEMORIALS LEFT BY THE SEA CHAP.
While the coarsest shingle usually accumulates towards the
upper part of the beach, the materials generally arrange them-
selves according to size and weight, becoming on the whole finer
as they are traced towards low-water mark. But patches of
coarse gravel may be noticed on any part of a beach, and large
boulders may be seen even below the limits of the lowest tides.
As a rule, the deposits formed along a beach, and in the sea
immediately beyond, include the coarsest kinds of marine sedi-
ment. They are also marked by frequent alternations of coarse
and fine detritus, these rapid interchanges pointing to the varying
action of the waves and strong shore -currents. Towards the
lower limit of breaker-action, fine gravel and sand are allowed to
settle down, and beyond these, in quiet depths where the bottom
is not disturbed, fine sand and mud washed away from the land
slowly accumulate.
The distance to which the finer detritus of the land is carried
by ocean-currents before it finds its way to the bottom, varies up
to 300 miles or more. Within this belt of sea, the land-derived
materials are distributed over the ocean -floor. Coarse and fine
gravel and sand are the most common materials in the areas
nearest the land. Beyond these lie tracts of fine sand and silt
with occasional patches of gravel. Still farther from the land, at
depths of 600 feet and upwards, fine blue and green muds are
found, composed of minute particles of such minerals as form the
ordinary rocks of the land. But traced out into the open ocean,
these various deposits of recognisable terrestrial origin give place
to thoroughly oceanic accumulations, especially to widespread
sheets of exceedingly fine red and brown clay. This clay, the
most generally diffused deposit of the deeper or abysmal parts of
the sea, appears to be derived from the decomposition of volcanic
fragments either washed away from volcanic islands or supplied
by submarine eruptions. That it is accumulated with extreme
slowness is shown by two curious and interesting kinds of evidence.
Where it occurs farthest removed from land, great numbers of
sharks' teeth, with ear-bones and other bones of whales, have been
dredged up from it, some of these relics being quite fresh, others
partially coated with a crust of brown peroxide of manganese,
while some are wholly and thickly enveloped in this substance.
The same haul of the dredge has brought up bones in all these
conditions, so that they must be lying side by side on the red
clay floor of the ocean abysses. The deposition of manganese is
no doubt an exceedingly slow process, but it is evidently faster
vii ABYSMAL DEPOSITS SUMMARY 89
than the deposition of the red clay. The bones dredged up
probably represent a long succession of generations of animals.
Yet so tardily does the red clay gather over them, that the older
ones are not yet covered up by it, though they have had time to
be deeply encased in oxide of manganese. The second kind of
evidence of the extreme slowness of deposit in the ocean abysses
is supplied by minute spherules of metallic iron, which occurring
in numbers dispersed through the red clay, have been identified
as portions of meteorites or falling stars. These particles no
doubt fall all over the ocean, but it is only where the rate of
deposition of sediment is exceedingly slow that they may be
expected to be detected.
Besides the sediments now enumerated, the bottom of the sea
receives abundant accumulations of the remains of shells, corals,
foraminifera and other marine creatures ; but these will be
described in the next chapter, where an account is given of the
various ways in which plants and animals, both upon the land
and in the sea, inscribe their records in geological history. It
must also be borne in mind that throughout all the sediments of
the sea-floor, from the upper part of the beach down to the
bottom of the deepest and remotest abyss, the remains of the
plants, sponges, corals, shells, fishes and other organisms of the
ocean may be entombed and preserved. It will suffice here to
remember that various depths and regions of the sea have their
own characteristic forms of life, the remains of which are preserved
in the sediments accumulating there, and that although gravel,
sand, and mud laid down beneath the sea may not differ in any
recognisable detail from similar materials deposited in a lake or
river, yet the presence of marine organisms in them would be
enough to prove that they had been formed in the sea. It is
evident, also, that if the sea-floor over a wide area were raised
into land, the extent of the deposits would show that they could
not have been accumulated in any mere river or lake, but must
bear witness to the former presence of the sea itself.
Summary. The sea records its work upon the surface of the
earth in a twofold way. In the first place, in co-operation with
the atmospheric agents of disintegration, it eats away the margin
of the land and planes it down. The final result of this process
if uninterrupted would be to reduce the level of the land to that
of a submarine platform, the position of the surface of which
would be determined by the lower limit of effective breaker-action.
In the second place, the sea gathers over its floor all the detritus
90 MEMORIALS LEFT BY THE SEA CHAP, vn
worn by every agency from the surface of the land. This material
is not distributed at random ; it is assorted and arranged by the
waves and currents, the coarsest portions being laid down nearest
the land, and the finest in stiller and deeper water. The belt of
sea-floor within which this deposition takes place probably does
not much exceed a breadth of 300 miles. Beyond that belt, the
bottom of the ocean is covered to a large extent with a red clay,
probably derived from the decomposition of volcanic material and
laid down with extreme slowness. This deposit and the wide-
spread layer of dead sea- organisms (to be described in next
chapter) are truly oceanic accumulations, recognisably distinct
from those derived from terrestrial sources within the narrow
zone of deposition near the land.
CHAPTER VIII
HOW PLANTS AND ANIMALS INSCRIBE THEIR RECORDS IN
GEOLOGICAL HISTORY
BROADLY considered, there are two distinct ways in which Plants
and Animals leave their mark upon the surface of the earth. In
the first place, they act directly by promoting or arresting the
decay of the land, and by forming out of their own remains
deposits which are sometimes thick and extensive. In the second
place, their remains are transported and entombed in sedimentary
accumulations of many different kinds, and furnish important
evidence as to the conditions under which these accumulations
were formed. Each of these two kinds of memorial deserves our
careful attention, for, taken together, they comprise the most
generally interesting departments of geology, and those in which
the history of the earth is principally discussed. 1
i. Direct action of living things upon the surface of the
globe. This action is often of a destructive kind, both plants
and animals taking their part in promoting the general disintegra-
tion of rocks and soils. Thus, by their decay they furnish to the
soil those organic acids already referred to (pp. 17, 27) as so im-
portant in increasing the solvent power of water, and thereby
promoting the waste of the land. Not only are existing rocks
thus disintegrated, but new rocks are formed out of the materials
removed. The iron, for example, which is abstracted from many
varieties of stone and carried off in solution, is deposited at the
bottom of bogs and lakes as an accumulation of iron-ore, which
is sometimes profitably employed as a source of the metal (ante,
p. 54). By thrusting their roots into crevices of cliffs, plants
1 In the Appendix a Table of the Vegetable and Animal Kingdoms is
given, from which the organic grade of the plants and animals referred to in
this and subsequent chapters may be understood.
91
92 RECORDS OF PLANTS AND ANIMALS CHAP.
loosen and gradually wedge off pieces of rock, and by sending
their roots and rootlets through the soil, they open up the subsoil
to be attacked by air and descending moisture (p. 16). The
action of the common earthworm in bringing up fine soil to be
exposed to the influences of wind and rain was noticed in Chapter
II. (p. 19). Many burrowing animals also, such as the mole and
rabbit, throw up large quantities of soil and subsoil which are
liable to be blown or washed away.
On the other hand, the action may be conservative, as, for
instance, where, by forming a covering of turf, vegetation protects
the soil underneath from being rapidly removed, or where sand-
loving plants bind together the surface of dunes, and thereby
arrest the progress of the sand, or where forests shield a
mountain-side from the effects of heavy rains and descending
avalanches.
(i) Deposits formed of the remains of Plants. But it is chiefly
by the aggregation of their own remains into more or less extensive
deposits that plants and animals leave their most prominent and
enduring memorials. As examples of the way in which this is
done by plants, reference may be made to peat-bogs, mangrove-
swamps, infusorial earth, and calcareous sea-weeds.
Peat-bogs. In temperate and arctic countries, marshy vege-
tation accumulates in peat-bogs, from an acre or two to many
square miles in extent, to a depth of sometimes 50 feet. These
deposits are largely due to the growth of bog-mosses and other
aquatic plants which, dying in their lower parts, continue to grow
upward on the same spot. On flat or gently-inclined moors, in
hollows between hills, on valley-bottoms, and in shallow lakes,
this marshy vegetation accumulates as a wet spongy fibrous mass,
the lower portions of which by degrees become a more or less
compact dark brown or black pulpy substance, wherein the
fibrous texture, so well seen in the upper or younger parts, in
large measure disappears. In a thick bed of peat, it is not
infrequently possible to detect a succession of plant remains,
showing that one kind of vegetation has given place to another
during the accumulation of the mass. In Europe, as already
mentioned (p. 4), peat-bogs often rest directly upon fresh-water
marl containing remains of lacustrine shells (i in Fig. 39). In
every such case, it is evident that the peat has accumulated
on the site of a shallow lake which has been filled up, and
converted into a morass by the growth of marsh-plants along its
edges and over its floor. The lower parts of the peat may contain
viii PEAT, MANGROVE-SWAMPS 93
remains of the reeds, sedges, and other aquatic plants which
choked up the lake (2, 3). Higher up, the peat consists almost
entirely of the matted fibres of different mosses, especially of the'
kind known as Bog-moss or Sphagnum
(4). The uppermost layers (5, 6) may
be full of roots of different heaths which
spread over the surface of the bog.
The rate of growth of peat has been
observed in different situations in Central I
Europe to vary from less than a foot to
about two feet in ten years ; but in
more northern latitudes the growth is
probably slower. Many thousand
square miles of Europe and North FlG . 39< _ Sec tio77a peat-bog.
America are covered with peat -bogs,
those of Ireland being computed to occupy a seventh part of the
surface of the island, or upwards of 4000 square miles.
As the aquatic plants grow from the sides toward the centre
of a shallow lake, they gradually cover over the surface of the
water with a spongy layer of matted vegetation. Animals, and
man himself, venturing on this treacherous surface, sink through
it, and may be drowned in the black peaty mire underneath.
Long afterwards, when the morass has become firm ground, and
openings are made in it for digging out the peat to be used as
fuel, their bodies may be found in an excellent state of preserva-
tion. The peaty water so protects them from decay that the very
skin and hair sometimes remain. In Ireland, numerous skeletons
of the great Irish elk have been obtained from the bogs, though
the animal itself has been extinct since before the beginning of
the authentic history of the country.
Mangrove-swamps. Along the flat shores of tropical lands,
mangrove trees grow out into the salt water, 'forming a belt
of jungle which runs up or completely fills the creeks and bays.
So dense is the vegetation that the sand and mud, washed into
the sea from the land, are arrested among the roots and radicles
of the trees, and thus the sea is gradually replaced by firm ground.
The coast of Florida is fringed with such mangrove-swamps for a
breadth of from 5 to 20 miles. In such regions, not only does
the growth of these swamps add to the breadth of the land, but
the sea is barred back, and prevented from attacking the newly-
formed ground inside.
Infusorial earth. A third kind of vegetable deposit to be
94
RECORDS OF PLANTS AND ANIMALS
CHAP.
referred to here is that known by the names of infusorial earth,
diatom-earth, and tripoli-powder. It consists almost entirely of
the minute frusrules of microscopic plants called diatoms, which
are found abundantly in lakes, and likewise in some regions of the
ocean (Fig. 40). These lowly organisms are remarkable for
secreting silica in their structure. As they die, their singularly
durable siliceous remains fall like a fine dust on the bottom of the
water, and accumulate there as a pale grey or straw-coloured
deposit, which, when dry, is like flour, and in its pure varieties is
made almost entirely of silica (90 to 97 per cent). Underneath
the peat-bogs of Britain a layer of this material is sometimes met
with. One of the most famous examples is that of Richmond,
FIG. 40. Diatom-earth from floor of Antarctic Ocean, magnified 300 diameters
(Challenger Expedition).
Virginia, where a bed of it occurs 30 feet thick. At Bilin in
Bohemia also an important bed has long been known. The
bottom of some parts of the Southern Ocean is covered with a
diatom-ooze made up mainly of siliceous diatoms, but containing
also other siliceous organisms (radiolaria) and calcareous fora-
minifera (Fig. 40).
Accumulations of sea-weeds. Yet one further illustration
of plant-action in the building up of solid rock may be given. As
a rule the plants of the sea form no permanent accumulations,
though here and there under favourable conditions, such as in
bays and estuaries, they may be thrown up and buried under
sand so as eventually to be compressed into a kind of peat. Some
sea-weeds, however, abstract from sea-water carbonate of lime,
which they secrete to such an extent as to form a hard stony
structure, as in the case of the common nullipore. When the
vin NULLIPORE SAND SHELL-BANKS 95
plants die, their remains are thrown ashore and pounded up
by the waves, and being durable they form a white calcareous
sand. By the action of the wind, this sand is blown inland and
may accumulate into dunes. But unlike ordinary sand, it is liable
to be slightly dissolved by rain-water, and as the portion so dis-
solved is soon redeposited by the evaporation of the moisture, the
little sand-grains are cemented together, and a hard crust is formed
which protects the sand underneath from being blown away.
Meanwhile rain-water percolating through the mounds gradually
solidifies them by cementing the particles of sand to each other,
and thick masses of solid white stone are thus produced. Changes
of this kind have taken place on a great scale at Bermuda, where
FIG. 41. Recent limestone (Common Cockle, etc., cemented in a matrix
of broken shells).
all the dry land consists of limestone formed of compacted cal-
careous sand, mainly the detritus of sea-weeds.
(2) Deposits formed of the remains of Animals.- Animals are,
on the whole, far more successful than plants in leaving enduring
memorials of their life and work. They secrete hard outer shells
and internal skeletons endowed with great durability, and capable
of being piled up into thick and extensive deposits which may be
solidified into compact and enduring stone. On land, we have
an example of this kind of accumulation in the lacustrine marl
already (pp. 4, 53, 92) described as formed of the congregated
remains of fresh-water shells.. But it is in the sea that animals,
secreting carbonate of lime, build up thick masses of rock, such as
shell-banks, ooze, and coral reefs (Fig. 41 ; see Chapter XL, p. 1 74).
Shell-banks. Some molluscs, such as the oyster, live in
populous communities upon submarine banks. In the course of
9 6
RECORDS OF PLANTS AND ANIMALS
CHAP.
generations, thick accumulations of their shells are formed on
these banks. By the action of currents also large quantities of
broken shells are drifted to various parts of the sea-bottom not
far from land. Such deposits of shells, in situ or transported,
may be more or less mixed with or buried under sand and silt,
according as the currents vary in direction and force. On the
other hand, they may be gradually cemented into a solid cal-
careous mass, as has been observed off the coast of Florida,
where they form on the sea-bottom a sheet of limestone, made
up of their remains.
Ooze. From observations made during the great expedition
of the Challenger, it has been estimated that in a square mile of
the tropical ocean down to a depth of i oo fathoms there are more
FIG. 42. Globigerina ooze dredged up by Challenger Expedition from a depth
of 1900 fathoms in the North Atlantic (\ 5 -).
than 1 6 tons of carbonate of lime in the form of living animals.
A continual rain of dead calcareous organisms is falling to the
bottom, where their remains accumulate as a soft chalky ooze.
Wide tracts of the ocean-floor are covered with a pale grey ooze
of this nature, composed mainly of the remains of the shells of the
foraminifer Globigerina (Fig. 42). In the north Atlantic this
deposit probably extends not less than 1 300 miles from east to
west, and several hundred miles from north to south.
Here and there, especially among volcanic islands, portions of
the sea-bed have been raised up into land, and masses of modern
limestone have thereby been exposed to view. Though they are
full of the same kind of shells as are still living in the neighbouring
sea, they have been cemented into compact and even somewhat
crystalline rock, which has been eaten into caverns by percolating
vin CORAL-REEFS 97
water, like limestones of much older date. This cementation, as
above remarked, is due to water permeating the stone, dissolving
from its outer parts the calcareous matter of shells, corallines, and
other organic remains, and redepositing it again lower down, so
as to cement the organic detritus into a compact stone.
Coral-reefs offer an impressive example of how extensive
masses of solid rock may be built up entirely of the aggregated
remains of animals. In some of the warmer seas of the globe,
and notably in the track of the great ocean-currents, where marine
life is so abundant, various kinds of coral take root upon the edges
and summits of submerged ridges and peaks, as well as on the
shelving sea-bottom facing continents or encircling islands ( I in
Fig. 43). These creatures do not appear to flourish at a greater
depth than 15 or 20 fathoms, and they are killed by exposure to
FIG. 43. Section of a coral-reef, i. Top of the submarine ridge or bank on which the
corals begin to build. 2. Coral-reef. 3. Talus of large blocks of coral -rock on
which the reef is built outward. 4. Fine coral-sand and mud produced by the
grinding action of the breakers on the edge of the reef. 5. Coral-sand thrown up
by the waves and gradually accumulating above their reach to form dry ground.
sun and air. The vertical space within which they live may there-
fore be stated broadly as about 100 feet. They grow in colonies,
each composed of many individuals, but all united into one mass,
which at first may be merely a little solitary clump on the sea-floor,
but which, as it grows, joins other similar clumps to form what is
known as a reef. Each individual secretes from the sea-water a
hard calcareous skeleton inside its transparent jelly-like body, and
when it dies, this skeleton forms part of the platform upon which
the next generation starts. Thus the reef is gradually built up-
ward as a mass of calcareous rock (2), though only its upper sur-
face is covered with living corals. These creatures continue to
work upward until they reach low-water mark, and then their
further upward progress is checked. But they are still able to
grow outward. On the outer edges of the reef they flourish most
vigorously, for there, amid the play of the breakers, they find the
food that is brought to them by the ocean-currents. From time
H
98 RECORDS OF PLANTS AND ANIMALS CHAP.
to time fragments are torn off by breakers from the reef and roll
down its steep front (3). There, partly by the chemical action of
the sea-water, and partly by the fine calcareous mud and sand (4),
produced by the grinding action of the waves and washed into
their crevices, these loose blocks are cemented into a firm, steep
slope, on the top of which the reef continues to grow outwards.
Blocks of coral and quantities of coral-sand are also thrown up on
the surface of the reef, where by degrees they form a belt of low
land above the reach of the waves (5). On the inside of the reef,
where the corals cannot find the abundant food-supply afforded by
the open water outside, they dwindle and die. Thus the tendency
of all reefs must be to grow seawards, and to increase in breadth.
Perhaps their breadth may afford some indication of their relative
age.
Where a reef has started on a shelving sea-bottom near the
coast of a continent, or round a volcanic island, the space of water
inside is termed the Lagoon Channel. Where the reef has been
built up on some submarine ridge or peak, and there is con-
sequently no land inside, the enclosed space of water is called a
Lagoon, and the circular reef of coral is known as an Atoll. If no
subsidence of the sea-bottom takes place, the maximum thickness
of a reef must be limited by the space within which the corals can
thrive that is, a vertical depth of about i oo feet from the surface
of the sea. But the effect of the destruction of the ocean-front of
the reef, and the piling up of a slope of its fragments on the sea-
bottom outside, will be to furnish a platform of the same materials
on which the reef itself may grow outward, so that the united mass
of calcareous rock may attain a very much greater thickness than
100 feet. On the other hand, if, as Darwin originally suggested,
the sea-bottom were to sink at so slow a rate that the reef-building
corals could keep pace with the subsidence, a thick mass of cal-
careous rock might obviously be formed by them (see p. 123).
It is remarkable how rapidly and completely the structure of
the coral skeleton is effaced from the coral-rock, and a more or
less crystalline and compact texture is put in its place. The
change is brought about partly by the action of both sea-water
and rain-water in dissolving and redepositing carbonate of lime
among the minute interstices of the rock, and partly also by the
abundant mud and sand produced by the pounding action of the
breakers on the reef, and washed into the crevices. On the
portion of a reef laid dry at low water, the coral-rock looks in
many places as solid and old as some of the ancient white lime-
vin ENTOMBMENT OF PLANTS AND ANIMALS 99
stones and marbles of the land. There, in pools where a current
or ripple of water keeps the grains of coral-sand in motion, each
grain may be seen to have taken a spherical form unlike that of
the ordinary irregularly rounded or angular particles. This arises
because carbonate of lime in solution in the water is deposited
round each grain as it moves along. A mass of such grains
aggregated together is called oolite, from its resemblance to fish-
roe. In many limestones, now forming wide tracts of richly culti-
vated country, this oolitic structure is strikingly exhibited. There
can be no doubt that in these cases it was produced in a similar
way to that now in progress on coral-reefs (see pp. 157, 171).
In the coral tracts of the Pacific Ocean there are nearly 300
coral islands, besides extensive reefs round volcanic islands.
Others occur in the Indian Ocean. Coral-reefs abound in the
West Indian Seas, where, on many of the islands, they have been
upraised into dry land, in Cuba to a height of 1 1 oo feet above
sea-level. The Great Barrier Reef that fronts the north-eastern
coast of Australia is 1250 miles long, and from 10 to 90 miles
broad.
There are other ways in which the aggregation of animal
remains forms more or less extensive and durable rocks. To
some of these reference will be made in later chapters. Enough
has been said here to show that by the accumulation of their hard
parts animals leave permanent records of their presence both on
land and in the sea.
ii. Preservation of remains of Plants and Animals in
sedimentary deposits. But it is not only in rocks formed out of
their remains that living things leave their enduring records.
These remains may be preserved in almost every kind of deposit,
under the most wonderful variety of conditions. And as it is in
large measure from their occurrence in such deposits that the
geologist derives the evidence that successive tribes of plants and
animals have peopled the globe, and that the climate and geo-
graphy of the earth have greatly varied at different periods, we
shall find it useful to observe the different ways in which the
remains both of plants and animals are at this moment being
entombed and preserved upon the land and in the sea. With
the knowledge thus gained, it will be easier to understand the
lessons taught by the organic remains that lie among the various
solid rocks around us.
It is evident that in the vast majority of cases, the plants and
animals of the land leave no perceptible trace of their presence.
TOO RECORDS OF PLANTS AND ANIMALS CHAP.
Of the forests that once covered so much of Central and Northern
Europe, which is now cultivated ground, most have disappeared,
and unless authentic history told that they had once flourished, we
should never have known anything about them. There were also
herds of wild oxen, bears, wolves, and other denizens contempor-
aneous with the vanished forests. But they too have passed away,
and we might ransack the soil in vain for any trace of them.
If the remains of terrestrial vegetation and animals are anywhere
preserved it must obviously be only locally, but the exceptionally
favourable circumstances for their preservation, although not every-
where to be found, do present themselves in many places if we seek
for them. The fundamental condition is that the relics should, as
soon as possible after death, be so covered up as to be protected
from the air and from too rapid decomposition. Where this con-
dition is fulfilled, the more durable of them may be preserved for
an indefinite series of ages.
(a) On the Land there are various places where the remains
both of plants and animals are buried and shielded from decay.
To some of these reference has already been made. Thus amid
the fine silt, mud, and marl gathering on the floors of lakes,
leaves, fruits, and branches, or tree -trunks, washed from the
neighbouring shores, may be imbedded, together with insects,
birds, fishes, lizards, frogs, field-mice, rabbits, and other inhabitants.
These remains may of course often decay on the lake-bottom,
but where they sink into or are quickly covered up by the sedi-
ment, they may be effectually preserved from obliteration. They
undergo a change, indeed, being gradually turned into stone, as
will be described in Chapter XV. But this conversion may be
effected so gently as to retain the finest microscopic structures of
the original organisms.
In peat -bogs also, as already stated (p. 93), animals are
often engulfed, and their soft parts are occasionally preserved as
well as their skeletons. The deltas of river-mouths must receive
the remains of many animals swept off by floods. As the
carcases float seawards, they begin to fall to pieces and the
separate bones sink to the bottom, where they are soon buried in
the silt. Among the first bones to separate from the rest of the
skeleton are the lower jaws (pp. 341, 346). We should therefore
expect that in excavations made in a delta these jaw-bones would
occur most frequently. The rest of the skeleton is apt to be
carried farther out to sea before it can find its way to the bottom.
The stalagmite floor of caverns has already been referred to
vin ORGANIC REMAINS ON THE SEA-FLOOR 101
(p. 65) as an admirable material for enclosing and preserving
organic remains. The animals that fell into these recesses, or
used them as dens in which they lived or into which they
dragged their prey, have left their bones on the floors, where,
encased in or covered by solid stalagmite, these relics have
remained for ages. Much of our knowledge of the animals which
inhabited Europe at the time when man appeared, is derived
from the materials disinterred from these Bone-caves. Allusion
has also been made to the travertine formed by mineral-springs
and to the facility with which leaves, shells, insects, and small birds,
reptiles, or mammals may be enclosed and preserved in it (p. 66).
Thus, while the plants and animals of the land for the most
part die and decay into mere mould, there are here and there
localities where their remains are covered up from decay and
preserved as memorials of the life of the time.
(^) On the bottom of the Sea the conditions for the pre-
servation of organic remains are more general and favourable than
on land. Among the sands and gravels of the shore, some of
the stronger shells that live in the shallower waters near land may
be covered up and preserved, though often only in rolled fragments.
It is below tide-mark, however, and more especially beneath the
limit to which the disturbing action of breakers descends, that the
remains of the denizens of the sea are most likely to be buried in
sediment, and to be preserved there as memorials of the life of the
sea. It is evident that hard and therefore durable relics have the
best chance of escaping destruction. Shells, corals, corallines,
spicules of sponges, teeth, vertebrae, and ear-bones of fishes may
be securely entombed in successive layers of silt or mud. But
the vast crowds of marine creatures that have no hard parts must
almost always perish without leaving any trace whatever of their
existence. And even in the case of those which possess hard
shells or skeletons, it will be easily understood that the great
majority of them must be decomposed upon the sea-bottom, their
component elements passing back again into the sea-water from
which they were originally derived. It is only where sediment is
deposited fast enough to cover them up and protect them before
they have time to decay, that they may be expected to be preserved.
In the most favourable circumstances, therefore, only a very
small proportion of the creatures living in the sea at any time
leave a tangible record of their presence in the deposits of the sea-
bottom. It is in the upper waters of the ocean, and especially in
the neighbourhood of land, that life is most abundant. The same
102 RECORDS OF PLANTS AND ANIMALS CHAP, vm
region also is that in which the sediment derived from the waste
of the land is chiefly distributed. Hence it is in these marginal
parts of the ocean that the conditions for preserving memorials of
the animals that inhabit the sea are best developed.
As we recede from the land, the rate of deposit of sediment on
the sea-floor gradually diminishes, until in the central abysses it
reaches that feeble stage so strikingly brought before us by the
evidence of the manganese nodules (p. 88). The larger and
thinner calcareous organisms are attacked by the sea-water and
dissolved, apparently before they can sink to the bottom ; at least
their remains are comparatively rarely found there. It is such
indestructible objects as sharks' teeth and the vertebrae and ear-
bones of whales that form the most conspicuous organic relics in
these abysmal deposits.
Summary. Plants and animals leave their records in geo-
logical history, partly by forming distinct accumulations of their
remains, partly by contributing their remains to be imbedded in
different kinds of deposits both on land and in the sea. As
examples of the first mode, of chronicling their existence, we may
take the growth of marsh -plants in peat-bogs, the spread of
mangrove- swamps along tropical shores, the deposition of
infusorial earth on the bottom of lakes and of the sea ; the
accumulation of nullipore sand into solid stone, the formation of
extensive shell-banks in many seas, the wide diffusion of organic
ooze over the floor of the sea, and the growth of coral reefs. As
illustrations of the second method, we may cite the manner in
which remains of terrestrial plants and animals are preserved
in peat-bogs, in the deltas of rivers, in the stalagmite of caverns,
and in the travertine of springs ; and the way in which the hard
parts of marine creatures are entombed in the sediments of the
sea-floor, more especially along that belt fringing the continents
and islands, where the chief deposit of sediment from the disinte-
gration of the land takes place. Nevertheless, alike on land and
sea, the proportion of organic remains thus sealed up and pre-
served is probably always but an insignificant part of the total
population of plants and animals living at any given moment.
How the remains of plants and animals when once entombed
in sediment are then hardened and petrified, so as to retain their
minute structures, and to be capable of enduring for untold ages,
will be treated of in Chapter XV.
CHAPTER IX
THE RECORDS LEFT BY VOLCANOES AND EARTHQUAKES
THE geological changes described in the foregoing chapters affect
only the surface of the earth. A little reflection will convince us
that they may all be referred to one common source of energy
the sun. It is chiefly to the daily influence of that great centre of
heat and light that we must ascribe the ceaseless movements of
the atmosphere, the phenomena of evaporation and condensation,
the circulation of water over the land, the waves and currents of
the sea, in short the whole complex system which constitutes
what has been called the Life of the Earth. Could this influence
be conceivably withdrawn, the planet would become cold, dark,
silent, lifeless.
But besides the continual transformations of its surface due to
solar energy, our globe possesses distinct energy of its own. Its
movements of rotation and revolution, for example, provide a
vast store of force, whereby many of the most important geological
processes are initiated or modified, as in the phenomena of day
and night and the seasons, with the innumerable meteorological
and other effects that flow therefrom. These movements, though
slowly growing feebler, bear witness to the wonderful vigour of
the earlier phases of the earth's existence. Inside the globe too
lies a vast magazine of planetary energy in the form of an interior
of intensely hot material. The cool outer shell is but an insigni-
ficant part of the total bulk of the globe. To this cool part the
name of " crust " was given at a time when the earth was believed
to consist of an inner molten nucleus enclosed within an outer solid
shell o*r crust (p. 104). The term is now used merely to denote
the cool solid external part of the globe, without implying any
theory as to the nature of the interior.
Condition of the Earth's Interior. It is obvious that we are
103
104 VOLCANOES AND EARTHQUAKES CHAP.
not likely ever to learn by direct observation what may be the
condition of the interior of our planet. The cool solid outer shell
is far too thick to be pierced through by human efforts ; but by
various kinds of observations, more or less probable conclusions
may be drawn with regard to this problem. In the first place, it
has been ascertained that all over the world, wherever borings are
made for water or in mining operations, the temperature increases
in proportion to the depth pierced, and that the average rate of
increase amounts to about one degree Fahrenheit for every 64 feet
of descent. If the rise of temperature continues inward at this
rate, or at any rate at all approaching it, then at a distance from
the surface, which in proportion to the bulk of the whole globe is
comparatively trifling, the heat must be as great as that at which
the ordinary materials of the crust would melt at the surface. In
the second place, thermal springs in all quarters of the globe,
rising sometimes with the temperature of boiling water, and occa-
sionally even still hotter, prove that the interior of the planet must
be very much warmer than its exterior. In the third place,
volcanoes widely distributed over the earth's surface throw out
steam and heated vapours, red-hot stones, and streams of molten
rock.
It is quite certain therefore that the interior of the globe must
be intensely hot ; but whether it is actually molten or solid has
been the subject of prolonged discussion. Three opinions have
found stout defenders, (i) The older geologists maintained that
the phenomena of volcanoes and earthquakes could not be
explained, except on the supposition of a crust only a few miles
thick, enclosing a vast central ocean of molten material. (2) This
view has been opposed by physicists who have shown that the
globe, if this were actually its structure, could not resist the
attraction of sun and moon, but would be drawn out of shape, as
the ocean is in the phenomenon of the tides, and that the absence
of any appreciable tidal deformation in the crust shows that the
earth must be practically solid, and as rigid as a ball of glass, or
of steel. (3) A third opinion has been advanced by some geologists
who, while admitting that the earth behaves on the whole as a
solid rigid body, yet believe that many geological phenomena can
only be explained by the existence of some liquid mass beneath
the crust. Accordingly they suppose that while the nucleus is
retained in the solid state by the enormous superincumbent
pressure under which it lies, and the crust has become solid by
cooling, there is an intermediate liquid or viscous layer which has
ix NATURE OF VOLCANOES 105
not yet cooled sufficiently to pass into the solid crust above, and
does not lie under sufficient pressure to form part of the solid
nucleus below. At present, the balance of evidence and argument
seems to be in favour of the practical rigidity and solidity of the
globe as a whole. But the materials of its interior must possess
temperatures far higher than those at which they would melt at
the surface. They are no doubt kept solid by the vast overlying
pressure, and any change which could relieve them of this pressure
would allow them to pass into the liquid form. This subject
will be again alluded to in Chapter XVI. Meanwhile, let us
consider how the intensely hot nucleus of the planet reacts upon
its surface.
Rocks are bad conductors of heat. So slowly is the heat of
the interior conducted upwards by them that the temperature of
the surface of the crust is not appreciably affected by that of the
intensely hot nucleus. But the fact that the surface is not warmed
from this source shows that the heat of the interior must pass off
into space as fast as it arrives at the surface, and proves that our
planet is gradually cooling. For many millions of years the earth
has been radiating heat into space, and has consequently been
losing energy. Its present store of planetary vitality therefore
must be regarded as greatly less than it once was.
VOLCANOES
Of all the manifestations of this planetary vitality, by far the
most impressive are those furnished by volcanoes. The general
characters of these vents of communication between the hot
interior and cool surface of the planet are doubtless already familiar
to the reader of these chapters the volcano itself, a conical hill
or mountain, formed mainly or entirely of materials ejected from
below, having on its truncated summit the basin-shaped crater, at
the bottom of which lies the vent or funnel from which, as well as
from rents on the flanks of the cone, hot vapours, cinders, ashes,
and streams of molten lava are discharged, till they gradually pile
up the volcanic cone round the vent whence they escape.
A volcanic cone, so long as it remains, bears eloquent testimony
to the nature of the causes that produced it. Even many centuries
after it has ceased to be active, when no vapours rise from any
part of its cold, silent, and motionless surface, its conical form, its
cup-shaped crater, its slopes of loose ashes, and its black bristling
lava-currents remain as unimpeachable witnesses that the volcanic
106 VOLCANOES AND EARTHQUAKES CHAP.
fires, now quenched, once blazed forth fiercely. The wonderful
groups of volcanoes in Auvergne and the Eifel are as fresh as if
they had not yet ceased to be active, but might break out again
at any moment ; yet they have been quiescent ever since the
beginning of authentic human history.
But in the progress of the degradation which everywhere slowly
changes the face of the land, it is impossible that volcanic hills
should escape the waste which befalls every other kind of eminence.
We can picture a time when the volcanic cones of Auvergne will
have been worn away, and when all the lava-streams that descend
from them will be cut into ravines and isolated into separate
masses by the streams that have even already deeply trenched
the oldest of them. Where all the ordinary and familiar signs
of a volcano have been removed, how can we tell that any
volcano ever existed ? What enduring record do volcanoes
inscribe in geological history ?
Now, it must be obvious that among the operations of an active
volcano, many of the most striking phenomena have hardly any
importance as aids in recognising the traces of long-extinct vol-
canic action. The earthquakes and tremors that accompany
volcanic outbursts, the constant and prodigious out -rushing of
steam, the abundant discharge of gases and acid vapours, though
singularly impressive at the time, leave little or no lasting mark of
their occurrence. It is not in phenomena, so to speak, transient
in their effects, that we must seek for a guide in exploring the
records of ancient volcanoes, but in those which fracture or other-
wise affect the rocks below ground, and pile up heaps of material
above.
Keeping this aim before us, we may obtain from an examina-
tion of what takes place at an active volcano such durable proofs
of volcanic energy as will enable us to recognise the former exist-
ence of volcanoes over many tracts of the globe where human eye
has never witnessed an eruption, and where, indeed, all trace of
what could be called a volcano has utterly vanished. A method
of observation and reasoning has been established, from the use of
which we learn that in some countries, Britain for example, though
there is now no sign of volcanic activity, there has been a succes-
sion of volcanoes during many protracted and widely separated
periods, and that probably the interval that has passed away since
the last eruptions is not so vast as that which separated these from
those that preceded them. A similar story has been made out in
many parts of the continent of Europe, in the United States, India,
ix VOLCANIC PRODUCTS 107
and New Zealand, and, indeed, in most countries where the subject
has been fully investigated.
A little reflection on this question will convince us that the
permanent record of volcanic action must be of two kinds : first
and most obvious are the piles of volcanic materials which have
been spread out upon the surface of the earth, not only round the
immediate vents of eruption, but often to great distances from
them ; secondly, the rents and other openings in the solid crust of
the earth caused by the volcanic explosions, and some of which
have served as channels by which the volcanic materials have
been expelled to the surface.
Volcanic Products. We shall first consider those materials
which are erupted from volcanic vents and are heaped up on the
surface as volcanic cones or spread out as sheets. They may be
conveniently divided into two groups : ist, Lava, and 2nd, Frag-
mentary materials.
(i) Lava.- Under this name are comprised all the molten rocks
of volcanoes. These rocks present many varieties in composition
FIG. 44. Cellular Lava with a few of the cells filled up with infiltrated
mineral matter (Amygdales).
and texture, some of the more important of which will be described
in Chapter XI. Most of them are crystalline that is, are made up
wholly or in greater part of crystals of two or more minerals, inter-
locked and felted together into a coherent mass. Some are chiefly
composed of a dark brown or black glass, while others consist of
a compact stony substance with abundant crystals imbedded in it.
Probably most of them, when in completes! fusion within the
earth's crust, existed in the condition of thoroughly molten glass,
io8
VOLCANOES AND EARTHQUAKES
CHAP.
the transition from that state to a stony or lithoid one being due
to a process of "devitrification" (p. 159) consequent on cooling.
During this process some of the component ingredients of the glass
crystallise out as separate minerals, and this crystallisation some-
times proceeds so far as to use up all the glass and to transform
it into a completely crystalline substance.
In many cases lavas are strikingly cellular that is to say, they
contain a large number of spherical or almond-shaped cavities
somewhat like those of a sponge or of bread, formed by the expan-
sion of the steam absorbed in the molten rock (Figs. 44 and 46 and
p. 1 6 1 ). Lavas vary much in weight and in colour. The heavier
kinds are more than three times the weight of water ; or, in other
words, they have a specific gravity ranging up to 3.3 ; and are
commonly dark grey to black. The lighter varieties, on the other
hand, are little more than twice the weight of water, or have a
specific gravity which may be as low as 2.3, while their colours
are usually paler, sometimes almost white.
When lava is poured out at the surface it issues at a white heat
that is, at a temperature sometimes above that of melting copper,
or more than 2204 Fahr. ; but its surface rapidly darkens, cools,
and hardens into a solid crust which varies in aspect according to
the liquidity of the mass. Some lavas are remarkably fluid, flow-
ing along swiftly like melted iron ; others move sluggishly in a
stiff viscous stream. In many pasty lavas, the surface breaks up
into rough cindery blocks or scoriae, like the slags of a foundry,
which grind upon each other as the still molten stream underneath
creeps forward (p. 161).
c-~-^), and scalenohedron (c).
axes cuts the vertical axis at a right angle, the other intersects the
vertical axis obliquely. Augite (Fig. 61), Hornblende (Fig. 68),
and Gypsum (Fig. 73) are examples.
VI. Triclinic, the most unsymmetrical of all the systems, all the axes
being unequal and placed obliquely to each other (Fig. 62).
FIG. 61. Monoclinic prism.
Crystal of Augite.
FIG. 62. Triclinic prism
Crystal of Albite felspar.
Every mineral that takes a crystalline form belongs to one or
other of these six systems, and through all its varieties of external
form the fundamental relations of the axes remain unchanged.
Some minerals have crystallised out of solutions in water. How
this may take place can be profitably studied by dissolving salt,
sugar, or alum in water, and watching how the crystals of these
substances gradually shape themselves out of the concentrated
solution, each according to its own crystalline pattern. Other
minerals have crystallised from hot vapours (sublimation), as may
be observed at the fissures of an active volcano (p. 1 1 8). Others
have crystallised out of molten solutions, as in the case of lava.
Thoroughly fused lava is a glassy or vitreous solution of all the
mineral substances that enter into the composition of the rock
x OXIDES QUARTZ 141
(p. 107), and when it cools, the various minerals crystallise out of
it. The order of their appearance appears to depend on conditions
not yet well understood ; though as a rule it may be said that
those which are least fusible take form first, the most fusible
coming last; but a residue of non- crystalline glass sometimes
remains even when the rock has solidified (p. 159). Many rocks
of igneous origin show by their internal structure that they have
consolidated at more than one period. The same mineral, for
example, may occur in them in two series of crystals, one of
which, developed during an early time, remains distinct, even
after the rock has been in great measure re-melted. The crystals
of the same mineral formed after this subsequent fusion, in a
second consolidation, are generally much smaller and more abun-
dant than the earlier series.
It is evident that minerals can only form perfect crystals where
they have room and time to crystallise. But where they are
crowded together, and where the solution in which they are dis-
solved dries or cools too rapidly, their regular and symmetrical
growth is arrested. They then form only imperfect crystals, but
their internal structure is crystalline, and if examined carefully will
be found to show that in the attempt to form definite crystals each
mineral has followed its own crystalline type. These characters
are of much importance in the study of rocks, for rocks are only
large aggregates of minerals, wherein definite crystals are excep-
tional, though the structure of the whole mass may still be quite
crystalline (see p. 177).
But minerals also occur in various indefinite or non-crystalline
shapes. Sometimes they are fibrous or disposed in minute fibre-
like threads (Fig. 67) ; or concretionary when they have been
aggregated into various irregular concretions of globular, kidney-
shaped, grape-like, or other imitative shapes (Figs. 72, 75, 76,
86); or stalactitic (Fig.- 26) when they have been deposited in
pendent forms like stalactites ; or amorphous when they have no
definite shape of any kind, as, for instance, in massive ironstone.
OXIDES occur abundantly as minerals. The most important
are those of Silicon (Quartz) and Iron (Haematite, Limonite,
Magnetite, Titanic Iron).
Quartz (Silica, Silicic Acid, SiO 2 ; sp. gr. 2.65), already
alluded to, is the most abundant mineral in the earth's crust. It
occurs crystallised, also in various crystalline and non-crystalline
varieties. In the crystallised form as common quartz it is clear
and glassy when pure, but is often coloured yellow, red, purple,
142 IMPORTANT MINERALS CHAP!
green, brown, or black, from various impurities. It crystallises in
the six-sided prisms and pyramids above referred to, the clear
colourless varieties being rock-crystal (Fig. 55). When purple it
owes its colour to the presence of oxide of manganese and is then
called amethyst; yellow and smoke-coloured varieties, found among
the Grampian Mountains of Scotland, owe their tints to iron oxide
and are popularly known as Cairngorm stones. In many places,
silica has been deposited from solution in water as Chalcedony, in
translucent masses with a waxy lustre, and pale grey, blue, brown,
red, or black colours. Deposits of this kind are not infrequent
among the cavities and fissures of rocks. The common pebbles
FIG. 63. Section of a pebble of chalcedony. The outer banded layers are
chalcedony, the interior being nearly filled up with crystalline quartz.
and agates with concentric bands of different colours are examples
of chalcedony, and show how the successive layers have been
deposited from the walls of the cavity inwards to the centre, which
is often filled with crystalline quartz (Fig. 63). The dark opaque
varieties are called Jasper.
Opal (sp. gr. 1.9-2.3) is a hydrated form of silica, found in
many different forms of aggregation, but not crystallised. It is
not quite so heavy as quartz, and is not infrequently found replacing
the substance of fossil plants and animals, the minutest organic
structures being replaced and exquisitely preserved. Flint and
Chert are impure forms of silica, frequently associated with the
remains of sponges, radiolaria, and other organisms in the rocks
of the earth's crust.
Quartz can be usually recognised by its vitreous lustre and
x OXIDES HEMATITE LIMONITE 143
hardness ; it cannot be scratched with a knife, but easily scratches
glass, and it is not soluble in the ordinary acids. It is an essential
constituent of many rocks, such as granite and sandstone. Silica
being dissolved by natural waters, especially where organic acids
or alkaline carbonates are present, is introduced by permeating
water into the heart of even the most solid rocks. Hence it is
found abundantly in strings and veins traversing rocks, also in
cavities and replacing the forms of plants and animals 'imbedded in
sedimentary deposits. Soluble silica is abstracted by some plants
and animals, and built up into their organic structures (diatoms,
radiolaria, sponges).
Four minerals composed of Oxides of Iron occur abundantly
among rocks. The peroxide is found in two frequent forms, one
without water (Haematite), the other with water (Limonite). The
peroxide and protoxide combine to form Magnetite, and a mixture
of the peroxide with the peroxide of the metal titanium gives
Titanic Iron.
Haematite or Specular Iron (Fe 2 O 3 = FeyoOao ; sp. gr. 5.19-
5-28) occurs in rhombohedral crystals that can with difficulty be
scratched with a knife ; but is more usually found in a massive
condition with a compact,
fibrous, or granular texture,
and dark steel-grey or iron-
black colour, which becomes
bright red when the mineral
is scratched or powdered.
The earthy kinds are red
in colour, and it is in this
earthy form that haematite
plays so important a part
as a colouring material in
nature. Red sandstone, FIG. 64. Piece of haematite, showing the
for example, owes its red nodular external form and the internal
. .... crystalline structure.
colour to a deposit of
earthy peroxide of iron round the grains ot sand. Haematite
occurs crystallised in fissures of lavas as a product of the hot
vapours that escape at these places ; but is more abundant in
beds and concretionary masses (Fig. 64) filling veins and cavities
among various rocks.
Limonite or Brown Iron-ore (2Fe 2 O 3 , 3H 2 O ; sp. gr. 3.6-4)
differs from Haematite in being lighter and softer, in containing
more than 1 4 per cent of water, which is combined with the iron to
144 IMPORTANT MINERALS CHAP.
form the hydrated peroxide, in being usually massive or earthy, in
presenting a dark brown to yellow colour (ochre), and in giving a
yellowish-brown to dull yellow powder when scratched or bruised.
It may be seen in the course of being deposited at the present time
through the action of vegetation in bogs and lakes (p. 54), hence
its name of Bog-iron-ore ; likewise in springs and streams where
the water carries much sulphate of iron. The common yellow and
brown colours of sandstones and many other rocks are generally
due to the presence of this mineral.
Magnetite (Fe 3 O 4 ; sp. gr. 4-9-5-2) occurs crystallised in
isometric octahedrons and dodecahedrons of an iron -black colour,
giving a black powder when scratched. It is found abundantly in
many rocks (schists, lavas, etc.), sometimes in large crystals (Fig.
FIG. 65. Octahedral crystals of magnetite in chlorite-schist.
65), sometimes in such minute form as can only be detected with
the microscope. It also forms extensive beds of a massive structure.
Its presence in rocks may be detected by its influence on a magne-
tised needle. By pounding basalt and some other rocks down to
powder, minute crystals and grains of magnetite may be extracted
with a magnet.
Titanic Iron, Ilmenite (FeTiO 3 ; sp. gr. 4.5-5.2) occurs
in iron-black crystals like those of haematite, from which they may
be distinguished by the dark colour and metallic lustre of the surface
when scratched. Though this ore is found in beds and veins in
certain kinds of rock (schists, serpentine, syenite), its most
generally diffused condition is in minute crystals and grains
scattered through many crystalline rocks (basalt, diabase, etc.)
and combined in small proportions in other iron-ores.
Manganese Oxides are commonly associated with those of
iron in rocks. They are liable to be deposited in the form of
SILICATES
bog-manganese, under conditions similar to those in which bog-
iron is thrown down. Earthy manganese oxide (wad) not
infrequently appears between the joints of fine-grained rocks in
arborescent forms that look so like plants as to have been often
mistaken for vegetable re-
mains. These plant-like
deposits are called Den-
drites or dendritic mark-
ings (Fig. 66).
SILICATES. Com-
pounds of Silica with
various bases form by far
the most numerous and
abundant series of minerals
in the earth's crust. They
may be grouped according
to the chief metallic base
in their composition. The
most important are the
Silicates of Alumina, and "" \ -.-* VlUkT 'rar *. I
the Silicates of Magnesia.
Of the aluminous silicates
we need consider here
only the Felspars, Zeolites,
and Micas. Among the
magnesian silicates it will
be enough to note the
leading characters of
Hornblende, Augite,
Olivine, Talc, Chlorite, and Serpentine. When the learner has
made himself so familiar with these as to be able readily to
recognise them, he may proceed to the examination of others, of
which he will find descriptions in treatises on Mineralogy and in
more advanced text-books of Geology.
Felspars. This family of minerals plays an important part in
the construction of the earth's crust, for it constitutes the largest
part of the crystalline rocks, which, like granite and lava, have
been erupted from below ; is found abundantly in the great series
of schists ; and by decomposition has given rise to the clays, out
of which so many sedimentary rocks have been formed. The
felspars are divided into two series, according to crystalline form
and chemical composition.
L
FIG. 66. Dendritic markings due to arborescent
deposit of earthy manganese oxide.
146 IMPORTANT MINERALS CHAP.
Orthoclase or potash-felspar contains about 16.89 P er cent of
potash, crystallises in monoclinic or oblique rhombic prisms, but
also occurs massive ; is white, grey, or pink in colour ; has a glassy
lustre but is not usually clear and transparent ; can with difficulty
be scratched with a knife, but easily with quartz, and has a
specific gravity of 2.50 to 2.59. Associated with quartz, it is an
abundant ingredient of many ancient crystalline rocks (granite,
felsite, gneiss, etc.). In the clear glassy form called Sanidim, it
is an essential constituent of many modern volcanic rocks.
Plagiodase. Under this name are grouped several species of
felspar which, differing from each other in chemical composition
and specific gravity (which ranges from 2.62 to 2.75), agree in
crystallising in the same type or system, which is that of a triclinic
or oblique rhomboidal prism. They are abundant ingredients
of rocks in which they appear as clear, colourless, or white turbid
glassy strips, on the flat faces of which a fine minute parallel ruling
may be detected with the naked eye, or with a lens. This striation
or lamellation, due to what is called " twinning," is a distinctive
character, which proves the crystals that display it not to be
orthoclase. The plagioclase felspars occur as essential constituents
of many volcanic rocks, and also among ancient eruptive masses
and schists. Among them are Microcline (a potash-felspar), with
1 5 per cent of potash ; Albite or Soda-felspar, containing nearly 1 2
per cent of soda (Fig. 62) ; Anorthite or Lime-felspar, with 20.10
per cent of lime ; Soda-lime felspar, Lime-soda felspar a group
of felspars containing variable proportions of soda, lime, and some-
times potash, of which the chief varieties are Oligoclase (Silica,
62-65 P er cent), Andesine (Silica, 58-61 per cent), Labradorite
(Silica, 50-56 per cent).
Closely related to the felspars as a rock-constituent is the
mineral Nepheline, which is a silicate of alumina, potash and soda
with a specific gravity of 2.6. It takes the place of felspar in one
group of basalts, and is a conspicuous ingredient in phonolites
and some forms of syenite. Another mineral which may be
mentioned here as occasionally abundant in the constitution of
some lavas is Leucite. It occurs in white dull 24-sided crystals, is
a silicate of alumina and potash, and has a specific gravity of 2.56.
Zeolites, a characteristic family of minerals, composed essen-
tially of silicate of alumina and some alkali, with water ; often
marked by a peculiar pearly lustre, especially on certain planes
of cleavage ; usually found filling up cavities in rocks where they
have been deposited from solution in water. Some of the species
x SILICATES 147
commonly crystallise in fine needles or silky tufts. The zeolites
have obviously been formed from the decomposition of other
minerals, particularly felspars. They are especially abundant in
the steam-cells of old lavas in which plagioclase felspars prevail,
either lining the walls of the cavities, and shooting out in crystals
or fibres towards the centre (Fig. 67), or filling the cavities up
entirely (Amygdales).
Another mineral substance produced by the decomposition of
Felspar is familiar under the name of clay. The purer forms are
known as Kaolin or China-clay.
Micas, a group of minerals (monoclinic) specially distinguished
by their ready cleavage into thin, parallel, usually elastic silvery
FIG 67. Cavity in a lava, filled with zeolite which has crystallised in long
slender needles.
laminae. They are aluminous silicates with potash (soda), or with
magnesia and ferrous oxide, and always with water. They occur
as essential constituents of granite, gneiss, and many other eruptive
and schistose rocks, also in worn spangles in many sedimentary
strata (micaceous sandstone). Among their varieties the two
most important are Muscovite (white mica, potash-mica) and
Biotite (black mica, magnesia-mica).
Hornblende or Amphibole, a silicate of magnesia, with lime,
iron-oxides, and sometimes alumina, occurs in monoclinic (oblique
rhombic) prisms, also columnar, fibrous, and massive ; sp. gr. 2.9-
3.5. Tt is divisible into (i) a group of pale-coloured varieties,
containing little or no alumina, white or pale green in colour, often
fibrous (Tremolite, Actinolite, Asbestus], found more particularly
i 4 8
IMPORTANT MINERALS
CHAP.
FIG. 68. Horn-
blende crystal.
among gneisses, marbles, and associated rocks, and (2) a dark
group containing 5 to 18 per cent of alumina, which replaces the
other bases ; dark green to black in colour, in stout, dumpy prisms
(Fig. 68), and in columnar or bladed aggregates (Common horn-
blende). Abundant in many eruptive rocks, and
also forming almost entire beds of rock among
the crystalline schists.
Augite (Pyroxene; sp. gr. 3-34-3-38), in
composition resembles hornblende ; indeed they
are essentially modifications of the same sub-
stance, differing slightly in crystalline form,
hornblende being generally the result of slow
and augite of rapid crystallisation. Many rocks
in which the dark silicate was originally augite
have that mineral now replaced by hornblende,
as the result of a gradual internal alteration (uralite). Like
hornblende, augite occurs in two groups : (i) pale non-aluminous,
found more especially among gneisses, marbles, and associated
rocks ; and (2) dark green or black (Fig. 61), occurring abundantly
in many eruptive rocks, such as black heavy lavas (basalts, etc.).
Olivine (Peridot) (SiO 2 41.01, MgO 49.16, FeO 9.83 ; sp. gr.
3.2 3.5) occurs in small orthorhombic prisms and glassy grains
in basalts and other lavas ; of a pale yellowish-
green or olive-green colour, whence its name.
These grains can often be readily detected on
the black ground of the rock, through which
they are abundantly dispersed. Olivine is
liable to alteration, and especially to conver-
sion into serpentine by the influence of perco-
lating water (Fig. 69).
Chlorite (SiO 2 25-28, A1 2 O 3 19-23, FeO
15-29, MgO 13-25, H 2 O 9-12). This term
includes a group of dark olive-green hydrated
magnesian silicates. They are so soft as to
be easily scratched with the nail, and occur in
small six-sided tables, also in scaly and tufted or
amorphous aggregates diffused through certain
rocks. Chlorite appears generally to be the result of the alteration of
some previous anhydrous magnesian silicate, such as hornblende.
Talc is the name given to another hydrous magnesian silicate
which is readily and deeply scratched with the nail, has a pearly
lustre and a soapy feel, and can be split into thin laminae which
FIG. 69. Magnified sec-
tion of an olivine crys-
tal; the light portions
represent the unde-
composed mineral, the
shaded parts show the
conversion of the oli-
vine into serpentine.
x CARBONATES 149
are not elastic as those of mica are. It has resulted from the
alteration of some older magnesian silicates.
Serpentine (Mg 3 Si 2 O r + 2H 2 O) is another hydrated magnesian
silicate, containing a little protoxide of iron and alumina, usually
massive, dark green but often mottled with red. It occurs in
thick beds among schists, is often associated with limestones, and
may be looked for in all rocks that contain olivine, of the altera-
tion of which it is often the result. In many serpentines, traces
of the original olivine and other crystals can be detected.
CARBONATES. Though these are abundant in nature, only
three of them require notice here as important constituents of the
earth's crust, those of lime, magnesia and lime, and iron.
Calcite (calcium-carbonate, carbonate of lime, CaCO g ) crystal-
lises in the hexagonal system, and has for its fundamental crystal-
FIG. 70. Calcite in the form of " nail-head spar."
line form the rhombohedron, as already mentioned (p. 138).
When quite pure it is transparent (Iceland spar, Fig. 56), with
the lustre of glass ; but more usually is translucent or opaque and
white. Its crystals, where the chief axis is shorter than the others,
sometimes take the form of flat rhombohedron s (nail-head spar,
Fig. 70) ; where, on the other hand, that axis is elongated, they
present pointed pyramids (scalenohedrons, dog-tooth spar, Fig.
71). The mineral occurs also in fibrous, granular, and compact
forms. The decomposition of silicates containing lime by per-
meating water gives rise to calcium-carbonate, which is removed
in solution. Being readily soluble in water containing carbonic
acid, this carbonate is found in almost all natural waters, by which
it is introduced into the cavities of rocks. Some plants and many
animals secrete large quantities of carbonate of lime, and their
remains are aggregated into beds of limestone, which is a massive
ISO IMPORTANT MINERALS CHAP.
and more or less impure form of calcite (pp. 170, 174). Calcite
is easily scratched with a knife, and is characterised by its
abundant effervescence when acid is dropped upon it. Its
specific gravity is 2.72.
A less frequent and stable form of calcium -carbonate is
Aragonite, which crystallises in orthorhombic forms, but is more
usually found in globular, dendritic, coral-like, or other irregular
shapes, and is rather harder and heavier than calcite.
Dolomite assumes a rhombohedral crystallisation, and is a
compound of 54.4 of magnesium-carbonate, with 45.6 of calcium-
carbonate. It has a specific gravity of 2.8-2.9. It is rather harder
than calcite, and does not effervesce so freely with acid. It
occurs in strings and veins like calcite, but also in massive beds
FIG. 71. Calcite in the form of dog-tooth spar.
having a prevalent pale yellow or brown colour (owing to hydrated
peroxide of iron), a granular and often cavernous texture, and a
tendency to crumble down on exposure (p. 171).
Siderite (chalybite, spathic iron, ferrous carbonate, FeCO 3 ),
another rhombohedral carbonate, contains 62 per cent of ferrous
oxide or protoxide of iron ; specific gravity 3.7-3.9. In its crystal-
line form it is grey or brown, becoming much darker on exposure,
as the protoxide passes into peroxide. It occurs abundantly
mixed with clay in concretions and beds, frequently associated
with remains of plants and animals (Sphcerosiderite, Clay-ironstone,
Figs. 72, 76).
SULPHATES. Two sulphates deserve notice for their import-
ance among rock-masses those of lime and baryta.
Gypsuin (hydrous calcium -sulphate, CaSO 4 + 2HO >2 ; sp. gr.
SULPHATES
2.2-2.4) occurs in monoclinic crystals, commonly with the form
of right rhomboidal pfisms (Fig. 73, a\ which not infrequently
appear as macles or twin-crystals (Fig. 73, b\ When pure it is clear
and colourless, with a peculiar pearly lustre (Stlenite] ; it is found
fibrous with a silky sheen (Satin-spar], also white and granular
(Alabaster). It is so soft as to
be easily cut with a knife or even
scratched with the finger-nails.
It is readily distinguished from
calcite by its crystalline form,
softness, and non-effervescence
with acid. When burnt it be-
comes an opaque white powder
(plaster of Paris). Gypsum
occurs in beds associated with
sheets of rock-salt and dolomite
(PP- 55> I 7 I )5 it * s soluble in
water, and is found in many
springs and rivers, as well as
in the sea. One thousand parts
of water at 32 Fahr. dissolve
2.05 parts of sulphate of lime;
but the solubility of the sub-
stance is increased in the pres-
ence of common salt, a thousand
parts of a saturated solution of common salt taking up as much
as 8.2 parts of the sulphate.
Anhydrous calcium -sulphate or Anhydrite is harder and
heavier than gypsum, and is found extensively in beds associated
with rock-salt deposits. By absorbing water, it increases in bulk
and passes into gypsum.
Barytes (Heavy spar, barium-sulphate, BaSO 4 ; sp. gr. 4.3-
4.7), the usual form in which the metal barium is distributed
over the globe, crystallises in orthorhombic prisms which are
generally tabular ; but most frequently it occurs in various massive
forms. The purer varieties are transparent or translucent, but in
general the mineral is dull yellowish or pinkish white, with a
vitreous lustre, and is readily recognisable from other similar
substances by its great weight ; it does not effervesce with acids.
Barytes is usually met with in veins traversing rocks, especially in
association v/ith metallic ores ; it occurs also diffused through
some sandstones.
FIG. 72. Sphaerosiderite or Clay-ironstone
concretion enclosing portion of a fern.
152
IMPORTANT MINERALS
OHAP.
PHOSPHATES. Only one of these requires to be enumerated
in the present list of minerals the phosphate of lime or Apatite.
Apatite (tricalcic phosphate, phosphate of lime ; sp. gr.
3.1-3.2) crystallises in hexagonal prisms which, as minute
colourless needles, are abundant in many crystalline rocks ; it
also occurs in large crystals and in amorphous beds associated
with gneiss. It is soluble in water containing carbonic acid,
ammoniacal salts, common salt, and other salts. Hence its
introduction into the soil, and its absorption by plants, as already
mentioned (p. 135).
FLUORIDES. The only member of this family occurring con-
spicuously in the mineral kingdom is calcium fluoride or Fluor-
FIG. 73. Gypsum crystals.
Spar (Fluorite, CaF 2 ; sp. gr. 3.1-3.2), which, in the form of
colourless, but more commonly light green, purple, or yellow cubes,
is found in mineral veins not infrequently accompanying lead-ores
(Fig. 74).
CHLORIDES. Reference has already been made to the only
chloride which occurs plentifully as a rock-mass, the chloride ol
sodium, known as Halite or Rock-salt (NaCl, chlorine 60.64,
sodium 39.36). It crystallises in cubical forms, and is also
found massive in beds that mark the evaporation of former salt-
lakes or inland seas (p. 172).
SULPHIDES. Many combinations of sulphur with the metals
occur, some of them of great commercial value ; but the only one
that need be mentioned here for its wide diffusion as a rock-
x SULPHIDES 153
constituent is the iron-disulphide (FeS 2 ), in which the elements
are combined in the proportion of 46.7 iron and 53.3 sulphur.
This substance assumes two crystalline forms : (i) Pyrite, which
occurs in cubes and other forms of the first or monometric
system, of a bronze-yellow colour and metallic lustre, so hard as
to strike fire with steel, giving a brownish -black powder when
scratched, and having a specific gravity of 4.9 to 5.2. This
mineral is abundantly diffused in minute grains, strings, veins,
concretions (Fig. 75, <:), and crystals in many different kinds of
rocks ; it is usually recognisable by its colour, lustre, and hard-
ness ; (2) Marcasite (white pyrite) crystallises in the tetragonal
system, is as hard as ordinary pyrites but paler in colour, not so
FIG. 74. Group of fluor-spar crystals.
heavy (sp. gr. 4.65-4.9), and much more liable to decomposi-
tion. This form, rather than pyrite, is usually associated with
the remains of plants and animals imbedded among rocks. The
sulphide has no doubt often been precipitated round decaying
organisms by their effect in reducing sulphate of iron. By its
ready decomposition, marcasite gives rise to the production of
sulohuric acid and the consequent formation of sulphates. One
of the most frequent indications of this decomposition is the rise
of chalybeate springs (p. 67). Weathered surfaces of pyritous
shale may sometimes be seen coated with crystals or an efflor-
escence of alum, due to the action of the sulphuric acid on the
alumina and alkalies of the stone. On an exposed pyritous
calcareous rock, minute groups of gypsum crystals may be detected,
showing that the sulphuric acid has combined with the lime.
CHAPTER XI
THE MORE IMPORTANT ROCKS OF THE EARTH'S CRUST
FROM the distribution of the more important elements in the
earth's crust and the mineral forms which they assume, we have
now to advance a stage farther and inquire how the minerals are
combined and distributed so as to build up the crust. As a rule,
simple minerals do not occur alone in large masses ; more usually
they are combined in various proportions to form what are known
as Rocks. A rock may be defined as a mass of inorganic matter,
composed sometimes of one but more usually of several minerals,
having for the most part a variable chemical composition, with no
necessarily symmetrical external form, and ranging in cohesion
from loose or feebly aggregated debris up to the most solid stone.
Blown sand, peat, coal, sandstone, limestone, lava, granite, though
so unlike each other, are all included under the general name of
Rocks.
In entering upon the study of rocks, or the division of geology
known as Petrography, it is desirable to be provided with such
helps as are needed for determining leading external characters ;
in particular, a hammer to detach fresh splinters of rock, a pocket-
knife for trying the hardness of minerals, a small phial of dilute
hydrochloric acid for detecting carbonate of lime, and a pocket
lens. The learner, however, must bear in mind that the thorough
investigation of rocks is a laborious pursuit, requiring qualifications
in chemistry and mineralogy. He must not expect to be able to
recognise rocks from description until he has made good progress
in the study. As already stated on a previous page, he must
examine the objects themselves, and for this purpose he will find
much advantage in procuring a set of named specimens, and
making himself familiar with such of their characters as he can
himself readily observe.
CHAP. XI
ROCKS OF EARTH'S CRUST
155
Great light has been thrown upon the structure and history of
rocks by examining them with the microscope. For this purpose,
a thin chip or slice of the rock to be studied is ground smooth
with emery and water, and after being polished with flour-emery
"upon plate-glass, the polished side is cemented with Canada
balsam to a piece of glass, and the other side is then ground
down, until the specimen is so thin as to be transparent. Thin
FIG. 75. Concretions.
, ^, " Fairy stones ;" )
extent to which shells or other organic remains are pulled out in
the direction of movement. In Fig. no the proper shape of a
trilobite (Angelina Sedgwickii) is given, and alongside of it is a
view of the same organism which has been elongated by the dis-
tortion of the mass of rock in which it lies. Further results of
shearing will be immediately referred to in connection with the
cleavage and metamorphism of rocks.
Cleavage. One of the most important structures developed by
FIG. 109. Section of folded and crumpled strata forming the Grosse Windgalle (10,482
feet), Canton Uri, Switzerland, showing crumpled and inverted strata (after Heim).
the great compression to which the rocks of the earth's crust have
been exposed is known as Cleavage. The minute particles of
rocks, being usually of irregular shapes, have been compelled to
arrange themselves with their long axes perpendicular to the
direction of pressure, during the interstitial movements consequent
upon intense subterranean compression. Hence, a fissile tendency
216 STRUCTURES OF SEDIMENTARY ROCKS CHAP.
has been imparted ta a rock, which will now split into leaves
along the planes of rearrangement of the particles. This super-
induced tendency to split into parallel leaves, irrespective of what
may have been the original structure of the rock, constitutes
cleavage. It is well developed in ordinary roofing-slate. Though
the leaves or plates into which a slate splits resemble those in a
shale, they have no necessary relation to the layers of deposition
but may cross them at any angle. In Fig. 1 1 1, for instance, the
original bedding is quite distinct and shows that the strata have
been folded by a force acting from the right and left of the section ;
the parallel highly inclined lines traversing the folds of the bedding
represent the planes of cleavage. Where the material is ojf ex-
ceedingly fine grain, such as fine consolidated mud, the original
bedding may be entirely effaced by the cleavage, and the rock
a b
FIG. no. Distortion of fossils by the shearing of rocks; (a), a Trilobite (Angelina Sedg-
ivickii) distorted by shearing, the direction of movement indicated by the arrows ;
(<), the same fossil in its natural form.
will only split along the cleavage-planes. Indeed, the finer the
grain of a rock, the more perfect may be its cleavage, so that
where alternations of coarser and finer sediment have been sub-
jected to the same amount of compression, cleavage may be perfect
in the one and rudely developed in the other, as is indicated in
Fig. in. It is possible that the lamination of fine argillaceous
sediments parallel to the stratification, in ancient and once deeply
buried formations, may sometimes be a cleavage structure that
has been superinduced by the enormous superincumbent pressure
of the vast mass of rock that has been worn away (p. 168).
Cleavage may be regarded as one of the first stages in the
mechanical deformation of a rock, and in the production of schistose
metamorphism (p. 186). Besides being compressed and having
its component particles rearranged in definite planes, the rock
may likewise reveal under the microscope that new minerals, such
XIII
DISLOCATION
217
for example as crystallites or minute flakes of some mica, have been
developed out of the general matrix, as may be seen in common
roofing - slate. By increasing stages of crystallisation we trace
gradations into phyllites and mica-schists.
Dislocation. Another important structure produced in rocks
after their formation is Dislocation. Not only have they been
folded by the great movements to which the crust of the earth has
been subjected, but the strain upon them has often been so great
that they have snapped across. Such ruptures of continuity pre-
FIG. in. Curved and cleaved rocks. Coast of Wigtonshire. The fine parallel oblique
lines indicate the cleavage, which is finer in the dark shales and coarser in the thicker
sandy beds.
sent an infinite variety in the position of the rocks on the two sides.
Sometimes a mere fissure has been caused, the rocks being simply
cracked across, but remaining otherwise unchanged in their relative
situations. But, in the great majority of instances, one or both of
the walls of a fissure have moved, producing what is termed a
Fault. Where the displacement has been small, a fault may
appear as if the strata had been sharply sliced through, shifted,
and firmly pressed together again (a in Fig. 112). Usually, how-
ever, they have not only been cut, but bent or crushed on one or
both sides (b) ; while not infrequently the line of fracture is repre-
sented by a band of broken and crushed material (Fault-rock, e).
218 STRUCTURES OF SEDIMENTARY ROCKS CHAP.
The fracture is seldom quite vertical ; almost always it is inclined
at angles varying up to 70 or more from the vertical. In by far
the largest number of faults, the inclination of the plane of the
fissure, or what is called the Hade of the fault, is away from the
side which has risen or toward that which has sunk. In the ex-
amples given in Fig. 112, a, b, this relation is expressed ; but in
nature it often happens that the beds on two sides of a
fault are entirely different (c\ and consequently that the side of
upthrow or downthrow cannot be determined by the identification
of the two severed positions of the same bed. But if the hade of
the fault can be seen, we may usually be confident that the strata
on the upper or hanging side belong to a higher part of the series
than those on the lower side. Faults that follow this rule (normal
faults) are by far the most frequent. They occur universally, and
are probably for the most part caused by subsidence in the earth's
crust. In adjusting themselves to the new position into which a
a b c
FIG. 112. Examples of normal Faults.
downward movement brings them, rocks must often be subject to
such strains that their limit of elasticity is reached, and they break
across, one portion settling down farther than the part next to it.
In a normal fault, the same bed can never be cut twice by a
vertical line.
In mountainous districts, however, and generally where the
rocks of the earth's crust have been disrupted and pushed over
each other, what are termed reversed faults occur. In these, the
hade slopes in the direction of upthrow, and a vertical line may
cut the same beds twice on opposite sides of the fracture (Fig.
1 1 3, c}. Such faults may be observed more particularly where
strata have been much folded. A fold may be seen to have
snapped asunder, the whole being pushed over, and the upper
side being driven forward over the lower (Fig. 1 13).
The amount of vertical displacement between the two fractured
ends of a bed is called the Throw of a fault. In Fig. 114, for
example, where bed a has been shifted from b to d t a vertical line
dropped from the end of the bed at b to the level of the corre-
DISLOCATIONS
219
spending part of the bed at e will give the amount of the subsid-
ence of 4 which is the throw. Faults may be seen with a throw
of less than an inch mere local cracks and trifling subsidences in
a mass of rock ; in others the throw may be several thousand feet.
Large faults often bring rocks of entirely different characters
together, as, for instance, shales against limestones or sandstones,
FIG. 113. Sections to show the relations of Plications (a, <5) to reversed Faults (c).
or sedimentary against eruptive rocks. Consequently they are
not infrequently marked at the surface by the difference between
the form of ground produced in the two kinds of rock through the
influence of denudation. One side, perhaps, rises into a hilly or
undulating region, while the other side may be a plain. Com-
paratively seldom does a fault make itself visible as a line of ravine
FIG. 114. Throw of a Fault.
or valley. Where it does so, the surface feature may usually be
traced to the effects of denudation, which has been more effective
on the broken and crushed rocks along the line of fault than
on the solid surrounding masses. In actual fact, most faults
cut across valleys or only coincide with them here and
there. They run in straight or wavy lines which, where the
amount of displacement is great, may be traced for many miles.
The Scottish Highlands, for example, are bounded along their
southern margin by a great fault which places a thick series of
220
STRUCTURES OF SEDIMENTARY ROCKS
CHAP.
sandstones and conglomerates on end against the flanks of the
mountains. This fault may be traced across the island from sea
to sea a distance of fully 1 20 miles, and by bringing two distinct
kinds of rocks next each other, along a nearly straight line, it has
given rise to the boundary between Highland and Lowland
scenery which, in some places, is so singularly abrupt.
In regions of the most intense terrestrial disturbance, tracts
of rock many square miles in area and hundreds or thousands of
feet in thickness, have been torn away and pushed upward and
forward, sometimes for distances of many miles, until they have
come to rest on rocks originally much higher in geological position.
Such displaced cakes or slices of the earth's crust sometimes rest
upon an almost horizontal or gently inclined platform of undis-
FIG. 115. Section showing thrust-planes, Loch Maree, Scotland, aa, Archaean gneiss ;
bb, Pre-Cambrian (Torridon) Sandstone ; cc, Quartzite (Cambrian) ; d, Dolomitic shales
with Olenellus-zonz ; e, Serpulite grit ', f, Dolomite ; TT, Thrust-planes.
turbed materials. Vertical or contorted strata are thus placed
above others which may be flat or but little inclined. The plane
of separation between the moved and unmoved masses is really
a dislocation, but to distinguish it from faults, which are generally
placed at steep angles, it is called a Thrust-plane. Structures of
this kind on a colossal scale are traceable for about 100 miles in
the north-west of Scotland. An example of this structure is given
in Fig. 115. It will be seen that the oldest rock there represented
is the ancient gneiss (a\ which is unconformably overlain by pre-
Cambrian sandstones and conglomerates (b\ which in turn are
separated by an important unconformability from the Cambrian
system (c,d,e,j] which overlies them (see p. 257). The upper part
of the dolomite (/) is abruptly cut off and a portion of the oldest
rocks has been thrust over it. First comes the gneiss, then its over-
lying sandstones. These masses have been thrown into folds, in
xiii REGIONAL METAMORPHISM 221
the cavities of which lie basins of the Cambrian strata, the whole
of these uptorn masses having been driven forward over a sole or
thrust-plane (T). Not infrequently the structure is much more
complicated than here represented, successive minor thrust-planes
being over-ridden by others of greater force.
In the Alps, in recent years, many remarkable illustrations of
similar structures have been observed by Dr. Rothpletz. Thus on
the northern side of the valley of the Rhine above Chur, the
formations follow each other in regular order until towards the
top of the higher mountain, where a portion of the most ancient
rock (gneiss) of the district has been torn up from below and
pushed for a long distance upon a thrust-plane so as to overlie
the youngest strata in the section. The strata have sometimes
been violently plicated, and the gneiss overrides them on the great
thrust-plane. In consequence of enormous denudation, the origin-
ally continuous cake of gneiss has been so much worn away that
only outliers of it are left capping the summits.
Regional Metamorphism. The last structure which will be
mentioned in this chapter as having been superinduced upon
rocks is connected with the movements to which plication,
cleavage, and reversed faults are due. So enormous has been
the energy with which these movements have been carried on,
that not only have the rocks been crumpled, ruptured, and
pushed over each other, but they have undergone such intense
crushing and shearing that their original structure has been
partially or wholly effaced. They have been so crushed that
their component particles have been reduced, as it were, to powder
(mylonite), and have assumed new crystalline arrangements
along the shearing-planes or surfaces of movement. A sandstone,
for example, which in its ordinary state shows, when magnified,
such a structure as is represented in Fig. 1 1 6, when it has come
within the influence of this crushing process has its grains of
quartz, felspar, and other materials flattened and squeezed against
each other in one general direction, as in cleavage, while out of
the crushed debris a good deal of new mica has been developed.
This change may be intensified until the component grains are
hardly, if at all, recognisable. Simultaneous with this mechanical
movement, or following closely on it, comes a chemical rearrange-
ment of the constituents of the rock. New combinations are
formed, and a more or less completely crystalline structure is
superinduced. In particular, mica is specially apt to be developed
and the rock passes into a mica-schist. Other minerals, such as
222 STRUCTURES OF SEDIMENTARY ROCKS CHAP.
garnet, felspars and others, likewise make their appearance, until
the rock assumes a wholly new crystalline character. Such an
alteration of the internal structure of a rock is known as Meta-
morphism. Where the change arises from mechanical movements
combined with chemical rearrangement, it usually affects a wide
district, and is then spoken of as regional metamorphism, as
distinguished from the more local alteration, effected round
the margins of intrusive rocks, which is known as contact-
metamorphism.
There are wide regions of the earth's surface where schists of
various kinds form the prevailing rock. Whether they have all
been produced by the shearing and alteration of previously-formed
rocks has not yet been determined. But that a large number of
FIG. 116. Ordinary unaltered red FIG. 117. Sheared red sandstone
sandstone, Keeshorn, Ross-shire forming now a micaceous schist,
(magnified). Keeshorn, Ross-shire '(magni-
fied).
schists are truly altered or metamorphosed rocks admits of no
doubt. Sandstones, shales, limestones, quartzites, diorites, syenites,
granites, in short, any rock that has corhe within the crushing
and shearing movements here referred to, has been converted into
schist. The gradation between the unaltered and the metamorphic
condition can often be clearly traced. Granite, by crushing,
passes into gneiss, diorite into hornblende-schist, sandstone into
quartz- schist or mica- schist, and so on. Even where it is no
longer possible to tell what the original nature of the meta-
morphosed material may have been, there is usually abundant
evidence that the rock has undergone great compression (see pp.
186-189).
Summary. In this Lesson attention has been directed to new
structures produced in sedimentary rocks after their formation.
xin SUMMARY 223
Beginning with the simplest and most universal of these, we find
that sediments have been consolidated into stone, partly by pressure,
and partly by some kind of cement, such as silica or carbonate of
lime. In the process of consolidation and contraction, they have
been traversed by systems of joints, or have had these subsequently
produced by the torsion accompanying movements of the crust.
Though at first nearly flat, they have, by these movements, been
thrown into various inclined positions, and more especially into un-
dulating folds, or more complicated plication and puckering. So
great has been the compression under which they have been moved,
that a cleavage has been developed in them. They have also
been everywhere more or less fractured, the dislocations being
due either to their gradual subsidence or to excessive plication.
The most gigantic displacements are seen where vast slices of
the terrestrial crust have been wrenched off and pushed bodily,
sometimes for many miles, over younger formations. The most
complete alteration of rocks is seen in metamorphism, where,
under the influence of intense shearing, their original structure
has been more or less completely effaced, and a new crystalline
rearrangement has been developed in them, converting them
into schists.
CHAPTER XIV
ERUPTIVE ROCKS AND MINERAL VEINS IN THE ARCHITECTURE
OF THE EARTH'S CRUST
NOT only have sedimentary formations since their deposition
been hardened, plicated, fractured, and sometimes even turned
into crystalline schists, but into the rents opened in them new
masses of mineral matter have been introduced which, in many
regions, have entirely changed the structure of the crust below
and the appearance of the surface above. Broadly speaking,
there are two ways in which these new masses have been wedged
into their places. First of all, eruptive material in a molten, or
at least in a viscous or plastic condition, has been thrust upward
into the cool and consolidated crust of the earth ; and in the next
place, various ores and minerals have been deposited from solution
in cracks and fissures, which they have entirely filled up. To
each of these two kinds of later rocks attention will be given in
this chapter.
Eruptive Rocks
The rise of eruptive matter, thrust upwards from lower depths
within the planet, is one of the causes by which the structure
of the crust has been most seriously affected. In Chapter IX.
reference was made to some of the features connected with the
protrusion of molten rocks in the production of volcanoes, and
more particularly to those subterranean changes which, when all
the outer and ordinary tokens of a volcano have been swept
away, remain as evidence of former volcanic action, even in
districts where every symptom of volcanic activity has long
vanished. We have now to inquire, generally, in what forms
eruptive matter has been built into the earth's, crust, and what
224
CHAP, xiv BOSSES 225
changes it has produced there, apart from those superficial
manifestations which are the visible signs of volcanic action.
When a mass of lava is forced upwards from the heated
interior of the earth towards the surface, the form which it finally
takes, and in which it cools and solidifies, must depend upon the
shape of the rent or cavity into which it has been thrust. We
may compare such a mass to a quantity of melted iron escaping
from a blast-furnace. The shape taken by the iron will, of course,
be fixed by that of the mould into which it is allowed to run.
The crust of the earth, as was pointed out in the previous chapter,
has undergone extensive movements, whereby its rocks have been
crumpled and broken. It consequently presents in different parts
very various degrees of resistance to any force acting upon it
from below. The eruptive materials have sometimes risen in the
fissures, sometimes have forced their way between the beds and
joints of the strata. According to the form of the mould in
which they have solidified, we may classify the eruptive rocks of
the crust into (i) bosses; (2) sheets or sills; (3) veins and
dykes ; and (4) necks.
Bosses. These are circular, elliptical, or irregularly shaped
masses of rock which, while still in a liquid or viscous state,
have been ejected into irregular rents of the earth's crust and
have solidified there. They consist of various crystalline rocks,
more especially granite, syenite, quartz-porphyry, trachyte, gabbro,
diorite, diabase, and basalt-rocks, and vary in width from a few
yards to several miles. Being generally harder than the sur-
rounding rocks, they commonly stand up as prominent knobs, hills,
or ridges. Their presence at the surface, however, is due, not to
their original protrusion there, as in a volcanic cone, but to the
removal of the overlying part of the original crust under which
they cooled and consolidated. Every boss is thus a witness of
the extensive wearing away of the surface of the land (Fig. 1 18).
In some large bosses there may have been a complex system
of fissures in which the eruptive material rose. Forced upwards
into these, the molten rock would no doubt envelope separated
masses of the crust, and might bear them along with it in its
ascent. We may even conceive it to have melted down such
enveloped masses. Pushing the rocks aside and thrusting itself
into every available crack in them, the eruptive mass would work
its way across the crust. Where it succeeded in opening a
passage to the surface, ordinary volcanic phenomena might take
place, such as disruption of the ground, ejection of stones and
Q
226
ERUPTIVE ROCKS
CHAP.
ashes, and outflow of lava. But, no doubt, in a vast number of
cases no such communication was ever effected. The eruptive
material paused in its upward passage and consolidated below
ground.
Where a body of eruptive material has pushed the rocks
upward into a dome-shaped form, and has collected beneath into a
thick lenticular mass, it forms what is known as a Laccolite.
This structure connects the Bosses with the Sills. It is not
infrequent in old volcanic districts. The admirable examples of
it, by which the name was suggested, were described by Mr. G.
K. Gilbert from the Henry Mountains in Southern Utah.
No rock affords more interesting bosses than granite. Two
FIG. 118. Outline and section of a Boss (a) traversing stratified rocks (b b).
features are especially well displayed by it the marginal veins or
dykes, and the surrounding ring of metamorphism produced in the
rocks through which granite has risen. Granite has invaded
many different kinds of rocks, and has effected various kinds of
change in them. Round its margin, large numbers of veins or
dykes of granite, aplite, quartz-porphyry or porphyrite, often strike
out from it into the surrounding rocks. There can be no doubt that
these are portions of the granite material, squeezed or injected
into cracks that opened in the crust around it during its ascent.
More important is the change that can be observed to have taken
place in the rocks immediately surrounding the boss. The granite
at the time of its protrusion was probably in a molten or pasty
condition, and impregnated with hot water or steam and vapours.
For a distance varying from a few feet up to two or three miles,
XIV
BOSSES
227
according chiefly to the size of the granite mass, the rocks next to it
have undergone alteration, the nature and amount of which appear to
have been in great measure dependent on the chemical and minera-
logical composition of the rocks themselves (Fig. 119). This kind
of metamorphism may sometimes consist in mere induration, but
more commonly it is accompanied by the development of new
minerals, or a new crystalline structure, even out of non-crystalline
sedimentary materials. The very same rock, which is elsewhere
a dark limestone full of shells, corals, or other organic remains,
may become a white crystalline marble next the granite, with no
trace of any organisms, and so unlike its usual condition that no
one would readily believe it to be the same rock. Again, a dark
shaly sandstone or greywacke traced towards the granite begins
FIG. 119. Ground-plan of Granite-boss with ring of Contact-Metamorphism. (a), Sand-
stones, shales, etc., dipping at high angles in the direction of the arrows ; (b), zone or
ring within which these rocks are metamorphosed ; (c), granite, sending out veins
into b.
to. show an increasing amount of mica, which has been developed
among the original sedimentary grains. Other new minerals like-
wise make their appearance, particularly garnets, until the rock
entirely loses its sedimentary structure and becomes a hornfels or
a garnetiferous mica-schist. Shales and slates, as they approach
the granite, likewise present a remarkable development of fine
mica-plates, and may pass into phyllites, with crystals of chiastolite
or other minerals developed in them. The alteration of rocks
round eruptive masses is called contact-metamorphism.
What the cause may be of this remarkable alteration has not
yet been satisfactorily made out. The mere heat of large masses
of eruptive material was probably sufficient to produce change.
There must often have been also a copious discharge of hot vapours
and water bearing mineralising agents, which would powerfully
228 ERUPTIVE ROCKS CHAP.
affect the adjacent rocks. Silica and other substances might then
be introduced, leading to induration and new chemical rearrange-
ments of the constituents. The protrusion of enormous bodies of
granite may also have given rise to mechanical movements in the
earth's crust, like those which have produced the shearing and
schistose structure, seen in regional metamorphism (p. 221).
Sills, Intrusive Sheets. Sometimes the easiest passage for the
erupted material from below has lain between the bedding-planes
of strata. The molten rock, after ascending some fissure or pipe,
has found its farther progress barred, and has escaped by forcing
up the overlying beds and thrusting itself in below them. On
cooling and consolidating, it appears as a sheet or bed intercalated
between older rocks. This structure is represented in Fig. 120.
Any one examining such a section on the ground, might naturally
regard the sheet s as a. bed of lava erupted at the surface, after the
d
FIG. 120. Sill or Intrusive Sheet.
formation of the strata a and before that of b. But various
features, characteristic of intrusive or subsequently injected sheets,
enable us to distinguish them from those which have been poured
out during the deposition of the strata among which they lie. For
example, sills break across the strata (as at d in Fig. 120) and
send veins into them. They are commonly most close-grained
along their edges ; sometimes, indeed, these edges have con-
solidated as a natural glass, showing that the rock at the time of its
intrusion was a molten vitreous mass which subsequently assumed
a more or less completely crystalline structure, except where it was
suddenly chilled by contact with the cool rocks between which it
was injected. True lava -streams, on the other hand, being
erupted above ground are generally most slaggy and scoriform on
their upper and under surfaces. Lastly, sills have generally
hardened and otherwise altered the rocks above and below them,
sometimes baking or even fusing them (p. 187). Where these
XIV
INTERSTRATIFIED LAVAS
229
characters are present, we may confidently infer that, though a
sheet of crystalline rock, so far as visible at the surface, may seem
to be regularly interstratified between sedimentary beds, as if it
had been contemporaneously poured forth among them, it has
FIG. 121. Interstratified or contemporaneous Sheets.
nevertheless been thrust in between them and may be of much
younger date.
Contemporaneous Sheets or Interstratified Lavas. A truly
contemporaneous sheet or group of sheets, marking the actual out-
pouring of lava-streams at the surface,
during the deposition of the strata I2
among which they now lie, may be
recognised by equally distinctive char- IX
acters. Thus a sheet having this origin I0
does not break across nor send veins g
into the overlying or underlying strata,
while its upper and under-surfaces, as 7
above stated, are usually the most open
cellular portions, though it is often 6
more or less vesicular or amygdaloidal
throughout. In Fig. 121 the beds 5
marked I, 2, 3, and 4 are sheets of
different lavas interstratified contem-
poraneously in the series of sandstones,
shales, limestones, and other strata
among which they lie. Fragments of
them are not infrequently to be FlG
detected in the overlying sediments,
which are thus shown to be of later
origin, and bands of tuff are commonly associated with them,
just as showers of ashes accompany the lava-streams of living
volcanoes. As an illustration of the way in which the evidence
of ancient volcanic action may be gathered, the section in Fig.
122 may be taken supplementary to the data given already in
122. Section to illustrate
evidence of contemporaneous
volcanic action.
230 ERUPTIVE ROCKS CHAP.
Chapter IX. At the bottom of the section we stand on the slaggy
upper surface of a lava-stream (i) which was poured out under
water, for directly above it comes a seam of dark shale (2) repre-
senting fine mud that was deposited from suspension in water.
That volcanic explosions still continued after the outflow of the
lava, is indicated by the abundant bits of slaggy lava and volcanic
detritus scattered through the shale, and that the scene of these
operations was the sea-floor is conclusively proved by the numerous
shells, crinoids, and other marine remains that lie in some bands
of the shale. The bottom must at that time have been muddy,
and therefore not so well suited as it afterwards became for the
support of life. Above the shale come two feet of limestone (3),
entirely made up of fragments of marine organisms, and showing
that the water had at last become clear, so that these sea-creatures
continued to flourish abundantly until their congregated remains
formed a bed of solid stone. But from some change in the geo-
graphy of the region, currents bearing dark mud once more in-
vaded this part of the sea, and threw down the material that now
forms the band of shale (4). The absence of organic remains in
this band probably indicates that the inroad of mud destroyed the
life previously so prolific. When this condition of things had been
brought about, renewed volcanic explosions took place in the
neighbourhood. First came showers of dust, ashes, and stones,
which fell over the sea, and are now represented by the band of
tuff (5). Then followed the outpouring of a stream of lava (6),
with its characteristic cellular structure. But this did not quite
exhaust the vigour of the volcano, for the band of tuff (7) points
to renewed showers of dust and stones. When the explosions
ceased, the deposition of dark mud, which had been interrupted
by the volcanic episode, was resumed, and the band of shale (8)
was laid down. From the fragments of ferns and other plants
in this shale, it is clear that land was not far off. The sea had
evidently been gradually shallowing by the infilling of sediment
and volcanic materials, and at last, on the muddy flat, represented
by the layer of fire-clay (9), marshy vegetation sprang up into a
thick jungle, like the mangrove-swamps of tropical shores at the
present day. After growing long enough to form the bed of
matted vegetable matter now represented by the coal-seam (10),
the verdant jungle was invaded by the sea, and sank under the
muddy water that threw down upon its submerged surface the grey
shale (n). In this shale we detect interesting traces of the
renewal of volcanic activity, more especially in occasional large
xiv INTERSTRATIFIED LAVAS 231
blocks of lava, which have evidently been ejected by volcanic
explosions in the near neighbourhood, as in the example already
cited on p. 112 (Fig. 47). A more vigorous volcanic outburst
FIG. 123. Succession of lava-sheets and volcanic conglomerates, Canon of Yellowstone
River, Yellowstone Natural Park. Photograph by Mr. C. D. Walcott, U.S. Geol. Survey.
poured out the stream of columnar lava (12) which buried the
whole and forms the top of the section.
In regions where volcanic activity has long ceased, and where
the erupted rocks have been for ages exposed to the universal
denudation that affects the dry land, the alternation of hard massive
lavas with softer tuffs and other fragmental materials has given
232 ERUPTIVE ROCKS CHAP.
rise to many striking topographical features. In Britain and the
Faroe Isles the lavas of Tertiary time have been dissected by the
sea and have been cut into stupendous precipices and isolated sea-
stacks. In Western America similar results have been achieved
by the erosive action of rivers combined with the other processes
of weathering (Fig. 123).
Veins and Dykes". These have already been referred to in
Chapter IX. as part of the evidence for volcanic action. We have
here to consider how they occur in connection with the protrusion
of eruptive material within the crust of the earth. Where the
material so erupted has solidified in a vertical or nearly vertical
fissure so as to form a wall-like mass, it is called a dyke (Fig. 53
and d in Fig. 120). Otherwise the portions of erupted rock that
have consolidated in irregular rents are known as veins.
Veins are of common occurrence round bosses of granite, where
they can be traced into the parent mass from which they have
proceeded (Fig. 119). They may likewise be observed in con-
nection with intrusive sheets and bosses of basalt, andesite, trachyte,
diorite, and other rocks from which they ramify outwards into the
surrounding parts of the earth's crust. Their occurrence there is
one of the proofs of the intrusive character and subsequent date
of such masses (pp. 226, 228).
Dykes vary from less than a foot to 100 feet or more in breadth,
and often run in nearly straight courses, sometimes for many miles.
They consist most usually of diabase, andesite, basalt, or some
allied rock. Sometimes they have risen along lines of fault ; but
in hundreds of instances in Great Britain, they do not appear to
be connected with any faults, but actually cross some of the largest
faults in the country without being deflected. The remarkable
way in which dykes have risen through a complicated series of
rocks and faults, and have preserved their courses, is exemplified
in Fig. 124.
Like intrusive sheets, but in a less degree, dykes harden or
otherwise alter the rocks on either side of them ; they likewise
present a similar closeness of grain or even a glassy texture along
their margins, where the molten rock was most rapidly chilled by
coining in contact with the cold walls of the fissure. Not infre-
quently, indeed, their sides are coated with a thin crust of black
glass, as if they had been painted with tar (see Basalt-glass, p. 183),
as has been already remarked with regard to many sills. No
doubt the whole material of such dykes, at the time when it rose
from below and filled up the space between the two walls of its
XIV
NECKS
233
opened fissure, was a molten glass. The portions that were at
once chilled by contact with the walls adhered as a layer of glass.
But inside this layer, the molten rock had more time to cool. In
cooling, its various minerals crystallised, and the present crystalline
FIG. 124. Map of Dykes near Muirkirk, Ayrshire, i, Silurian rocks ; 2, Lower Old
Red Sandstone ; 3, Carboniferous rocks \f,f,f, Faults ; d, fi, Dykes.
structure was developed. But even yet, though most of the rock
is formed of crystalline minerals, portions of the original glass may
not infrequently be detected between them, when thin sections are
placed under the microscope (p. i 59).
Necks. These are the filled-up pipes or funnels of former
FIG. 125. Section of a volcanic neck. The dotted lines suggest the original form
of the volcano.
volcanic vents. Their connection with volcanic action has been
already alluded to on p. i 1 6. They are circular or elliptical in
ground-plan, and vary in diameter from a few yards up to a mile
or more (see Figs. 49-52). They consist of some form of lava
(quartz-porphyry, andesite, trachyte, diorite, basalt, etc.) or of the
fragmentary materials which, after being ejected from the volcanic
234 MINERAL VEINS CHAP.
chimney, fell back into it and consolidated there. They occur
more particularly in districts where beds of lava and tuff are inter-
stratified with other rocks. The necks, in fact, represent vents from
which these volcanic materials were ejected. In Fig. 125, for
example, the beds of lava and tuff (b b} interstratified between the
strata a a and c c have been folded into an anticline. In the
centre of the arch rises the neck (ii\ which has probably been the
chimney that supplied these volcanic sheets, and which has been
filled up with coarse tuff, and traversed with dykes and veins of
basalt (*). The dotted lines, suggestive of the outline of the
original volcano, may serve to indicate the connection between
the neck and its volcanic sheets, and also the effects of denudation.
Necks are frequently traversed by dykes (* in Fig. 125), as we
know ako to be the case with the craters of modern volcanoes.
The rocks surrounding a neck are sometimes bent down round it,
as if they had been dragged down by the subsidence of the
material filling up the vent ; they are also frequently much
hardened and baked. When we reflect upon the great heat of
molten lava and of the escaping gases and vapou-rs, we may well
expect the walls of a volcanic vent to bear witness to the effects of
this heat. Sandstones, for instance, as already remarked, have
been indurated into quartzite, and shales have been baked into a
porcelain-like substance (p 187).
Mineral Veins
Into the fissures opened in the earth's crust there have been
introduced various simple minerals and ores which, solidifying
there, have taken the form of Mineral Veins. These materials
are to be distinguished from the eruptive veins and dykes above
described. A true mineral vein consists of one or more minerals
filling up a fissure which may be vertical, but is usually more or
less inclined, and may vary in width from less than an inch up to
150 feet or more. The commonest minerals (or veinstones] found
in these veins are quartz, calcite, barytes, and fluor-spar. The
metalliferous portions (or ores} are sometimes native metals (gold
and copper, for example), but are more usually metallic oxides,
silicates, carbonates, sulphides, chlorides, or other combinations.
These materials are commonly arranged in parallel layers, and it
may often be noticed that they have been deposited in duplicate
on each side of a vein. In Fig 1 26, for instance, we see that
each wall (w w) is coated with a band of quartz (i, i), followed
XIV
MINERAL VEINS
235
successively by one of blende (sulphide of zinc, 2, 2), galena (sul-
phide of lead, 3, 3), barytes (4, 4), and quartz (5, 5). The central
portion of the vein (6) is sometimes empty or may be filled up
with some veinstone or ore. Remarkable variations in breadth
characterise most mineral veins. Sometimes the two walls come
together and thereafter retire from each other far enough to allow
a thick mass of mineral matter to have been deposited between
them. Great differences may also be observed in the breadth of
the several bands composing a vein. One of these bands may
swell out so as to occupy the whole breadth of the vein, and then
rapidly dwindle down. The ores are more especially liable to
1234
FIG. 126. Section of a Mineral vein.
such variations. A solid mass- of ore may be found many feet in
breadth and of great value ; but when fallowed along the course
of the vein, it may die away into mere strings or threads through
the veinstones.
The duplication of the layers in mineral veins shows that the
deposition proceeded from the walls inwards to. the centre. In
the diagram (Fig. 126) it is evident that the walls of the open
fissure were first coated with quartz. The next substance intro-
duced into the vein was sulphide of zinc, a layer of which was
deposited on the quartz. Then came sulphide of lead, and lastly,
quartz again. The way in which the quartz-crystals project from
the two sides shows that the space between them was free, and,
as above stated, it has sometimes remained unfilled up.
There appears to be no reason to doubt that the sub-
stances deposited in mineral veins were mainly introduced
dissolved in water. Not improbably heated waters rose in the
236 MINERAL VEINS CHAP, xiv
fissures, and as they cooled in their ascent, they coated the walls
with the minerals which they held in solution. These minerals
may sometimes have been abstracted from the surrounding rocks
by the permeating water ; more usually perhaps they have been
carried up from some deeper source within the crust. During
the process of infilling, or after it was completed, a fissure has
sometimes reopened, and a new deposition of veinstones or ores
has taken place. Now and then, too, land-shells and pebbles are
found far down in mineral veins, showing that during the time
when the layers of mineral matter were being deposited, the
fissures sometimes communicated with the surface.
Summary. In this chapter it has been shown that, in many
cases, rents and cavities in the earth's crust have been filled up
with mineral matter introduced into them, either (i) in the molten
state, or (ii) in solution in water.
(i) The forms assumed by the masses of eruptive rock injected
into the crust of the earth have depended upon the shape of the
openings into which the melted matter has been poured, as the
form of a body of cast-iron is regulated by that of the mould into
which the melted metal is allowed to run. Taking this principle
of arrangement, we find that eruptive rocks may be grouped into
(i) Bosses, or irregularly-shaped masses, which have risen through
and solidified in fissures or orifices, and now, owing to the removal
of the rock under which they lay, form hills or ridges. The
eruptive material sends out veins into the surrounding rocks which
are sometimes considerably altered, forming a metamorphic ring
round the eruptive rock. (2) Sills or sheets which have been
thrust between the bedding-planes of strata. These resemble
truly interstratified beds, but the difference between the two kinds
of structure can be readily appreciated. Interstratified lavas and
tuffs mark the occurrence of volcanic phenomena at the surface,
during the time of the formation of the strata among which they
occur. Intrusive sheets, on the other hand, are always subsequent
in date to the rocks between which they lie. (3) Veins and
dykes, consisting of eruptive rock which has been thrust between
the walls of irregular rents or straight fissures. (4) Necks, or the
filled-up pipes of former volcanic vents.
(ii) Mineral veins are masses of mineral matter which has been
deposited, probably in most cases from aqueous solution, between
the walls of fissures in the earth's crust, and consists of bands of
veinstones (quartz, calcite, barytes, etc.) and ores (native metals,
or oxides, sulphides, etc., of metals).
CHAPTER XV
HOW FOSSILS HAVE BEEN ENTOMBED AND PRESERVED, AND
HOW THEY ARE USED IN INVESTIGATING THE STRUC-
TURE OF THE EARTH'S CRUST, AND IN STUDYING
GEOLOGICAL HISTORY
IN an earlier part of this volume (Chapter VIII.) attention was
called to the various circumstances under which the remains of
plants and animals may be entombed and preserved in sedi-
mentary accumulations. When these remains have thus been
buried they are known as Fossils.
Nature and use of Fossils. The word "fossil," meaning
literally " dug up," was originally applied to all kinds of mineral
substances taken out of the earth ; but it is now exclusively used
for the remains or traces of plants and animals imbedded by
natural causes in any kind of rock, whether loose and incoherent,
like blown sand, or solid, like the most compact limestone. It
includes not only the actual remains of the organisms. The
empty mould of a shell which has decayed out of the stone that
once enveloped it, or the cast of the shell which has been entirely
replaced by inorganic sand, mud, calcite, silica,, etc., are fossils.
The very impressions left by organisms, such as the burrow or
trail of a worm in hardened mud, and the footprints of birds and
quadrupeds upon what is now sandstone, are undoubted fossils.
In short, under this general term is included whatever bears
traces of the form, structure, or presence of organisms preserved
in the sedimentary accumulations of the surface, or in the rocks
underneath.
In geological history fossils are of fundamental importance.
They enable us to investigate conditions of geography, of climate,
and of life in ancient times, when these conditions were very
237
238 NATURE AND USE OF FOSSILS CHAP.
different from those which now prevail on the earth's surface.
They likewise furnish the ground on which the several epochs of
geological history can be determined, and on which the stages
of that history in one country can be compared with those in
another. So valuable and varied is the evidence supplied by
fossils to the geologist, that he regards them as among the most
precious documents accessible to him for unravelling the past
history of the earth. Some knowledge of the structure and classi-
fication of plants and animals is essential for an intelligent
appreciation of the use of fossils in geological inquiry. To aid
the learner, a synopsis of the Vegetable and Animal Kingdoms is
given in the Appendix, with especial reference to the fossil forms ;
but it must be understood that for adequate information on this
subjects recourse should be had to text -books of Botany and
Zoology.
Conditions for the preservation of Organic Remains. It is
obvious that all kinds of plants and animals have not the same
chances of being preserved as fossils. In the first place, only
those, as a rule, are likely to become fossils whose remains can
be kept from decay and dissolution by being entombed in some
kind of deposit. Hence land -animals and plants have, on the
whole, less chance of preservation than those living in the sea,
because deposits capable of receiving and securing their remains
are exceptional on land, but are generally distributed over the floor
of the sea (pp. 100, 101). Moreover, the ocean covers now, and
probably always has covered, a far larger area of the earth's surface
than the land. We should expect, therefore, that among the records
of past time, traces of marine should largely preponderate over
traces of terrestrial life. Now this is everywhere the case. We
know relatively little of the assemblages of plants and animals
which in successive epochs have lived upon the dry land, but we
have a comparatively large amount of information regarding those
which have tenanted the sea. For this reason, marine fossils are
more valuable than terrestrial, in comparing the records of the
successive epochs of geological history in different parts of the
globe.
In the second place, from their own chemical composition and
structure, plants and animals present extraordinary differences in
their aptitude for preservation as fossils. Where they possess no
hard parts, and are liable to speedy decay, we can hardly expect
that they should leave behind them any enduring relic of their
existence. Hence a large proportion, both of the vegetable and
xv DURABLE PARTS OF PLANTS 239
animal kingdoms, may at once be excluded as inherently unlikely
to occur in the fossil condition. Of course, under exceptional
circumstances, traces of almost any organism may be preserved,
and therefore we should probably not be justified in saying that
by no chance might some recognisable vestige of it be found fossil.
Nothing seems more perishable than the tiny gnats and other
forms of insect life that fill the air on a summer evening. Yet
many of these short-lived flies have been sealed up within the
resin of trees (amber), and their structure has been admirably
preserved. Such exceptional instances, however, only bring out
more distinctly how large a proportion of the living tribes of the
land must utterly perish, and leave no recognisable record of
their ever having existed.
But, where there are hard parts in an organism, and especially
where, from their chemical composition, they can for some time
resist decay, they may, under favourable conditions, be buried in
sedimentary deposits, and may remain for indefinite ages locked
up there. It is obvious, therefore, that animals possessing hard
parts are much the most likely to leave permanent relics of their
presence, and ought to occur most frequently as fossils. It is
these animals whose remains are preserved in peat-mosses, river-
gravels, lake-marls, and on the sea-floor at the present time. Yet,
if we were to judge of the extent of the whole existing animal
kingdom solely from the fragmentary remains so preserved, what
an utterly inadequate conception of it we should form ! So, too,
if we estimate the variety of the living creatures of past time
merely from the evidence of the fossils that have chanced to be
preserved among the rocks, we shall probably arrive at quite as
erroneous a conclusion. There can be no doubt that from the
earliest time only an insignificant fraction of the varied life of each
period has been preserved in the fossil state, as is unquestionably
the case at the present day.
Durable parts of Plants. The essential parts of the solid frame-
work of plants consist of the substances known as cellulose and
vasculose, which, when kept in dry air, or when water-logged and
buried in stiff mud, may remain undecomposed for long periods.
The timber beams in the roofs and floors of old buildings are
evidence that, under favourable conditions, wood may last for
many centuries. Some plants eliminate carbonate of lime from
solution in water, and form with it a solid substance which requires
no further treatment to enable it to endure for an indefinite period,
when screened from the action of water. Still more durable are
240 NATURE AND USE OF FOSSILS CHAP.
the remains of those plants which abstract silica and build it up
into their framework, such as the diatoms of which the frustules
become remarkably permanent fossils, in the form of diatom-earth
or tripoli-powder, which is made up of them (p. 94).
Durable parts of Animals. The hard parts of animals may
be preserved with little or no chemical change, and remain as
durable relics. The hard horny integuments of insects, arachnids,
Crustacea, and some other animals, are composed essentially of the
substance called chitin, which can long resist decomposition, and
which may therefore be looked for in the sedimentary deposits of
the present time, as well as of former periods. The chitin of
some fossil scorpions, admirably preserved among the Carboniferous
rocks of Scotland, can hardly be distinguished from that of the
living scorpion. Many of the lower forms of animal life secrete
silica, and their hard parts are consequently easily preserved, as
in the case of radiolaria and sponges. In the great majority of
instances, however, the hard parts of invertebrates consist mainly
of carbonate of lime, and are readily preserved among sedimentary
deposits. The skeletons of corals, the plates of echinoderms, and
the shells of molluscs, are examples of the abundance of calcareous
organisms, and the frequency of their remains in the fossil state
shows how well fitted they are for preservation. Among verte-
brates the hard part consists chiefly of phosphate of lime. In
some forms (ganoid fishes and crocodiles, for example) this sub-
stance is partly disposed outside the body (exo-skeleton) in the
form of scales, scutes, or bony plates. But more usually it is
confined to the internal skeleton (endo-skeleton). It is mainly by
their bones and teeth that the higher vertebrates can be recognised
in the fossil state. Sometimes the excrement has been preserved
(Coprolites\ and may furnish information regarding the food of
the animals, portions of undigested scales, teeth, and bones being
traceable in it (Fig. 76).
Fossilisation. The process by which the remains of a plant
or animal are entombed and preserved in the fossil state is termed
Fossilisation. It varies greatly in details, but all these may be
reduced to three leading types.
i. Entire or partial preservation of the original substance.
In rare instances, the entire animal or plant has been preserved,
of which the most remarkable examples are those where carcases
of the extinct mammoth have been sealed up in the frozen mud
and peat of Siberia, and have thus been preserved in ice. Insects,
as above mentioned, have been involved in the resin of trees, and
xv CONDITIONS OF FOSSILISATION 241
may now be seen, embalmed like mummies, in amber. More
usually, however, a variable proportion of the organic matter has
passed away, and its more durable parts have been left, as in the
carbonisation of plants (peat, lignite, coal) and the disappearance
of the organic matter from shells and bones, which then become
dry and brittle and adhere to the tongue.
2. Entire removal of the original substance and internal
structure, o?ily the external form being preserved. When a dead
animal or plant has been entombed, the mineral matter in which
it lies hardens round it and takes a mould of \ts form. This may
be accomplished with great perfection if the material is sufficiently
fine-grained and solidifies before the object within has time to
FIG. 127. Common Cockle (Cardhtm ed-ule} \ (a), side view of both valves ; (b), mould of
the external form of one valve taken in plaster of Paris ; (c\ side view of cast in plaster
of Paris of interior of the united valves.
decay. Carbonate of lime and silica are specially well adapted
for taking the moulds of organisms, but fine mud, marl, and sand
are also effective. The organism may then entirely decay, and its
substance may be gradually removed by percolating water, leaving
a hollow empty space or mould of its form. Such moulds are
of frequent occurrence among fossiliferous rocks, and are specially
characteristic of molluscs, the shells of which are so abundant,
and occur imbedded in so many different kinds of material.
Sometimes it is the external form of the shell that has been taken,
the shell itself having entirely disappeared ; in other cases a cast
of the interior of the shell has been preserved. How different
these two representations of the same shell may be is shown in
Fig. 127, wherein a represents a side view of the common cockle,
while c is a cast of the interior of the shell in plaster of Paris.
The contrast between a mould of the outside and inside of the
242 NATURE AND USE OF FOSSILS CHAP.
same shell is shown by the difference between b and c, which are
both impressions taken in plaster.
After the decay and removal of the substance of the enclosed
organisms, the moulds may be filled up with mineral matter,
which is sometimes different from the surrounding rock. The
empty cavities have formed convenient receptacles for any deposit
which permeating water might introduce. Hence we find casts of
organisms in sand, clay, ironstone, silica, limestone, pyrites, and
other mineral substances. Of course, in such cases, though the
external form of the/ original organism is preserved, there is no
trace of internal structure. No single particle of the cast may
ever have formed part of the plant or animal.
3. Partial or entire petrifaction of organic structure by mole-
cular replacement Plants and animals which have undergone this
change have had their substance gradually removed and replaced,
particle by particle, with mineral matter. This transformation
has been effected by percolating water containing mineral solu-
tions, and has proceeded so tranquilly, that sometimes not a
delicate tissue in the internal structure of a plant has been dis-
placed, and yet so rapidly, that the plant had not time to rot
before the conversion was completed. Accordingly, in \x\3Apetri-
factions, that is, plants or animals of which the structure has been
more or less perfectly preserved in stone, the petrifying material
is always such as may have been deposited from water. The
most common substance employed by nature in the process of
petrifaction is carbonate of lime, which, as we have seen, is almost
always present in the water of springs and rivers. Organic struc-
tures replaced by this substance are said to be calcified. Fre-
quently the carbonate of lime has assumed, more or less completely,
a crystalline structure after its deposition, and in so doing has
generally injured or destroyed the organic structure which it ori-
ginally replaced. Where the calcareous matter of -an organism
has been removed by percolating water, as often happens in sands,
gravels, or other porous deposits, the fossil is said to be decalcified
Another abundant petrifying medium in nature is silica, which, in
its soluble form, is generally diffused in terrestrial waters, where
humous acids or organic matter are present in solution. The re-
placement of organic structures by silica, called silicification, fur-
nishes the most perfect form of petrifaction. The interchange of
mineral matter has been so complete that even the finest micro-
scopic structures have been faithfully preserved. Silicified wood
is an excellent example of this perfect replacement. Sulphides,
xv FOSSILS PROVE GEOGRAPHICAL CHANGES 243
which are often produced by the reducing action of decaying
organic matter upon sulphates, occur also as petrifying media, the
most common being the iron sulphide, usually in the less stable
form of marcasite, but sometimes as pyrite. Carbonate of iron
likewise frequently replaces organic structures ; the clay-ironstones
of the Carboniferous system abound with the remains of plants,
shells, fishes, and other organisms which have been converted
into siderite (Figs. 72, 76).
The chief value of fossils in geology is to be found in the light
which they cast upon former conditions of geography and climate,
in the clue which they furnish as to the relative ages of different
geological formations, and in the materials which they supply
for a history of the evolution of organised existence upon the
earth.
i. How Fossils indicate former changes in Geography.
Terrestrial plants and animals obviously point to the existence
of land. If their remains are found in strata wherein most of the
fossils are marine, they usually show that the deposits were laid
down upon the sea-floor not far from land. But where they occur
in the positions in which they lived and died, they prove that their
site was formerly a land-surface. The stumps of trees remaining
in their positions of growth, with their roots branching out freely
from them in the clay or loam underneath undoubtedly mark the
position of an ancient woodland. If, besides these remains, there
are associated in the same strata leaves, fruits, or seeds, together
with wing-cases of beetles, bones of birds and of land-animals,
additional corroborative evidence is thereby obtained as to the
existence of the ancient land. More usually, however, it is by
deposits left on lake-bottoms that the land of former periods of
geological history is known. As already pointed out (Chapter
IV.), the fine mud and marl of lakes receive and preserve abundant
relics of the vegetation and animal life of the surrounding regions.
As illustrations of lacustrine formations, from which most of our
knowledge of the contemporary terrestrial life is obtained, reference
may be made to the Molasse of Switzerland, the limestones and
marls of the Limagne d'Auvergne, in Central France, and the vast
depth of strata from which so rich an assemblage of plant and
animal remains has been obtained in the Western Territories of
the United States (see Chapter XXV.). Alternations of buried
forests or peat-mosses, with lake deposits, show how lakes have
successively increased and diminished in volume. The frequent
occurrence of a bed of lacustrine marl at the bottom of a peat-bog
244 NATURE AND USE OF FOSSILS CHAP.
proves how commonly shallow lakes have been filled up and dis-
placed by the growth of marshy vegetation (pp. 4, 92).
Remains of marine plants and animals almost invariably
demonstrate that the locality in which they are found was once
covered by the sea. Exceptions to this rule are so few as hardly
to be worthy of special notice, as, for instance, when molluscs,
crustaceans, and other forms of marine life are carried up by sea-
birds to considerable elevations, where, after their soft parts have
been eaten, their hard shells and crusts may be preserved in truly
terrestrial deposits, or when sea-shells, tossed up by breakers
above the tide-line, are swept inland by wind.
Rolled fragments of shells, mingled in well-rounded gravel and
sand, point to some former shore where these materials were
ground down by beach-waves. Fine muddy sediment, containing
unbroken shells, echinoderms, crustaceans, and other relics of the
sea, indicate deeper water beyond the scour of waves, tides, and
currents. Beds of limestone, full of corals and crinoids, mark the
site of a clear sea, in which these organisms were allowed to
flourish undisturbed for many generations. It may often be
observed that the fossils, which are abundant and large in a lime-
stone, become few in number and small in size in an overlying bed
of shale or clay ; or that they wholly disappear in the argillaceous
rock. The meaning of this can hardly be mistaken. The clear
water in which the marine creatures were able to build up the
limestone was at last invaded by some current carrying mud.
Consequently, while the more delicate forms perished, others con-
tinued to live on in diminished numbers and dwarfed development,
until at last the muddy sediment settled down so thickly that the
animals, whose hard parts might have been preserved, were driven
away from that area of the sea-bottom.
2. How Fossils indicate former conditions of Climate.
The remains of plants or animals characteristic of tropical countries
may be taken to bear witness to a tropical climate at the time
which they represent. If, for example, a deposit were found con-
taining leaves of palms and bones of tigers, lions, and elephants,
we should infer that it was formed in tropical conditions, such as
are now presented by the warmer parts of Africa or Asia. On
the other hand, were a stratum to yield leaves of a small birch
and willow, with bones of reindeer, musk-ox, and lemming, we
would regard it as evidence of a cold climate. Such inferences,
however, must be based either upon the occurrence of the very
same species as are now living, and the characteristic climate of
xv FOSSILS AND GEOLOGICAL CHRONOLOGY 245
which is known, or upon assemblages of plants or animals which
may be compared with corresponding assemblages now living.
We may be tolerably confident that the existing reindeer has
always been restricted to a cold climate, and that the living
elephants have as characteristically been confined to warm
climates. But it would be rash to assume that all deer prefer
cold and all elephants choose heat. The bones of an extinct
variety of elephant and one of rhinoceros, have long been known
as occurring e^ven up within the Arctic regions, and when these
remains were first found the conclusion was naturally drawn that
they proved the former existence of a warm climate in the far
north. But the subsequent discovery of entire carcases of the
animals covered with a thick mat of woolly hair, showed that
they were adapted for life in a cold climate, and their occurrence
in association with the remains of animals which still live in the
Arctic regions, proved beyond doubt that the original inference
regarding them was erroneous. In drawing conclusions as to
climate from fossil evidence, it is always desirable to base them
upon the concurrent testimony of as large a variety of organisms
as possible, and to remember that they become less and less reliable
in proportion as the organisms on which they are founded depart
from the species now living.
3. How Fossils indicate Geological Chronology. As the
result of careful observations all over the world, it has been
ascertained that in the youngest strata the organic remains are
nearly or quite the same as species now living, but that, as we
proceed into older strata, the number of existing species diminishes,
and the number of extinct species increases, until at last no living
species is to be found. Moreover, the extinct species found in
younger strata disappear as we trace them back into older rocks,
and their places are taken by other extinct species. Every great
series of fossiliferous rocks is thus characterised by its own peculiar
assemblage of species. Not only do the species change ; the
genera, too, disappear one by one as we follow them into older
rocks, until among the earliest strata only a few of the living
genera are represented. Whole families and orders of animals
which once flourished have utterly vanished from the living world,
and we only know of their existence from the remains of them
preserved among the rocks.
A certain definite order of succession has been observed among
the organic remains imbedded in the stratified rocks of the earth's
crust, and this order has been found to be broadly alike all over
246 NATURE AND USE OF FOSSILS CHAP.
the world. The fossils of the oldest fossiliferous rocks of Europe,
for instance, are like those of the oldest fossiliferous rocks of Asia,
Africa, America, and Australasia, and those of each succeeding
series of rocks follow the same general sequence. It is obvious,
therefore, that fossils supply us with an invaluable means of fixing
the relative position of rocks in the series of geological formations.
Whether or not the same type of fossils was always contem-
poraneous over the whole planet cannot be determined ; but it
generally occupied the same place in the procession of life. Hence
stratified formations, which may be quite unlike'each other in
regard to the nature of their component materials, if they contain
similar organic remains, may be compared with each other, and
classed under the same name.
Fossils characteristic of particular subdivisions of the series of
geological formations (see Table, p. 256) are of great service as
guides to the relative age of the rocks that contain them. Of
these the following are examples :
Lepidodendra and Sigillariae, characteristic of Old Red Sandstone and Car-
boniferous rocks (pp. 288, 306).
Cycads, characteristic of Mesozoic rocks (pp. 318, 323, 325, 332, 350).
Graptolites, characteristic of Silurian rocks (pp. 270, 279, 292).
Trilobites ,, Cambrian to Carboniferous rocks (pp. 271,
281, 293, 307).
Cystideans, characteristic of Silurian rocks (Fig. 137).
Blastoids ,, Carboniferous rocks (Fig. 165).
Hippurites ,, Cretaceous rocks (p. 353).
Orthoceratites ,, Palaeozoic rocks (Figs. 144, 172).
Ammonites ,, Mesozoic rocks (Figs. 182, 191, 205).
Cephalaspids ,, Silurian, Old Red Sandstone (pp. 284, 290).
Ichthyosaurus and Plesiosaurus Mesozoic rocks (Figs. 328, 338, 356).
Iguanodon Cretaceous rocks (p. 356).
Toothed birds Jurassic and Cretaceous rocks (pp. 341, 357).
Nummulites, Palseotherium, Anoplotherium, Deinocerata, characteristic of
older Tertiary rocks (pp. 368, 370, 371, 372, 377).
Mastodon, Elephas, Equus, Cervus, Hyaena, Apes, characteristic of younger
Tertiary and Recent rocks (pp. 382, 387, 388, 390, 400, 408).
By attentive study and comparison, the fossiliferous rocks in
different countries have been subdivided into sections, each
characterised by its own facies or type of organic remains. Con-
sequently, beginning with the oldest and proceeding upward to
the youngest, we advance through natural chronicles of the suc-
cessive tribes of plants and animals which have lived on the earth's
surface. These chronicles, consisting of sandstones, shales, lime-
stones, and the other kinds of stratified deposits, form what is
XV THE GEOLOGICAL RECORD 24?
called the Geological Record. In order to establish their true
sequence in time, their Order of Superposition must first be
determined ; that is, it is requisite to know which lie at the
bottom, and must have been formed first, and in what order the
others succeed them. When this fundamental question has once
been settled, then the fossils characteristic of each group of strata
serve as a guide for recognising that group wherever it may be
found.
While fossils enable us to divide the Geological Record into
chapters, they also show how strikingly imperfect this record is as
a history of the plants and animals that have lived on the surface
of the earth, and of the revolutions which that surface has under-
gone. We may be sure that the progress of life, from its earliest
appearance in lowly forms of plant or animal, has been continuous
up to the present condition of things. But in the Geological
Record there occur numerous gaps. The fossils of one group of
recks are succeeded by a more or less completely different series
in the next group. At one time it was supposed that such breaks
in the continuity of the record marked terrestrial convulsions which
caused the destruction of the plants and animals of the time, and
were followed by the creation of new tribes of living things. But
evidence has every year been augmenting to indicate that no such
general destruction and fresh creation ever took place. The gaps
in the record mark no real interruption of the life of the globe.
They are rather to be looked upon as chapters that have been
torn out of the annals, or which never were written. We have
already learned in Chapter VIII. how many chances there must be
against the preservation of anything like a complete record of the
life of the globe at any particular time. It is also clear that even
where the chronicle may have been comparatively full, it is exposed
to many dangers afterwards. The rocks containing it may be
hidden beneath the sea, or raised up into land and entirely worn
away, or entombed beneath volcanic ejections, or so crushed and
crumpled as to become no longer legible.
Taking fossils as a guide, geologists have partitioned the
fossiliferous rocks into what are called stratigraphical subdivisions
as follows : A bed, or limited number of beds, in which one or
more distinctive species of fossils occur, is called a zone or horizon,
and may be named after its most typical fossil. Thus in the
Lias, the zone in which the ammonite known as Ammonites
Jamesoni occurs, is spoken of as the "zone of Ammonites Jame-
soni" or " Jamesom-zQne." Two or more zones, united by the
2 4 8
NATURE AND USE OF FOSSILS
CHAP.
occurrence in them of a number of the same characteristic species
or genera, form what are known as Beds or an Assise. Two or
more of such beds or assises may be termed a Group or Stage.
Where the number of assises in a stage is large they may be
subdivided into Sub-stages or Sub-groups. The stage or group
will then consist of several sub-stages, and each sub-stage or sub-
group of several assises. A number of groups or stages is com-
bined into a Series, Section, or Formation, and a number of
series, sections, or formations constitute a System. A number
of systems are connected together to form each of the great
divisions of the Geological Record. This classification will be
best understood if placed in tabular form, as in the subjoined
subdivisions, which occur in the Cretaceous System. 1
Stratigraphical Components.
A stratum, layer,"
seam, or bed, or a
number of such
minor subdivisions,
characterised by
some distinctive
fossil
Two or more zones
Two or more sets of con-
nected beds or assises =
Two or more groups or
stages
Several related forma-
tions
Descriptive Names
Zone or horizon
Beds or an assise
(Group or stage,
which may be
subdivided into
sub-groups or sub-
stages
Series, section, or for-
mation
System
Examples from the Cre-
taceous System of Europe.
Zone of Pecten asper.
Warminster beds.
Cenomanian stage, com-
prising the Rotho-
magian and Caren-
tonian sub-stages.
Neocomian formation.
Cretaceous System.
The names by which the larger subdivisions of the Geological
Record are known have been adopted at various times and on
no regular system. Some of them are purely lithological ; that
is, they refer to the mere mineral nature of the strata, apart
altogether from their fossils, such as Coal-measures, Chalk, Green-
sand, Oolite. These names belong to the early years of the
progress of geology, before the nature and value of organic
remains had been definitely realised. Other epithets have been
suggested by localities where the strata were first noticed, as Bath
1 For an account of the Cretaceous System, see Chapter XXIV.
xv THE GEOLOGICAL RECORD 249
Oolite (Bathonian), Oxford Clay (Oxfordian), Portland Stone
(Portlandian). The more recent names for the larger divisions
have, in general, been chosen from districts where the formations
are typically developed, or where they were first critically studied,
e.g. Silurian, Devonian, Permian, Jurassic. In some cases, the
larger subdivisions have received names from some distinguishing
feature in their fossil contents, as Eocene, . Miocene, Pliocene. 1
But it is mainly to the minor sections that the characters of the
fossil contents have supplied names.
The designation of any particular group of strata has gradually
come to acquire a chronological meaning. Thus the term Car-
boniferous formations or system was originally applied to a series
of strata in which the occurrence of coal and carbonaceous shales
is a distinctive feature. It includes a thick series of limestones,
clays, sandstones, and other strata, replete with organic remains,
and containing the records of a long interval of geological time,
which were first observed in Europe, but of which representatives
have since been found all over the globe. Though it does not
always contain coal, yet the name Carboniferous is retained
for any group of strata that includes some of the typical fossils
of the system. We also speak of the Carboniferous period
a phrase which, in the strict grammatical use of the word,
is of course incorrect, but which conveniently designates the
period of geological time during which the great series of
Carboniferous strata was deposited, and when the abundant life
of which they contain the remains flourished on the surface of the
earth. This chronological meaning has indeed come to be the
more usual sense in which the names of the major subdivisions
of the Geological Record are generally employed. Such adjec-
tives as Devonian and Jurassic do not so much suggest to the
mind of the geologist Devonshire and the Jura Mountains, from
which they were taken, nor even the rocks to. which they are
applied, as the great sections of the earth's history of which these
rocks contain the memorials. He compares the Jurassic or
Devonian rocks of one country with those of another, studies the
organic remains contained in them, and then obtains materials
for forming some conception of what were the conditions of
geography and climate, and what was the general character of
the vegetable and animal life of the globe, during the periods
which he classes as Jurassic and Devonian.
1 For the meanings of these names see Chapter XXV. p. 367.
250 NATURE AND USE OF FOSSILS CHAP, xv
Summary. Fossils are the remains or traces of plants and
animals which have been imbedded in the rocks of the earth's crust.
From the exceptional nature of the circumstances in which these
remains have been entombed and preserved, only a comparatively
small proportion of the various tribes of plants and animals living at
any time upon the earth is likely to be fossilised. Those organisms
which contain hard parts are best fitted for becoming fossils.
The original substance of the organism may, in rare cases, be
preserved ; more usually the organic matter is partially or wholly
removed. Sometimes a mere cast of the plant or animal in
amorphous mineral matter retains the outward form without any
trace of the internal structure. In other instances, true petrifaction
has taken place, the organic structure being reproduced in calcite,
silica, or other mineral by molecular replacement.
Fossils are of the utmost value in geology, inasmuch as they
indicate (i) former changes in geography, such as the existence
of ancient land-surfaces, lakes, and rivers, the former extension
of the sea over what is now dry land, and changes in the currents
of the ocean ; (2) former conditions of climate, such as an Arctic
state of things as far south as Central France, where bones of
reindeer and other Arctic animals have been found ; (3) the
chronological sequence of geological formations, and, consequently,
the succession of events in geological history, each great group
of strata being characterised by its distinctive fossils. This is
the most important use of fossils. Having ascertained the order
of .superposition of fossiliferous rocks, that is, the order in which
they were successively deposited, and having found what are the
characteristic fossils of each subdivision, we obtain a guide by
which to identify the various rock-groups from district to district,
and from country to country. By means of the evidence of
fossils the stratified rocks of the Geological Record have been
divided into sections and sub-sections, to which names are applied
that have now come to designate not merely the rocks and their
fossils, but the period of geological time during which these rocks
were accumulated and these fossils actually lived.
PART IV
THE GEOLOGICAL RECORD OF THE
HISTORY OF THE EARTH
CHAPTER XVI
THE EARLIEST CONDITIONS OF THE GLOBE THE
ARCH^AN PERIODS
THE foregoing chapters have dealt chiefly with the materials of
which the crust of the earth consists, with the processes whereby
these materials are produced or modified, and with the methods
pursued by geologists in making their study of these materials and
processes subservient to the elucidation of the History of the
Earth. The soils, rocks, and minerals beneath our feet, like the
inscriptions and sculptures of a long -lost race of people, are in
themselves full of interest, apart from the story which they
chronicle ; but it is when they are made to reveal the history of
land and sea, and of life upon the earth, that they are put to their
noblest use. The investigation of the various processes whereby
geological changes are carried on at the present day is undoubtedly
full of fascination for the student of nature ; yet he is conscious
that it gains enormously in interest when he reflects that in watch-
ing the geological operations of the present day he is brought face
to face with the same instruments whereby the very framework of
the continents has been piled up and sculptured into the present
outlines of mountain, valley, and plain.
The highest aim of the geologist is to trace the history of the
earth. All his researches, remote though they may seem from this
252 PRIMITIVE CONDITION OF THE GLOBE CHAP.
aim, are linked together in the one great task of unravelling the
successive mutations through which each area of the earth's sur-
face has passed, and of discovering what successive races of plants
and animals have appeared upon the globe. The investigation of
facts and processes, to which the previous pages have been devoted,
must accordingly be regarded as in one sense introductory to the
highest branch of geological inquiry. We have now to apply the
methods and principles already discussed to the elucidation of the
history of our planet and its inhabitants. Within the limits of this
volume only a mere outline of what has been ascertained regard-
ing this history can be given. I shall arrange in chronological
order the main phases through which the globe seems to have
passed, and present such a general summary of the more important
facts regarding each of them as may, I hope, convey an adequate
outline of what is at present known regarding the successive
periods of geological history.
As the primitive stages of mankind upon the earth and the early
progress of every race fade into the obscurities of mythology and
archaeology, so the story of the primeval condition of our globe is
lost in the dim light of remote ages, regarding which almost all
that is known or can be surmised is furnished by the calculations
and speculations of the astronomer. If the earth's history could
only be traced out from evidence supplied by the planet itself, it
could be followed no further back than the oldest portions of the
earth now accessible to us. Yet there can be no doubt that the
planet must have had a long history before the appearance of any
of the solid portions now to be seen. That such was the case is
made almost certain by the traces of a gradual evolution or
development which astronomers have been led to recognise among
the heavenly bodies. Our earth being only one of a number of
planets revolving round the sun, the earliest stages of its separate
existence must be studied in reference to the whole planetary
system of which it forms a part. Thus, in compiling the earliest
chapter of the history of the earth, the geologist turns for evidence
to the researches of the astronomer among stars and nebulas.
In recent years, more precise methods of inquiry, and, in par-
ticular, the application of the spectroscope to the study of the stars,
have gone far to confirm the speculation known as the Nebular
Hypothesis. According to this view, the orderly related series of
heavenly bodies, which we call the Solar System, existed at one
time, enormously remote from the present, as a Nebula that is, a
cloudy mass of matter, like one of those nebulous, faintly luminous
xvi EARLY GEOLOGICAL HISTORY 253
clouds which can be seen in the heavens. This nebula probably
extended at least as far as the outermost planetary member of the
system is now removed from the sun. It may have consisted en-
tirely of incandescent gases or vapours, or of clouds of stones in
rapid movement, like the stones that from time to time fall through
our atmosphere as meteorites, and reach the surface of the earth.
The collision of these stones moving with planetary velocity would
dissipate them into vapour, as is perhaps the case in the faint
luminous tails of comets. At all events, the materials of the
nebula began to condense, and in so doing threw off, or left
behind, successive rings (like those around the planet Saturn),
which, in obedience to the rotation of the parent nebula, began to
rotate in one general plane around the gradually shrinking nucleus.
As the process of condensation proceeded, these rings broke up,
and their fragments rushed together with such force as not improb-
ably to generate heat enough to dissipate them again into vapour.
They eventually condensed into planets, sometimes with a further
formation of rings, or with a disruption of these secondary rings,
and the consequent formation of moons or satellites round the
planets. The outer planets would thus be the oldest, ar.d, on the
whole, the coolest and least dense. Towards the centre of the
nebula the heaviest elements might be expected to condense, and
there the high temperature would longest continue. The sun is
the remaining intensely hot nucleus of the original nebula, from
which heat is still radiated to the furthest part of the system.
When a planetary ring broke up, and by the heat thereby
generated was probably reduced to the state of vapour, its
materials, as they cooled, would tend to arrange themselves in
accordance with their respective densities, the heaviest in the
centre, and the lightest outside. In process of time, as cooling
and contraction advanced, the outer layers might grow quite cold,
while the inner nucleus of the planet might still be intensely hot.
Such, in brief, is the well-known Nebular Hypothesis.
Now the present condition of our earth is very much what,
according to this hypothesis or theory, it might be expected to
be. On the outside comes the lightest layer or shell in the form
of an Atmosphere, consisting of gases and vapours. Below this
gaseous envelope which entirely surrounds the globe lies an inner
envelope of water, the Ocean or hydrosphere, which covers about
two-thirds of the earth's surface, and is likewise composed mainly
of gases in a liquid form. Underneath this watery covering, and
rising above it in dry land, rests the solid part of the globe
254 PRIMITIVE CONDITION OF THE GLOBE CHAP.
(lithosphere) which, so far as accessible to us, is composed of rocks
twice or thrice the weight of pure water. But observations with
the pendulum at various heights above the sea show that the
attraction of the earth as a whole indicates that the globe probably
has a density about five and a half times that of water. Hence
its inner nucleus has been supposed to consist of heavy, possibly
metallic, materials.
Again, the outside of the earth is now quite cool ; but abun-
dant proof exists that at no great distance below the surface the
temperature is high. Volcanoes, hot springs, and artificial borings
all over the world testify to the abundant store of heat within the
earth. Probably at a depth of not more than 20 or 25 miles from
the surface the temperature is as high as the melting-point of any
ordinary rock at the surface. By far the largest part of the planet,
therefore, is hotter than molten iron. We need have no hesitation
in admitting it to be highly probable that the earth was formerly
in the state of incandescent vapour, and that it has ever since that
time been cooling and contracting. Some physicists, indeed,
believe that the central mass of the planet still remains in a
gaseous condition at an enormously high temperature and under
vast pressure ; that, as it slowly cools, it condenses on the out-
side into a layer or shell of molten material, and that this thin
shell by cooling becomes solid, and thus increases the depth of the
crust, which may be 25 miles thick. The flattening at the poles
and bulging at the equator, or what is called the oblately spheroidal
figure of the planet, is just the shape which a plastic mass would
have assumed in obedience to the influence of the movement of
rotation, imparted to it when detached from the parent nebula.
At present a complete rotation is performed by the earth in
twenty -four hours. But calculations have been made with the
result of showing that originally the rate of rotation was much
greater. Fifty-seven millions of years ago it was about four times
faster, the length of the day being only six and three-quarter hours.
The moon at that time was only about 35,000 miles distant from
the earth, instead of 239,000 miles as at present. Since these early
times the rate of rotation has gradually been diminishing, and the
figure of the earth has been slowly tending to become more spheri-
cal, by sinking in the equatorial and rising in the polar regions. .
Of the first hard crust that formed upon the surface of the
earth no trace has yet been found. Indeed, there is reason to
suppose that this original crust would break up and sink into the
molten mass beneath, and that not until after many such formations
xvi EARLY GEOLOGICAL HISTORY 255
and submergences did a crust establish itself of sufficient strength
to form a permanent solid surface. Even though solid, the
surface may still have been at a glowing red-heat, like so much
molten iron. Over this burning nucleus lay the original atmo-
sphere, consisting not merely of the gases in the present atmo-
sphere, but of the hot vapours which subsequently condensed into
the ocean, or were absorbed into the crust. It was a hot,
vaporous envelope, under the pressure of which the first layers of
water that condensed from it may have had the temperature of
molten lead.
Regarding these early ages in the earth's history we can only
surmise, for no direct record of them has been preserved. They
are sometimes spoken of as pre- geological ; but geology really
embraces the whole history of the planet, no matter from what
sources the evidence may be obtained. Deposits from this original
hot ocean have been supposed to be recognisable in the very oldest
crystalline schists ; but for this supposition there does not a-ppear
to be any good ground. The early history of our planet, like that
of man himself, is lost in the dimness of antiquity, and we can
only speculate about it on more or less plausible suppositions.
When we come to the solid framework of the earth we stand
on firmer footing in the investigation of geological history. The
terrestrial crust, or that portion of the globe which is accessible to
human observation, has been found to consist of successive layers
of rock, which, though far from constant in their occurrence, and
though often broken and crumpled by subsequent disturbance,
have been recognised over a large part of the globe. They con-
tain the earth's own chronicle of its history, which has already
been referred to as the Geological Record, and the subdivision of
which into larger and minor sections, according mainly to the
evidence of fossils, was explained in the preceding chapter.
Had the successive layers of rock that constitute the Geological
Record remained in their original positions, only the uppermost,
and therefore most recent, of them would have been visible, and
nothing more could have been learnt regarding the underlying
layers, except in so far as it might have been possible to explore
them by boring into them. But the deepest mines do not reach
greater depths than between 3000 and 4000 feet from the surface.
Owing, however, to the way in which the crust of the earth has
been plicated and fractured, portions of the bottom layers have
been pushed up to the surface, and those that lay above them
have been thrown into vertical or inclined positions, so that we
256 PRIMITIVE CONDITION OF THE GLOBE CHAP.
can walk over their upturned edges and examine them, bed by bed.
Instead of being restricted to merely the uppermost few hundred
feet of the crust, we are enabled to examine many thousand feet
of its rocks. The total mean thickness of the accessible fossilifer-
ous rocks of Europe has been estimated at 75,000 feet, or upwards
of 14 miles. This vast depth of rock has been laid bare to
observation by successive disturbances of the crust.
The main divisions of the Geological Record and, we may also
say, of geological time, are five: (i) Archaean, embracing the
periods of the earliest rocks, wherein few or no traces of organic
life occur ; (2) Palaeozoic (ancient life) or Primary, including the
long succession of ages during which the earliest types of life
existed ; (3) Mesozoic (middle life) or Secondary, comprising a
series of periods when more advanced types of life flourished ; (4)
Cainozoic (recent life) or Tertiary, embracing the ages when the
existing types of life appeared, but excluding man ; and (5) Quater-
nary er Post-tertiary and Recent, including the time since man
appeared upon the earth. It must not be supposed that each of
"these five divisions was of the same duration. The Palaeozoic
ages were probably vastly more prolonged than those of Lny
later division; while the Quaternary periods doubtless comprise
a very much briefer time than any of the other four groups.
Each of these main sections is further subdivided into systems
or periods, and each system into formations as already explained.
Arranged in their order of sequence, the various divisions of the
Geological Record may be placed as in the accompanying Table.
Though the broad outlines of the sequence of living things has
been the same all over the world, many local diversities may be
traced in the nature and grouping of the sedimentary materials in
which these outlines have been preserved. The subdivisions in
Europe and in North America are here shown.
THE GEOLOGICAL RECORD
or, Order of Succession of the Stratified Formations of the Earth's Crust
Europe.
North America.
& C
t! a;
Recent and Prehistoric.
Recent.
.B K
Pleistocene or Glacial.
Pleistocene or Glacial.
1?
XVI
DIVISIONS OF GEOLOGICAL RECORD
257
Europe.
North America.
g Pliocene.
Pliocene.
sl
Miocene.
Miocene.
Is
Oligocene.
Oligocene.
rj j_ Eocene.
Eocene.
o
b
o ^ Cretaceous.
Cretaceous.
S g j Jurassic.
Jurassic.
8
S2
Triassic.
Triassic.
o
Permian.
Permian or Permo-Carbon-
iferous.
Carboniferous.
Carboniferous.
Coal-measures.
Coal-measures (Upper Car-
Millstone Grit.
boniferous).
Carboniferous Limestone
Sub - Carboniferous (Lower
series.
Carboniferous).
Devonian and .Old Red
Devonian.
Sandstone. Upper (Catskill, Chemung,
b
Upper (Famennian, Fras- Portage and Genesee groups)
a
nian). Middle (Hamilton, Marcellus
c
c
Middle (Givetian, Eifelian). groups).
OH
Lower (Coblentzian, Gedin-
Lower (Corniferous, Onon-
fe
nian).
daga, Oriskany groups).
.a
1
Silurian.
Silurian.
Upper (Ludlow, Wenlock,
Upper (Lower Helderberg,
2
Llandovery groups).
Water-lime, Niagara, Clin-
Lower (Caradoc or Bala,
ton, and Medina groups).
Llandeilo and Arenig
Lower (Cincinnati, Utica,
groups).
Trenton, Chazy and Calci-
ferous groups).
Cambrian or Primordial.
Cambrian or Primordial.
Upper or Olenidian series.
Potsdam {Olenidian series).
Middle or Paradoxidian series.
Acadian ( Paradoxidian series).
Lower or Olenellus series.
Georgian (Olenellus series).
imbrian.
Longmyndian \ England and
Uriconian j Wales.
[Dalradianl 1 ,-, ., ,
Torfidonian j S<
.2 I Keweenawan.
c -! Upper Huronian.
Jp I Lower Huronian (Keewatin).
w
U
.
c (
fi
$ ( Lewisian (Fundamental
3 J "Fundamental Complex" of
P-,
.C 4 gneiss of Scandinavia,
,c 1 gneiss, etc. (Laurentian).
1 I etc -)- 3 ^
258 PRE-CAMBRIAN CHAP.
THE PRE-CAMBRIAN PERIODS
Owing to the revolutions which the crust of the earth has
undergone, there have been pushed up to the surface, from under-
neath the oldest fossiliferous strata, certain very ancient crystalline
rocks which form what is termed the Archaean system. As al-
ready mentioned, these rocks have by some geologists been
supposed to be a part of the primeval crust of the planet, which
solidified from fusion. By others they have been thought to
have been formed in the boiling ocean, which first condensed
upon the still hot surface of the globe. But we are still ignorant
as to the conditions under which they arose, and have hardly any
means of ascertaining in what order they were formed. We
know no method of determining whether those of one region
belong to the same period as those of another. Nor can we
always be sure that masses which have been called Archaean may
not belong to a much later part of the Geological Record, their
peculiar crystalline structure having been superinduced upon them
by some of those subterranean movements described in Chapter
XIII.
It has been observed that in all parts of the world, wherever
the most ancient mineral masses appear at the surface, they
present a remarkable sameness of character. They consist for
the most part of thoroughly crystalline rocks, which range from
acid amorphous granites to the most basic and finely foliated
silky schists. They are generally characterised by a schistose
structure. The most universally abundant of them may be classed
as gneisses, which pass into granites, syenites and diorites, and
often include interstratified bands of various hornblendic, pyrox-
enic, and garnetiferous rocks. These various materials are
usually more or less distinctly bedded ; but the beds are for the
most part inconstant, swelling out into thick zones, and then
rapidly diminishing and dying out. As this bedding somewhat
resembles that of sedimentary rocks, the inference has been
drawn that the Archaean crystalline series was really deposited
on the floor of the primeval ocean, as chemical precipitates or
mechanical sediments which have since been more or less
crystallised and disturbed. But from what has been brought
forward in Chapter XIII. regarding the totally new structures
which have been developed in rocks by subterranean movement,
it is evident that a bedded arrangement and a crystalline texture,
xvi PRE-CAMBRIAN 259
like those ot the Archaean system, have sometimes been induced
in rocks by excessive crumpling, fracture, and shearing. How
far, therefore, the apparent bedding of Archaean gneisses and
schists is their original condition, or is the result of subsequent
disturbance, is a question that cannot yet be definitely answered.
The alternations of gneiss and other crystalline masses form
bands which are usually placed on end or at high angles, and are
often intensely crumpled and puckered, having evidently under-
gone enormous crushing (Fig. 128). Attempts have been made
to subdivide them into groups or series, according to their ap-
parent order of succession and lithological characters. But such
subdivisions are probably entirely without any solid basis. We
FIG. 128. Fragment of crumpled Schist.
have no evidence that the banding of the gneisses has any
stratigraphical value.
So far as these rocks can be compared with any of the later
portions of the earth's crust they find their nearest analogies in
the structure of the larger bosses of eruptive material which have
been intruded into the various geological formations. It seems
at present most probable that they are really of igneous origin, and
that they represent deep-seated portions of very ancient protrusions
of molten material from the interior, their upward prolongations
having long ago been removed by denudation. Their alternations
of different mineral composition may have arisen like the banding
which is found in great bosses of gabbro ; their schistose character
points to great compression and shearing, and their complicated
puckerings and folds show how intense must have been the
movements to which their original bands and their foliation-layers
must have been subsequently exposed.
260 PRE-CAMBRIAN
CHAP.
Nevertheless, even amidst these relics of what were probably
intrusions of acid and basic material into the early terrestrial crust,
there are indications that, in some regions, this crust already in-
cluded sedimentary formations. Masses of limestone, graphite-
schist, mica-schist, and quartzite have been crushed and involved
among the gneisses ; and though the relations of the two groups of
rocks have been greatly obscured, it may be conjectured that the
metamorphic series represents a group of sedimentary formations
into which the gneisses were intruded.
No unquestionable relic of organic existence has been met
with among Archaean rocks. Some of the Archaean limestones of
Canada have yielded a peculiar mixture of serpentine and calcite,
with a structure which has been regarded by some able naturalists
as that of a reef-building foraminifer. It occurs in masses, and
was supposed by these writers to have grown in large, thick
sheets or reefs over the sea-bottom. By most observers, however,
this supposed organism (to which the name of Eozoon has been
given) is now regarded as merely a mineral segregation, and
various undoubted mineral structures are pointed to in illustration
and confirmation of this view.
Pre-Cambrian rocks cover a large area in Europe. Among
the Hebrides and along the north-west coast of the Scottish
Highlands, where they are largely developed, they consist of a
very ancient group of rocks, of which the most conspicuous are
various forms of gneiss to which the name of Lewisian has been
given, from its abundant and characteristic development in the
Island of Lewis. These rocks consist of a complicated series of
what have probably been deep-seated igneous masses successively
intruded into the terrestrial crust. They include a succession of
basic and acid dykes which in many respects resemble those of
much more recent geological periods. At different times all these
rocks have undergone intense mechanical crushing and deformation,
and they now present a strikingly banded and foliated structure. At
one or two places, in the west of the counties of Ross and Inver-
ness, certain mica-schists, graphitic schists, and limestones have
bsen found apparently involved among the gneisses. They are
probably metamorphosed sediments, and they may represent sedi-
mentary rocks of the crust into which the gneisses and dykes
were intruded.
The Lewisian gneiss of North-West Scotland gives rise to a
singular type of scenery. Over much of that region it forms
hummocky bosses of naked rock, with tarns and peat-bogs lying
xvi DISTRIBUTION OF PRE-CAMBRIAN ROCKS 261
in the hollows, seldom rising into mountains, but forming the plat-
form which supports the singular group of red sandstone mountains
mentioned below. Here and there it mounts up into solitary
hills or groups of hills. The highest point it reaches on the
mainland is among the mountains on the east side of Loch Maree,
in Ross-shire, where it attains an elevation of 3000 feet. Some
of its masses in that region were mountains at the time of the
deposition of the overlying Torridon sandstone, which when
removed by denudation reveals a system of hills and valleys the
oldest topography that has been preserved in Europe. In the
Island of Harris the gneiss sweeps upwards into rugged moun-
tainous ground, of which the highest summits rise more than 2600
feet out of the Atlantic, and are visible far and wide as a notable
landmark. Rocks of similar character appear likewise in Ireland :
while in Anglesey, and possibly in the south-west of England,
other scattered bosses of them rise to the surface.
Much later than the Lewisian, and lying upon it with a violent
unconformability, comes a remarkable group of red sandstones with
some dark shales and calcareous bands, to which the name of
Torridonian has been given from its great development at Loch
Torridon in the west of Ross-shire. This group reaches a thick-
ness of 8000 or 10,000 feet, and is almost entirely confined to
the west of the counties of Sutherland and Ross. It there forms
a remarkable group of pyramidal mountains, to which their nearly
horizontal stratification gives a characteristic architectural aspect.
No unquestionable relics of plant or animal life have yet been
found in this thick mass of sedimentary material. But certain
phosphatic nodules recently obtained in the shales are not improb-
ably of organic origin, and may indicate the presence of Crustacea
or of horny brachiopods in the waters in which the strata were
deposited. The great antiquity of these Torridonian sediments is
proved by the fact that they are unconformably overlain by the
base of the Cambrian system in which the Olenellus zone is well
represented.
The term " Dalradian " has been applied to a thick series
of metamorphosed sedimentary and igneous rocks forming the
Central and Southern Highlands of Scotland. They must be
of great thickness, but their true geological position is not yet
ascertained. They may possibly contain altered representatives
of the Lewisian gneiss, Torridon sandstone and Cambrian quartz-
ites and limestones of the north-west, and, probably, even of
Silurian (Arenig) formations.
262 PRE-CAMBRIAN CHAP.
On the borders of Wales and Shropshire a thick series of
sedimentary rocks (Longmyndian) forms the Longmynd country.
It appears to be pre-Cambrian, and may be partly the equivalent
of the Torridonian Sandstone of the north-west. It is underlain by
a group of felsitic lavas and tuffs named Uriconian.
On the continent of Europe, pre-Cambrian rocks have their
greatest extension in Scandinavia, where they evidently belong to
the same ancient land as that of which the Hebrides and Scottish
Highlands are fragments. They include a fundamental gneiss
and other crystalline rocks like those included in the Lewisian
series of Scotland. This ancient group is overlain by various
younger schists and gneisses, the geological equivalents of which in
other countries have not been satisfactorily determined, though they
are classed by some Scandinavian geologists with the Algonkian
series of North America. That some of these rocks are of Silurian
age is proved by the occurrence of corals, graptolites, and other
fossils (probably Upper Silurian forms) in mica-schists and lime-
stones not far from Bergen.
Pre-Cambrian rocks range widely across Finland into Russia,
appearing in the centre of the chain of, the Ural Mountains.
They form likewise the nucleus of the Carpathians and the Alps,
and appear in detached areas in Bavaria, Bohemia, France, and
the Pyrenees.
Rocks belonging to pre-Cambrian time attain an enormous
development on the western side of the Atlantic, where they are
estimated to cover a region more than 2,000,000 square miles
in extent, which stretches from the great lakes northwards into
the Arctic regions. They have been divided into two great
sections which appear to correspond, on the whole, with those
recognised in Europe. At the base lies the Archaean gneiss
a vast mass of foliated and unfoliated granites, gneisses,
syenites, gabbros, schists, and peridotites, which resemble deep-
seated eruptive rocks, but contain no certain trace of sedimentary
origin. Above this most ancient or fundamental formation lies
the great series known as Algonkian, which is classed in three
divisions. Of these the lowest (i) Lower Huronian (Keewatin
group), about 5000 feet thick, consists of conglomerates, quartz-
ites, dolomites, and slates with important iron-ores. This great
succession of sediments must be enormously younger than the
Archaean rocks, for it rests upon them with a violent unconforma-
bility. On the other hand, it is seen to be vastly older than
the next group (2) Upper Huronian, which lies upon its up-
xvi DISTRIBUTION OF PRE-CAMBRIAN ROCKS 263
turned and denuded edges. This middle group is said to reach
a thickness of 12,000 feet. It consists of various sedimentary
formations, often more or less metamorphosed, together with
included masses of eruptive rocks. The third group (3), known
as Keweenawan, is stated to be sometimes 50,000 feet thick. It
is made up mainly of volcanic accumulations, with sedimentary
deposits intercalated in and overlying them. It is surmounted by
the Cambrian system, and is thus certainly pre-Cambrian.
In Newfoundland and in the Grand Canon region of the
Colorado, thick sedimentary formations underlying Cambrian
strata have yielded a number of shells and other organisms which
comprise all the pre-Cambrian fossils yet discovered, and have a
special interest as being the oldest forms of life that have yet
been found.
It will be observed that both in the Old and New World the
pre-Cambrian rocks are chiefly exposed in the northern tracts of
the continents. The areas which they there overspread were
probably land at an early geological period, and it was the waste
of this land that mainly supplied the original materials out of
which enormous masses of stratified rocks were formed.
In the southern hemisphere, also, ancient gneisses and other
schists rise from under the oldest fossiliferous formations. In
Australia and in New Zealand they cover large tracts of country,
and appear in the heart of the mountain ranges.
CHAPTER XVII
THE PAL/EOZOIC PERIODS CAMBRIAN
THE portion of geological history which embraces those ages in
which the earliest known types of plants and animals lived has
been termed Palaeozoic (Ancient Life). Of the first appearance of
organic life upon our planet we know nothing. Whether plants or
animals came first, and in what forms they came, are questions to
which as yet no satisfactory answer can be given. The oldest dis-
covered fossils are assuredly not vestiges of the first living things
that peopled the globe. There is every reason, indeed, to hope
that as researches in all parts of the world are pushed into the
pre-Cambrian sedimentary formations, more numerous and more
ancient organisms than those yet found may be discovered. But
it is in the highest degree improbable that any trace of the earliest
beginnings of life will ever be detected. The first plants and the
first animals were probably of a lowly kind, with no hard parts
capable of preservation in the fossil state. Moreover, the sedi-
mentary rocks which may have chronicled the first advent of
organised existence are hardly likely to have escaped the varied
revolutions to which all parts of the crust of the earth have been
exposed. They have more probably been buried out of sight, or
have been so crushed, broken, and metamorphosed, that their
original condition, together with any fossils they may have en-
closed, is no longer to be recognised. The first chapters have
been, as it were, torn out from the chronicle of the earth's history.
The Palaeozoic rocks, which, leaving out of account the somewhat
scanty and obscure organic remains obtained fi>m pre-Cambrian
sediments, contain the earliest record of plant and animal life,
consist mainly of the hardened mud, sand, and gravel of the sea-
bottom. Here and there they include beds, or thick groups of
beds, of limestone composed of marine shells, crinoids, corals, and
264
CHAP, xvii CAMBRIAN 265
other denizens of salt water. They are thus essentially the chronicles
of the sea. But they also contain occasional vestiges of shores,
and even of the jungles and swamps of the land, with a few rare
glimpses into the terrestrial life of the time. Everywhere they
abound in evidence of shallow water ; for though chiefly marine,
they appear to have been generally accumulated not far from land.
We may believe that in the earliest periods, as at the present day,
the sediment washed away from the land has been deposited on
the sea-floor, for the most part at no great distance from the coast.
The land from the waste of which the Palaeozoic rocks were
formed lay, in Europe and North America, chiefly towards the
north. It no doubt consisted of such pre-Cambrian rocks as still rise
out from under the oldest Palaeozoic formations. As already
mentioned, the north-west Highlands of Scotland, part of the
table-land of Scandinavia, and most of North America to the north
of the great lakes, are probably portions of that earliest land,
which, after being deeply buried under later geological accumula-
tions, have once more been laid bare to the winds and waves.
We can form some conception of the bulk of the primeval
northern land by noting the thickness of sedimentary rocks that
were formed out of its detritus during the Palaeozoic periods. The
older half of the Palaeozoic rocks in the British Islands, for
example, is at least 1 6,000 feet or 3 miles thick, and covers an
area of not less than 60,000 square miles. This material, derived
from the waste of pre-Cambrian rocks, would make a table-land
larger than Spain, with an average height of 5000 feet, or a
mountain chain 1800 miles long, with an average elevation of
16,000 feet. Of the general form and height of the northern
land that supplied this vast mass of sedimentary matter nothing
is known. Perhaps it was lofty ; but it may have been slowly
uplifted, so that its rise compensated for the ceaseless degradation
of its surface.
Among the pre-Cambrian formations of Europe and of North
America abundant evidence has been obtained that, even in the
primeval period which they represent, volcanic action was in full
vigour, and that sheets of lava and showers of ashes formed thick
accumulations on the sea-floor. Volcanic energy continued all
through Palaeozoic time, and heaped up huge piles of lavas and
tuffs. We find also many indications of upward and downward
movements of the crust of the earth. The mere fact of the super-
position of many thousands of feet of shallow-water strata, one
above another, is proof of a gradual sinking of the sea-floor. For
266 PALEOZOIC PERIODS CHAP.
it is evident that the accumulation of such a thickness of
sediment, and the continuance of a shallow sea over the area
of deposition, could only take place during a progressive sub-
sidence (see p. 203).
The vegetable and animal life of the Palaeozoic periods, so far
as known from the fossils which have been obtained from the rocks,
appears to have been far more uniform over the whole globe than
at any subsequent epoch in geological history. For instance, the
same species of fossils are found in corresponding rocks in Britain,
Russia, United States, China, and Australia. The climate of the
globe at that ancient date vtfas doubtless more uniform than it
afterwards became, and was probably also generally warmer.
Palaeozoic fossils, obtained from high northern latitudes, are
precisely similar to those that abound in England, whence it
may be inferred that not only was there a greater uniformity of
climate, but that the great cold which now characterises the Arctic
regions did not then exist.
In the earlier Palaeozoic periods, the animal life of the globe
appears to have been entirely invertebrate, the highest known
types being chambered shells, of which our living nautilus is a
representative. In the middle periods vertebrate life appeared.
The earliest known vertebrate forms are fishes akin to some
modern sharks and to the sturgeon, the polypterus of the Nile,
and the gar-pike of American lakes. The most highly organised
forms of existence upon the earth's surface in the later Palaeozoic
periods were amphibians a class of animals represented at the
present day by frogs, toads, newts, and salamanders. It is evident,
however, that the number and kinds of animal remains preserved
in Palaeozoic rocks afford only an imperfect record of the animal
life of these early ages. Whole tribes of creatures no doubt existed
of which no trace whatever has yet been recovered. An accidental
discovery may at any moment reveal the former presence of some
of these vanished forms. For example, the examination of a fossil
tree-trunk imbedded among the coal-strata of Nova Scotia led to
the finding of the first and as yet almost the only traces of
Palaeozoic land-shells, though thousands of species of marine shells,
belonging to the same period, had long been known. Every year
is enlarging our knowledge in these respects; but from the very
nature of the circumstances in which the records of the rocks were
formed, we cannot expect this knowledge ever to be more than
fragmentary.
The Palaeozoic rocks are divided into five systems which in the
xvn CAMBRIAN 267
order of their age have been named : (i) Cambrian ; (2) Silurian ;
(3) Devonian; (4) Carboniferous; (5) Permian.
CAMBRIAN
The strata containing the earliest organic remains were formerly
known as Greywacke, from the rock which is specially abundant
among them. They were also termed Transition, from the sup-
position that they were deposited during a transitional period,
between the time when no organic life was possible on the earth's
surface and the time when plant and animal life abounded. But
Murchison, who first explored them, showed that they contain a
series of formations, each characterised by its own assemblage of
organic remains. He called them the Silurian system, after the
name of the old British tribe the Silures, who lived on the
borders of England and Wales, where these rocks are especially
well developed. This name soon passed into use all over the
world as the designation of those stratified formations which
contain the same or similar organic remains to those found in the
typical region described by Murchison.
While the succession of the rocks and fossils was established
by that geologist in South Wales, and in the border counties of
Wales and England, Sedgwick was at work among similar rocks
in North Wales. These were at first believed to be all older
than those called Silurian, and were accordingly named CAMBRIAN,
after the old name for Wales, Cambria. In the end, however, it
was found that throughout a large part of them, the same fossils
occurred as in the Silurian series, and they were accordingly
claimed as Silurian. Much controversy has since been carried on
regarding the limits and names to be assigned to these rocks,
and geologists are not yet agreed upon the nomenclature that
should be followed. Murchison and his followers claimed the
Cambrian as the lowest portion of the Silurian system, while
Sedgwick and his disciples maintained that the lower half of the
Silurian system should be included in his Cambrian series. There
can. be no doubt that the first succession of organic remains
established among these ancient members of the great Palaeozoic
series of formations was that worked out by Murchison and named
by him Silurian. But it has been found convenient to retain the
name Cambrian for the oldest group of Palaeozoic fossiliferous
formations. It may be well to repeat that these words, like all
those adopted by geologists to distinguish the successive rock-
268 PALEOZOIC PERIODS CHAP.
groups of the earth's crust, have acquired a chronological meaning.
We speak, not only of Cambrian and Silurian strata and Cambrian
and Silurian fossils, but of Cambrian and Silurian time. The
terms are used to denote those particular periods in the history
of the earth when Cambrian and Silurian strata were respec-
tively deposited, and when Cambrian and Silurian fossils were the
living denizens of sea and land.
The rocks of which the Cambrian system is composed, like those
of the whole of the Lower Palaeozoic formations, present consider-
able uniformity over the whole globe. They consist of grey and
reddish grits, sandstones, greywackes, quartzites, and conglomer-
ates, with thick groups of shale, slate, or phyllite. These
sedimentary accumulations attain a great thickness in some
countries. In Wales they have been estimated by some observers
to be at least 20,000 feet in depth. Their ripple-marks, pebble-
beds, and frequent alternations of coarse and fine sediment, point
to their having probably been laid down in comparatively shallow
water, during a period of prolonged subsidence of the sea-bottom.
They include tuffs and basic lavas which indicate contemporaneous
submarine eruptions.
With regard to the occurrence of fossils among the older
Palaeozoic formations, and indeed among stratified rocks in general,
it is worthy of notice that they are far from being equally distri-
buted ; that, on the contrary, they occur by preference in certain
kinds of material rather than in others. Grits and sandstones, for
instance, are comparatively unfossiliferous, while fine shales, slates,
and limestones are often crowded with fossils. It is not that life
was probably on the whole more abundant at the time of the
deposition of some kinds of strata, but that the local conditions for
its growth and for the subsequent entombment and preservation of
its remains were then more favourable. At the present time, for
example, dredging operations show the most remarkable variations
between different and even adjacent parts of the sea-bottom,
as regards the abundance of marine life. Some tracts are almost
lifeless, while others are crowded with a varied and prolific fauna.
We can easily understand that if, from the nature of the bottom,
plants and smaller animals cannot flourish on a particular tract,
the larger kinds that feed on them will also desert it. Even if
organisms live and die in some numbers over a part of the sea-
bed, the conditions may not be suitable there for the preservation
of their remains. The rate of deposit of sediment, for instance,
may be so slow that the remains may decay before there is time
CAMBRIAN
269
for them to be covered up ; or the sediment may be unfitted for
effectually preserving them, even when they are buried in it. We
must not lose sight of these facts in our explorations of the Geo-
logical Record. A relation has generally existed between the
abundance or absence of fossils in a sedimentary rock and the
circumstances under which the rock was originally formed.
The Cambrian or Primordial group of sedimentary formations
contains a remarkable assemblage of animal remains, which,
being nearly the earliest known traces of the animal life of the
globe, might have been anticipated to belong to the very lowest
tribes of the animal kingdom. But they are by no means of such
humble organisation. On the contrary, they include no represen-
tatives of many of the groups of simpler
invertebrates, which we may be sure were
nevertheless living at the same time. Not
only so, but some of the fossils belong to
comparatively high grades in the scale of in-
vertebrate life, such as chambered molluscs.
From this incompleteness, and from the
wide differences in the organic grade of
the forms actually preserved in the rocks,
we may reasonably infer that only a most
meagre representation of the life of the
time has come down to us in the fossil
state. Some of the fossils, moreover, have
been so indistinctly preserved that consider-
able difficulty is experienced in deciding to
what sections of the animal or vegetable
kingdoms they should be assigned.
Among the markings which have given
rise to much discussion allusion may be
made to plant-like impressions, some o f FIG. 129 -Fucoid-likeimpres-
r *. ' s\on(Eoj>kytonLtnneanum)
which, like Eophyton (Fig. 1 29), have been from Cambrian rocks ), Agnos-
tus princeps (|) ; (c), Olenus tnicrurus (natural size) ; (d), Ellipsocephalus Hojfi
(natural size).
with bivalve shell-like carapaces, which protected the head and
upper part of the body, while the jointed tail projected beyond it.
Most of them were of small size (see Fig. 140). The character-
istic Cambrian genus is Hymenocaris.
Of all the divisions of the animal kingdom none is so
important to the geologist as that of the Mollusca. When one
walks along the shores of the sea at the present time, by far the
most abundant remains of the marine organisms to be there
observed are shells. They occur in all stages of freshness* and
CAMBRIAN 273
decay, and we may trace even their comminuted fragments forming
much of the white sand of the beach. So in the geological
formations, which represent the shores and shallow sea-bottoms
of former periods, it is mainly remains of the marine shells that
have been preserved. From their abundance and wide diffusion,
they supply us with a basis for the comparison of the strata of
different ages and countries, such as no other kind of organic
remains can afford.
It is interesting and important to find that among the fossils of
the oldest fossiliferous rocks the remains of molluscan shells occur,
and that they are of kinds which can be satisfactorily referred to their
place in the great series of the Mollusca.
The most abundant of them are repre-
sentatives of the Brachiopods or Lamp-
shells. Among these are species of the
genera Lingula (Lingulella, Fig. 133) and
Discina which have a peculiar interest,
inasmuch as they are the oldest known
, j i i- FIG. 133. Cambrian Bra-
molluscs, and are still represented by living chi ~ od (Llngulella
species in the ocean. They have persisted Davisii, natural size),
v/ith but little change during the whole of
geological time, from the early Palaeozoic periods downwards, for
the living shells do not appear to indicate any marked divergence
from the earliest forms. They possess horny shells which are not
hinged together by 'teeth. A more highly organised order of
brachiopods possesses two hard calcareous shells articulated by
teeth on the hinge-line. These forms, apparently later in their
advent, soon vastly outnumbered the horny lingulids and discinids.
So abundant are they, both in individuals and in genera and
species, among the older Palaeozoic rocks, that the period to which
these rocks belong is sometimes spoken of as the " Age of
Brachiopods."
The ordinary bivalve shells or Lamellibranchs had their re-
presentatives even in Cambrian times. From that early period
they have gradually increased in numbers, till they have attained
their maximum at the present time. Among the known Cambrian
genera are Ctenodontci allied to the living " ark-shells," and Modio-
lopsis, probably representing some of the modern mussels.
The Gasteropods or common univalve shells, now so abundant
in the ocean, made their advent not later than Cambrian time,
for the remains of the genus Bellerophon (see Fig. 143) are found
in the group of strata known as the Lingula-flags in Wales.
T
274 PALEOZOIC PERIODS CHAP.
The highest division of the molluscs, the Cephalopods, to
which the living nautilus and cuttle-fish belong, is but poorly re-
presented at the present time. But during the Palaeozoic and
Secondary periods it flourished exuberantly, both as regards
number of individuals and variety of forms. It is divisible into
two great orders. In one of these, the shell is usually internal
and sometimes chambered ; in the other, the shell is chambered
and external, the chambers being connected by a tube or siphuncle.
The former order includes all the living cuttle-fishes, squids, and
the paper-nautilus ; the latter comprises only one living represen-
tative the pearly nautilus. It is to the family of chambered
cephalopods that the Palaeozoic forms are all referable. In some
the shell was straight, in others it was variously curved. Only
scanty traces of cephalopodan life have yet been found among
the Cambrian rocks. But occasional examples of the important
genus Orthoceras (see Fig. 144) show that this great division of
the molluscs had even in the earliest Palaeozoic ages appeared
upon the earth.
Taking advantage of the observed distribution of the trilobites
in the Cambrian strata, geologists have classed these rocks in
three great divisions : ( I ), Lower or Olenellus group, in which
the genus Olenellus is specially characteristic ; (2), Middle or
Paradoxidian, distinguished by the prevalence of the genus
Paradoxides; and (3), Upper or Olenidian, wherein the character-
istic trilobite genus is Olenus.
As the term Cambrian denotes, the rocks to which this
name is applied are well developed in Wales. There, and in
the border English counties, they attain a depth of perhaps more
than 12,000 feet. They are found also in the east of Ireland,
while in the north-west of Scotland they are well represented by a
group of quartzites full of annelid burrows, surmounted by dolomitic
shales, containing Olenelhis and other forms, and then by a group
(1500 feet thick) of dolomites and limestones, which contain a
large and varied assemblage of fossils, having a general affinity
with those of Canada and the United States rather than with those
of Wales.
The following Table gives the commonly accepted subdivisions
of the Cambrian rocks in Britain.
( Tremadoc group dark grey slates, with Olenus,
\ Asaphus, Angelina, Ogygia, etc.
o 1 Lingula Flags bluish and black slates, flags, and sand-
1. stones, with Lingulella, Discina, Olenus, Conocoryphe, etc.
XVII
CAMBRIAN
275
MIDDLE C Solva group of St. David's, with Paradoxides, Plutonia,
or | Agnostus, etc.
PARA- 1 Menevian group sandstones, shales, slates, and grits,
DOXIDIAN. ^ with Paradoxides, Agnostus, Conocoryphe, etc.
LOWER C Harlech and Llanberis group of purple, red, and grey flags,
or ) sandstones, slates, conglomerates, and volcanic rocks. In
OLENELLUS "i Shropshire Olenelhis, Ellipsocephalus, Kutorgina, and other
ZONES. \. fossils have been obtained from the lowest Cambrian strata.
The characteristic Cambrian or Primordial fauna has a world-
wide distribution. In Europe it has been detected at intervals
from Scandinavia through Belgium, France, Spain, the Thuringer
Wald and Bohemia to Sardinia and eastwards into Russia, whence
it appears to range into Asia even as far as China. It has been
met with in the Salt Range of India, in Southern Australia and
Tasmania, and in South America. Nowhere has it been found with
so varied an assemblage of organic remains as in North America,
where in the United States and the British Possessions it runs
along the margins of the pre-Cambrian rocks and presents the
threefold grouping of the Old World as shown in the subjoined
Table.
UPPER
or
POTSDAM
(OLENIDIAN).
MIDDLE
or
ACADIAN
(PARADOXI-
DIAN).
LOWER
or
GEORGIAN
(OLENELLUS
FAUNA).
Seen on the north and east sides of the Adirondack
Mountains of New York, and stretching into Canada by
New Brunswick and Cape Breton into Newfoundland ; in
the upper Mississippi valley, South Dakotah, Wyoming,
Montana and Colorado, North Arizona, and Nevada.
Developed in Eastern Massachusetts, New Brunswick, and
Eastern Newfoundland ; also in New York, Tennessee,
Alabama, Central Nevada, and British Columbia.
Typically displayed in Vermont ; seen also on west side
of Green Mountains, and Appalachian chain in Pennsylvania,
Virginia, Tennessee, Georgia, Alabama ; likewise in the
eastern region by S. Massachusetts, New Brunswick, and
Newfoundland into Labrador. It has been recognised in
the Wahsatch Mountains and in British Columbia.
CHAPTER XVIII
SILURIAN
THE origin and use of the term SILURIAN have already been
given (p. 267). The rocks embraced under this term form a mass
of strata which in some countries (Wales and Scotland) must be
many thousand feet thick. Like the Cambrian system below, into
which they graduate downward, they consist mainly of greywackes,
sandstones, shales, or slates ; but they are marked by the occa-
sional occurrence of bands of limestone a rock which from this
part of the geological record appears in increasing quantity on-
wards to recent times. Some highly characteristic bands of dark
carbonaceous shale are in some countries persistent for long dis-
tances, and contain abundant graptolites. Not infrequently these
dark shales are full of pyritous impregnations, which, when the
rock weathers, give rise to an efflorescence of alum or the forma-
tion of chalybeate springs ; such bands are sometimes called ahun-
slates. In Wales, the Lake District of the north of England, and
in the south of Scotland, remains of submarine volcanic eruptions
of Silurian time appear as intercalated sheets of tuff and different
lavas.
In certain regions (Russia, New York) Silurian rocks have
undergone little change since the time of their deposition ; but, as
a rule, they have been more or less indurated, plicated, and dis-
located (Wales, Lake District, etc.), while in some districts (parts
of Norway and Scotland) they have been so crushed and meta-
morphosed as to have assumed the character of schistose rocks
(phyllites, mica-schists, etc.)
Murchison subdivided his Silurian system into two great sec-
tions, Lower and Upper. This arrangement still holds, though
the limits and nomenclature of the several component groups have
not been exactly maintained. It has been proposed to separate
276
CHAP, xviii SILURIAN 277
the lower division as a distinct system under the name of " Ordo-
vician," restricting the name Silurian to the upper division only,
and this classification has been adopted by many writers. In
justice, however, to the great pioneer by whom these ancient rocks
were first worked out, his terminology, which is still perfectly
applicable, ought to be maintained. The arrangement of the
various subdivisions, as followed in Britain and North America, is
shown in the tables on p. 286.
Taking the fossils of the Silurian system as a whole, we find
that they prolong and amplify the peculiar type of life found to
characterise the Cambrian system. They include both plants and
animals. The flora, however, is exceedingly meagre. It consists
almost entirely of sea-weeds, which occur usually in the form of
fucoid-like impressions. But, as already remarked in reference to
the so-called plants of the Cambrian rocks, many of the supposed
vegetable remains are almost certainly not such (see p. 269).
Some of them may be tracks left upon soft mud or sand by worms,
crustaceans, or other marine
creeping or crawling creatures ;
others may be casts of hollows
made by trickling water or yield-
ing sediment ; while others
seem to be the result of some
peculiar crumpling or pucker-
ing of the strata. But un-
doubted remains of sea-weeds
do occur. Some of these are
delicate branching forms, like
some still living, as shown in
the organism figured in Fig.
134 from the Upper Silurian Fl ?l. 134 ;~ An u PP er Silurian s f" weed
J ; (Chondntes vensimilis), natural size.
series. Among the Upper
Silurian strata, also, traces of land-vegetation have been detected
in the form of spores and stems of cryptogamous plants. Lycopods
or club-mosses and ferns appear to have been the chief types in the
earliest terrestrial floras ; at least, it is remains referable to them
that chiefly occur in the older Palaeozoic rocks. They reached a
great development in the Carboniferous period, in the account
of which a fuller description of them will be given. We can dimly
picture the Silurian land with its waving thickets of fern, above
which lycopod trees raised their fluted and scarred stems, threw
out their scaly moss-like branches, and shed their spiky cones.
2 7 8
PALAEOZOIC PERIODS
The fauna of the Silurian period has been more abundantly
preserved than that of the Cambrian, and appears to have been
more varied and advanced. Among its simpler forms were For-
aminifera and sponges. A foraminifer (of which there were no
doubt representatives in Cambrian times, and there are still many
living types in the present ocean, see Fig. 42) is generally a
minute animal, composed of a jelly-like substance which, possess-
ing no definite organs, has in some kinds the power of secreting
a hard calcareous or horny shell, through openings or pores
(foramina} in which filaments from the jelly-like mass are pro-
truded. By other kinds, grains of sand are cemented together
D
FIG. 135. Graptolites from Silurian rocks. A, Rastrites Linncei '; B, Monograptus
priodon ; C, Diplograptus pristis ; D, Phyllograptus typus ; E, Didymograptus
Murchisoni (all natural size).
to form a protecting shell. It is these calcareous and sandy
coverings which occur in the fossil state, and prove the presence of
foraminifera in the older oceans of the globe. Sponges also are
known to have existed in the Cambrian and Silurian seas, and
their remains have been met with in all parts of the Geological
Record down to the present day. It is, of course, only where these
animals secrete hard durable parts that they can be detected as
fossils. A sponge is a mass of soft, transparent, jelly-like sub-
stance, perforated by tubes or canals, and supported on an internal
network of minute calcareous or siliceous spicules, or of interlacing
horny fibres. Most fossil sponges are calcareous or siliceous, and
their hard parts, being durable, have been preserved sometimes in
xvin SILURIAN . 279
prodigious numbers and in wonderful perfection. The common
sponge of domestic use is an example of the horny type.
The Hydrozoa were abundantly represented in the Silurian
seas by graptolites (see p. 270), of which there were many kinds.
Some of the more characteristic of these are shown in Fig. 135.
They abound in certain bands of shale, both in the Lower and
Upper Silurian series, the double forms (such as C, Fig. 135) being
more characteristic of the Lower division, while the single forms
run throughout the system.
Qorals abound in some parts of the Silurian seas. Their
remains chiefly occur in the limestones, doubtless because
these rocks were formed in comparatively clear water, in
FIG. 136. Silurian Corals, (a), Rugose Coral (Omphymct turbinatum, $) ; (),
Alcyonarian Coral (ffeliolites interstinctus, natural size).
which the corals could flourish. But they differed in struc-
ture from the familiar reef -building corals of the present day.
The great majority of them belonged to the Rugose corals,
now only sparingly represented in the waters of the present
ocean. As their name denotes, they were particularly marked
by their thick rugged walls. Many of them were single inde-
pendent individuals ; some lived together in colonies ; while
others were sometimes solitary, sometimes gregarious. A
typical example of these rugose forms is Omphyma, shown in
Fig. 136 (a}. Other genera were Cyathaxonia, Cyathophyllum,
and Zaphrentis. There were likewise less numerous and more
delicate compound forms belonging to what are known as the
Tabulate corals (Favosites, Halysites}, while another type
(Heliolites, Fig. 136, V) represented in ancient times the
Alcyonarian corals {Heliopora) of the present time.
280
PAL/EOZOIC PERIODS
CHAP.
Crinoids or stone-lilies played an important part in the earlier
seas of the globe. In some regions they lived in such abundance
on the sea-floor that their aggregated remains formed solid beds
of limestone, hundreds of feet thick and covering thousands of
square miles. As their name denotes, crinoids are lily-shaped
animals, having a calcareous, jointed flexible stalk fixed to the
bottom, and supporting at its upper end the body, which is com-
posed of calcareous plates furnished with branched calcareous
arms (see Figs. 164, 180, 188). It is these hard calcareous
parts which have been so abundantly preserved in the fossil state.
FIG. 137. Silurian Echinoderms. (a), Cystidean (Pseudocrimtes quadrifasciatus^
natural size) ; (l>), Star-fish (Palceasterina stellata, 35).
Remains of crinoids are found in various parts of the Silurian
system (Dendrocrinus, Glyptocrinus\ chiefly in the limestones,
but not in such abundance and variety as in later portions of
the Palaeozoic formations (compare pp. 293, 306, and Figs. 164,
1 80, and 1 88). Allied to the crinoids were the Cystideans, a
curious order of echinoderms, with rounded or oval bodies en-
closed in calcareous plates, possessing only rudimentary arms,
and a comparatively small and short jointed stalk. They first
appeared in the Cambrian period (Protocystites\ but attained
their chief development during Silurian time, thereafter diminish-
ing in numbers. They are thus characteristically Silurian types
xviii SILURIAN 281
of life. One of them is represented in Fig". 137 (a"). Star-fishes
and brittle-stars likewise occur as fossils among the Silurian rocks.
These marine creatures, still represented in our present seas,
possess hard calcareous plates and spines, which, being imbedded
in a tough leathery integument, have not infrequently been pre-
served in their natural position as fossils. Some of the
genera of star-fishes found in the Silurian system are Palceaster,
Palceasterina (Fig. 137, b\ Palceochoma. Brittle-stars were re-
presented by Protasler.
In the Silurian system are found many tracks and burrows
like those of the Cambrian rocks, indicative of the presence of
different kinds of sea-worms. Throughout great thicknesses of
strata, indeed, these markings
are sometimes the only or
chief fossils to be found.
Names have been given to
the different kinds of burrows
(Arenicolites, Scolithus, Lum-
bricaria, Fig. 138), and of trails
( Pal&ochorda, Palceophycus] .
There were likewise repre-
sentatives of the familiar
Serpula, which is found SO FlG " ^.-Filled-up Burrows ,or Trails left by
'* a sea-worm on the bed of the bilunan sea
abundantly on the present (Lumbricaria antiqua, 4).
sea-bottom, encrusting shells
and stones with a calcareous protecting tube, inside of which the
annelide lives. This tube has been preserved in the fossil
state in rocks of all ages.
The Trilobites, which had already appeared in Cambrian time,
attained their maximum development during the Silurian period.
A few of the primordial or Cambrian types continued to live into
this period, but many new genera appeared. . In the Lower
Silurian series some of the more abundant genera are Asaphus,
Ampyx, Ogygia, and Trinudeus ; in the Upper Silurian division
characteristic genera are Calytnene, Phacops, Encrinunis, Illcenus,
and Homalonotus (Fig. 139). Trilobites continued to flourish,
but in gradually diminishing variety, during the Devonian and
Carboniferous periods, after which they seem to have died out.
They are thus a distinctively Palaeozoic type of life, each great
division of the Palaeozoic rocks being characterised by its own
varieties of the type.
Phyllocarid crustaceans likewise attained to greater variety
282
PALEOZOIC PERIODS
CHAP.
during the Silurian period ; some of the more frequent genera are
Ceratiocaris (Fig. 140), Discinocaris, and Caryocaris.
The Mollusca are far more abundant and varied in the Silurian
FIG. 139. Lower and Upper Silurian Trilobites. (a), Asaphus tyrannus (J) ; (), Ogygia
Buchii (i) ; (c~), Illcemis barriensis () ; (d), Trinucleus concentricus (natural size) ;
(e), Homo. lonotus delphinocephalus (J).
than in the Cambrian rocks. Among the more characteristic
Silurian genera of Brachiopods are Atrypa, Leptccna, Orthis,
Pentamerus, Rhynchonella, and Strophomena (Fig. 141). Among
the Lamellibranchs we find the Cambrian genera Ctenodonta and
SILURIAN
283
Modiolopsis, with new forms such as Orthonota (Fig. 142),
Cleidophorus and Ambonychia.
The Gasteropods played an important part in the fauna of
the Silurian sea, for upwards of 1300
species of them have been found in
Silurian rocks. Among the more
frequent genera are Bellerophoji (Fig.
143), Ophileta, Hoi ope a, Murchisonia,
Platyschisma.
Numerous representatives of the
chambered Cephalopods have been found
in the Silurian rocks, especially in the
upper division. Among the more fre-
quent genera are Orthoceras (straight,
Fig. 144 a\ Cyrtoceras (curved), As-
coceras (globular or pear-shaped),
Lituites (coiled, Fig. 144 ), and also Nautilus, a genus which
FIG. 140. Silurian Phyllocarid
Crustacean (Ceratiocaris
papilio).
FIG. 141. Silurian Brachiopods. (a), Atrypa reticularis (natural size), Caradoc beds to
Lower Devonian ; (), Orthis actonia- (natural size) ; (c), Rhynchonella borealis
(natural size) ; (d), Pentamerus galeatus (natural size).
has persisted through the greater part of geological time to the
284 PALEOZOIC PERIODS CHAP.
present day, and now remains the only representative of the
chambered cephalopods formerly so abundant.
Remains of Ostracoderms and fishes detected in the Upper
Silurian rocks are the earliest traces of vertebrate life yet known.
They consist partly of plates which are regarded as portions of
the bony covering of certain " placoderms " l or bone-plated forms
{Pteraspis, Cephalaspis, Fig. 148, Auchenaspis] ; partly of curved
spines and shagreen -like fragments. The creatures of which
these are relics appeared as forerunners of the remarkable
assemblage of organisms which characterised the next geological
period (see p. 289). All the animal remains hitherto enumerated
are relics of the inhabitants of the sea. Of the land-animals
of the time nothing was known until the year 1884, when, by a
FIG. 142. Silurian Lamellibranch (OrtJw-
nota semisulcata, natural size).
FIG. 143. Silurian Gasteropod
(Bellerophon dilatatus, J).
curious coincidence, the discovery was made of the remains
of scorpions in the Silurian rocks of Sweden, Scotland, and the
United States (compare Fig. 157), and of an insect allied to the
living cockroach (Palceoblattina) in those of France. If scorpions
and insects existed during this ancient period we may be sure
that other forms of terrestrial life were also present. A new
interest is thus given to the prosecution of the search for fossils
among the older formations.
Putting together the evidence furnished by the rocks and
fossils of the Silurian system, we get a glimpse of the aspect of
the globe during the early geological period which they represent.
The rocks bring before us the sand, mud, and gravel of the
bottom of the sea, and tell of some old land from which these
1 The organisms called "placoderms" and hitherto regarded as fishes,
are now believed by some palaeontologists not to have been true fishes, and
they are placed by these authors in the sub-class Ostracodermi.
SILURIAN 285
materials were worn away. The detritus carried out from the
shores of that land was laid down upon the sea-bottom, just as
similar materials are being disposed of at the present day. The
area occupied by Silurian rocks marks out the tracts then covered
by the sea. Following these upon a map we perceive that vast
regions of the existing continents were then parts of the ocean-
floor. In Europe, for example, Silurian rocks underlie the greater
part of the British Islands, whence they stretch northwards across
a large part of Scandinavia and the basin of the Baltic. They
rise to the surface in many places on the continent from Spain
to the Ural Mountains. They have yielded an extraordinary
abundance and variety of organic forms in Bohemia. In the New
FIG. 144. Silurian Cephalopods. (a), Orthoceras cmeritum (J) ; (), Trochoceras
(Lituttes) cornu-arietis (^).
World also they are well developed over Canada and the adjacent
portions of the United States. They are found forming parts of
some of the great mountain-chains of the globe, as, for instance,
in the Cordilleras of South America, in the Rocky and Wahsatch
Mountains, in the Alps, and in the Himalayas. Even at the
antipodes they are met with as thick masses in Australia and
New Zealand. It is evident that the geography of the globe in
Silurian times was utterly unlike what it is now. A large part of
the present land was then covered with shallow seas, in which the
Silurian sedimentary rocks were laid down. There would seem
to have been extensive masses of land in the boreal part of the
northern hemisphere, connecting the European, Asiatic, and
American continents. Along the coast-line of the northern land,
and across the shallow seas lying to the south of it, the same
286 PAL/EOZOIC PERIODS CHAP, xvm
species of marine organisms migrated freely between the Old and
the New Worlds.
The Silurian system of Britain has a total thickness of nearly
20,000 feet, and has been classified into the subdivisions shown in
the following Table :
ILudlow group (mudstone and Aymestry Limestone) Kirkby Moor
and Bannisdale Flags and Slates.
Wenlock group (shales and limestones) Denbighshire and Coniston
Grits and Flags.
Llandovery group May Hill Sandstones, Tarannon Shales.
IBala and Caradoc group sandstones, slates, and grits, with Bala
(Coniston) Limestone.
Llandeilo group dark argillaceous and sometimes calcareous flag-
stones and shales.
Arenig group dark slates, flags, and sandstones.
In the United States and Canada the Silurian system is
arranged as folio ws: -
Lower Helderberg group (see p. 295), comprising
(3) Upper Pentamerus Limestone.
(2) Delthyris (Shaly or Catskill) Limestone.
( i ) Lower Pentamerus Limestone.
Onondaga, Water-lime (a hydraulic magnesian limestone), and
Salina (reddish marls, dolomite, gypsum, and rock-salt) group.
Niagara Shale and Limestone, full of corals (like Wenlock Lime-
stone).
Clinton group : may be paralleled with the Tarannon Shales of
Wales.
Medina group of sandstones with the Oneida conglomerate below.
Hudson River Shales and Cincinnati Limestones and Shales.
Utica Shales.
Trenton group, composed mostly of dark carbonaceous limestone
(Trenton Limestone, Black River Limestone, Bird's-eye Limestone).
Chazy Limestone (dolomite, with Maclurea, Orthoceras, Illcenus], etc.
Calciferous group of arenaceous cherty, magnesian limestones, with
rare fossils corresponding to those of the Welsh Arenig rocks.
CHAPTER XIX
DEVONIAN AND OLD RED SANDSTONE
THE DEVONIAN system, which comes next in order, was named by
Sedgwick and Murchison after the county of Devon, where they
studied its details. In Europe, and likewise in the eastern part
of North America, it occurs in two distinct types, which bring
before us the records of two very different conditions in the
geography of these regions during the time when the rocks
composing the system were being deposited. The ordinary type,
which occurs all over the world, represents the tracts that were
covered by the sea, and has preserved the remains of many forms
of the marine life of the period. It is that to which the name
Devonian is more particularly applicable. The less frequent type
is characterised by thick accumulations of sandstones, flagstones,
and conglomerates that appear to have been laid down in lakes
and inland seas, and contain a distinct assemblage of land and
probably fresh-water fossils. This lacustrine type is known by
the name of OLD RED SANDSTONE.
In general lithological characters the Devonian rocks resemble
those of the Silurian system underneath. In Central Europe,
where they attain a thickness of many thousand feet, their lower
division consists mainly of sandstones, grits, greywackes, slates,
and phyllites. The central zone contains thick masses of lime-
stone, often full of corals and shells, while the upper portions
comprise thin-bedded sandstones, shales, and limestones. These
various strata represent the sediments intermittently laid down
upon the bottom of the sea which then covered the greater part
of Europe. Here and there, they include bands of diabase and
tuff, which show that submarine volcanic eruptions took place
during their deposition.
In the north-west of Europe, however, the floor of the Silurian
287
288 PALEOZOIC PERIODS CHAP.
sea was irregularly ridged up into land, and large water-basins
were formed, more or less completely shut off from the sea, into
which rivers from the ancient northern continent poured enormous
quantities of gravel, sand, and silt. The sites of these inland seas
or lakes can be traced in Scotland, the north of England, and
Ireland. Similar evidence of land and lake -waters is found in
New Brunswick and Nova Scotia. That some of the larger
basins were marked by lines of active volcanoes is well shown in
Central Scotland, where the piles of lava and ashes left by the
eruptions are more than 6000 feet thick.
The occurrence of both marine and lacustrine deposits is of the
highest interest; for, on the one hand, we learn what kinds of
a b
FIG. 145. Plants of the Devonian period, (a), Psilophyton (J) ; (K), Pal&opteris (\)
animals lived in the sea in succession to those that peopled the
Silurian waters, and, on the other hand, we meet with the first
abundant remains of the vegetation that covered the land, and of
the fishes that inhabited the inland waters. The terrestrial flora
of the Devonian period has been only sparingly preserved in the
marine strata ; but occasional drifted specimens occur to show
that land was not very distant from the tracts on which these
strata were laid down. In the lacustrine series or Old Red
Sandstone of Britain more abundant remains have been met with ;
but the chief sources of information regarding this flora are to be
sought in New Brunswick and Gaspe, where upwards of 100
species of plants have been discovered. Both in Europe and in
North America, the Devonian vegetation was characterised by
the predominance of ferns, lycopods (Lepidodendron, etc.), and
xix DEVONIAN, OLD RED SANDSTONE 289
calamites. It was essentially acrogenous that is, it consisted
mainly of flowerless plants like our modern ferns, club-mosses,
and horse-tail reeds. One of the most characteristic plants, called
Psilophyton, is represented in Fig. 145. Traces of coniferous
plants show that on the upland of the time pine-trees grew, the
stems of which were now and then swept down by floods into the
lakes or the sea.
While the general aspect of the flora was uniformly green and
somewhat monotonous, the fauna had now become increasingly
varied. We know that these early woodlands were not without
insect life, for neuropterous and orthopterous wings have been
preserved in the strata of New Brunswick. Some of these remains
indicate the existence of ancient forms of ephemera or May-fly,
one of which was so large as to have a spread of wing measuring
5 inches across. In the Lower Old Red Sandstone of Scotland
traces have been found of millipedes, which fed on the decayed
wood of the forests. Relics of land-snails too have been detected
among the fossil vegetation in the New Brunswick deposits. It
is evident, however, that the plant and animal life of the land has
only been sparingly preserved ; and though our knowledge of it
has in recent years been largely increased, we shall probably never
discover more than a mere fragmentary representation of what the
original terrestrial flora and fauna really were.
The water-basins of the Old Red Sandstone have yielded large
numbers of remains of the fishes of the time. These are members
of the remarkable order of Ganoids the earliest known type of
fishes which, though so abundant in early geological time, is
represented at the present day by only a few widely scattered
species, such as the sturgeon, the polypterus of the Nile, and the
bony pike or garpike of the American lakes. These modern
forms are denizens of fresh water, and there is reason to believe
that their early ancestors were also inhabitants of lakes and rivers,
though many of them may also have been able to pass out to the
sea. The ganoids are so named from the enamelled scales and
plates of bone in which they are encased. In some of the fossil
forms, this defensive armour consisted of accurately fitting and
overlapping scales (Figs. 146, 147). Some of the most charac-
teristic scale-covered genera are Osfe0tepif(ig. 1 47, a\ Diplopterus,
Glyptolcemus, Holoptychius. The acanthodians (Fig. 147, <), an
order of elasmobranchs, distinguished by the thorn -like spines
supporting their fins, reached their greatest development during
the Devonian period. Of the plate-covered " placoderms " some of
U
290
PALEOZOIC PERIODS
the most characteristic were the curious Cephalaspis (Fig. 148, #),
with its head -buckler shaped like a saddler's awl, the Pteraspis,
which, with Cephalaspis^ had already appeared in the Silurian
period, and the Pterichthys (Fig.
148, b}. The true affinities of
these forms, however, are doubt-
ful, and some authors do not
regard them as true fishes.
One of the fishes of the Old
Red Sandstone, named Dipterus,
has been found to have a singular
modern representative in the
barramunda or mud-fish (Cera-
todus} of the Queensland rivers
IMG. 140. Overlapping scales of an Old A ,. ,-. ... ui i
Red Sandstone fish (Hoioftychius m Australia. Dtpterus resembled
Andersoni, natural size). the ganoids in its external enamel
and strong bony helmet, but its
jaws present the characteristic teeth, and its scales have the
rounded or " cycloid " form of Ceratodus. The curious genus
Coccostetis, which is found in the Old Red Sandstone, may also
FIG. 147 Scale-covered Old Red Sandstone fishes, (a), Osteolepis ; (ff), Acanthodes
(both reduced).
have Dipnoan affinities. Its head and body were armoured with
bony plates. Some of its American allies were of large size, one
of which, the Dinichthys, found in Ohio, had a head -buckler
3 feet long armed with formidable teeth, while another, the
Titanichthys, is said to have reached a length of 2 5 feet.
xix DEVONIAN, OLD RED SANDSTONE 291
Some of the fishes swarmed in the waters of the Old Red
Sandstone, as is shown by the prodigious numbers of their
remains occasionally preserved in the sandstones and flagstones.
Their bodies lie piled on each other in such numbers, and
often so well preserved, as to show that probably the animals
were suddenly killed, and were covered up with sediment before
their remains had time to decay and to be dispersed by the
currents of water. Perhaps earthquake shocks, or the copious
discharge of mephitic gases, or other sudden baneful influence,
may have been the cause of the extensive destruction of life in
these ancient waters.
That some of the fishes found their way to the sea, as our
FIG. 148. Old Red Sandstone Placoderms. (a), Cephalaspis ; (b), Pterichthys
(both reduced).
modern salmon does, is indicated by the occasional occurrence of
their remains among those of the truly marine fauna of the Devon-
ian rocks. But the rarity of their presence there, compared with
their prodigious abundance in some parts of the Old Red Sand-
stone, probably serves to show that they were essentially inhabitants
of the inland waters of the time.
Among the animals that appear to have been migratory between
the outer sea and the inland basins, were the curious forms
known as Eurypterids, which, though generally classed with the
crustaceans, possibly had affinities with the arachnids or scorpions.
One of the most remarkable of these creatures was the Pterygotus,
of which the general form is shown in Fig. 149. Most of the
species are small, though one of them found in Scotland must
have attained a length of 5 or 6 feet.
But it is the marine or Devonian fauna which is most widely
292
PALEOZOIC PERIODS
spread over the globe, and from its extensive distribution is of
most importance to the geologist. Taken as a whole, it presents
a general resemblance to that of the
Silurian period, which it succeeded.
Some of the Silurian species survived
in it, and new species of the old genera
made their appearance. But important
differences are to be observed between
the faunas of the two systems, showing
the long lapse of time, and the changes
that were gradually brought about in
the life of the globe.
It is specially interesting to mark
how some of the characteristic Silurian
types dwindle and finally die out in the
Devonian system. One of the best
examples of this survival and dis-
appearance is supplied by the Grapto-
lites. It will be remembered how
prodigiously abundant these creatures were in the Silurian seas.
They are met with also in scattered specimens in the lower
division of the Devonian system, but their rarity there affords a
FIG. 149. Devonian Eurypterid
Crustacean (Pterygotus, re-
duced).
FIG. 150. Devonian Trilobites. (a), Bronteus jlabellifer (J) ; (b), Dalmania rngosa
(4) 5 (f)i Homalonotus armatus (i) ; (d\ Harpes macrocephalus ().
striking contrast to their profusion among the Silurian strata, and
they seem to have entirely died out before the end of the Devonian
period, for no traces of them occur in the higher parts of the
xix DEVONIAN, OLD RED SANDSTONE 293
system, and they have never been met with in any later geological
formation.
Again, Trilobites, which form such a predominant and striking
feature of the Silurian fauna, occur in greatly diminished number
and variety among the Devonian rocks. Most of the Silurian
genera are absent. Among the most frequent Devonian types
are species of Phacops, Cryphtzus, Homalo?iottis, Dalmania, and
Bronteus (Fig. i 50). We shall find that this peculiarly Palaeozoic
type of Crustacea finally died out in the next or Carboniferous
period. But while the trilobites were waning, the eurypterids,
already referred to, appeared and attained a great development.
In the clearer parts of the sea vast numbers of rugose corals
flourished, and, with other calcareous organisms, built up solid
masses of limestone. Some of the characteristic genera were
Frc. 151. Devonian Corals. (), Cyathophyllumceratites(s)\ (V), Cakcola sandalina().
Cyathophylhim (Fig. 151), Acervularia, Cystiphyllum, and the
curious Calceola which, after being successively placed among the
lamellibranchs and the brachiopods, is now regarded as a rugose
coral with an opercular lid. With these were likewise associated
vast numbers of crinoids, of which the genera Cyathocrinus and
Cupressocrinus were especially characteristic.
The Brachiopods reached their maximum of development in
the Devonian seas, upwards of 60 genera and 1 100 species having
been described from Devonian rocks. Comparing them with
those of the Silurian system, we notice that some of the most
characteristic Silurian types, such as forms of Orthis and Stropho-
mena, became fewer in number, while forms of Prodnctus and
Chonetes increased. The most abundant families were those of
the Spirifers (Uncites, Cyrtia, Athyris, Atrypa] and Rhynchonel-
lids (Fig. 152). Two distinctly Devonian brachiopods were
294 PALEOZOIC PERIODS CHAP.
Stringocephalus and Rensseleria, allied to the still living Tere-
FIG. 152. Devonian Brachiopods. (a), Uncites gryphus () ; (l>), Stringocephalus
Burtini () ; (c\ Spirifera Vemeuillii (disjunct a) (J).
bratula. The former is especially characteristic of one of the
Middle limestones (see Table on p. 295).
FIG. 153. A, Devonian Lamellibranch (Cucull&a Hardingii, ) ; B, Devonian
Cephalopod (Clymcnia Sedgwickii, ).
The Mollusca appear to have been well represented in the
Devonian seas. Of the lamellibranchs, Pterinea is particularly
xix DEVONIAN, OLD RED SANDSTONE 295
abundant in the lower part of the system, Cucullcea (Fig. 153, A)
in the upper part. The Devonian cephalopods included many
species of the genera Orthoceras, Cyrtoceras, Clymenia, Goniatites,
and Bactrites (Fig. I 5 3, B).
The Devonian system in Europe is subdivided as in the sub-
joined Table :
IPilton and Pickwell-Down Group of England Upper Old Red
Sandstone of Scotland ; Famennian and Frasnian sandstones,
shales, and limestones of the north of France and Belgium
Psammites de Condroz ; Cypridina shales, Spirifer sandstone,
Rhynchonella cuboides beds of Germany.
nifracombe and Plymouth Limestones, grits, and conglomerates of
) Devonshire ; Limestone of Givet, and Calceola shales of north
3 1 of France; Stringocephalus limestone of the Eifel Calceola group
^ of Germany.
f Linton Slates and sandstones of Devon and Cornwall Lower Old
Lower - Red Sandstone of Scotland and Wales ; Coblenzian, Taunusian,
[_ and Gedinnian rocks of the Ardennes and Taunus.
In North America the following subdivisions have been
made :
Catskill Red Sandstone and conglomerate, 6000 feet thick (Upper
Old Red Sandstone).
Chemung group, 3300 feet thick in Pennsylvania (Spirifera Ver-
Upper -{ neuillii).
Portage group of shales and shaly sandstones (Goniatites, Cardiola,
Clymenia).
Genesee group of dark shales (with a Rhynchonella like R. cuboides}.
Hamilton group of shaly sandstone, shales, and thin limestones
,,. , ,, | (Phacops, Homalonotus, etc. ).
1 Marcellus group of soft dark shales with a thin limestone at the
\_ bottom containing Goniatites.
fCorniferous Limestone with abundant masses oA
chert or flint and numerous corals which some- I rj pper Helder-
times assume the form of reefs (Spirifera acumi- \ hers" proui
nata, Dalmania, etc. \ Schoharie grit, Cauda-
galli grit. J
Oriskany Sandstone (Spirifera arenosa, Rensseleria ovoides] connected
with the Lower Helderberg group (p. 286) in stratigraphical
relations but containing Devonian fossils.
CHAPTER XX
CARBONIFEROUS
THE next great division of the Geological Record has received the
name of CARBONIFEROUS, from the beds of coal (Latin Carbo) which
form one of its most conspicuous features. The rocks of which it
consists reach sometimes a thickness of fully 20,000 feet, and con-
tain the chronicle of a remarkable series of geographical changes
which succeeded the Devonian period. They include limestones
made up in great part of corals, crinoids, polyzoa, brachiopods,
and other calcareous organisms which swarmed in the clearer
parts of the sea ; sandstones often full of coaly streaks and remains
of terrestrial plants ; dark shales not infrequently charged with
vegetation, and containing nodules and seams of clay-ironstone ;
and seams of coal varying from less than an inch to several feet
or yards in thickness, and generally resting on beds of fire-clay.
These various strata are disposed in such a way as to afford
clear evidence of the physical geography of large areas of the
earth's surface during the Carboniferous period. The limestones
attain a thickness of sometimes several thousand feet, with hardly
any intermixture of inorganic sedimentary material. They consist
partly of aggregated masses of corals and coralloid animals, which
grew on the sea-floor, somewhat after the manner of modern coral-
reefs ; partly of aggregated stems and joints of crinoids, which
must have flourished in prodigious numbers on the bottom, mixed
with fragments of other organisms, the whole being aggregated
into sheets of solid stone. Thus, in Europe, the Carboniferous or
Mountain Limestone, which forms the lower part of the Carboni-
ferous system, stretches from the west of Ireland eastwards for a
distance of 750 miles, across England, Wales, Belgium, and
Rhineland into Westphalia. In the basin of the Meuse it is not
less than 2500 feet thick, and in Lancashire, where it attains its
maximum development, it exceeds 6000 feet. Such an enormous
296
CHAP, xx CARBONIFEROUS 297
accumulation of organic remains shows that, during the time of
its deposition, a wide and clear sea extended into the centre of
Europe. But as the limestone is traced northwards, it is found to
diminish in thickness. Beds of sandstone, shale, and coal begin
to make their appearance in it, and rapidly increase in importance,
as they are followed away from the chief limestone area ; while
the limestone itself is at last reduced in Scotland to a few beds,
each only a yard or two in thickness. From this change in the
character of the rocks, the inference may be drawn that, while
the sea extended from the west of Ireland eastwards into West-
phalia, land lying to the north supplied sand, mud, and drifted
plants, which, being scattered over the sea- floor, prevented the
calcareous organisms of the thick limestone from extending con-
tinuously northwards. These detrital materials now form the
masses of sandstone and shale that take the place of the lime-
stone in the north of England and in Scotland. The northward
extension of a few limestone beds full of marine organisms serves
to show that during longer or shorter intervals, the water cleared,
sand and mud ceased to be carried so far southward, and the
corals, crinoids, and other limestone-building creatures were able
to spread themselves farther over the sea-floor. But the thinness
of such intercalated limestones also indicates that the intervals
favourable for their formation were comparatively short, the sandy
and muddy silt being once again borne southward from the land,
killing off or driving away the limestone-builders, and spreading
new sheets of sand and mud upon the bottom of the sea.
There can be no doubt that, while these changes were in
progress, the whole wide area of deposition in Western and
Central Europe was undergoing a gradual depression. The sea-
bottom was sinking, but so slowly that the growth of limestone
and the deposit of sediment probably on the whole kept pace
with it. The actual depth of the water may not have varied
greatly even during a subsidence of several thousand feet. That
this was the case may be inferred from the structure of the lime-
stone itself. We have seen that this rock sometimes exceeds
6000 feet in thickness. Had there been no subsidence of the
sea-floor during the accumulation of so thick a mass of organic
debris, it is evident that the first beds of limestone must have
been begun at a depth of at least 6000 feet below the surface of
the sea, and that, by the gradual increase of calcareous matter,
the sea was eventually filled up to that amount, if it was not filled
up entirely. But we can hardly suppose that the same kinds of
298 PALEOZOIC PERIODS CHAP.
organisms could live at a depth of 6000 feet and also at or near
the surface. We should expect to find the organic contents of
the lower parts of the limestone strikingly different from those in
the upper parts. But though there are differences sufficient to
admit of the limestone being separated into stages, each marked
by its own distinctive assemblage of fossils, the general character
or facies of the organisms remains so uniform and persistent
throughout, as to make it quite certain that the conditions under
which the creatures lived on the bottom and built up the lime-
stone continued with but little change during the whole time
when the 6000 feet of rock were being deposited. As this could
not have been the case had there been a gulf of 6000 feet to
fill up, we are led to conclude that the bottom slowly subsided
until its original level, on which the limestone began to form, had
sunk at least 6000 feet.
This conclusion is borne out by many other considerations.
Thus the sedimentary strata that replace the limestone on its
northern margin are also several thousand feet thick. But from
bottom to top they abound with evidence of shallow-water con-
ditions of deposition. Their repeated alternations of sandstone,
grit (even conglomerate), and shale ; the presence in them of
constant current- bedding ; the frequent occurrence of ripple-
marked and sun-cracked surfaces ; the preservation of abundant
remains of terrestrial vegetation much of it evidently in its
position of growth prove that the mass of sediment was not laid
down in a deep hollow of the sea-bottom, but on the sinking floor
of shallow waters not far from the margin of the land.
But probably the most interesting evidence of long-continued
subsidence during the Carboniferous period is furnished by the
history of the coal-seams. Coal is composed of compressed and
mineralised vegetation. In most coal-fields each layer of coal is
usually underlain by a bed of fire-clay, or at least of shale, through
which roots and rootlets, descending from the under surface of the
coal-seam, branch freely. There can be little doubt that each bed
of fire-clay is an old soil, while the coal lying upon it represents
the matted growth of vegetation which that soil supported.
Hence the association of a fire-clay and a coal-seam furnishes
distinct evidence of a terrestrial surface. 1
1 In some coal-fields there is evidence that coal has likewise been formed
out of matted vegetation which has been swept down by floods and been
buried under sand, gravel, and other sediment. In such circumstances, there
is no usual accompaniment of an underclay below each coal-seam.
CARBONIFEROUS
299
In many regions the Carboniferous system comprises a series
of sandstones, shales, and other strata, many thousands of feet in
thickness, throughout which, on successive platforms, there lie
hundreds of seams of coal (Fig. 154).
If each of these seams marks a former
surface of terrestrial vegetation, how is
this succession of buried land-surfaces to
be accounted for? There is obviously
but one solution of the problem. The area
over which the coal-seams extend must
have been slowly sinking. During this
subsidence, sand, mud, and silt were
transported from the neighbouring land,
and in such quantity as to fill up the
shallow waters. On the muddy flats
thus formed, the vegetation of the flat
marshy swamps spread seaward. There
may not improbably have been pauses
in the downward movement, during
which the maritime jungles and forests
continued to flourish and to form a
thick matted mass of vegetable matter.
When the subsidence recommenced,
this mass of living and dead vegetation
was carried down beneath the water
and buried under fresh deposits of
sand and mud. As the weight of sedi-
ment increased, the vegetable matter
would be gradually compressed and
would slowly pass into coal. But
eventually another interval of rest or
of slower subsidence would allow the
shallow sea once more to be silted up.
Again the marsh-loving plants from the
neighbouring swampy shores would
creep outward and cover the tract with
a new mantle of vegetation, which, on
the renewal of the downward movement, would be submerged
and buried.
In the successive strata of a coal-field, therefore, we are
presented with the records of a prolonged period of subsidence,
probably marked by longer or shorter intervals of rest. These
FIG. 154. Section of part of
the Cape Breton coal-field,
showing a succession of buried
trees and land surfaces. (),
sandstones ; (ft), shales ; (c),
coal - seams ; (), Eremopteris
(Spkenopteris) artemisicefolia (i) ; (c), A lethopteris (Pecopteris) lonchitica ().
the shallow waters, and gradually forming a belt of swampy jungle
several miles broad. That the coal-jungles extended into the sea
is shown by the occurrence of marine shells and other organisms
in the coal itself. But there were probably also wide swamps
wherein the water was brackish or fresh. A single coal-seam may
sometimes be traced over an area of more than 1000 square miles,
showing how widespread and uniform were the conditions in
which it was formed.
During the subterranean movements that marked the Car-
boniferous period, the Devonian physical geography was entirely
remodelled. The lake-basins of the Old Red Sandstone were
effaced, and the sea of the Carboniferous limestone spread over
their site. Much of the Devonian marine area was upridged into
land, and the rocks eventually underwent that intense compres-
XX
CARBONIFEROUS
301
sion and plication which have given them their cleaved, crumpled,
and metamorphic aspect, and in connection with which they were
invaded by granite and intersected with mineral veins. It is
deserving of remark that volcanic action, which played so notable
a part in Devonian time, was continued, but with diminished
vigour, in the Carboniferous period. During
the earlier half of the period, volcanic out-
bursts were frequent in different parts of
Britain, particularly in Derbyshire, the Isle
of Man, central and southern Scotland, and
the south-west of Ireland. The lava and
ashes ejected in some of these areas
during the time of the Carboniferous Lime-
stone now form conspicuous groups of
hills.
Of the plant and animal life of the
Carboniferous period much is known from
the abundant remains which have' been pre-
served of the terrestrial surfaces and sea-
floors of the time. Beginning with the flora,
we have first to notice its general re-
semblance to that of the Devonian period.
Many of the genera of the older time survived
in the Carboniferous jungles ; but other
forms appeared in vast profusion, which have
not been met with in any Devonian or Old
Red Sandstone strata. The Carboniferous
flora, like that which preceded it, must have been singularly
monotonous, consisting as it did almost entirely of flowerless
plants. Not only so, but the very same species and genera
appear to have then ranged over the whole world, for their
remains are found in Carboniferous strata from the Equator
to the Arctic Circle. Ferns, lycopods, and equisetacese, consti-
tuted the main mass of the vegetation. The ferns recall not a
few of their modern allies, some of the more abundant kinds being
Spkenopteris, Neuropteris, and Pecopteris (Fig. 155). Among the
lycopods the most common genus is Lepidodendron, so named
from the scale-like leaf-scars that wind round its stem (Fig. 156).
Its smaller branches, closely covered with small pointed leaves,
and bearing at their ends little cones or spikes (Lepidostrobus\
remind one of the club-mosses of our moors and mountains ; but
instead of being low-growing or creeping plants, like their modern
FIG. 156. Carboniferous
Lycopod (Lepidodendron
Sternbergii, J).
302
PALEOZOIC PERIODS
representatives, they shot up into trees, sometimes 50 feet or
more in height. Equisetacea? abounded in the Carboniferous
FIG. 157. Carboniferous Equisetaceous Plants, (a), Calautitcs Lindlcyi( C.
Mougeoti, LindL, J) ; (b\ Asterophyllites dcnsifolius ()
swamps, the most frequent genus being Calamites, the jointed
and finely-ribbed stems of which are frequent fossils in the sand-
FiG. 158. Sigillaria with Stigmaria roots (much reduced)-
stones and shales (Fig. 157, a\ This plant probably grew in
dense thickets in the sandy and muddy lagoons, and bore as its
xx CARBONIFEROUS 303
foliage slim branches, with whorls of pointed leaves set round the
joints (Asterophyllites, Fig. 157, b\ The Sigillarioids were among
the most abundant, and, at the same time, most puzzling members
of the Carboniferous flora. They do not appear to have any close
modern allies, and their place in the botanical scale has been a
subject of much controversy. The stem of these trees, sometimes
reaching a height of 50 feet or more, was fluted, each of the
parallel ribs being marked by a row of leaf-scars, hence the name
Sigillaria, from the seal-like impressions of the scars (Fig. 158).
These surface-markings disappeared as the tree grew, and in the
lower part of the trunk they passed down into the pitted and
tubercular surface characteristic of the roots (Stigmaria), still so
FIG. 159. Cordaites alloidius (i) with Carpolitkes attached.
abundant in their position of growth in fire-clay, and also as
drifted broken specimens in sandstones and shales. Another
plant that took a prominent part in the Carboniferous flora was
that named Cordaites (Fig. 159). Its true botanical place is still
matter of dispute ; some writers placing it with the lycopods,
others with the cycads, or even among the conifers. It bore
parallel-veined leaves somewhat like those of a yucca, which, when
they fell off, left prominent scars on the stem, and it also
carried spikes or buds (Carpolithes, Fig. 159). All the plants
now enumerated probably flourished on the lower grounds and
swamps. Cut on the higher and drier tracts of the interior
there grew araucarian pines (Dadoxylon, Araucarioxylori), the
trunks of which, swept down by floods, were imbedded in some of
the sands of the time and now appear petrified in the sandstones.
While the terrestrial vegetation of the Carboniferous period has
304 PALEOZOIC PERIODS CHAP.
been so abundantly entombed, the fauna of the land has been but
scantily preserved. That air-breathers existed, however, has been
made known by the finding of specimens of scorpions, myriapods,
true insects, and amphibians. Vast numbers of the remains of
scorpions have been discovered in the Carboniferous rocks of
Scotland. These ancient forms (Eo$corpiu$) Fig. 1 60) presented
a remarkably close resemblance to the living scorpion, and so
well have they been preserved among
the shales that even the minutest parts
of their structure can be recognised.
They possessed stings like their
modern descendants, whence we may
infer the presence of other forms of
lift which they killed. The Carboni-
ferous woodlands had plant -eating*
millipedes, and theirsilence was broken
by the hum of insect-life ; for ancestral
forms of dragon - flies (Libellul(z\
May -flies (Ephemerid
FIG. 165. Carboniferous Blastoid (Cup of
Pentremite, magnified). (a), View from
above ; (b\ side view.
FIG. 166. Carboniferous Tri-
lobite (fhilltysia derbiensis,
natural size).
contrast to those of earlier geological time. In particular, the
great family of the Trilobites, so characteristic of the older
Palaeozoic systems, now died out altogether. Instead of its
numerous types in the Silurian and Devonian rocks, it is repre-
sented in the Carboniferous system by only four genera, all the
308 PALAEOZOIC PERIODS CHAP.
species of which are small (Phillipsia, Fig. 166, Griffithides,
Brachymetopits], and none of which rises into the next succeeding
system. The most abundant crustaceans were ostracods an
order still abundantly represented at the present day. They are
minute forms enclosed within a bivalve shell or carapace which
entirely invests the body. Many of these live in fresh water ; the
Cypris, for example, being abundant in ponds and ditches.
Others are marine, while some are brackish-water forms. In the
Carboniferous lagoons, as at the present time, they lived in
enormous numbers ; their little seed -like valves are crowded
together in some parts of the shale which represents the mud of
these lagoons ; sometimes they even form beds of limestone.
Doubtless, they served as food to the smaller fishes whose remains
are usually to be found where the ostracod valves are plentiful.
One of the principal genera is Leperditia. There were likewise
long- tailed shrimp-like crustaceans {Anthrapal&mon, Palceo-
crangori), and king-crabs (Prestwichia) ; while in the earlier part
of the period Eurypterids still survived in the waters.
Some of the most delicately beautiful fossils of the Carboni-
ferous Limestone belong to the Polyzoa. These animals, of which
familiar living examples are the com-
mon sea-mats of our shores, are char-
acterised by their compound calcareous
or horny framework studded with
minute cells, each of which is occupied
by a separate individual, though the
whole forms one united colony. One
of the most abundant Carboniferous
genera is Fenestella (Fig. 167). So
numerous are the polyzoa in some
bands of limestone as to constitute
the in P art of ^ stone. Their
delicate lace-hke fronds are best seen
where the rock has been exposed for a time to the action of the
weather ; they then stand out in relief and often retain perfectly
their rows of cells.
The Brachiopods, so preponderant among the molluscs of the
earlier divisions of Palaeozoic time, now decidedly wane before the
great advance of the more highly organised lamellibranchs and
gasteropods. Some of the most characteristic genera (Fig.
1 68) are Productus, Spirifera, Streptorhynchus, Rhynchonella,
Athyris, Chonetes, Terebratula (Dielasma), Lingula, Distina.
xx CARBONIFEROUS 309
Some of the species appear to range over the whole world, for
^^ ^^^^^^
FIG. 168. Carboniferous Brachiopods. (a), Streptorhynchus crenistria (J) ;
(), Productus semireticulatus () ; (c), Spirifera striata (J).
they have been met with across Europe, in China, Australia, and
North America. Among these cosmopolitan forms are Productus
FIG. 169. Carboniferous Lamellibranchs. (a), Edmondia sulcata ; (
Spirifera glabra, Terebratula hastata.
3 io
PALEOZOIC PERIODS
CHAP.
Some of the more common Lamellibranch molluscs (Fig. 169)
belong to the genera Aviculopecten, Nuculana, Nucula, Edmondia,
Modiola, Anthraconiya. Among the Gasteropods Euomphalus,
Pleurotomaria, Loxonema, and Bellerophon (Fig. 170) are not
infrequent. A Pteropod (Conularia^ Fig. 171) may be gathered
FIG. 170. Carboniferous Gasteropods. (a), Euomphalus fcntangulat
(/>), Bellerophon tenuifascia (ff).
in great numbers in some parts of the Carboniferous Limestone.
The Cephalopods were represented by numerous species of Orlho-
ceras, Nautilus, and Goniatites ( Fig. 172).
Remains of fishes are not infrequent in the Carboniferous
Limestone. But they present a striking contrast to those of the
FIG. 171. Carboniferous
Pteropod (Conularza
quadrisulcata ().
a b
FIG. 172. Carboniferous Cephalopods
(a), Orthoceras goldfuss i am mi (5) ; (l>
Goniatites sphcericus (natural size).
black shales and ironstones of the Coal-measures. They con-
sist for the most part of teeth or of spines belonging to large
predatory sharks. These teeth were placed as a kind of pavement
and roof in the mouth, and were used as effective instruments for
crushing the -hard parts of the animals, on which these larger
creatures preyed. If, as is probable, the sharks fed upon the
ganoid fishes of the time, they must have required a powerful
CARBONIFEROUS
apparatus of teeth for crushing the hard, bony armour in which
these fishes were encased. Of the commoner genera of sharks,
which have been named from the forms of their teeth the only
hard parts of their structure that have survived the following may
be mentioned: Cochliodus, Orodus (Fig. 173, b\ Psammodus,
Petalodus. The small ganoids that so abound in the black
shales, ironstones, and coal-seams which represent the deposits
of the sheltered lagoons of the coal-jungles, are hardly to be
found in the thick limestone, whence we may infer that they were
FIG. 173. Carboniferous Fishes, (a), Tooth of Rhizodus Hibberti(); (b), tooth of
Orodus ramosus () ; (c), Ichthyodorulite or Fin-spine of Pleuracanthus Icevissimus ().
inhabitants of the quiet shore-waters, and did not venture out into
the open sea, where the sharks found their congenial element.
But the occasional occurrence of the teeth and spines of sharks
in the Coal- measure shales and coal-seams shows that these
monsters now and then made their way into the inland waters,
where they would find abundant food.
The Carboniferous system in Europe presents at least two
well-marked subdivisions. In the lower section the strata are in
large measure marine, for they include the Carboniferous Lime-
stone ; in the upper part they consist mainly of sandstones, shales,
fire-clays, and coal-seams, constituting what are called the Coal-
312
PAL/EOZOIC PERIODS
CHAP.
Lagoon type. <
measures, or coal-bearing division of the system. The subjoined
Table shows the order of succession of the rocks in Britain :
Coal-Measures. At the top, red and grey sandstones, clays,
and thin limestone, resting upon a great thickness of
white, grey, and yellow sandstones, clays, shales, and
fire-clays, with numerous workable coal-seams, and with
a lower subdivision of coal-bearing beds, among which
there occur marine fossils (Orthoceras, Posidonomya, etc.).
Thickness in South Wales, 12,000 feet ; South Lanca-
shire, 8000 feet ; Central Scotland, 3000 feet.
'Millstone Grit. Grits, flagstones, sandstones, and shales,
with thin seams of coal and occasional bands containing
marine fossils. Thickness 400-1000 feet, increasing in
Lancashire to 5500 feet.
Carboniferous Limestone. Consisting typically of massive
Marine type, but marine limestones and shales, but passing laterally into
passing north- I sandstones and shales, with thin coal-seams, which in-
wards into that j dicate alternations of marine and brackish water conditions,
of the lagoons. Thickness in South Wales, 500 feet, increasing north-
wards to more than 4000 feet in Derbyshire, and to up-
wards of 6000 feet in Lancashire, but diminishing north-
wards into Scotland.
The base of the Carboniferous Limestone series passes
down conformably into the Upper Old Red Sandstone.
The Carboniferous system occupies a number of detached areas
on the European continent. Its largest tract extends from the
north of France, through Belgium, into Westphalia. The most
important coal-fields of continental Europe in this system are those
of Belgium, Westphalia, the north of France, Saarbriicken, St.
Etienne in Central France, Bohemia, and the Donetz in Southern
Russia. Carboniferous rocks have been detected by means of
their characteristic fossils in the Alps, and even as far north as
Spitzbergen. They have been found also in Northern Africa, in
the peninsula of Sinai, in Palestine, and in Cape Colony, while in
Asia they are largely developed, covering many thousands of
square miles in China. In Australia and New Zealand also
thick masses of sedimentary strata contain recognisable Carboni-
ferous organic remains. In New South W r ales they include a
valuable succession of coal-seams.
The system is largely developed in the United States, where
it presents a wide diversity in its stratigraphical development.
Along the eastern parts of the Continent, from Newfoundland
southwards, across Pennsylvania and Western Virginia into
Alabama and westwards beyond the Mississippi, the European
type of lagoon-deposits is well displayed in a succession of im-
CARBONIFEROUS
313
portant coal-fields. In the western regions of the interior, however,
the marine type prevails, being represented there by thick and wide-
spread accumulations of limestone with no trace of coal.
In Pennsylvania the following subdivisions are recognised :
Upper productive coal-measures (about 500 feet), containing
a number of workable seams of coal intercalated among
sandstones, shales, fire-clays, clay-ironstones, etc.
Barren measures (650 feet), consisting of thick sandstones
and shales, with thinner bands of fire-clay, limestone, and
clay-ironstone, and a number of thin coals.
Lower productive coal-measures (200 to 300 feet) generally
similar to the upper productive series, with a group of
good seams of coal.
Pottsville Conglomerate or Millstone Grit a compacted
quartzose gravel, which is from 800 to 1700 feet thick in
the anthracite region of Pennsylvania.
' Mauch Chunk reddish shales and shaly sandstones, with
some thin siliceous limestone.
Pocono sandstone and conglomerete hard grey rocks
which, sometimes 1400 feet thick, cap the plateau in the
north of the State and are said to form the higher peaks
of the Catskill Mountains lying immediately on the
Upper Devonian strata.
Upper Car-
boniferous.
Lower or Sub-
Carboniferous.
CHAPTER XXI
PERMIAN
THE prolonged subsidence during which the Coal-measures were
accumulated was at last brought to an end in Europe by a series
of terrestrial disturbances, whereby the lagoors and coal-growing
swamps were in great measure effaced from the geography of
the region. So abrupt in some regions is the discordance between
the Coal-measures and the next series of strata, that geologists
have naturally been led to regard this break as one of great
chronological importance, serving as the boundary between two
distinct systems of strata and two well-marked divisions of
geological time. Nevertheless, so far as the evidence of fossils
goes, there is no such interruption of the Geological Record as
might be supposed from this stratigraphical unconformability,
some of the Carboniferous types of life having survived the
terrestrial disturbances. Though the discordance among the
strata is, in many parts of Europe, particularly in England,
most striking, yet it is by no means universal. On the contrary,
some localities (Autun in France, and the Bohemian coal-field, for
example) escaped the upheaval and prolonged denudation which
elsewhere have produced so marked a hiatus in the chronicle.
And in these places a gradual passage can be traced from the
strata and fossils of the Coal-measures into those of the next suc-
ceeding division of the series, no sharp line being there discoverable,
nor any evidence to warrant the separation of the overlying strata
as an independent system distinct from the Carboniferous. Hence,
by many geologists, the rocks now to be described are regarded
as the upper part of the Carboniferous system.
To these overlying rocks the name of PERMIAN was given, from
the Russian province of Perm, where they are well developed.
In Europe they consist of red sandstones, marls, conglomerates,
CHAP, xxi PERMIAN 315
and breccias, with limestones and dolomites. . In Germany they
are often called Dyas, because they are there easily grouped in
two great divisions. The coarsest strata breccias and con-
glomerates are composed of rounded and angular fragments of
granite, diorite, gneiss, greywacke, sandstone, and other crystalline
and older Palaeozoic rocks, which must have been upheaved and
exposed to denudation before Permian time. The sandstones
are usually bright brick-red in colour, owing to the presence of
earthy peroxide of iron which has cemented the particles of
sand together. The shales or marls are coloured by the same
pigment. So characteristic indeed is the red colour of the rocks
that they form part of a great series of strata, originally known as
the New Red Sandstone. Generally, greenish or whitish spots
and streaks occur in the red beds, marking where the iron-oxide
has been reduced and removed by decaying organic matter.
Red strata are, as a rule, singularly barren of organic remains,
probably because the water from which the iron -peroxide was
precipitated must have been unfitted for the support of life. The
red Permian rocks are generally unfossiliferous. Among them,
however, as developed more especially in Germany, occur dark
shales or "marl-slate," which have yielded numerous remains
of fishes. The limestones too are fossiliferous, but they are
associated with unfossiliferous dolomite, gypsum, anhydrite, and
rock-salt. In some places seams of coal also occur.
This European development of the Permian formations tells
distinctly the story of their origin. Such strata as red sandstone,
dolomite, gypsum and rock-salt could not have been deposited in
the open sea, but rather in basins more or less shut off from it,
wherein the water was charged with iron and was liable to
concentration, with the consequent precipitation of its solutions.
The beds of anhydrite, gypsum, and rock-salt are direct memorials
of different stages of these processes. The dolomite may at first
have been laid down as limestone which afterwards was converted
into dolomite by the action of the magnesian salts in the concen-
trated water. In such intensely saline and bitter solutions, animal
life would not be likely to flourish, and hence, no doubt, the
poverty of fossils in the Permian series of rocks. But it is
observable that where evidence occurs of the cessation of ferruginous,
saliferous, and gypseous deposition, fossils not infrequently appear.
The German brown Marl-Slate, for example, and the thick beds
of limestone are sometimes abundantly fossiliferous, and indeed
are almost the only bands of rock in the whole series where
316 PALEOZOIC PERIODS CHAP.
organic remains occur. They were probably deposited during
intervals when the barriers of the inland seas or salt-lakes were
broken down, or, at least, when from some cause the waters came
to be connected with the open sea, and when a portion of the
ordinary marine fauna swarmed into them. Volcanic action
showed itself during Permian time in many parts of Western,
Central, and Southern Europe. There was a group of small
volcanoes in the south of Scotland. Great eruptions took place
in Germany, notably in the area of the present Vosges Mountains,
and the region of volcanic activity extended across the region
where now the Alps stand, as far south as Cannes on the shores
of the Mediterranean.
The Permian system covers by far the largest part of European
Russia. Over many thousands of square miles its nearly hori-
zontal strata of sandstone, marl, shale, conglomerate, limestone,
dolomite, gypsum, rock-salt and thin coal stretch across the vast
plain up to the flanks of the Ural Mountains, and from the White
Sea to the Khirgis Steppes. It reappears in Asia with similar
characters and is extensively developed in the Salt Range of the
Punjab. Farther south in India it seems to form the lower part
of the great freshwater series of deposits known as the Gondwana
system, and includes come remarkable conglomerates (Talchir)
which contain boulders with smoothed and striated faces, suggestive
of ice-action. In Southern Africa a similar group of rocks likewise
contains a conglomerate (Dwika), which has been compared to
a glacial boulder -clay. Still more striking are the analogous
strata in New South Wales, where a group of coal-bearing strata
overlies the Coal-measures and includes boulder-beds (Bacchus
Marsh), which contain well-striated stones and lie upon polished and
striated rock-surfaces, closely resembling the glacial phenomena
of Post-tertiary time in the northern hemisphere.
In North America sedimentary deposits believed to represent
the Permian system of Europe are best developed in Texas and
Kansas, where they include some marine bands in their lower
portions, while their upper parts display proofs of enclosed
basins like those of Europe, in which chemical deposits accumulated,
such as gypsum, rock-salt, and dolomite. Farther east and
north the Permian formations diminish in importance. In the
Pennsylvanian coal-field, where they follow conformably upon the
top of the Coal-measures, and are known as the " Upper Barren
Measures," they consist of sandstones, shales, limestones, and
thin coals, and become very red towards the top.
XXI
PERMIAN
317
From the peculiar geographical conditions in which the Permian
strata seem to have been laid down over a large part of the globe,
the flora and fauna of their time have been but scantily preserved
and are comparatively little known. The small number of species
and genera obtained from Permian rocks forms a singular contrast
to the ample assemblages which have been recovered from the
older systems. But that the land of these times was still
richly clothed with vegetation and the open sea abundantly
FIG. 174. Permian Plants, (a), Callipteris conferta () ; (&), Walchia piniformis (5).
stocked with animal life, there can be no doubt. The flora
appears to have closely resembled that of the Carboniferous
period, a considerable proportion of the species of plants being
survivals from the Carboniferous jungles and forests. The Lepi-
dodendra, Sigillariae, and Calamites, which had been such ccn-
spicuous members of all the Palaeozoic floras, now appear in
diminishing number and variety, and finally die out. With their
cessation, new features arise in the vegetation. Among these may
be mentioned the abundance of tree-ferns, which, though they
PAL/EOZOIC PERIODS
CHAP.
sparingly existed even as far back as Devonian times, now attained
a conspicuous development (Psaronius, Caulopteris]. The genus
of ferns called Callipteris likewise played a prominent part in the
Permian woodlands (Fig. 174, a). Other genera of ferns were
Pecopteris, Sphenoptcris, Tccniopteris, Neuropteris. But perhaps
the most remarkable feature in the flora was the abundance of
its conifers, and the appearance of the earliest forms of cycads
(Pterophylluiii}. The yew-like conifer Walchia (Fig. 174, ^), if we
may judge from the abundance of its remains, flourished in great
profusion on the drier grounds, mingled with others that bore
FIG. 175. Permian Brachiopods. (), Productus horridus (reduced) ; (b), Strophalosia
Goldfussi; (c), Camarophoria humbletonensis ().
cones (Ullmannici). The cycads, which now made their advent,
continued during Mesozoic time to give the leading character to
the vegetation of the globe.
The scanty relics of the Permian fauna, as above stated, have
been almost wholly preserved in those strata which were deposited
during temporary irruptions of the open sea into the inland salt-
basins of the time. Among these marine forms of life reference
may be made here to occasional corals (Stenopora), polyzoa
(Fenestella, Polypora), and crinoids (Cyatkocrinus). Some of the
Carboniferous genera of brachiopods still survived Productus,
Spirifera and Strophalosia being conspicuous (Fig. 175).
XXI
TERMIAN
319
Among the lamellibranchs Bakevellia and Schizodus are frequent
forms (Fig. 176). Among the higher molluscs, which have been
but sparingly preserved in the European rocks, the old types of
OrthoceraS) Cyrtoceras, and Nautilus are still to be noticed. But
FIG. 176. Permian Lamellibranchs. (a), Bakevellia tumida (natural size);
(/')} Schizodus Schlotheimi (natural size).
in the Permian deposits that represent the opener seas of the
time a remarkable advent of new types of cephalopods has been
detected. These were the forerunners of the great Ammonite
family of later ages. They are found in the Alps, in the basin
of the Mediterranean, in the Ural region, in India, and in Texas.
FIG. 177.-- Permian Ganoid Fish (Platysoinus striattis, i).
Among their more frequent genera are Medlicottia, Popanoceras,
Stacheoceras, and Cyclolobus. In Europe, the fishes of the time
have been chiefly sealed up in the marl-slate or copper-shale
(Kupferschiefer) ; two of the most frequent genera being Palceo-
niscus and Platysomus (Fig. 177).
Labyrinthodonts continued to abound in the waters. Some of
320 PAL/EOZOIC PERIODS CHAP.
the Carboniferous genera still survived, but with these were
associated many new forms, outwardly resembling modern sala-
manders and lizards, most of which have been discovered
in the strata overlying the true Coal-measures of Bohemia
Some of these genera are Branchiosaurus (Fig. 178), Dawsonia^
Sparodus, and Linmerpeton. But a great onward step in the
advance of animal organisation was made in Permian time by the
appearance of the earliest known reptiles. These ancestral forms
include the genus Proterosaurns, which, like the living crocodile,
had its teeth implanted in distinct sockets. Palcechatteria was
a form that presented structural resemblances to the amphibia.
Other genera, regarded as reptiles but possessing amphibian
FIG, 178. Permian Labyrinthodont {Branchiosaurus salamanctroides, natural size).
character, are Pantylus, Bolosaurus, Diadectes, and Empedias
found in the Permian formations of Texas.
In Britain the Permian strata rest unconformably on the
Carboniferous system, which must have been greatly disturbed
and denuded before they were deposited. They consist of the
following subdivisions :
Upper red sandstones, clays, and gypsum (50 to 100 feet thick in the east of
England, but swelling out west of the Pennine Chain to 600 feet).
Magnesian limestbne a mass of dolomite ranging up to 600 feet in thickness,
and the chief repository of the Permian fossils ; remarkable for the curious
concretionary forms assumed by many of its beds on the coast of Durham
(Fig. 86). [Zechstein of Germany.]
Marl-slate a hard brown shale with occasional limestone bands. [Kupfer-
schiefer. ]
Lower red and variegated sandstones with conglomerates and breccias. This
division attains a thickness of 3000 feet in Cumberland, but is hardly
represented in the east of England. [Rothliegende of Germany.]
In Germany, where the Dyas or twofold development of the
Permian rocks is so well displayed, the lower sub-division, called
xxi PERMIAN 321
Rothliegende, consists of great masses of conglomerate with sand-
stones, shales, thin limestones, and important intercalations of
contemporaneous volcanic rocks, both lavas and tuffs. The upper
section is composed chiefly of limestone called Zechstein, and
answering to the Magnesian limestone of England. With it are
associated beds of anhydrite, gypsum, rock-salt, and bituminous
limestone, and underneath it lies the celebrated Kupferschiefer or
copper-shale a black bituminous shale, about two feet thick,
which has long been extensively worked on the flanks of the Hartz
Mountains for the ores of copper with which it is impregnated.
This shale, which is the great repository in Europe for the fossil
fishes of the Permian period, was probably deposited in one of
the inland basins, which at first may have maintained a free
communication with the open sea. But eventually mineral
springs, not improbably connected with the volcanic action of
the time, brought up such an abundant supply of dissolved
metallic salts as to kill the fish and render the water unsuitable
for their existence. The metallic salts were reduced and pre-
cipitated as sulphides round the organisms, and impregnated the
surrounding mud. In the overlying succession of strata, we see
how the area was once more overspread by the clearer -and
opener water, which brought in the fauna of the Zechstein, and
then how the basin gradually came to be shut off once more,
until from its concentrated waters the various beds of anhydrite,
gypsum, and rock-salt were thrown down.
In the heart of France, at Autun, the Coal-measures pass up-
ward into Permian strata, as already stated. That area appears
to have escaped the disturbance which in Western Europe placed
the Permian unconformably upon the Carboniferous rocks. It
presents a mass of sandstones, shales, coal-seams, and some bands
of magnesian limestone, the whole having a thickness of more
than 3000 feet referred to the Permian system. The plants in the
lower part of this group of strata are unmistakably Carboniferous,
but Permian forms appear in increasing numbers as the beds are
followed upwards until the highest stage presents a predominant
Permian flora. Besides the characteristic Permian fishes, these
strata have yielded remains of several of the salamander-like
animals (Branchiosaunis or Protriton, Melanerpetori), and of some
labyrinthodonts (Actinodon, Euchirosaurus, etc.).
As in Europe the Coal-measures of North America, especially
in Nova Scotia, New Brunswick, Prince Edward Island and the
Appalachian coal-field, pass up into reddish sandstone and shales
Y
322 PALEOZOIC PERIODS CHAP, xxi
in which the plants show a commingling of Carboniferous and
Permian types, but in which there are comparatively few animal
remains. These strata comprise the " Upper Barren Measures "
(1000 feet thick) of Pennsylvania, which immediately overlie the
upper productive Coal-measures. In Kansas the red and green
strata that overlie the Carboniferous formations include seams of
limestone and masses of gypsum and rock-salt, and contain some
Permian genera of shells (Bakevellia}. But it is in Texas that
the system is best developed. It there attains a thickness of
more than 6000 feet and is divided into three sections. A lower
group, known as the " Witchita beds," consists of red and mottled
clays, sandstones, and concretionary limestones, from which a
flora has been obtained similar to that found in the " Upper
Barren Measures " of the Appalachian coal-field, together with
many of the ammonoid cephalopods above mentioned. The
middle division, called the Clear Fork group, consists mainly of
marine limestones, while in the Upper or Double Mountain group
the proofs of concentrated inland water-basins are once more
displayed in deposits of gypsum and saliferous clay and shale.
Further relics of these inland seas are traceable westward in the
Grand Canon region and in southern Utah, where deposits of
bright red sandstones with gypsum cover considerable areas.
CHAPTER XXII
THE MESOZOIC PERIODS TRIASSIC
THE great series of red strata referred to in the foregoing chapter
as overlying the Carboniferous system in England was called
" New Red Sandstone," to distinguish it from the " Old Red
Sandstone" which underlies that system. But the progress of
geology on the European continent eventually proved that, not-
withstanding their general similarity of lithological character, two
series of rocks had been com prised under the general title of New
Red Sandstone. The older of these, separated from the rest under
the name of Permian, was placed at the top of the great suc-
cession of Palaeozoic formations. The younger division (still
sometimes spoken of in England as New Red Sandstone) was
called Trias, and was regarded as the first system in the great
Mesozoic (Middle Life] or Secondary succession.
Essentially the Permian strata form merely the upper part of
the Carboniferous system. Their types of life are fundamentally
Palaeozoic, but, as we have seen, both the flora and fauna are
marked by a decrease in the number and variety of old forms,
and by the advent of the precursors of a new order of things.
Conifers and cycads now began to replace the early types of
lepidodendron and sigillaria ; ammonoid mollusca appeared in
numbers as precursors of the Mesozoic ammonites, amphibians
became more abundant, and saurians now took their place at the
head of the animal world.
But when we ascend into the Trias, though in Europe the
physical conditions of deposition remained much the same as in
Permian time, we meet with a decided contrast in the organic
remains. A new and more advanced phase of development pre-
sents itself in that richer and more varied assemblage of plant
and animal life which characterised Mesozoic or Secondary time.
323
324 MESOZOIC PERIODS CHAP.
The word TRIAS has reference to the marked threefold division
of the rocks of this system in Germany. In that country, and
generally in Western Europe, the rocks consist of bright red
sandstones and marls or clays, with beds of gypsum, anhydrite,
rock-salt, dolomite, and limestone. These rocks, so closely re-
sembling the Permian series below, had evidently a similar origin.
They were in large part deposited in inland seas or salt-lakes,
wherein, by evaporation and concentration of the water, the
dissolved salts were precipitated upon the bottom, and where,
consequently, the conditions must have been extremely unfavourable
for the presence of living things. The sites of these inland basins
can still be partially traced. They extended at least as far west
as the north of Ireland. One or more of them lay across the site
of the plains of Central England. Others were dotted over the
lowlands of middle Europe. The largest of them occupied an
extensive area now traversed by the Rhine. It stretched, on the
one hand, from Basel to the plains of Hanover, and, on the other,
from the highlands of Saxony and Bohemia across the site of the
Vosges Mountains westward to the flank of the Ardennes. The
continent must then have been somewhat like the steppes of
Southern Russia a region of sandy wastes and salt-lakes, with a
warm and dry climate. Probably higher land rose to the north,
as in earlier geological times, for traces of its vegetation have been
found in Sweden. But southwards lay the more open sea, spread-
ing over part at least of the site of the modern Alps, and thence
probably across much of Asia to the Indian and Pacific Oceans.
So long as only the deposits of the salt-basins had been ex-
plored, it was but natural that comparatively little should be known
of the flora and fauna of the Triassic period. The climate around
these lakes was perhaps not a very salubrious one, and hence
there may have been only a scanty terrestrial fauna in their imme-
diate vicinity, while the waters of the lakes themselves were
unsuited for the support of life. It is not surprising, therefore,
that the strata deposited in these tracts are on the whole unfossili-
ferous ; that, indeed, fossils only abound where there are indications
that, owing to some temporary depression or breaking down of the
barriers, the open sea spread into these basins, and carried with
it the organisms whose remains gathered into beds of limestone.
But over the tracts that lay under the open sea, a more abundant
marine fauna lived and died. It is in the records of that sea-
bottom, rather than in those of the salt-basins, that we must seek
for the evidence of the general character of the life over the globe,
XXII
TRIASSIC
325
and for the fossil data with which to compare together the Triassic
rocks of distant regions.
There are traces of contemporaneous volcanic action among the
Triassic strata. A group of volcanoes appears to have existed
during Triassic time in the region of the Eastern Alps, especially
around Predazzo in the Tyrol.
The flora of the Triassic period has been preserved chiefly in
the dark shales and coal-seams formed in some of the inland
basins. So far as known to us it consisted chiefly of ferns,
equisetums or horse-tails, conifers, and cycads, which in some
FIG. 179. Triassic Plants, (a), Horse-tail Reed (Equisetum columnare, \) ; (b), Conifer
{Voltzia heterophylla, ) ; (c\ Cycad (Pterophyllum Blasii, J).
places accumulated in such quantities as to form matted deposits
that eventually became beds of coal. Among the ferns a few
Carboniferous genera still survived (Sphenopferis, Pecoptcris,
Cyclopteris], but some of the characteristic forms were mostly new
(Glossopteris, T),
Ditto (nat. size) ; (J), Tnassic time ; but these became much
Ditto, front side (}). more abundant and varied in the succeed-
ing geological age. They will be more
particularly alluded to in the next chapter. The earliest known
crocodiles have been found in Triassic rocks ; some of the scutes
or scales of one of these animals are shown in Fig. 184. But
possibly the most important advance in the fauna of the globe
during the Triassic period was the first appearance of mam-
malian life. Detached teeth and lower jaws have been met with
FIG. 185. Triassic
Marsupial? (Microles-
tes Moorei). (a),
xxii TRIASSIC 329
in the uppermost parts of the Triassic system, which have been
described as possessing structures like those of the marsupial
Myrmecobius or Banded Ant-eater of Australia (Microlestes (Fig.
185), Dromatheriiim, Microconodon}. It is interesting to know
that the earliest representatives of the great class of the Mam-
malia, if these remains be truly mammalian, belonged to one
of its lowest divisions. They were small creatures, some of
them probably resembling the Ornithorhynchits and Echidna of
Australia.
The Triassic strata of the inland basins of Europe (England,
Germany, France, etc.) have been subdivided into the following
groups :
f Red, green, and grey marls, black shales, sandstones,
bone-beds, and in Germany sometimes thin seams
Rhn-tir J ^ coa ^ Characteristic fossils are Cardium rhceti-
Icum, Avicula contorta, Pectcn valoniensis, Pullastra
arenicola, Acrodus, Ceratodus, Hybodus, Saurians,
^ Microlestes.
f Red, grey, and green marls, with beds of rock-salt and
Keuper or Upper &yP sum -
Trias \ sandstones and marls (England) ; grey sandstones
and dark marls and clays, with thin seams of earthy
^ coal (Germany).
( Limestones and dolomites, with bands of anhydrite,
Muschelkalk or | gypsum, and rock-salt. The limestones are the
Middle Trias. ~| great repository of the fossils. This subdivision is
V. absent or only feebly represented in England.
Bunter or Lower /Mottled red or green sandstones, marls, and some-
Trias. ^ times pebble- beds.
The salt-beds of Cheshire have long been worked for com-
mercial purposes. The lower bed is sometimes more than 100
feet thick ; but the salt deposits of Germany are much more
important. Thus at Sperenberg, 20 miles south of Berlin, a
boring was put down through about 290 feet of gypsum, and then
through upwards of 5000 feet of rock-salt, without reaching the
bottom of the deposit.
The alternation of bands of rock-salt with thin layers of
anhydrite or of gypsum no doubt marks successive periods of
desiccation and inflow ; in other words, each seam of sulphate
of lime (which is the least soluble salt, and is therefore thrown
down first) seems to indicate a renewed supply of salt water from
outside, probably from the open sea, while the overlying rock-salt
shows continued evaporation, during whi-ch the water became
330 MESOZOIC PERIODS CHAP.
a concentrated solution and deposited a thicker layer of sodium
chloride. Sometimes the concentration continued until still more
soluble salts, such as chlorides of potassium and magnesium, were
also eliminated. These phenomena are well displayed at the
great salt-mines of Stassfurt, on the north flank of the Harz
Mountains. The lowest rock there found is a mass of pure, solid,
crystalline rock-salt of still unknown thickness, but which has
been pierced for about 1000 feet. This rock is separated into
layers, averaging about 3^ inches in thickness, by partings of
anhydrite J inch thick or less. If each of these " year rings," as
the German miners call them, represents the deposit formed
during the dry season of a single year, then the mass of i ooo feet
has taken more than 3000 years for its formation. But there
do not appear to be any good grounds for believing that each
band marks one year's accumulation. Above the rock-salt lie
valuable deposits of the more soluble salts, particularly chlorides
of potassium and magnesium, with sulphates of lime and magnesia.
Among these salts, the compound known as Carnallite (a double
chloride of potassium and magnesium) is now the chief source
of the potash salts of commerce.
In the Rhastic group of England, one of the most interesting
bands is the so-called "bone-bed" a thin layer of dark sand-
stone, charged with bones, teeth, and scales of fishes and saurians,
which can be followed for many miles. A similar bone-bed runs
through Hanover, Brunswick, and Franconia. A thin seam of
limestone in the same group of strata in England (Gotham
Stone) contains wings and wing-cases of insects.
The type of Triassic deposits which represents the tract of open
sea is well developed in the Eastern Alps, where it reaches a thick-
ness of many thousand feet, and forms great ranges of mountains.
The lower division of that region, probably equivalent to the Bunter
series of Central Europe, contains certain red, sandy, and micaceous
shales (Werfen beds), and runs throughout the Alps with consider-
able uniformity of character, so that it forms a useful platform from
which to investigate the complicated geological structure of these
mountains. The Muschelkalk is represented by a great group of
marine limestones and dolomites arranged in lenticular reef-like
masses. It contains some of the typical Muschelkalk fossils, but
is distinguished by the presence of abundant ammonites (Ptychites,
Trachyceras, Arcestes, etc.). The Upper Alpine Trias consists
of several thousand feet of shales, marls, limestones, and dolomites,
while the Rhaetic group swells out into a great succession of
xxil TRIASSIC 331
limestones and dolomites, with' reefs of coral. During the time
when the Triassic sea stretched over the site of the Alps there
were evidently considerable oscillations of level, and there like-
wise occurred extensive volcanic eruptions, whereby large masses
of lavas and tuffs were ejected. These rocks now form con-
spicuous hills in the Tyrol.
Triassic rocks have been traced in Beloochistan, the Salt Range
of the Punjab, Northern Kashmir, and Western Thibet. They
have been recognised in Australia and New Zealand. Rocks
which have been assigned to the same geological period (Karoo
beds) occur in South Africa, and have there yielded a remarkable
series of amphibian and reptilian remains.
The two types of Trias, that of inland seas, as in Germany and
that of the x more open ocean, as in the Alps and the north of
India, are well developed in North America. The former type
prevails over the Atlantic border and the interior, while the latter
appears on the Pacific side of the continent. From Nova Scotia
southwards to South Carolina, red sandstones, conglomerates,
shales, and thin limestones appear in detached areas and represent
the Triassic system. These strata, like the similar deposits of
Europe, are generally poor in organic remains. In some places
(North Carolina and Virginia) they include thick seams of
workable coal, but for the most part the flora of the time has only
been scantily preserved. Some sandstones (in Connecticut and
elsewhere) are covered with bird-like footprints of deinosaurs which
frequented the shores of the inland waters. Remains of the lavas
which were poured out at the surface mark some of the volcanoes
of the time. On the Pacific slope, on the other hand, a thick
mass of strata containing marine fossils represents the pelagic or
deep sea type of the Alps and Asia. These fossils include the
same commingling as in Europe of Palaeozoic forms of life with
such characteristic Mesozoic forms as Ammonites.
CHAPTER XXIII
JURASSIC
THE system which follows the Trias, though it has been traced by
means of its characteristic fossils over much of the Old World and
the New, is most fully developed in Europe, and has there been
most fully studied. It has received its name, JURASSIC, from the
Jura Mountains, where it is specially well represented. It contains
the record of a great series of geographical changes, which in
Europe entirely effaced the inland basins and sandy wastes of
the previous period, and during which sedimentary rocks were
accumulated that now extend in a broad belt across England, from
the coasts of Dorset to those of Yorkshire, cover an enormous
area of France and Germany, and sweep along both sides of the
Alps and the Apennines. These strata vary greatly in composi-
tion and thickness as they are traced from country to country.
In one district they present a series of limestones which, as they
are followed into another area, pass into shales or sandstones.
The widespread uniformity of lithological character, so marked
among the Palaeozoic systems, gives place in the Mesozoic series
to greater variety. Sandstones, shales, and limestones alternate
more rapidly with each other, and are more local in their extent.
They indicate greater vicissitudes in the process of deposition,
more frequent alternations of sea and land, and not improbably
greater differences of climate than in Palseozoic time.
The flora of the Jurassic period is marked by the same general
characters as that of the Trias ferns (Akthopteris, Sphenoptcris,
Phlebopteris, Oleandridiuni, T), Jaw, natural size.
lithographic limestone of Solenhofen, was about the size of a
rook.
Marsupials, which may possibly have made their appearance
in Triassic time, continued to be the only representatives of the
Mammalia during the Jurassic period, at least no other types
have yet been discovered among the fossils. Lower jaws and
detached teeth (Fig. 198) have been obtained from two distinct
platforms in England the Stonesfield Slate and" Purbeck beds
and have been referred to a number of genera which seem to find
their nearest modern representatives in the Australian bandicoots
and in the American opossums (Plagiaulax, Ctenacodon, Bolodon,
Phascolotherium (Fig. 198), Dryolestes, Amphitherium, Spalaco-
therium, Priacodori).
The Jurassic system of Western Europe was first studied in
England, where it is remarkably well developed. The names
originally given there to its subdivisions have in large part been
adopted in other countries, as will be seen from the subjoined
Table.
342
MESOZOIC PERIODS
( Upper fresh-water beds (Purbeck).
-! Middle marine beds v " f ^ ,
| Lower fresh-water beds
Limestones and calcareous freestones (Portland
Stone) ; Cerithium portlandicum, Ammonites
giganteus, Trigonia gibbosa.
I Sandstones and marls ( Portland Sand ) ; A mmonites
\ (Perisphinctes] biplex, Exogyra bruntrutana.
/Dark shales and clays (Kirneridge Clay) ; Ain-
\ monites decipiens, Exogyra virgula.
?Coral rag (limestone with corals), clays, and
I calcareous grits ; Thamnastrcea, Isastrcea,
\ Cidaris florigemma, Ammonites (Cardioceras]
\ cordatus (Fig, 191, c}.
?Blue and brown clay (Oxford Clay) ; Ammonites
I (Cosmoceras] , Jason (Fig. 191, d).
1 Calcareous sandstone (Kellaways Rock Callo-
V vian) ; Ammonites (Kepplerites] calloviensis.
Shelly limestones, clays, and sands (Cornbrash,
Bradford Clay, and Forest Marble). Am-
monites (Oxynoticeras} discus.
Shelly limestones (Great or Bath Oolite), Stones-
field Slate; Ammonites gracilis.
Fuller's Earth.
'Marine calcareous freestones and grits (Chelten-
ham), containing zones of Ammonites (Parkin-
sonia] Parkinsoni, A. (Stephanoceras} Hum-
phriesianus, A. (Licdwigia] Murchisonce ;
represented in Yorkshire by 800 feet or more
of estuarine sandstones, shales, and limestones,
with beds of coal.
'Sandy beds and clays (Upper Lias, Toarcian) ;
Ammonites (Dactylioceras] communis, A.
(Harpoceras] serpentinus.
Limestones, sands, clays, and ironstones (Middle
Lias, Marlstone) ; Ammonites (Amaltheus)
margaritatus, A, (Amaltheus} spinatus.
Thin blue and brown limestones, and dark shales
(Lower Lias, Sinemurian and Hettangian) ;
Ammonites (Psiloceras] planorbis, A. (Oxyno-
ticeras] oxynotus, A. (Aegoceras] Jamesoni.
I. The Lias, so called originally by the Somerset quarrymen
from its marked arrangement into "layers," extends completely
1 So called from the Isle of Purbeck in Dorset, where the group is typically displayed.
2 From the Isle of Portland in Dorset.
3 From Kimeridge, a parish in Dorset.
4 From the abundant corals in the group.
5 From the county of Oxford.
6 From the city of Bath.
7 From Bayeux, in the Department of Calvados France.
8 From " Lias," the Somerset provincial word first adopted for the formation by William
Smith, the " Father of English Geology. "
8. Purbeckian 1 .
j. Portlandian 2 .
6. Kimeridgian 3 .
5. Corallian 4
4. Oxfordian 5
3. Bathonian 6 .
2. Bajocian 7 .
(Inferior Oolite)
i. Liassic 8
xxni JURASSIC 343
across England from Lyme Regis to Whitby. It can be divided
into three distinct sections ; (a) A lower group of thin blue lime-
stones and dark shales with limestone nodules, the limestones
being largely used for making cement. This is one of the chief
platforms for the reptilian remains, entire skeletons of ichthyo-
saurus, plesiosaurus, etc., having been exhumed at Lyme Regis ;
(<) Marlstone or Middle Lias hard argillaceous or ferruginous
limestones which form a low ridge or escarpment rising from the
plain of the Lower Lias ; in Yorkshire it contains a thick series of
beds of earthy carbonate of iron, which are extensively mined as a
source for the manufacture of iron ; (c] Upper Lias clays and shales
surmounted by sandy beds (Upper Lias Sands). The organic
remains of the Lias are abundant and well preserved. They are
chiefly marine ; but that the rocks containing them were de-
posited near land is indicated by the numerous leaves, branches,
and fruits imbedded in them, and by the various insect-remains
that have been obtained from them.
In Germany, where the Lias is well developed and presents a
general resemblance to the English type, it is known as the Lower
or Black Jura. It is still better shown in France, where its three
stages attain in Lorraine a united thickness of more than 600 feet.
To the south, however, in Provence, it reaches the great thickness
of 2300 feet.
2. The Bajocian stage is so named from Bayeuxin Normandy,
where it is well displayed. In England, under the name of
Inferior Oolite, it presents two distinct types, being a thoroughly
marine formation in the south-western counties, and passing
northward into a series of strata which were accumulated in
an estuary and which contain the chief repositories of the
British Jurassic flora. Among the estuarine beds of Yorkshire
a few thin coal-seams occur, which have been worked to some
extent.
On the European continent, this division is characteristically
marine ; it reaches its greatest development in Provence, where it
is 950 feet thick. It runs through the Jura Mountains, where it
is made up of more than 300 feet of strata, chiefly limestone. In
Germany the strata from the top of the Lias to the base of the
Callovian group that is, the two stages of Bajocian and Bathonian
are classed together as the Middle, Dogger, or Brown Jura,
its prevalent colours being dark, owing to the preponderance of
brown sandstones and shales.
3. The Bathonian stage is named from Bath in the south-
344 MESOZOIC PERIODS CHAP.
west of England, where its subdivisions are admirably exposed.
At its base lies a local argillaceous band known as Fuller's Earth,
because long used for fulling cloth. The chief member of the
stage in the south-west of England is the Great or Bath Oolite, a
succession of limestones, often oolitic, with clays and sands. The
Stonesfield Slate is the name locally given to some thin-bedded
limestones and sands, forming the lower part of the Great Oolite,
and of high geological interest from having supplied among their
fossils remains of land -plants, numerous insects, bones of
enaliosaurs and deinosaurs, and of small marsupials. The Great
Oolite abounds in corals, and contains numerous genera of
mollusca, fishes, and reptiles. The Cornbrash (so named from its
friable (brashy) character, and from its forming good soil for corn)
is one of the most persistent bands in the English Jurassic system,
retaining its characters all the way from the south-western counties
to near the Humber.
On the mainland of Europe this stage is well represented. In
Normandy it includes the famous building-stone of Caen, which
from its saurian and other fossils may be paralleled with the
Stonesfield Slate. In Northern Germany the abundant limestones
of the western region are represented mainly by clays and shales,
with bands of oolitic ironstone.
4. The Oxfordian stage, sometimes called the Middle or Oxford
Oolite, in its English development consists of a lower zone of
calcareous sandstone, known as the Kellaways rock or Callovian,
from the name of a place in Wiltshire, and of a thick upper stiff
blue and brown clay, called, from the district where it is well
developed, the Oxford Clay, and containing numerous ammonites,
belemnites, and oysters, but no corals. In Germany, the strata
from the base of the Callovian to the top of the Purbeckian group
are known as the Malm or White Jura. They attain a thickness
of more than 1000 feet, and consist mainly of white limestones
and marls, whence the name bestowed on them, in contrast to the
more sombre tints of the Brown Jura below. In France, the sub-
division is found well represented on the coast of Calvados, but it
diminishes towards the Jura, and is only feebly developed in the
Alps. Yet the Oxfordian fossils are found to characterise a
particular group of dark sandy clays, which form the widely
extended Jurassic system of Russia. Some of the characteristic
ammonites of the formation have even been recognised in Cutch,
where both the Oxfordian and its Callovian sub-stage appear to
be represented.
xxiir JURASSIC 345
5. The Oorallian stage, so named from the corals with which
it abounds, is one of the most distinctive in the Jurassic system.
It is traceable across the greater part of England, over the
continent of Europe from Normandy to the Mediterranean,
through the east of France, and along the whole length of
the Jura Mountains and the flank of the Swabian Alps. While
it was being formed, the greater part of Europe lay beneath
a shallow sea, the floor of which was clustered over with reefs
of coral.
6. The Kimeridgian group or stage is typically displayed
at Kimeridge on the coast of Dorsetshire, whence its name. It
there consists of dark shales, some of which are so highly
bituminous as to burn readily, and which may be eventually
of commercial value as a source for the distillation of mineral oil.
This group of strata has yielded a larger number of reptilian
genera and species than any other in the Mesozoic system of
Britain plesiosaurs, ichthyosaurs, pterosaurs, deinosaurs, turtles,
and crocodiles. It is well developed in the north of France,
where the clays of England are represented by a succession of
limestones and marls between 500 and 600 feet thick. These
strata extend southwards into the Jura, where they include as their
central member a mass of coral-reef more than 300 feet thick.
They are prolonged also into Germany, where their most celebrated
member is the famous lithographic stone of Solenhofen near
Munich, from which so remarkable a series of terrestrial organic
remains has been obtained.
7- The Portlandian stage, so called from the Isle of Portland,
where it is well seen, consists of a lower set of sandy beds (Port-
land Sand), and a higher and thicker series of limestones and
calcareous freestones, some of the beds containing abundant
nodules and layers of flint. These rocks are prolonged into
France near Boulogne-sur-Mer, and by their characteristic fossils
are recognisable also in Germany. In the basin of the Mediter-
ranean, however, the rapid alternations of limestones, sandstones,
shales, and clays so characteristic of the Jurassic system are
replaced, as regards the formations above the Oxfordian, by a
series of singularly uniform limestones known as Tithonian, which
in the Basses Cevennes attain a thickness of between 1200 and
1400 feet. Such a contrast of lithological character indicates
great difference in the conditions of sedimentation. The later
Jurassic rocks of England and the northern part of the continent
were deposited during a time of considerable terrestrial oscillation
346 MESOZOIC PERIODS CHAP.
and disturbance, whereas in the south of Europe they seem to
have accumulated, with little or no interruption, in deeper water
and at a greater distance from land.
8. The Purbeckian group or stage is best seen in the Isle of
Purbeck, hence its name. It lies on an upraised surface of Port-
landian beds, showing that after the deposition of these strata there
was some disturbance of the sea-floor, portions of which were
uplifted partly into land and partly into shallow brackish and
fresh waters. The Purbeck Beds are subdivided into three sub-
stages : the lowest consisting of fresh-water limestones, with layers
of ancient soil ("dirt-beds"), in which the stumps of cycadaceous
trees (Fig. 186) still stand in the positions in which they grew ;
the middle sub -stage contains oysters and other marine shells
which prove that the area subsequently sank under the sea ;
while in the higher subdivision fresh- water fossils reappear.
Among the more interesting organisms yielded by the Purbeck
Beds are the remains of numerous insects and of the marsupials
already referred to, which chiefly occur as lower jaws in a stratum
about five inches thick. When the bodies of dead animals float
out to sea, the first bones likely to drop out of the decomposing
carcases are the lower jaws ; hence the greater frequency of these
bones in the fossil state. Strata belonging to the Purbeckian
stage, including red and green marls, with dolomite and gypsum,
are found in North- Western Germany, showing in that region
also the elevation of the floor of the Jurassic sea into detached
basins.
In India a mass of strata in Cutch, which from its fossils is
believed to represent the European Jurassic system from the
Bajocian up to the top of the Portlandian stage, attains a thick-
ness of 6300 feet. In Australia and New Zealand, recognisable
Jurassic fossils have also been found, showing the extension of
the Jurassic system even to the Antipodes.
In North America, Jurassic rocks have not been found to
be largely developed. They appear to be entirely absent from
the Atlantic side of the United States, unless some representatives
of them occur in Mexico. They are found, however, in the interior
and still more distinctly along the Pacific border. In California
and Oregon a series of strata is developed which from their fossils
may be paralleled with the Lias of Europe. Upper Jurassic rocks,
recognisable by their fossils, attain a thickness of about 1 800 feet
in the Wasatch Mountains, but in California and British Columbia
they are much thicker, and consist largely of slates and meta-
JURASSIC 347
morphic schists, with accompanying volcanic tuffs and veins of
auriferous quartz. In Colorado certain strata, which by some
observers have been classed in the Jurassic system, by others in
the Cretaceous, have yielded an abundant series of organic remains,
including fishes, tortoises, pterosaurs, deinosaurs, crocodiles, and
marsupials.
CHAPTER XXIV
CRETACEOUS
THE CRETACEOUS system received its name in Western Europe,
because in England and in Northern France its most conspicuous
member is a thick mass of white chalk (Latin, Cretd). Appearing
in many detached but often extensive areas, it covers a large part
of the surface of this continent, especially towards the west and
east. Its western extremity reaches to the north of Ireland
and the Western Islands of Scotland. It spreads over a large
part of the east and south of England, stretching thence into
France, where it forms a broad band, encircling the Tertiary
basin of Paris. It sweeps across Belgium into Westphalia, under-
lies the vast plain of Northern Germany and Denmark, whence it
is prolonged into Southern Russia, where it overspreads many
thousands of square miles. It flanks most of the principal
mountain-chains of Europe the Pyrenees, Alps, Apennines, and
Carpathians. It spreads far and wide over the basin of the
Mediterranean Sea, extending across vast tracts of Northern
Africa, and from the Adriatic athwart Greece and Turkey into
Asia Minor, whence it is prolonged through the Asiatic continent.
As most of the rocks of the system are of marine origin, we at
once perceive how entirely different the Cretaceous geography
must have been from that of the present day, and to what a great
extent the existing land of the Old World lay then below the sea.
But in tracing out the distribution of the rocks, geologists have
found that the Cretaceous sea did not sweep continuously across
Europe. On the contrary, as they have ascertained, the old
northern land still rose over the site of Northern Britain and
Scandinavia, while to the south of it a wide depression extended
across the area of Southern Britain, Northern France, Belgium,
and the North German plain, eastwards to Bohemia and Silesia.
348
CHAP, xxiv CRETACEOUS 349
This vast northern basin was the theatre of a remarkable succession
of geological revolutions. While its eastern portions, during the
earlier part of the Cretaceous period, were submerged under the
sea, its western tracts were the site of the delta of a great river,
probably descending from the land that still lay massed towards
the north. During the later ages of the period, the whole of this
area formed a broad and long gulf or inlet, the southern margin
of which seems to have been defined by the ridge of old rocks that
runs from the headlands of Brittany through Central France, the
Black Forest, and the high grounds of Bohemia. South of that
ridge lay the open ocean which extended all over Southern Europe
and the north of Africa, and spread eastwards into Asia.
Bearing in mind this peculiar disposition of sea and land, we
can understand why the European development of the Cretaceous
system, alike in regard to its deposits and its fossils, should be
so different in the area of the northern basin from that of the
southern regions. In the one case, we meet with the local and
changing accumulations of a comparatively shallow and somewhat
isolated portion of the sea-bed, wherein were mingled abundant
traces of the proximity of land. In the other, we are presented
with evidence of a wide open sea, where the same kinds of deposits
and the same forms of marine life extended with little change
over vast distances, and continued in existence for a long interval of
time. It will be remembered that this contrast in the geography
of the north and south of the continent had already been established
before the end of the Jurassic period. Obviously, it is not the
local type of the northern basin, but the more general and wide-
spread type of Southern Europe that should be taken for the
distinctive characteristics of the Cretaceous system. But the
northern basin was the first to be systematically explored, and is
still the best known, and hence its features have not unnaturally
usurped the place of importance, which ought -properly to be
assigned to the other wider area.
In North America also, the marine and terrestrial types of
Cretaceous geography are well displayed. The marine formations
of the Southern United States are even more extensively developed
than those of Southern Europe, while in the centre and west
of the continent a marvellous series of lacustrine and terrestrial
deposits has been accumulated, replete with the remains of the
fauna and flora of the land of the period. These rocks are more
particularly referred to on p. 363.
Regarding the period as a whole, let us first consider the
35*3
MESOZOIC PERIODS
CHAP.
general character of its distinguishing flora and fauna, and then
pass on to trace the history of the period as revealed by the
succession of strata. The plants of the Cretaceous system show
that the vegetable kingdom had now made a most important
advance in organisation. In the lower half of the system the fossil
FIG. 199. Cretaceous Plants, (a), Quercns rinkiana, () ; (), Cinnamomum sezannense
(); (f\ Ficus afavina (%); (d), Sassafras recurva /(); (e), Juglans arctica().
plants hitherto found are on the whole like those of the Jurassic
rocks that is, they include some of the same genera of ferns,
cycads, and conifers which these rocks contain. But already
the ancestors of our common trees and flowering plants must have
made their appearance, for in the upper half of the system their
remains occur in abundance. This earliest dicotyledonous flora
numbered among its members species of maple, alder, aralia,
poplar, myrica, oak, fig, walnut, beech, plane, sassafras, laurel,
CRETACEOUS
cinnamon, ivy, dogwood, magnolia, gum-tree, ilex, buckthorn,
cassia, credneria, and others. The modern aspect of this assem-
blage of plants is in striking contrast to the more antique look of
FIG. 200. Cretaceous Foraminifera. (a), Textularia baudouiniana (2,' 1
(b\ Globigerina cretacea. ( J ~^) ; (c), Rotalia voltziana ( s f).
all the older floras. There were likewise species of pine (Pinus),
Californian pine (Sequoia), juniper, and other conifers, various
cycads, forms of screw-pine (Pandanus\ palms (Sabal), and
numerous ferns (Gleichenia, Asplenium, etc.). This flora spread
over the land surrounding the northern
Cretaceous basin, and extended north-
wards even as far as North Greenland,
from which some 200 species of Cretaceous
plants have been obtained. The inference
may be deduced that the climate of the
globe must then have been much warmer
than at present. The luxuriant vegeta-
tion disinterred from the Cretaceous rocks
of North Greenland includes more than
forty kinds of ferns, besides laurels, figs,
magnolias, and other plants, which show
that, though the winters were no doubt
dark, they must have been extremely mild.
There could have been no perpetual frost
and snow in these Arctic latitudes in
Cretaceous times.
Foraminifera abound in some of the
FIG. 201 Cretaceous Sponge
(Ventriculites decurrens, %).
Cretaceous limestones, indeed, in some places they form almost
the only constituent of these rocks. They are plentiful in the
white chalk of England, France, and Belgium, one of the more
frequent genera being Globigerina (Fig. 200) which still lives in
enormous numbers in the Atlantic, and forms at the bottom of that
ocean a grey ooze not unlike chalk (Fig, 42). Sponges lived in
352
MESOZOIC PERIODS
great numbers in the Cretaceous sea. Their minute siliceous
spicules are abundant in the chalk, and even entire sponges en-
veloped in flint are not uncommon (Ventriculites, Fig. 201). Sea-
urchins are among the most familiar fossils of the chalk, and must
FIG. 202. Cretaceous Sea-urchins, (a), Echinoconusconicus, (^^Galeritesalbo-galerrts),
under surface and side view ; (b), A nanchytes cn'atus (J), side view and under surface ;
(c), Micraster cor-anguinum (J), upper and under surface.
have lived in great numbers on the Cretaceous sea-bottom. Some
of their genera are still living, and have been dredged up in recent
years from great depths in the ocean. Among the more character-
istic Cretaceous types are Ananchytes, Holaster, Micraster, and
Echinoconus (Fig. 202). The brachiopods were still represented
CRETACEOUS
353
chiefly by the ancient genera Terebratula and Rhynchonella.
Lamellibranchs abounded, especially the genera Ostrea, Exogyra,
FIG. 203. Cretaceous Lamellibranchs. (a), Trigonia alifortnis (J) ; (b\ Inoceramus
sulcatus (5) ; (c), Nuculci bivirgata (natural size).
Inoceramus (Fig. 2 03), Lima, Pecten, and the various forms of
Hippuritids. These last (Hippurites^ Radiolites, Caprina, Plagi-
FIG. 204. Cretaceous Lamellibranchs (Hippurites). (), Radiolites acuticostata (^) ; (V),
Hippurites toucasiana (^) ; (c\ Plagioptychus Aguilloni(\) ; (rf), Requienia toucasi-
anus (J).
optychus, Requienia, etc., Fig. 204) are specially characteristic,
being, so far as we know, confined to the Cretaceous system ; hence
2 A
354 MESOZOIC PERIODS CHAP.
their occurrence serves to indicate the Cretaceous age of the rock
FIG. 205. Cretaceous Cephalopods. (a), Baculites anceps (^) ; (/'), Ptychoceras emerict-
anum () ; (c), Toxoceras bituberculatum () ; (J), Hamites rotundus (4) ; (e), A ncylo-
ceras renauxianum ($*) ', (/) Scaphites a>qualis () ; (g\ Crioceras villiersianum (^) ;
(A), Helicoceras annulatum ; (z), A mmonites (Schloenbachia) restrains (J) ; (k),
Turrilites catenatus (1).
containing them. They have been imbedded in such numbers
in the limestones of the south of Europe as to give the name of
XXIV
CRETACEOUS
355
"hippurite-limestone ;; to these rocks. They are comparatively
infrequent in the strata of the northern Cretaceous basin.
Probably the most distinctive feature in the molluscan life of
the Cretaceous seas was the extraordinary variety in the develop-
ment of the cephalopods. This is all the more remarkable from
the fact that before the next geological period the great majority
of these types appear to have become extinct. The ammonites
and belemnites, which played so important a part in the fauna of
Mesozoic time, died out about the close of that long succession of
periods. At least in Europe, while their remains continue to
present themselves up to the top of the Cretaceous system, they
disappear entirely from the overlying strata. It is curious to
observe that while these important tribes were about to vanish,
FIG. 206. Cretaceous Fish (Beryx lewesiensis, J)
other cephalopods of new and varied types nourished contempor-
aneously with them. Never before or since, indeed, have the
cephalopodan types been so manifold (Fig. 205). For instance,
Baculites is a straight -chambered shell reminding us of the
ancient Orthoceras. In Toxoceras the shell is bent into the
form of a bow. In Hamites it is long, tapering, and curved
upon itself like a hook. In Ancyloceras it is coiled at the
posterior end, the other being bent back upon itself; while in
Scaphites the coils are adherent. In Ptychoceras the shell is long,
tapering, and bent once back on itself, the two portions being in
contact. In Crioceras it is coiled, and the coils are not adherent,
as they are in the ammonites. In Helicoceras the shell is coiled
spirally, the coils remaining free, while in Turrilites they are
adherent.
356 MESOZOIC PERIODS CHAP.
The fishes of the Cretaceous period are chiefly known by teeth
belonging to various genera of sharks (Otodus, Oxyrhina\ But
they also include representatives of the modern osseous or
teleostean fishes, such as the herring, salmon, and cod (Osnieroides,
Enchodus, Beryx, etc., Fig. 206).
Already reptilian life seems to have been on the decline, at
least there is much less variety and abundance of it in the
Cretaceous system than in that which immediately preceded it.
Turtles and tortoises continued to haunt the low shores of the time.
Ichthyosaurs, plesiosaurs, pterosaurs, and deinosaurs still lived,
but in diminishing numbers, and they are not known to have
FIG. 207. Cretaceous Deinosaur (Iguanodon, about t Jn).
survived the Cretaceous period. One of the most remarkable of
the deinosaurs, and interesting from being one of the last of its
race, is that known as Iguanodon (Fig. 207). Only scattered teeth
and bones of this animal were known, until a few years ago the
fortunate discovery of a number of entire skeletons in Belgium en-
abled its structure to be almost completely made known, and threw
much fresh light on the osteology of the deinosaurs. It was a herb-
ivorous and probably amphibious creature, able, no doubt, to walk
along the shores, with an unwieldy gait, on its long hind legs, and
balancing itself by its strong massive tail, which was doubtless a
powerful instrument of propulsion through the water. Its extra-
ordinary fore legs, with the strong spurs on the digits, must have
been formidable weapons of defence against its carnivorous con-
xxiv CRETACEOUS 357
temporaries. Another gigantic reptile, the Mosasaurus, believed
to have been 75 feet long, was furnished with fin-like paddles for
swimming. Several kinds of crocodiles have also been disinterred
from Cretaceous rocks in Europe.
Still more remarkable is the assemblage of remains of animal
life exhumed from corresponding rocks in the Western Territories
of North America. Among these the Cimoliasaurus was a snake-
like animal some 40 feet long, with a swan-like neck supporting
a slim head which it could raise 20 feet out of the water, or dart
to the bottom and catch its prey. The pythonomorphs or sea-
serpents were especially numerous.
The remains of true birds have been obtained from the
Cretaceous rocks both of Europe and North America. Some are
related to the living ostrich, but were furnished with teeth set in a
continuous groove (Hesperornis), others had large teeth in distinct
sockets (Ichthyornis).
From different members of the Cretaceous series of North
America a varied assemblage of small mammals has been obtained.
These organisms show close affinities to those of Jurassic and
Triassic times, being representatives of the modern Monotremes
and Marsupials, but with no rodents, ungulates, or carnivores.
Among those allied to monotremes are the genera Meniscoessus,
Cimolomys, and Camptomus. Among the Marsupials are Didel-
phops, Cimolestes and Dryolestes.
The following are the principal subdivisions of the Cretaceous
system in Europe in descending order. The stages are based
upon more or less well marked fossil evidence, but they are also
for the most part to be distinguished by lithological characters :
r /Tisolitic limestone of Paris basin ; Chalk of Hainault,
. I Ciply, Maestricht, Faxoe in Denmark, and the south
"j of Sweden ; absent in England (Belemnitella mucro-
\ nata, Baculites Faujasii, Nautilus danicus, etc.).
Chalk -with -flints of Norwich, Brighton, Flamborough
Head, and Dover, north of France (Belemnitella
Senonian . . mucronata, Marsupites ornatus, Micraster cor-
anguinum, M. cor - testudinarium} ; sandstones of
Westphalia and Saxony.
Chalk -without -flints of Dover and north of France
(Holaster planus, Terebratulina gracilis, Inoceramus
Turonian . . labiatus] ; sandstones, limestones, and marls of
Saxony and Bohemia ; Hippurite limestone of South-
ern France and Mediterranean basin.
Grey Chalk of Folkestone (Belemnitella' plena, Holaster
Cenomanian . subglobosus], Chalk-Marl, red chalk of Hunstanton,
Glauconitic Marl and Upper Greensand (Ammonites
358
MESOZOIC PERIODS
CHAP.
Cenomanian
Albian
Neocomian
(Schloenbachia] rostratus, Pecten asper] ; Chalk of
Rouen ; earthy limestones and marls in Hanover re-
placed southwards by plant-bearing sandstones, clays,
and thin coal-seams ; Hippurite limestones of Southern
Europe.
JGault (Ammonites (Schloenbachia} cristatus, A. (Hof-
\ lites] lautus, A. (Hoplites} auritus),
'In Southern England a fluviatile (partly marine) succes-
sion of sands and clays (Wealden), surmounted by
sands, clays, and limestones (Lower Greensand) ; in
Northern England a series of clays and limestones,
with marine fossils (upper part of Speeton Clay) ;
limestones and marls of Neuchatel ; compact crystal-
line limestones in Provence (Ammonites (Hoplites}
Deshayesi, A. (Placenticeras} nisus in upper division ;
abundant Ancyloceras with Pecten cinctus in middle ;
Ammonites (Hoplites} noricus, A. (Olcostephanus}
astieranus, Ostrea Couloni in lower).
It will be remembered that towards the close of the Jurassic
period the floor of the sea in the western part of the European
area was gently raised, some of the younger Jurassic marine
limestones being ridged up into islets or low land, with
lakes or estuaries in which the Purbeck beds were deposited.
This terrestrial condition of the geography was maintained
and extended in the same region during the early part of the
Cretaceous period. The geological history of Europe as revealed
by the various subdivisions in the foregoing Table may be
briefly given.
Neocomian (from Neocomum, the old Latin name of Neuchatel
in Switzerland). This stage in the south of England, and thence
eastwards across Hanover, consists of a mass of sand and clay
sometimes 1800 feet thick, representing the delta of a river.
Only a portion of this delta remains, but as it extends in an east
and west direction for at least 200, and from north to south for
perhaps 100 miles, its total area may have been 20,000 square
miles, indicating a large river comparable with the Quorra of the
present day. This stream not improbably descended from the
north or north-west. It carried down the drifted vegetation of the
land, together with occasional carcases of the iguanodons and other
terrestrial or amphibious creatures of the time. From their great
development in the Weald of Sussex, these delta -deposits have
been called Wealden. They there consist of the following sub-
divisions in descending order.
xxiv CRETACEOUS 359
Weald Clay ....... 1000 feet.
Hastings Sand group, comprising
3. Tunbridge Wells Sand . . . 140 to 380 , ,
2. Wadhurst Clay . . . . . 120 to 180 ,,
i. Ashdown Sand ..... 40010500 ,,
Beyond the area overspread by the sand and mud of the
delta, the ordinary marine sediments accumulated, with their
characteristic organic remains. We find these sediments in York-
shire (upper part of Speeton Clay), which must then have lain
beyond the estuary of the river. Careful examination of the
sections exposed on the Yorkshire coast, compared with those
which have been studied in Russia, has established the exist-
ence of a succession of zones in the Neocomian division, each
characterised by a distinct assemblage of fossils and recognisable
more particularly by different species of belemnites. At the base
lies the zone of Belemnites lateralis. Higher come in succession
the zone of B. jaculntn^ that of B. semicanaliculatiis and that
of B. minimus. The Lower Greensand which overlies the
Wealden group in the south of England contains marine fossils,
and points to the submergence of the delta.
The Neocomian stage is well displayed in the eastern part of
the Paris basin, where it rests unconformably upon the uppermost
Jurassic rocks ; but it attains a much greater development in the
south of France, where it consists of limestones, replaced in large
measure by marls towards the south and reaching a thickness of
1600 feet. At Neuchatel, the typical district for this subdivision
of the Cretaceous system, the Neocomian strata are separable
into two sub-stages, of which the lower (Valenginian) is composed
of 130 to 260 feet of limestones and marls (Toxaster Campichei,
Belemnites dilatatus, Ammonites (Oxynoticeras] gevriliamis] ;
while the upper (Hauterivian) consists of about 250 feet of blue
marls (Toxaster complanatus, Exogyra Coiiloni, Ammonites
(Hoplites} radiatus). Above the Neocomian rocks the French
geologists have found a group of strata which they have called
Urgonian (from Orgon, near Aries) and which differ widely from
the northern type, inasmuch as they consist of massive hippurite
limestones. A higher group of marls and limestone well seen at
Apt in Vaucluse is known as Aptian.
Albian (from the department of the Aube in France). In
England this stage nearly corresponds to the band of dark, stiff,
blue clay known as the Gault. Extending over the Wealden
sands and clays, the Gault (100 to 200 feet or more in thickness),
360 MESOZOIC PERIODS CHAP.
with its abundant marine fossils, shows how thoroughly the
Wealden delta was now submerged beneath the sea.
The Albian stage is continued through the north of France in
the form of greensands and clays and a peculiar calcareous and
argillaceous sandstone called Gaize. It is prolonged into north-
western Germany in various clays containing characteristic Albian
fossils and surmounted by a dark clay with flame -like streaks
( Flammenmergel).
Cenomanian (from Coenomanum, the old Latin name of the
town of Mans in the department of Sarthe, France). This stage
comprises a group of impure chalky, glauconitic, and sandy
deposits lying at the base of the Chalk in England and the north
of France. It is often spoken of in England as the Lower Chalk,
where it is more than 300 feet thick, and is separable into the
following subdivisions in descending order :
Grey chalk forming the base of the Chalk.
Chalk Marl (Red Chalk of Hunstanton).
Glauconitic Marl.
Upper Greensand.
Certain sandy portions of this group have been called the Upper
Greensand. The Glauconitic (or Chloritic) Marl is an im-
pure, dull white, or yellowish chalk, sometimes I 5 feet thick, with
grains of glauconite and phosphatic nodules. The Chalk-Marl
is an impure band of chalk, occasionally more than loofeet thick,
overlain by a zone of Grey Chalk which attains a maximum
thickness of about 200 feet, and forms the base of the true Chalk-
without-flints. All these deposits are marked by zones whereof
particular species of fossils are specially characteristic. They
indicate the accumulations of a shallow sea, probably not far
from land.
Traced eastwards into Germany, the Cenomanian stage under-
goes great changes in lithological characters, passing at last in
Saxony and Bohemia into sandstones and clays (Quader) full of
remains of terrestrial vegetation, and even including some thin
seams of coal. It is in these beds that the oldest dicotyledonous
plants in Europe have been found. It is evident that land existed
in the heart of Germany during this stage of the Cretaceous
period. In Southern France, on the other hand, the corresponding
strata are massive hippurite-limestones which sweep through the
great Mediterranean basin, and show how large an area of
Southern Europe then lay under the sea.
CRETACEOUS 361
Turonian (from Touraine). This stage, sometimes called the
Middle Chalk, includes the lower part of the Chalk, above the
Grey Chalk. The thick mass of white crumbly limestone known
as the Chalk, which has been referred to as the most conspicuous
member of the Cretaceous system in the west of Europe, has long
been grouped in England into two parts, a lower band of "Chalk-
without-flfnts," and an upper band of " Chalk-with-flints." The
former corresponds, on the whole, with the Turonian stage, which
in England is sometimes more than 200 feet thick. The Chalk,
as a whole, is a remarkably pure limestone, composed chiefly of
crumbled foraminifera, urchins, molluscs, and other marine
organisms. It must have been laid down in a sea singularly
free from ordinary sandy or muddy sediment ; but there is no
evidence that this sea was one of great depth. On the contrary,
though the Chalk itself resembles the Globigerina ooze of the
deeper parts of the Atlantic Ocean, the characters of its foramini-
fera and other organic remains indicate comparatively shallow-
water conditions. The basin in which it was laid down shallowed
eastwards, where, from the evidence of sandstones, coal-seams,
and plants, there was land at the time ; while, probably, towards
the west there was connection with the open sea.
The English type of this stage is prolonged into northern
France, but traced into Germany it undergoes a change similar to
that of the underlying parts of the Chalk, passing into massive
sandstones, limestones, and marls. In the south and south-east
of France the type of hippurite limestones sets in, and stretches
across the centre of Europe and along both sides of the Mediter-
ranean basin into Asia. As above stated, this development of the
Cretaceous rocks has a much wider range than the Chalk from
which the system derives its name.
Senonian (from Sens, in the department of Yonne). This
stage corresponds generally with the original English Upper
Chalk, or Chalk-with-flints, which is the thickest subdivision,
since it reaches a thickness of 700 feet. Its most conspicuous
feature is the presence of the layers of nodules or irregular
lumps of black flint which mark the stratification of the Chalk.
The origin of these concretions has been the subject of much
discussion among geologists, and it cannot be said to have been
even yet satisfactorily solved. Some marine plants (diatoms)
and animals (radiolarians, sponges, etc.) secrete silica from sea-
water, and build it up into their framework. But the flints are
not mere siliceous organisms, though organic remains may often
362 MESOZOIC PERIODS CHAP.
be observed enclosed within them. They are amorphous lumps
of dark silica, containing a little organic matter. By some process,
not yet well understood, these aggregations of silica have gathered
usually round organic nuclei, such as sponges, urchins, shells, etc.
The decomposition of organic matter on the sea-floor may have
been the principal cause in determining the abstraction and
deposition of silica. Not infrequently an organism, such as a
brachiopod or echinus, originally composed of carbonate of lime,
has been completely transformed into flint.
Two well-marked divisions of the Senonian stage are character-
ised, the lower by the abundance of sea-urchins belonging to the
genus Micraster (M. cor-testudinarium in the under part, and
M. cor-anguinum in the higher part), and the upper by the preval-
ence of belemnites of the genus Belemnitella (B, qtiadrata and
B. mucronata~}.
The total thickness of the English Chalk, including the Ceno-
manian, Turonian, and Senonian stages, exceeds 1200 feet. It
is well exposed along the sea-cliffs of the east and south of
England. It forms the promontories of Flamborough Head,
Dover, Beachy Head, and the Needles in the Isle of Wight.
The white cliffs of Kent are repeated on the opposite coast of
France, where the same general type of Senonian calcareous sedi-
ments is developed. Towards the Mediterranean basin, the hip-
purite limestones with sandstones and marls take the place of the
northern Chalk. But they include some fresh-water deposits
and beds of lignite, which point to the shallowing of the sea
there towards the end of Cretaceous time and the uprise of land.
In Germany, the Senonian stage displays a still greater develop-
ment of thick sandstones, which form the picturesque district
known as Saxon Switzerland.
Danian (from Denmark). This stage has not been recognised
in England. Its component chalky strata occur in scattered
patches over Northern France, Belgium, and Denmark, to the
south of Sweden.
The Cretaceous hippurite-limestones of Southern Europe and
the basin of the Mediterranean are prolonged through Asia Minor
into Persia, where they cover a vast area. They have been found
likewise on the flanks of the Himalaya Mountains, so that the
open Cretaceous sea must have stretched right across the heart
of the Old World. .In the Indian Deccan, a great extent of
country, estimated at 200,000 square miles, lies buried under
horizontal or nearly horizontal sheets of lava, which have a united
xxiv CRETACEOUS 363
thickness of from 4000 to 6000 feet or more, and were erupted
during the later ages of the Cretaceous period. These eruptions,
from the presence of interstratified layers containing remains of
fresh-water shells, land-plants, and insects, are believed to have
taken place on land and not under the sea.
Cretaceous rocks cover an enormous area in North America
and in some regions attain a thickness of many thousand feet.
They include marine and fresh- water strata, and thus reveal a wide
variety of geographical conditions during their deposition, so that
the succession of formations in the system varies widely in
different parts of the continent. In the Eastern States, from
Rhode Island southward into Georgia, a strip of Cretaceous
formations has long been known. In New Jersey, the clays and
sands have furnished an abundant marine fauna, while in Virginia
there is a characteristic terrestrial flora. Stretching westward
beyond the Mississippi into Texas, Oklahoma, and New Mexico,
the Cretaceous system attains a great development, until it is said
to be from 10,000 to 20,000 feet thick. In that region the
marine type of sediments is well displayed and the limestones
contain abundant hippurites, like those of Europe. Where they
have remained undisturbed the strata retain much of their original
soft chalky or marly character, but where they have been ridged
up into mountain ranges they have acquired the hardness of solid
rocks.
In the vast interior region including Colorado, Utah, Wyoming,
and a wide expanse of British territory from Manitoba across
the Rocky Mountain region westward to the Pacific coast, the
Cretaceous system covers many thousands of square miles
and sweeps northward into the Arctic regions. In Utah,
Wyoming, and the surrounding regions, it consists of enormous
piles of sediment which appear to have been laid down for the
most in large fresh-water lakes, though on several distinct horizons
proofs of the intervention of the sea at intervals are furnished by
clays, shales, and limestones, containing such characteristic marine
Cretaceous shells as Inoceramus, Baculites, Scaphites and Belem-
nitella. The highest formation in the series, known as the
Laramie group, has furnished a large assemblage of land-plants,
half of which are allied to still living American trees, and in some
places these plants are aggregated into valuable seams of coal.
The numerous reptilian and bird remains found in these strata
have been already noticed. Towards the close of the Cretaceous
period volcanic activity prevailed extensively in the western
364 MESOZOIC PERIODS CHAP, xxiv
portions of the continent, and some of the uppermost of the
Cretaceous formations in that region consist mainly of volcanic
tuffs. There was likewise great disturbance of the terrestrial crust,
which was powerfully ridged up into mountains and plateaux, such
as those of the Rocky Mountains, the Pacific coast-ranges, and
the high tablelands of Arizona and Utah.
Rocks assigned to the Cretaceous system cover a wide region
of Queensland, and also attain a considerable thickness in New
Zealand.
CHAPTER XXV
THE TERTIARY OR CAINOZOIC PERIODS EOCENE OLIGOCENE
THE Cretaceous system closes the long succession of Secondary
or Mesozoic formations. The rocks which come next in order
are classed as Tertiary or Cainozoic (Recent Life). When
these names were originally chosen, geologists in general believed
not only that the divisions into which they grouped the stratified
rocks of the earth's crust correspond on the whole with well-
defined periods of time, but that the abrupt transitions, so often
traceable between systems of rocks, serve to mark geological
revolutions, in which old forms of life, as well as old geographical
conditions, disappeared and gave place to new. One of the most
notable of such breaks in the record was supposed to separate
the Cretaceous system from all the younger rocks. This opinion
arose from the study of the geology of Western Europe, and more
especially of South-Eastern England and North-Western France.
The top of the Chalk, partly worn down by denudation, was found
to be abruptly succeeded by the pebble-beds, sands, and clays of
the lower Tertiary groups. No species of fossils found in the
Chalk were known to occur also in the younger strata. It was
quite natural, therefore, that the hiatus at the -top of the Creta-
ceous system should have been regarded as marking the occurrence
of some great geological catastrophe and new creation, and, con-
sequently, as one of the great divisional lines of the Geological
Record.
More detailed investigation, however, has gradually overthrown
this belief. In Northern France, Belgium, and Denmark, various
scattered deposits (Danian, p. 362) serve to bridge over the gap
that was supposed to separate Mesozoic and Cainozoic formations.
In the Alps, no satisfactory line has been found to separate un-
doubtedly Cretaceous strata from others as obviously Tertiary.
365
366 TERTIARY PERIODS CHAP.
And in various parts of the world, especially in Western North
America, other testimony has gradually accumulated to show that
no general convulsion marked the end of the Secondary and
beginning of the Tertiary periods, but that the changes on the
earth's surface proceeded in the same orderly connection and
sequence as during previous and subsequent geological ages.
The break in the continuity of the deposits in Western Europe only
means that in that part of the world, owing to some important
geographical changes, specially to elevation of the sea-floor, the
record of the intervening ages has not been preserved. Either
strata containing the record were never deposited in the region in
question, or, having been deposited, they have subsequently been
removed by denudation.
Bearing in mind, then, that such geological terms are only
used for convenience of classification and description, and that
what is termed Mesozoic time glided insensibly into what is called
Cainozoic, we have now to enter upon the consideration of that
section of the earth's history comprised within the Tertiary or
Cainozoic periods. The importance of this part of the geological
chronicle may be inferred from the following facts. During
Tertiary time the sea-bed was ridged up into land to such an
extent as to give the continents nearly their existing area and
contour. The crust of the earth was upturned into great
mountain ranges, and notably into that long band of lofty ground
stretching from the Pyrenees right through the heart of Europe
and Asia to Japan. Some portions of the Tertiary sea-bed now
form mountain peaks 16,000 feet or more above the sea. The
generally warm climate of the globe, indicated by the world-wide
diffusion of the same species of shells in Palaeozoic, and less
conspicuously in Mesozoic time, now slowly passed into the
modern phase of graduated temperatures, from great heat at the
equator to extreme cold around the poles. At the beginning of
the Tertiary or Cainozoic periods, the climate was mild even far
within the Arctic Circle, but at their close, it became so cold that
snow and ice spread far southward over Europe and North
America.
The plants and animals of Tertiary time are strikingly modern
in their general aspect. The vegetation consists, for the most
part, of genera that are still familiar in the meadows, woodlands,
and forests of the present day. The assemblage of animals, too,
becomes increasingly like that of our own time, as we follow the
upward succession of strata in which the remains are preserved.
xxv TERTIARY PERIODS 367
In one strongly marked feature, however, does the Tertiary fauna
stand contrasted alike with everything that preceded and followed
it. If the Palaeozoic or Primary periods formed the " Age of
Invertebrates and Fishes," and if the Mesozoic or Secondary
periods could appropriately be grouped together under the name
of the " Age of Reptiles," Cainozoic or Tertiary time may not less
fitly be called the "Age of Mammals." As the manifold reptilian
types died out, the mammals, in ever-increasing complexity of
organisation, took their place in the animal world. By the end
of the Tertiary periods they had reached a variety of type and a
magnitude of size altogether astonishing, and far surpassing what
they now present. The great variety of pachyderms is an especi-
ally marked feature among them.
The rocks embraced under the terms Cainozoic or Tertiary
have been classified according to a principle different from any
followed with regard to the older formations. When they began
to be sedulously studied in Western Europe, it was found that the
percentage of recent species of shells became more numerous as
the strata were followed from older to newer platforms. The
French naturalist Deshayes determined the proportions of these
species in the different Tertiary groups of strata, and the English
geologist Lyell proposed a scheme of classification based on these
ratios. His names, with modifications as to their application,
have been generally adopted. They are compounds of the Greek
KGUVOS, recent, with affixes denoting the proportion of living species.
To the oldest Tertiary deposits, containing only about 3 per
cent of living species of shells, the name Eocene (dawn of the
recent) was given. The next series, containing a larger number
of living species, has received the name of Oligocene (few
recent). The third division in order is named Miocene, to
indicate that the living species, though in still larger proportions,
are yet a minority of the whole shells. The- overlying series
forming the uppermost of the Tertiary divisions is termed Plio-
cene (more recent), because the majority are now living species.
The same system of nomenclature has been retained for the next
overlying group, which forms the lowest member of the Post-
tertiary or Quaternary series. This group is called Pleistocene
(most recent), and all the species of shells in it are still living at
the present time. It must not be supposed that the mere per-
centage of living or of extinct species of shells in a deposit always
affords satisfactory evidence of geological age. Obviously, there
may have been circumstances favourable or unfavourable to the
368 TERTIARY PERIODS CHAP.
existence of some shells on the sea-bottom which that deposit
represents, or to the subsequent preservation of their remains.
The system of classification by means of shell-percentages must
be used with some latitude, and with due regard to other evidence
of geological age.
EOCENE
In Europe great geographical changes took place at the close
of the Cretaceous period. The wide depression in which the
Chalk had been deposited was gradually and irregularly elevated,
and over its site a series of somewhat local deposits of clay, sand,
marl, and limestone was laid down, partly in small basins of the
sea-floor, and partly in estuaries, rivers, or lakes. In Southern
Europe, however, the more open sea maintained its place, and
over its floor were accumulated widespread and thick sheets of
limestone which, from the crowded nummulites which they con-
tain, are known as Nummulitic Limestone. These characteristic
rocks extend all over the basin of the Mediterranean, stretching
far into Africa and sweeping eastwards through the Alps,
Carpathians, and Caucasus, across Asia to China and Japan.
In North America the rocks classed as Eocene present two
contrasted types. Down the eastern and western borders of the
continent, from the coast of New Jersey into the Gulf of Mexico
on the one side, and along the coast ranges of California and
Oregon on the other, they are marine deposits, though occasion-
ally presenting layers of lignite with terrestrial plants. Over the
vast plateaux which support the Rocky Mountains, however, they
are of lacustrine origin, and show that in what is now the heart
of the continent the bed of the Cretaceous sea was upraised into
a succession of vast lakes, round which grew a luxuriant vegeta-
tion. In these lakes a total mass of Eocene strata, estimated at
not less than 12,000 feet, was deposited, entombing and preserv-
ing an extraordinarily abundant and varied record of the plant
and animal life of the time.
The Eocene flora points to a somewhat tropical climate.
Among its plants are many which have living representatives
now in the hotter parts of India, Australia, Africa, and
America. Above the ferns (Lygodium, Aspleniuni, etc.) which
clustered below, rose clumps of palms, cactuses, and aroids ;
numerous conifers and other evergreens gave the foliage an
umbrageous aspect, while many deciduous trees ancestors of
XXV
EOCENE
369
some of the familiar forms of our woodlands raised their
branches to the sun. Among the conifers were many cypress-
like trees (Callitris), pines (Pinus, Sequoia),
and yews (Salisburia or Ginko). Species
of aloe (Agave), sarsaparilla (Smilax), and
amomum were mingled with fan-palms
(Sabal, Chamcerops) and screw-pines (Pan-
danus, Nipa), together with early forms of
fig (Ficus), elm (Ulmus), poplar (Populus),
willow (Salix), hazel (Corylus), hornbeam
(Carpinus), chestnut (Castanea), beech
(Fagus\ plane (Platanus), walnut (Juglans),
liquidambar, magnolia, alder -like plants,
water - bean (Nehtmbiuni), water - lily Fia 2 8 ' -Eocene Plant (/w-
v /J * rcphiloides Richardsomi\
(Victoria), maple (Acer), gum-tree (Eu- natura i s i ze .
calyptus), cotoneaster, plum (Primus),
almond (Amygdalus), laurel (Laurus), cinnamon tree (Cinna-
momuni), and many more (Fig. 208).
The fauna likewise points to the extension of a warm climate
FIG. 209. Eocene Molluscs. (), Valuta l-uctatrix () ; (^), Olivet Branderi (natural
size) ; (c), Cerithiuin tricarinatum (f).
over regions that are now entirely temperate. This is particularly
noticeable with regard to the mollusca. The species are, with
perhaps a few exceptions, all extinct, but many of the genera are
2 B
370 TERTIARY PERIODS CHAP.
still living in the warmer seas of the globe. Some of the most
characteristic forms are species of Nautilus, Oliva, Valuta, Conus,
Mitra, Cyrena, Cytherea, Chama. The genus of Foraminifera,
called Nummulites from the fancied resemblance of the organism
to a piece of money, is enormously abundant in the limestones
above referred to as nummulitic limestones. It must have
flourished in vast profusion over the floor of the sea, which in
older Tertiary time spread across the heart of the Old World
from the Atlantic to the Pacific Oceans. Some of the most
common fish-remains found in the Eocene strata, chiefly in the
form of scattered teeth and ear-bones, belong to the genera
Lamna, Myliobatis, Pristis. Reptilian life, which enjoyed such
a preponderance during the Mesozoic ages, is conspicuously
FIG. 210. Eocene Mammal (Palteotherium magnutn^
diminished in the Eocene deposits alike in number of individuals
and variety of structure. The genera are chiefly turtles, tortoises,
crocodiles, and sea-snakes, presenting in their general assemblage
a decidedly modern aspect, compared with the reptilian fauna of
the Secondary rocks. Remains of birds are comparatively rare as
fossils. We have seen that the earliest known type has been
obtained in the Jurassic system, and that others have been found
in the Cretaceous rocks. Still more modern forms occur in Eocene
strata ; they include one (Argillorms) which may have been a
forerunner of the living albatross ; another, of large size (Dasornis},
possibly akin to the gigantic extinct ostrich-like moa (Dinornis)
of New Zealand ; a third (Agnopterus) shows an affinity with the
flamingo ; while the buzzard, woodcock, quail, pelican, ibis, and
African hornbill are represented by ancestral forms.
But, as stated above, it was chiefly in higher forms of life that
xxv EOCENE 371
the fauna of early Tertiary time stood out in strong contrast with
that of previous ages of geological history. The mammalia now
took the leading place in the animal world, which they have
retained ever since. Among the Eocene mammals reference may
here be made to the numerous tapir-like creatures which then
flourished (Coryphodon, Palcsotheritim, Fig. 210, Anchilophits, etc.).
Some of the forms were intermediate in character between tapirs
and horses, and included the supposed ancestors of the modern
FIG. 211. Skull of UintatheriuiJi (JFinoceras) ingens (about -fa).
horse (Eohippus, etc.) small pony-like animals, with three,
four, and even traces of five toes on each foot. Many of
the mammals of Eocene time presented more or less close
resemblances to wolves, foxes, wolverines, and other modern
forms. There were likewise true opossums. Numerous herds of
hog-like animals (Hyopotamus} and of hornless deer and antelopes
wandered over the land, while in the woodlands lived early
ancestors of our present squirrels, hedgehogs, bats, and lemurs.
Among these various tribes which recall existing genera, others
of strange and long-extinct types roamed along the borders of the
372 TERTIARY PERIODS CHAP.
great lakes in western North America. The Tillodonts were a re-
markable order, in which the characters of the ungulates, rodents,
and carnivores were curiously combined. These animals, perhaps
rather less in size than the living tapir, had skeletons resembling
those of carnivores, but with large prominent incisor teeth like
those of rodents, and with molar teeth possessing grinding crowns
like those of ungulates. Still more extraordinary were the forms
to which the name of Deinocerata has been given (Uintatherium,
Fig. 2 1 1 ). These were somewhat like elephants in size, and like
rhinoceroses in general build, but the skull bore a pair of horn-
like projections on the snout, another pair on the forehead, and
one on each cheek.
The west -European type of the Eocene deposits is well
displayed in England, France, and Belgium. In England it is
confined to the south-eastern part of the country, from the coast
of Hampshire into Norfolk. The strata "vary in character from
district to district, sands and gravels being replaced by clays
according to the conditions in which the sediment was accumu-
lated. A similar succession of deposits is prolonged from
Hampshire into the Paris basin and from the London area into
the Belgian basin. Arranged in tabular form this succession
may be grouped as follows :
[TABLE.
XXV
EOCENE
373
ENGLAND.
Barton Clay of Hampshire
Basin ; Upper Bagshot
Sands of London Basin.
Bracklesham Beds of Hamp-
shire (leaf-beds of Alum
Bay and Bournemouth),
Middle and part of Lower
Bagshot Sands of London
Basin.
FRANCE AND BELGIUM.
Marine gypsum and marls of Paris ;
sands and calcareous sandstones
of Belgium (Wemmelian).
Sands (Sables Moyens) marine,
with estuarine and fresh-water
limestones, etc.
Calcaire Grossier divided into (3)
Caillasses, upper limestones, with
marine and fresh-water fossils ; (2)
middle limestones, with marine
shells and terrestrial vegetation ; ( i )
lower glauconitic marine limestones
and sands.
Sandstones and sands (Lackenian
and Bruxellian) of Belgium.
Part of Lower Bagshot
Sands.
London Clay (Bognor Beds).
Oldhaven Beds.
Woolwich and Reading Beds.
Thanet Sand.
Paniselian sands of Belgium.
Ypresian clays and overlying sands of
Belgium. Absent in Paris basin.
Landenian gravels and sands of
Belgium.
Sands of Bracheux (Paris basin),
Heersian beds of Belgium, marls
of Meudon ; fresh- water limestones
of Rilly and Suzanne. Limestone
of Mons in Belgium.
In striking contrast with these comparatively thin and locally
developed deposits are those of* the Alps, Southern Europe, and
the basin of the Mediterranean. Masses of nummulitic limestone
and sandstone, several thousand feet thick, have been upraised,
folded, and fractured, and now form important parts of the great
mountain chains which run through Europe and the north of
Africa. Similar rocks have been uplifted along the flanks of the
great chain of heights that sweeps through the heart of Asia,
reaching in the Himalaya range a height of 16,500 feet above
the sea-level. We thus learn not only that a large part of the
existing continents lay under the sea during Eocene time, but
that the principal mountain-chains of the Old World have been
upheaved to their present altitudes since the beginning of the
Tertiary periods. In North America the two contrasted types of
the Atlantic border and the interior are grouped in the following
subdivisions :
374
TERTIARY PERIODS
CHAP.
ATLANTIC BORDER (CHIEFLY
MARINE.)
INTERIOR (LACUSTRINE).
I
ex
D
Vicksburg group of lime-
stones, blue marls, and
lignitic clays and lig-
nites ; numerous marine
fossils (Cardium, Panopcea,
Cyprcea, Mitra, Conus,
Madrepores, Orbifoides).
Uinta group of lacustrine strata
("Diplacodon Beds").
Middle.
Jackson group of white and
blue marls with marine
fossils, underlain by
lignitic clay and lignite.
Claiborne group of white
and blue marls and sands,
with marine shells, corre-
sponding to the Calcaire
Grossier of the Paris Basin.
Buhrstone or Lower (siliceous)
Claiborne group of sand-
stones and impure siliceous
limestones, with marine
fossils like those of the
group above.
Bridger group consisting of some
5000 feet of lacustrine deposits,
which include the ' ' Deinoceras
Beds " of Professor Marsh. Huer-
fano lacustrine group of Southern
Colorado.
Green River (Wind River) group of
lacustrine strata (2000 feet).
Lower.
Lignitic sands and clays, with
remains of a terrestrial
flora and marine fossils in
some of the strata.
1
Wahsatch (Vermilion Creek) group ;
Coryphodon beds, consisting of
about 5000 feet of sediments,
marking the site of one or more
large lakes.
In the western regions of the United States, a marked feature
of the scenery of the Tertiary strata is that of the so-called " Bad
Lands " tracts of nearly horizontal clays, rnarls, limestones, and
sandstones which, under the influence of atmospheric denudation,
in a somewhat arid climate, have been carved into an intricate
network of gullies, chasms, ridges, and buttes, nearly or wholly
devoid of vegetation and with the aspect of almost crumbling into
dust under one's eyes. It is a repulsive landscape, verdureless,
treeless, and waterless. Some of its characteristic aspects are
represented in Fig. 212.
OLIGOCENE.
Under this name geologists have placed a group of strata
usually of comparatively insignificant thickness, chiefly of fresh-
XXV
OLIGOCENE
375
water and estuarinc, but partly also of marine origin, which, in
Western and Central Europe, show how the bays and shallow seas
of that region in the Eocene period were gradually obliterated, and
replaced by land and by sheets of fresh water. They attain in
Switzerland a thickness of several thousand feet, composed of
376 TERTIARY PERIODS CHAP.
sandstones, conglomerates, and marls, almost entirely of lacustrine
origin, and forming a group of massive mountains (Rigi, Rossberg).
A large lake occupied their site and continued to be an important
feature in the geography of Central Europe during this and the
following geological period. Other sheets of fresh water were
scattered over the west of .Europe. One of the largest of these
lay in Central France, over the old district known as the Limagne
d'Auvergne. In Germany, lacustrine and terrestrial deposits,
including numerous seams of lignite or brown coal, are separated
by a group of strata full of marine shells, foraminifera, etc.,
showing that for a time the lakes and woodlands were submerged
beneath the sea. In the Paris basin, and in the Isle of Wight, the
strata were chiefly deposited in fresh-water, but contain occasional
marine intercalations. Evidently the Oligocene period, throughout
the European area, was one of considerable oscillation in the earth's
crust. During this time, too, the volcanic eruptions took place
whereby the great sheets of basalt that form the terraced hills of
the north of Ireland, the Western Islands of Scotland, and the
Faroe Isles, were thrown out.
An epoch of frequent change in the relative positions of sea
and land is one in which there may be exceptional facilities for
the preservation of a record of the plants and animals of the time.
Oligocene strata in Europe have accordingly a peculiar interest
from the abundant remains they contain of the contemporaneous
terrestrial plants and animals. The land flora of that period is
probably better known than that of any other section of the
Geological Record, chiefly from the extraordinary abundance of
its remains which have been preserved in the sediments of the
ancient Swiss lake. Judging of it from these remains, we learn
that it was in great measure made up of evergreens, and in various
ways resembled the existing vegetation of tropical India and
Australia and that of sub-tropical America. Its fan-palms, feather-
palms, conifers, evergreen oaks, laurels, and other evergreen trees,
gave a peculiarly verdant umbrageous character to the landscape
in all seasons of the year, while numerous proteaceous shrubs
glowed with their bright blooms on the lower grounds.
Of the terrestrial fauna numerous remains have been found in
the lacustrine deposits of the time. We know that the borders of
the lakes in Central France were frequented by many different
kinds of birds paroquets, trogons, flamingoes, ibises, pelicans,
maraboots, cranes, secretary birds, eagles, grouse, and other forms.
This association of birds recalls that around the lakes of Southern
xxv OLIGOCENE 377
Africa at the present time. The mammals appeared in still
more numerous and abundant types. Among them came the
Anoplotherium a slender, long-tailed animal, about the size of
an ass, with three toes on each foot ; certain transitional types of
ungulates, with affinities to the pigs, peccaries, and chevrotains
(Anthracotkerium, Cheer opotamus, Hyopotamus, etc.) ; various
forms of the tapir family, and of dogs, civets, martens, marmots,
bats, moles, and shrews. The carnivora still presented mar-
supial characters, and in not a few of the animal types features
of structure were combined which ai now only found in distinct
genera. The Eocene palaeotheres and the Oligocene anoplotheres
appear to have died out before the end of the Oligocene period.
The fresh water teemed with molluscs, belonging chiefly to genera
a be
FIG. 213. Oligocene Molluscs, (a), Ostrea I'entilabrum (^) ; (b), Corbula subpisum (f) ;
(c), Vivipara lento, (natural size).
that still live in our rivers and lakes, such as Unio, Cyrena,
Paludina, Planorbis, Limnaa, Helix, and others (Fig. 2 1 3), while
the seas were tenanted by species of Oyster, Pecten, Nucula,
Cardium, Murex, Typhis, Conus, Voluta, and others.
In the Isle of Wight the highest Eocene strata were followed
by a group of fresh-water, estuarine, and marine deposits, formerly
classed as Upper Eocene, but now placed in the Oligocene divi-
sion. They are arranged in the following manner in descending
order :
Hamstead group clays, marls, and shelly layers, with marine shells in a
band at the top, while the main part of the group contains fresh-water and
estuarine shells and land-plants. About 260 feet.
Bembridge group marls and limestone, with fresh-water estuarine and
marine shells above, and fresh-water and land-shells forming a band of
limestone below. About no feet.
Osborne group clays, marls, sands, and limestones, with abundant fresh-
water shells. About 100 feet.
378 TERTIARY PERIODS CHAP.
Headon group consisting of an upper and lower division, containing fresh
and brackish water fossils, and a middle group in which marine shells
and corals occur. 100 to 350 feet.
These Isle of Wight strata, having a total depth of more than
600 feet, were for many years the only known examples in Britain
referable to this portion of the Geological Record, and they form
still the only series in this country which, in its abundant molluscs,
allows a comparison to be made between it and corresponding
rocks on the Continent. But at Bovey Tracey in Devonshire a
small lake-basin has been discovered, the deposits of which have
yielded a large number of terrestrial plants comparable with those
found in the Oligocene strata of Switzerland and Germany.
Between the great sheets of basalt, also, that form the plateaux of
Antrim and the Inner Hebrides, numerous remains of a similar
vegetation have been discovered. There can be no doubt that
these volcanic rocks were poured out over the surface of the land,
and that the plants, whose remains have been disinterred from
the intercalated layers of lignite, tuff, and hardened clay, grew
upon that land. The basalts and other lavas, even after the
great denudation which they have undergone, are still in some
places more than 3000 feet thick. They were poured out in wide-
spreading sheets that completely buried the previous topography,
and extended as vast lava -plains, like those of younger date
which form so impressive a feature in the scenery of Montana,
Idaho, and Oregon, in western North America.
In the Paris basin, the Oligocene strata follow immediately
upon the Eocene group described on p. 373. They consist of (i)
a lower division of gypsum (65 feet) and marls, with terrestrial
shells, and remains of palaeotheres and anoplotheres ; (2) a
middle band of marl, limestone, and sand, with lacustrine
and estuarine shells ; and (3) an upper division, in which
the most conspicuous members are the Helix-limestone of the
Orleanais and the sands and hard siliceous sandstone of
Fontainebleau.
In Switzerland the Oligocene series of formations attains a
thickness of more than 9000 feet. Rising into prominent groups
of mountains, it has preserved a singularly full and interesting
record of the terrestrial life of the time, together with proofs of
the early presence of the sea. By far the largest part of
these deposits consists of compacted sands, gravels, and clays,
which were laid down in a lake. These strata are arranged in
the two following groups.
xxv OLIGOCENE 379
2. Aquitanian stage, or Red Molasse a great development of red sand-
stones, marls and conglomerates, containing an abundant terrestrial
vegetation, sometimes aggregated into seams of lignite.
I. Tongrian stage or Lower marine Molasse, consisting of sandstones which
enclose marine and brackish-water shells.
In Northern Germany the subjoined succession of "strata in
descending order has been noted.
( Marine marls, clays, and sands.
-I
Upper - Brown coal of the Lower Rhine, with abundant terrestrial vegeta-
[ tion and some marine bands.
. J Sands and Septaria-clay, with abundant marine fauna ; occasion-
' \ ally a brown-coal group occurs.
'Marine beds of Egeln, with marine shells and corals.
Amber beds of Konigsberg, containing 4 or 5 feet of glauconitic
sand, with abundant pieces of amber, which is the fossil resin
of different species of coniferous trees. A large number of
Lower ^ species of insects has been enclosed and preserved in the
amber.
Lower Brown coal sands, sandstones, clays, and conglomer-
ates, with interstratified seams of brown coal and an abundant
terrestrial flora, in which coniferae are prominent.
In North America, the probable representatives of the European
Oligocene formations include no marine bands, but consist of
lacustrine and fluviatile sands and clays (White River group),
which mark the former presence of a series of large lakes in the
interior of the continent. The most extensive of these inland
waters stretched across South Dakota and the west of Nebraska,
southwards into Colorado and westwards into Wyoming. Other
lakes lay farther north, at least as far as the Cypress Hills of
Western Canada. In Colorado, the shales at Florissant have
yielded an abundant assemblage of terrestrial plants and insects.
In upper Missouri and across the Rocky Mountains into Utah,
the White River group of lacustrine deposits- has furnished a
striking series of vertebrate remains, including three -toed horses
(Anckitkermm, Miohippus, Mesohippus\ tapir - like animals
(Lophiodori], hogs as large as rhinoceroses (Elotherium\ true
rhinoceroses, huge elephant-like creatures allied to Deinoceras and
tapir (Brontotheiium, Titanotheritint), and carnivorous genera, some
of which are like European Tertiary wolves, lions, and bears.
CHAPTER XXVI
MIOCENE PLIOCENE
THE geological period at which we are now arrived, one of the
most important in the history of the configuration of the existing
continents, embraced that portion of geological time during which
the great mountain-chains of the globe were uplifted into their
present commanding positions. There is good reason to believe
that these lines of elevation are of great geological antiquity, and
that they have again and again been pushed upward during great
terrestrial disturbances. But the intervals between these successive
upthrusts were probably often of immense duration, so that the
mountains, being exposed to continuous and prolonged denudation,
were worn down, sometimes perhaps almost to the very roots.
In all probability the nucleus of the line of the Alps, for example,
dates back to a remote geological period. But only in Tertiary
time did it attain its present dimensions. We have seen that,
during the Eocene period, the sea of the nummulitic limestone
extended over at least a considerable part of the Alpine region,
and that, as the limestone now forms crumpled and dislocated
mountainous masses, the great upheaval of the chain must have
taken place after Eocene time. Not improbably the process was
a prolonged one, advancing in successive uplifts, with intervals of
rest. The final upheaval that gave the Alps their colossal bulk
did not take place until the Miocene period or later, for the
Miocene strata have been involved in the earth-movements, and
have been thrust up, bent, and broken. Nor were the terrestrial
convulsions confined to Central Europe, all over the globe there
seem to have been extensive disturbances. The Eocene sea-bed
with its thick accumulations of nummulite-limestone was ridged
up into land, and portions of it, as already remarked, were carried
upward on the flanks of the mountains, in the Himalayas to a
height of 16,500 feet above the sea.
380
CHAP. XXVI
MIOCENE
While these revolutions were taking place in its topography,
Europe continued to enjoy a climate which, to judge from the
remains of plants and animals preserved in the Miocene rocks,
must still have been of a somewhat tropical character. The flora
that clothed the slopes of the Alps was not unlike that of the
forests of India and Australia at the present time. Palms of
various kinds still flourished all over Central and Western Europe,
mingled with conifers, laurels, evergreen oaks, magnolias, myrtles,
mimosas, acacias, sumachs, figs, oaks, and various still living
d
FIG. 214. Miocene Plants, (a), Magnolia Inglefieldi (i) ; (b), Rhus Meriani (natural
size) ; (c), Ficus decandolleana () ; (d), Quercus ilicoides ().
genera of proteaceous shrubs (Fig. 214). But there is evidence
of the incoming of a more temperate climate, for, in the higher
parts of the Miocene series of strata, the vegetation was charac-
terised by the abundance of its beeches, poplars, hornbeams,
elms, laurels, pondweeds, etc.
Remains of the terrestrial fauna have been well preserved in
the deposits that gathered over the floors of the lakes. We know,
for instance, that in the woodlands surrounding the large Miocene
lake of Switzerland insect life was remarkably abundant. From
the proportions of the different kinds that have been exhumed, it
has been inferred that the total insect population was then more
382
TERTIARY PERIODS
CHAP.
varied in some respects than it is now in any part of Europe,
wood-beetles being especially numerous and large. In the thick
underwood, frogs, toads, lizards, and snakes found their food.
Through the forests there roamed antelopes, deer, and three-toed
horses, while opossums, apes, and monkeys (Pliopithecus, Dryo-
pithecus, Oreopithecus} gambolled among the branches. Wild
cats, bears (Hycenarctos], and sabre-toothed lions (Machairodus}
were among the prominent carnivores of the time. But the most
striking denizens of these scenes were undoubtedly the huge
proboscidian creatures, among which the Mastodon and Deino-
therium took the lead. The now long extinct mastodon (Fig.
FIG. 215. Mastodon angustidens (j" 2 ).
215) was a large form of elephant, which, besides tusks in the
upper jaw, had often also a pair in the lower jaw. The deino-
therium (Fig. 216) possessed two large tusks in the lower jaw
which were curved downwards. This huge animal probably
frequented the rivers of the time, using its powerful curved
tusks to dig up roots, and perhaps to moor itself to the banks.
Contemporaneous with these colossal pachyderms were species
of rhinoceros, hippopotamus, and tapir. The rivers were
haunted by crocodiles, turtles, beavers, and otters ; while the
seas were tenanted by ancestors of our living morse, sea-calf,
dolphin, and lamantin. It is strange to reflect that such an
assemblage of animals should once have found a home all over
Europe.
The deposits referable to the Miocene period in Europe indi-
MIOCENE
383
cate a great change in the geography of the region since Eocene
and Oligocene times. While most of the Continent remained
land, with large lakes scattered over its surface, certain tracts had
subsided beneath shallow seas which penetrated here and there
by long arms into the very heart of the region. Britain continued
to be a land surface, and as such was continuously exposed to
denudation, so that, instead of the formation of new deposits, there
was an uninterrupted waste of those already existing. So vast in-
deed has been the destruction of the Tertiary strata of Britain that
it has evidently been in progress for an enormous period of time.
Much of it, no doubt, took place during the long interval required
FIG. 216. Skull of Deinotherium giganteum (reduced).
elsewhere for the accumulation of the Miocene series of rocks.
Not only were the soft sands and clays of the older Tertiary
groups of south-eastern England worn away from hundreds of
square miles which they originally covered, but even the hard
basalt-sheets of Antrim and the inner Hebrides were so cut down
by the various agents of denudation that wide and deep valleys
were carved out of them, and hundreds of feet of solid rock were
gradually removed from their surface.
While Britain remained land, arms of the sea spread over what
is now Belgium, likewise over the basins of the Loire, Indre, and
Cher, stretching across Southern France to the Mediterranean,
passing along the northern base of the Alps, running into the valley
of the Rhine as far north as Mainz, sweeping eastwards round the
384 TERTIARY PERIODS CHAP.
eastern end of the Alps, and expanding into the broad gulf of
Vienna among the submerged heights of Austria and Hungary.
The strata that tell this story of submergence contain an
abundant assemblage of marine shells, many of which belong to
genera that now live in warmer seas than those which at present
bathe the coasts of Europe. Among them are Cancellaria, Cyprcea,
Mitra, Murex, Strombus, Area, Cardita, Cytherea, Pectuncuhis,
Spondylus, together with genera, such as Ostrea, Pecten, Cardium,
Tapes, Tellina, which are familiar in the northern seas.
The district of France, formerly called Touraine, is largely
overspread with shelly sands and marls, rarely more than 50 feet
thick, and locally known as " Faluns." These deposits represent
the floor of the shallow Miocene strait which extended across
France. They have yielded upwards of 300 species of shells, the
general character of which marks a warmer climate than now
exists in Southern Europe. The tableland of Spain, with its
northern mountainous border, rose along the southern margin of
this strait which connected the Atlantic and the Mediterranean.
Through this broad passage the large cetaceans of the time passed
freely from sea to sea, for their bones are found in the upraised
sea -bottom. The carcases of the mammals that then lived
among the Pyrenees mastodons, rhinoceroses, lions, giraffes, deer,
apes, and monkeys were likewise swept down into the sea. The
deposits of the shallow Miocene straits and bays thus supply us
with evidence of the position of the land and the character of its
inhabitants. Eastwards the sea appears to have deepened over
the region now occupied by the Gulf of Genoa and the encircling
mountain ranges, for the Miocene deposits of that part of the basin
of the Mediterranean, consisting' almost wholly of blue marls, are
said to reach the great thickness of more than 10,000 feet.
Beyond that depression, the sea once more shallowed across the
site of South-Eastern Europe. In the Vienna basin, its deposits
are well developed and consist of two divisions : ( i ) a lower
group (Mediterranean or marine stage) of limestones, marls, clays,
and sands, containing an abundant assemblage of shells, some of
which belong to species still living in the present Mediterranean
Sea, or off the west coast of Africa, and also numerous remains of
land-plants which again recall the living floras of India and
Australia ; and (2) an upper group (Sarmatian or Cerithium
stage) of sands, gravels, and clays in which the shells and terres-
trial plants point to a much more temperate climate than that
indicated by the lower group.
MIOCENE 385
On the northern side of the Swiss Alps, the lake which was
formed by the uplifting of the Eocene sea-floor, and in which so
thick a succession of Oligocene strata was laid down, eventually
disappeared among the terrestrial movements that submerged so
much of Europe beneath the Miocene sea. Marine bands con-
taining undoubted Miocene shells extend across Switzerland ; but
among them there are such abundant remains of terrestrial vegeta-
tion as to show that the land was not far off. No doubt the Alps,
not yet uplifted to their ultimate height, rose along the southern
borders of the strait that ran across Central Europe, and bore on
their slopes luxuriant forest-growths. In Switzerland, however,
we learn that before the close of the Miocene period the sea was
once more excluded from the district, and another lake made its
appearance. The marls, limestones, and sandstones accumulated
in this lake (CEningen Beds) are among the most interesting
geological deposits in Europe, from the great number and perfect
preservation of the plants, insects, fishes, and mammals which
have been obtained from them. A large part of our knowledge
regarding the terrestrial vegetation and animal life of the Miocene
period has been derived from these strata.
Passing beyond the European area, we find that some of the
characteristic vegetation of Miocene time spread northwards far
within the Arctic Circle. In Spitsbergen and in North Greenland
an abundant series of plant-remains has been discovered, including
a good many which occur also as fossils in the Miocene deposits
of Central Europe. More than half of them are trees, among
which are thirty species of conifers, also beeches, oaks, planes,
poplars, maples, walnuts, limes, and magnolias. This flora has
been traced as far as 81 45' north latitude, where the last naval
expedition sent out from England found a seam of coal 25 to 30
feet thick, covered with black shales full of plant-remains.
The same twofold development marine and lacustrine which
characterised the earlier ages of Tertiary time in North America,
continued to prevail during the rest of the period. The Miocene
strata of the Atlantic border are unequivocally marine deposits, as
are likewise those on the western margin of the Continent, while
the vast interior region presents a succession of lacustrine
sediments. The marine Miocene type is displayed along the
coast of New England and southwards from New Jersey into
Texas, where the strata reach a thickness of 1500 feet. Three
groups have been recognised in this series. At the base lies the
Chattahoochee stage, which contains an assemblage of fossils like
2 C
386 TERTIARY PERIODS CHAP.
those of the Miocene rocks of the West Indies ; next comes the
Chipola stage, characterised by a shell-bearing sand from which
several hundred species of molluscs have been obtained, having
affinities with a warm or sub-tropical fauna ; the uppermost stage
(Yorktown) contains an assemblage of shells that marks a more
temperate climate than that of the strata below.
In the lacustrine Miocene development of the interior two
stages have been discriminated. The lower of these (John Day
stage) is typically seen in Eastern Oregon between the Cascade
and Blue Mountains, w 7 here it reaches a thickness of between
3000 and 4000 feet, and consists in great part of stratified volcanic
tuffs. The higher stage (Loup Fork) is well displayed in
Nebraska, whence it stretches southward, but not continuously,
into Mexico. The flora of the Miocene deposits of the interior
approximates more closely to that of these regions at the present
time, though still indicating a warmer climate. It included species
of beech, elm, hickory, maple, oak, and poplar. The fauna
comprised forms of mastodon, numerous three-toed horses more
like modern types than those of previous periods, tapiroid animals,
hogs as large as rhinoceroses, true rhinoceroses, huge elephant-
like creatures allied to deinoceras and tapir, stags, camels, beavers,
wolves, bears, and lions. As in Europe, the close of the Miocene
period in North America witnessed a series of important movements
of the earth's crust. The Mesozoic and older Tertiary formations
along the oceanic border in California and Oregon were plicated
and upheaved into mountainous land. This period was likewise
characterised by the great vigour of its volcanic activity all over
the western half of t"he interior down into Mexico and Central
America.
PLIOCENE
The last division of the Tertiary series of formations lays before
us the history of the geological changes that brought about the
present general distribution of land and sea, and completed the
existing framework of the continents. Contrasted with the previous
Tertiary groups, it is, on the whole, insignificant in thickness and
extent, and it probably records the passing of a much less period
of time, during which the amount of terrestrial revolution was
comparatively trifling. Only in the basin of the Mediterranean
are there any European Pliocene strata worthy of note on account
of their thickness. The floor of that sea slowly subsided until
PLIOCENE 387
sands, clays, and accumulated shell-beds had been piled up to a
depth of several thousand feet. An important volcanic episode
then took place. Etna, Vesuvius, and the other volcanoes of
Central Italy began their eruptions. Thick masses of Pliocene
sediments were ridged up on both sides of the Apennines, and in
Sicily were upheaved to a height of nearly 4000 feet above the
present sea-level. This elevation of the Pliocene sea-bed in the
Mediterranean area was not improbably connected with other
movements within the European region. The shallow firths and
bays which still indented the Continent were finally raised into dry
land, and the Alps may then have received their final uplift.
While the European Pliocene deposits have their maximum thick-
ness in the Mediterranean basin, they elsewhere represent the
sediments of shallow seas and of lakes and rivers.
The flora of the Pliocene period affords evidence of the con-
tinued advance of a more temperate climate. The tropical types
of vegetation one by one retreated southwards in the European
region, leaving behind them a vegetation that partook of the
characters of those of the present Canary Islands, of North
America, and of Eastern Asia and Japan, but which, as time wore
on, approached more and more to the present European flora (Fig.
2 1 7). It included species of bamboo, sarsaparilla (Smt7ax),g\yp\.o-
strobus, taxodium, sequoia, magnolia, tulip-tree (Liriodendrori),
maple (Acer), buckthorn (Rhamnus\ sumach (Rhits\ plum
(Prtimes), laurel (Latirus), cinnamon-tree (Cinnamomum\ sassa-
fras, fig (Ficus\ elm (Ultmis), willow (Satix), poplar (Populus),
alder (Alnus), birch (Betula\ liquidambar, oak (Querctts\
evergreen oak (^Quercus ilex), plane (Platamts\ walnut (Juglans),
hickory (Carya), and other now familiar trees.
The fauna presented likewise evidence that the climate, during
at least the earlier part of the Pliocene period,- still continued
warm enough to permit tribes of animals to roam over Europe,
the descendants of which are now confined to regions south of the
Mediterranean basin. Some of the huge mammalian types that
had survived from an earlier time now died out ; such appears
to have been the case with the deinotherium and (at least in
Europe) the mastodon. Herds of pachydermatous animals
formed a distinguishing feature of the fauna rhinoceroses,
hippopotamuses, and elephants, with troops of herbivorous
quadrupeds gazelles, antelopes, deer, giraffes, horses, oxen, and
strange types that linked together genera which are at present
quite distinct. There were, likewise, carnivores (wild-cats, bears,
388
TERTIARY PERIODS
CHAP.
hyaenas, etc.), and many monkeys. The remains of monkeys
have been found fossil in Europe 14 farther north than their
descendants now live.
FIG. 217. Pliocene Plants. (A), Populus canesccns ; ('), Salix alba ; (C) Glyptostrofats
europ&us; (/>), Alnus glutinosa; (E), Platanus aceroides (all natural size except
E, which is J).
The shells of the Pliocene deposits afford important evidence
regarding the gradual change of climate. The great majority of
them belong to still living species (Fig. 2 1 8). They consequently
PLIOCENE
389
supply an excellent basis for comparison with the existing distribu-
tion of the same species. When the deposits containing them
are examined with reference to the present habitats of the species,
it is found that the percentage of what are now northern shells
increases from the lower to the higher parts of the series. Each
species, no doubt, flourished only in that part of the Pliocene
sea where it found its congenial temperature and food. We
infer that its requirements are still the same at the present
day, in other words, that the temperature of the regions within
FIG. 218. Pliocene Marine Shells, (a), A' hynchonclla psiitacea. (natural size); (/>)>
Panopcea norvegica (^) ; (c), Purpura lapillus () ; (has meridionalis, Mastodon
arvernensis}.
Astian, marine sands and gravels, with 20 per cent
of extinct molluscs ; represented in France by
fresh - water deposits containing Mastodon
L arvernensis, etc.
( Plaisancian marls and clays, with abundant marine
I shells, of which from about a third to a half
belong to living species.
j Messinian or Zanclean sandy marls, with seams of
i gypsum and limestone. This group marks
I alternations of brackish water and marine condi-
tions. It contains about 83 per cent of extinct
I shells.
Perhaps the most curious and interesting assemblage of the
land-fauna of Europe during Pliocene time has been found in
FIG. 219. Helladotherium Duvernoyi ( T *JJ) a gigantic animal belonging to the same
family as the living giraffe, Pikermi, Attica.
some hard red clays, alternating with gravels, at Pikermi in Attica.
Thirty-one genera of mammals have there been obtained, of which
twenty-two are extinct. The ruminants, specially well represented
among these remains, include species of giraffe, helladotherium
(Fig. 2i9\ antelopes, gazelles, and other forms allied to, but
distinct from, any living genera. There are likewise the bones
of gigantic wild boars, several species of rhinoceros, mastodon,
xxvi PLIOCENE 393
deinotherium, porcupine, hyaena, various extinct carnivores, and a
monkey.
In India a somewhat similar fauna has been obtained from
a massive series of fresh-water sandstones, known as the Siwalik
group. A large proportion of the organic remains belong to existing
genera of animals, such as macaque, bear, elephant, horse, hippo-
potamus, giraffe, ox, porcupine, goat, sheep, and camel. Various
extinct types were contemporary with these animals, two of the
most extraordinary of them being the Sivatherium and Brama-
therium colossal, four -horned creatures, allied to our living
antelopes and prong-bucks.
Pliocene deposits do not appear, on the whole, to be well de-
veloped in North America. They are best seen in Florida and
some of the neighbouring States, where they contain numerous
marine shells (Aira, Chavia, Strombus, etc.) They reach, how-
ever, a great thickness on the Pacific border, where the Merced
group of San Francisco is stated to consist of nearly 6000 feet of
sandstone. In the interior of the continent a series of lacustrine
deposits, believed to be referable to Pliocene time, occurs in Texas,
Kansas, and Oregon. Volcanic action continued to manifest itself
during this period on a great scale in that region.
CHAPTER XXVII
POST-TERTIARY OR QUATERNARY PERIODS PLEISTOCENE OR
POST-PLIOCENE RECENT
WE have now arrived at the last main division of the Geological
Record, that which is named POST-TERTIARY or QUATERNARY, and
which includes all the formations accumulated from the close of
the Tertiary periods down to the present day. But no sharp line
can be drawn at the top of the Tertiary groups of strata. On the
contrary, it is often difficult, or indeed impossible, satisfactorily to
decide whether a particular deposit should be classed among
the younger Tertiary or among the Post-tertiary groups. All
the molluscs of Post-tertiary deposits are believed to belong to
still living species, and the mammals, although also mostly of
existing species, include some which have become extinct. These
extinct forms are numerous in proportion to the antiquity of the
deposits in which they have been preserved. Accordingly, a
classification of the Quaternary strata has been adopted, in which
the older portions, containing a good many extinct mammals, have
been formed into what is termed the Pleistocene, Post-pliocene,
or Glacial group, while the younger deposits, containing few or no
extinct mammals, are termed Recent.
The gradual refrigeration of climate which is revealed to us by
the shells of the Crag was prolonged and intensified in Post-tertiary
time. Ultimately the northern part of the northern hemisphere
was covered with snow and ice, which extended into the heart of
Europe, and descended beyond the fortieth parallel of latitude in
North America. The previous denizens of land and sea were in
large measure driven out, or even in many cases wholly extirpated
by the cold, while northern forms advanced southward to take
their places. The reindeer, for instance, wandered in great numbers
across Southern France, while in North America its bones have
394
CHAP, xxvii PLEISTOCENE 395
been found as far south as New Haven. An Arctic vegeta-
tion spread all over Northern and Central Europe, even to the
Pyrenees. After the cold had reached its climax the ice-fields
began to retreat, and the northern flora and fauna to retire before
the advance of the plants and animals which had been banished
by the increasingly severe temperature. And at last the present
conditions of climate were reached. The story of this Ice Age
is told by the Pleistocene or Post-pliocene formations, while that
of the changes which immediately led to the establishment of the
present order of things is made known in the Recent deposits.
PLEISTOCENE, POST-PLIOCENE, OR GLACIAL
The evidence from which geologists have unravelled the history
of the Ice Age or cold episode, which came after the Tertiary
periods in the northern hemisphere, may here be briefly given.
All over Northern Europe and the northern part of North America
the solid rocks, where of hardness sufficient to retain it, are found
to present a characteristic smoothed, polished, and striated surface.
Even on crags and rocky bosses that have remained for long
periods exposed to the action of the weather this peculiar worn
surface may be traced ; but where they have been protected by a
covering of clay, even the finest striae are often as fresh as when
they were first made. The groovings and scratches do not occur
at random, but in every district run in one or more determinate
directions. The faces of rock that look one way are rounded off,
smoothed, and polished ; those that face to the opposite quarter
are more or less rough and angular. The quarter to which the
worn faces are directed corresponds with that to which the
trend of the striae and grooves on the rock-surfaces points.
There can be no doubt that all this smoothing, polishing, grooving,
and striation has been done by land-ice ; that the striae mark the
direction in which the ice moved, those faces of rock which looked
towards the ice being ground away, while those that looked away
from it more or less escaped. By following out the directions
of the rock-striae we can still trace the march of the ice across
the land (see Chapter VI.)
As the ice travelled it carried with it more or less detritus, as
a glacier does at the present day. Some of this material may
have lain on the surface, but probably most of it was pushed along
at the bottom or within the lower part of the body of the ice.
Accordingly, above the ice-worn surfaces of rock there lies a
396 POST-TERTIARY PERIODS CHAP.
great deposit of clay and boulders, evidently the debris that
accumulated under the ice-sheet and was left on the surface of the
ground when the ice retired. This deposit, called Boulder-Clay or
Till, bears distinct corroborative testimony to the movement of the
ice. It is always more or less local in origin, but contains a
variable proportion of stones which have travelled for a greater
or less distance, sometimes for several hundred miles. When
these stones are traced to their places of origin, which are often
not hard to find, they are found to have come from the same
quarter as that indicated by the striation of the rocks. If, for
example, the ice-worn bosses of rock show the ice to have crept
from north to south, the boulders will be found to have had a
northern source. The height to which striated rock-surfaces and
scattered erratic blocks can be traced affords some measure of the
depth of the ice-sheet.
From this kind of evidence it has been ascertained that the
whole of Northern Europe, amounting in all to probably not less
than 770,000 square miles, was buried under one vast expanse of
snow and ice. The ice-sheet was thickest in the north and west,
whence it thinned away southward and eastward. Upon Scandi-
navia it was not improbably between 6000 and 7000 feet thick.
It has left its mark at heights of more than 3000 feet in the
Scottish Highlands, and over North- Western Scotland it was prob-
ably not less than 5000 feet thick. Where it abutted upon the
range of the Harz Mountains it appears to have been still not far
short of 1500 feet in thickness.
This vast mantle of ice was in continual motion, creeping out-
ward and downward from the high grounds to the sea. The
direction taken by its principal currents can still be followed. In
Scandinavia, as shown by the rock-striae and the transport of
boulders, it swept westward into the Atlantic, eastward into the
Gulf of Bothnia, which it completely filled up, and southward
across Denmark and the low grounds of Northern Germany. The
basin of the Baltic was completely choked up with ice ; so also
was that of the North Sea as far south as the neighbourhood of
London. From the same evidence we know that the ice which
streamed off the British Islands moved eastward from the slopes
of Scotland into the hollow of the North Sea, part of it turning to
the left to join the south-western margin of the Scandinavian sheet,
and move with it northwards and westwards across the Orkney
and Shetland Islands into the Atlantic, and another branch bend-
ing southwards and moving with the southerly expansion of the
xxvii PLEISTOCENE 397
Scandinavian ice along the floor of the North Sea and the low
grounds of the east of England ; and that on the west side of
Scotland the ice filled up and crept down all the fjords, burying
the Western Islands under its mantle and marching out into the
Atlantic. . The western margin of the ice-fields, from the south-
west of Ireland to the North Cape of Norway, must have pre-
sented a vast wall of ice some 1200 or I 500 miles long, and prob-
ably several hundred feet high, breaking off into icebergs which
floated away with the prevailing currents and winds. The Irish
Sea was likewise filled with ice, moving in a general southerly
direction.
Northern Europe must thus have presented the aspect of
North Greenland at the present time. The evidence of rock-stricB
and ice-borne blocks enables us to determine approximately the
southern limit to which the great ice-cap reached. As even the
southern coast of Ireland is intensely ice-worn, the edge of the
ice must have extended some distance beyond Cape Clear, rising
out of the sea with a precipitous front that faced to the south.
Thence the ice-cliff swung eastwards, passing probably along the
line of the Bristol Channel and keeping to the north of the valley
of the Thames.
That the northern ice moved down the bed of the North Sea
is shown by the boulder-clays and transported stones of the eastern
counties of England, among which fragments of well-known Nor-
wegian rocks are recognisable. Its southern margin ran across
what is now Holland, and skirted the high grounds of Westphalia,
Hanover, and the Harz, which probably arrested its southward
extension. There is evidence that the ice swept round into
the lowlands of Saxony up to the chain of the Erz, Riesen, and
Sudeten Mountains, whence its southern limit turned eastward
across Silesia, Poland, and Galicia, and then swung round to the
north, passing across Russia by way of Kieff and Nijni Novgorod
to the Arctic ocean.
In North America three great centres of accumulation and dis-
persion of the sheet of land-ice have been recognised. One of
these covered the region of Labrador, and streamed thence south-
ward over the Eastern States and into the basin of the Mississippi.
The second lay over the country on the west side of Hudson Bay,
whence it marched across the plains westward to the Rocky
Mountains and southward across Canada as far as Iowa. The
third ice-sheet had its centre of origin on the great mountain
ranges of British Columbia. To the south of these vast sheets
398 POST-TERTIARY PERIODS CHAP.
of northern ice separate systems of glaciers were nourished in the
higher groups of mountains, such as the Sierra Nevada and the
Rocky Mountains.
In Europe no distinct topographical feature appears to mark
the southern limit reached by the ice-sheet ; this limit can only
be approximately fixed by the most southerly localities where
striated rocks and transported blocks have been observed. In
North America, however, the margin of the great ice-cap is
prominently defined by a mound or series of mounds of detritus
which seem to have been pushed in front of the ice. These
mounds, beginning on the coast of Massachusetts, run across the
Continent with a wonderful persistence for several thousand
miles. They form what American geologists call the "terminal
moraine."
The detritus left by the ice-sheet consists of earthy, sandy, or
clayey material (Boulder- Clay, Till) more or less charged with
stones of all sizes up to blocks weighing many tons. For the
most part it is unstratified, and- bears witness to the irregular way
in which it was tumbled down by the ice. In some districts,
where it has been more or less arranged in water, it assumes a
stratified character. The stones in the detritus, more especially
where they are hard and are imbedded in a clayey matrix, present
smooth striated surfaces, the striae usually running along the
length of the stone, but not unfrequently crossing each other, the
older being partially effaced by a newer set (Fig. 32). This
characteristic striation points unmistakably to the slow creeping
motion of land-ice.
But the boulder-clays, earths, and gravels left by the great ice-
sheet are not simply one continuous deposit. On the contrary,
they contain intercalations of stratified sand, clay, and even peat.
In these included strata, organic remains occur for the most part
those of terrestrial plants and animals, showing that the ice again
and again retreated, leaving the country to be covered with
vegetation, and to be tenanted by land -animals ; but that after
longer or shorter periods of diminution it once more advanced
southward over its former area. These intervals of retreat are
known as " interglacial periods." Probably they were of prolonged
duration, the climate becoming comparatively mild and equable
while they lasted. The occurrence of boulder-clays above the
interglacial deposits shows a subsequent lowering of the tempera-
ture, with a consequent renewal of glacial conditions.
The Pleistocene deposits thus reveal to us a prolonged period
PLEISTOCENE 399
of cold broken up by shorter intervals of milder climate. The
fossils which they contain throw curious and interesting light on
these oscillations of temperature. Among the plants, leaves of
Arctic species of birch and willow are found far to the south of
their present limits ; on the other hand, remains of plants now
confined to temperate latitudes are found fossil in Siberia, and
6 /
FIG. 220. Pleistocene or Glacial Shells, (a), Pecten islandicus (5) ; (b\ Nucucana
truncata () ; (c), Nuculana lanceolata. () ; (d), Tellina lata (i) ; (e), Saxicava
rugosa (J) ; (/), Natica clausa (?) ; (if), Trophon scalariforme (i).
others, now living in more genial climates than those of Central
Europe, are associated in interglacial deposits with the remains
of the still indigenous vegetation.
To the same effect, but still more striking, is the -testimony of
the Pleistocene fauna, with its strange mingling of northern and
southern forms. The marine shells imbedded in the glacial clays,
though chiefly belonging to species that still live in the adjoining
seas, include a few that are now restricted to more northern latitudes
400
POST-TERTIARY PERIODS
CHAP.
(Pecten islandicus, Nuculana lanceolata, N. truncata, Yoldia arctica,
Tellina lata, etc., Fig. 220). Turning- to the terrestrial mammals,
we find among the Pleistocene deposits the remains of the last of
FIG. 221. Mammoth (Elephas fr imigenius) from the skeleton in the Musee
Royal, Brussels.
the huge pachyderms which, through Tertiary time, had been so
striking a feature of the animal population of Europe. The hairy
mammoth (Elephas primigenitts, Fig. 221) and the woolly rhino-
ceros (R. tickorhinus) now roamed all over the Continent and
across Britain, which had not yet
become an island. During the
retreat of the snow and ice they
found their way into the forests
and pastures of Northern Siberia.
Driven southwards when the cold
increased, they were accompanied
or followed by numerous Arctic
animals which have not yet be-
come extinct. Herds of reindeer
FIG. 222. Back view of skull of musk- (Cetvus tarandus) sought the
sheep (Ovibos moschatus, j), Brick- pastures o f Central France and
earth. Cray ford. Kent. * . . , , . , ~ ,
Switzerland ; the glutton (Gulo
luscus] came to the south of England and to Auvergne ; the
musk-sheep (Ovibos moschattts, Fig. 222) and Arctic fox {Canis
lagopus} wandered southward to the Pyrenees. But as each
xxvii PLEISTOCENE 401
oscillation of climate slowly brought in a milder temperature, and
pushed the snow and ice northward, animals of southern types
made their way into Southern and Central Europe. Among
these immigrants were the porcupine (HystrLr\ leopard (Felis
pardtts}, African lynx (Felts pardina), lion (Felts leo], hyaena,
elephant, and hippopotamus, the bones of which have been found
in the Pleistocene deposits.
After the height of the cold period or Ice Age had been reached
and the general temperature of the northern hemisphere began to
rise again, the ice retreated from the low grounds, but still con-
tinued among the mountains. The existing snow-fields and
glaciers of the Alps, the Pyrenees, and Scandinavia are the lineal
descendants of those vaster ice-sheets which formerly overspread
so much of Europe. The glaciers of the Alps, large though they
are, can be shown to be merely the relics of their former size.
The glacier of the Rhone, for example, as is proved by rock-
strias and transported blocks, once extended i 70 miles in direct
distance from its modern termination, and rose hundreds of feet
above its present surface, burying the valleys and overflowing
considerable ridges of hills. The glacier of the Aar stretched
once as far as Berne a distance of about 70 miles from its
present termination ; and, judging from the marks it has left on
the mountains, it must have been not less than 4000 feet thick at
the Lake of Brienz.
Though elsewhere in Europe the glaciers have long ago
vanished from most of the high grounds, they have left unmis-
takable traces of their former presence. Thus in hundreds of
valleys among the Highlands of Scotland, in the Lake District,
and North Wales, admirably ice-worn bosses of rock and beauti-
fully perfect moraines may be seen. We can even trace, in the
succession of moraines that become smaller as .they approach the
head of a valley, the stages of retreat of the original glacier as
it shrank before the increasing warmth, till at last it disappeared
together with the snow-basin that fed it.
The spread of great sheets of land-ice and the growth of
valley-glaciers led to considerable interruption of the water-
drainage in the areas that were not overspread with ice. The
water was ponded back and formed lakes, which continued in
existence as long as their ice-barriers remained, and which, as
these barriers shrank, left memorials of their successive levels in
lines of horizontal terrace formed of their shore-deposits. The
most stupendous examples of such glacial lakes are to be found
2 D
402 POST-TERTIARY PERIODS CHAP.
in North America. The largest of them,, called Lake Agassiz
after the pioneer of glacial geology, is shown by its shore-lines to
have covered Manitoba and Minnesota for a length of 700 miles.
Its site is now partly occupied by Lakes Winnipeg and Manitoba
and a host of smaller sheets of water. The present Great Salt
Lake is the mere shrunk remnant of a vast lake which once
covered a great part of Utah, and to which the name of Lake
Bonneville has been given in memory of the explorer. Further
west lay another large expanse of water (Lake Lahontan). So
greatly has the climate changed in this region since glacial times
that the shrunken lakes of the great inland basin, having now
no outlet to the sea, have become saline and bitter. In Europe
some of the most famous glacial lakes are those of which the
successive levels are marked by the terraces known as " Parallel
Roads" in the west of Scotland (Fig. 20).
Other relics of the retirement of the ice-sheet are supplied by
the long mounds and heaps of gravel and sand, so abundantly
strewn over many low lands of Northern Europe. These some-
times form ridges, rising 20 or 30 feet above the ground on either
side of them, and running for a number of miles. Elsewhere they
are heaped together irregularly, often enclosing pools of water.
They are known as Osar in Sweden, Kames in Scotland, and
Eskers in Ireland.
During the later stages of the Ice Age the level of the land
in Western Europe was lower than it is now. When elevation
began, the upward movement continued, with long intervals of
rest, until the land reached its present position. These pauses
during the prolonged upheaval are marked by lines of raised beach
(p. 123), well seen along both sides of Scotland, and also along
the sea-margin of northern Norway. In North America also there
is evidence that the land stood at a lower level than now during
some part of the Glacial period. The depression in the valley
of the St. Lawrence appears to have been as much as from 500
to 600 feet. In consequence of this subsidence the sea deposited
over the submerged low grounds sheets of sand and gravel
(Champlain series), with marine shells and bones of cetacea.
So slowly and gradually did the great cold disappear that the
Ice Age insensibly passed into the Recent or existing period.
There can be no doubt that man appeared in Europe before the
climate had become as mild as it now is, for his flint-flakes and
bone implements are found associated with the bones of Arctic
anin'als in Central France,, and traces of his presence in rudely
xxvii RECENT 403
chipped stone instruments occur in deposits which point to frozen
rivers. Indeed, in a certain sense, it may be said that both in
Europe and in North America the Ice Age still survives among
the remaining snow-fields and glaciers.
Arranged in chronological order, the evidence from which the
history of the Pleistocene period is determined may be given as
follows :
Last traces of local glaciers ; terminal and lateral moraines ; shore-lines
(" parallel roads ") of ice-dammed lakes.
Marine terraces or raised beaches, sometimes with moraines resting upon
them ; rock-shelves cut probably by waves and floating ice, and marking
former levels of the sea. These beaches and shelves indicate pauses
during the last upheaval of the land. Marine deposits with Arctic shells
and bones of whales, walruses, and northern seals.
Erratic blocks chiefly transported by the great ice-sheet, but partly also by
floating ice during the rise of the land, and by valley-glaciers.
Sands and gravels (kames) arranged in heaps, mounds, and ridges, and due
in some way to the melting of the edges of the ice-sheet, often associated
with lacustrine deposits formed in their hollows, and containing lake-
shells and terrestrial plants and animals.
Boulder-clay, till, or bottom-moraine of the great ice-sheet ; the upper part
sometimes rudely stratified, and in some regions separated from the
lower part by a series of "middle sands and gravels" ; the lower part
unstratified and full of transported stones and boulders. Finely lamin-
ated clays, sands, layers of peat, and traces of terrestrial surfaces occur
at different levels in the boulder-clay, and mark intervals, or what have
been called " interglacial periods," of milder climate.
Polished and striated surfaces of rock, ground down by the movement of the
ice-sheet.
RECENT
The insensible gradation of what is termed the Pleistocene
into the Recent series of deposits affords a good illustration of the
true relations of the successive geological formations to each
other. We can trace this gradual passage because it is so recent
that there has not yet been time for those geological revolutions,
which in the past have so often removed or concealed the
evidence that would otherwise have been available to show that
one period or one group of formations merged insensibly into that
which followed it.
The recent formations are those which have been accumulated
since the present general arrangement of land and sea, the
present distribution of climate, and the present floras and faunas
of the globe were established. They are particularly distinguished
by traces of the existence of man. Hence the geological age to
404 POST-TERTIARY PERIODS CHAP.
which they belong is spoken of as the Human period. But, as
has already been pointed out, there is good evidence that man
had already appeared in Europe during Pleistocene time, so that
the discovery of human relics does not afford certain evidence
that the deposit containing them belongs to the Recent series.
Nevertheless, it is in this series that vestiges of man become
abundant, and that the proofs of his advancing civilisation are
contained.
Man differs in one notable respect from the other mammals
whose remains occur in a fossil state. Comparatively seldom are
any of his bones discovered as fossils ; but he has left behind
him other more enduring monuments of his presence in the form
of implements of stone, metal, bone, or wood. These relics are
in a sense more valuable than his bones would have been, for
while they afford us certain testimony to his existence, they give
at the same time some indication of his degree of civilisation and
his employments. His handiwork thus comes to possess much
geological value ; his stone hatchets, flint -flakes, bone needles,
and other pieces of workmanship are to be regarded as true
fossils, from which much regarding his early history may be
determined.
In the river valleys of the north-west of France and south-east
of England human implements have been found imbedded in
the higher alluvial terraces. After careful exploration, it has been
ascertained that these objects have not been buried there sub-
sequently, but must have been covered up at the time the gravel
was being formed. The higher terraces are, of course, the older
deposits of the rivers, which have since deepened their valleys, until
they now flow at a much lower level (p. 43). The excavation of
valleys is a slow process. Within a human lifetime no appreci-
able lowering of the ground from this cause may be detected.
Even during the many centuries of which we have authentic human
records we can hardly anywhere obtain signal proof of such a
change. How vast then must have been the interval between the
time when the rivers flowed at the level of the upper terraces and
the present day ! Other evidence of the great age of these higher
alluvia is to be found in the number of extinct animals whose
remains are buried in them. The human implements likewise
bear their testimony in support of the antiquity of the terraces, for
they are extremely rude in design and construction, indicative of a
race not yet advanced beyond the early stages of barbarism. In the
lower., and therefore younger terraces, and in other deposits which
xxvir RECENT 405
may also be regarded as belonging to a later date, the articles of
human fabrication exhibit evidence of much higher skill and more
tasteful design, whence they have been inferred to be the work-
manship of a subsequent period when men had made considerable
progress in the arts of life. Accordingly, a classification has
been adopted based upon the amount of finish in the stone
weapons and implements, the ruder workmanship being assumed
to mark the higher antiquity. The older deposits, with coarsely
chipped and roughly finished human stone implements, are
termed Palaeolithic, and the younger deposits with more
artistically finished works in stone, bone, or metal, are known as
Neolithic. It will be understood that this arrangement is one
rather for convenience of description than for a determination of
true chronological sequence. It is quite probable, for example,
that some of the palaeolithic gravels date back to the Pleistocene
Ice Age, while other deposits containing similar weapons, together
with an assemblage of extinct mammals, may belong to a much
later time, when the ice had long retreated to the north. It is
obvious, too, that we know nothing of the relative progress made
in the arts of life by the early races of man. One race may have
continued fashioning the palaeolithic type of implement long after
another race had already learnt to make use of the neolithic type.
Even at the present day we see some barbarous races employing
rude weapons of stone, not unlike those of the palaeolithic gravels,
while others fabricate stone arrow-heads and implements of bone
exactly resembling those of the neolithic deposits. It would
hardly be incorrect to say that, in some respects, certain tribes
of mankind are still in the palaeolithic or neolithic condition of
human progress.
i. Palaeolithic
The formations included under this term are distinguished by
containing the rudest shapes of human stone implements, asso-
ciated with the remains of mammals, some of which are entirely
extinct, while others have disappeared from the districts where
their remains have been found. These deposits may be con-
veniently classed under the heads of alluvium, brick-earth, cavern-
beds, calcareous tufas, and loess.
Alluvium. Reference has just been made to the upper
river-terraces, which, rising sometimes 80 or 100 feet above the
present level of the rivers, belong to a very ancient period in the
406
POST-TERTIARY PERIODS
CHAP.
history of the excavation of the valleys, and yet contain rude
human implements. The mammalian bones found in the sands,
loams, and gravels of these terraces, include extinct species of
elephant, rhinoceros, hippopotamus, and other animals. The
human tools are roughly- chipped pieces of flint or other hard
stone, and their abundance in some river-gravels has suggested
the belief that they were employed when the rivers were frozen
over, for breaking the ice and other operations connected with
FIG. 223. Palaeolithic Implements, (a), Flint implement, reculver (^), chipped out of a
rounded pebble ; (), flint implement (J) from old river-gravel at Biddenham, Bedford,
where remains of cave-bear, reindeer, mammoth, bison, hippopotamus, rhinoceros,
and other mammalia have been found ; (c), bone harpoon-head (t) from the red
cave-earth underlying the stalagmite floor of Kent's Cavern (a and b reduced from
Sir John Evans's " Ancient Stone Implements ").
fishing. The high river-gravels of the Somme and of the valleys
in the south-east of England have been specially piolific in these
traces of early man.
Brick-earth. On gentle slopes and on plains, the slow
drifting action of wind and rain transports the finer particles of
soil, and accumulates them as a superficial layer of loam or brick-
earth. In the south-east of England considerable tracts of
country have been covered with a deposit of this nature. It is
still in course of accumulation, but, as already stated (p. 20), its
lower parts must date back to a high antiquity, for they contain
xxvn RECENT 407
the bones of extinct mammals, together with human implements
of Palaeolithic type.
Cave-earth and stalagmite. The origin of caverns in lime-
stone districts was described in Chapter V., and reference was
made to the formation of stalagmite on their floors, and to the
remarkably perfect preservation of animal remains in and beneath
that deposit. Many of these caves were dens tenanted by hyaenas
or other beasts of prey (p. 65). Some of them were inhabited by
man. In certain cases they have communicated with the ground
above by openings in their roofs, through which the bodies of
animals have fallen or been washed by floods. The stalagmite,
by covering over the bones left on the floor of the caverns, or in
the earth deposited there by water, has preserved them as a
singularly interesting record of the life of the time.
Calcareous Tufa. Here and there the incrustation of tufa
formed round the outflow of calcareous springs has preserved the
remains of the vegetation and of rhe land-animals of the Palaeolithic
time (compare Fig. 27).
Loess. This is the name given to a remarkable accumulation
of pale yellowish calcareous sandy earth which occurs in some of
the larger river valleys of Central Europe, especially in those of
the Rhine and the Danube ; it likewise covers vast regions of
China, and is found well developed in the basin of the Mississippi.
It is unstratified and tolerably compact, so that it presents steep
slopes or vertical walls along some parts of the valleys, and can
be excavated into chambers and passages. In China subterranean
villages have been dug out of it along the sides of the valleys
which it has filled up. It contains remains of terrestrial plants
and snail-shells, also occasional bones of land-animals. It bears
little or no relation to the levels of the ground, for it crosses over
from one valley to another, and even mounts up to heights several
thousand feet above the sea and far above the surrounding valleys.
Its origin has been the subject of much discussion among geologists
and travellers. But the result of much careful investigation
bestowed upon it goes to show that the loess is probably, for the
most part, a sub -aerial deposit formed by the long -continued
drifting of fine dust by the wind. It was probably accumulated
during a comparatively dry period. At that time the climate of
Central Europe, after the disappearance of the ice-sheet, probably
resembled that of the steppes of the south-east of Russia at the
present day. The assemblage of animals whose bones have been
found in the loess closely resembles that of those steppes ; for it
408
POST-TERTIARY PERIODS
CHAP.
includes species of jerboa, porcupine, wild horse, antelope, etc.
Among its fossils, however, there occur also the bones of the
mammoth, woolly rhinoceros, musk-sheep, hare, wolf, stoat, etc.,
together with Palaeolithic stone implements.
Thus the association of animals in the Palaeolithic formations
shows a commingling of the denizens of warmer and colder
climates, like that already noticed as characteristic of the Ice Age,
and hence the inference above alluded to has been drawn, that
1
FIG. 224. Antler of Reindeer (,' T ) found at Bilney Moor, East Dereham, Norfolk.
the Palaeolithic gravels may themselves be interglacial. Among
the animals distinctively of more southern type mention may
be made of the lion, hyasna, hippopotamus, lynx, leopard,
Cafifer cat ; while among the northern forms are the glutton,
Arctic fox, reindeer (Fig. 224), Alpine hare (Leflus variabilis},
Norwegian lemming (Myodes torquatus), and musk-sheep. The
animals which then roamed over Europe, but are now wholly
extinct, included the mammoth, woolly rhinoceros, and other
species of the same genus, Irish deer (Megaceros hibernicus),
and cave-bear ( Ursus spelaus). The traces of man consist almost
RECENT 409
entirely of pieces of his handiwork ; only rarely are any of his
bones to be seen. Besides the rudely-chipped flints, he has left
behind him, on tusks of the mammoth and horns and bones of
the reindeer and other animals, preserved in the stalagmite of
cavern -floors, vigorous incised outline sketches and carvings re-
presenting the species of animals with which he was familiar, and
some of which have long died out. He was evidently a hunter
and fisher, living in caves and rock -shelters, and pursuing with
flint-tipped arrow and javelin the bison, reindeer, horse, mammoth,
rhinoceros, cave-bear, and other wild beasts Of his time.
2. Neolithic
In this division the human implements indicate a considerable
advance in the arts of life, and the remains of the mammoth,
rhinoceros, and other prevalent extinct forms of the Palaeolithic
series are absent. The deposits here included consist of river-
gravels, cave -floors, peat -bogs, lake bottoms, raised beaches,
sand-hills, pile-dwellings, shell-mounds, and other superficial
accumulations in which the traces of human occupation have been
preserved.
After the extinction of the huge pachyderms the European
fauna assumed the general character which it now presents, but
with the presence of at least one animal, the Irish deer, that has
since become extinct, and of others, such as the reindeer, elk, wild
ox or urus, grizzly bear, brown bear, wolf, wild boar, and beaver,
which, though still living, have long been extirpated from many
districts wherein they were once plentiful. This local extinction
has no doubt, in many if not in most cases, been the result, directly
or indirectly, of human interference. But man not only drove out
or annihilated the old native animals. As tribe after tribe of
human population migrated into Europe from some region in Asia,
they carried with them the animals they had domesticated the
hog, horse, sheep, goat, shorthorn, and dog. The remains of
these creatures never occur among the Palaeolithic deposits ; they
make their appearance for the first time in the Neolithic accumula-
tions, whence the inference has been drawn that they never formed
part of the aboriginal fauna of Europe, but were introduced by the
human races of the Neolithic period.
The stone articles of human workmanship found in Neolithic
deposits consist of polished celts and other weapons, together with
hammers, knives, and many other implements of domestic use.
4io
POST-TERTIARY PERIODS
Knives, needles, pins, and other objects were made out of bone or
horn. There is evidence also that the arts of spinning, weaving,
and pottery-making were not unknown. The discovery of several
kinds of grain shows that the Neolithic folk were also farmers.
Vast numbers of these various relics have been found at the pile-
dwellings of Switzerland and other countries. For purposes of
security these people were in the habit of constructing their
FIG. 225. Neolithic Implements, (a), Stone axe-head (J) ; (3), harbed flint arrow-head
(natural size) ; (c), roughly-chipped flint celt (); (d), polished celt (J), with part or
its original wooden hand still attached, found in a peat-bog, Cumberland ; (e), bone-
needle (natural size), Swiss lake dwellings ; a, l>, c, d, reduced from Sir John
Evans's "Ancient Stone Implements.'
wooden dwellings in lakes, on foundations of beams, wattled-work,
stones, and earth. Sometimes these erections were apt to be
destroyed by fire, as well as to decay by age. And their places
were taken by new constructions of a similar kind built on their
site. Hence, as generation after generation lived there, all kinds
of articles dropped into the lakes were covered up in the silt that
slowly gathered on the bottom. And now, when the lakes are
drained, or when their level is lowered by prolonged drought,
these accumulated droppings arc laid open for the researches of
antiquaries and geologists.
xxvii RECENT 411
Many important relics of Neolithic man have likewise been
obtained from the floors of caverns and rock-shelters places
that from their convenience would continue to be used as
in Paleolithic time. Interesting evidence, also, of the succes-
sive stages of civilisation reached by early man in Europe
is supplied by the older Danish peat-bogs, in the lower parts of
which remains of the Scotch fir (Pinus sylvestris), a tree that
had become extinct in that country before the historic period,
are associated with Neolithic implements. In a higher layer of
the peat trunks of common oak are found, together with bronze
implements, while in the uppermost portion the beech-tree and
iron weapons take their place.
Between the Neolithic and the present period no line can be
drawn. They shade insensibly into each other, and the materials
from which the history is compiled of their geographical and
climatal vicissitudes, their changes of fauna and flora, and their
human migrations and development, form a common ground for
the labours of the archaeologist, the historian, and the geologist.
During the Recent period the same agencies have been and
are at work as those which were in progress during the vast
succession of previous periods. In the foregoing pages we have
followed in brief outline each of these great periods, and after
this survey we are led back again to the world of to-day with
which the first chapters of this book began. In this circle of
observation no trace can anywhere be detected of a break in the
continuity of the evolution through which our globe has passed.
Everywhere in the rocks beneath our feet, as on the surface of the
earth, we see proofs of the operations of the same laws and the
working of the same processes.
Such, however, have been the disturbances of the terrestrial
crust that, although undoubtedly there has -been no general
interruption of the Geological Record, local interruptions have
almost everywhere taken place. The sea-floor of one period has
been raised into the dry land of another, and again, the dry land,
with its chronicles of river and lake, has been submerged beneath
the sea. Each hill and ridge thus comes to possess its own
special history, which it will usually reveal if questioned in the
right way.
We are surrounded with monuments of the geological past.
But these monuments are being slowly destroyed by the very
same processes to which they owed their origin. Air, rain, frost,
springs, rivers, glaciers, the sea, and all the other connected agents
412 POST-TERTIARY PERIODS CHAP, xxvn
of demolition, are ceaselessly at work wherever land rises above
the ocean. It is in the course of this demolition that the character-
istic features of the scenery of the land are carved out. The
higher and harder parts are left as mountains and hills, the softer
parts are hollowed out into valleys, and the materials worn away
from them are strewn over plains. And as it is now, so doubtless
has it been through the long ages of geological history. Decay
and renovation in never-ending cycles have followed each other
since the beginning of time.
But amid these cycles there has been a marvellous upward
progress of organic being. It is undoubtedly the greatest triumph
of geological science to have demonstrated that the present plants
and animals of the globe were not the first inhabitants of the
earth, but that they have appeared only as the descendants of a vast
ancestry, as the latest comers in a majestic procession which
has been marching through an unknown series of ages. At the
head of this procession we ourselves stand, heirs of all the progress
of the past and moving forward into the future, wherein progress
towards something higher and nobler must still be for us, as it has
been for all creation, the guiding law.
APPENDIX
THE VEGETABLE KINGDOM
I. CRYPTOGAMS OR FLOWERLESS PLANTS 1
THESE bear spores that differ from true seeds in consisting only of one or
more cells without an embryo. They include the following divisions :
Algae Fungi. These embrace the smallest and simplest forms of
vegetation fresh-water confervae, desmidiae, mushrooms, lichens, sea-
weeds, etc. Some of them secrete carbonate of lime and form a stony
crust, as in the case of the marine nullipores (p. 94), others secrete
silica, as in the frustules of diatoms (p. 40, Fig. 94). These hard
parts are most likely to occur as fossils ; but impressions of some of
the larger kinds of sea- weeds may be left in soft mud or sand (pp. 269,
277). Fungi are not well adapted for preservation, but traces of them
have been noticed even in rocks of the Carboniferous period.
Characese are fresh-water plants, some of which abstract carbonate of
lime from the water and deposit it as an incrustation on their surface.
Hence their calcined nucules or spiral seed -like bodies [gyrogonites]
and stems may accumulate at the bottom of lakes.
Muscineae, mosses, and liverworts afford little facility for fossilisation.
But some of the mosses (sphagnum, etc.) form beds of peat (p. 92).
Filices, ferns, bearing fronds on which are placed the sporangia or
spore-cases. Many of them possess a tough tissue which can for
some time resist decomposition. Traces of ferns are consequently
abundant among the fossiliferous rocks (Figs. 145, 155, 174).
Ophioglossaceae, adder's tongues and moonworts.
Rhizocarpese, pepperworts.
Equisetacese, horse-tails, with hollow striated siliceous jointed stems or
shoots (Figs. 157, i7"9). These stems possess considerable durability,
and where buried in mud or marl may retain their forms for an in-
definite period. Allied plants \_Calamites, Fig. 157] have been
abundantly preserved among some of the older geological formations
(Old Red Sandstone, Carboniferous, Permian).
Lycopodiacese, club-mosses, plants with leafy branches like mosses,
growing in favourable conditions into tree -like shrubs that might be
1 Names placed within square brackets [ ] are fossil forms.
413
4 i4 APPENDIX
mistaken for conifers. Their dichotomous stems and their fertile
branches, which resemble cones and bear spore-cases, offer themselves
for ready preservation as fossils. The spores are highly inflammable,
and it is worthy of notice that similar spores have been detected in
enormous abundance in the Carboniferous system. Lycopodium and
Selaginella are familiar living genera. (For an extinct form see Fig.
156, p. 301.)
II. PHANEROGAMS OR FLOWERING PLANTS
i. GYMNOSPERMS or plants with naked seeds ; that is, seeds not enclosed
in an ovary.
Cycadese, small plants resembling both palms and tree-ferns. The
pinnate leaves are hard and leathery, and have been frequently pre-
served as fossils. Cycas and Zamia are two typical genera (Figs.
179 , 186).
' Coniferee, the Pine family. The stiff hard leaves and the hard seed-
cones may be looked for in the fossil state (Figs. 174^, 179^). The
resinous wood also sometimes long resists decomposition, and may be
gradually petrified. Trunks of pine are often met with in peat-mosses.
The Coniferas include the following subdivisions :
1. Cupressineas, cypresses, including Jitniperus (Juniper), Libo-
cedrus, Thuja, Thujopsis, Cupressus, Taxod^^lm, Glyptostrobus.
2. Abietineae, pines and firs, including Pinus, Abies, Cedrus,
Araucaria (p. 333), Dammara, Cunninghamia, Sequoia.
3. Podocarpeae, trees growing in New Zealand, Java, China,
Japan, etc., bearing a succulent fruit or a thick fleshy stalk.
4. Taxineas, yews, plants with fleshy fruit, including the genera
Taxus, Salisburia, Phyllocladi) Trichechids or walruses ; (c)
Phocids or true seals.
Primates, the highest division of vertebrate life, comprising (i) the
Lemuroid animals ; (2) the Hapalids or marmosets ; (3) the Cebids
or American monkeys ; (4) the Cercopithecids, the monkeys of the Old
World, exclusive of the apes ; (5) the Simiids or man-like apes
(Troglodytes, Gorilla, Simia, and Hylobates] ; (6) Man.
INDEX
An asterisk (*) denotes that a figure of the subject will be found on the page indicated.
Aar Glacier, former extension of,
401
Abies, 390
Abysmal deposits of the ocean, 88,
94*, 96*. 102
Acacia, fossil, 381
Acadian series, place of, in Geological
Record, 257, 275
Acanthodes, 290*
Acanthodian fishes, 289
Acer, 369, 387
Acervularia, 293
Acid rocks, 178
Acids and bases, 129
Acids, organic or humous, influence
of, in geological changes, 17, 27,
54, 60, 91, 175
Acrodus, 327, 337
Acrssalenia, 334
Acrydiidse, fossil, 304
Acteeon, 390
Actinodon, 321
Actinolite, 147, 189
Actinoliteschist, 190
Adelsberg, caverns at, 61
sEgoceras, 337
Africa, Carboniferous system in, 312 ;
Permian rocks of, 316 ; Trias in,
331 ; Cretaceous system in, 349 ;
Eocene rocks in, 368
Agave, 369
Agglomerate, 170
Agnopterus, 370
Agnostus, 271, 272*
Air, geological work of the, 1 1
Air-breathers, fossil, 304
Alabaster, 151
Alaska, glaciers of, 74*
Albian stage, 358, 359
Albite, 146, 178
Alcyonarian corals, 279*
Alder, fossil, 350, 387, 388*
Alethopteris, 300*, 332
Algae ; see Seaweeds
Algonkian, place of, in Geological
Record, 257 ; rocks described,
262
Alkali metals, 136
Alkaline carbonates, 133, 143
Alkaline earths, 136
Allotriomorphic crystals, 177
Alluvial cones or fans, 40*
Alluvium, formation of, 38, 42* ;
palaeolithic remains in, 405
Almond, fossil, 369
Alnus, 387, 388*
Aloe, fossil, 369
Alps, glaciers of, 72, 74, 79, 401 ;
great thrust-planes in, 221 ; pre-
Cambrian nucleus of, 262 ; Silurian
rocks in, 285 ; Carboniferous rocks
in, 312 ; Permian volcanic action
in, 316 ; Permian system in, 319 ;
Trias of, 324, 326, 330 ; Jurassic
rocks in, 344, 345 ; Cretaceous
rocks of, 348 ; Tertiary formations
in, 365 ; Eocene of, 368, 373 ;
Miocene of, 383, 385 ; successive
uplifts of, 366, 380, 385, 387
Alum, 153, 188
Alum-slate, 188, 276
Alumina, 131 ; silicates of, 131, 145
430
INDEX
Aluminium in earth's crust, 129, 131
Alveolaria, 391
Alveolites, 306
Amaltheus, 337
Amber, insects in, 239, 240
Amber Beds of Konigsberg, 379
Ambonychia, 283
America, North, glaciation of, 77 ;
peat-bogs of, 93 ; fissure-eruptions
of, 119 ; Geological Record in,
256 ; pre-Cambrian rocks of, 262 ;
Cambrian rocks of, 275 ; Silurian
system in, 286 ; Devonian system
in, 287, 295 ; Carboniferous system
in, 312 ; Permian rocks of, 316,
321 ; Trias of, 331 ; Jurassic rocks
in, 346 ; Cretaceous rocks of, 349,
357, 363 ; Tertiary formations in,
366 ; Eocene of, 368, 372, 374 ;
Oligocene of, 379 ; Miocene of,
385 ; Pliocene of, 393 ; glaciation
of, 394- 397
Amethyst, 142
Ammonia, 137
Ammonites, 246, 319, 322, 323, 326,
3 2 7*. 33- 336*, 354*, 305
Amomum, 369
Amorphous condition of minerals,
141
Amphibia, fossil, 304, 305, 319, 320*,
323- 326
Amphibole, 147
Amphibolites, 190
Amphitherium, 341
Am pyx, 281
Amygdaloidal structure, 107*, 108,
109*. 147*, 183
Amygdalus, 369
Ananchytes, 352*
Anchilophus, 371
A nchitherium ,379
Anchor-ice, 69
Ancyloceras, 354*, 355
Andalusite-slate, 188
Andes, volcanic rocks of, 183
Andesine, 146
Andesite, 182
Angelina, 174
Anhydrite, 151, 172, 315, 321, 324,
330
Animals and plants as material's for
geological history, 6 ; preservation
of remains of, 6, 91 ; geological
action of, 91 ; deposits formed of
remains of, 95 ; preservation of
remains of, in sediments, 99 ; dis-
appearance of terrestrial, 100, 239 ;
conditions for preservation of re-
cords of, 100, 101, 238 ; durable
parts of, 240
Annelids, earliest known, 271 ;
Silurian, 281
Anoplotherium, 246, 377
' Anorthite, 146
Ant, white, removal of soil by, 19
Antelopes, fossil, 371, 382, 387,
408
Anthracite, 175
Anthracomya, 304, 309*
Anfkracoiaurus, 305
Anthracosia, 304
Anthracotherium, 377
Anthrapalsemon, 308
Anticline, 213*, 215*, 217*
Apatite, 152
Apes, fossil, 246, 382, 388
Aplite, 179
Aptian, 359
Aqueous, definition of, 158
Aqueous solution, crystallisation from,
158
Aquitanian stage, 379
Arachnids, fossil, 240
Aragonite, 150
Aralia, 350
Araucarian pines, fossil, 303, 332
Araucarioxylon, 303
Araucarites, 325
Area, 384, 391, 393
Arcesles, 326
Archaean, place of, in Geological
Record, 257; formations described,
258
Archseocidans, 306, 307
Archeeopteryx, 340*, 341
Archegosaurus, 305
Architecture and Geology compared,
7
Arctic regions, Jurassic flora of, 333 ;
Miocene flora of, 385
Arctic vegetation once spread over
much of Europe, 395
Annicolites, 281
Arenig group, place of, in Geological
INDEX
Record, 257, 286 ; possibly in-
cluded in "Dalradian," 261
Argillaceous cement in sandstone,
167, 168
Argillornis, 370
Aridity and weathering, 24
Arietites, 337
Arnusian, 392
Aroids, fossil, 368
Asaphns, 174, 281, 282*
Asbestus, 147
A sc oc eras, 283
Ashdown Sand, 359
Ashes, volcanic, in, 169, 190, 229*,
210
Aspidoceras, 337
Asplenium, 351, 368
Assise in stratigraphy, 248
Astarte, 335, 390
Asterophyllites, 302*, 303
Astian, 392
Astronomy and Geology, 252
Athyris, 293, 308
Atlanlosaurus, 341
Atmosphere, composition of, 129 ;
probable origin of the, 253, 254
Atolls, 98, 123
Atrypa, 282, 283*, 293
Auchenaspis, 284
Augite, 140*, 148, 184
Augite-andesite, 182
Augite-diorite, 182
Augite-picrite, 184
Australia, Great Barrier Reef of, 99 ;
pre-Cambrian rocks of, 263 ; Cam-
brian rocks of, 275 ; Silurian rocks
of, 285 ; Permian rocks of, 316 ;
Trias in, 331 ; Jurassic rocks in,
346 ; Cretaceous rocks in, 364
Auvergne, extinct volcanoes of, 106
Avalanches, 70
Avicula, 326, 327*
Aviculopecten, 305, 309*
Axes of crystals, 138
Axmouth, landslip of, 58
Aymestry Limestone, 286
Babylon, buried under wind -borne
soil, 21
" Backs" in quarrying, 208
Bactrites, 295
Baculites, 354*. 355
Bad lands of the United States, 374,
375*
Bagshot Sands, 373
Baiera, 325
Bajocian, 342, 343
Bakevellia, 319*
Bala group, place of, in Geological
Record, 257, 286
Baltic Sea, once filled with ice, 74,
396
Bamboo, fossil, 387
Banding of gneiss, 258, 260
Bannisdale Flags, 286
Baphetes, 305
Barium in earth's crust, 129, 136,
IS 1 . 2 34
Barnacles as evidence of elevation of
land, 123
Bars at river-mouth and on coast, 86
Barton Clay, 373
Barytes, 136, 151, 234
Basalt, 184, 185*; altered into am phi-
bolite, 190
Basalt-glass, 183, 232
Basalt -rocks, 183
Basalt-tuff, 169
Basaltic (columnar) structure, 184
Base-level of erosion, 38, 85
Base or ground -mass of igneous
rocks, 159, 177
Bases and acids, 129
Bath Oolite, 342, 344
Bathonian, 342, 343
Bats, fossil, 371, 377
Beaches, raised, 123, 403
Bears, fossil, 379, 382, 386, 387,
408, 409
Beavers, fossil, 382, 386, 390, 409
Bed (in stratigraphy), 158, 194, 247
Bedding, false, 195 ; deceptive in
schists, 258
Beech, fossil, 350, 369, 381; -in
Danish peat-bogs, 411
Beetles, fossil, 337, 382
Belemnitella, 357
Belemnites, 336*, 355, 359
Bellerophon, 273, 283, 284*, 310*
Bembridge group, 377
Bermuda, limestone formed out of
calcareous sand at, 95, 167
Beryl, 179
Beryx, 355
432
INDEX
Betula, 387
Biotite, 147
Birch, fossil, 387, 399
Birds, fossil, 246, 340*, 341, 357,
370
Bird's-eye Limestone, 286
Bison, 409
Black Jura (of Germany), 343
Black River group, 286
Blackthorn, fossil, 390
Blastoid Echinoderms, 246, 307*
Blattidaz, fossil, 304
Bleaching of rocks by organic matter,
17
Blende, 235
Blocks, erratic, 72*, 73*, 76*, 396 ;
volcanic, 112, 169, 229
Blow-holes, 80, 81*
Boar, fossil, 392, 409
Bog-bean, fossil, 390
Bog-iron-ore, 144
Bog-manganese, 145
Bognor Beds, 373
Bogs ; see Peat
Bolodon, 341
Bolosaurtis, 320
Bombs, volcanic, 169
Bone-beds, 176, 330, 407
Bone-breccia, 176
Bone-caves, 65, 101, 176, 407, 409,
411
Bosses, 225, 226*, 227*
Boulder-clay, 396, 403
Bracheux, sands of, 373
" Brachiopods, Age of," 273
Brachiopods, fossil. 273*, 282, 283,
294*, 308, 309*, 318*. 334, 352
Brachymetopus, 308
Bracklesham Beds, 373
Bradford Clay, 342
Brahmaputra, delta of, 86
Bramatherium, 393
Branchiosaurus, 320*
Breakers ; see Waves
Breaks in stratigraphical succession,
247
Breccia, Brecciated, 164, 165*, 169
Brick-clay, 168
Brick-earth, 20* ; relics of man in,
406
Bridger group, 374
Britain, progress of sand-dunes in,
21 ; amount of dissolved mineral
matter removed annually from
parts of, 29; lake-marl of, 53; salt
and gypseous deposits in, 55; land-
slips in, 58, 59*, 60 ; caverns of,
61; glaciation of, 73*, 74, 79, 396,
401 ; force of breakers on coasts
of, 80, 83* ; waste of coast-line of,
82 ; gain of land in, 87 ; former
volcanic action in, 106, 112, 232,
268, 276, 288, 301, 316, 376, 377;
volcanic dust from Iceland trans-
ported by winds to, 113 ; fissure-
eruptions in, 1 20 ; pitchstone of,
181 ; trachyte of, 182 ; curved
strata in, 213*, 214*; cleaved strata
in, 217; lines of great fault in, 219,
220* ; dykes crossing faults in,
2 33* ! fossil scorpions of, 240,
304*; pre-Cambrian rocks of, 260 ;
Cambrian rocks of, 274 ; Silurian
rocks of, 276, 285, 286; Devonian
system in, 287, 295; Old Red Sand-
stone of, 288; Carboniferous system
in, 296, 301, 312 ; Permian rocks
of, 314, 316, 320 ; Trias of, 323,
329 ; Jurassic system in, 341 ;
Tertiary formations of, 367; Eocene
f. 373 I Oligocene of, 376, 377 ;
denudation of, inTertiarytime, 383;
Pliocene of, 389 ; Pleistocene of,
396, 397, 401, 402; Recent forma-
tions of, 404, 406
Brittle-stars, 281
Bronleus, 292*, 293
Brontosaurus, 340
Brontotherium, 379
Bronzite, 184, 186
Brooks, transport of soil by, 22 ;
chemical action of, 27, 28* ;
mechanical action of, 29
Brown coal, 175, 376, 379
Brown, colour, cause of, in rocks,
132, 144, 167
Brown iron-ore, 143, 173
Bruxellian, 373
Buckthorn, fossil, 351, 387
Buhrstone, 374
Bunter group, 329
Burrows of worms, 92, 237, 281
Buttes or rock-masses left by sub-
aerial waste, 23*
INDEX
433
Cactus, fossil, 368
Caen-stone, 344
Caffer cat, fossil, 408
Caillasses, 373
Cainozoic formations, place of, in
Geological Record, 257 ; account
of, 3 6 5
Cairngorm stones, 142
Catamites, 289, 302*, 317
Calc-sericite-schist, 190
Calc-silicate-hornfels, 188
Calc-sintcr, formation of, 65 ; pre-
servation of remains of plants and
animals in, 66, 101
Calcaire-grossier, 373
Calceola, 293*
Calciferous group, place of, in Geo-
logical Record, 257, 286
Calcification of organisms, 242
Calcite, 138*, 149*, 150*, 156 ; in
mineral veins, 234
Calcium, in earth's crust, 129, 132
Calcium-carbonate; j^Lime, Carbon-
ate of
Calcium-sulphate ; see Gypsum
Callipteris, 317*, 318
Ca Hi iris, 369
Callovian, 342, 344
Calymene, 281
Camarophoria, 318*
Cambrian, place of, in Geological
Record, 257; formations described,
267 ; origin of name, 267
Camels, fossil, 386, 393
Camptonnis, 357
Camptonite, 181
Canada, frozen rivers of, 69 ; coast-
ice of, 69 ; ancient ice-sheets of,
74. 79. 397 I Archaean rocks of,
262 ; Cambrian rocks of, 275 ;
Silurian rocks of, 285 ; Devonian
and Old Red Sandstone of, 288,
289, 295 ; Carboniferous system
in, 299 ; Permian system of, 321 ;
Trias in, 331 ; Jurassic rocks in,
346 ; Cretaceous rocks of, 363 ;
older Tertiary formations in, 379 ;
Pleistocene deposits in, 402
Cancellaria, 384, 390
Canis, 400
Canons, erosion of, 36, 37*
Caprina, 353
Capulus, 390
Caradoc group, place of, in Geological
Record, 257, 286
Carbon in earth's crust, 129, 134,
137
Carbon-dioxide, 134 ; proportion of,
in the atmosphere, 134 ; solubility
of, in water, 134
Carbonates, formed by rain-water,
14 ; oxidation and precipitation of,
17 ; in saline lakes, 55, 56 ; solu-
tion of, by percolating water, 61 ;
alkaline, 133, 134 ; in the earth's
crust, 137, 149
Carbonic acid, influence of, in weather-
ing, 14 ; action of, in solution of
carbonates, 61, 95, 96 ; com-
position of, 134
Carboniferous, place of, in Geological
Record, 257 ; system, account of,
296
Carboniferous Limestone, 257, 296,
35- 3 12
Carbonisation of plants, 241
Cardioceras, 336
Cardita, 384
Cardium, 326, 327*, 377, 384, 390
Carnallite, 330
Carnivores, fossil, 372, 377, 382,
387
Carpinus, 369
Carpolithes, 303*
Carya, 387
Caryocaris, 282
Cassia, fossil, 351
Castanea, 369
Casts and moulds of organisms in
rocks, 241*
Cat, fossil, 382, 387
Catopterus, 327
Catskill group, place cf, in Geological
Record, 257, 295
Cauda-galli grit, 295
Caulopteris, 318
Cave-bear, 408
Cave-earth, human relics in, 407
Caverns, formation of, in limestone,
61, 62* ; preservation of animal
remains in, 407, 408 ; sometimes
hollowed out by the sea, 80, 84*
Cellular structure, 107*, 108, 109*,
1 60
2 F
434
INDEX
Cellulose of plants, 239
Cement-stone, 342, 343
Cementation of sediment, 207
Cenomanian stage, 357, 360
Cephalaspis, 246, 284, 290, 291*
Cephalopods, early fossil, 274, 283,
285*, 294*. 295, 310*. 319, 326,
336*, 354*. 355
Ceratiocaris, 282, 283*
Ceratites, 326, 327*
Ceratodus, 290, 327
Ceratophyllum, 390
Cerithium, 342, 369*
Cerithium-stage (Miocene), 384
Cervus, 246, 400
Ceteosaurus, 340
Chseropoiamus, 377
Ch&tetes, 306
Chalcedony, 142*
Chalk, 174, 361
Chalk formation, 348, 357, 360, 361,
368
Chalk-marl, 360
Chalybeate springs, 67, 153
Chalybite, 150
Chama, 370, 393
Chamaerops, 369
Champlain series, 402
Chattahoochee stage, 385
Chazy group, place of, in Geological
Record, 257, 286
Cheirodus, 305
Chemung group, place of, in Geo-
logical Record, 257, 295
Chert, 142, 176
Chestnut, fossil, 369
Chiastolite-slate, 188, 227
Chilled edge of intrusive rocks, 183,
228, 232
Chillesford Clay, 390
China-clay, 147
Chipola stage, 385
Chitin, preservation of, 240
Chlorides, 118, 129, 137, 152, 329
Chlorine in earth's crust, 129, 136
Chlorite, 148
Chlorite-schist, 190
Chloritic Marl, 360
Chondrites, 277*
Chonetes, 293, 308
Chromic-iron, 186
Chrysotile, 186
| Cidaris, 334
: Cimolestes, 357
Cimoliasaurus, 357
Cimolomys, 357
Cincinnati group, place of, in Geo-
logical Record, 257, 286
Ciiitiamomujn, 350*, 369, 387
Cipollino, 189
Civet, fossil, 377
Clastic, definition of, 155 ; rocks,
164
Clathropteris, 325
Clay, composition of, 131, 145, 147 ;
kinds of, 168 ; red, as an oceanic
deposit, 88 ; associated with lime-
stone, 200
Clay-ironstone, 150, 151,* 156,* 173,
176, 194, 199 ; as a petrifying
medium, 243
Clay-slate, 187
! Clayborne group, 374
, Clear Fork group, 322
Cleavage in minerals, 138* ; in rocks,
168, 187, 215, 217*
Cleidophorus, 283
Cliff-debris, 164
Climate indicated by fossils, 237, 244,
266, 388, 394 ; uniformity of, in
Palaeozoic ages, 266 ; in Mesozoic
time, 332, 351 ; in Tertiary time,
366, 368, 369, 388, 394 ; in Post-
tertiary time, 394, 407
Clinometer, 210*
Clinton group, place of, in Geological
Record, 257, 286
Clisiophylhtm, 306
Club-mosses, fossil, 277, 289, 301*
Clymenia, 294*, 295
Coal, composed mainly of carbon,
134 ; varieties of, 175 ; mode of
formation of, 194, 298
Coal-gas, 135
Coal-measures, place of, in Geological
Record, 257 ; account of, 312
Coblentzian, place of, in Geological
Record, 257, 295
Coccosfeus, 290
Cochliodus, 311
Cockroaches, fossil, 284, 304, 337
Coleoptera, 337, 382
Colorado River, grand capon of, 37*,
38
INDEX
435
Columnar structure, 184, 185*
Compression, effect of, on rocks, 209,
214*
Conchoidal fracture, 180
Concretionary, definition of, 156 ;
structure in minerals, 141, 150,
151*. 155* ; in rocks, 199
Conformability, 204
Conglomerate, 165, 166*, 194 ;
schistose, 189 ; not associated
with shale, 200 ; local character
of, 201
Coniferae, fossil forms of, 289, 303,
318, 323, 325*. 332, 351, 368,
369- 376, 381
Coniston grits, 286
Conocoryphe, 274
Contact metamorphism, 187, 188,
226, 227*, 228, 232, 234
Contemporaneous sheets, 229
Continents, evolution of the, 265,
284, 296, 366
Contortion of strata, 214*, 215*
Conularia, 310*
Conus, 370, 377
Copper-ores, 321
Coprolites, 156*, 176, 240, 305
Coral-reefs, 97*, 123, 173, 174, 295,
296, 33 T - 333*. 345
Corals, fossil, 279*, 293*, 306*, 318,
333*- 345
Corallian stage, 342, 345
Coralline Crag, 391
Corbula, 377*
Cordailes, 303*
Cornbrash, 342, 344
Corniferous group, place of, in Geo-
logical Record, 257, 295
Corylus, 369
Coryphodon, 371
Coryphodon Beds, 374
Cosmic dust, 131
Cosmoceras, 336*, 337
Gotham stone, 330
Cotoneaster, fossil, 369
Crabs, fossil, 337
Crag, 390
Cranes, fossil, 376
Crania, 335
Crater, volcanic, 105, 114
Cray-fish, fossil, 337
Credneria, fossil, 351
Cretaceous system, place of, in Geo-
logical Record, 257 ; account of,
348
Crevasses, 71
Crickets, fossil, 304
Crinoids, fossil, 271, 280, 293, 296,
306, 307*, 318, 326*. 334*
Crinoidal limestone, 174, 175*, 306
Crioceras, 354*. 355
Crocodiles, fossil, 328*, 357, 370,
382
Crust of the earth, defined, 103, 254 ;
elements composing, 128 ; sedi-
mentary rocks of, 192 ; general
arrangement of, 255
Crustacea, fossil, 271, 272*, 281,
282*, 283*, 292*, 293, 307*,
337* I chitin of, 240
Crushing of rocks, 221, 260
Cryphseus, 293
Crystals, geometrical forms of, 138 ;
gas and other inclusions in, 158*,
1 60 ; zones of growth in, 160
Crystalline structure, definition of,
158 ; superinduced in calcareous
materials by infiltrating water con-
taining dissolved carbonic acid, 64,
95, 98, 170 ; of lavas, 107, 108 ;
conditions for development of, 141,
158, 233 ; types of, 159 ; in
regional metamorphism, 221
Crystallites, 158, 159*, 169, 180,
217
Ctenacodon, 341
Ctenodonta, 273, 282
Cubical system in crystallography,
139*
Cucullea, 294*, 295
Cupressocrinus, 293
Cupularia, 391
Current-bedding, 42*, 195
Curvature of strata, 212*, 214*, 215*
"Cutters" in quarrying, 208
Cuttle-fishes, 274
Cyathaxonia, 279
Cyathocrinus, 293, 306, 318
Cyathophyllum, 279, 293*
Cycads, fossil, 246, 303, 318, 323,
325*, 332, 333*, 350
" Cycads, Age of," 326
Cycadeoidea, 333*
Cycadites, 332
436
INDEX
Cyclolobus, 319
Cyclopteris, 325
Cyprxa, 384
Cypridina-shales, 295
Cypris, 308
Cyrena, 370, 377
Cyrtia, 293
Cyrtoceras, 283, 295, 319
Cystideans, 246, 271, 280*
Cystiphyllicm, 293
Cytherea, 370, 384
Dacite, 182
Dactylioceras, 336*
Dadoxylon, 303
Dalmania, 292*, 293
Dalradian, place of, in Geological
Record, 257 ; described, 261
Danian stage, 357, 362, 365
Dapedius, 337
Darton, Mr. N. H., photographs
by, 23*. 375*
Darwin on action of earth-worms, 19;
on coral reefs, 123
Dasornis, 370
Darvsonia, 320
Dead Sea, 55, 173
Decalcification of organisms, 242
Deer, fossil, 271, 382, 387
Deer, Irish, 408, 409
Deformation of rocks, 190, 191, 216,
260
Deinoceras Beds, 374
Deinocerata, 246, 372, 379
Deinosaurs, 328, 339, 356*
Deinotherium, 382, 383*, 387
Deltas in lakes, 51 ; in the sea, 86 ;
preservation of animal remains in,
100 ; relics of ancient, 358
Denbighshire Grits, 286
Dendrerpeton, 305
Dendrites, 145*
Dendrocrinus, 280
Denudation, effects of, 204*, 225,
231*, 233*, 383 ; rate of, 28 (see
Weathering, Rain, Springs, Rivers,
Glaciers, Sea)
Deserts or sand-wastes, 22, 166
Desiccation, influence of, in weather-
ing, 13
Devitrification, 108, 159*. 169, 177,
180, 183
Devonian system, place of, in Geolo-
gical Record, 257 ; description of,
287 ; disturbance of rocks of, 300
Diabase, 184 ; altered into arnphibo-
lite, 190
Diadectes, 320
Diadema, 334
Diamond, 134
Diatom earth, 94*
Diatoms, secretion of silica by, 94,
240, 361
Dicotyledons, fossil, 350, 360
Dictyograptus, 270*
Dictyonema, 270*
Dicynodon, 328
Didelphops, 357
Didymograptus, 278*
Dielasma, 308
Diestian, 391
Dimetric system in crystallography,
139*
Dimorphodon, 339
Dinichthys, 290
Dinar nis, 370
Diorite, 181 ; altered into amphibo-
lite, 190, into hornblende schist,
222
Dip of strata, 209, 210*, 211*
Dip-joints, 208
Diplacodon Beds, 374
Diplograptus , 278*
Diplopterus, 289
Diplurus, 327
Dipterus, 290
Dirt Beds, 346
Discina, 273, 305, 308, 335
Discinocaris, 282
Dislocation of strata, 217, 220*
Distortion of rocks, measurement of,
215, 216*
Dog, domesticated, 409
Dog, fossil, 377
Dogger, or Brown Jura, 343
Dogwood, fossil, 351
Dolerite, 184; altered to am phibolite,
190
Dolomite, 133, 150, 171, 172*,
315, 324 ; metamorphism of,
189
Dolphin, fossil forms of, 382
Dorygnathus, 339
Double Mountain group, 322
INDEX
437
Dragon-flies, fossil, 304, 337
Drainage, affected by earthquakes,
122
Dromatherium, 329
Dryolestes, 341, 357
Dryopithecus, 381
Dunes, 21, 22*, 166 ; protected by
vegetation, 92
Dunile, 186
Dust, transport of, by wind, 18, 21 ;
cosmic, 89, 132
Dyas, 315, 320
Dykes, 118, 119*, 232, 233*, 234
Eagles, fossil, 374
Earth, history of the, 4, 7, 8, 10,
251 ; crust of, 103, 254 ; condi-
tion of interior of, 103, 104, 254 ;
internal heat of, 104, 254 ; con-
tinued loss of heat by, 105 ;
tremors of, 121 ; earliest condition j
of, 252 ; density of, 254 ; form of,
254 ; former greater velocity of
rotation of, 254
Earth-tremors, 121
Earthquakes, effects of, 2, 121, 122;
causes of, 121
Earthworms, influence of, upon
soil, 16, 19, 92
Echinoconus, 352*
Echinoderms", fossil, 271, 280
Eclogite, 191
Edmondia, 309
Egeln Beds, 379
Elseolite-syenite, 181
Elasmobranch fishes, 289
Elements, simple, in earth's crust,
128
Elephant, fossil forms of, 246, 379,
382, 387, 390, 400*'
Elevation of land, influence of, on
rivers, 44 ; proofs of, 123, 402
Elk, 409
Ellipsocephalus, 272*
Elm, fossil, 369, 381, 387
Elotherium, 379
Empedias, 320
Enaliosaurs, or sea-lizards, 338*
Enchodus, 356
Encrinite-limestone, 174, 175*, 306
Encrinurus, 281
Encrimis, 326*
Enstatite, 184, 186
Enstatite-picrite, 186
Eocene definition of term, 367 ; for-
mations, place of, in Geological
Record, 257 ; account of, 368
Eohippus, 371
Eophyton, 269*
Eoscorpius, 304*
Eozoon, nature of, 260
Ephemera, fossil, 289
Epidiorite, 190
Equisetaceae, fossil, 301, 302*, 325*.
332
Equisetum, 325*
Eremopteris, 300*
Erosion, base-level of, 38, 85 ; by
weathering, 22, 23* ; by running
water, 32 ; by glaciers, 76 ; by the
sea, 84*
Erratic-blocks, 72, 403
Eruptive, definition of, 158 ; rocks,
176, 224
Eskers, 402, 403
Eucalyptus, 369
Euchirosaurus, 321
Euomphalus, 310*
Eurite, 179
Europe, composition of water of
rivers of, 28 ; sediment carried by
rivers of, 30, 31 ; mean height of,
32 ; former glaciers of, 74 ; peat-
bogs of, 93 ; disappearance of
forests of, 100 ; bone -caves of,
101; extinct volcanoes of, 106 ;
fissure-eruptions of, 120; lacustrine
formations of, 243 ; mean thick-
ness of fossiliferous rocks of, 256 ;
pre-Cambrian rocks of, 260 ; oldest
topography of, 261 ; Cambrian of,
275 ; Silurian rocks of, 276, 285 ;
Devonian system in, 287, 295 ;
Carboniferous system, 296, 312 ;
Permian system in, 314, 316, 320;
Trias of, 323, 329 ; Jurassic system
in, 332, 341 - 346 ; Cretaceous
system in, 348, 357, 358 ; Tertiary
formation of, 367 ; Eocene of, 372 ;
Oligocene of, 375 ; Miocene of,
382 ; Pliocene of, 386, 391 ; glacia-
tion of, 394
Eurypter id Crustacea, 291, 292^293,
38, 337
438
INDEX
Evergreen oak, 376, 381, 387
Exogyra, 335, 353
Fagus, 369
Fairy stones, 155*, 199
False-bedding, 195, 196*
Faluns of Touraine, 384
Famennian, place of, in Geological
Record, 257, 295
Fan-palms, fossil, 369, 376
Fascicularia, 391
Fault- rock, 217
Faults, 217, 218*, 219*
Favosites, 279, 306
Feather-palms, 376
Felis, 401
Felsite, 179, 180
Felsitic, 159
Felspars, 145, 177
Felted structure (in Andesite), 182
Fenestella, 308*, 318
Ferns, fossil, 277, 289, 300*, 325,
332, 351, 368
Ferric oxide, 132
Ferro-magnesian minerals, 179
Ferrous carbonate, 150
Ferrous oxide, 132, 150
Ferruginous minerals, decomposition
of, by organic matter, 17
Fibrous structure in minerals, 141
Ficus, 350*, 369, 381*. 387
Fig, fossil, 350*. 369, 381*, 387
Fir, fossil, 390 ; in Danish peat-bogs,
411
Fireclay, 168, 194; represents former
soil, 298
Fishes, fossil, 284, 289, 290*, 291*,
305, 310, 311*. 319*. 321, 327,
337> 355*' 37 I sudden destruc-
tion of, 291
Fissure-eruptions, 119
Fissures, volcanic, 113, 118, 232 ;
caused by earthquakes, 122 ; filled
by mineral veins, 234 ; reopening
of, 236
Fjords, 51
Flamingoes, fossil, 376
Flammenmergel, 360
Fleckschiefer, 188
Flint, 142, 176, 199, 361
Flint-implements, 406* ; found under
London, 3
Flood-plain of a river, 44
Flow-structure, 161*, 162, 180
Fluid-cavities in crystals, 158*
Fluor-spar, 136, 139, 152, 153*,
234
Fluorides, 137, 152
Fluorine in earth's crust, 129, 136
Fluvio-marine Crag, 390
Fluxion-structure, 161*, 162, 180
Foliated, 162, 186
Fontainebleau Sandstone, 378
Footprints in sedimentary rocks, 196,
327, 328
Foraminifera, in diatom-ooze, 94*,
ooze formed of, 96* ; fossil forms
^ of, 278, 305, 306*, 351*. 370
Forest- Bed group, 390
Forest Marble, 342
Forests, cause of decay of, 18 ; pro-
tective influence of, 92 ; disappear-
ance of, 100
Formation in stratigraphy, 248
Fossanian group, 392
Fossils, definition of, 237 ; nature
and use of, 237 ; as guides to
former geographical conditions,
243, 296 ; as an indication of
former climates, 244 ; in relation
to geological chronology, 245
Fossilisation, 99, 240
Fox, fossil, 390, 400, 408
Fragmental, definition of, 155 ; rocks,
164
Frasnian, place of, in Geological
Record, 257, 295
Freestone, 167
Frogs, fossil, 382
Frost, destructive effects of, 2 ; influ-
ence of, in weathering, 13 ; on
rivers and lakes, 69
Fruchtschiefer, 188
Fucoids, fossil, 269, 277
Fuller's Earth, 342, 344
Fundamental Gneiss, place of, in
Geological Record, 257
Fusulina, 305, 306
Gabbro, 183 ; altered into amphi-
bolite, 190
Gaize, 360
Gale, effects of a, i
Galena, 235
INDEX
439
Galerites, 352*
Ganoids, fossil, 289, 290*, 305,
311*, 319*, 327, 337
Garbenschiefer, 188
Garnet, 188, 191
Gas enclosed in crystals, 158
Gasteropods, fossil, 273, 283, 310
Gault, 358, 359
Gazelles, fossil, 387
Gedinnian, place of, in Geological
Record, 257, 295
Genesee group, place of, in Geological
Record, 257, 295
Geneva, Lake of, 34, 49
Geographical conditions indicated by
fossils, 237, 243
Geological history, materials for, 3,
4, 5, 10, 124; breaks in, how
marked, 205 ; use of fossils in,
238
Geological Record, 247, 251, 255,
256
Geology, scope of, 4, 6, 8, 251 ;
based on observation, 8, 9
Georgian series, place of, in Geo-
logical Record, 257, 275
Gervillia, 335
Geysers, 173
Giants' kettles, 78*
Gilbert, Mr. G. K. , on laccolites,
226 ; photographs by, 52*, 74*,
200*
Ginko, fossil, 369
Giraffes, fossil, 384, 387, 392*
Glacial deposits, their place in the
Geological Record, 256
Glaciation, 72*, 75*, 76*, 78 ; of
the northern hemisphere, 394
Glaciers, 70 ; transport by, 71* ;
striation of rock by, 75*, 76* ;
erosion by, 76, 77 ; former greater
size of, 401
Glass, volcanic, 107, 140, 158, 159,
169, 177, 180, 181, 232
Glauconite as a green colouring
material, 167
Glauconitic Marl, 357, 360
Gleichenia, 351
Globigerina, 96*, 351*
Glossopteris, 325
Glutton, fossil, 390, 400, 408
Glypticus, 334
I Glyptocrinus, 280
; Glyptolsemus, 289
| Glyptostrobus, 387, 388*
| Gneiss, 191, 258 ; intrusive, 260
Goat, fossil, 393 ; domesticated, 409
Gold, 137
Goniatites, 295, 305, 310*
Gorges eroded by rivers, 35*
Granite, decay of, into soil, 15* ; an
eruptive rock, 158; holocrystalline
structure of, 159, 178 ; description
of, 178* ; varieties in character of
peripheral parts of, 179, 182 ;
metamorphism by, 188 ; meta-
morphosed into gneiss, 222 ; bosses
of, 226, 227*
j Granitic type of rocks, 177
i Granitite, 179
; Granitoid (like granite), 181, 182,
183
Granophyre, 179
Granulite, 191
Graphic structure, 179
Graphite, 134
Graphite-schist, 260
Graptolites, 246, 270*, 278*, 279,
292
Grasshopper, fossil, 337
Gravel, geological history of, 4, 165 ,
limited extent of, 201
Green colour, origin of, in some rocks,
132
Green River group, 374
Greensand, Upper, 357; Lower, 358,
359
Greenstone, 182
Greywacke, 167, 187 ; as the name
of a series of rocks, 267
Griffithides, 308.
1 Grit, 167 ; schistose, 189
Grizzly bear, 409
1 Grottoes, subterranean, cause of, 64
Ground-ice, 69
I Ground-mass (in rocks), 159, 177,
182, 184
Group (in stratigraphy), 248
Grouse, fossil, 376
Gryllidae, fossil, 304
Gryphsea, 335*
Gryphite Limestone, 335
Guano, 176
Gulo, 400
440
INDEX
Gum-tree, fossil, 351, 369
Gypsum, in sea-water, 28 note; in
river- water, 29 ; in salt lakes, 55 ;
composition of, 129 ; crystalline
form of, 140, 151, 152* ; composi-
tion and occurrence of, 150 ; solu-
bility of, 151 ; as a rock-former,
170, 171, 315, 321, 322, 324, 329
Gyracanthus, 305
Gyrolepis, 327
Hade of a fault, 218*
Haematite, 143*, 173 ; formation of,
17
Halite, 152
Halobia, 326
Ha ly sites, 279
Hamilton group, place of, in Geo-
logical Record, 257, 295
Hamites, 354*. 355
Hamstead group, 377
Hardness in water, cause of, 132
Hare, Alpine, 408 ; fossil, 408
Harlech group, 275
Harpes, 292*
Harpoceras, 337
Hastings Sand, 359
Hauterivian, 359
Hazel, fossil, 369, 390
Headon group, 378
Heavy spar, 136, 151
Hedgehogs, fossil, 371
Heersian Beds, 373
Helderberg group, place of, in Geo-
logical Record, 257, 286, 295
Helicoceras, 354*, 355
Heliolites, 279
Heliopora, 279
Helix, 377
Helix-limestone, 378
Helladotkerium, 392*
Hemicidaris, 334
Hernicrystalline, 159
Hesperornis, 357
Hettangian, 342
Hexagonal system in crystallography,
139*
Hickory, fossil, 386, 387
Hill, Mr. R. T., photograph by, 116*
Hippopodium, 335
Hippopotamus, fossil, 382, 387, 401,
408
Hippurite limestone, 355, 357, 358,
360, 361, 362
Hippurites, 246, 353*
Hog, fossil, 379, 386 ; domesticated,
409
Holaster, 352
Holocrystalline, 159, 177
Holopea, 283
Holoptychius, 289, 290*
Homalonotus, 281, 282*, 292*, 293
Honestone, 188
Hoplites, 358
Horizon in stratigraphy, 247
Hornbeam, fossil, 369, 381
Hornblende, 140, 147, 148*
Hornblende-andesite, 182
Hornblende-diorite, 182
Hornblende-picrite, 184
I Hornblende-rock, 190
j Hornblende-schist, 190 ; produced
by the crushing of diorite, etc.,
222
Hornfels, 188, 227
Hornwort, fossil, 390
Horse (Equus] characteristic of
younger Tertiary and Recent rocks,
246 ; ancestral forms of, 371, 382,
386 ; fossil, 387, 390, 408 ;
domesticated, 409
Horse-tail reeds, fossil, 301, 302*,
325*
Hudson River group, 286
Huerfano group, 374
Human Period, 404
Humous Acids ; see Organic Acids
Humus, origin of, 15
Huronian, place of, in Geological
Record, 257 ; rocks described,
262
Hyaenas, fossil, 246, 388, 390, 401,
408
Hyalomelan, 183
Hybodus, 327, 337
Hydraulic limestone, 171
Hydrocarbons, 135
Hydrochloric acid, 135
Hydrogen in earth's crust, 129, 135
Hydrosphere, 253
Hydrozoa, fossil, 246, 270*, 278*,
279, 292
Hymenocaris , 272
Hyopotamus, 371, 377
INDEX
441
Hyperodapedon, 328
Hyperite, 183
Hypersthene-andesite, 182
Hypogene, definition of, 158, 177
Hystrix, 401
Ibis, fossil, 376
Ice, transport of boulders by, 69, 72 ;
striation of rock by, 75*, 76*. 395 ;
erosion by, 76
Ice Age, history of the, 395
Ice-sheets, 70, 395, 397
Iceland-spar, 138*, 149
Ichthyodorulite or fish-spine, 311*
Ichthvornis, 357
Ichthyosaurs, 246, 328, 338*, 356
Idiomorphic crystals, 177
Igneous, definition of, 1 58 ; rocks,
176
fguanodon, 356
Ilex, fossil, 351, 387
llhr.nus, 281, 282*
Ilmenite, 144
Imagination, use of, in geology, 194
Implements, human, in Palaeolithic
deposits, 404, 405, 406* ; in
Neolithic deposits, 409, 410*
Inclination of strata, 209
India, coast-lagoons and bars of, 86 ;
extinct volcanoes of, 106 ; Cam-
brian rocks of, 275 ; Silurian rocks
of, 285 ; Permian rocks of, 316 ;
Trias of, 331 ; Jurassic rocks in,
344, 346 ; Cretaceous rocks of,
362 ; Eocene of, 373 ; Miocene of,
380 ; Pliocene of, 393
Infusorial earth, 93
Inoceramus, 353*
Insects in amber, 239, 240 ; preser-
vation of chitin of, 240 ; fossil
forms of, 289, 304, 330, 337, 346,
38i
Insect-beds, 337
Interglacial periods, 398
Intermediate rocks, 181
Intrusive sheets, 228*
Iron, in earth's crust, 129, 131 ; as a
colouring matter in nature, 132,
167; titanic, 133, 144; spathic,
i So; disulphide, 153; chromic,
1 86; meteoric, in 4 abysmal deposits,
89 ; specular, 118
Iron-carbonate, 150, 151*, 156*,
173
Iron-oxide, deposited in lakes and
bogs, 54, 91 ; in chalybeate springs,
67 ; in earth's crust, 131, 132 ;
formation of, 130 ; varieties of,
M3
Ironstone, 173, 175 ; associated with
clays and shales, 200
hastrasa, 333*, 334
Ischypterus, 327
Isometric system in crystallography,
139*
Ivy, fossil, 351
Jackson group, 374
: Jasper, 142
Jaws, lower, frequent as fossils, 100,
34i. 346
Jerboa in Loess, 408
John Day stage, 386
Joints of rocks, 207
Juglans, 350*, 369, 387
Juniper, fossil, 351
Jura, Black, 343 ; Brown, 343 ;
White, 344
Jurassic system, place of, in Geologi-
cal Record, 257 ; account of, 332
Kanies, 402, 403
Kaolin, 147, 168
Keewatin, place of, in Geological
Record, 257 ; rocks described,
262
Kellaways Rock, 342, 344
Kepplerites, 342
Kersantite, 181
Keuper group,. 329
Keweenawan, place of, in Geological
Record, 257 ; rocks described, 263
Kimmeridgian, 342, 345
King-crabs, fossil, 308
Kirkby Moor Flags, 286
Knotted slate, 188
Kupferschiefer, 319, 320, 321
Kutorgina, 275
Kyanite, 191
Labradorite, 146
Labyrinthodonts, 305, 319, 327
Laccolite, 226
442
INDEX
Lackenian, 373
Lacustrine deposits, '4, 51, 52*,
53*, 92, 93*, 100, no, 112, 243,
287
Lagoons on coasts, 86 ; at coral-reefs,
98
Lagoon -channels at coral-reefs, 98
Lakes, disappearance of, 2 ; filter
river-water, 33, 48 ; of fresh water,
48 ; silting up of, 48, 49, 51, 93 ;
terraces of, 49* ; deposits in, 4,
50*, 51*, 52*, 54, 243, 368 ;
formed by ice-dams, 50, 402 ;
shell-marl of, 53*, 93* ; iron-ore
formed in, 54, 144 ; of salt-water,
54, 173 ; bitter, 55 ; frozen,
69 ; preservation of remains
of animals in, 100, 243, 409 ;
evidence for former, 1 10 ; formed
by earthquakes, 122 ; earliest
traces of, 287 ; Cretaceous, 368 ;
Tertiary, 375, 378, 379, 385;
glacial, 402
Lamantin, fossil, 382
Lamellibranchs, fossil, 273, 284*,
294*. 309*. 3 J 9*. 326, 327*, 335,
353*
Laminae, 194
Laminated structure, 195
Lamination of shale, possibly some-
times a kind of cleavage-structure,
168, 216
Lamna, 370
Lamprophyre, 181
Land, weathering of surface of, n,
12*, 15, 22, 23*, 27, 28*, 31 ; rate
of lowering of surface of, 31 ;
average general height of, 31 ; |
elevation and subsidence of, 123 ;
earliest known, 265 ; ancient
northern, 285
Landscape, changes of, i, 22
Land-shells, earliest known, 266
Landslips, 58, 59*, 60, 122
Land-snails, fossil, 289, 304
Land -surfaces, traces of former, 196 ; :
evidence for, 298
Landenian, 373
Lapilh, 169
Laramie group, 363
Laurel, fossil, 350, 369, 376, 381,
387
Laurentian, place of, in Geological
Record, 257
Laurys, 369, 387
Lava, 105 ; characters of, 107 ;
temperature of, 108 ; structure of
sheets of, 108 ; original molten
condition of, 146 ; an eruptive
rock, 158; proofs of interstratified
character of, 229
Lead sulphide, 235
Leda-myalis Bed, 390
Lemming, 408
Lemurs, fossil, 371
Lenham Beds, 391
Leopard, 401, 408
Leperditia, 308
Lepidodendron, 246, 288, 301*, 317
Lepidopteris, 325
Lepidostrobus , 301
Lepidotus, 337
Leptsena, 282
Leptaenids, disappearance of, 335
Leptynite, 191
Lepus, 408
Leucite, 146, 182, 184
Levant, dried water-courses of the,
38
Lewisian gneiss, place of, in Geo-
logical Record, 257 ; account of,
260
Liassic formations, 342
Libellulee, fossil, 304
Life, uniformity of, in Palaeozoic
time, 266
Lignite, 175, 374, 376
Lignitic sands (Eocene), 374
Lima, 335, 353
Limburgite, 184
Lime, carbonate of, in river-water,
28, 132 ; solution of, by springs,
60, 63, 132 ; precipitation of, 65,
66; composition of, 132; test for,
132, 150, 154, 171 ; composition
of, 134 ; crystalline forms of, 149;
abundance of, in nature, 170, 240;
eliminated by some aquatic plants,
239 ; as a petrifying medium,
242
Lime, sulphate of, 132 ; in river-
water, 28 ; in springs, 132, 149 ;
in sea-water, 132, 239 (see also
under Gypsum)
INDEX
443
Lime, phosphate of, 135, 152, 176,
240
Limes, fossil, 385
Lime-silicate-rocks, 188, 189
Limestone, solution of, by water, 27,
61, 63 ; formed by rain out of
calcareous sand, 95, 166 ; formed
of recent marine shells, 95*, 96,
97 ; abundant in nature, 135 ;
chiefly of animal origin, 135, 149,
170, 174, 296 ; formed by chemi-
cal precipitation, 170 ; alteration
of, 1 88 ; formation of, from
animal remains, 194 ; associated
with clays, 200 ; slow growth of,
20 1 ; proofs of subsidence of
sea - floor furnished by, 296 ;
made of calcareous organisms,
3015 ; formed of ostracods, 308 ;
formed of polyzoa, 308 ; gryphite,
335
Limnaea, 377
Limnerpeton, 320
Limonite, 17, 143, 173, 176
Lingnla, 273, 305, 308, 335
Lingula-flags, 272, 273
Lingulella, 273*
Linton Slates, 295
Lion, fossil forms of, 379, 382, 386,
401, 408
Liparite, 180
Liparoceras, 336*
Liquiclambar, fossil, 369, 387
Liriodendron, 387
Lithosphere, 254
Lit has trot ion, 306*
Lituites, 283, 285*
Lizards, fossil, 382
Llandeilo group, place of, in Geo-
logical Record, 257, 286
Llandovery group, place of, in Geo-
logical Record, 257, 286
Loam, 168 ; origin of, 17
Lobsters, fossil, 337
Locusts, fossil, 304
Loess, 169, 407
London, geological records of the
history of, 3
London Clay, 373
Longmyndian, place of, in Geological
Record, 257 ; rocks of, 262
Lonsdaleia, 306
Lophiodon, 379
Loup Fork stage, 386
Loxomma, 305
Loxonema, 310
Ludlow rocks, place of, in Geological
Record, 257, 286
Ludwigia , 342
Lumbricaria, 281*
Lycopods, fossil, 277, 301*
Lydian-stone, 187
Lyell, Tertiary classification of, 367
Lygodium, 368
Lynx, 401, 408
lytoceras, 337
Macaque, fossil, 393
Machairodus, 382, 390
Macles, 151, 152*
Maclurea, 286
Macrotceniopteris, 325
Magma, 158, 169, 184
Magnesia, carbonate of, 170 ; sul-
phate of, 330
Magnesian limestone, 133, 150, 199,
320
Magnesian silicates, 133, 145
Magnesium in earth's crust, 129, 132
Magnesium-chloride in bitter lakes,
55 ; in sea-water, 133 ; precipita-
tion of, 330
Magnetite, 139, 144*, 173
Magnolia, fossil, 351, 369, 381*,
387
Malm or White Jura, 344
Mammalia, fossil remains ot, 328,
34i. 357. 370*. 37L 377
Mammaliferous crag, 390
" Mammals, Age of," 367
Mammoth, 400, 408 ; carcases of,
preserved, in frozen mud, 240
Man, brief geological experience of,
124 ; earliest appearance of, 402,
403 ; proofs of presence of, 404 ;
early carvings and incised drawings
by, 409
Manganese in earth's crust, 129, 135 ;
peroxide in abysmal deposits, 88,
1 02 ; association of oxides of,
144
Mangrove-swamps, 93, 194, 300
Maple, fossil, 350, 369, 387
Maraboot, fossil, 376
444
INDEX
Marble, 188 ; alteration of limestone
into, 227 ; decay of, in large
towns, 15
Marcasite, 153, 156
Marcel lus group, place of, in Geo-
logical Record, 257, 295
Marine organisms, special value of,
in geological history, 238
Marl, history of lacustrine, 4, 53*,
92, 93*. 95- i74. 243
Marl Slate, 315
Marlstone (Lias), 343
Marmots, fossil, 377
Marsupials, fossil, 328, 341*, 357
Marsupites, 357
Martens, fossil, 377
Masonry, effects of weathering on,
n
Massive, definition of, 158
Mastodon, 246, 382*, 387, 390
Mastodonsaurus, 327
Mauch Chunk shales, 313
May-flies, fossil, 289, 304, 337
May Hill Sandstone, 286
Medina group, place of, in Geological
Record, 257, 286
Mediterranean stage (Miocene), 384
Medlicottia, 3 [9
Megaceros, 408, 409
Megalichthys, 305
Megalosaurus , 340
Megaptilus, 304
Melanerpeton, 321
Meniscoessus, 357
Menyanthes, 390
Merced group, 393
Mesohippus, 379
Mesozoic, place of, in Geological
Record, 257, 323
Messinian, 392
Metalloids, 129
Metals, 131
Metamorphic rocks, 186
Metamorphism, 163, 186, 216, 221,
226
Meteoric iron in abysmal deposits,
89 ; in meteorites, 132
Meudon, marls of, 373
Miarolitic structure, 178
Mica, 147 ; development of, in
regional metamorphism, 221
Mica-andesite, 182
Mica-diorite, 182
Mica-schist, 189, 221, 222, 227
Mica-slate, 188, 189
Mica-traps, 181
Micaceous, 167
Mice, influence of, in th removal of
soil, 19
Micraster, 352*
Microcline, 146
Microconodon, 329
Microfelsitic, 159
Microgranitic structure, 179
Micrographic structure, 179
Microlestes, 328*
Microscope, use of, in the study of
rocks, 155, 158, 180, 216, 233
Millipedes, fossil, 289, 304
Millstone grit, place of, in Geological
Record, 257, 312
Mimosas, fossil, 381
Minerals of earth's crust, 137 ; modes
of origin of, 140 ; order of appear-
ance of, in crystalline rocks, 146
Mineral-oil, 135
Mineral veins, 234, 235*
Minette, 181
Miocene, definition of term, 367
Miocene formations, place of, in
Geological Record, 257 ; account
of, 380
Miohippus, 379
Mitra, 384
Modiola, 310
Modiolopsis, 273, 283
Molasse, 379
Moles, influence of, in the removal
of soil, 19, 92 ; fossil, 377
Mollusca, importance of, in geology,
% 272 ; as a basis of classification for
the Tertiary formations, 367
Monkeys, fossil, 382, 388
Monoclinic system in crystallography ,
140*
Monograptus, 278*
Monometric system in crystallo-
graphy, 139*
Monotis, 326
Monotremes, fossil, 357
Mons, limestone of, 373
Montlivaltia, 334
Moon formerly nearer to the earth,
254
INDEX
445
Moraines, 71, 164, 398, 403
Morasses (see Peat)
Morse, fos il forms of, 382
Mosasaurus, 357
Mosses, precipitation of carbonate of
lime by, 66
Moulin pot-holes, 78*
Mountain-chains, of different ages,
123 ; relative age of, 205 ; suc-
cessive uplifting of, 364, 366, 373,
380, 386
Mountain -limestone, 296
Mud, 1 68 ; wide area of deposit of,
201 ; unfavourable to many forms
of marine life, 193, 230, 244
Mudstone, 168
Murchison on Silurian system, 267,
276 ; with Sedgwick named the
Devonian system, 287
Murchisonia, 283
Murex, 377, 384
Muschelkalk, 326, 329
Muscovite, 147
Musk-sheep, fossil, 390, 400*, 408
Myliobatis, 370
Mylonitic, 162, 221
Myodes, 408
Myophoria, 326, 327*
Myriapods, fossil, 289, 304
Myrica, fossil, 350
Myrtles, fossil, 381
Natica, 399*
Nautilus, living pearly, 274 ; fossil,
283, 310, 319, 357, 370
Nebular hypothesis, 252
Necks, volcanic, 116*, 117,* 118*,
233*.
Nelumbium, 369
Neocomian stage, 358
Neolithic deposits, 404, 409
Nepheline, 1.46, 184
Nepheline-syenite, 181
Neuroptera, fossil forms of, 289,
337
Neuropteris, 300*, 301, 318
New Red Sandstone, 315, 323
New Zealand, hot springs of, 68 ;
extinct volcanoes of, 107 ; pre-
Cambrian rocks of, 263 ; Silurian
rocks of, 285 ; Carboniferous
system in, 312 ; Trias in, 331
New Zealand, Jurassic rocks in, 346 ;
Cretaceous rocks in, 364
Niagara group, place of, in Geologi-
cal Record, 257, 286
Niagara River, filtered by Lake
Erie, 38 ; gorge of, 35, 36 ; falls
of, 36*
Nineveh, buried under wind -borne
soil, 21
Nipa, 369
Nitrogen in the atmosphere, 136 ;
in the earth's crust, 137
Non-metals, 129
Norite, 183
North Sea, once filled with ice, 74
Norway, ice-transported stones from,
74 ; glacier-erosion in, 77 ; meta-
morphism of limestone in, 188 ;
fossiliferous schists of, 190
Norwich Crag, 390
Nosean, 182
Nucufa, 310, 353*. 377
Nuculana, 310, 390, 399*
Nullipores, 94
Nummulites, 246, 368, 370
Nummulitic Limestone, 368, 370,
373
Nuphar, 390
Nympheea, 390
Oak, fossil, 350*, 376, 381, 387,
390 ; in Danish peat-bogs, 411
Observation, faculty of, in geology,
8, 9
Obsidian, 159, 161*, 162, 180
Oceans, position and probable history
of the, 253
Oceanic deposits, 88, 94
Ochre, precipitation of, by chalybeate
water, 67 ; composition of, 144
CEningen Beds, 385
Ogygia, 174, 281, 282*
Olcostephanus, 358
Old Red Sandstone, place of, in Geo-
logical Record, 257 ; account of,
287
Oldhamia, 269, 270*
Oldhaven Beds, 373
Oleandrideum, 332
Olenellus, 274
Olenellus series, place of, in Geological
Record, 257, 274
446
INDEX
Olenidian series, place of, in Geologi-
cal Record, 257, 274
Olenus, 272*, 274
Oligocene formations, place of, in
Geological Record, 257 ; definition
of term, 367 ; account of, 374
Oligoclase, 146, 178
Oliva, 369
Olivine, 148*, 183, 184
Olivine-gabbro, 183
Omphacite, 191
Omphyma, 279*
Onondaga group, place of, in Geo-
logical Record, 257, 286
Ontario, Lake, shingle formed by,
52*
Oolite, formed on coral-reefs, 99 ;
origin of, 157
Oolite-limestone, 171
Oolitic, definition of, 157*
Oolites in Jurassic system, 342
Ooze, diatom, 94*; globigerina, 96*,
174
Opal, 142
Ophicalcite, 189
Ophite ta, 283
Opossums, fossil, 371, 382
Oppellia, 337
Orbitoides, 374
Order of succession in the appearance
of organisms on the earth, 245 ;
of superposition, 247
Ordovician, 277
Oreopitkecus, 382
Ores, metallic, 234
Organic acids, geological action of,
17, 27, 91, 132, 175
Organic matter in soil, 17 ; bleaching
effect of, 315
Organic remains, conditions for
preservation of, 238
Oriskany group, place of, in Geo-
logical Record, 257, 295
Orodus, 311*
Orthls, 282, 283*, 293
Orthoceras, 246, 274, 283, 285*,
295, 310*, 319, 326
Orthoclase, 146, 178
Orthoclase-porphyry, 181
Orthonota, 283, 284*
Orthophyre, 181
Orthoptera, fossil, 289, 337
Orthorhombic system in crystallo-
.. gnvphy, 139*
Osar, 402
Osborne group, 377
Osmeroides, 356
Osfeolepis, 289, 290*
Ostracoderms, 284
Ostracods, fossil, 308
Ostrea, 335, 353, 377*, 384
Otodus, 356
Otters, fossil, 382
Outcrop, 211*
Overlap, 203, 204*
Ovibos, 400
Oxen, fossil, 387
Oxfordian stage, 342, 344
Oxides, 129, 137, 141
Oxidation due to rain, 14
Oxygen, influence of, in Weathering,
14 ; in earth's crust, 129 ; at
volcanic vents, 129 ; constant re-
moval of, from atmosphere, 130
Oxynoticeras, 342
Oxyrhina, 356
Pachyderms, variety of, at the close
of Tertiary time, 367
False aster, 281
Palasasterina, 280*, 281
Palseoblattina, 284
Palseochoma, 281
Palseochorda, 281
Palseocrangon, 308
Palasohatteria, 320
Palaeolithic deposits, 404
Paleeoniscus, 319
Paleeophycus, 281
Paleeopteris, 288*
False -otherium, 246, 370*, 371, 377
Palaeozoic, place of, in Geological
Record, 257 ; systems described,
364 ; uniformity of life, 266
Palms, fossil, 351, 368, 369, 381
Paludina, 377
Pandanus, 351, 369
Paniselian, 373
Panop&a, 374, 389*
Pantylus, 320
Paradoxidean series, place of, in
Geological Record, 257, 274
Paradoxides, 271, 272*, 274
INDEX
447
Parallel Roads or Lake-terraces, 49*,
402
Paroquets, fossil, 376
Past, interpreted by the Present, 5, 1 1
Pearlstone, 180
Pea-stone, 157*, 171
Peat and Peat-bogs, history of, 2, 4,
92 ; solvent action of water from,
27, 28* ; rate of growth of, 93 ;
animal remains in, 93, 100 ; anti-
septic quality of, 93 ; sometimes
formed of sea- weeds, 94 ; varieties
of, 174 ; alternation of, with
lacustrine deposits, 243; succession
of trees in , 411
Pecopteris, 300*, 301, 318, 325
Pecten, 326, 327*. 335, 353, 377,
384, 399*. 400
Pecttmculus, 384
Pegmatite, 179
Pelican, fossil, 376
Pentacrinus, 334*
Pentamerus, 282, 283*
Pentremites, 307*
Perched Blocks, 72*, 164
Peridot, 148
Peridotites, 184
Perisphinctes, 337
Perlidse, fossil, 304
Perlitic, 160, 180
Permian system, place of, in Geo-
logical Record, 257 ; account of,
3H
Permo-Carboniferous, place of, in
Geological Record, 257
Petalodits, 311
Petrifaction, 100, 242
Petrography, 154
Pelrophiloides, 369*
Phacops, 281, 293
Phascolotherium, 341*
Phasmidas, fossil, 304
Phenocrysts, 159
Phillipsia, 367*, 308
Phlebopteris, 332
Pholidophorus, 327, 337, 338*
Phonolite, 182
Phosphates, 152
Phosphorus in earth's crust, 129,
135- 152
Phyllite, 188, 227
Phyllocarid fossils, 272, 281, 283*
Phylloceras, 337
Phyllograptus, 278*
Pickwell Down group, 295
Picrite, 184
Pig, fossil, 390
Pikermi, deposits of, 392
Pile-dwellings, 410
Pilton group, 295
Pinacoceras, 326
Pinna, 335
Pinus, 351, 369, 390, 411
Pisolite, 170
Pisolitic, denned, 157*
Pitchstone, 180
Placenticeras, 358
Placodenns, 284, 289, 291*, 337
Plagiaulax, 341
Plagioclase, 146
Plagioptychus, 353*
Plaisancian, 392
Plane, fossil, 350, 369, 387
Planets, origin of the, 253
Planorbis, 377
Planorbis-zone, 336
Plants as materials for geological
history, 6 ; conditions for preserva-
tion of remains of, 6, 100, 101,
238 ; geological action of, 91 ;
durable parts of, 239
Plaster of Paris, 151
Platanus, 387, 388*
Platycrinus, 306
Platyschisma, 283
Platysomus, 319*
Pleistocene, definition of term, 367 ;
formations, place in stratigraphy,
256 ; account of, 394, 395
Plesiosaurs, 246, 328, 338, 356
Pleuracanthus, 305 , 311*
Pleuroloma, 390
Pleurotomaria, 310
Plication of rocks, 214
Plicatula, 335*
Pliocene, definition of term, 367 ;
formations, place of, in the Geo-
logical Record, 257 ; account of,
386
Pliopithec-us, 382
Plum, fossil, 369, 387
Plutonia, 275
Plutonic, definition of, 158 ; rocks,
177
44 8
INDEX
Pocono sandstone, 313
Podozamites, 326
Polypora, 318
Polyzoa, fossil, 308*, 318
Pond-lily, fossil, 390
Pondweeds, fossil, 381
Popanoceras, 319
Poplar, fossil, 350, 369, 381, 387
Populus, 369, 387, 388*
Porcellanite, 187
Porcupine, fossil, 393, 401, 404
Porphyrite, 183
Porphyritic, 159, 160*
Porphyry, 160
Portage group, place of, in Geological
Record, 257, 295
Portlandian, 342
Post-pliocene group of strata, 394
Post- tertiary formations, relative
place of, in the Geological Record,
256 ; account of, 394
Potash, carbonate of, in soil, 133
Potash, silicates of, 133
Potassium in earth's crust, 129, 133;
in the sea, 133
Potassium-chloride, 133, 330
Potassium-sulphate, 133
Poteriocrinus, 306
Pot-holes, excavation of, 32, 33*, 78
Potsdam series, place of, in Geo-
logical Record, 257, 275
Pottsville Conglomerate, 313
Prawns, fossil, 337
Pre-Cambrian, place of, in Geological
Record, 257 ; formations, 258 ;
chiefly found in northern regions,
263
Precipitation of mineral matter, 54,
62, 67 ; rocks formed by, 170
Prehistoric formation, 256
Present a key to the Past, 5, u
Pressure, in consolidation of sedi-
ment, 207
Prestwichia, 308
Priacodon, 341
Primary, place of, in Geological
Record, 257
Primordial, place of, in Geological
Record, 257
Pristis, 370
Productus, 293, 308, 309*, 318*
Pro taster, 281
Proteaceous plants, fossil, 376, 381
Proterosaurns, 320
Protocystites ', 280
Protriton, 321
Prunus, 369, 387, 390
Psammites de Condroz, 295
Psammodus, 311
Psaronius, 318
Pseudocrinites, 280*
Psiloceras, 342
Psilophyton, 288*, 289
Pteraspis, 284, 290
Pterichthys, 290, 291*
Pterinea, 294
Pterodactylus, 339
Pterophyllum, 318, 325*, 326, 332
Pteropods, fossil, 310
Pterosaurs, 339*, 356
Pterygotus, 291, 292*
Ptychites, 330
Ptychoceras, 354*, 355
Pullastra, 326
Pumice, 180
Pumiceous, 161
Pupa, fossil, 304
Purbeckian, 342, 346, 358
Purpura, 389*
Pycnodus, 337
Pygaster, 334
Pyrite, 153, 155*, 156
Pyroxene, 148, 188 ; altered to horn-
blende, 190
Pythonomorphs, 357
Quader (Saxony), 360
Quartz, 130, 131*, 138, 140; charac-
ters of, 141, 142* ; in veins, 173,
234 ; in igneous rocks, 178
Quartz-diorite, 182
Quartz-gabbro, 183
I Quartz-mica-diorite, 182
I Quartz-norite, 183
Quartz-porphyry, 179
Quartz -schist, 189 ; formed from
sandstone, 222
Quartz- veins in granite, 16
Quartzite, 187, 189
Quaternary Formations, 394
Quercus, 350*, 381*, 387
Rabbits, influence of, in the removal
of soil, 19, 22, 92
INDEX
449
Radiolaria, secretion of silica by,
94*
Radiolites, 353*
Rain, destructive effects of, i ; influ-
ence of, in weathering, 14; removal
of soil by, 1 8, 26, 29 ; chemical
action of, 27, 60 ; cements cal-
careous detritus into limestone, 95,
96
Rainfall, influence of variations in, on
the transporting power of streams,
30
Rain-prints in sedimentary rocks, 196,
198*
Rain- wash, 20*
Raised Beaches, 123, 402, 403, 409
Rastrites, 278*
Ravines, eroded by rivers, 35*, 36*,
37*
Recent deposits, 256, 394, 403
Red colour, cause of, in rocks, 132,
I 43' 3 X 5 I strata, cause of un-
fossiliferous character of, 315, 326
Red Crag, 390
Regional metamorphism, 221
Regular system in crystallography,
I39 *
Reindeer, 394, 400, 408*, 409
Rensseleria, 294
" Reptiles, Age of," 338, 367, 370
Reptiles, fossil, 320, 327, 338, 356
Reqnienia, 353*
Resinous lustre, 181
Retinite, 180
Reuss, River, 49
Reversed Faults, 218
Rhastic group, 329, 330
Rhamnus, 387
Rhamphocephalus, 339
Rhamphorhynchus, 339
Rhinoceroses, fossil, 379, 382, 386,
387, 400, 408
Rhizodus, 305, 311*
Rhone, filtered by Lake of Geneva,
33 I g r g e f. 35 I delta of, in
Lake of Geneva, 49 ; ancient
glacier of, 74
Rhus, 381*, 387
Rhynchocephalia, fossil, 327
Rhynchonella, 282, 283*, 293, 308,
335- 353- 389*
tfhynchosaurus, 328
Rhyolite, 179
Ripple-marks, 196, 197*
Rivers, effects -of flooded, i ; geo-
logical operation of, 26 ; chemical
action of, 27, 95 ; mineral matter
held in solution by, 28, 29 ; trans-
porting power of, 29, 30, 38 ;
proportion of sediment in water
of, 30, 31 ; erosive action of, 32 ;
sinuous courses of, 34*, 35* ;
ravines of, 35*, 36*, 37* ; filtered
by lakes, 33 ; limit to erosive
action of, 36 ; deposit of sediment
by, 38, 40*, 41* ; terraces formed
by, 43*, 44*, 404; flood-plains of,
44 ; affected by elevation of land,
44 ; plants^nd animals swept away
and entombed by, 45, 48 ; deltas
of, in lakes, 51 ; action of frozen.
69 ; marine deltas of, 85 ; flow
of, affected by earthquakes, 122;
traces of ancient, 358; human relics
preserved in high terraces of, 404,
405, 409
"Roches moutonn&s," 72*, 78
Rock-crystal, 130, 138
Rock-salt, 152, 171, 172, 315, 321,
322, 324, 329
Rock-shelters, 411
Rocks, definition of, 154 ; bad con-
ductors of heat, 105 ; methods of
investigating, 154 ; classification
of, 163; sedimentary, 163, 192;
fragmental or clastic, 164 ; formed
from chemical precipitation, 170 ;
formed of remains of plants and
animals, 173 ; eruptive or igneous,
176, 224; acid, 177, 178; inter-
mediate, 177, '181 ; basic, 177, 183 ;
metamorphic, 186, 221 ; depth of
fossiliferous, 256
Roofing-slate, 187, 216
Rota Ha, 351*
Rothliegende, 320, 321
Rothpletz, Dr. , on thrust-planes in
the Alps, 221
Rugose corals, 279*, 293*, 306*
Rust, cause of, 14, 130
Rutile, 133
Sabal, 351, 369
Sables Moyens, 373
450
INDEX
Sacammina, 306
St. Erth Beds, 391
St. Lawrence River, ice of, 69, 70
Sal-ammoniac in volcanic sublimates,
118
Salina group, 286
Salisburia, 369
Salix, 369, 387, 388*
Salt-lakes, 54, 173, 315, 324
Salts, 129
Sand, geological history of, 4 ; cal-
careous, formed by nullipores, 94,
1 66, 174 ; varieties of, 166 ; ex-
tent of deposition of, 201
Sand-dunes, 21, 166 ; neolithic re-
mains in, 409
Sandstone, decay of, into soil, 15* ;
kinds of, 167 ; indurated, 187,
234 ; changed to quartzite, 189,
234 ; comparatively rapid forma-
tion of, 202 ; changed into rnica-
schist, 222, 227
Sanidine, 146, 178
Sarmatian stage (Miocene), 384
Sarsaparilla, fossil, 369, 387
Sassafras, 350*, 387
Satellites, origin of, 253
Satin-spar, 151
Saturation, influence of, in weather-
ing. 13
Saurians, fossil, 320, 323
Saxicava, 399*
Scandinavia, ice-borne stones from,
74 ; glaciation of, 77, 79 ; uprise
of, 123 ; pre-Cambrian rocks of,
262 ; glaciation of, 396
Scapheus, 337
Scaphites, 354*
Scaphognathus, 339*
Scenery, slow changes in, i
Schist, 163, 186, 222, 258
Schistose structure, 162'"', 186, 190,
216
Schizodus, 319
Schloenbachia, 354
Schoharie grit, 295
Scolithus, 281
Scoriaceous, 161
Scorpions, fossil, 240, 284, 304*
Screes, origin of, 20, 164
Screw- pines, fossil, 351, 369
Sea, destructive and reproductive
effects of, 2 ; demolition of land by,
80 ; chemical action of water of, 80 ;
force of breakers of, 80 ; erosion
only by upper part of, 82 ; rate of
erosive action of, 84, 85* ; accumu-
lations formed by, 85 ; transport
of sediment by, 88 ; slow deposition
in abysses of, 88 ; proportion of cal-
careous organisms in tropical waters
of, 96 ; preservation of animal-
remains on floor of, 101, 238 ; evi-
dence of the presence of, 4, no,
244 ; volcanic detritus on floor of,
112 ; proportion of carbonate and
sulphate of lime in water of, 132
Sea-calf, fossil forms of, 382
Sea-mats, fossil, 308
Sea-serpents, fossil, 357, 370
Sea-shells, geological inference from,
4, no
Sea-urchins, fossil, 306, 334, 352*
Sea-weeds, accumulations of, 94 ;
fossil, 269, 277*
Sea- worms, 277, 281*
Seals, fossil, 390, 403
Secondary rocks in Geological Record,
257
Secretary-birds, fossil, 376
Section in stratigraphy, 248
Sedgwick on Cambrian system, 267 ;
with Murchison named the Devon-
ian system, 287
Sediment, slow changes of, 201
Sedimentary, definition of, 156, 163 ;
rocks, account of, 163, 192 ; most
ancient forms of, 260
Selenite, 151
Semionotus, 327
Senonian stage, 357, 361
Septaria, 156*, 199
Septaria Clay, 379
Sequoia, 351, 369, 387
Sericite (Muscovite mica), 190
Sericite-schist, 190
Series in stratigraphy, 248
Serpentine, 148, 149, 186 ; schistose,
191
Serpentine-schist, 191
Serpula, 281
Shale, 168 ; baked, 187
Sharks, fossil, 310 ; teeth of, in
abysmal deposits, 88, 102
INDEX
451
Shearing of rocks, 162, 186, 214,
215, 221
Sheep, fossil, 393 ; domesticated,
409
Sheets, intrusive, 228*; interstratified,
229*
Shell-banks, 95*
Shell-marl, 4, 53*, 92, 93*, 95, 174
Shells, evidence from, in geological
history, 4
Shingle, 165
Shores, proofs of former, 195
Shorthorn, domesticated, 409
Shrews, fossil, 377
Shrimps, fossil, 337
Siclerite, 150, 156*, 173
Sigillaria, 246, 302*, 303
Sigillarioid plants, 303, 317
Silica, or silicic acid in earth's crust,
130, 141 ; soluble form of, 143 ;
in springs, 67 ; secreted by plants,
94*, 239, 361 ; secreted by animals
94, 246, 361 : as a petrifying
medium, 242
Silicates, solution of, 61 ; in earth's
crust, 130, 131, 133, 137, 145,
177
Siliceous pebbles, durability of, 165
Siliceous sinter, 67, 173
Silicification, 242
Silicon in earth's crust, 129, 130
Sills, 228*
Silurian, place of, in Geological
Record, 257 ; origin of name, 267;
system, description of, 276
Sinter, calcareous, 65 ; siliceous, 67,
173
Sivatherium, 393
Siwalik group, 393
Slaggy structure, 161
Slate, 187, 216
Smilax, 369, 387
Snails, fossil, 289, 304
Snakes, fossil, 382
Snow, geological action of, 70
Sodium in earth's crust, 129, 133 ;
in sea- water, 133
Sodium-carbonate in bitter lakes, 55
Sodium-chloride in salt lakes, 55,
133 ; in the sea, 133, 136 ; as a
rock-former, 170
Soil, effects of frost on, 13 ; forma-
tion of, 15*, 16*, 18, 20*, 164 ;
causes of variation in, 17 ; re-
moval of, by rain, wind, and worms,
1 8 ; final transport of, to the sea,
22
Solar system, evolution of, 252
Spa lacotherium , 341
Spar, formation of, 64
Sparodus, 320
Spectre-insects, fossil, 304
Specular iron, 143
Speeton Clay, 358, 359
Sphaerosiderite, 150, 151*, 156*, 173
Sphenopteris, 300*, 301, 318, 325,
332
Spherulites, 160, 161*, 180
Spilosite, 188
Spirifers, 293, 294*, 308, 309*, 318,
335
Spirifer-sandstone, 295
Spondylus, 384
Sponges, fossil, 278, 351*
Spotted slate, 188
Springs, mechanical action of, 57 ;
chemical action of, 60 ; deposits
from, 62 ; calcareous, 63 ; chaly-
beate, 67 ; siliceous, 67 ; thermal,
103, 173 ; containing metallic
solutions, 321
Spruce, fossil, 390
Squalor aia, 337
Squids, 274
Squirrels, fossil, 371
Stacheoceras, 319
Stage (in stratigraphy), 248
Stagonolepis, 328
Stags, fossil, 386
Stalactite, 63, 64*
Stalactitic condition of minerals, 141
Stalagmite, 63 ; preservation of
animal -remains in, 65, 100 ;
human relics in, 407
Star-fishes, fossil, 271, 280*, 281
Staurolite-slate, 188
Steam in volcanic eruptions, 161
Sfegosaurus, 341
Steneosaurus, 338
Stenopora, 318
Stephanoceras, 337
Stigmaria, 302*
j Stoat, fossi', 408
! Stone-flies, fossil, 304
452
INDEX
Stone implements, geological evidence
furnished by, 404, 405
Stonesfield Slate, 344
Storm -beaches, 87*
Strand-lines, 123, 124*
Strata, nomenclature of, 194 ; asso-
ciation and alternation of, 199; rela-
tive areas of, 200 ; chronological
value of, 20 1 ; consolidation of,
207 ; original horizontality of, 209
Stratified, definition of, 158; struc-
ture, 45, 163, 193
Stratigraphy, definition of, 9, 195 ;
divisions of, 247
Stratum, defined, 194
Strepsodus, 305
Streptorhynchus, 308, 309*
Strike of strata, 210*, 211*
Strike-joints, 208
Stringocephalus, 294*
Strombus, 384, 393
Strophalosia, 318*
Strophomena, 282, 293
Sub-Carboniferous, place of, in Geo-
logical Record, 257, 313
Sub-group in stratigraphy, 248
Sublimates, volcanic, 118 ; origin of
minerals, 140, 143 ; crystalline
structure in, 158
Submarine plane of erosion, 84*
Submerged forests, 123
Subsidence, produced by earthquakes,
122 ; secular, 123 ; proofs of, 203,
265, 298, 299
Subsoil, origin of, 16, 18, 164
Sub-stage in stratigraphy, 248
Suffolk Crag, 390
Sulphates, 136, 137, 150, 153
Sulphides, 129, 136, 137, 152 ; as
petrifying agents, 242, 321
Sulphur in volcanic sublimates, 118 ;
in earth's crust, 129, 135, 137, 152
Sulphuric acid, 129, 153
Sumachs, fossil, 381, 387
Sun, history of the, 253
Sun-cracks in sedimentary rocks, 196
Superposition, order of, 3
Switzerland, landslips in, 60 ; glaciers
of, 72, 74
Syenite, 181
Syncline, 213
System in stratigraphy, 248
Tabulate corals, 279
Tachylyte, 183
Tseniopteris, 318, 325, 332
Talc, 148
Talc-schist, 190
Talus, origin of, 20*
Tapes, 384
Tapir, fossil forms of, 371, 377, 379,
382
' Taunusian rocks, 295
I Taxodium, 387
Teleosaurus, 338
I Telerpeton, 328*
I J^ellina, 384, 390, 399*
j Temperature, influence of, in weather-
ing, 13, 1 66
Terebratula, 294, 308, 335, 353
Terebratulina, 357
Termidse, fossil, 304
Terminal moraine in United States,
398
Termite, influence of, upon soil, 19
Terrestrial surfaces, evidence of, no
Tertiary formation, place of, in
Geological Record, 257 ; account
of. 3 6 5
Tesseral system in crystallography,
139*
Tetragonal system in crystallography,
139*
Texiularia, 351*
Thamnastreea, 334
Thanet Sand, 373
Thecosmilia, 334
Throw of a fault, 218, 219*
Thrust plane, 220
Till or Boulder-Clay, 396, 403
Tillodonts, 372
Time, popular notions regarding the
influence of, n, 12 ; in geology,
201 ; geological names for divisions
of, in geological history, 249, 268
Tinoceras, 371
Titanic iron, 133, 144
Titanichthys, 290
Titanium in earth's crust, 129, 133
Titanotherium, 379
Tithonian, 345
Toads, fossil, 382
Toarcian, 342
Tonalite, 182
Tongrian stage, 379
INDEX
453
Topaz, 179
Topographical features due to
weathering, 22
Torridonian, place of, in Geological
Record, 257 ; formation described,
261
Tortoises, fossil, 356, 370
Toxoceras, 354*. 355
Trachyceras, 326
Trachyte, 182
Trachyte-tuff, 169
Trails of worms, 28 1
Transition rocks, 267
Travertine, formation of, 65, 66*,
101 ; characters of, 171
Trees, evidence from, as to geologi-
cal time, 201
Tree-ferns, fossil, 317
Tremadoc group, 274
Trematosaurus, 327
Tremolite, 147, 189
Trenton group, place of, in Geologi-
cal Record, 257, 286
Triassic system, place of, in Geologi-
cal Record, 257 ; account of, 323
Triclinic system in crystallography,
140
Trigonia, 335*, 353*
Trilobites, 246, 271, 272*, 274, 281,
282*, 292*, 293, 307*, 337
Trinucleus, 281, 282*
Tripoli-powder, 94, 240
Trochoceras, 285*
Trogons, fossil, 376
Trogontherium, 390
Trophon, 389*, 399*
Tufa, calcareous, 65, 135, 171, 407
Tuffs, volcanic, in, 169
Tulip-tree, fossil, 387
Tunbridge Wells Sand, 359
Turner, Mr. H. W. , photograph by,
78*
Turonian stage, 357, 361
Turrilites, 354*, 355
Turtles, fossil, 338, 356, 370, 382
Twinning of crystals, 146, 152*
Typhis, 377
Uinta group, 374
Uintatheriiim, 371"", 372
Ullmannia, 318
Ulmus, 369, 387
Ultra-basic rocks, 184
Uncites, 293, 294*
Unconformability, 204* ; examples
of, 261, 262
Unio, 377
United .States, sand-wastes of, 22 ;
Bad Lands of, 24, 374, 375*;
canons of, 36, 37* ; salt lakes of,
55 ; caverns of, 62 ; hot springs of,
67 ; ancient ice-sheets of, 74, 79 ;
erosion off coasts of, 82 ; coast-
lagoons and bars of, 85, 93 ; man-
grove swamps of, 93 ; diatom-
earth of, 94 ; extinct volcanoes of,
106, 114 ; volcanic necks in, 116* ;
fissure-eruptions of, 120 ; laccolites
of, 226 ; volcanic scenery of,
231* ; lacustrine formations of,
243 ; geological record in, 256 ;
pre- Cambrian rocks of, 262 ;
Cambrian rocks of, 275 ; Silurian
rocks of, 276, 285, 286 ; Devonian
system in, 287 ; Carboniferous
system in, 312 ; Permian system
in, 321 ; Trias in, 331 ; Jurassic
rocks in, 346 ; Cretaceous system
in, 349, 357, 363 ; Eocene of, 368,
374 ; Miocene of, 385 ; Pliocene
of . 393 I glaciation of, 394, 397
Unstratified, definition of, 158
Upheaval from earthquakes, 122 ;
secular, 123
Uralite, 148
Urgonian, 359
Uriconian, place of, in Geological
Record, 257 ; volcanic rocks, 262
Ursus, 408
Urus or wild ox, 409
Utah, Great Salt Lake of, 55
Utica group, place of, in Geological
Record, 257, 286
Valenginian, 359
Valleys, excavation of, 24 ; usually
independent of faults, 219
Vasculose of plants, 239
Vegetation, influence of, in formation
of soil, 16, 18
Veins, igneous, 118, 232 ; mineral,
234
Vein-quartz, 173
Veinstones, 234
454
INDEX
Velutina, 390
Ventriculites, 351*, 352
Vents, volcanic, 105, 113
Vermilion Creek group, 374
Vertebrates, earliest known, 266
Vesicular, 160
Vicksburg group, 374
Victoria, fossil, 369
Villafrancian, 392
Vitreous condition of rocks, 140, 159
Vitrophyric condition of igneous
rocks, 181
Vivipara, 377*
Vogesite, 181
Volcanic, definition of, 158, 177 ;
fragmental rocks, 169 ; ash, 169
Volcanoes, effects of, on landscape,
2 ; as evidence of the earth's
internal heat, 104 ; structure of,
105 ; denudation of, 106 ; perma-
nent records of, 106 ; products of,
107-113 ; submarine, 112 ; illus-
tration of the records of ancient,
229, 265, 268, 276, 287, 288, 301,
316, 32!, 325, 331, 347, 362,
3 6 3. 37 6 - 377. 3 86 , 393
Valuta, 369*, 377
Voltzia, 325
Wad, 145
Wadhurst clay, 359
Wahsatch group, 374
Walchia, 317*, 318
Walcott, Mr. C. D. , photograph by,
231
Walnut, fossil, 350, 369, 387
Walruses, fossil, 403
Water, in geological changes, i, 14,
18, 26, 27, 29, 57 ; underground,
57, 60 ; composition of , 129, 135 ;
crystalline form of, 139
Water-bean, fossil, 369
Waterfalls, recession of, 35 ; some-
times caused by earthquakes, 122
Water-line, place of, in Geological
Record, 257, 286
Water-lily, fossil, 369, 390
Water-worn rocks, 32
Waves, effects of, 80 ; caused by
earthquakes, 123
Wealden formation, 358, 360
Weather, ancient indications of, 198
Weathering, n, 12*, 15, 132 ;
feeblest condition of, 18 ; results
of, 22 ; topographical features
carved by, 22, 23*
Wemmelian, 373
Wenlock group, place of, in Geo-
logical Record, 257, 286
Werfen Beds, 330
West Indies, coral-reefs of, 99
Wey borne Crag, 390
Whale, fossil, 390, 403 ; ear-bones
of, in abysmal deposits, 88, 102
Whet-slate, 188
White-ants, fossil, 304
White Crag, 391
White River group, 379
Willow, fossil, 369, 387, 399
Wind, dried soil removed by, 18,
21 ; transport of volcanic dust by.
"3
W T ind River group, 374
Witchita Beds, 322
Wollastonite, 188, 189
Wolves, fossil, 379, 386, 390, 408,
409
Woodocrinus, 307*
Woolwich and Reading Beds, 373
Worms, in relation to soil, 16, 19,
92 ; tracks and burrows of, 277,
281*
Xenocrysts, 160
Yellow colour, cause of, in rocks, 132,
144
Yellowstone Park, hot springs of, 67
Yew-trees, fossil, 369
Yoldia, 400
Yorktown stage, 386
Ypresian, 373
Zamites, 326, 332
Zanclean, 392
Z.aphrentis, 279, 306*
Zechstein, 320, 321
Zeolites, 146
Zinc, sulphide, 235
Zoisite, 189, 191
Zone in stratigraphy, 247
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