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diff --git a/33925.txt b/33925.txt new file mode 100644 index 0000000..6226aab --- /dev/null +++ b/33925.txt @@ -0,0 +1,4524 @@ +The Project Gutenberg EBook of The Geological Story of the Isle of Wight, by +J. Cecil Hughes + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Geological Story of the Isle of Wight + +Author: J. Cecil Hughes + +Illustrator: Maud Neal + +Release Date: October 14, 2010 [EBook #33925] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE GEOLOGICAL STORY OF THE *** + + + + +Produced by Tom Cosmas and the Online Distributed +Proofreading Team at http://www.pgdp.net (This file was +produced from images generously made available by The +Internet Archive/American Libraries.) + + + + + + + + + + THE GEOLOGICAL STORY OF + THE ISLE OF WIGHT. + + + + + [Illustration: _Photo by J. Milman Brown, Shanklin._] + + GORE CLIFF--UPPER GREENSAND WITH CHERT BEDS + + + + + The Geological Story + of the + Isle of Wight + + + BY THE + Rev. J. CECIL HUGHES, B.A. + + + _With Illustrations of Fossils by + MAUD NEAL_ + + + LONDON: + + EDWARD STANFORD, LIMITED + 12, 13, & 14 LONG ACRE, W.C. 2. + 1922 + + + + +PREFACE + + +No better district could be chosen to begin the study of Geology than +the Isle of Wight. The splendid coast sections all round its shores, +the variety of strata within so small an area, the great interest of +those strata, the white chalk cliffs and the coloured sands, the +abundant and interesting fossils to be found in the rocks, awaken in +numbers of those who live in the Island, or visit its shores, a desire +to know something of the story written in the rocks. The Isle of Wight +is classic ground of Geology. From the early days of the science it +has been made famous by the work of great students of Nature, such as +Mantell, Buckland, Fitton, Sedgwick, Owen, Edward Forbes, and others, +who have carried on the study up to the present day. Many of the +strata are known to geologists everywhere as typical; several bear the +names of the Island localities, where they occur; some--and those not +the least interesting--are not found beyond the limits of the Island. +Though studied for so many years, there is no exhausting their +interest: new discoveries are constantly made, and new questions arise +for solution. To those who have become interested in the rocks of the +Island, and the fossils they have found in them, and who wish to learn +how to read the story they tell, and to know something of that story, +this book is addressed. It is intended to be an introduction to the +science of Geology, based on the Geology of the Isle of Wight, yet +leading on to some glimpse of the history presented to us, when we +take a wider outlook still, and try to trace the whole wondrous path +of change from the world's beginning to the present day. + +I wish to express my warmest thanks to Miss Maud Neal for the +beautiful drawings of fossils which illustrate the book, and to +Professor Grenville A. J. Cole, F.R.S., for his kindness in reading +the manuscript, and for valuable suggestions received from him. I have +also to acknowledge my indebtedness to Mr. H. J. Osborne White's new +edition of the _Memoir of the Geological Survey of the Isle of Wight_, +1921; and to thank Mr. J. Milman Brown, of Shanklin, for the three +photographs of Island scenery, showing features of marked geological +interest, and Mr. C. E. Gilchrist, Librarian of the Sandown Free +Library, for kindly reading the proofs of the book. + + + J. CECIL HUGHES. + + Mar., 1922. + + + + + CONTENTS + + + Chap. Page + + I. The Rocks and Their Story 1 + + II. The Structure of the Island 10 + + III. The Wealden Strata: The Land of the Iguanodon 15 + + IV. The Lower Greensand 23 + + V. Brook and Atherfield 29 + + VI. The Gault and Upper Greensand 37 + + VII. The Chalk 42 + + VIII. The Tertiary Era: The Eocene 54 + + IX. The Oligocene 63 + + X. Before and After: The Ice Age 70 + + XI. The Story of the Island Rivers; and How the Isle of + Wight Became An Island 86 + + XII. The Coming of Man 97 + + XIII. The Scenery of the Island: Conclusion 105 + + + + + ILLUSTRATIONS OF FOSSILS + + + _PLATE I.--Facing page 20._ + + Wealden Cyrena Limestone + Vertebra of Iguanodon + + Lower Greensand Perna Mulleti + Meyeria Vectensis (Atherfield Lobster) + Panopaea Plicata + Terebratula Sella + + + _PLATE II.--Facing page 23._ + + Lower Greensand Trigonia Caudata + Trigonia Daedalea + Gervillia Sublanceolata + + Upper Greensand (Ammonite) Mortoniceras Rostratum + Nautilus Radiatus + + + _PLATE III.--Facing page 45._ + + Lower Greensand Thetironia Minor + Rhynchonella Parvirostris + + Upper Greensand (Pecten) Neithea Quinquecostata + + Chalk (Ammonite) Mantelliceras Mantelli + (Sea Urchins) + Micraster Cor-Anguinum + Echinocorys Scutatus + (Internal cast in flint) + + _PLATE IV.--Facing page 61._ + + Eocene Cardita Plarnicosta + Turritella Imbricataria + Nummulites Laevigatus + (Fusus) Leiostoma Pyrus + + Oligocene Limnaea Longiscata + Planorbis Euomphalus + Cyrena Semistriata + + + + + DIAGRAMS + + Facing page + + 1. Coast, Sandown Bay 10 + + 2. Coast, Atherfield 29 + + 3. Coast, Whitecliff Bay 56 + + 4. Section Through Headon Hill and High Down. + (Strata Seen at Alum Bay) 58 + + 5. St George's Down 79 + + 6, 7. Development of River Systems 86 + + 8. The Old Solent River 94 + + 9. Shingle at Foreland 79 + + +PHOTOGRAPHS + + Facing page + + 1. Gore Cliff. _Frontispiece._ + + 2. Chalk at the Culver Cliffs. 46 + + 3. Chalk at Scratchell's Bay. 51 + + + GEOLOGICAL MAP OF THE ISLE OF WIGHT 112 + + + + +Chapter I + +THE ROCKS AND THEIR STORY + + +Walking along the sea shore, with all its varied interest, many must +from time to time have had their attention attracted by the shells to +be seen, not lying on the sands, or in the pools, but firmly embedded +in the solid rock of the cliffs and of the rock ledges which run out +on to the shore, and have, it may be, wondered sometimes how they got +there. At almost any point of the coast of the Isle of Wight, in bands +of limestone and beds of clay, in cliffs of sandstone or of chalk, we +shall have no difficulty in finding numerous shells. But it is not +only in the rocks of the sea coast that shells are to be found. In +quarries for building stone and in the chalk pits of the downs we see +shells in the rock, and may often notice them in the stones of walls +and buildings. How did they get there? The sea, we say, must once have +been here. It must have flowed over the land at some time. Now let us +think. We are going to read a wonderful story, written not in books, +but in the rocks. And it will be much more valuable if we learn to +read it ourselves, than if we are just told what other people have +made out. We know a thing much better if we see the answers to +questions for ourselves than if we are told the answers, and take some +one else's word for it. And if we learn to ask questions of Nature, +and get answers to them, it will be useful in all sorts of ways all +through life. Now, look at the shells in the rock of cliff and quarry. +How are they there? The sea cannot have just flowed over and left +them. The rock could not have been hard, as it is now, when they got +in. Some of the rocks are sandstone, much like the sand on the sea +shore, but they are harder, and their particles are stuck together. +Does sand on a sea shore ever become hard like rock, so that shells +buried in it are found afterwards in hard rock? Now we are getting the +key to a secret. We are learning the way to read the story of the +rocks. How? In this way. Look around you. See if anything like this is +happening to-day. Then you will be able to read the story of what +happened long, long ago, of how this world came to be as it is to-day. +We have asked a question about the sandstone. What about the clays and +the limestone? As before, what is happening to-day? Is limestone being +made anywhere to-day, and are shells being shut up in it? Are shells +in the sea being covered up with clay,--with mud,--and more shellfish +living on the top of that; and then, are they, too, being covered up? +So that in years to come they will be found in layers of clay and +stone like those we have been looking at in quarry and sea cliff? + +We have asked our questions. Now we must look around, and see if we +can find the answers. After it has been raining heavily for two or +three days go down to the marshes of the Yar, and stand on one of the +bridges over the stream. We have seen it flowing quite clear on some +days. Now it is yellow or brown with mud. Where did the mud come from? +Go into a ploughed field with a ditch by the side. Down the ditch the +rain water is pouring from the field away to the stream. It is thick +with mud. Off the ploughed field little trickles of water are running +into the ditch. Each brings earth from the field with it. Off all the +country round the rain is trickling away, carrying earth into the +ditches and on into the stream, and the stream is carrying it down +into the sea. Now think. After every shower of rain earth is carried +off the land into the sea. And this goes on all the year round, and +year after year. If it goes on long enough--? Look a long way ahead, a +hundred years,--a thousand,--thousands of years. We shall be talking +soon of what takes many thousands of years to do. Why, you say, if it +goes on long enough, all the land will be carried into the sea. So it +will be. So it must be. You see how the world is changing. You will +soon see how it has changed already, what wonderful changes there have +been. You will see that things have happened in the world which you +never guessed till you began to study Geology. + +Now, let us go a bit further. What becomes of all the mud the streams +and rivers are carrying down into the sea? Look at a stream coming +steeply down from the hills. How it rushes along, rolling pebbles +against one another, sweeping everything before it, clearing out its +channel, polishing the rocks, and carrying all it rubs off down +towards the sea. Now look at a river near its mouth in flat lowland +country. It flows now much slower; and so it has not power to bear +along all the material it swept down from the hills. And so it drops +a great deal; it is always silting up its own channel, and in flood +time depositing fresh layers of mud on the flat meadow land,--the +alluvial flat,--through which it generally flows in the last part of +its course. But a good deal of sediment is carried by the river out to +sea. The water of the river, moving slower as it enters the sea, has +less and less power to sweep along its burden of sand and mud, and it +drops it on the sea bottom,--first the bigger coarser particles like +the sand, then the mud; farther out, the finer particles of mud drop +to the bottom. + +During the exploring cruise of the _Challenger_, under the direction +of Sir Wyville Thomson, in 1872-6, the most extensive exploration of +the depths of the sea that has been made up to the present time, it +was found that everything in the nature of gravel or sand was laid +down within a very few miles, only the finer muddy sediments being +carried as far as 20 to 50 miles from the land, the very finest of +all, under most favourable conditions, rarely extending beyond 150, +and never exceeding 300 miles from land into the deep ocean. So +gradually layer after layer of sand and mud cover the sea bed round +our coasts; and shells of cockles and periwinkles, of crabs and sea +urchins, and other sea creatures that have lived on the bottom of the +sea are buried in the growing layers of sand and mud. As layer forms +on layer, the lower layers are pressed together, and become more and +more solid. And so we have got a good way towards seeing the making of +clay and sandstone with shells in them, such as we saw in the sea +cliffs and the quarries. + +But it is not only rain and rivers that are wearing the land away. All +round the coasts the sea is doing the same work. We see the waves +beating against the shores, washing out the softer material, hollowing +caves into the cliffs, eating away by degrees even the hardest rock, +leaving for a while at times isolated rocks like the Needles to mark +the former extension of the land. Most people see for themselves the +work of the sea, but do not notice so much what the rain and the +frost, the streams and the rivers are doing. But these are wearing +away the ground over the whole country, while the sea is only eating +away at the coast line. So the whole of the land is being worn away, +and the sand and mud carried out into the sea, and deposited there, +the material of new land beneath the waters. + +How do these beds rise up again, so that we find them with their sea +shells in the quarry? Well, we look at the sea heaving up and down +with the tides, and we think of the land as firm and fixed. And yet +the land also is continually heaving up and down--very slowly,--far +too slowly for it to be noticed, but none the less surely. The exact +causes of this are not yet well understood, because we know but little +about the inside of the earth. The deepest mine goes a very little +way. We know that parts of the interior are intensely hot. The +temperature in a mine becomes hotter, about 1 deg.F. for every 60 ft. we go +down on the average. We know that there are great quantities of molten +rock in places, which, in a volcanic eruption is poured out in sheets +of lava over the land. There are great quantities of water turned into +steam by the heat, and in an eruption the steam pours out of the +crater of the volcano like the clouds of steam out of the funnel of a +locomotive. The people who live about a volcano are living, as it +were, on the top of the boiler of a steam engine; and their country is +sometimes shaken up and down like the lid of a kettle by the escaping +steam. In such a country the land is often changing its level. A few +miles from Naples at Pozzuoli, the ancient Puteoli, may be seen +columns of what appears to be an ancient market hall, though it goes +by the name of the Temple of Serapis. About half way up the columns +are holes bored by boring shellfish, such as we may find on the shore +here at low tide. We see from this that since the building was +constructed in Roman times the land has sunk, and carried the columns +into the sea, and shellfish have bored into them. Then the land has +risen, and lifted the columns out of the sea again. + +But it is not only in the neighbourhood of volcanoes that the land is +moving. Not suddenly and violently, but slowly and gradually great +tracts of land rise and sink. Sometimes the land may remain for a long +time nearly stationary. The Southern coasts of England seem to stand +at much the same level as in the time of the Romans 1,500 or 2,000 +years ago. On the other hand there is evidence which seems to show +that the coast of Norway has for some time been gradually rising. + +It was thought at one time that the interior of the earth was liquid +like molten lava, and that the land we see was a comparatively thin +crust over this like the crust of a pie. But it is now believed for +various mathematical reasons, that the main mass of the earth is rigid +as steel. Still underneath the surface rocks there must be a quantity +of semi-fluid matter, like molten rock, and on this the solid land +sways about, as we see the ice on a pond sway with the pressure of the +skaters on it. So the solid land, pressed by internal forces, rises +and falls like the elastic ice, sometimes sinking and letting the sea +flow over, then rising again, and bringing up the land from beneath +the sea. + +Again, as the heated interior of the earth gradually cools by the +radiation of the earth's heat into space, it will tend to shrink away +from the cooler rocks of the crust. This then, sinking in upon the +shrinking interior, will be thrown into folds, like the skin on a +shrivelled apple. Seeing, as we often do, layers of rock thrown into +numerous folds, so as to occupy a horizontal space far less than that +in which they were originally laid down, we can hardly resist the +conclusion that shrinkage of the cooling interior of the earth has +been a chief cause of the greatest movements of the surface, and of +the lateral pressure we so often find the strata to have undergone. + +As we study geology we shall find plenty to show that the land does +rise and fall, that where now is land the sea has been, that land once +stretched where now is sea, though there is still much which is not +well understood about the causes of its movements. We have seen how +many of the rocks are made in the sea,--the sandstones and the +clays,--but there are two other kinds of rocks, about which we must +say a little. The first are the Igneous rocks, which means rocks made +by fire. These rocks have solidified, most frequently in crystalline +forms, from a molten mass. Lava, which flows hot and fluid, from a +volcano, and cooling becomes a sheet of solid rock, is an igneous +rock. Some igneous rocks solidify under ground under great pressure, +and become crystalline rocks such as granite. We shall not find these +rocks in the Isle of Wight. We should find them in Cornwall, Wales, +and Scotland; and, if we could go deep enough, we should find some +such rock as granite underneath the other rocks all the world over. +The other rocks, such as the sandstones and clays, are called +Sedimentary rocks, because they are formed of sediment, material +carried by the sea and rivers, and dropped to the bottom. They are +also called Stratified rocks, because they are formed of Strata, +_i.e._, beds or layers, as we see in cliff and quarry. + +But we have seen another kind of rock,--the limestones. In Sandown Bay +towards the Culvers, bands of limestone run through the dark clay +cliffs, and broken fragments lie on the shore, looking like pieces of +paving stone. Examining these we find that they are made up of shells, +one band of small oysters, the others of shells of other kinds. You +see how they have been made. There has been an oyster bed, and the +shells have been pressed together, and somehow stuck together, so +that they have formed a layer of rock. They are stuck together in this +way. The atmosphere contains a small quantity of carbonic dioxide, and +the soil a larger quantity, the result of vegetable decomposition. +Rain water absorbs some of it, and carries it into the rocks, as it +soaks into the ground. This gas has the property of combining with +carbonate of lime,--the material of which shells and limestone are +made. The bicarbonate of lime so formed is soluble in water, which is +not the case with the simple carbonate. Water containing carbonic +dioxide soaking into a limestone rock or a mass of shells dissolves +some of the carbonate of lime, and carries it on with it. When it +comes to an open space containing air, some of the carbonic dioxide is +given off, leaving the insoluble carbonate of lime again. So by +degrees the hollows are filled up, and a solid layer of rock is +formed. Even while gathering in the sea the shell-fragments may be +cemented by the deposit of carbonate of lime from sea-water containing +more of the soluble bicarbonate than it can hold. + +These limestones are examples of rocks which are said to be of organic +origin, that is to say, they are formed by living things. Organic +rocks may be formed by animal or vegetable growth. Rocks of vegetable +origin are seen in the coals. A peat bog is composed of a mass of +vegetable matter, chiefly bog moss, which for centuries has been +growing and accumulating on the spot. At the bottom of the bog will +frequently be found trunks of oak, or other trees, the remains of a +forest of former days. The wood has undergone chemical changes, has +lost much of its moisture, and often become very hard, as in bog oak. +Beds of coal have been formed by a similar process, on a much vaster +scale, and continued much longer. The remains of ancient forests have +been buried under sand stones and other rocks, have undergone chemical +change, and been compressed into the hard solid mass we call coal. +Fossil wood, which has not reached the stage of hard coal, but forms a +soft brown substance, is called lignite. This is of frequent +occurrence in various strata in the Isle of Wight. + +Of organic rocks of animal origin the most remarkable are the chalk, +of which we shall speak later, and the coral-reefs, which are found in +the warm waters of tropical seas. Sailing over the South Pacific you +will see a line of trees--coconut trees chiefly--looking as if they +rose up from the sea. Coming nearer you see that they grow on a low +island, which rises only a few feet above the water. These islands are +often in the form of a ring, and look "like garlands thrown upon the +waters." Inside the ring is a lagoon of calm water. Outside the heavy +swell of the Southern Ocean thunders on the coral shore. If a sounding +line be let down from the outer edge of the reef, it will be found +that the wall of coral goes down hundreds of feet like a precipice. On +an island in the Southern Sea, Funafuti, a deep boring has been made +1,114 ft. deep. As far as the boring went all was coral. All this mass +of coral is formed by living things,--polyps they are called. They are +like tiny sea anemones, only they grow attached to one another, +forming a compound animal, like a tree with stem and branches, and +little sea anemones for flowers. The whole organism has a sort of +shell or skeleton, which is the coral. Blocks are broken off by the +waves, and ground to a coral mud, which fills up the interstices of +the coral; and as more coral grows above, the lower part of the reef +becomes, by pressure and cementing, a solid coral limestone. Once upon +a time there were coral islands forming in a sea, where now is +England. These old coral reefs form beds of limestone in Devon, +Derbyshire, and other parts of England. In the Isle of Wight we have +no old coral reefs, but we shall easily find fossil corals in the +rocks. They helped to make up the rocks, but there were not enough +here to make reefs or islands all of coral. + +The great branching corals that form the reefs can only live in warm +waters. So we see that when corals were forming reefs where now is +England the climate must have been warm like the tropics. That is a +story we shall often read as we come to hear more about the rocks. We +shall find that the climate has often been quite warm as the tropics +are now: and we shall also read another wonderful story of a time when +the climate was cold like the Arctic regions. + + + + +Chapter II. + +THE STRUCTURE OF THE ISLAND. + + +The best place to begin the study of the Geology of the Isle of Wight +is in Sandown Bay. North of Sandown, beyond the flat of the marshes, +are low cliffs of reddish clay, which has slipped in places, and is +much covered by grass. At low tide we shall see the coloured clays on +the shore, unless the sand has covered them up. Variegated marls they +are called--_marl_ means a limy clay, _loam_ a sandy clay; and very +fine are the colours of these marls, rich reds and purples and browns. +Beyond the little sea wall below Yaverland battery we come to a +different kind of clay forming the cliff. It is in thin layers. Clay +in thin layers like this is called _shale_. Some of these shales are +known as paper shales, for the layers are thin almost like the leaves +of a book. The junction of the shales with the marls is quite sharp, +and we see that the shales rest on the coloured marls, not +horizontally, but sloping down towards the North. Bands of limestone +and sandstone running through the shales, and a hard band of brown +rock which runs out on the shore as a reef, slope in the same +direction. As we pass on by the Red Cliff to the White Cliffs we +notice that the strata slope more steeply the further North we go. We +have seen that these strata were laid down layer by layer at the +bottom of the sea. If we find a lot of things lying one on top of +another, we may generally conclude that the ones at the bottom were +put there first, then the next, and so on to the top. And this will +generally be true with regard to the rocks. The lowest rocks must have +been laid down first, then the next, and so on. But these layers of +shale with shells in them, and layers of limestone made of shells, +must have been laid down at first fairly flat on the sea floor; but as +they were upheaved out of the sea they have been tilted, so that we +now see them in an inclined position. And when we come to the chalk, +we should see, if we looked at the end of the Culver Cliffs from a +boat, that the lines of black flints that run through the chalk are +nearly vertical. The strata there have been tilted up on end. + + + [Illustration: FIG. 1.] + DIAGRAM OF COAST, SANDOWN BAY, DUNNOSE TO CULVER CLIFF. + + W _Wealden._ + P _Perna Bed._ + LG _Lower Greensand._ + Cb _Clay Bands._ + S _Sandrock and Carstone._ + g _Gault._ + UG _Upper Greensand._ + C _Chalk._ + Sc _Shanklin Chine._ + Lc _Luccombe Chine._ + + +In describing how strata lie, we call the inclination of the strata +from the horizontal the _dip_. The direction of a horizontal line at +right angles to that of the dip is called the _strike_. If we compare +the sloping strata to the roof of a house, a line down the slope of +the roof will mark the direction of the dip, the ridge of the roof +that of the strike. The strata we are considering dip towards the +North; the line of strike is East and West. + +Returning towards Sandown we see the strata dipping less and less +steeply, till near the Granite Fort the rocks on the shore are +horizontal. Continuing our walk past Sandown to Shanklin we pass the +same succession of rocks we have been looking at, but in reverse +order, and sloping the other way. It is not very easy to see this at +first, for so much is covered by building; but beyond Sandown we see +Sandstone Cliffs like the Red Cliff again, the strata dipping gently +now to the south, and in the downs above Shanklin we see the chalk +again. So we have the same strata north and south of Sandown, forming +a sort of arch. But the centre of the arch is missing. It must have +been cut away. We saw that the land was all being eaten away by rain +and rivers. Now we see what they have done here. Go up on to the +Downs, and look over the central part of the Island. We see two ranges +of downs running from east to west,--the Central Downs of the Island, +a long line of chalk down 24 miles from the Culver Cliff on the east +to the Needles on the west; and the Southern Downs along the South +Coast from Shanklin to Chale. In the Central Downs the chalk rises +nearly vertically, and turns over in the beginning of an arch towards +the South. Then comes a big gap, and the chalk appears again in the +Southern Downs nearly horizontal, sloping gently to the south. The +chalk was once joined right across the central hollow, where now we +see the villages of Newchurch, Godshill, and Arreton. All that +enormous mass of rock that once filled the space between the downs has +been cut away by running water. + +An arch of strata like this [Inverted-U], such as the one we are looking +at, is called an _anticline_. When the arch is reversed, like this [U], +it is called a _syncline_. Looking north from the Central Downs over the +Solent we are looking at a syncline. The chalk, which dips down at the +Culvers and along the line of the Central Downs, runs like a trough +under the Solent, and rises again, as we see it on the other side, in +the Portsdown Hills. + +We might suppose the top of an anticlinal arch would be the highest +part of the country; that, even if rain and running water have worn +the country down, that would still stand highest, and be worn down +least. But there are reasons why this need not be so. For one thing, +when the horizontal strata are curved over into an arch, they +naturally crack just at the top of the curve, so and into the cracks +the rain gets, and so a stream is started there, which cuts down and +widens its channel, and so eats the land away. Again, the rising land +only emerges gradually from the sea, and the sea may cut off the top +of the arch before it has risen out of its reach. Moreover on the +higher land the fall of rain and snow is greater, and the frosts are +more severe; so that it is just there that the forces wearing down the +land are most effective. + + + [Illustration: curve with two v-shaped marks at center] + + +We must notice another thing which happens when rocks are being +upheaved and bent into curves. The strain is very great, and sometimes +the strata crack and one side is pushed up more than the other. These +cracks are called _faults_. At Little Stairs, about half way between +Sandown and Shanklin, two or three faults may be seen in the cliff. +The effect of two of the faults may be easily seen by noticing the +displacement of a band of rock stained orange by water containing +iron. The strata are thrown down towards the north about 8 ft. A third +fault, the effect of which is not so evident at first sight, throws +the strata down roughly 50 ft. to the south. These are only small +faults, but sometimes faults occur, in which the strata have been +moved on opposite sides of the fault thousands of feet away from one +another. We might think we should see a wall of rock rising up on the +surface of the ground where a fault occurs; but the faults have mostly +taken place ages ago; and, when they do happen, the rocks are +generally moved only a little way at a time. Then after a while +another push comes on the rocks, and they shift again at the same +place, and go a bit further. All this time frost and rain and rivers +are working at the surface, and planing it down; so that the +unevenness of the surface caused by faults is smoothed away; and so +even a great fault does not show at the surface. + +As we follow the Sandown anticline westward it gradually dies away, +the upheaved area being actually a long oval--what we may call a +turtle-back. As the Sandown anticline dies out, it is succeeded by +another a little further south, the Brook anticline. There are in fact +a series of these east and west anticlines in the Island and on the +adjacent mainland, caused by the same earth movement. As a consequence +of the arching of the strata we find the lowest beds we saw in Sandown +Bay running out again on the west of the Island in Brook Bay, and a +general correspondence of the strata on the east and west of the +Island; while, as we travel from Sandown or Brook northward to the +Solent, we come to continually more recent beds overlying those which +appear to the south of them. + +When, as in the south side of our central downs, the strata are +sharply cut away by denudation, we call this an _escarpment_. The +figure shows the structure of the Sandown anticline we have described. +We must now examine the rocks more closely, beginning with the lowest +strata in the Island, and try to read the story they have to tell. + + + + +Chapter III + +THE WEALDEN STRATA: THE LAND OF THE IGUANODON + + +The lowest strata in the Isle of Wight are the coloured marls and +blue-grey shales we have already observed in Sandown Bay, which run +through the Island to Brook Bay. They are known as the Wealden Strata, +because the same strata cover the part of Kent and Sussex called the +Weald. They consist of marls and shales with bands of sandstone and +limestone. The marls and shales in wet weather become very soft, and +flow out on to the shore, causing large slips of land.[1] Now, what we +want to find out is what the world was like ages ago, when these +Wealden Strata were being formed. We have learnt something of how +clays and sandstones and limestones are formed: to learn more we must +see what sort of fossils we can find in these rocks. "Fossil" means +something dug up; and the word is generally used for remains of +animals or plants which we find buried in the rocks. We have seen +shells in these strata. These we must examine more closely. And as we +walk on the shore we shall find other fossils. In the marls and shales +exposed on the shore we are pretty sure to see pieces of wood, black +as coal, sometimes quite large logs, often partly covered with shining +iron pyrites. Perhaps you say--I hope you do--there must have been +land not far away when these marls and shales were forming. Always try +to see what the things we find have to tell us. The sort of place +where we should be most likely to find wood floating in the sea to-day +would be near the mouth of a great river like the Mississippi or the +Amazon,--rivers which bring down numerous logs of wood from the forest +country through which they flow. + +Examine the shales and limestone bands. On the surface of some of the +paper-shales are numbers of small round or oval white spots. They are +the remains of shells of a very minute crustacean, Cypris and +Cypridea, from which the shales are known as Cyprid shales. In other +bands of shale are quantities of a bivalve shell called _Cyrena_. +There is a band of limestone made up of Cyrena shells, containing also +little roundish spiral shells called _Paludina_.[2] This limestone +resembles that called Sussex or Petworth Marble, which is mainly +composed of shells of Paludina, but some layers also contain bivalve +shells. It is hard enough to take a good polish, and may be seen, like +the similar Purbeck marble, in some of our grand old churches. Another +band of limestone running through the shales is made up of small +oysters (_Ostrea distorta_). + +We shall see fossil shells best on the _weathered_ surfaces of rocks, +_i.e._, surfaces which have been exposed to the weather. One +beginning geological study will probably think we shall find fossils +best by looking at fresh broken surfaces of rock. This is not so. If +you want to find fossils, look at the rock where it has been exposed +to the weather. The action of the weather--rain, carbonic dioxide in +the rain water, etc.--is to sculpture the surface of the rock, so that +the fossils stand out in relief. A weathered surface is often seen +covered with fossils, when a new broken one shows none at all. + +Many of the shells in the limestones are very like shells which are +found at the present day. We must know where they are found now. Well, +these Paludinas are a kind of freshwater snail; and, in fact, all the +shells we find in the Wealden strata are freshwater shells, till we +come near the top, and find the oysters, which live in salt or +brackish water. There were quantities in Brading Harbour in old days, +before it was reclaimed from the sea. Now, this is a very important +point, that our Wealden shells are freshwater shells. For what does it +tell us? Why, we see that the first strata we have come to examine +were not laid down in the sea at all. Then where were they formed? +They seem to be the Delta of a great river, long since passed away, +like the Nile, the Amazon, or the Niger at the present day. When these +great rivers near the sea, they spread out in many channels, and +deposit the mud they have brought down over a wide area shaped like a +V, or like the Greek letter $Delta$ (Delta). Hence we speak of the +Delta of the Nile. Some river deltas are of immense size. That of the +Niger, for instance, is 170 miles long, and the line where it meets +the sea is 300 miles long. Our old Wealden river must have been a +great river like the Niger, for the Wealden strata stretch,--often +covered up for a long way by later rocks, then appearing again,--as +far as Lulworth on the Dorset coast to the west, into Buckinghamshire +on the north, while to the north east they not only cover the Weald, +but pass under the Straits of Dover into Belgium, and very similar +strata are found in Westphalia and Hanover. The ancient river delta +must have been 200 miles or more across. + +You must not think this great river flowed in the Island of England as +it is to-day. England was being made then. This must have been part of +a great continent in those days, for such a great river to flow +through, and form a delta of such size. We cannot tell quite what was +the course of this river. But to the north of where we are now must +have stretched a great continent, with chains of lofty mountains far +away, from which the head waters of the river flowed. Near its mouth +the river broke up into many streams, separated by marsh land; while +inside the sand banks of the sea shore would be large lagoons as in +the Nile delta at the present day. In these waters lived the shellfish +whose shells we are finding. And flowing through great forests the +river carried down with it logs of wood and whole trees, and left them +stuck in the mud near its mouths for us to find to-day. + +What kind of trees grew in the country the river came from? Well, +there were no oaks or beeches, no flowering chestnuts or apples or +mays. But there were great forests of coniferous trees; that is trees +like our pines and firs, cedars and yews, and araucarias; and there +were cycads--a very different kind of tree, but also bearing +cones--which you may see in a greenhouse in botanical gardens. They +have usually a short trunk, sometimes nearly hemispherical, with +leaves like the long leaves of a date palm. They are sometimes called +sago trees, for the trunk has a large pith, which, like some palms, +gives us sago. Stems of cycads, covered with diamond-shaped scars, +where the leaf stalks have dropped off, are found in the Wealden +deposits. Most of the wood we find is black and brittle. Some, +however, is hard as stone, where the actual substance of the wood has +been replaced by silica, preserving beautifully the structure of the +wood. Specially noteworthy are fragments of a tree called +_Endogenites_ (or _Tempskya_) _erosa_, because it was at first +supposed to belong to the endogens,--the class to which the palm +bamboo belong; it is now considered to be a tree-fern. Many specimens +of this wood are remarkably beautiful, when polished, or in their +natural condition. Here, by the way, it may be well to explain how we +name animals and plants scientifically. We have English names only for +the commoner varieties. So we have to invent names for the greater +number of living and extinct animals and plants. And the best way is +found to be this. We give a name, generally formed from the Latin--or +the Greek--to a group of animals or plants, which closely resemble one +another; the group we call a _genus_. Then for the _species_, the +particular kind of animal or plant of the group, we add a second name +to the first. Thus, if we are studying the apple and pear group of +fruit trees, we call the general name of the group _Pyrus_. Then the +crab apple is _Pyrus malus_, the wild pear _P. communis_, and so on. +So that when you arrange any of your species, and put down the +scientific names, you are really doing a bit of classification as +well. You are arranging your specimens with their nearest relations. + +To return to our ancient river. With the logs and trunks of trees, +which the river brought down, came floating down also the bodies of +animals, which had lived in the country the river flowed through. What +kind of animals? Very wonderful animals, some of them, not like any +living creature that lives to-day. By the time they reached the mouth +of the river the bodies had come to pieces, and their bones were +scattered about the river mouth. On the shore where we are walking we +may find some of these bones. But it is rather a chance whether we +find any in any one walk we take. The best time to find them is when +rough seas in winter have washed some out of the clay, and left them +on the shore. It is only rarely that large bones are found here; but +you should be able to find some small ones fairly often. The bones are +quite as heavy as stone, for all the pores and cavities have been +filled with stone, generally carbonate of lime, in the way we +explained in describing the formation of beds of limestone. This makes +them quite different from any present-day bones that may happen to lie +on the shore. So that you cannot mistake them, if once you have seen +them. They are bones of great reptiles,--the class of creatures to +which lizards and crocodiles belong. But these were much larger than +crocodiles, and quite peculiar in their appearance. The principal one +was the Iguanodon. He stood on his hind legs like a kangaroo, with a +great thick tail, which may have helped to support him. When full +grown he stood about 14 ft. high. You may find on the shore vertebrae, +_i.e._, joints of the backbone, sometimes large, sometimes quite small +if they come from the end of the tail. I have found several here about +5 inches long by 4 or 5 across. A few years ago I found the end of a +leg bone almost a foot in diameter. Dr. Mantell, a great geological +explorer in the days when these reptiles were first discovered about +80 years ago, estimated from the size of part of a bone found in +Sandown Bay that one of these reptiles must have had a leg 9 ft. long. +It was a long time after the bones of these creatures were first found +before it was known what they really looked like. The animals lived a +long way from here, and by the time the river had washed them down to +its mouth the skeletons were broken up, and the bones scattered. At +last a discovery was made, which told us what the animals were like. +In a coal mine at Bernissart in Belgium the miners found the coal seam +they were following suddenly come to an end, and they got into a mass +of clay. After a while it was seen what had happened. They had struck +the buried channel of an old river, which in the Wealden days had +flowed through and cut its channel in the coal strata, which are much +older still than the Wealden. And in the mud of the ancient buried +river what should they come upon but whole skeletons of Iguanodons. In +the days of long ago the great beasts had come down to the river to +drink, and had got "bogged" in the soft clay. The skeletons were +carefully got out, and set up in the Museum at Brussels. Without going +so far as that, you may see in the Natural History Museum in London, +or the Geological Museum at Oxford, a facsimile of one of these +skeletons, large as life, and have some idea of the sort of beast the +Iguanodon was. I should tell you why he was so named. Before it was +known what he was like in general form, it was found that his teeth, +which are of a remarkable character, were similar to those of the +Iguana, a little lizard of the West Indies. So he was called +Iguanodon,--an animal with teeth like the Iguana (fr. _Iguana_, and +Gk. $odous$ g. $odontos$ a tooth). He was quite a harmless beast, +though he was so large. He was a vegetarian. There were other great +reptiles, more or less like him, which were also vegetable feeders. +But there were also carnivorous reptiles, generally smaller than the +herbivorous, whose teeth tell us that they preyed on other animals. + + + [Illustration: PL. I] + + Perna Mulleti Meyeria Vectensis + (Atherfield Lobster) + + Panopaea Plicata Terebratula Sella + + Cyrena Limestone Iguanodon Vertebra + + WEALDEN AND LOWER GREENSAND + + +Those were the days of reptiles. Now the earth is the domain of the +mammalia. But then great reptiles like the Iguanodon wandered over the +land; great marine reptiles, such as the Plesiosaurus, swam the +waters; and wonderful flying reptiles, the Pterodactyls, flew the air. +Some species of these were quite small, the size of a rook: one large +species found in the Isle of Wight had a spread of wing of 16 feet. +Imagine this strange world,--its forests with pines and monkey puzzles +and cycads,--ferns also, of which many fragments are found,--its great +reptiles and little reptiles, on land, in the water and the air. Were +there no birds? Yes, but they were rare. From remains found in Oolitic +strata,--somewhat older than the Wealden,--we know that birds were +already in existence; and they were as strange as anything else. For +they had jaws with teeth like the reptiles. They had not yet adopted +the beak. And instead of all the tail feathers starting from one +point, as in birds of the present day, these ancient birds had long +curving tails like reptiles, with a pair of feathers on each joint. +Birds of similar but slightly more modern type have been found in +Cretaceous strata (to which the Wealden belongs) in America, but so +far not in strata of this age in Britain. + +Among other objects of interest along this Wealden shore may be +noticed a curious transformation which has affected the surface of +some of the shell limestones after they were formed, which is known as +cone-in-cone structure. It has quite altered the outer layer of the +rock, so that all trace of the shells of which it consists is +obliterated. Numerous pieces of iron ore from various strata lie on +the shore. Through most of English history the Weald of Kent and +Sussex was the great iron-working district of England. The ore from +the Wealden strata was smelted by the help of charcoal made from the +woods that grew there, and gave the district its name;--for _Weald_ +means "forest." This industry gradually ceased, as the much larger +supplies of iron ore found near the coal in the mines of the North of +England came to be worked. Iron pyrites, sulphide of iron in +crystalline form, was formerly collected on the Sandown shore, and +sent to London for the manufacture of sulphuric acid. This mineral is +often found encrusting fossil wood. It also occurs as rounded nodules +(mostly derived from the Lower Chalk) with a brown outer coat, and +often showing a beautiful radiated metallic structure, when broken. +(This form is called marcasite.) + +As we walk by the edge of the water, we shall see what pretty stones +lie along the beach. When wet with the ripples many look like polished +jewels. Some are agates, bright purple and orange in colour, some +clear translucent chaldedony. We shall have more to say about these +later on. They do not come from the Wealden, but from beds of flint +gravel, and are washed along the shore. But there are also jaspers +from the Wealden. These are opaque, generally red and yellow. There +are also pieces of variegated quartz, and other beautiful pebbles of +various mineral composition. These are stones from older rocks, which +have been washed down the Wealden rivers, and buried in the Wealden +strata, to be washed out again after hundreds of thousands of years, +and rolled about on the shore on which we walk to-day. + + + [Footnote 1: Blue clays of various geological age, which in wet + weather become semi-liquid, and flow out on to the shore, are + known in the Island by the local name of _Blue Slipper_.] + + [Footnote 2: The name now adopted is _Viviparus_. There is also + a band of ferruginous limestone mainly composed of _Viviparus_.] + + + [Illustration: PL. II] + + Trigonia Caudata Trigonia Daedalea + + Gervillia Sublanceolata + + (Ammonite) Nautilus Radiatus + Mortoniceras Rostratum + + LOWER AND UPPER GREENSAND + + + + +Chapter IV + +THE LOWER GREENSAND + + +For ages the Wealden river flowed, and over its vast delta laid down +its depth of river mud. The land was gradually sinking; for +continually strata of river mud were laid down over the same area, all +shallow-water strata, yet counting hundreds of feet in thickness in +all. At last a change came. The land sank more rapidly, and in over +the delta the sea water flowed. The sign of coming change is seen in +the limestone band made up of small oysters near the top of the +Wealden strata. Marine life was beginning to appear. + +Above the Wealden shales in Sandown Bay may be seen a band of brown +rock. It is in places much covered by slip, but big blocks lie about +the shore, and it runs out to sea as a reef before we come to the Red +Cliff. The blocks are seen to consist of a hard grey stone, but the +weathered surfaces are soft and brown. They are full of fossils, all +marine, sea shells and corals. The sea has washed in well over our +Wealden delta, and with this bed the next formation, the Lower +Greensand, begins. The bed is called the Perna bed, from a large +bivalve shell (_Perna mulleti_) frequently to be found in it, though +it is difficult to obtain perfect specimens showing the long hinge of +the valve, which is a marked feature of the shell. Among other shells +are a large round bivalve _Corbis_ (_Sphaera_) _corrugata_, a flatter +bivalve _Astarte_,--and a smaller oblong shell _Panopaea_,--also a +peculiar shell of triangular form, _Trigonia_,--one species _T. +caudata_ has raised ribs running across it, another _T. daedalea_ has +bands of raised spots. A pretty little coral, looking like a +collection of little stars, _Holocystis elegans_, one of the Astraeidae, +is often very sharply weathered out. + +Above the Perna bed lies a mass of blue clay, weathering brown, called +the Atherfield clay, because it appears on a great scale at Atherfield +on the south west of the Island. It is very like the clay of the +Wealden shales, but is not divided into thin layers like shale. + +Next we come to the fine mass of red sandstone which forms the +vertical wall of Red Cliff. Not many fossils are to be found in these +strata. Let us note the beauty of colouring of the Red Cliff--pink and +green, rich orange and purple reds. And then let us pass to the other +side of the anticline, and walk on the shore to Shanklin. Here we see +the red sandstone rocks again, but now dipping to the south. You +probably wonder why these red cliffs are called Greensand. But look at +the rocks where they run out as ledges on the shore towards Shanklin. +Here they are dark green. And this is really their natural colour. +They are made of a mixture of sand and clay coloured dark green by a +mineral called glauconite. Grains of glauconite can easily be seen in +a handful of sand,--better with a magnifying glass. This mineral is a +compound of iron, with silica and potash, and at the surface of the +rock it is altered chemically, and oxide of iron is formed--the same +thing as rust. And that colours all the face of the cliff red. The +iron is also largely responsible for our finding so few fossils in +these strata. By chemical changes, in which the iron takes part, the +material of the shells is destroyed.[3] Near Little Stairs hollows in +the rock may be seen, where large oyster shells have been. In some you +may find a broken piece of shell, but the shells have been mostly +destroyed. Nearer Shanklin we shall find large oysters, _Exogyra +sinuata_, in the rock ledges exposed at low tide. Some are stuck +together in masses. Evidently there was an oyster bank here. And here +the shells have not been destroyed like those in the cliff. + +From black bands in the cliff water full of iron oozes out, staining +the cliff red and yellow and orange, and trickling down, stains the +flint stones lying on the shore a bright orange. At the foot of the +cliff you may sometimes see what looks like a bed of conglomerate, +_i.e._, a bed of rounded pebbles cemented together. This does not +belong to the cliff, but is made up of the flint pebbles on the shore, +and the sand in which they lie, cemented into a solid mass by the iron +in the water which has flowed from the cliff. It is a modern +conglomerate, and shows us how old conglomerates were formed, which we +often find in the various strata. The cement, however, in these is not +always iron oxide. It may be siliceous or of other material. The +iron-charged water is called chalybeate; springs at Shanklin and Niton +at one time had some fame for their strengthening powers. The strata +we have been examining are known as the Ferruginous sands, _i.e._, +iron sands (Lat. _ferrum_, "iron"). Beyond Shanklin is a fine piece of +cliff. Look up at it, but beware of going too close under it. The +upper part consists of a fine yellow sand called the Sandrock. At the +base of this are two bands of dark clay. These bands become filled +with water, and flow out, causing the sandrock which rests on them to +break away in large masses, and fall on to the beach. + +It is clay bands such as these which are the cause of our Undercliffs +in the Isle of Wight. Turn the point, and you see exactly how an +undercliff is formed. You see a wide platform at the level of the +clay, which has slipped out, and let down the sandrock which rested on +it. Beyond Luccombe Chine a large landslip took place in 1910, a great +mass of cliff breaking away, and leaving a ravine behind partly filled +with fallen pine trees. The whole fallen mass has since sunk lower and +nearer to the sea. The broken ground overgrown with trees called the +Landslip, as well as the whole extent of the ground from Ventnor and +Niton, has been formed in a similar way. But the clay which by its +slip has produced these is another clay called the Gault, higher up in +the strata. At the top of the high cliff near Luccombe Chine a hard +gritty stratum of rock called the Carstone is seen above the Sandrock, +and above it lies the Gault clay, which flows over the edge of the +cliff. + +In the rock ledges and fallen blocks of stone between Shanklin and +Luccombe many more fossils may be found than in the lower part of the +Ferruginous sands. Besides bands of oysters, blocks of stone are to be +found crowded with a pretty little shell called _Rhynchonella_. There +are others with many _Terebratulae_, and others with fragments of sea +urchins. The Terebratulae and Rhynchonellae belong to a curious group +of shells, the Brachiopods, which are placed in a class distinct from +the Mollusca proper. They were very common in the very ancient seas of +the Cambrian period,--the period of the most ancient fossils yet +found,--and some, the Lingulae, have lived on almost unchanged to the +present day. One of the two valves is larger than the other, and near +the smaller end you will see a little round hole. Out of this hole, +when the creature was alive, came a sort of neck, which attached it to +the rock, like the barnacles. There is a very hard ferruginous band, +of which nodules may be found along the shore, full of beautifully +perfect impressions of fossils, though the fossils themselves are +gone. Casts of a little round bivalve shell, _Thetironia minor_, may +easily be got out. The nodules also contain casts of Trigonia, +Panopoea, etc. A stratum is sometimes exposed on the shore +containing fossils converted into pyrites. A long shell, _Gervillia +sublanceolata_, is the most frequent. + +All the shells we have found are of sea creatures, and show us that +the Greensand was a marine formation. But the strata were formed in +shallow water not far from the shore. We have learnt that coarse +sediment like sand is not carried by the sea far from the coast. And a +good deal of the Greensand is coarser than sand. There are numerous +bands of small pebbles. The pebbles are of various kinds; some are +clear transparent quartz, bits of rock-crystal more or less rounded by +rolling on the shore of the Greensand period. These go by the name of +Isle of Wight diamonds, and are very pretty when polished. Another +mark of the nearness of the shore when these beds were laid down is +the current bedding, of which a good example may be seen in the cliff +at the north of Shanklin parade. It is sometimes called false bedding, +for the sloping bands do not mark strata laid down horizontally at the +bottom of the sea, but a current has laid down layers in a sloping +way,--it may be just over the edge of a sandbank. Again notice how +much wood is to be seen in the strata. Land was evidently not far off. +All along the shore you may find hard pieces of mineralised wood, the +rings of growth often showing clearly. Frequently marine worms have +bored into them before they were locked up in the strata; the holes +being generally filled afterwards with stone or pyrites. + +The wood is mostly portions of trunks or branches of coniferous trees. +We also find stems of cycads. There has been found at Luccombe a very +remarkable fruit of a kind of cycad. We said that in the Wealden +period none of our flowering plants grew. But these specimens found at +Luccombe show that cycads at that time were developing into flowering +plants. Wonderful specimens of what may almost be called cycad flowers +have been found in strata of about this age in Wyoming in America; and +this Luccombe cycad,--called Benettites Gibsonianus,--shows what these +were like in fruit. Remains of various cycadeous plants have been +found in the corresponding strata at Atherfield; and possibly by +further research fresh knowledge may be gained of an intensely +interesting story,--the history of the development of flowering +plants. + +On the whole the vegetation of the period was much the same as in the +Wealden. But these flowering cycads must have formed a marked addition +to the landscape,--if indeed they did not already exist in the Wealden +times. The cones of present day cycads are very splendidly +coloured,--orange and crimson,--and it can hardly be doubted that the +cycad flowers were of brilliant hues. + +The land animals were still like the Wealden reptiles. Bones of large +reptiles may at times be found on the shore at Shanklin. Several have +been picked up recently. From the prevalence of cycads we may conclude +that the climate of the Wealden and Lower Greensand was sub-tropical. +The existing Cycadaceae are plants of South Eastern Asia, and +Australia, the Cape, and Central America. The forest of trees allied +to pines and firs and cedars probably occupied the higher land. +Turtles and the corals point to warm waters. The existing species of +Trigonia are Australian shells. This beautiful shell is found +plentifully in Sydney harbour. It possesses a peculiar interest, as +the genus was supposed to be extinct, and was originally described +from the fossil forms, and was afterwards found to be still living in +Australia. + + + [Footnote 3: Carbonate of lime has been replaced by carbonate of + iron, and the latter converted into peroxide of iron. At Sandown + oxidation has gone through the whole cliff.] + + + [Illustration: FIG. 2] + + COAST ATHERFIELD TO ROCKEN END + + Wl _Wealden Beds._ + P _Perna Bed._ + A _Atherfield Clay._ + Ck _Cracker Group._ + Lg _Lower Gryphaea Beds._ + Sc _Scaphite. "_ + Lc _Lower Crioceras "_ + W _Walpen Clay._ + Uc _Upper Crioceras Beds._ + WS _Walpen and Ladder Sands._ + Ug _Upper Gryphaea Beds._ + Ce _Cliff End Sands._ + F _Foliated Clay._ + SU _Sands of Walpen Undercliff._ + Fer _Ferruginous Bands of Blackgang Chine._ + B _Black Clay._ + S _Sandrock and Clays._ + Wh _Whale Chine._ + L _Ladder Chine._ + Wp _Walpen Chine._ + Bg _Blackgang Chine._ + + + + +Chapter V + +BROOK AND ATHERFIELD + + +To most Sandown Bay is by far the most accessible place in the Island +to study the earlier strata; and for our first geological studies it +has the advantage of showing a succession of strata so tilted that we +can pass over one formation after another in the course of a short +walk. But when we have learnt the nature of geological research, and +how to read the record of the rocks, and examined the Wealden and +Greensand strata in Sandown Bay, we shall do well, if possible, to +make expeditions to Brook and Atherfield, to see the splendid +succession of Wealden and Greensand strata shown in the cliffs of the +south-west of the Island. It is a lonely stretch of coast, wild and +storm-swept in winter. But this part of the Island is full of +interest and charm to the lover of Nature and of the old-world +villages and the old churches and manor houses which fit so well into +their natural surroundings. The villages in general lie back under the +shelter of the downs some distance from the shore; a coastguard +station, a lonely farm house, or some fishermen's houses as at Brook, +forming the only habitations of man we come to along many miles of +shore. Brook Point is a spot of great interest to the geologist. Here +we come upon Wealden strata somewhat older than any in Sandown Bay. +The shore at the Point at low tide is seen to be strewn with the +trunks of fossil trees. They are of good size, some 20 ft. in length, +and from one to three feet in diameter. They are known as the Pine +Raft, and evidently form a mass of timber floated down an ancient +river, and stranded near the mouth, just as happens with great +accumulations of timber which float down the Mississippi at the +present day. The greater part of the wood has been replaced by stone, +the bark remaining as a carbonaceous substance like coal, which, +however, is quickly destroyed when exposed to the action of the waves. +The fossil trees are mostly covered with seaweed. On the trunks may +sometimes be found black shining scales of a fossil fish, _Lepidotus +Mantelli_. (A stratum full of the scales of _Lepidotus_ has been +recently exposed in the Wealden of Sandown Bay.) The strata with the +Pine Raft form the lowest visible part of the anticline. From Brook +Point the Wealden strata dip in each direction, east and west. As the +coast does not cut nearly so straight across the strata as in Sandown +Bay, we see a much longer section of the beds. On either side of the +Point are coloured marls, followed by blue shales, as at Sandown. To +the westward, however, after the shales we suddenly come to variegated +marls again, followed by a second set of shales. There was long a +question whether this repetition is due to a fault, or whether local +conditions have caused a variation in the type of the beds. The +conclusion of the Geological Survey Memoir, 1889, rather favoured the +latter view, on the ground of the great change which has taken place +in the character of the beds in so short a distance, assuming them to +be the same strata repeated. The conjecture of the existence of a +fault has, however, been confirmed; for during the last years a most +interesting section has been visible at the junction of the shales and +marls, where a fault was suspected. The shales in the cliff and on the +shore are contorted into the form of a Z. The section appears to have +become visible about 1904 (it was in the spring of that year that I +first saw it), and was described by Mr. R. W. Hooley, F.G.S. (_Proc. +Geol. Ass._, vol. xix., 1906, pp. 264, 265). It has remained visible +since. + +The Wealden of Brook and the neighbouring coast is celebrated for the +number of bones of great reptiles found here, from the early days of +geological research, the '20's and '30's of last century, when +admirable early geologists, such as Dr. Buckland and Dr. Mantell, were +discovering the wonders of that ancient world, to the present time. +Various reptiles have been found besides the Iguanodon--the +Megalosaurus, a great reptile somewhat similar, but of lighter build, +with sabre-shaped teeth, with serrated edges: the Hylaeosaurus, a +smaller creature with an armour of plates on the back, and a row of +angular spines along the middle of the back; the huge _Hoplosaurus +hulkei_, probably 70 or 80 feet in length; the marine Plesiosaurus and +Ichthyosaurus, and several more; also bones of a freshwater turtle and +four types of crocodiles. In various beds a large freshwater shell, +_Unio valdensis_, occurs, and in the cliffs of Brook have been found +many cones of Cycadean plants. In bands of white sandy clay are +fragments of ferns, _Lonchopteris Mantelli_. In the shales are bands +of limestone with Cyrena, Paludina, and small oysters, and paper +shales with cyprids, as at Sandown. The shore near Atherfield Point is +covered with fallen blocks of the limestones. + +The Lower Greensand is seen in Compton Bay on the northern side of the +Brook anticline. Here is a great slip of Atherfield clay. The beds +above the clay are much thinner than at Atherfield, and fossils are +comparatively scarce. On the south of the anticline the Perna bed +slopes down to the sea about 150 yards east of Atherfield Point, and +runs out to sea as a reef. Large blocks lie on the shore, where +numerous fossils may be found on the weathered surfaces. The ledges +which here run out to sea form a dangerous reef, on which many vessels +have struck. There is now a bell buoy on the reef. On the headland is +a coastguard station, and till lately there has been a sloping wooden +way from the top of the cliff to bring the lifeboat down. This was +washed away in the storms of the winter 1912-13. + +Above the Perna bed lies a great thickness of Atherfield clay. Above +this lies what is called the Lower Lobster bed, a brown clay and sand, +in which are numerous nodules containing the small lobster _Meyeria +vectensis_,--known as Atherfield lobsters. Many beautiful specimens +have been obtained. + +We next come to a great thickness of the Ferruginous Sands, some 500 +feet. The Lower Greensand of Atherfield was exhaustively studied in +the earlier days of geology by Dr. Fitton, in the years 1824-47, and +the different strata are still referred to according to his divisions. +The lowest bed is the Crackers group about 60 ft. thick. In the lower +part are two layers of hard calcareous boulder-shaped concretions, +some a few feet long. The lower abound in fossils, and though hard +when falling from the cliffs are broken up by winter frosts, showing +the fossils they contain beautifully preserved in the softer sandy +cores of the concretions. _Gervillia sublanceolata_ is very frequent, +also _Thetironia minor_, the Ammonite _Hoplites deshayesi_, and many +more. Beneath and between the nodular masses caverns are formed, the +resounding of the waves in which has given the name of the "Crackers." +In the upper part of this group is a second lobster bed. + +The most remarkable fossils in the Lower Greensand are the various +genera and species of the ammonites and their kindred. The Ammonite, +through many formations, was one of the largest, and often most +beautiful shells. There were also quite small species. The number of +species was very great. Now the whole group is extinct. They most +resembled the Pearly Nautilus, which still lives. In both the shell is +spiral, and consists of several chambers, the animal living in the +outer chamber, the rest being air-chambers enabling it to float. The +class Cephalopoda, which includes the Ammonites, the Nautilus, and +also the Cuttle-fish, is the highest division of the Mollusca. The +animals all possess heads with eyes, and tentacles around the mouth. +They nearly all possess a shell, either external, as in the Nautilus, +or internal, as in the cuttle-fishes, the internal shell of which is +often washed ashore after a rough sea. The Cephalopods are divided +into two orders. The first includes the Cuttle-fish and the Argonaut +or Paper Nautilus. Their tentacles are armed with suckers, and they +have highly-developed eyes. They secrete an inky fluid, which forms +sepia. The internal shell of extinct species of cuttle-fish, of a +cylindrical shape, with a pointed end, is a common fossil in various +strata, and is known as a Belemnite (Gr. $belemnon$ "a dart".) The +second order includes the Pearly Nautilus of the present day, and the +numerous extinct Nautiloids and Ammonoids. The tentacles of the Pearly +Nautilus have no suckers; and the eyes are of a curiously primitive +structure,--what may be called a pin-hole camera, with no lens. The +shells of the Nautilus and its allies are of simpler form, while the +Ammonites are characterised by the complicated margins of the partition +walls or septa, by which the shells are sub-divided. The chambers of +the fossil Ammonites have often been filled with crystals of rich +colours; and a polished section showing the chambers is then a most +beautiful object.[4] + +Continuing along the shore, we come to the Lower Exogyra group, where +_Terebratula sella_ is found in great abundance. A reef with _Exogyra +sinuata_ runs out about 350 yards west of Whale Chine. The group is 33 +ft. thick, and is followed by the Scaphites group, 50 ft. The beds +contain _Exogyra sinuata_, and a reef with clusters of Serpulae runs +out from the cliff. In the middle of the group are bands of nodules +containing _Macroscaphites gigas_. The Lower Crioceras bed (16 ft.) +follows, and crosses the bottom of Whale Chine. The Scaphites and +Crioceras are Cephalopoda, related to the Ammonites; but in this Lower +Cretaceous period a remarkable development took place; many of the +shells began to take curious forms, to unwind as it were. Crioceras, a +very beautiful shell, has the form of an Ammonite, but the whorls are +not in contact; thus making an open spiral like a ram's horn, whence +its name (Gk. $keras$, ram, $krios$, horn). Ancyloceras begins like +Crioceras, but from the last whorl continues for some length in a +straight course, then bends back again; Macroscaphites is similar, but +the whorls of the spiral part are in contact. In Scaphites, a much +smaller shell, the uncoiled part is much shorter, and its outline more +rounded. It is named from its resemblance to a boat (Gk. $skaphe$).[5] + +The Walpen and Ladder Clays and Sands (about 60 ft.) contain nodules +with Exogyra and the Ammonite _Douvilleiceras martini_. The +dark-green clays of the lower part form an undercliff, on to which +Ladder Chine opens. The Upper Crioceras Group (46 ft.), like the +Lower, contains bands of Crioceras? also _Douvilleiceras martini_, +Gervillia, Trigonia, etc. It must be stated that there is some +uncertainty with regard to the ammonoids found in this neighbourhood, +Macroscaphites having been described as Ancyloceras, and also +sometimes as Crioceras. The discovery of the true Ancyloceras +(_Ancyloceras Matheronianum_) at Atherfield is described (and a figure +given) by Dr. Mantell; but what is the characteristic ammonoid of the +"Crioceras" beds requires further investigation. The neighbourhood of +Whale and Walpen Chines is of great interest. Ammonites may be found +in the bottom of Whale Chine fallen out of the rock. Red ferruginous +nodules with Ammonites lie on the shore, in the Chines, and on the +Undercliff, some of the ammonites more or less converted into +crystalline spar. Hard ledges of the Crioceras beds run into the sea. +The shore is usually covered deep with sand and small shingle; but there +are times when the sea has washed the ledges clear; and it is then that +the shore should be examined. + +The Walpen and Ladder Sands (42 ft.); the Upper Exogyra Group (16 +ft.); the Cliff End Sand (28 ft.); and the Foliated Clay and Sand (25 +ft.), consisting of thin alternations of greenish sand and dark-blue +clay, follow. Then the Sands of Walpen Undercliff (about 100 ft.); +over which lie the Ferruginous Bands of Blackgang Chine (20 ft.). Over +these hard beds the cascade of the Chine falls. Cycads and other +vegetable remains are found in this neighbourhood. Throughout the +Atherfield Greensand fragments of the fern _Lonchopteris_ +(_Weichselia_) _Mantelli_ are found. 220 ft. of dark clays and soft +white or yellow sandrock complete the Lower Greensand. In the upper +beds of the Greensand few organic remains occur. A beautiful section +of Sandrock with the junction of the Carstone is to be seen inland at +Rock above Bright-stone. The Sandrock here is brightly coloured like +the sands of Alum Bay,--though it belongs to a much older +formation,--and shows current bedding very beautifully. The junction +of the Sandrock and Carstone is also well seen in the sandpit at +Marvel. + +We have now come to the end of the Lower Cretaceous, in which are +included the Wealden and the Lower Greensand. Judged by the character +of the flora and fauna, the two form one period, the main difference +being the effect of the recession of the shore line, due to the +subsidence which let in the sea over the Wealden delta, so that we +have marine strata in place of freshwater deposits. But that the +plants and animals of the Wealden age still lived in the not distant +continent is shown by the remains borne down from the land. These +strata are an example of a phenomenon often met with in geology,--that +of a great thickness of deposits all laid down in shallow water. The +Wealden of the Isle of Wight are some 700 feet thick, in Kent a good +deal thicker, the Hastings Sands, the lower part of the formation, +being below the horizon occurring in the Island: the Lower Greensand +is some 800 feet thick. In the ancient rocks of Wales, the Cambrian +and Silurian strata, are thousands of feet of deposits, mostly laid +down in fairly shallow water. In such cases there has been a +long-continued deposition of sediment, while a subsidence of the area +in which it was laid down has almost exactly kept pace with the +deposit. It is difficult not to conclude that the subsidence has been +caused by the weight of the accumulating deposit,--continuing until +some world-movement of the contracting globe has produced a +compensating elevation of the area. + + [Footnote 4: Some fine ammonites may be seen at the Clarendon + Hotel, Chale,--one about 5 ft. in circumference.] + + [Footnote 5: _See Guide to Fossil Invertebrata_, Brit. Mus. Nat. + Hist.] + + + + +Chapter VI + +THE GAULT AND UPPER GREENSAND + + +We have seen how the continent through which the great Wealden river +flowed began to sink below the sea level, and how the waters of the +sea flowed over what had been the delta of the river, laying down the +beds of sandstone with some mixture of clay which we call the Lower +Greensand. The next stratum we come to is a bed of dark blue clay more +or less sandy, called the Gault. In the upper beds it becomes more +sandy and grey in colour. These are known as the "passage beds," +passing into the Upper Greensand. The thickness of the Gault clay +proper varies from some 95 to 103 feet. Compared to the mainland the +Gault is of small thickness in the Island, though the dark clay bands +in the Sandrock mark the oncoming of similar conditions. The fine +sediment forming the clay points to a further sinking of the sea bed. +In general, we find very few fossils in the Gault in the Island, +though it is very fossiliferous on the mainland at Folkestone. North +of Sandown Red Cliff the Gault forms a gully, down which a footpath +leads to the shore. It is seen at the west of the Island in Compton +Bay, where in the lower part some fossil shells may be found. + +The Upper Greensand is not very well named, as the beds only partially +consist of sandstone, in great part of quite other materials. Some +prefer to call the Lower Greensand Vectian, from Vectis, the old name +of the Isle of Wight, and the Upper Greensand Selbornian, a name +generally adopted, because it forms a marked feature of the country +about Selborne in Hampshire.[6] But, though the Upper Greensand covers +a less area in the Isle of Wight than the Lower, it forms some of the +most characteristic scenery of the Island. One of the most striking +features of the Island is the Undercliff, the undulating wooded +country from Bonchurch to Niton, above the sea cliff, but under a +second cliff, a vertical wall which shelters it to the North. This +wall of cliff consists of Upper Greensand. In a similar way to the +small undercliffs we saw at Luccombe, the Undercliff has been formed +by a series of great slips, caused here by the flowing out of the +Gault clay, which runs in a nearly horizontal band through the base of +all the Southern Downs of the Island, the Upper Greensand lying above +it breaking off in masses, and leaving vertical walls of cliff. These +walls are seen not only in the Undercliff, but also on the northern +side of the downs, where they form the inland cliff overhanging a +pretty belt of woodland from Shanklin to Cook's Castle, and again +forming Gat Cliff above Appuldurcombe. We have records of great +landslips at the two ends of the Undercliff, near Bonchurch and at +Rocken End, about a century ago. But the greater part of the +Undercliff was formed by landslips in very ancient times, before +recorded history in this Island began. The outcrop of the Gault is +marked by a line of springs on all sides of the Southern Downs. The +strata above, Chalk and Upper Greensand, are porous and absorb the +rainfall, which permeates through till it reaches the Gault Clay, +which throws it out of the hill side in springs, some of which furnish +a water supply for the surrounding towns and villages. + +Where the Upper Greensand is best developed, above the Undercliff, the +passage beds are followed by 30 feet of yellow micaceous sands, with +layers of nodules of a bluish-grey siliceous limestone known as Rag. +The nodules frequently contain large Ammonites and other fossils. Next +follow the Sandstone and Rag beds, about 50 feet of sandstone with +alternating layers of rag. The sandstones are grey in colour, +weathering buff or reddish-brown, tinged more or less green by grains +of glauconite. Near the top of these strata is the Freestone bed, a +thick bed of a close-grained sandstone, weathering a yellowish grey, +which forms a good building stone. Most of the churches and old manor +and farm houses in the southern half of the Island are built of this +stone. Then forming the top of the series are 24 feet of chert +beds,--bands of a hard flinty rock called chert alternating with +siliceous sandstone, the sandstone containing large concretions of rag +in the same line of bedding. The chert beds are very hard, and where +the strata are horizontal, as above the Undercliff, project like a +cornice at the top of the cliff. Perhaps the finest piece of the Upper +Greensand is Gore Cliff above Niton lighthouse, a great vertical wall +with the cornice of dark chert strata overhanging at the top. The +thickness in the Undercliff, including the Passage Beds, is from 130 +to 160 ft. + +The Upper Greensand may be studied at Compton Bay, and at the Culvers; +and along the shore west of Ventnor the lower cliff by the sea +consists largely of masses of fallen Upper Greensand, many of which +show the chert strata well. In numerous walls in the south of the +Island may be seen stone from the various strata--sandstone, blue +limestone or rag, and also the chert. + +Let us think what was happening when these beds were being formed. The +sandstone is much finer than that of the Lower Greensand; and we have +limestones now,--marine, not freshwater as in the Wealden. Marine +limestones are formed by remains of sea creatures living at some depth +in clear water. And now we come to a new material, chert. It is not +unlike flint, and flint is one of the mineral forms of silica. Chert +may be called an impure or sandy flint. The bands of chert appear to +have been formed by an infiltration of silica into a sandstone, +forming a dense flinty rock, which, however, has a dull appearance +from the admixture of sand, instead of being a black semi-transparent +substance like flint. But where did the silica come from? In the +depths of the sea many sea creatures have skeletons and shells formed +of silica or flint, instead of carbonate of lime, which is the +material of ordinary shells and of corals. Many sponges, instead of +the horny skeleton we use in the washing sponge, have a skeleton +formed of a network of needles of silica, often of beautiful forms. +Some marine animalcules, the Radiolaria, have skeletons of silica. And +minute plants, the Diatoms, have coverings of silica, which remain +like a little transparent box, when the tiny plant is dead. Now, much +of the chert is full of needles, or spicules, as they are called, of +sponges, and this points to the source from which some at least of the +silica was derived. To form the chert much of the silica has been in +some manner dissolved, and deposited again in the interstices of +sandstone strata. We shall have more to say of this process when we +come to speak of the origin of the flints in the chalk. Sponges +usually live in clear water of some depth; so all shows that the sea +was becoming deeper when these strata were being formed. + +Along the shore of the Undercliff, Upper Greensand fossils may be +found nicely weathered out. Very common is a small curved bivalve +shell,--a kind of small oyster,--_Exogyra conica_, as are also +serpulae, the tubes formed by certain marine worms. Very pretty pectens +(scallop shells) are found in the sandstone. Many other shells, +_Terebratulae_, _Trigonia_, _Panopaea_, etc., occur, and several species +of ammonite and nautilus.[7] A frequent fossil is a kind of sponge, +Siphonia. It has the form of an oblong bulb, supported by a long stem, +with a root-like base. It is often silicified, and when broken shows +bundles of tubular channels. + +In the chert may often be seen pieces of white or bluish chalcedony, +generally in thin plates filling cracks in the chert. This is a very +pure and hard form of silica, beautifully clear and translucent. +Pebbles which the waves have worn in the direction of the plate are +very pretty when polished, and go by the name of sand agates. They may +sometimes be picked up on the shore near the Culvers. + + [Footnote 6: Names proposed by the late A. J. Jukes-Browne.] + + [Footnote 7: Of Ammonites, _Mortoniceras rostratum_ and + _Hoplites splendens_ may be mentioned: and of Pectens, _Neithea + quinquecostata_ and _quadricostata_, _Syncyclonema orbicularis_, + and _AEquipecten asper_.] + + + + +Chapter VII + +THE CHALK + + +As we have traced the world's history written in the rocks we have +seen an old continent gradually submerged, a deepening sea flowing +over this part of the earth's surface. Now we shall find evidence of +the deepening of the sea to something like an ocean depth. We are +coming to the great period of the Chalk, the time when the material +was made which forms the undulating downs of the south-east of England, +and of which the line of white cliffs consists, which with sundry +breaks half encircles our shores, from Flamborough Head in Yorkshire, +by Dover and the Isle of Wight, to Bere in Devon. Across the Channel +white cliffs of chalk face those of England, and the chalk stretches +inland into the Continent. Its extent was formerly greater still. +Fragments of chalk and flint are preserved in Mull under basalt, an +old lava flow, and flints from the chalk are found in more recent +deposits (Boulder Clay) on the East of Scotland, pointing to a former +great extension northward, which has been nearly all removed by +denudation. In the Isle of Wight the chalk cliffs of Freshwater and +the Culvers are the grandest features of the Island; while all the +Island is dominated by the long lines of chalk downs running through +it from east to west. Now what is the chalk? And how was it made? The +microscope must tell us. It is found that this great mass of chalk is +made up principally of tiny microscopic shells called Foraminifera, +whole and in crushed fragments. There are plenty of foraminifera in +the seas to-day; and we need not go far to find similar shells. On the +shore near Shanklin you will often see streaks of what look like tiny +bits of broken shell washed into depressions in the sand. These, +however, often consist almost entirely of complete microscopic shells, +some of them of great beauty. The creature that lives in one of these +shells is only like a drop of formless jelly, and yet around itself it +forms a complex shell of surprising beauty. The shells are pierced +with a number of holes, hence their name (fr. Lat. _foramen_, a hole, +and _ferre_, to bear). Through these holes the animal puts out a +number of feelers like threads of jelly, and in these entangles +particles of food, and draws them into itself. Now, do we anywhere +to-day find these tiny shells in such masses as to build up rocks? We +do. The sounding apparatus, with which we measure the depths of the +sea, is so constructed as to bring up a specimen of the sea bottom. +This has been used in the Atlantic, and it is found that the really +deep sea bottom, too far out for rivers and currents to bring sand and +mud from the land, is covered with a white mud or ooze. And the +microscope shows this to be made up of an unnumerable multitude of the +tiny shells of foraminifera. As the little creatures die in the sea, +their shells accumulate on the bottom, and in time will be pressed +into a hard mass like chalk, the whole being cemented together by +carbonate of lime, in the way we explained in describing the making of +limestones. So we find chalk still forming at the present day. But +what ages it must take to form strata of solid rock of such tiny +shells! And what a vast period of time it must have required to build +up our chalk cliffs and downs, composed in large part of tiny +microscopic shells! With the foraminifera the microscope shows in the +chalk a multitude of crushed fragments, largely the prisms which +compose bivalve shells, flakes of shells of Terebratula and +Rhynchonella, and minute fragments of corals and Bryozoa. Scattered in +the chalk we shall also find larger shells and other remains of the +life of the ancient sea. The base of the cliffs and fallen blocks on +the shore are the best places to find fossils. Much of the base of the +cliffs is inaccessible except by boat. The lower strata may be +examined in Sandown and Compton Bays, and the upper in Whitecliff Bay. +A watch should always be kept on the tide. The quarries along the +downs are not as a rule good for collecting, as the chalk does not +become so much sculptured by weathering. + +The deep sea of the White Chalk did not come suddenly. In the oncoming +of the period we find much marl--limy clay. As the sea deepened, +little reached the bottom but the shells of foraminifera and other +marine organisms. How deep the sea became is uncertain: there is +reason to believe that it did not reach a depth such as that of the +Atlantic. + +It is difficult to draw the line between the Upper Greensand and the +Chalk strata. Above the Chert beds is a band a few feet thick known as +the Chloritic Marl, which shows a passage from sand to calcareous +matter. It is named from the abundance of grains of green colouring +matter, now recognised as glauconite; so that it would be better +called Glauconitic Marl. It is also remarkable for the phosphatic +nodules, and for the numerous casts of Ammonites, Turrilites, and +other fossils mostly phosphatized, which it contains. This band is one +of the richest strata in the Island for fossils. It differs, however, +in different localities both in thickness and composition. It is best +seen above the Undercliff, and in fallen masses along the shore from +Ventnor to Niton. It is finely exposed on the top of Gore Cliff, where +the flat ledges are covered with fossil Ammonites, Turrilites, +Pleurotomaria, and other shells. The Ammonite (_Schloenbachia +varians_) is especially common. The sponge (_Stauronema carteri_) is +characteristic of the Glauconitic Marl. As the edge of the cliff is a +vertical wall, none should try this locality but those who can be +trusted to take proper care on the top of a precipice. When a high +wind is blowing the position may be especially dangerous. + + + [Illustration: PL. III] + + (Pecten) Neithea Quinquecostata + + Thetironia (Ammonite) Rhynchonella + Minor Mantelliceras Mantelli Parvirostris + + (Sea Urchins) + Micraster Cor-Anguinum Echinocorys Scutatus + (Internal cast in flint) + + LOWER AND UPPER GREENSAND AND CHALK + + +The Chloritic Marl is followed by the Chalk Marl, of much greater +thickness. This consists of alternations of chalk with bands of Marl, +and contains glauconite and also phosphatic nodules in the lower part. +Upwards it merges into the Grey Chalk, a more massive rock, coloured +grey from admixture of clayey matter. These form the Lower Chalk, the +first of the three divisions into which the Chalk is usually divided. +Above this come the Middle and Upper, which together form the White +Chalk. They are much purer white than the lower division, which is +creamy or grey in colour. The Chalk Marl and Grey Chalk are well seen +at the Culver Cliff, and run out in ledges on the shore. The lower +part of this division is the most fossiliferous, and contains various +species of Ammonities, Turrilites, Nautilus, and other Cephalopoda. +(Of Ammonites _Schloenbachia varians_ is characteristic. Also may be +named _S. Coupei_, _Mantelliceras mantelli_, _Metacanthoplites +rotomagensis_, _Calycoceras naviculare_, the small Ammonoid Scaphites +aequalis; and of Pectens, _AEquipecten beaveri_ and _Syncyclonema +orbicularis_ may be mentioned). White meandering lines of the sponge +_Plocoscyphia labrosa_ are conspicuous in the lower beds. The Chalk +Marl is well shown at Gore Cliff, sloping upwards from the flat ledges +of the Chloritic Marl. It may be studied well, and fossils found, in +the cliff on the Ventnor side of Bonchurch Cove,--which has all +slipped down from a higher level. + +The uppermost strata of the Lower Chalk are known as the Belemnite +Marls. They are dark marly bands, in which a Belemnite, _Actinocamax +plenus_, is found. The hard bands known as Melbourn Rock and Chalk +Rock, which on the mainland mark the top of the Lower and Middle Chalk +respectively, are neither of them well marked in the Isle of Wight. In +the Middle Chalk _Inoceramus labiatus_, a large bivalve shell, occurs +in great profusion; and in the Upper flinty Chalk are sheets of +another species, _I. Cuvieri_. It is hardly ever found perfect, the +shells being of a fibrous structure, with the fibres at right angles +to the surface, and so very fragile. + +There is a striking difference between the Middle and Upper Chalk, +which all will observe. It consists in the numerous bands of dark +flints which run through the Upper Chalk parallel to the strata. The +Lower Chalk is entirely, and the Middle Chalk nearly, devoid of flint. +Though the line at which the commencement of the Upper Chalk is taken +is rather below the first flint band of the Upper Chalk, and a few +flints occur in the highest beds of the Middle Chalk; yet, speaking +generally, the great distinction between the Middle and Upper Chalk, +the two divisions of the White Chalk, may be considered to be that of +flintless chalk and chalk with flints. + +Early in our studies we noticed the great curves into which the +upheaved strata have been thrown, and that on the northern side of the +anticline the strata are in places vertical. This can be well observed +in the Culver Cliffs and Brading Down, where the strata of the Upper +Chalk are marked by the lines of black flints. In the large quarry on +Brading Down the vertical lines of flint can be clearly seen; and by +walking at low tide at Whitecliff Bay round the corner of the cliff, +or by observing the cliff from a boat, we may see a beautiful section +of the flinty chalk, the lines of black flints sloping at a high +angle. The flints in general form round or oval masses, but of +irregular shape with many projections, and the masses lie in regular +bands parallel to the stratification. The tremendous earth movement +which has bent the strata into a great curve has compressed the +vertical portion into about half its original thickness, and has made +the chalk of our downs extremely hard. It has also shattered the +flints in the chalk into fragments. The rounded masses retain their +form, but when pulled out of the chalk fall into sharp angular +fragments, and we find they are shattered through and through. + + + [Illustration: _Photo by J. Milman Brown, Shanklin._] + CULVER CLIFFS--HIGHLY INCLINED CHALK STRATA + + +Now, what are flints, and how were they formed? Flints are a form of +silica, a purer form than chert, as the chalk in which they are +embedded was formed in the deep sea, and so we have no admixture of +sand. Flints, as we find them in the chalk, are generally black +translucent nodules, with a white coating, the result of a chemical +action which has affected the outside after they were formed. Flint is +very hard,--harder than steel. You cannot scratch it with a knife, +though you may leave a streak of steel on the surface of the flint. +This hardness is a property of other forms of silica, as quartz and +chalcedony. The question how the flints were formed is a difficult +one. As to this much still remains obscure. The sea contains mineral +substances in solution. Calcium sulphate and chloride, and a small +amount of calcium carbonate (carbonate of lime) are in solution in the +sea. From these salts is derived the calcium deposited as calcium +carbonate to form the shells of the Foraminifera and the larger +shells in the Chalk. There is also silica in small quantity in sea +water. From this the skeletons of radiolaria and diatoms and the +spicules of sponges are formed. Now, many flints contain fossil +sponges, and when broken show a section of the sponge clearly marked. +Especially well can this be seen in flints which have lain some time +in a gravel bed formed of flints worn out of the chalk by denudation. +Hard as a flint seems, it is penetrated by numerous fine pores. The +gravel beds are usually stained yellow by water containing iron, and +this has penetrated by the pores through the substance of the flints, +staining them brown and orange. Many of the stained flints show +beautifully the sponge markings,--a wide central canal with fine +thread-like canals leading into it from all sides. + +The Chalk Sea evidently abounded in siliceous organisms, and it cannot +be doubted that it is from such organisms that the silica was derived, +which has formed the masses of flint. Silica occurs in two forms--in a +crystalline form as quartz or rock crystal, and as amorphous, _i.e._, +formless or uncrystalline (also called opaline) silica. The siliceous +skeletons of marine organisms are formed of amorphous silica. Flint +consists of innumerable fine crystalline grains, closely packed +together. Amorphous silica is less stable than crystalline, and is +capable of being dissolved in alkaline water, _i.e._, water containing +carbonate of sodium or potassium in solution. If the silica so +dissolved be deposited again, it is generally in the crystalline form. +It seems probable, therefore, that the amorphous silica of the +skeletal parts of marine organisms has been dissolved by alkaline +water percolating through the strata, and re-deposited as flint. + +As the silica was deposited, chalk was removed. The large irregular +masses of flint lying in the Chalk strata have clearly taken the place +of chalk which has been removed. Water charged with silica soaking +through the strata has deposited silica, and at the same time +dissolved out so much carbonate of lime. Bivalve shells, originally +carbonate of lime, are often replaced, and filled up by flint, and +casts of sea urchins in solid flint are common, and often beautiful +fossils. This process of change took place after the foraminiferal +ooze had been compacted into chalk strata; and to some extent at any +rate, there has been deposition of silica after the chalk had become +hard and solid; for we find flat sheets, called tabular flint, lying +along the strata, or filling cracks cutting through the strata at +right angles. But in all probability the re-arrangement of the +constituents of the strata took place in the main during the first +consolidation, as the strata rose above the sea-level, and the +sea-water drained out. A suggestion has been made by R. E. Liesegang, +of Dresden, to explain the occurrence of the flints in the bands with +clear interspaces between, which are such a marked feature of the +Upper Chalk. He has shown how "a solution diffusing outward and +encountering something with which it reacts and forms a precipitate, +moves on into this medium until a concentration sufficient to cause +precipitation of the particular salt occurs. A zone of precipitation +is thus formed, through which the first solution penetrates until the +conditions are repeated, and a second zone of precipitate is thrown +down. Zone after zone may thus arise as diffusion goes on." He +suggests that the zones of flint may be similar phenomena, water +diffusing through the masses of chalk taking up silica till such +concentration is reached that precipitation takes place, the water +then percolating further and repeating the process.[8] + +The precipitation of silica and replacement of the chalk occurs +irregularly along the zone of precipitation, forming great irregular +masses of flint, which enclose the sponges and other marine organisms +that lay in the chalk strata. Where a deposit of silica has begun, it +will probably have determined the precipitation of more silica, in the +manner constantly seen in chemical precipitation; and it would seem +that siliceous organisms as sponges have to some extent served as +centres around which silica has been precipitated, for flints are very +commonly found, having the evident external form of sponges. + +It will be well to say something here of the history of the flints as +the chalk which contains them is gradually denuded away. Rain water +containing carbonic dioxide has a great effect in eating away all +limestone rocks, chalk included. A vast extent of chalk, which +formerly covered much of England has thus disappeared. The arch of +chalk connecting our two ranges of downs has been cut through, and +from the top of the downs themselves a great thickness of chalk has +been removed. The chalk in the downs above Ventnor and Bonchurch is +nearly horizontal. It consists of Lower and Middle Chalk; and probably +a small bit of the Upper occurs. But the top of St. Boniface Down is +covered with a great mass of angular flint gravel, which must have +come from the Upper Chalk. The gravel is of considerable thickness, +perhaps 20 ft., and on the spurs of the down falls over to a lower +level like a table-cloth. It is worked in many pits for road metal. +This flint gravel represents the insoluble residue which has been left +when the Chalk was dissolved away. + +On the top of the cliffs between Ventnor and Bonchurch, at a point +called Highport, is a stratum of flint gravel carried down from the +top of the down. The shore here is strewn with large flints fallen +from the gravel. The substance of many of the flints has undergone a +remarkable change. Instead of black or dull grey flint it has become +translucent agate, of splendid orange and purple colours, or has been +changed into clear translucent chalcedony. In the agate the forms of +fossil sponges can often be beautifully seen. The colours are due to +iron-charged water percolating into the flint in the gravel bed, but +further structural changes have altered the form of the silica; +chalcedony having a structure of close crystalline fibres, revealed by +polarized light: when variously stained and coloured, it is usually +called agate. Many of these flints, when cut through and polished, are +of great beauty. The main force of the tides along these shores is +from west to east; and so there is a continual passage of pebbles on +the shore in that direction. The flints in Sandown Bay have in the +main travelled round from here; and towards the Culvers small handy +specimens of agates and chalcedonies rounded by the waves may be +collected. + + + [Illustration: _Photo by J. Milman Brown, Shanklin._] + SCRATCHELL'S BAY--HIGHLY INCLINED CHALK STRATA + + +The extensive downs in the centre of the Island are largely overspread +with angular flint gravel similarly formed to that of St. Boniface. Of +other beds of gravel, which have been washed down to a lower level by +rivers or other agency we shall have more to say later. + +The Chalk strata in the Isle of Wight are of great thickness. In the +Culver Cliff there are some 400 feet of flintless Chalk (Lower and +Middle Chalk), and then some 1,000 feet of chalk with flints. There is +some variation in the thickness of the strata in different parts of +the Island, and the amount of the Upper strata, which has been +removed by denudation, varies considerably. The average thickness of +the white chalk in the Island is about 1,350 feet.[9] Including the +Lower Chalk, the maximum thickness of the Chalk strata is 1,630 ft. + +The divisions of the chalk we have so far considered depend on the +character of the rock: we must say a word about another way of +dividing the strata. It is found that in the chalk, as in other +strata, fossils change with every few feet of deposit. We may make a +zoological division of the chalk by seeing how the fossils are +distributed. The Chalk was first studied from this point of view by +the great French geologist, M. Barrois, who divided it into zones, +according to the nature of the animal life, the zones being called by +the name of some fossil specially characteristic of a particular zone. +More recently Dr. A. W. Rowe has made a very careful study of the +zones of the White Chalk, and is now our chief authority on the +subject. The strata have been grouped into zones as follows:-- + + + Zones. Sub-Zones. + + { Belemnitella mucronata. + { Actinocamax quadratus. + { { Offaster pilula. + Upper { Offaster pilula. { Echinocorys depressus. + Chalk. { + { Marsupites { Marsupites. + { testudinarius. { Uintacrinus. + { Micraster cor-anguinum. + { Micraster cor-testudinarium. + { Holaster planus. + + Middle { Terebratulina lata. + Chalk. { Inoceramus labiatus. + + { Holaster subglobosus. { Actinocamax + Lower { { plenus (at top). + Chalk. { Schloenbachia varians.{ Stauronema + { { carteri (at base). + + +The method of study according to zoological zones is of great +interest. The period of the White Chalk was of long duration, and the +physical conditions remained very uniform. So that by studying the +succession of life during this period we may learn much about the +gradual change of life on the earth, and the evolution of living +things. + +We have seen that the whole mass of the chalk is made up mainly of the +remains of living things,--mostly of the microscopic foraminifera. We +have seen that sponges were very plentiful in that ancient sea. Of +other fossils we find brachiopods--different species of Terebratula +and Rhynchonella--a large bivalve _Inoceramus_ sometimes very common; +the very beautiful bivalve, _Spondylus spinosus_, belemnites, serpulae; +and different species of sea-urchin are very common. A pretty +heart-shaped one, _Micraster cor-anguinum_, marks a zone of the higher +chalk, which runs along the top of our northern downs. Other common +sea urchins are various species of _Cidaris_, of a form like a turban +(Gk. _cidaris_, a Persian head-dress); _Cyphosoma_, another circular +form; the oval _Echinocorys scutatus_, which, with varieties of the +same and allied species, abounds in the Upper Chalk, and the more +conical _Conulus conicus_. The topmost zone, that of _B. Macronata_, +would yield a record of exuberant life, were the chalk soft and +horizontal. There was a rich development of echinoderms (sea urchins +and star fishes), but nothing is perfect, owing to the hardness of the +rock (Dr. Rowe). The general difference in the life of the Chalk +period is the great development of Ammonites and other Cephalopods in +the Lower Chalk, and of sea urchins and other echinoderms in the +Upper, while the Middle Chalk is wanting in the one and the other. +Shark's teeth tell of the larger inhabitants of the ocean that flowed +above the chalky bottom. + +Many quarries have been opened on the flanks of the Chalk Downs, of +which a large number are now disused. They occur just where they are +needed for chalk to lay on the land, the pure chalk on the north of +the Downs to break up the heavy Tertiary clays, which largely cover +the north of the Island; the more clayey beds of the Grey Chalk on the +south of the downs to stiffen the light loams of the Greensand.[10] + + + [Footnote 8: See _Common Stones_, by Grenville A. J. Cole, + F.R.S. 1921.] + + [Footnote 9: 1,472 ft. at the western end of the Island, 1,213 + ft. at the eastern.--Dr. Rowe's measurements.] + + [Footnote 10: Dr. A. W. Rowe.] + + + + +Chapter VIII + +THE TERTIARY ERA: THE EOCENE + + +Ages must have passed while the ocean flowed over this part of the +world, and the chalk mud, with its varied remains of living things, +gradually accumulated at the bottom. At last a change came. Slowly the +sea bed rose, till the chalk, now hardened by pressure, was raised +into land above the sea level. As soon as this happened, sea waves and +rain and rivers began to cut it down. There is evidence here of a wide +gap in the succession of the strata. Higher chalk strata, which +probably once existed, have been washed away, while the underlying +strata have been planed off to an even surface more or less oblique to +the bedding-planes. The highest zone of the chalk in the Island (that +of _Belemnitella macronata_) varies greatly in thickness, from 150 ft. +at the eastern end of the Island to 475 at the western. The latest +investigations give reason to conclude that this is due to gentle +synclines and anticlines, which have been planed smooth by the erosion +which preceded the deposition of the next strata,--the Eocene.[11] At +Alum Bay the eroded surface of the chalk may be seen with rolled +flints lying upon it, and rounded hollows or pot-holes, the appearance +being that of a foreshore worn in a horizontal ledge of rock, much +like the Horse Ledge at Shanklin. + +The land sank again, but not to anything like the depth of the great +Chalk Sea. We now come to an era called the Tertiary. The whole +geological history is divided into four great eras. The first is the +Eozoic, or the age of the Archaean,--often called Pre-Cambrian--rocks; +rocks largely volcanic, or greatly altered since their formation, +showing only obscure traces of the life which no doubt existed. Then +follow the Primary era, or, as it is generally called, the Palaeozoic; +the Secondary or Mesozoic; and the Tertiary or Kainozoic. Palaeozoic is +used rather than Primary, as this word is ambiguous, being also used +for the crystalline rocks first formed by the solidification of the +molten surface of the earth. But Secondary and Tertiary are still in +constant use. These long ages, or eras, were of very unequal duration; +yet they mark such changes in the life of animal and plant upon the +earth that they form natural divisions. The Palaeozoic was an immense +period during which life abounded in the seas,--numberless species of +mollusca, crustaceans, corals, fish are found,--and there were great +forests, which have formed the coal measures, on land,--forests of +strange primeval vegetation, but in which beautiful ferns, large and +small, flourished in great numbers. The Secondary Era may be called +the age of reptiles. To this era all the rocks we have so far studied +belong. Now we come to the last era, the Tertiary, the age of the +mammals. Instead of reptiles on land, in sea and air, we find a +complete change. The earth is occupied by the mammalia; the air +belongs to the birds such as we see to-day. The strange birds of the +Oolitic and Cretaceous have passed away. Birds have taken their modern +form. In some parts of the world strata are found transitional between +the Secondary and Tertiary. + +The Tertiary is divided into four divisions,--the Eocene, the +Oligocene (once called Upper Eocene), the Miocene, and the Pliocene; +which words signify,--Pliocene the more recent period, Miocene the +less recent, Eocene the dawn of the recent. + +In the Eocene we shall find marine deposits of a comparatively shallow +sea, and beds deposited at the mouth of great rivers, where remains of +sea creatures are mingled with those washed down from the land by the +rivers. These strata run through the Isle of Wight from east to west, +and we may study them at either end of the Island, in Whitecliff and +Alum Bays. The strata are highly inclined, so that we can walk across +them in a short walk. Some beds contain many fossils, but many of the +shells are very brittle and crumbly; and we can only secure good +specimens by cutting out a piece of the clay or sand containing them, +and transferring them carefully to boxes, to be carried home with +equal care. Often much of the face of the cliff is covered with slip +or rainwash, and overgrown with vegetation. Sometimes a large slip +exposes a good hunting ground. + +Now let us walk along the shore, and try to read the story these +Tertiary beds tell us. We will begin in Whitecliff Bay. Though easily +accessible, it remains still in its natural beauty. The sea washes in +on a fine stretch of smooth sand sheltered by the white chalk wall +which forms the south arm of the bay. North of the Culver downs the +cliffs are much lower, and consist of sands and clays of varying +colour, following each other in vertical bands. Looking along the line +of shore we notice a band of limestone, at first nearly vertical like +the preceding strata, then curving at a sharp angle as it slopes to +the shore, and running out to sea in a reef known as Bembridge Ledge. +This is the Bembridge limestone; and the beginning of the reef marks +the northern boundary of Whitecliff Bay, the shore, however, +continuing in nearly the same line to Bembridge Foreland, and showing +a continuous succession of Eocene and Oligocene strata. The strata +north of the limestone are nearly horizontal, dipping slightly to the +north. In the Bembridge limestone we see the end of the Sandown +anticline, and the beginning of the succeeding syncline. The strata +now dip under the Solent, and rise into another anticline in the +Portsdown Hills. North and south of the great anticline of the Weald +of Kent and Sussex are two synclinal troughs known as the London and +Hampshire basins. Nearly the whole of our English Eocene strata lies +in these two basins, having been denuded away from the anticlinal +arches. The Oligocene only occur in the Hampshire basin, the higher +strata only in the Isle of Wight. + + + [Illustration: FIG. 3.] + + COAST SECTION, WHITECLIFF BAY. + + BM _Bembridge Marls._ + BL _Bembridge Limestone._ + O _Osborne Beds._ + H _Headon Beds._ + BS _Barton Sand._ + B _Barton Clay._ + Br _Bracklesham Beds._ + Bg _Bagshot Beds._ + L _London Clay._ + R _Reading Beds._ + Ch _Chalk._ + P _Pebble Beds._ + S _Sandstone Band._ + + +Above the Chalk we come first to a thick red clay called Plastic clay. +It is much slipped, and the slip is overgrown. The only fossils found +in the Island are fragments of plants; larger plant remains on the +mainland show a temperate climate. This clay was formerly worked at +Newport for pottery. The clay is probably a freshwater deposit formed +in fairly deep water. On the mainland we find on the border shallow +water deposits called the Woolwich and Reading beds. (The clay is 150 +to 160 ft. thick at Whitecliff Bay, less than 90 ft. at the Alum Bay.) +We come next to a considerable thickness of dark clay with sand, at +the surface turned brown by weathering. This is the London clay, so +called because it underlies the area on which London is built. At the +base is a band of rounded flint pebbles, which extends at the base of +the clay from here to Suffolk. In it, as well as in a hard sandstone +18 inches higher up, are tubular shells of a marine worm, _Ditrupa +plana_. The sandstone runs out on the shore. About 35 ft. above the +basement bed is a zone of _Panopaea intermedia_ and _Pholadomya +margaritacea_, at 50 ft. another band of _Ditrupa_, and at about 80 +ft. a band with a small _Cardita_. In the higher part of the clay are +large septaria,--rounded blocks of a calcareous clay-ironstone, with +cracks running through them filled with spar. _Pinna affinis_ is found +in the septaria. The thickness of the clay in Whitecliff Bay is 322 +feet. It can be seen on the shore, when the tide happens to have swept +the sand away. Otherwise the lower beds are hardly visible, there +being no cliff here, but a slope overgrown with vegetation. + +In Alum Bay the London clay, about 400 ft. in thickness, consists of +clays, chiefly dark blue, with sands, and lines of septaria. In the +lower part is a dark clay with _Pholadomya margaritacea_, still +preserving the pearly nacre. There are also _Panopaea intermedia_, and +in septaria _Pinna affinis_. All these with their pearly lustre, are +beautiful fossils. A little higher is a zone with _Ditrupa_, and +further on a band of _Cardita_. Other shells also are found in the +clay, especially in the lower part. They are all marine, and indicate +a sub-tropical climate. Lines of pebbles show that we are near a +beach. In other parts of the south of England remains from the land +are found, borne down an ancient river in the way we found before in +the Wealden deposits. + +But times have changed since the Wealden days, and the life of the +Tertiary times has a much more modern appearance. From leaves and +fruits borne down from the forest we can learn clearly the nature of +the early Eocene land and climate. Leaves are found at Newhaven, and +numerous fossil fruits at Sheppey. The character of the vegetation +most resembled that now to be seen in India, South Eastern Asia, and +Australia. Palms grew luxuriantly, the most abundant fruit being that +of one called Nipadites, from its resemblance to the Nipa palm, which +grows on the banks of rivers in India and the Philippines. The forests +also included plants allied to cypresses, banksia, maples, poplars, +mimosa, custard apples, gourds, and melons. The rivers abounded in +turtle--large numbers of remains of which are found in the London clay +at the mouth of the Thames--crocodiles and alligators. With the +exception of the south east of England, all the British Isles formed +part of a continental mass of land covered with a tropical vegetation. +The mountain chains of England, Scotland, and Wales rose as now, but +higher. Long denudation has worn them down since. In the south-east of +England the coast line fluctuated; and sea shells, and the remains of +the plant and animal life of the neighbourhood of a great tropical +river alternate in the deposits. + + + [Illustration: FIG. 4] + + SECTION THROUGH HEADON HILL AND HIGH DOWN. + SHOWING STRATA SEEN AT ALUM BAY. + + G _Gravel Cap._ + Bm _Bembridge Limestone._ + O _Osborne Beds._ + UH _Upper Headon._ + MH _Middle " ._ + LH _Lower Headon._ + BS _Barton Sand._ + B _Barton Clay._ + Br _Bracklesham Beds._ + Bg _Bagshot Sands._ + L _London Clay._ + R _Reading Beds._ + Ch _Chalk._ + + +The London clay is succeeded by a great thickness of sands and clays +which form the Bagshot series. These are divided in the London basin +into Lower, Middle, and Upper Bagshot. In the Hampshire basin the +strata are now classified as Bagshot Sands, Bracklesham Beds, Barton +Beds, the last comprising the Barton Clay and the Barton Sand, +formerly termed Headon Hill Sands. There is some uncertainty as to the +manner in which these correspond to the beds of the Bagshot district, +as the Tertiary strata have been divided by denudation into two +groups, and differ in character in the two areas. It is possible that +the Barton Sand represents a later deposit than any in the London +area. + +Almost the only fossil remains in the Bagshot Sands are those of +plants, but these are of great interest. In Whitecliff Bay the beds +consist for the most part of yellow sands, above which is a band of +flint pebbles, which has been taken as the base of the Bracklesham +series, for in the clay immediately above marine shells occur. The +Bagshot Sands, in Whitecliff Bay, are about 138 feet thick, in Alum +Bay, 76 feet, according to the latest classification. In Alum Bay the +strata consist of sands, yellow, grey, white, and crimson, with clays, +and bands of pipe clay. This is remarkably white and pure, as though +derived from white felspar, like the China clay in Cornwall. The pipe +clay contains leaves of trees, sometimes beautifully preserved. +Specimens are not very easy to obtain, as only the edges of the leaves +appear at the surface of the cliff. They have been found chiefly in a +pocket, or thickening of the seam of pipe clay, which for forty years +yielded specimens abundantly, afterwards thinning out, when the leaves +became rare. The leaves lie flat, as they drifted and settled down in +a pool. With them are the twigs of a conifer, occasionally a fruit or +flower, or the wing case of a beetle. The leaves show a tropical +climate. The flora is a local one, differing considerably from those +of Eocene deposits elsewhere. The plants are nearly all dicotyledons. +Of palms there are only a few fragments, while the London clay of +Sheppey is rich in palm fruits, and many large palms are found in the +Bournemouth leaf beds, corresponding in date to the Bracklesham. The +differences may be largely due to conditions of locality and +deposition. The Alum Bay flora is characterised by a wealth of +leguminous plants, and large leaves of species of fig (_Ficus_); +simple laurel and willow-like leaves are common, of which it is +difficult to determine the species, and there is abundance of a +species of _Aralia_. The character of the flora resembles most those +of Central America and the Malay Archipelago. + + + [Illustration: PL. IV] + + Nummulites Laevigatus + + Turritella Limnaea + Imbricataria Longiscata + + Cardita Planicosta + + (Fusus) Planorbis + Leiostama Pyrus Euomphalus + + Cyrena Semistriata + + EOCENE AND OLIGOCENE + + +The Bracklesham Beds in Alum Bay (570 ft. thick) consist of clays, +with lignite forming bands 6 in. to 2 ft. thick; white, yellow, and +crimson sands; and in the upper part dark sandy clays, with bands +showing impressions of marine fossils. Alum Bay takes its name from +the alum formerly manufactured from the Tertiary clays. The coloured +sands have made the bay famous. The colours of the sands when freshly +exposed, and of the cliffs when wet with rain, are very rich and +beautiful,--deep purple, crimson, yellow, white, and grey. Some of the +beds are finely striped in different shades by current bedding. The +contrast of these coloured cliffs with the White Chalk, weathered to a +soft grey, of the other half of the bay is very striking and +beautiful. About 45 ft. from the top is a conglomerate of flint +pebbles, some of large size, cemented by iron oxide. In Whitecliff Bay +the Bracklesham Beds (585 ft.) consist of clays, sands, and sandy +clays, mostly dark, greenish and blue in colour, containing marine +fossils and lignite. Sir Richard Worsley, in his History of the Isle +of Wight, tells that in February, 1773, a bed of coal was laid bare in +Whitecliff Bay, causing great excitement in the neighbourhood. People +flocked to the shore for coal, but it proved worthless as fuel. It +has, however, been worked to some extent in later years. In some of +the beds are many fossils. Numbers have lately been visible where a +large founder has taken place. There are large shells of _Cardita +planicosta_ and _Turritella imbricataria_. They are, however, very +fragile. In a stratum just above these are numbers of a large +Nummulite (_Nummulites laevigatus_). These are round flat shells like +coins,--hence the name (Lat. _nummus_, a coin). They are a large +species of foraminifera. We may split them with a penknife; and then +we see a pretty spiral of tiny chambers. A smaller variety, _N. +variolarius_, occurs a little further on, and a tiny kind, _N. +elegans_, in the Barton clay. One of the most striking features of the +later Eocene is the immense development of Nummulite limestones--vast +beds built up of the delicate chambered shells of Nummulites,--which +extend from the Alps and Carpathians into Thibet, and from Morocco, +Algeria, and Egypt, through Afghanistan and the Himalaya to China. The +pyramids of Egypt are built of this limestone. + +The Bracklesham beds are followed by the Barton clay, famous for the +number of beautiful fossil shells found at Barton on the Hampshire +coast. At Whitecliff Bay the fossils are, unfortunately, very friable. +At Alum Bay the pathway to the shore is in a gully in the upper part +of the Barton clay. The strata consist of clays, sands, and sandy +clays. The base of the beds is marked by the zone of _Nummulites +elegans_. Numerous very pretty shells of the smaller Barton types may +be found, with fragments of larger ones; or a whole one may be found. +Owing to the cliff section cutting straight across the strata, which +are nearly vertical, there is far less of the beds open to observation +than at Barton, which probably accounts for the list of fossils being +much smaller. The shells are chiefly several species of _Pleurotoma_, +_Rostellaria_, _Fusus_, _Voluta_, _Turritella_, _Natica_, a small +bivalve _Corbula pisum_, a tubular shell of a sand-boring mollusc +_Dentalium_, _Ostroea_, _Pecten_, _Cardium_, _Crassatella_. The +fauna is like a blending of Malayan and New Zealand forms of marine +life. Throughout the Eocene from the London clay onward the shells are +such as abound in the warm sea south east of Asia. Similarly the plant +remains take us into a tropic land, where fan palms and feather palms +overshadowed the country, trees of the tropics mingling with trees we +still find in more Northern latitudes. The general character of the +flora as of the shells was Oriental and Malayan; both being succeeded +in later strata by a flora and fauna with greater analogy to that now +existing in Western North America. + +In Alum Bay the Barton clay is suddenly succeeded by the very fine +yellow and white sands which run along the western base of Headon +Hill, the curve of the syncline bringing them round from a nearly +vertical to an almost horizontal position. These are now known as the +Barton Sand. They are 90 ft. thick, the whole of the Barton beds being +338 ft. in Alum Bay, 368 ft. in Whitecliff. The sands were formerly +extensively used for glass making. They are almost unfossiliferous. +The passage from Barton clay to the sands in Whitecliff Bay is more +gradual. The sands here show some fine colouring which reminds us of +the more celebrated sands of Alum Bay. + + + [Footnote 11: See Memoir of Geological Survey of I. W. by H. J. + Osborne White, F.G.S. 1921, p. 90.] + + + + +Chapter IX + +THE OLIGOCENE + + +We pass on to strata which used to be called Upper Eocene, but are now +generally classified as a period by themselves, and called the +Oligocene. They are also known as the Fluvio-marine series. Large part +was deposited in freshwater by rivers running into lagoons, or in the +brackish water of estuaries, while at times the sea encroached, and +beds of marine origin were laid down. + +The west of the Island is much the best locality for the lower strata, +those which take their name from Headon Hill between Alum and Totland +Bays. There are three divisions of the Headon strata, marine beds in +the middle coming between upper and lower beds formed in fresh and +brackish water. Light green clays are very characteristic of these +beds, and at the west of the Island thick freshwater limestones, which +have died out before the strata re-appear in Whitecliff Bay. The +strongest masses of limestone in Headon Hill belong to the Upper +division. The limestones are full of freshwater shells, nearly all the +long spiral Limnaea and the flat spiral disc of Planorbis, perhaps the +most abundant species being _L. longiscata_ and _P. euomphalus_. The +limestones themselves are almost entirely the produce of a freshwater +plant _Chara_, which precipitates lime on its tissues, in the same +manner as the sea weeds we call corallines. On the shore round the +base of Headon Hill lie numerous blocks of limestone, the debris of +strata fallen in confusion, in which are beautiful specimens of Limnaea +and Planorbis. The shells, however, are very fragile. The marine beds +of the Middle Headon are best seen in Colwell Bay, where a few yards +north of How Ledge they descend to the beach, and a cliff is seen +formed of a thick bed of oysters, _Ostrea velata_. The oysters occupy +a hollow eroded in a sandy clay full of _Cytherea incrassata_, from +which the bed is known as the "Venus" bed, the shell formerly being +called _Venus_, later _Cytherea_, at present _Meretrix_. The marine +beds contain many drifted freshwater shells as Limnaea and Cyrena. The +How Ledge limestone forms the top of the Lower Headon. It is full of +well-preserved Limnaea and Planorbis. + +The Upper and Lower Headon are mainly fresh or brackish water +deposits. The purely freshwater beds contain _Limnaea_, _Planorbis_, +_Paludina_, _Unio_, and land-shells. In the brackish are found +_Potamomya_, _Cyrena_, _Cerithium_ (_Potamides_), _Melania_ and +_Melanopsis_. _Paludina lenta_ is very abundant throughout the +Oligocene. A large number of the marine shells of the Headon beds are +species also found in the Barton clay. _Cytherea_, _Voluta_, +_Ancillaria_, _Pleurotoma_, _Natica_ are purely marine genera. + +In White Cliff Bay the beds are mostly estuarine. Most of the fossils +are found in two bands, one about 30 ft. above the base of the series, +the other a stiff blue clay, about 90 feet higher, which seems to +correspond with the "Venus Bed" of Colwell Bay. Many of the fossils +are of Barton types. + +The Headon beds are about 150 feet thick at Headon Hill, 212 ft. in +Whitecliff Bay; and are followed by beds varying from about 80 to 110 +ft. in thickness, known as the Osborne and St. Helens series. They +consist mainly of marls variously coloured, with sandstone and +limestone. In Headon Hill is a thick concretionary limestone, which +almost disappears northward. The Oligocene strata often vary +considerably within short distances. The Osborne beds are exposed +along the low shore between Cowes and Ryde, and from Sea View to St. +Helens. In Whitecliff Bay they are not well seen, occurring in +overgrown slopes. They consist mostly of red and green clays. A band +of cream-yellow limestone a foot thick is the most conspicuous +feature. The fossils resemble those from the Headon beds, but are much +less plentiful. The marls seem to have been mostly deposited in +lagoons of brackish water, which at the present day are favourite +places for turtles and alligators, and of these many remains are found +in the Osborne beds. The beds are specially noted for the shoals of +small fish, _Diplomystus vectensis_ (_Clupea_), first observed by Mr. +G. W. Colenutt, F.G.S., and prawns found in them, and also remains of +plants. The beds that appear in the neighbourhood of Sea View and St. +Helens are divided into Nettlestone Grits and St. Helen's Sands, the +former containing a freestone 8 feet thick. + +Above these beds lies the Bembridge limestone, which is so +conspicuous in Whitecliff Bay, and forms Bembridge Ledge. On the north +shore of the Island the strata rise slightly on the northern side of +the syncline. There are also minor undulations in an east and west +direction. The result is to bring up the Bembridge limestone at +various points along the north shore, where it forms conspicuous +ledges--Hamstead Ledge at the mouth of the Newtown river, ledges in +Thorness Bay, and Gurnard Ledge. In Whitecliff Bay the limestone, +about 25 feet thick, forms the conspicuous reef called Bembridge +Ledge. The Bembridge limestone consists of two or more bands of +limestone with intercalated clays. It is usually whiter than the +Headon limestones, and the fossils occur as casts, the shells being +sometimes replaced by calc-spar. The limestone has been much used as a +building stone for centuries, not only in the Island, but for +buildings on the mainland. The most famous quarries were those near +Binstead, from which Quarr, the site of the great Abbey, now almost +entirely disappeared, derives its name. From these quarries was +obtained much of the stone for Winchester Cathedral and many other +ancient buildings. In the old walls and buildings of Southampton the +stone may be recognised at once by the casts of the Limnaeae it +contains. The quarries at Quarr were noted in more ways than one. In +later times the remains of early mammalia,--Palaeotherium, +Anoplotherium, and others--have been found. The quarries are now +abandoned and overgrown. The limestone may be seen inland at Brading, +where it forms the ridge on which the Church stands. + +The limestone is a freshwater formation, and the fossils are mostly +freshwater shells, of the same type as the Headon, Limnaea and +Planorbis the most common. There are also land shells, especially +several species of Helix, the genus which includes the common +snail,--_H. globosa_, very large,--and great species of _Bulimus_ +(_Amphidromus_) and _Achatina_ (_B. Ellipticus_, _A. costellata_). +These interesting shells were chiefly obtained in the limestone at +Sconce near Yarmouth, a locality now inaccessible, being occupied by +fortifications. The land shells have an affinity to species now found +in Southern North America. The limestone also abounds in the so-called +"seeds" of Chara. The reproductive organs,--the "seeds,"--of this +curious water-plant, allied to the lower Algae, are, like the rest of +the plant, encased in carbonate of lime, and are very durable. Large +numbers are found in the Oligocene strata. Under the microscope they +are seen to be beautifully sculptured in various designs, with a +delicate spiral running round them. Above the limestone lie the +Bembridge marls, varying in thickness in different localities from 70 +to 120 feet. North of Whitecliff Bay they stretch on to the Foreland. +They are in the main a freshwater formation, but a few feet above the +limestone is a marine band with oysters, _Ostrea Vectensis_. It runs +out along the shore, where the oysters may be seen covering the +surface. The Lower Marls consist chiefly of variously-coloured clays +with many shells, chiefly _Cyrena pulchra_, _semistriata_, and +_obovata_, _Cerithium mutabile_, and _Melania muricata_ (_acuta_); and +red and green marls, in which are few shells, but fragments of turtle +occur. A little above the oyster bed is a band of hard-bluish +septarian limestone. Sixty years ago Edward Forbes remarked on the +resemblance of this band to the harder insect-bearing limestones of +the Purbeck beds. In a limestone exactly resembling this, and +similarly situated in the lower part of the marls in Gurnard and +Thorness Bays, numerous insects were afterwards found,--beetles, +flies, locusts, and dragonflies, and spiders. Leaves of plants, +including palms, fig, and cinnamon, have also been found in this bed, +showing that the climate was still sub-tropical. The upper Marls +consist chiefly of grey clays with abundance of _Melania turritissima_ +(_Potamaclis_). The chief shells in the marls are _Cyrena_, _Melania_, +_Melanopsis_ and _Paludina_ (_Viviparus_). They are often beautifully +preserved; the species of Cyrena often retain their colour-markings. + +Bembridge Foreland is formed by a thick bed of flint gravel resting on +the marls, which are seen again in Priory Bay, where in winter they +flow over the sea-wall in a semi-liquid condition. They lie above the +limestone at Gurnard, Thorness, and Hamstead. West of Hamstead Ledge +the whole of the beds crop out on the shore, where beautifully +preserved fossils may be collected. Large pieces of drift wood occur, +also seeds and fruit. Many fragments of turtle plates may be found. +Large crystals of selenite (sulphate of lime) occur in the Marls. + +Last of the Oligocene in the Isle of Wight are the Hamstead beds. +These strata are peculiar to the Isle of Wight. The Bembridge beds +also are not found on the mainland, except a small outlier at +Creechbarrow Hill in Dorset. The Hamstead beds consist of some 250 +feet of marls, in which many interesting fossils have been found. They +cover a large area of the northern part of the Island, largely +overlaid by gravels, and are only seen on the coast at Hamstead, where +they form the greater part of the cliff, which reaches a height of 210 +ft., the top being capped by gravel. In winter the clays become +semi-liquid, in summer the surface may be largely slip and rainwash, +baked hard by the sun. The lower part of the strata may be best seen +on the shore. The strata consist of 225 ft. of freshwater, estuarine, +and lagoon beds, with _Unio_, _Cyrena_, _Cyclas_, _Paludina_, +_Hydrobia_, _Melania_, _Planorbis_, _Cerithium_ (rare), and remains of +turtles, crocodiles, and mammals, leaves and seeds of plants; and +above these beds 31 feet of marine beds with _Corbula_, _Cytherea_, +_Ostrea callifera_, _Cuma_, _Voluta_, _Natica_, _Cerithium_, and +_Melania_. + +Except for the convenience of dividing so large a mass of strata, it +would not be necessary to divide these from the Bembridge beds, as no +break in the character of the life of the period occurs at the +junction. The basement bed of the Hamstead strata is known as the +Black Band, 2 feet of clay, coloured black with vegetable matter, with +_Paludina lenta_ very numerous, _Melanopsis carinata_, _Limnaea_, +_Planorbis_, a small _Cyclas_ (_C. Bristovii_), seed vessels, and +lumps of lignite. It rests on dark green marls with _Paludina lenta_ +and _Melanopsis_, and full of roots. This evidently marks an old land +surface. About 65 feet higher is the White Band,--a white and green +clay full of shells, mostly broken. There are bands of tabular +ironstone containing _Paludina lenta_. Clay ironstone was formerly +collected on the shore between Yarmouth and Hamstead and sent to +Swansea to be smelted. The strata consist largely of mottled green and +red clays, probably deposited in brackish lagoons. These yield few +fossils except remains of turtle and crocodile and drifted plants. The +blue clays are much more fossiliferous. Among other plants are leaves +of palm and water-lily. The strata gradually become more marine +upwards. The marine beds were called by Forbes the Corbula beds, from +two small shells, _C. pisum_ and _C. vectensis_, of which some of the +clays are full. Remains of early mammalia are found in the Hamstead +beds, the most frequent being a hog-like animal, of supposed aquatic +habits, Hyopotamus, of which there are more than one species. + +The fauna and flora of the Oligocene strata show that the climate was +still sub-tropical, though somewhat cooling down from the Eocene. +Palms grew in what is now the Isle of Wight. Alligators and crocodiles +swam in the rivers. Turtle were abundant in river and lagoon. +Specially interesting in the Eocene and Oligocene are the mammalian +remains. They show us mammals in an early stage before they branched +off into the various families as we know them to-day. The Palaeotherium +was an animal like the tapir, now an inhabitant of the warmer regions +of Asia and America. Recent discoveries in Eocene strata in Egypt show +stages of development between a tapir-like animal and the elephant +with long trunk and tusks. There were in those days hog-like animals +intermediate between the hogs and the hippopotami. There were +ancestors of the horse with three toes on each foot. There were +hornless ancestors of the deer and antelopes. Many of the early +mammals showed characters now found in the marsupials, the order to +which the Kangaroo and Opossum belong, members of which are found in +rocks of the Secondary Era, and are the only representatives of the +mammalia in that age. Some of the early Eocene mammalia are either +marsupials, or closely related to them. In the Oligocene we find the +mammalian life becoming more varied, and branching out into the +various groups we know to-day; while the succeeding Miocene Period +witnesses the culmination of the mammalia--mammals of every family +abounding all over the earth's surface, in a profusion and variety not +seen before--or since, outside the tropics. + + + + +Chapter X + +BEFORE AND AFTER.--THE ICE AGE. + + +We have read the story written in the rocks of the Isle of Wight. What +wonderful changes we have seen in the course of the long history! +First we were taken back to the ancient Wealden river, and saw in +imagination the great continent through which it flowed, and the +strange creatures that lived in the old land. We saw the delta sink +beneath the sea, and a great thickness of shallow water deposits laid +down, enclosing remains of ammonites and other beautiful forms of +life. Then long ages passed away, while in the waters of a deeper sea +the great thickness of the chalk was built up, mainly by the +accumulation of microscopic shells. In time the sea bed rose, and new +land appeared, and another river bore down fruits to be buried with +sea shells and remains of turtles and crocodiles in the mud deposited +near its mouth to form the London clay. We followed the alternations +of sea and land, and the changing life of Eocene and Oligocene times. +We have heard of the early mammalia found in the quarries of Quarr, +and have learnt from the leaf beds of Alum Bay that at that time the +climate of this part of the world was tropical. Indeed, I think +everything goes to prove that through the whole of the times we have +been studying,--except perhaps the earliest Eocene, that of the +Reading beds,--the climate was considerably warmer than it is at the +present day. After all these changes do you not want to know what +happened next? Well, at this point we come to a gap in the records of +the rocks, not only in the Isle of Wight, but also in the British +Isles. The British Isles, or even England and Wales alone, are almost, +if not quite unique in the world in that, in their small extent, they +contain specimens of nearly every formation from the most ancient +times to the present day. In other parts of the world we may find +regions many times this area, where we can only study the rocks of +some one period. But just at this point in the story comes a +period,--a very important one, too,--the Miocene--of which we have no +remains in our Islands. We must hear a little of what happened before +we come back to the Isle of Wight again in comparatively recent times. + +But, first, perhaps, I had better tell,--just in outline,--something +of the earlier history of the world, before any of our Isle of Wight +rocks were made. For, if I do not, quite a wrong idea may be formed of +the world's history. The time of the Wealden river has seemed to us +very ancient. We cannot say how many hundreds of thousands, or rather +millions of years have passed since that ancient Wealden age. And you +may have thought that we had got back then very near the world's +birthday, and were looking at some of the oldest rocks on the globe. +But no. We are not near the beginning yet. Compared with the vast ages +that went before, our Wealden period is almost modern. We cannot tell +with any certainty the comparative time; but we may compare the +thickness of strata formed to give us some sort of idea. Now to the +first strata in which fossil remains of living things are found we +have in all a thickness of strata some 12 times that of all the rocks +we have been studying from Wealden to Oligocene, together with the +later rocks, Miocene and Pliocene, not found in the Isle of Wight. And +before that there is, perhaps, an equal thickness of sedimentary +deposits; though the fossils they, no doubt, once contained have been +destroyed by changes the rocks have undergone. + +Now let me try to give you some idea of the world's history up to the +point where we began in the Isle of Wight. If we could see back +through the ages to the furthest past of geological history, we should +see our world,--before any of the stratified rocks were laid down in +the seas,--before the seas themselves were made,--a hot globe, molten +at least at the surface. How do we know this? Because under the rocks +of all the world's surface we find there is granite or some similar +rock,--a rock which shows by its composition that it has crystallised +from a molten condition. Moreover we have seen that the interior of +the earth is intensely hot. And yet all along the earth must be +radiating off heat into the cold depths of space, and cooling like any +other hot body surrounded by space cooler than itself. And this has +gone on for untold ages. Far enough back we must come to a time when +the earth was red hot,--white hot. In imagination we see it +cooling,--the molten mass solidifies into Igneous rock,--the clouds of +steam in which the globe is wrapped condense in oceans upon the +surface. The bands of crystalline rock that rise above the primeval +seas are gradually worn down by rain and rivers and waves, and the +first sedimentary deposits laid down in the waters. And in the waters +and on the land life appeared for the first time,--we know not how. + +A vast thickness of stratified rocks was formed, which are called +Archaean ("ancient"). They represent a time, perhaps, as great as all +that has followed. These rocks have undergone great changes since +their formation. They have been pressed under masses of overlying +strata, and have come into the neighbourhood of the heated interior of +the earth; they have been burnt and baked and compressed and folded, +and acted on by heated water and steam, and their whole structure +altered by heat and chemical action. Limestones, _e.g._, have become +marble, with a crystalline structure which has obliterated any fossils +they may have once contained. Yet it is probable that, like nearly all +later limestones, they are of organic origin. These Archaean rocks +cover a large extent of country in Canada. We have some of them in our +Islands, in the Hebrides, and north-west of Scotland and in Anglesey, +and rising from beneath later rocks in the Malvern Hills and Charnwood +Forest.[12] + +The Archaean rocks are succeeded by the most ancient fossiliferous +rocks, the great series called the Cambrian, because found, and first +studied, in Wales. They consist of very hard rocks, and contain large +quantities of slate. They are followed by another series called the +Ordovician; and that by another the Silurian. These three great +systems of rocks measure in all some 30,000 ft. of strata. They form +the hills of Wales and the English Lake District. They contain large +masses of volcanic rocks. We can see where were the necks of old +volcanoes, and the sheets of lava which flowed from them. The +volcanoes are worn down to their bases now; and the hills of Wales +and the Lakes represent the remains of ancient mountain chains, which +rose high like the Alps in days of old, long before Alps or Himalayas +began to be made. These ancient rocks contain abundant remains of +living things, chiefly mollusca, crustaceans, corals, and other marine +organisms, showing that the waters of those ages abounded with life. + +We must pass on. Next comes a period called the Devonian, or Old Red +Sandstone, when the Old Red rocks of Devon and Scotland were laid +down. These contain remains of many varieties of very remarkable fish. +A long period of coral seas succeeded, when coral reefs flourished +over what was to be England; and their remains formed the +Carboniferous Limestone of Derbyshire and the Mendip Hills. A period +followed of immense duration, when over pretty well the whole earth +there seem to have been comparatively low lands covered with a +luxuriant and very strange vegetation. The remains of these ancient +forests have formed the coal measures, which tell of the most +widespread and longest enduring growth of vegetation the world has +seen. Strange as some of the plants were--gigantic horsetails and +club-mosses growing into trees--many were exquisitely beautiful. There +were no flowering plants, but the ferns, many of them tree ferns, were +of as delicate beauty as those of the present day. Many of the ferns +bore seeds, and were not reproduced by spores, such as we see on the +fronds of our present ferns. That is a wonderful story of plant +history, which has only been read in recent years. + +After the long Carboniferous period came to an end followed periods in +which great formations of red sandstone were made,--the Permian, and +the New Red Sandstone or Trias. During much of this time the +condition of the country seems to have resembled that of the Steppes +of Central Asia, or even the great desert of Sahara--great dry sandy +deserts--hills of bare rock with screes of broken fragments heaped up +at their base,--salt inland lakes, depositing, as the effect of +intense evaporation, the beds of rock salt we find in Cheshire or +elsewhere, in the same manner as is taking place to-day in the Caspian +Sea, in the salt lakes of the northern edge of the Sahara, and in the +Great Salt Lake of Utah. + +At the close of the period the land here sank beneath the sea--again a +sea of coral islands like the South Pacific of to-day. There were many +oscillations of level, or changes of currents; and bands of clay, when +mud from the land was laid down, alternate with beds of limestone +formed in the clearer coral seas. These strata form a period known as +the Jurassic, from the large development of the rocks in the Jura +mountains. In England the period includes the Liassic and Oolitic +epochs. The Liassic strata stretch across England from Lyme Regis in +Dorset to Whitby in Yorkshire. Most of the strata we are describing +run across England from south-west to north-east. After they were laid +down a movement of elevation, connected with the movement which raised +the Alps in Europe, took place along the lines of the Welsh and Scotch +mountains and the chain of Scandinavia, which raised the various +strata, and left them dipping to the south-east. Worn down by +denudation the edges are now exposed in lines running south-west to +north-east, while the strata dip south-east under the edges of the +more recent strata. The Lias is noted for its ammonites, and +especially for its great marine reptiles, Ichthyosaurus and +Plesiosaurus. The Oolitic Epoch follows--a long period during which +the fine limestone, the Bath freestone, was made; the limestones of +the Cotswolds, beds of clay known as the Oxford and Kimmeridge clays; +and again coral reefs left the rock known as coral rag. In the later +part of the period were formed the Portland and Purbeck beds, marine +and freshwater limestones, which contain also an old land surface, +which has left silicified trunks of trees and stems of cycads. + +And now following on these came our Wealden strata, the beginning of +the Cretaceous period. You see what ages and ages had gone before, and +that when Wealden times came, far back as they are, the world's +history was comparatively approaching modern times. We must remember +that all these formations, of which we have given a rapid sketch, are +of great thickness,--thousands of feet of rock,--and represent vast +ages of time. See what we have got to from looking at the shells in +the sea cliff! We have come to learn something of the world's old +history. We have been carried back through ages that pass our +imagination to the world's beginning, to the time of the molten globe, +before ever it was cool enough to allow life--we know not how--to +begin upon its surface. And Astronomy will take us back into an even +more distant past, and show us a nebulous mist of vast extent +stretching out into space like the nebulae observed in the heavens +to-day, before sun and planets and moons were yet formed. So we are +carried into the infinite of time and space, and questions arise +beyond the power of human mind to solve. + +Now we have, I hope, a better idea of the position the strata we have +been specially studying occupy in the geological history, and shall +understand the relation the strata we may find elsewhere bear to those +in the Isle of Wight and the neighbouring south of England. + +After this sketch of what went before our Island story, we must see +what followed at the end of the Oligocene period. We said that there +are no strata in the British Isles representing the next period, the +Miocene. But it was a period of great importance in the world's +history. Great stratified deposits were laid down in France and +Switzerland and elsewhere, and it was a great age of mountain +building. The Alps and the Himalaya, largely composed of Cretaceous +and Eocene rocks, were upheaved into great mountain ranges. It is +probable that during much of the period the British Isles were dry +land, and that great denudation of the land took place. But in the +first part of the period at all events this part of the world must +have been under water, and strata have been laid down, which have +since been denuded away. For our soft Oligocene strata, if exposed to +rain and river action during the long Miocene period and the time +which followed, would surely have been entirely swept away. The +Miocene was succeeded by the Pliocene, when the strata called the +Crag, which cover the surface of Norfolk and Suffolk, were formed. +They are marine deposits with sea shells, of which a considerable +proportion of species still survive. + +We have seen that through the ages we have been studying the climate +was mostly warmer than at the present day. The climate of the Eocene +was tropical. The Miocene was sub-tropical and becoming cooler. Palms +become rarer in the Upper strata. Evergreens, which form three-fourths +of the flora in the Lower Miocene, divide the flora with deciduous +trees in the Upper. And through the Pliocene the climate, though still +warmer than now, was steadily becoming cooler; till in the beginning +of the next period, the Pleistocene, it had become considerably colder +than that of the present day. And then followed a time which is known +as the great Ice Age, or the Glacial Period,--a time which has left +its traces all over this country, and, indeed all over Northern Europe +and America, and even into southern lands. The cold increased, heavy +snowfalls piled up snow on the mountains of Wales, the Lake District, +and Scotland; and the snow remained, and did not melt, and more fell +and pressed the lower snow into ice, which flowed down the valleys in +glaciers, as in Switzerland to-day. Gradually all the vegetation of +temperate lands disappeared, till only the dwarf Arctic birch and +Arctic willows were to be seen. The sea shells of temperate climates +were replaced by northern species. Animals of warm and temperate +climates wandered south, and the Arctic fox, and the Norwegian +lemming, and the musk ox which now lives in the far north of America +took their place; and the mammoth, an extinct elephant fitted by a +thick coat of hair and wool for living in cold countries, and a +woolly-haired rhinoceros, and other animals of arctic regions occupied +the land. When the cold was greatest, the glaciers met and formed an +ice-sheet; and Scotland, northern England and the Midlands, Wales, and +Ireland were buried in one vast sheet of ice as Greenland is to-day. + +How do we know this? To tell how the story has been read would be to +tell one of the most interesting stories of geology. Here we can only +give the briefest sketch of this wonderful chapter of the world's +history. But we must know a little of how the story has been made out. +We have already seen that the changes in plant and animal life point +to a change from a hot climate, through a temperate, at last to arctic +cold. Again, over the greater part of Northern England the rocks of +the various geological periods are buried under sheets of tough clay, +called boulder clay, for it is studded with boulders large and small, +like raisins in a plum pudding. No flowing water forms such a deposit, +but it is found to be just like the mass of clay with stones under the +great glaciers and ice sheets of arctic regions; and just such a +boulder clay may be seen extending from the lower end of glaciers in +Spitzbergen, when the glacier has temporarily retreated in a +succession of warm summers. The stones in our boulder clay are +polished and scratched in a way glaciers are known to polish and +scratch the stones they carry along, and rub against the rocks and +other stones. The rock over which the glacier moves is similarly +scratched and polished, and just such scratching and polishing is +found on the rocks in Wales and the Lake District. Again, we find +rocks carried over hill and dale and right across valleys, it may be +half across England. We can trace for great distances the lines of +fragments of some peculiar rock, as the granite of Shap in +Westmorland; and even rocks from Norway have been carried across the +North Sea, and left in East Anglia. This will just give an idea how we +know of this strange chapter in the history of our land. For, by this +time it was our land--England--much as we know it to-day; though at +times the whole stood higher above sea level, so that the beds of the +Channel and the North Sea were dry land. But, apart from variation of +level, the geography was in the main as now. + + + [Illustration: FIG. 9] + + SHINGLE AT FORELAND + + Bm _Bembridge Marls._ + S _Shingle._ + b _Brick Earth._ + Cf _Old Cliff in Marls._ + + + [Illustration: FIG. 5] + + DIAGRAM OF STRATA BETWEEN SOUTHERN DOWNS AND ST. GEORGE'S DOWN. + + Dotted Lines _Former extension of Strata._ + Broken Line _Former Bed of Valley sloping to St. George's Down._ + + +The ice sheet did not come further south than the Thames valley. What +was the country like south of this? Well, you must think of the land +just outside the ice sheet in Greenland, or other arctic country. No +doubt the winters must have been very severe,--hard frosts and heavy +snows,--the ground frozen deep. Some arctic animals would manage to +live as they do now just outside the ice sheet in Greenland. Now, have +we any deposits formed at that time in the Isle of Wight? I think we +have. A large part of the surface of the Island is covered by sheets +of flint gravel. The gravels differ in age and mode of formation. We +have already considered the angular gravels of the Chalk downs, +composed of flints which have accumulated as the chalk which once +contained them was dissolved away. But there are other gravel beds, +which consist of flints which, after they were set free by the +dissolution of the chalk, have been carried down to a lower level by +rivers or other agency, and more or less rounded in the process. Many +of these beds occur at a high level; and, as they usually cap +flat-topped hills, they are known as Plateau Gravels. Perhaps the +most remarkable is the immense sheet of gravel which covers the flat +top of St. George's Down between Arreton and Newport. Gravel pits show +upwards of 30 feet of gravel, consisting of flints with some chert and +ironstone, and the greatest thickness is probably considerably more +than this. The southern edge of the sheet is cut off straight like a +wall. To the north it runs out on ridges between combes which have cut +into it. In places in the mass of flints occur beds of sand, which +have all the appearance of having been laid down by currents of water. +The base of the gravel where it is seen on the steep southern slope of +the down has been cemented by water containing iron into a solid +conglomerate rock. The flints forming this gravel have not simply sunk +down from chalk strata dissolved away; for they lie on the upturned +edges of strata from Lower Greensand to Upper Chalk, which have been +planed off, and worn into a surface sloping gently to the north; and +over this surface the gravel has somehow flowed. The sharp wall in +which it ends at the upper part of the slope shows that it once +extended to the south over ground since worn away. Clearly, the gravel +was formed before denudation had cut out the great gap between the +central and southern downs of the Island. The down where the gravel +lies is 363 ft. above sea level, 313 ft. above the bottom of the +valley below. So that, though the gravel sheet is much newer than the +strata we have been studying, it must nevertheless be of great +antiquity. + +It seems that at the top of St. George's Down we are standing on what +was once the floor of an old valley. In the course of denudation the +bottom of a river valley often becomes the highest part of a district. +For the bed of the valley is covered by flint gravel, and flint is +excessively hard, and the bed of flints protects the underlying rock; +so that, while the rocks on each side are worn away, what was the +river bed is eventually left high above them. Thus the highest points +of a district are often capped by flint gravel marking the beds of old +streams. Tracing up this old valley to the southward, at a few miles +distance it will have reached the chalk region on the south of the +anticline: and the flints carried down the valley may have come from +beds of angular flints already dissolved out of the chalk such as we +find on St. Boniface Down. + +But how have these great masses of flints been swept along? Can the +land have been down under the sea; and have sea waves washed the +stones along? But these flints, though water-worn, are not rounded as +we find beach shingle. What immense rush of water can have spread +these flints 30 feet deep along a river valley? We must go to mountain +regions for torrents of this character. And then, mountain torrents +round the stones in their bed while these are mostly angular. The +history of these gravels is a difficult one. I can only give what +seems to me the most probable explanation. It appears to me probable +that in the Ice Age, south of the ice sheet, the ground must have been +both broken up by frosts, and also held together by being frozen hard +to some depth. Then when thaws came in the short but warm summers, or +when an intermission of the severe cold took place, great floods would +flow down the valleys in the country south of the ice sheet, and +masses of ice with frozen earth and stones would be borne along in a +sort of semi-liquid flow. In this way Mr. Clement Reid explains the +mass of broken-up chalk with large stones found on the heads of cliffs +on the South coast, and known by the name of "combe-rock" or "head." + +The Ice Age was not one simple period, and it is still difficult to +fit together the history we read in different places, and in +particular to correlate the gravels of the south of England with the +boulder clays of the glaciated area. There were certainly breaks in +the period, during which the climate became much milder, or even +warm; and these were long enough for southern species of animals and +plants to migrate northward, and occupy the lands where an arctic +climate had prevailed. There were moreover considerable variations in +the relative level of land and sea. So that we have a very complex +history, which is gradually coming into clearer light. + +That the gravels of the south of England belong largely to the age of +ice, is shown by remains of the mammoth contained in many. These, +however, are found in later gravels than those we have considered so +far, gravels laid down after the land had been cut down to much lower +levels. These lower gravels are known as Valley gravels, because they +lie along the course of existing valleys, the Plateau gravels having +been laid down before the present valleys came into existence. Teeth +of the mammoth are found in the Thames valley, and on the shores of +Southampton Water, in gravels about 50 to 70 feet above sea level, and +have been found also in the Isle of Wight at Freshwater Gate, at the +top of the cliffs near Brook, and in other places. The gravels near +Brook with the clays on which they rest have been contorted, and the +gravel forced into pockets in the clay, in a manner that suggests the +action of grounding ice ploughing into the soil. + +The high level gravels must belong to an early stage of the Glacial +Epoch. We get some idea of the great length of time this age must have +lasted, as we look from St. George's Down over the lower country of +the centre of the Island. After the formation of the St. George's Down +gravel the vast mass of strata between this and the opposite downs of +St. Boniface and St. Catherine's was removed by denudation; and +gravels were then laid down on the lower land, along Blake Down, at +Arreton, over Hale common, and along the course of the Yar. Patches of +gravel occur on the Sandown and Shanklin cliffs. At Little Stairs a +gravel, largely of angular chert, reaches a thickness of 12 feet, and +in parts are several feet of loam above gravel. + +At the west of the Island a great sheet of gravel covers the top of +Headon Hill, reaching a height of 390 feet. It appears sometimes to +measure 30 feet in thickness. Like that on St. George's Down it slopes +towards the Solent, resting on an eroded surface, in this case of +Tertiary strata; and here too the upper part of the sheet has been +removed by the wearing out of the deep valley between the Hill and the +Freshwater Downs. The sheet lies on an old valley bottom, which sloped +from the chalk downs on the south, then much higher and more extensive +than now. Here too we may see something of the length of the Glacial +Period. For at Freshwater Gate is a much later gravel, in which teeth +of the mammoth have been found. It was probably derived from older +gravels that once lay to the south, as the flints are rounded by +transport. But the formation of all these gravels appears to belong to +the Glacial Period; and as we stand in Freshwater Gate, and look at +this great gap in the downs worn out by the Western Yar, and think of +the time when a river valley passed over the tops of the High Downs +and Headon Hill, we receive a strong impression of the length of the +great Ice Age. + +Now surely the question will be asked, what caused these changes of +climate in the world's past history--so that at times a tropical +vegetation spread over this land, and vegetation flourished sufficient +to leave beds of coal within the Arctic circle, and in the Antarctic +continent, and at another the climate of Greenland came down to +England, and an ice sheet covered nearly the whole country? This still +remains one of the difficult problems of Geology. An explanation has +been attempted by Astronomical Theory, according to which the varying +eccentricity of the earth's orbit--that is to say a slight change in +the elliptic orbit of the Earth, by which at times it becomes less +nearly circular--a change which is known to take place--may have had +the effect of producing these variations of climatic conditions. The +theory is very alluring, for if this be the cause, we can calculate +mathematically the date and duration of the Glacial Period. But, +unfortunately, supposing the astronomical phenomena to have the effect +required, the course of events given by the astronomical theory would +be entirely different to that revealed by geological research. +Geographical explanations have usually failed through being of too +local a character to explain a phenomenon which affected the whole +northern hemisphere, and the effects of which reached at least as far +south as the Equator,[13] and are seen again in the southern hemisphere +in Australia, New Zealand, and South America. It is now believed that +great world-movements take place, due to the contraction by cooling of +the Earth's interior, and the adjustment of the crust to the +shrinkage.[14] Possibly some explanation might be found in these +world-wide movements; but their effect seems to last through too long +periods of time to suit our Ice Ages. Again, while the geographical +distribution of animals and plants in the present and past seems to +imply very great changes in the land masses and oceanic areas,[15] +these changes appear to bear no relation to glacial epochs. The cause +of the Ice Ages remains at present an unsolved problem. More than one +Ice Age has occurred during the long geological history. The marks of +such a period are found in Archaean rocks, in the Cambrian, when +glaciers flowed down to the sea level in China and South Australia +within a few degrees of the tropics, and above all in early Permian +times. The Dwyka conglomerate of the Karroo formation of South Africa +(deposits of Permo-Carboniferous age) show evidence of extensive +glaciation; deposits of the same age in Northern and Central India, +even within the tropics, a glacial series of great thickness in +Australia, and deposits in Brazil, appear to show a glaciation greater +than that of the recent glacial period. Yet these epochs formed only +episodes in the great geological eras. On the whole the climate +throughout geological time would seem to have been warmer than at the +present day. It may, perhaps, be doubted whether the earth has yet +recovered what we may call its _normal_ temperature since the Glacial +Epoch. + +Note on Astronomical Theory.--If the Ice Age be due to the increased +eccentricity of the Earth's orbit, the theory shows that a long +duration of normal temperature will be followed by a group of Glacial +Periods alternating between the northern and southern hemispheres, the +time elapsing between the culmination of such a period in one +hemisphere and in the other being about 10,500 years. While one +hemisphere is in a glacial period, the other will be enjoying a +specially mild,--a "genial" period. Now, according to the record of +the rocks, the "genial" periods were far from being those breaks in +the Glacial which we know as Inter-glacial periods. We have the +immensely long warm period of the Eocene and Oligocene, the Miocene +with a still warm but reduced temperature, and then the gradual +cooling during the Pliocene, till the drop in temperature culminates +in the Ice Age. Moreover, the duration of each glaciation during this +Ice Age is usually considered to have been much longer than the 10,000 +years or so given by the Astronomical Theory. Add to this that the +periods of high eccentricity of the Earth's orbit, though occurring +at irregular intervals, are, on the scale of geological time, pretty +frequent; so that several of such periods would have occurred during +the Eocene alone. Yet the geological evidence shows unbroken +sub-tropical conditions in this part of the world throughout the +Eocene. + + + [Footnote 12: The older division of the Archaean rocks--the + Lewisian gneisse--consists entirely of metamorphic and igneous + rocks; a later division--the Torridonian sandstones--is + comparatively little altered, but still unfossiliferous.] + + [Footnote 13: The great equatorial mountains Kilimanjaro and + Ruwenzori show signs of a former extension of glaciers.] + + [Footnote 14: For an account of such movements, see Prof. + Gregory's _Making of the Earth_ in the Home University Library.] + + [Footnote 15: See The _Wanderings of Animals_. By H. Gadow, + F.R.S., Cambridge Manuals.] + + + + +Chapter XI + +THE STORY OF THE ISLAND RIVERS; AND HOW +THE ISLE OF WIGHT BECAME AN ISLAND + + +We must now consider the history of the river system of the Isle of +Wight, to which our study of the gravels has brought us. For rivers +have a history, sometimes a most interesting one, which carries us +back far into the past. Even the little rivers of the Isle of Wight +may be truly called ancient rivers. For though recent in comparison +with the ages of geological time, they are of a vast antiquity +compared with the historical periods of human history. + +To understand our river systems we must go back to the time when +strata formed by deposit of sediment in the sea were upheaved above +the sea level. To take the simplest case, that of a single anticlinal +axis fading off gradually at each end, we shall have a sort of turtle +back of land emerged from the sea, as in figure 6, _aa_ being the +anticlinal axis. From this ridge streams will run down on either side +in the direction of the dip, their course being determined by some +minor folds of the strata, or difference of hardness in the surface, +or cracks formed during elevation. On each side of the dip-streams +smaller ones will flow, more or less in the direction of the strike, +and run into the main streams. Various irregularities, such as started +the flow of the streams, will favour one or another. Consider three +streams, _a_, _b_, _c_, and let us suppose the middle one the +strongest, with greatest flow of water, and cutting down its bed most +rapidly. Its side streams will become steeper and have more erosive +force, and so will eat back their courses most rapidly until they +strike the line of the streams on either side. Their steeper channels +will then offer the best way for the upper waters of the streams they +have cut to reach the sea; and these streams will consequently be +tapped, and their head waters cut off to flow to the channel of the +centre stream. We shall thus have for a second stage in the history a +system such as is shown in fig. 7. The same process will continue till +one river has tapped several others; and there will result the usual +figure of a river and its tributaries, to which we are accustomed on +our maps. We shall observe that tributaries do not as a rule gradually +approach the central stream, but suddenly turn off at nearly a right +angle from the direction in which they are flowing, and, after a +longer or shorter course, join at another sharp angle a river flowing +more or less parallel to their original direction. + + +[Illustration: FIG. 6] + +[Illustration: FIG. 7] + +DEVELOPMENT OF RIVER SYSTEMS + + +The Chalk and overlying Tertiary strata were uplifted from the sea in +great folds forming a series of such turtle-backs as we have been +considering. The line of upheaval was not south-west and north-east, +as that which raised the older formations in bands across England, but +took place in an east and west direction. The main upheaval was that +of the great Wealden anticline. Other folds produced the Sandown and +Brook anticlines, and that of the Portsdown Hills. The upheaval seemed +to have been caused by pressure acting from the south, for the steeper +slope of each fold is on the northern side. Our latest Oligocene +strata are tilted with the chalk, showing that the upheaval took place +after Oligocene times. But the great movement was in the main earlier +than the Pliocene. For on the North Downs near Lenham is a patch of +Lower Pliocene deposit resting directly on the Chalk, the older +Tertiary strata having been removed by denudation, clearly due to the +uplift of the Wealden anticline. The raising of the Pliocene deposit +to its present position proves that the same movement was continued at +a later time, probably during the Pleistocene. But the greater part of +the movement may be assigned to the Miocene, the period of great +world-movements which raised the Alps and the Himalaya. + +Many remarkable, and, at first sight, very puzzling features connected +with the courses of rivers find an explanation when we study the river +history. Thus, looking at the Weald of Kent and Sussex, we see that it +consists of comparatively low ground rising to a line of heights east +and west along the centre, and surrounded on all sides but the +south-east by a wall of Chalk downs. If we considered the subject, we +should suppose that the drainage of the country would be towards the +south-east, which is open to the sea. Not so. All the rivers flow from +the central heights north and south,--go straight for the walls of +chalk downs, and cut through the escarpment in deep clefts to flow +into the Thames and the Channel. This is explained when we remember +that the rivers began to flow when the great curve of strata rose +above the sea. Though eroded by the sea during its elevation, yet when +it rose above the waters the arch of chalk must have been continuous +from what are now North Downs to South. And from the centre line of +the great turtle back the streams began to flow north and south, +cutting in the course of ages deep channels for themselves. The +greater erosion in their higher courses has cut away the mass of chalk +from the centre of the Weald, but the rivers still flow in the +direction determined when the arch was still entire. + +We have a similar state of things in the Isle of Wight. Any one not +knowing the geological story, and looking at the geography of the +Island, might naturally suppose that there would be a stream flowing +from west to east, through the low ground between the two ranges of +downs, and finding its way into the sea in Sandown Bay. Instead of +this the three rivers of the Island, the two Yars and the Medina, all +flow north, and cut through the chalk escarpment of the Central downs, +as if an earthquake had made rifts for them to pass, and so find their +way into the Solent. The explanation is the same as in the case of the +Weald. The rivers began to flow when the Chalk strata were continuous +over the centre of the Island; and their course was determined when +the east and west anticlinal axis rose above the sea. + +We shall notice, however, that the Island rivers start from south of +the anticlinal axis. The centre of the Sandown anticline runs just +north of Sandown, but the various branches of the Yar and Medina flow +from well south of this. The explanation would appear to be that the +anticline is almost a monoclinal curve,--that is to say, one slope is +steep, the other not far from horizontal. Streams starting from the +ridge would flow with much greater force down the northern than the +southern side, and would cut back their course much more quickly. +Thus they would continually cut into the heads of the southern +streams, and turn the water supplying them into their own channels. + +In its early history a river cuts out its bed, and carries along +pebbles, sand and mud to the sea. The head waters are constantly +cutting back, and the slope becoming less steep, till a time comes +when the stream in its gently inclined lower course has no more power +to excavate, and the finer sediment, which is all that now reaches the +lower river, begins to fill up the old channel. And so the alluvium is +formed which fills the lower portions of our river valleys. + +Beyond this, the great rush of waters from melting snows and ice of +the Glacial Period has come to an end. The gentler and diminished +streams of a drier age have no power to roll flint stones along and +form beds of gravel. Gravel terraces border our river valleys at a +higher level than the present streams. Periods alternated during which +gravels were laid down by the river, and when the river acquiring more +erosive force, by an elevation of the land giving its bed a steeper +gradient, or a wetter climate producing a greater rush of water, cut a +new channel deeper in the old valley. So our valleys in Southern +England are frequently bordered by a succession of gravel terraces, +the higher ones being the older, dating from times when the river +flowed at a higher level than at present. Such terraces may be seen +above the Eastern Yar and its tributary streams. In the centre of the +old gravels is the alluvial flat of a later age. + +The Island rivers cut out their channels when the land stood at a +higher level than at present. The old channels of the lower parts of +the rivers are now filled with alluvium, partly brought down by the +rivers and partly marine. The channels are cut down considerably below +sea level; and by the sinking of the land the sea has flowed in, and +the last parts of the river courses are now tidal estuaries. The sea +does not cut out estuaries. They are the submerged ends of river +valleys. + +Some idea may be formed of the antiquity of our Island rivers by +observing the depth of the clefts they have cut through the downs at +Brading, Newport, and Freshwater. But to this we must add the depth at +which the old channels lie below the alluvium. It would be interesting +to know the thickness of the alluvium. But it is not often that +borings come to be made in river alluvia. However, in the old Spithead +forts artesian wells are sunk; and these pass through 70 to 90 feet of +recent deposits before entering Eocene strata. Under St. Helen's Fort, +at the mouth of Brading Harbour, are 80 feet of recent deposits. The +old channel of the Yar, at its mouth, must lie at least at this depth. + +Before it passes through the gap in the Chalk downs the Yar has +meandered about, and formed the alluvial flat called Morton marshes. +These marshes stretch out into the flat known as Sandown Level, which +occupies the shore of the bay between Sandown and the Granite Fort. +What is the meaning of this extension of the alluvium away from the +course of the river out to the sea at Sandown? A glance at it as +pictured on a geological map will suggest the answer. We see clearly +the alluvia of two streams converging from right and left, and uniting +to pass to the sea through Brading Harbour. But the stream to the +right has been cut off by the sea encroaching on Sandown Bay: only the +last mile of alluvium is left to tell of a river passed away. We must +reconstruct the past. We see the Bay covered by land sloping up to +east and south east, the lines of downs extending eastward from +Dunnose and the Culvers, and an old river flowing northward, and +cutting through the chalk at Brading after being joined by a branch +from the west. This old river must have been the main stream. For it +was a transverse stream, flowing nearly at right angles to the ridge +of the anticline; while the Yar comes in as a tributary in the +direction of the strike. Of other tributary streams, all from the +right are gone by the destruction of the old land. On the left streams +would flow in from the combes at Shanklin and Luccombe--streams which +have now cut out Shanklin and Luccombe chines. + +Passing the gap in the downs the river meandered about, and, with +marine deposit, washed in by the tides, formed the expanse of alluvium +which occupies what was Brading Harbour,--a harbour which in old times +presented at high tide a beautiful spectacle of land-locked water +extending up to Brading. Inclosures and drainings have been made from +time to time, the upper part near Yarbridge being taken in in the time +of Edward I. Further innings were made in the reign of Queen +Elizabeth; and Sir Hugh Middleton, who brought the New River to +London, made an attempt to enclose the whole, but the sea broke +through his embankment. The harbour was finally reclaimed at great +cost in 1880, the present embankment enclosing an area of 600 acres. + +The history of the Western Yar is similar to that of the Eastern. The +main stream must have flowed from land now destroyed by the sea +stretching far south of Freshwater Gate. All that is left is its tidal +estuary, and the gravel terraces and alluvial flat formed in the last +part of its course. Of a tributary stream an interesting relic +remains. For more than 2 miles from Chilton Chine through Brook to +Compton Grange a bed of river gravel lies at the top of the cliff, +marking the course of an old stream, of which coast erosion has made a +longitudinal section. This was a tributary of the Yar, when the +mammoth left his remains in the gravel at Grange Chine and Freshwater +Gate. Down the centre of the gravels lies a strip of alluvium laid +down by a stream following the same course in later days. The sea had +probably by this time cut into the stream; and it most likely flowed +into the sea somewhere west of Brook. In the alluvium hazel nuts and +twigs of trees are found at Shippard's Chine near Brook. + +The lower course of the Medina is a submerged river valley, the tide +flowing up to Newport. The river rises near Chale, and flows through a +strip of alluvium, overgrown with marsh vegetation, known as "The +Wilderness." This upper course of the Medina, from the absence of +gravels or brick earth, has the appearance of a comparatively modern +river. But the Medina has a further history. If you look at the map +you will see branches of the Yar running south to north as transverse +streams, but the main course is that of a lateral river. Look at the +two chief sources of the Yar--the stream from near Whitwell and Niton, +and that from the Wroxall valley. When they get down to the marshes +near Rookley and Merston, they are not flowing at all in the direction +of Sandown or Brading. They rather look as if they would flow along +the marshy flat by Blackwater into the Medina. But the Yar cuts right +across their course, and carries them off eastward to Sandown. When we +look, we find a line of river valley with a strip of alluvium running +up from the Medina at Blackwater in the direction of these two +streams--a valley which the railway up the Yar valley from Sandown +makes use of to get to Newport. There can be little doubt that these +streams from Niton and Wroxall originally ran along this line into the +Medina; but the Yar, cutting its course backward, has captured them, +and diverted their course. They probably represent the main branches +of the Medina in earlier times, the direction of flow from south-east +to north-west instead of south to north being possibly due to the +overlapping in the neighbourhood of Newport of the ends of the Brook +and Sandown anticlines. The sheet of gravel on Blake Down belongs to +this period of the river's history. The river must have diverted +between the deposition of the Plateau Gravels and that of the Valley +Gravels of the Yar. For the former follow the original valley, the +latter the new course of the river. + +We must now take a wider outlook, and see what became of our rivers +after they had flowed across what is now the Isle of Wight from south +to north. We have been speaking of times when the Island was of much +greater extent than at present. Standing on the down above the +Needles, and looking westward, we see on a clear day the Isle of +Purbeck lying opposite, and we can see that the headland there is +formed by white chalk cliffs like those beneath us. In front of them +stand the Old Harry Rocks, answering to the Needles, both relics of a +former extension of the land. In fact Purbeck is just like a +continuation of the Isle of Wight. South of the Chalk lie Greensand +and Wealden strata in Swanage Bay, and north towards Poole are +Tertiaries. Clearly these strata were once continuous with those of +the Isle of Wight. We must imagine the chalk downs of the Island +continued as a long range across what is now sea, and on through +Purbeck. A great Valley must have stretched from west to east, north +of this line, along the course of the Frome, which runs through +Dorset, and now enters the sea at Poole Harbour, on by Bournemouth, +and along the present Solent Channel--a valley still much above sea +level, not yet cut down by rivers and the sea--and down the centre of +this valley a river must have flowed, which may be called the River +Solent. It received as tributaries from the south the rivers of the +Isle of Wight, and others from land since destroyed by the sea. There +flowed into it from the north the waters of the Stour and Avon, and an +old river which flowed down the line of what is now Southampton Water. +Southampton Water looks like the valley of a large river, much larger +than the present Test and Itchen. Its direction points to a river from +the north west; and it has been shown by Mr. Clement Reid that the +Salisbury rivers--Avon, Nadder, and Wily--at a former time, when they +flowed far above their present level--continued their course into the +valley of Southampton Water. For fragments of Purbeck rocks from the +Vale of Wardour, west of Salisbury, have been found by him in gravels +on high land near Bramshaw, carried right over the deep vale of the +Avon in the direction of the Water. The lower Avon would originally be +a tributary of the Solent River; and it enters the sea about mid-way +between the Needles and the chalk cliffs of Purbeck, just opposite the +point where we might suppose the sea would have first broken through +the line of chalk downs. No doubt it broke through a gap made by the +course of an old river from the south, as it is now breaking through +the gap made by the old Yar at Freshwater. When the river Solent had +been tapped at this point, the Avon just opposite would have acquired +a much steeper flow, causing it to cut back at a faster rate, till it +cut the course of the old river which ran by Salisbury to Southampton, +and, having a steeper fall, diverted the upper waters of this river +into its own channel. + + + [Illustration: FIG. 8 + THE OLD SOLENT RIVER] + + +Frost and rain and rivers cut down the valleys of the river system for +hundreds of feet; the sea which had broken through the chalk range +gradually cut away the south side of the main river valley from Purbeck +to the Needles; and eventually the valley itself was submerged by a +subsidence of the land, and the sea flowed between the Isle of Wight +and the mainland. + +A gravel of somewhat different character to the rest is the sheet of +flint shingle at Bembridge Foreland. It forms a cliff of gravel about +25 feet high resting on Bembridge marls, and consists of large flints, +with lines of smaller flints and sand showing current bedding, and also +contains Greensand chert and sandstone, which must have been brought +from some district beyond the Chalk. The shingle slopes to north-east. +To the south-west it ends abruptly, the dividing line between shingle +and marls running up steeply into the cliff. This evidently marks an +old sea cliff in the marls, against which the gravel has been laid +down.[16] + +One or two comparatively recent deposits may be mentioned here. At the +top of the cliff in Totland Bay, about 60 ft. above the sea, for a +distance of 350 yards, is a lacustrine deposit, consisting in the main +of a calcareous tufa deposited by springs flowing from the limestone of +Headon Hill. The tufa contains black lines from vegetable matter, and +numerous land and freshwater shells of present-day species--many species +of Helix, especially H. nemoralis and H. rotundata, Cyclostoma elegans, +Limnaea palustris, Pupa, Clausilia, Cyclas, and others. + +On the top of Gore Cliff is a deposit of hard calcareous mud, reaching +a thickness of about 9 feet, and forming a small vertical cliff above +the slopes of chalk marl. It extends north a few yards beyond the +chalk marl on to Lower Greensand. It has been formed by rainwash from +a hill of chalk, which must once have existed to the south. The +deposit contains numerous existing land-shells, especially _Helix +nemoralis_ and other species of Helix. + +Between Atherfield and Chale at the top of the cliff is a large area +of Blown Sand. The sand is blown up from the face of the cliff below. +It reaches a thickness of 20 feet, and possibly more in places, and +forms a line of sand dunes along the edge of the cliff. The upper part +of Ladder Chine shows an interesting example of wind-erosion. The sand +driven round it by the wind has worn it into a semi-circular hollow +like a Roman theatre. + +Small spits, consisting partly of blown sand, extend opposite the +mouths of the Western Yar, the Newtown river, and the most +extensive--at the mouth of the old Brading Harbour, separating the +present reduced Bembridge Harbour from the sea. This is called St. +Helen's Spit, or "Dover,"--the local name for these sand spits. + + + [Footnote 16: Fig. 9, p. 79.] + + + + +Chapter XII + +THE COMING OF MAN. + + +We have watched the long succession of varied life on the earth +recorded in the rocks, and now we come to the most momentous event of +all in the history--the coming of Man. The first certain evidence of +the presence of man on the earth is found with the coming of the +Glacial Period,--unless indeed the supposed flint implements found by +Mr. Reid Moir, under the Crag in Suffolk, should prove him earlier +still. It is a rare chance that the skeleton of a land animal is +preserved; especially rare in the case of a skeleton so frail as that +of man. The best chance for the preservation of bones is in deposits +in caves, which were frequently the dens of wild beasts and the +shelters of man. But the implements used by early man were happily of +a very imperishable nature. His favourite material, if he could get +it, was flint. Flint could by dexterous blows have flake after flake +taken off, till it formed a tool or weapon with sharp point and +cutting edge. The implements, though only chipped, or flaked, were +often admirably made. They have very characteristic shapes. Moreover, +the kind of blow--struck obliquely--by which these early men made +their tools left marks which stamp them as of human workmanship. The +flake struck off shows what is called a "bulb of percussion"--a +swelling which marks the spot where the blow was struck--and from this +extends a series of ripples, producing a surface like that of a shell, +from which this mode of breaking is called conchoidal fracture. Often, +by further chipping the flake itself is worked into an implement. +Implements have also been made of chert, but it is far more difficult +to work, as it naturally breaks in an irregular way into sharp angular +fragments. Flint, on the other hand, lent itself admirably to the use +of early man, who in time acquired a perfect mastery of the material. +The working of flints is so characteristic that, once accustomed to +them, you cannot mistake a good specimen. Sea waves dashing pebbles +about will sometimes produce a conchoidal fracture, but never a series +of fractures in the methodical way in which a flint was worked by man. +And, of course, specimens may be found so worn that it is difficult to +be sure about their nature. Again early man may, especially in very +early times, have been content to use a sharp stone almost as he found +it, with only the slightest amount of knocking it into shape. So that +in such a case it will be very difficult to decide whether the stones +have formed the implements of man or not. In later times men learnt to +polish their implements, and made polished stone axes like those the +New Zealanders and South Sea Islanders used to make in modern times. +The old age of chipped or flaked implements is called the Palaeolithic; +the later age when they were ground or polished the Neolithic. (Simple +implements, as knives and scrapers, were still unpolished.) The +history of early man is a long story in itself, and of intense +interest. But we must not leave our geological story unfinished by +leaving out the culmination of it all in man. In the higher +gravels--the Plateau Gravels--no remains of man are found; but in the +lower--the Valley Gravels,--of the South of England is found abundant +evidence of the presence of man. Large numbers of flint implements +have been collected from the Thames valley and over the whole area of +the rivers which have gravel terraces along their course. Over a large +sheet of gravel at Southampton, whenever a large gravel pit is dug, +implements are found at the base of the gravel.[17] The occurrence of +the mammoth and other arctic creatures in the gravels shows that in +the Glacial Period man was contemporary with these animals. Remains in +caves tell the same story. In limestone caverns in Devon, Derbyshire, +and Yorkshire, implements made by man are found in company with +remains of the cave bear, cave hyaena, lion, hippopotamus, rhinoceros, +and other animals either extinct or no longer inhabitants of this +country--remains which have been preserved under floors of stalagmite +deposited in the caves. In caves of central France men have left +carvings on bone and ivory, representing the wild animals of that +day--carvings which show a remarkable artistic sense, and a keen +observation of animal life. Among them is a drawing of the mammoth on +a piece of mammoth ivory, showing admirably the appearance of the +animal, with his long hair, as he has been found preserved in ice to +the present day near the mouths of Siberian rivers. Drawings of the +reindeer, true to life, are frequent. + +Till recently very few Palaeolithic implements had been recorded as +found in the Isle of Wight. In the Memoir of the Geological Survey +(1889) only one such is recorded, found in a patch of brick earth near +Howgate Farm, Bembridge.[18] A few more implements, which almost +certainly came from this brick-earth, have been found on the shore +since. In recent years a large number of Palaeolithic implements have +been found at Priory Bay near St. Helen's. They were first observed on +the beach by Prof. E. B. Poulton, F.R.S., in 1886, and were traced to +their source in the gravel in the cliff by Miss Moseley in 1902. From +that time, and especially from 1904 onwards, many have been found by +Prof. Poulton, by R. W. Poulton (and others). Up to 1909 about 150 +implements had been found, and there have been more finds since.[19] + +The most important finds, besides those at Priory Bay, have been those +of Mr. S. Hazzledine Warren at Freshwater, especially in trial borings +in loam and clay below the surface soil in a depression of the High +Downs, south of Headon Hill, at a level of about 360 ft. O.D., in +which a number of Palaeolithic tools, flakes, and cores were found[20]. +Isolated implements have been found in recent years in various +localities in the Island. There are references to finds of implements +at different times in the past, but the descriptions are generally too +vague to conclude certainly to what date they belong. Much of the +gravel used in the Island comes from the angular gravel on St. +Boniface Down, or the high Plateau Gravel of St. George's Down; but in +the lower gravels and associated brick earth, it is highly probable +that more remains of Palaeolithic man will yet be found in the Island, +and quite possible that such have been found in the past, but for +want of accurate descriptions of the circumstances of the finds are +lost to us. + +We must pass on to the men of the Neolithic or later stone age. The +Palaeolithic age was of very great duration, much longer than all +succeeding human history. Between Palaeolithic and Neolithic times +there is in England a large gap. In France various stages have been +traced showing a continual advance in culture. In England little, if +anything, has been found belonging to the intermediate stages. Such +remains may yet be found in caves, or in lower river gravels, now +buried below the alluvium. The gap between Palaeolithic and Neolithic +is marked by the great amount of river erosion which took place in the +interval. Palaeolithic implements are found in gravels formed when the +rivers flowed some 100 feet above their present courses. Take, _e.g._, +the Itchen at Southampton. After the 100 foot gravels were deposited +the river cut down, not merely to its present level, but to an old bed +now covered up by various deposits beneath the river. After cutting +down to that bed the river laid down gravels upon it; and then--the +land standing at a higher level than to-day--the river valley and the +surrounding country were covered by a forest, which, as the climate +altered and became damper, was succeeded by the formation of peat. The +land has since sunk, and the peat, in parts 17 ft. thick, is now found +under Southampton Water, covered by estuarine silt. The Empress Dock +at Southampton was dug where a mud bank was exposed at low water. The +mud bank was formed of river silt 12 to 17 feet thick. Below this was +the peat, resting on gravel. On the gravel horns of reindeer were +found. In the peat were large horn cores of the great extinct ox, _Bos +primigenius_, also horns of red deer, and also in the peat were found +neolithic flint chips, a circular stone hammer head, with a hole bored +through for a wooden handle, and a large needle made of horn. Here, at +a great interval of time after Palaeolithic man, as we see by the +history of the river we have just traced, we come to the new race of +men, the Neolithic. + +When Neolithic man appeared the land stood higher than at present, +though not so high as during great part of the Pleistocene. Britain +was divided from the Continent, but the shores were a good way out +into what is now sea round the coasts, and forests clothed these +further shores. Remains of these, known as submerged forest, are found +below the tide mark round many parts of our coast. Peat as at +Southampton Docks, is found under the estuarine mud off Netley. The +wells at the Spithead Forts show an old land surface with peat more +than 50 feet below the tide level. The old bed of the Solent river +lies much lower still--124 feet below high tide at Noman's Land Fort; +this channel was probably an estuary after the subsidence of the land +till it silted up with marine deposits to the level on which the +submerged forest grew. + +When the Solent and Southampton Water were wooded valleys with rivers +flowing down the middle, the Isle of Wight rivers were tributaries to +the Solent river, and the forest, as might be expected, extended up +their valleys, and covered the low ground of the Island. Under the +alluvial flats are remains of buried forests. In digging a well at +Sandford in 1906 large trunks of hard oak were found blocking the +sinking of the well. When the land sank the sea flowed up the river +valleys, converting them into strait and estuary, and largely filling +up the channels with the silt, which now covers the peat. In the silt +of Newtown river are found bones of _Bos primigenius_, which was found +with the Neolithic remains in the peat of Southampton docks. + +The remains of Neolithic man are not only found in submerged forests, +but over the present surface of the land, or buried in recent +deposits. He has left us the tombs of his chiefs, known as long +barrows--great mounds of earth covering a row of chambers made of +flat stones, such as the mounds of New Grange in Ireland, and the +cromlechs or dolmens still standing in Wales and Cornwall. These +consist of a large flat or curved stone--it may be 14 feet in +length,--supported on three or four others. Originally a great mound +of earth or stones was piled on top. These have generally been removed +since by the hand of later man. The stones have been taken for road +metal, the earth to lay on the land. The great cromlech at Lanyon in +Cornwall was uncovered by a farmer, who had removed 100 cart loads of +earth to lay on his stony land before he had any idea that it was not +a natural mound. Then he came on the great cromlech underneath. +Another form of monument was the great standing stone or menhir, one +of which, the Longstone on the Down above Mottistone still stands to +mark the tomb of some chieftain of, it may be, 4,000 years ago. + +The implements of Neolithic man are found all over England, the smooth +polished axe head, commonly called a celt (Lat. _celtis_, a chisel), +the chipped arrow head, the flaked flint worked by secondary chipping +on the edge into a knife, or a scraper for skins; and much more common +than the implement, even of the simplest description, are the waste +flakes struck off in the making. Very few stone celts have been found +in the Isle of Wight. The flakes are extremely numerous, and a scraper +or knife may often be found. They are turned up by the plough on the +surface of the fields, in the earth of which they have been preserved +from rubbing and weathering. They have however, acquired a remarkable +polish, or "patina"--how is not clearly explained--which distinguishes +their surface from the waxy appearance of newly-broken flint. In +places the ground is so covered with flakes that we can have no doubt +that these are the sites of settlements. The implements were made from +the black flints fresh out of the chalk, and we can locate the +Neolithic flint workings. In our northern range of downs where the +strata are vertical the layers of flint in the Upper Chalk run out on +the top of the downs, only covered with a thin surface soil. In +places where this soil has been removed--as in digging a quarry--the +chalk is seen to be covered with flakes similar to those found on the +lower ground, save that they are weathered white from lying exposed on +the hard chalk, instead of on soft soil into which they would +gradually sink by the burrowing of worms. It is probable that these +flakes would be found more or less along the range of downs under the +surface soil. + +In places on the Undercliff have been found what are known as Kitchen +Middens--heaps of shells which have accumulated near the huts of +tribes of coast dwellers, who lived on shellfish. One such was +formerly exposed in the stream below the old church at Bonchurch, and +is believed to extend below the foundations of the Church. + +After a long duration of neolithic times a great step in civilisation +took place with the introduction of bronze. Bronze implements were +introduced into this country probably some time about B.C. 1800-1500; +and bronze continued to be the best material of manufacture till the +introduction of iron some two or three centuries before the visit of +Julius Caesar to these Islands. To the early bronze age belong the +graves of ancient chieftains known as round barrows, of which many are +to be seen on the Island downs. Funeral urns and other remains have +been found in these, some of which are now in the museum at +Carisbrooke Castle. Belonging to later times are the remains of the +Roman villa at Brading and smaller remains of villas in other places; +and cemeteries of Anglo-Saxon date, rich in weapons and ornaments, +which have been excavated on Chessil and Bowcombe Downs. But the study +of the remains of ancient man forms a science in itself--Archaeology. +In studying the periods of Palaeolithic and Neolithic man we have stood +on the borderland where Geology and Archaeology meet. We have seen that +vast geological changes have taken place since man appeared on earth. +We must remember that the geological record is still in process of +being written. It is not the record of a time sundered from the +present day, but continuous with our own times; and it is by the study +of processes still in operation that we are able to read the story of +the past. + + + [Footnote 17: Mr. W. Dale, F.S.A.] + + [Footnote 18: See figure 9, p. 79.] + + [Footnote 19: See account by R. W. Poulton in F. Morey's "Guide + to the Natural History of the Isle of Wight."] + + [Footnote 20: Surv. Mem., I.W., 1921, p. 174.] + + + + +Chapter XIII. + +THE SCENERY OF THE ISLAND--Conclusion. + + +After studying the various geological formations that enter into the +composition of the Isle of Wight, and learning how the Island was +made, it will be interesting to take a general view of the scenery, +and see how its varied character is due to the nature of its geology. +It would hardly be possible to find anywhere an area so small as this +little Island with such a variety of geological formations. The result +is a remarkable variety in the scenery. + +The main feature of the Island is the range of chalk downs running +east and west, and terminating in the bold cliffs of white chalk at +Freshwater and the Culvers. Here we have vertical cliffs of great +height, their white softened to grey by weathering and the soft haze +through which they are often seen. In striking contrast of colour are +the Red Cliff of Lower Greensand adjoining the Culvers, and the +many-coloured sands of Alum Bay joining on to the chalk of Freshwater. +The summits of the chalk downs have a characteristic softly rounded +form, and the chalk is covered with close short herbage suited to the +sheep which frequently dot the green surface. Where sheets of flint +gravel cap the downs, as on St. Boniface, they are covered by furze +and heather, producing a charming variation from the smooth turf where +the surface is chalk. The Lower Greensand forms most of the undulating +country between the two ranges of downs; while the Upper Greensand, +though occupying a smaller area, produces one of the most conspicuous +features of the scenery--the walls of escarpment that form the inland +cliffs between Shanklin and Wroxall, Gat Cliff above Appuldurcombe, +the fine wall of Gore Cliff above Rocken End, and the line of cliffs +above the Undercliff. To the Gault Clay is due the formation of the +Undercliff--the terrace of tumbled strata running for miles well above +the sea, but sheltered by an upper cliff on the north, and in parts +overgrown with picturesque woods. The impervious Gault clay throws out +springs around the downs, which form the headwaters of the various +Island streams. The upper division of the Lower Greensand, the +Sandrock, forms picturesque undulating foothills, often wooded, as at +Apsecastle, and at Appuldurcombe and Godshill Park. On a spur of the +Sandrock stands Godshill Church, a landmark visible for miles around. +At Atherfield we have a fine line of cliffs of Lower Greensand, while +the Wealden Strata on to Brook form lower and softer cliffs. + +To the north of the central downs the Tertiary sands and clays, often +covered by Plateau gravel, form an extended slope towards the Solent +shore, much of it well wooded, and presenting a charming landscape +seen from the tops of the downs. This slope of Tertiary strata is +deeply cut into by streams, which form ravines and picturesque creeks, +as Wootton Creek, 200 feet below the level of the surrounding country. +While much of the Island coast is a line of vertical cliff, the +northern shores are of gentler aspect, wooded slopes reaching to the +water's edge, or meadow land sloping gradually to the sea level. +Opposite the mouths of streams are banks of shingle and sand dunes, +forming the spits locally known as "dovers." Some of these, in +particular, St. Helen's Spit, afford interesting hunting grounds for +the botanist. + +The great variety of soil and situation renders the Isle of Wight a +place of interest to the botanist. We have the plants of chalk downs, +of the sea cliff and shore, of the woods and meadows, of lane and +hedgerow, and of the marshes. The old villages of the Island, often +occupying very picturesque situations--as Godshill on a spur of the +southern downs, Newchurch on a bluff overlooking the Yar valley, +Shorwell nestling among trees in a south-looking hollow of the downs, +Brighstone with its old church cottages and farmhouses among trees and +meadows between down and sea--the old and interesting churches, the +thatched cottages, the old manor houses of Elizabethan or Jacobean +date, now mostly farm houses, for which the Island is famous, add to +the varied natural beauty. + +One of the most characteristic features of the southern coasts of the +Island, should be mentioned, the Chines,--narrow ravines which cut +inland from the coast through the sandstone and clays of the Greensand +and Wealden strata, and along the beds of which small streams flow to +the sea. Narrow and steep-sided,--the name by which they are called is +akin to _chink_--they are in striking contrast to the more open +valleys of the streams which flow into the Solent on the north shore +of the Island. The most beautiful is Shanklin Chine. The cliff at the +mouth of the chine, just inside which stands a picturesque fisherman's +cottage with thatched roof, is 100 ft. high; and the chasm runs inland +for 350 yds., to where a very reduced cascade (for the water thrown +out of the Upper Greensand by the Gault clay is tapped at its source +for the town supply) falls vertically over a ledge produced by hard +ferruginous beds of the Greensand. Above the cascade the ravine runs +on, but much shallower, for some 900 yards. The lower ravine has much +beauty, tall trees rising up the sides, and overshadowing the chasm, +the banks thickly clothed with large ferns and other verdure. Much +wilder are the chines on the south-west of the Island. The cascade at +Blackgang falls over hard ferruginous beds (to which the beds over +which Shanklin cascade falls--though on a smaller scale--probably +correspond). The chine above these beds, being hollowed out in the +soft clays and sands of the Sandrock series, is much more open. Whale +Chine is a long winding ravine between steep walls, the stream at the +bottom making its way through blocks of fallen strata. + +The cause of these chines seems to be the same in all cases. It may be +noticed that Shanklin and Luccombe chines are cut in the floors of +open combes,--wide valleys with gently sloping floors; and at each +side of these chines is to be seen the gravel spread over the floor of +the old valley. It can scarcely be doubted that these combes are the +heads of the valleys of the old streams, which flowed down a gradual +slope till they joined the old branch (or, rather the old main +river)[21] of the Yar, flowing over land extending far over what is now +Sandown Bay. When the sea encroached, and cut into the course of this +old river, and on till it made a section of what had been the left +slope of the valley, the old tributaries of the Yar now fell over a +line of cliff into the sea. They thus gained new erosive power, and +cut back at a much greater rate new and deeper channels; with the +result that narrow trenches were cut in the floors of the old gently +sloping valleys. The chines on the S.W. coast are to be explained in a +similar way. They have been cut back with vertical sides, because the +encroachment of the sea caused the streams to flow over cliffs, and so +gave then power to cut back ravines at so fast a rate that the +weathering down of the sides could not keep pace with it. The +remarkable wind-erosion of these bare south-westerly cliffs by a sort +of sand-blast driven before the gales to which that stretch of coast +is exposed has already been referred to. + +A few words in conclusion to the reader. I have tried to show you +something of the interest and wonder of the story written in the +rocks. We have seen something of the world's making, and of the many +and varied forms of life which have succeeded each other on its +surface. We have had a glimpse of great and deep problems suggested, +which are gradually receiving an answer. Geology has the advantage +that it can be studied by all who take walks in the country, and +especially by those who visit any part of the sea coast, without the +need of elaborate and costly scientific instruments and apparatus. Any +country walk will suggest problems for solution. I have tried to lead +you to observe nature accurately, to think for yourselves, to draw +your own conclusions. I have shown you how to try to solve the +questions of geology by looking around you at what is taking place +to-day, and by applying this knowledge to explain the records which +have reached us of what has happened in the past. You are not asked to +accept the facts of the geological story on the word of the writer, or +on the authority of others, but to think for yourselves, to learn to +weigh evidence, to seek only to find out the truth, whether it be +geology you are studying or any other subject, and to follow the truth +whithersoever it leads. + + + [Footnote 21: See p. 91.] + + + + +TABLE OF STRATA + + +Recent. Peat and River Alluvium. + +Pleistocene. Plateau Gravels: Valley Gravels and Brick-Earth. + + { Pliocene} Absent from the Isle of Wight. + { Miocene } + + { { { Marine, Corbula Beds + { { Hamstead { Freshwater & Estuarine. + { { + { { { Bembridge Marls + { { Bembridge { + { { Beds { Bembridge Limestone + { { + { Oligocene { Osborne and St. Helen's Beds. + { { + Tertiary { { { Upper. Freshwater and Brackish + { { Headon { Middle. Marine + { { Beds { Lower. Freshwater and Brackish + { + { { Barton} Barton Sand. + { { Beds} Barton Clay. + { { + { Eocene { Bracklesham Beds. + { { Bagshot Sands + { { London Clay + { { Plastic Clay (Reading Beds) + + { { White { Upper Chalk (Chalk with flints) + { { Chalk { Middle Chalk (Chalk + { { { without flints) + { { + { { { A. plenus Marls + { Upper { Lower { Grey Chalk + { Cretaceous { Chalk { Chalk Marl + { { { Chloritic Marl + { { + { { { Upper { Chert Beds + { { Selbornian { Greensand { Sandstone and + { { { Rag Beds + Mesozoic { { Gault + or { + Secondary{ { Carstone + { { Lower { Sandrock and Clays + { { Greensand { Ferruginious Sands + { { { Atherfield Clay + { Lower { { Perna Bed + { Cretaceous { + { { { Shales + { { Wealden { Variegated Marls + + + + +FOR FURTHER STUDY. + + +Memoirs of the Geological Survey. General Memoir of the Isle of Wight, +date 1889. New edition, entitled "A short account of the Geology of +the Isle of Wight," by H. J. Osborne White, F.G.S., 1921, price 10s. +The Memoirs are the great authority for the Geology of the Island: +technical; books for Geologists. The New Edition is more condensed +than the original, but contains much later research. Mantell's +"Geological Excursions round the Isle of Wight," 1847. By one of the +great early geologists. Long out of print, but worth getting, if it +can be picked up second-hand. + +Norman's "Guide to the Geology of the Isle of Wight," 1887, still to +be obtained of Booksellers in the Island. Gives details of strata, +and lists of fossils, with pencil drawings of fossils. + +Other books bearing on the subject have been mentioned in the text and +foot-notes. + +An excellent geological map of the Island, printed in colour, scale +1 in. to the mile, full of geological information, is published by the +Survey at 3s. + +A good collection of fossils and specimens of rocks from the various +strata of the Isle of Wight has recently been arranged at the Sandown +Free Library, and should be visited by all interested in the Geology +of the Island. It should prove a most valuable aid to all who take up +the study, and a great assistance in identifying any specimens they +may themselves find. + + + + + [Illustration] + GEOLOGICAL MAP OF THE ISLE OF WIGHT + + + + + INDEX + + + Words in Italics refer to a page where the meaning of a + term is given. + + + Agates, 22, 41, 50 + + Alum Bay, 56-62 + + Ammonites, 32, 34, 39, 44 + + _Anticline_, 12 + + Astronomical Theory of Ice Age, 83, 85 + + Atherfeld, 29 + + Avon River, 94 + + + Barrows, 102, 104 + + Barton, 61 + + Belemnites, 33 + + Bembridge Limestone, 65 + -- shingle at, 95 + + Benettites, 27 + + "Blue Slipper," 15 + + Bonchurch, 50, 103 + + Bos primigenius, 101, 102 + + Botany, 106 + + Bracklesham, 59, 60 + + Brading Harbour, 90, 91 + + Bronze age, 103 + + Brook, 29 + + Building Stone, 39, 65 + + + Carstone, 26, 35 + + Chalcedony, 22, 41, 50 + + Chale, 33 + + Chalk, divisions of, 45, 51, 52 + -- Marl, 45 + -- Rock, 45 + + Chalybeate Springs, 25 + + Chert, 39 + + Chloritic Marl, 44 + + Climate. + + Coal, 8, 61 + + Colwell Bay, 64 + + Compton Bay, 31, 39 + + Conglomerate, modern, 25 + + "Crackers," 32 + + Cretaceous. + + Crioceras, 34 + + Current Bedding, 27 + + Cycads. + + + Denudation, 3, 12, 76, 80, 82 + + _Dip_, 11 + + + Echinoderms, 48, 52 + + Eocene, 54 + + Erosion, marine, 4 + " pre-Tertiary, 54 + + _Escarpment_, 14 + + + _Faults_, 13 + + Fault at Brook, 30 + + Flint, origin of, 47 + " implements, 97 + + Flora, Alum Bay, 59 + " Eocene, 58, 62 + " Wealden, 18, 27 + + Foraminifera, 42, 61 + + + Gat Cliff, 38 + + Gault, 37 + + Glacial Period, 77-85 + + Glauconite, 24, 39, 44 + + Gore Cliff, 39, 44 + + Greensand, Lower, 23-36 + " Upper, 37 + + Gravels, 50, 79, 89, 93-95 + + + Hamstead, 65, 67 + + Headon Hill, 62-64 + + Hempstead, see Hamstead. + + Hyopotamus, 69 + + + Ice Age, 77-85 + + Iguanodon, 20 + + Insect Limestone, 67 + + Iron Ore, 22, 24 + + Iron pyrites, 22 + + + Landslips, 25, 38 + + Limnaea, 63, 64, 66 + + Lobsters, Atherfield, 32 + + London Clay, 57 + + Luccombe, Landslip at, 25 + + + Mammalian Remains, 66, 69 + + Mammoth, 77, 81 + + Marvel, 35 + + Medina, 93 + + Melbourn Rock, 45 + + Miocene, 69, 71, 76 + + + Nautilus, 32, 45 + + Needles, 4 + + Neolithic Man, 100 + + Newtown River, 102 + + Nummulites, 61 + + + Oligocene, 63 + + + Palaeolithic Man, 97 + + Perna Bed, 23, 31 + + Pine Raft, 29 + + Planorbis, 63, 64, 66 + + Plastic Clay, 57 + + Priory Bay, 99 + + Purbeck Marble, 16 + + + Quarr, 65 + + + Rag, 38 + + Rock (place), 35 + + Roman Villas, 104 + + + St. Boniface Down, 50, 100, 105 + + St. George's Down, 79, 100 + + Sandown Anticline, 11-13, 89 + + Sandrock, 25, 35 + + Scaphites, 34 + + Scenery, 105 + + Sea Urchins, 48, 52, + + Shanklin Chine, 107 + + Solent, 94 + + Southampton Dock, 101 + " Water, 94 + + Sponges in Flint, 47 + + Stone Age, 97 + + Strata, Table of, 110, 111 + + _Strike_, 11 + + Submerged Forest, 101 + + Swanage, 93 + + _Syncline_, 12 + + + Table of Strata, 110, 111 + + Tertiary, 54 + + Totland Bay, 63, 95 + + Tufa, 45 + + Turtle, 58, 65, 68 + + + Undercliff, formation of, 25, 38 + + + Volcanic Action, 5 + + + Wealden, 15 + + Whitcliff Bay, 56-67 + + Wood, Fossil, 8, 15, 18, 27, 29 + + + Yar, Eastern, 89-91 + " Western, 92 + + + Zones of Chalk, 51, 52 + + +_Printed by The Crypt House Press, Bell Lane, Gloucester._ + + + + +Transcriber's Notes + +With the exception of the changes noted below, the text in this file +is the same as that in the original printed version. These may include +alternate spelling from what may be common today (for example, +gneisse); punctuational and/or grammatical nuances. Additionally, +several missing periods were inserted; but are not listed below. +Lastly, the Index seems to be missing a few references to page numbers +and were left as originally printed. + +Emphasis Encoding + + _Text_ - Italicized Text + $Text$ - Greek translation + +Typographical Corrections + + Page 69: regious => regions + + Page 101: sourrounding => surrounding + + Page 102: remains In the peat => ... in ... + + Page 106: surounding => surrounding + + + + + + +End of the Project Gutenberg EBook of The Geological Story of the Isle of +Wight, by J. 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