J. Cecil Hughes

“ 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. ”

“ 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 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. ”

“ 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. ”

“ 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. ”

“ The Palæozoic 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. ”

“ 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. ”

“ 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! ”

“ 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. ”

“ 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. ”

“ 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 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. ”

“ 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? ”

“ 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 ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 [Pg 8] 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 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. ”

“ 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. ”

“ 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. ”

“ We must pass on to the men of the Neolithic or later stone age. The Palæolithic age was of very great duration, much longer than all succeeding human history. Between Palæolithic 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. ”

“ 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. ”

“ 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. ”