Front matter

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); punctuation and/or grammatical nuances. There are numerous instances of words appearing as hyphenated versions and without a hyphen (e.g., north-west and north west, south-east and south east, etc.). 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.

Typographical Corrections

Page 69: regious => regions

Page 101: sourrounding => surrounding

Page 102: remains In the peat => ... in ...

Page 106: surounding => surrounding

THE GEOLOGICAL STORY OF

THE ISLE OF WIGHT.

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 Story1

II.The Structure of the Island10

III.The Wealden Strata: The Land of the Iguanodon15

IV.The Lower Greensand23

V.Brook and Atherfield29

VI.The Gault and Upper Greensand37

VII.The Chalk42

VIII.The Tertiary Era: The Eocene54

IX.The Oligocene63

X.Before and After: The Ice Age70

XI.The Story of the Island Rivers; and How the Isle of Wight became an Island86

XII.The Coming of Man97

XIII.The Scenery of the Island: Conclusion105

ILLUSTRATIONS OF FOSSILS

PLATE I.—Facing page 20.

Wealden ... Cyrena Limestone Vertebra of Iguanodon

Lower Greensand ... Perna Mulleti Meyeria Vectensis (Atherfield Lobster) Panopæa Plicata Terebratula Sella

PLATE II.—Facing page 23.

Lower Greensand ... Trigonia Caudata Trigonia Dædalea 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 Lævigatus (Fusus) Leiostoma Pyrus

Oligocene ... Limnæa Longiscata Planorbis Euomphalus Cyrena Semistriata

DIAGRAMS

Facing page

1.Coast, Sandown Bay10

2.Coast, Atherfield29

3.Coast, Whitecliff Bay56

4.Section through Headon Hill and High Down. (Strata seen at Alum Bay)58

5.St George's Down79

6, 7.Development of River Systems86

8.The old Solent River94

9.Shingle at Foreland79

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 WIGHT112

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°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.

Fig. 1

DIAGRAM OF COAST, SANDOWN BAY, DUNNOSE TO CULVER CLIFF.

WWealden. gGault.

PPerna Bed. UGUpper Greensand.

LGLower Greensand. CChalk.

CbClay Bands. ScShanklin Chine.

SSandrock and Carstone. LcLuccombe 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 , such as the one we are looking at, is called an anticline. When the arch is reversed, like this , 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.

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 Δ). 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 vertebræ, 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. όδούς g. όδόντυς 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.

PL. I

Perna Mulleti Meyeria Vectensis (Atherfield Lobster)

Panopæa 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.

PL. II

Trigonia Caudata Trigonia Dædalea

Gervillia Sublanceolata

(Ammonite) Mortoniceras Rostratum Nautilus Radiatus

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 (Sphæra) corrugata, a flatter bivalve Astarte,—and a smaller oblong shell Panopæa,—also a peculiar shell of triangular form, Trigonia,—one species T. caudata has raised ribs running across it, another T. dædalea has bands of raised spots. A pretty little coral, looking like a collection of little stars, Holocystis elegans, one of the Astræidæ, 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 Terebratulæ, and others with fragments of sea urchins. The Terebratulæ and Rhynchonellæ 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 Lingulæ, 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, Panopœa, 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 Cycadaceæ 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.

Fig. 2

COAST ATHERFIELD TO ROCKEN END

WlWealden Beds. WWalpen Clay. FerFerruginous Bands of Blackgang Chine.

PPerna Bed. UcUpper Crioceras Beds. BBlack Clay.

AAtherfield Clay. WSWalpen and Ladder Sands. SSandrock and Clays.

CkCracker Group. UgUpper Gryphæa Beds.

LgLower Gryphæa Beds. CeCliff End Sands.

ScScaphite. " FFoliated Clay.

LcLower Crioceras " SUSands of Walpen Undercliff.

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 Hylæosaurus, 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. βελεμων "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 Serpulæ 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. κέρος, ram, κριός, 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. σκάφη).[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.

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 serpulæ, the tubes formed by certain marine worms. Very pretty pectens (scallop shells) are found in the sandstone. Many other shells, Terebratulæ, Trigonia, Panopæa, 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.

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.

PL. III

(Pecten) Neithea Quinquecostata

Thetironia Minor (Ammonite) Mantelliceras Mantelli Rhynchonella Parvirostris

(Sea Urchins)

Micraster Cor-AnguinumEchinocorys 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 æqualis; and of Pectens, Æquipecten 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.

Photo 1

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.