The Story of our Planet ... Illustrated

Preface

. In writing this volume I have not had any intention of attempting to add another to the Text-books of Geology in the English language. Of these there is already an ample supply. Sir A. Geikie's " Text-book of Geology," Professor Prestwich's " Geology," and the edition of Phillips' " Manual of Geology " by Professor H. G. Seeley and Mr. R. Etheridge leave no gap to be filled among works of larger size, while a student not yet ripe for these has ample choice among books on smaller scale, which can be arranged in a graduated series from Mr. Jukes-Browne's " Handbook " to the most elementary " Primer." So I have not endeavoured to write a book which is designed to prepare for an examination or to serve as a guide to the literature of the subject. A class of persons, however, still exists to whom I hope this volume may be acceptable and useful.

Many who, to use the common phrase, have received a good education, though they feel much interest in the history of the earth on which they live, have neither the leisure nor the inclination to master the technicalities or to enter into the minute details of any one branch of science. At the present time there is, I think, a real danger lest such persons should be repelled from all know ledge of science by its increasing complexity. To speak of geology only : Forty years since, a book dealing with the main principles of geology, such as Sir C. Lyell's well-known work, PREFa4.CE. would have been understood with little difficulty by any man of good general education: two pages of print would have con tained all the technical terms which had to be mastered. But these have now become so numerous that the beginner has not only to comprehend new ideas, but also to learn a new language.

To some extent this is inevitable. As science increases in scope and complexity technical terms become more necessary. They are helpful in expressing ideas concisely and precisely ; still, they tend inevitably to diminish the number of those who take an interest in any subject and to restrict all study of it to those who make it a profession. This may prove ultimately preju dicial, by fostering a narrowness in its votaries, both of views and of sympathies. No doubt the judgment of experts is less fallible than vox populi ; but experts sometimes suffer from an hypertrophy of learning and an atrophy of common sense to which men of wider outlook and more general culture can apply a wholesome correction. Technical terms also, as I venture to think, are sometimes coined without good cause. The use of them seems to be pleasing to some minds, for it indicates an initiation in mysteries and a superiority to the common herd.

But from a terminology not generally intelligible, worse evils than the gratification of personal vanity are apt to arise — namely, the worship of phrases and the substitution of words for ideas. Science, as it grows, suffers from its epidemics, and high-sounding words are often the bacteria which communicate disease to mental constitutions of the less vigorous type. To some persons a sonorous term seems to be so satisfactory that it passes current for an idea, and is a mask for any amount of hazy indefiniteness. We are often told that plain living and high thinking go together in the daily life ; may it not be that plain speech and accurate thought are not so far apart in science ? An English phrase

PREFACE.

. V may require, when printed, a few more letters than a misbegotten compound of Greek words (often barbarous to the ears of a scholar) ; but it possesses this advantage, that he who runs may read, and he who speaks cannot clothe himself with grandi loquence as with a cloak and conceal mental poverty beneath verbal splendour. So, though technical terms cannot be wholly avoided, and the scientific names for plants and animals, as a rule, must be employed for the sake of precision, I have striven, as far as possible, to abstain from them, and to write as addressing men and women of good general education who might desire to know something of the methods of reasoning which are adopted in geology and of the general conclusions to which these have led. But in trying to tell " the Story of our Planet " in fairly plain words I have not shrunk from dealing with some of the more difficult questions which it involves.

In short, the plan on which this book has been framed is generally similar to that adopted by Sir C. Lyell in his great work, " The Principles of Geology." But as it is now twenty-one years since the last edition of " The Principles " was published, and the representatives of its author, doubtless through reverence for his memory, have not attempted to revise or alter a work which is rightly numbered among our classics, there is, I believe, room for a book which covers somewhat the same ground. Still, I have not adhered at all closely to the lines followed by Sir C. Lyell, because at the time when he wrote many things had to be fully demonstrated which now (thanks largely to him) may be taken almost for granted. In some instances, however, I have ventured to draw upon the materials collected by him, and have freely used, throughout this book, such facts as may be called the common property of all teachers of geology without

PREFACE.

. VI deeming it necessary always to indicate the source from which they were derived. As a rule, I have only inserted references where the actual words of an author have been quoted ; since, as already stated, this is not meant to be a text-book. It is founded on a part of my lecture notes, and, as everyone knows who has taught for a good many years, ideas borrowed from books, picked up in conversation, and originated in one's own brain, get at last hopelessly mixed up together in a kind of mental conglomerate. Not seldom also a teacher recognises in the writings of a former pupil a flower the seed of which was sown in his own lecture-room. Of this he cannot complain, for it is one of his highest rewards. A teacher does not and should not claim any copyright in his thoughts : he is doing his duty best when he drops each conception of his own mind, as it is duly ripened, into the receptive mental soil of his abler students, thei*e to germinate and bear fruit, perhaps better than on the exhausted arable field of his own wear}* brain.

So I may be some times suspected of plagiary when it is really from myself; and if in these pages any geologist recognises ideas of his own, used without acknowledgment, I crave his pardon, and trust to the liberality of true men of science. We borrow and we give : "Hanc veniam petimusque damusque vicissim." It may be well to observe that I have excluded from this book a few topics on the ground of their being either too technical to be made intelligible to the general reader, or at present too uncertain in their bearing on the subject to be of any real service to him. As a rule I have confined myself to the more important questions (as they seemed to me), and have set forth the views which are the more generally entertained. Still, I have not thought it needful entirely to sink my own individuality, and on one or two points have expressed opinions which, just at

PREFACE.

. VII the present time, are those of the minority (though a large one) rather than of the majority of geologists. As my excuse for so doing, I must plead that these questions for many years have been to me subjects of special study, and that in regard to them I have had rather exceptional opportunities of forming an opinion. Chief of these are — the physical geography of Britain in the earlier part of the Triassic period, the effects and former extent of glaciers, and the history and age of certain crystalline rocks. The last question, which is one of great interest and far-reaching importance, practically indicates my position in regard to the " Uniformitarian creed " in geology, and the one matter on which a slight difference in opinion from the revered author of " The Principles " will be perceptible.

To " Catastrophical geology " I am no less opposed than were our great masters, Hutton and Lyell. I fully accept the leading principles of Uniformitarian geology, but I cannot close my ears to the conclusions of men eminent in experimental and mathematical physics, or insist on regarding " the universe as a self-winding clock." Nay, I venture to think that even in the earth itself we can discover, by processes strictly inductive, some sign of its beginning and some fore shadowing of its end. I hope that no serious errors are lurking in these pages ; but geology has now become so vast a subject that perfection in all its branches would almost be another name for scientific omniscience ; and nothing makes one so conscious of the truth of the saying, Humanum est errare, as writing a book. Besides the errors due to the author's own ignorance or to the unac countable freaks and perversities of his memory, there are those typographical mistakes which so often contrive to elude his notice as to tempt him to believe that beings not Avholly beneficent haunt the precincts of the printing-office. If errors prove

PREFACE.

. VIII to be few in number, this is largely due to the kind assistance which I have received, in the revision of the proofs, from Miss C. A Raisin, B.Sc, a former pupil and now frequent helper in scientific work, to whom I tender my most grateful thanks. These also are due to the authors, scientific societies, and publishers, hereafter more particularly enumerated, who have permitted the use of illustrations which were their property. The study of geology has added much to the happiness of my own life ; it has taught me to appreciate more fully the beauties and the marvels of Nature ; it has often restored me, when weary and jaded, to bodily health ; it has helped me in bearing those trials which are the common lot ; if, then, this book is so fortunate as to interest others in the subject, I shall count that a high reward. T. G. BONNEY. University College, London, 1893. CONTENTS.

Part I. The Story

: ITS BOOKS AND THEIR SPEECH. CHAPTER PAGE I. Introductory ... ... ... ... ... ... ... ... 3 II. The Land Region 13 III. The Air Region 29 IV. The Water Region 56

Part II. The Processes Of Sculpture And Moulding

I. The Work of the Atmosphere ... ... ... ... ... ... 91 II. Rain and Rivers as Sculptors ... ... ... ... ... ... 103 III. Rivers as Transporters 129 IV. Ice as Sculptor 143 V. Ice as a Carrier 157 VI. The Work of the Ocean — Marring and Making ... ... ... 168 VII. The Proletariat of Nature 191

Part III. Changes From Within

I. Movements of the Crust 221 II. Volcanic Action and its Effects 244 III. Earthquakes and their Effects 291 IV. Internal Changes in the Earth's Crust CONTEXTS. X

Part IV. The Story Of Past Ages

CHAPTER PACE I. Meteors and the Earth's Beginning ... ... 329 II. The Eras and Subdivisions in Geological History 353 III. The Archæan Era .* 372 IV. The Building of the British Isles ... ... ... ... ... 393 V. The Building of Europe and other Continents ... ... ... 449 VI. A Sketch of the Earth's Life-History ... ... ... ... 478

Part V. On Some Theoretical Questions

I. The Age of the Earth 533 II. The Permanence of Ocean Basins and Land Areas ... ... 538 III. Climatal Change: its Cause and History ... ... ... ... 543 IV. The Distribution and the Descent of Life ... ... LIST OF ILLUSTRATIONS. FIG. PAGE 1. Cardlta planicosta (Upper Eocene); Melania inquinata (Lower Eocene); Terebratuta semiglobosa (Chalk) ... ... ... .. ... 3 2. Chalk of Gravesend ... ... ... ... ... ... ... ... 5 3. Sequence of Masses of Rock ... ... ... ... ... ... ... 8 4. Comparative Size of the Sun and the Earth ... ... ... ... 11 5. The Alps, from Berne ... ... ... ... ... ... ... ... 15 6. A Volcanic Hill (Vesuvius, from the Sea) ... ... ... ... ... 17 7. Land Hemisphere ... ... ... ... ... ... ... ... 18 S. Ocean Hemisphere ... ... ... ... ... ... ... ... 19 9. Block of Pudding-Stone 22 10.

Stratified Rocks 23 11. A Case of False Bedding- 24 12. Joints exhibited in a Mountain Ruin, from the Dolomites of Cortina, S.E. Tyrol 25 13. Columnar Jointing 26 14. Columnar Basalt, Fingal's Cave ... ... ... ... ... ... 27 15. Diagram of Air Currents and Atmospheric Circulation ... ... ... 35 16. Chart of a Cyclonic Disturbance over the British Isles 40 17. A Tornado, from a Photograph ... ... ... ... ... ... 44 18. The Course of a Tornado in the West Indies, 1868 47 19. Map of North-Western Europe, with the Submarine Contours ... ... 59 20. Diagram to Explain the Attraction of the Moon in Producing Tides ... 66 21. Currents in the Ocean ... ... 68 22. Direction of Currents to and from the Arctic Ocean ... ... ... 72 23. Snow Crystals 77 24. Terminal Ice-cave and Birthplace of a River ' ... 80 25.

Crevasses in a Glacier ... ... ... ... ... ... ... ... 86 26. Diagram showing Rate of Movement in a Glacier .. . 87 27. Wind-worn Rocks, Yellowstone Park 94 28. Diagram showing the Formation of a Dune... ... ... ... ... 95 29. Blown Sand advancing on Cultivated Land, Bermuda 97 30. Tower of Eccles Church, a.d. 1839 98 31. Tower of Eccles Church, November, a.d. 1862 99 32. A Granite Tor on Dartmoor 106 33. A Sand-pipe LIST OF ILLUSTRATIONS. PAGE FIG. 34. Fossil Rain-prints ... ... HO 35. Earth-Pillars on the Rittnerhorn IH 36. Section of Glen with Earth- Pillars 112 37. A Waterfall 118 38. Diagram of a Cirque, Surenen Pass 119 39. Terraced Cliff 121 40. Gorge in Sloping Beds ... ... ... ... ••• 121 41. The Gorge of the Tamina, Pfiifers, Switzerland ... ... ... ... 122 42. In the Bed of a Canon 123 43.

Diagram of Course of a River ... ■■■ 124 44. Diagram of Winding River ... ... ... ... 125 45. Geyser and Mound of Silica ... ... ... ... ... 132 46. Terraces at Rotomahaiia ... ... ... ... ... ... ... 133 47. Map of Volcanic District, Rotomahana ... ... ... ... ... 134 48. Sketch Map showing Former Extent of Alpine Glaciers (N. side) ... 148 49. Bird's-eye View of Pot-holes in Glacier Garden, Lucerne... ... ... 149* 50. Roches Moitton nces — the Grimsel ... ... ... ... ... ... 150 51. Map of the Great Lakes of Canada and United States ... ... ... 155 62. Glacier with Moraine [Mer de G lace) ... ... ... ... ... 158 53. Glacier-Tables 160 54. A Perched Block 161 55. On a Greenland Ice-sheet ... ... ... ... ... ... ... 164 56. The Formation of an Iceberg ... ... ... ... ... 165 57. Icebergs Floating out to Sea ... ... 166 58.

Ice-worn Headland in Fjord, near Laurvik, Norway ... ... ... 171 59. Ice-worn Rock Torn by Waves, near Langesund, Norway ... ... 172 60. Waves Breaking on the Beach ... ... ... ... 173 61. Old Harry Rocks, near Swanage ... ... ... ... ... ... 175 62. Gulleys in place of Dykes, Strathaird, Skye ... ... ... ... 177 63. The Frying-pan, Cadgwith, looking Seaward 180 64. Inland Cliff and old Sea-bed, West Coast of Scotland 181 65. Insulated Rocks near the Lizard ... ... ... ... 183 66. Shoals and Channels at the Mouth of the Thames ... ... ... ... 185 67. The Mississippi Delta 188 68. Bird's-eye View of the Nile Delta, looking Southward ... ... ... 189 69. Concretions ... ... ... ... ... ... ... ... ... 194 70. Thin Slice of Shale from Kettle Point, Lake Huron 200 71. A Living Foraminifer (Miliola) ... ... ... ... ... ... 201 72.

A Living Chambered Foraminifer (Pulvintt/ina) ... ... 202 73. The Shell of a Globigerina 203 74. Coccoliths and Coccospheres ... ... ... ... ... ... ... 204 75. A Radiolarian {Haliomma) ... ... ... ... ... ... ... 205 76. Holtcnia carpenteri ... ... ... ... ... ... ... ... 206 77. Glauconitic Cast of a Chambered Foraminifer, showing the Passages between the Chambers ... ... ... ... ... ... ... 208 78. Masamarhu Island, Map and Section ... ... ... .. ... 215 79. Masamarhu Island ... ... ... ... ... ... ... ... 216 80. Limestone with Crinoid Stems ... ... ... ... LIST OF ILLUSTRATIONS. XIII FIG. PAGE 81. Nummulitic Limestone ... 218 82. Columns in the "Temple of Serapis" 222 83. The Temple of Serapis, at the time of deepest submergence ... ... 225 84. Terraces Cut by the Sea, Malanger Fjord, Norway ... 228 85.

Sea-cut Grooves in Smoothed Rock, N. of Alten Fjord, Norway ... 229 86. Diagram of a Fault 232 87. Diagram of a Reversed Fault 232 88. Flexures in Bedded Limestone, Draughton, near Skipton .. . ... ... 233 89. Diagram of Folds in Stratified Rocks 234 SO. Diagram of Faults in Stratified Rocks 235 91. Folded Strata (Lower Tertiary) in the Hausstock ... 237 92. Process of Conversion of a Fold through an Oversold into an Overthrust Fault 238 93. Section across the Alps in the general direction of the St. Gothard Road 239 94. Diagram illustrating Favre's Experiment ... ... ... ... ... 240 95. An Ejected Clot of Lava ... 245 96. Mud Volcanoes, Turbaco, Colombia ... ... ... ... ... ... 246 97. Monte Nuovo, from the Sea-shore 248 98. Hawaii, with the Craters and Lava Streams of various Eruptions ... 250 99.

Map of Krakatoa, before the Eruption of 1883 252 100. Section of Krakatoa, before the Eruption of 1883 254 101. Section of Krakatoa, after the Eruption of 1883 ... .. ... ... 255 102. Cotopaxi, from San Rosario (10,356 ft.) 258 103. Dust-cloud from Cotopaxi ... 261 104. Vesuvius, from the Bay of Naples ... ... ... ..". ... ... 262 105. Outline of Monte Somma .. ... 263 106. Breached Craters, Auvergne ... ... ... ... ... ... ... 272 107. Section of the Great Geyser 279 108. Diagram Illustrating Mallet's Theory of the Direction of Movement from an Earthquake Focus ... ... ... ... ... ... 292 109. Diagram of Seismic Circles ... ... ... ... ... ... ... 293 110. Street Houses in Charleston Damaged in the South Carolina Earthquake of 1886 297 111. Fissure produced hy an Earthquake, Bella, Calabria ... ... ... 300 112.

Cathedral of Tito, Calabria, after the Earthquake of 1857 304 113. Street View in La Polla after the Earthquake of 1857 305 114. Earthquake Map ofthe World 311 115. Spheroids inside a Column, showing Independence of these and the Sides (Auvergne) ... ... 319 116. Spheroidal Structure in a Mass of Volcanic Ash (Burntisland) ... ... 319 117. Cheese Grotto, near Bertrich Baden .. . ... ... ... ... ... 320 118. Surface of the Sun, as shown by a Solar Spot ... ... ... ... 333 119. The Annular Nebula in Lyra 335 120. Some of the Latest Fossils. (From the Scottish Glacial Clays) 355 121. A Group of Crystals (Quartz) 356 122. Palæolithic Flint Implements, from St. Acheul, near Amiens 357 123. Rocks (Quadersandstein) : Marterstelle, from the Basteibriicke in Saxon Switzerland, contemporaneous with the Chalk of England LIST OF ILLUSTRATIONS.

FIG. PA0E 124. Unconformity : Upper Old Red Sandstone resting on Silurian 363 125. Loch Maree— among the " Foundation Stones " of Scotland 374 126. Ben Slioch — a Mountain of Torridon Sandstone 375 127. Polished Slab of Eozoon Canadense 384 128. Structure of Enzoon Canadense... ... ... ... ... ... ••■ 38o 129. Diagrammatic Section of Eozoon Canadense ... ... ... ... ■■■ 386 130. Vertical Section of a Nummulite ... ... ... ... ... ■•■ 386 131. Diagram of Rock at Cote St. Pierre 388 132. A Lower Cambrian Trilobite (Parados ides) ... ... 395 133. Restoration of the Geography of Britain in Early Carboniferous Times... 40-! 134. Restoration of the Geography of Britain in Keuper Times ... ... 410 135. Suncraeks and Footprints, Trias, Hessberg .. . ... ... ... ... 417 136. Map of Deep Borings in the South-East of England ... ... ... -422 137.

Restoration of the Geography of Britain in London Clay Times .. . ... 431 138. Section of the Scuir of Eigg 434 139. Section at Lcnham ... ... ... ... ... ... ... ... 435 140. Section of Buried River-Channel in Essex ... ... ... ... ... 440 141. Sictiun of Thames Valley at Goring ... ... ... ... ... ... 441 142. Map illustrating how a Rise of 600 ft. (100 fathoms) would unite Great Britain with Ireland and the British Isles with the Continent ... 443 143. The North Downs and Weald Valley 447 144. Basaltic Plateaux of the Coiron in the Ardeche ... ... ... ... 451 145. Septum and Sutures of Ammonites, Ceratites and Nautilus... ... ... 484 146. Catamites cannœformis ... ... ... ... ... ... ... ... 488 147. Lepidodendron elegans ... ... ... ... ... ... ... ... 489 148. Sigillaria lœvigata ... ... ... ... ... ... ... ... 489 149.

Restoration of Olenelhis 491 150. Structure of a Graptolite ... ... 493 151. Halysites catenulatus ... ... ... ... ... ... ... ... 494 152. Euryptcrus remipes ... ... ... ... ... ... ... ... 495 153. Ganoid Fishes (Old Red Sandstone) 497 154. Devonian and Carboniferous Fossils 498 155. Cypris 500 156. Eentacrinus briareus (Extracrinus) ... ... ... ... 506 157. Encrinus (Triassic) ... ... ... ... 507 158. Shell of a Trigonia ... ... ... ... ... ... 508 159. Skeletons of Ichthyosaurus and Plesiosauras (restored) ... ... ... 510 160. Pterodactylus brerirostris ... ... ... ... ... ... ... 514 161. Cretaceous Fossils ... ... ... 517 162. Skeleton of Iguanodon .. . ... ... 519 163. Engraving of Mammoth, from the Dordogne Caves (reduced) ... ... 528 164. Mean Annual Isotherms of the Norwegian Sea ... ... ... ... 543 165.

Diagram of the Course of the Winter Isotherms in the Northern Hemisphere .. ... ... ... ... ... ... ... 544 166. Diagram of the Course of the Annual Isotherms in the Northern Hemisphere ... ... ... ... ... ... ... 545 167. Surface Isotherms of the Sea in January and February ... ... ... 547 168. Diagram of an Elliptical Orbit ... ... ... LIST OF ILLUSTRATIONS. XV FIG. PAGE 169. Map showing how the deep narrow Strait between Bali and Lombok separates the Australasian from the Indo-Malayan Fauna ... 567 170. Various Forms of Feet, illustrating Development of one Digit and Abortion of Others ... ... ... 570 Note. — The publishers desire to express their thanks to Mr. Murray for his kindness in granting them permission to include Figs. 30 and 31, from Lyell's " Principles of Geology " ; to Messrs. Macmillan, for the use of Fig. 75 from " The Voyage of the Challenger," and for Figs. 78 and 79, from Captain Wharton's paper in Nature; to Messrs. Bell and Son, for the use of Figs. 12, 24, 25, and 41.

To the Royal Society they are indebted for the use of Figs. 99, 100, and 101 ; Mr. Whymper has also been good enough to lend two blocks (Figs. 102 and 103) from his " Travels in the Great Andes " ; and to the Council of the Geological Society they are indebted for Figs. 38. 115, 116, 51 (Spencer), 136 and 140 (Whitaker), 138 (Sir A. Geikie), 139 and 141 (Prestwich); while for permission to include Fig. 149 they have to thank the editor of Natural Science. Figs. 12, 58, 59, 62, 84, 85, 105, 124 and 131 are from sketches by the author. LIST OF PLATES. A Glacier — Mer de Glace, with the Grandes Jorasses in the Distance Frontis. Map showing the Contours of the Atlantic Ocean ... To face p. 60 Map showing the Contours of the Pacific Ocean ... ... „ 62 Bird's-eye View of the Canons of Colorado ... ... ... „ 192 Vaagekallen, Lofoten Islands — the Work of Weather and Glacier ... ... ... ... 320 A Lava-stream Flowing into a Lake, Hawaii... ... ... „ Part I. THE STORY: ITS BOOKS AND THEIR SPEECH. Planet

Chapter I. Introductory

Flu. 1.— (1) Cardita planicosta (Upper Eocene) ; (2) Melania inquinata (Lower Eocene) ; (3) Terebratula semiglobosa (Chalk). All about half natural size. THESE drawings represent three specimens, taken almost haphazard, from a collection of fossils. Each of them, beyond all doubt, once must have been part of a living creature. The first was dug out of a sandy clay, between highand low water mark, at a place called Bracklesham, on the Sussex coast. AVhat of that ? it may be asked ; what wonder at finding a sea-shell in such a position ? This only : that nothing exactly resembling it could now be discovered alive in British seas — or, indeed, in any other seas. Yet it was formerly common enough, for dozens of similar specimens could have been picked up where it was lying. But more than this : many other shells were abundant in that clay, not one of which is now to be found in British waters.

Indeed, we notice on closer study that they are more like the shells which come from shores much PLaINET. nearer to the equator than those of our islands. Evidently it is many a long year since their tenants died. Every trace of ornamental colouring has disappeared ; all the specimens have become of a uniform grey tint. They have lost the animal matter which strengthens the shell of the living creature ; all are more or less brittle — some break almost at a touch. So it scciiis reasonable to infer that since these molluscs lived and died, the climate of Britain has greatly altered. The next fossil came from a dark bedded mud in the Thames valley, which also was crowded with various kinds of shells, all extinct sj.ccies, all bearing moro resemblance to those which now inhabit warmer regions than Britain.

The animals which, at the present day, are more nearly related to them live in rivers, especially where these begin to broaden out into estuaries. So far, then, there is nothing surprising in finding such fossils in tho valley of the Thames, some three or four leagues below the Port of London. But the clay in which they were lying is at least fifty feet above the present level of the river, and was evidently deposited, as may be seen on closer examination, by a broader and grander stream than now glides below tho slopes of Richmond Hill and under the bridges of London. Thc first specimen indicated a change in the tenants of this part of the globe and suggested a change in climate. This one not only gives confirmatory evidence, but also intimates that the physical geography of thc district must have been considerably altered.

Let the third specimen now tell its tale. Like the others, it does not represent any creature actually living, though kindred forms are not uncommon, and it can be referred, like them, to a well-known genus. All three, however, are best represented, and may be said to be at home, in distant seas. But this specimen was obtained in a pit on the slopes of the Downs, some five hundred feet above the present sea-level. Yet more, if wo minutely examine the pure white chalk in which this shell was embedded, if we separate it carefully particle from particle, and place the dust, properly mounted, under a microscope, we shall find that not a little of this apparently formless powder has once been part of a living organism, which can be often identified with some tiny creature, a tenant of the open ocean far away INTRODUCTORY. 5 from shore.

So this last specimen carries us yet a step further than the other two. They intimate both a change in climate and geographical conditions not wholly identical with the present ; this tells of a time when, instead of a green sward, dark-spotted with old yew-trees, instead of trailing hops and golden corn, a waste of salt waters extended far and wide, and Fig. 2. — Chalk of Gravesend. Showing foraminifera, with sponge spicules. (Much magnified.) the sea lay deep where now the Kentish Downs overlook the Sussex Weald. Is it, however, possible to find any other explanation of the occurrence of these shells which might enable us to avoid con clusions so startling ? At first men were content to regard them as freaks of Nature — mere imitative shapes, like tthe " birds' heads " and other " curiosities " which are sometimes brought to the geologist by ignorant folk in country places.

But, as a closer study showed, the resemblance was too perfect ; for these objects copied not only the external form, but also the internal structure of shell or of bone ; and it became clear at last that the remains of the creatures, which had been dead but a few years or centuries, could be linked on, by imperceptible gradations, to those which were embedded in the solid rock, and had V. n subjected to great mineral change. By some persons fossils were formerly explained as the results of a " plastic force " in Nature ; preliminary and abortive efforts to produce the more perfect form — very much as when, according to Burns, " Her 'prentice han' she tried on man, An' then she made the lasses, 0 ! " But such an explanation obviously was no better than a mental stop-gap, like the answers with which parents, not too learned try to satisfy inquisitive children.