Read Ebook: The Geological Story of the Isle of Wight by Hughes J Cecil John Cecil

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es near Chale, and flows through a strip of alluvium, overgrown with marsh vegetation, known as "The Wilderness." This upper course of the Medina, from the absence of gravels or brick earth, has the appearance of a comparatively modern river. But the Medina has a further history. If you look at the map you will see branches of the Yar running south to north as transverse streams, but the main course is that of a lateral river. Look at the two chief sources of the Yar--the stream from near Whitwell and Niton, and that from the Wroxall valley. When they get down to the marshes near Rookley and Merston, they are not flowing at all in the direction of Sandown or Brading. They rather look as if they would flow along the marshy flat by Blackwater into the Medina. But the Yar cuts right across their course, and carries them off eastward to Sandown. When we look, we find a line of river valley with a strip of alluvium running up from the Medina at Blackwater in the direction of these two streams--a valley which the railway up the Yar valley from Sandown makes use of to get to Newport. There can be little doubt that these streams from Niton and Wroxall originally ran along this line into the Medina; but the Yar, cutting its course backward, has captured them, and diverted their course. They probably represent the main branches of the Medina in earlier times, the direction of flow from south-east to north-west instead of south to north being possibly due to the overlapping in the neighbourhood of Newport of the ends of the Brook and Sandown anticlines. The sheet of gravel on Blake Down belongs to this period of the river's history. The river must have diverted between the deposition of the Plateau Gravels and that of the Valley Gravels of the Yar. For the former follow the original valley, the latter the new course of the river.

We must now take a wider outlook, and see what became of our rivers after they had flowed across what is now the Isle of Wight from south to north. We have been speaking of times when the Island was of much greater extent than at present. Standing on the down above the Needles, and looking westward, we see on a clear day the Isle of Purbeck lying opposite, and we can see that the headland there is formed by white chalk cliffs like those beneath us. In front of them stand the Old Harry Rocks, answering to the Needles, both relics of a former extension of the land. In fact Purbeck is just like a continuation of the Isle of Wight. South of the Chalk lie Greensand and Wealden strata in Swanage Bay, and north towards Poole are Tertiaries. Clearly these strata were once continuous with those of the Isle of Wight. We must imagine the chalk downs of the Island continued as a long range across what is now sea, and on through Purbeck. A great Valley must have stretched from west to east, north of this line, along the course of the Frome, which runs through Dorset, and now enters the sea at Poole Harbour, on by Bournemouth, and along the present Solent Channel--a valley still much above sea level, not yet cut down by rivers and the sea--and down the centre of this valley a river must have flowed, which may be called the River Solent. It received as tributaries from the south the rivers of the Isle of Wight, and others from land since destroyed by the sea. There flowed into it from the north the waters of the Stour and Avon, and an old river which flowed down the line of what is now Southampton Water. Southampton Water looks like the valley of a large river, much larger than the present Test and Itchen. Its direction points to a river from the north west; and it has been shown by Mr. Clement Reid that the Salisbury rivers--Avon, Nadder, and Wily--at a former time, when they flowed far above their present level--continued their course into the valley of Southampton Water. For fragments of Purbeck rocks from the Vale of Wardour, west of Salisbury, have been found by him in gravels on high land near Bramshaw, carried right over the deep vale of the Avon in the direction of the Water. The lower Avon would originally be a tributary of the Solent River; and it enters the sea about mid-way between the Needles and the chalk cliffs of Purbeck, just opposite the point where we might suppose the sea would have first broken through the line of chalk downs. No doubt it broke through a gap made by the course of an old river from the south, as it is now breaking through the gap made by the old Yar at Freshwater. When the river Solent had been tapped at this point, the Avon just opposite would have acquired a much steeper flow, causing it to cut back at a faster rate, till it cut the course of the old river which ran by Salisbury to Southampton, and, having a steeper fall, diverted the upper waters of this river into its own channel.

Frost and rain and rivers cut down the valleys of the river system for hundreds of feet; the sea which had broken through the chalk range gradually cut away the south side of the main river valley from Purbeck to the Needles; and eventually the valley itself was submerged by a subsidence of the land, and the sea flowed between the Isle of Wight and the mainland.

A gravel of somewhat different character to the rest is the sheet of flint shingle at Bembridge Foreland. It forms a cliff of gravel about 25 feet high resting on Bembridge marls, and consists of large flints, with lines of smaller flints and sand showing current bedding, and also contains Greensand chert and sandstone, which must have been brought from some district beyond the Chalk. The shingle slopes to north-east. To the south-west it ends abruptly, the dividing line between shingle and marls running up steeply into the cliff. This evidently marks an old sea cliff in the marls, against which the gravel has been laid down.

One or two comparatively recent deposits may be mentioned here. At the top of the cliff in Totland Bay, about 60 ft. above the sea, for a distance of 350 yards, is a lacustrine deposit, consisting in the main of a calcareous tufa deposited by springs flowing from the limestone of Headon Hill. The tufa contains black lines from vegetable matter, and numerous land and freshwater shells of present-day species--many species of Helix, especially H. nemoralis and H. rotundata, Cyclostoma elegans, Limnaea palustris, Pupa, Clausilia, Cyclas, and others.

Between Atherfield and Chale at the top of the cliff is a large area of Blown Sand. The sand is blown up from the face of the cliff below. It reaches a thickness of 20 feet, and possibly more in places, and forms a line of sand dunes along the edge of the cliff. The upper part of Ladder Chine shows an interesting example of wind-erosion. The sand driven round it by the wind has worn it into a semi-circular hollow like a Roman theatre.

Small spits, consisting partly of blown sand, extend opposite the mouths of the Western Yar, the Newtown river, and the most extensive--at the mouth of the old Brading Harbour, separating the present reduced Bembridge Harbour from the sea. This is called St. Helen's Spit, or "Dover,"--the local name for these sand spits.

THE COMING OF MAN.

We have watched the long succession of varied life on the earth recorded in the rocks, and now we come to the most momentous event of all in the history--the coming of Man. The first certain evidence of the presence of man on the earth is found with the coming of the Glacial Period,--unless indeed the supposed flint implements found by Mr. Reid Moir, under the Crag in Suffolk, should prove him earlier still. It is a rare chance that the skeleton of a land animal is preserved; especially rare in the case of a skeleton so frail as that of man. The best chance for the preservation of bones is in deposits in caves, which were frequently the dens of wild beasts and the shelters of man. But the implements used by early man were happily of a very imperishable nature. His favourite material, if he could get it, was flint. Flint could by dexterous blows have flake after flake taken off, till it formed a tool or weapon with sharp point and cutting edge. The implements, though only chipped, or flaked, were often admirably made. They have very characteristic shapes. Moreover, the kind of blow--struck obliquely--by which these early men made their tools left marks which stamp them as of human workmanship. The flake struck off shows what is called a "bulb of percussion"--a swelling which marks the spot where the blow was struck--and from this extends a series of ripples, producing a surface like that of a shell, from which this mode of breaking is called conchoidal fracture. Often, by further chipping the flake itself is worked into an implement. Implements have also been made of chert, but it is far more difficult to work, as it naturally breaks in an irregular way into sharp angular fragments. Flint, on the other hand, lent itself admirably to the use of early man, who in time acquired a perfect mastery of the material. The working of flints is so characteristic that, once accustomed to them, you cannot mistake a good specimen. Sea waves dashing pebbles about will sometimes produce a conchoidal fracture, but never a series of fractures in the methodical way in which a flint was worked by man. And, of course, specimens may be found so worn that it is difficult to be sure about their nature. Again early man may, especially in very early times, have been content to use a sharp stone almost as he found it, with only the slightest amount of knocking it into shape. So that in such a case it will be very difficult to decide whether the stones have formed the implements of man or not. In later times men learnt to polish their implements, and made polished stone axes like those the New Zealanders and South Sea Islanders used to make in modern times. The old age of chipped or flaked implements is called the Palaeolithic; the later age when they were ground or polished the Neolithic. The history of early man is a long story in itself, and of intense interest. But we must not leave our geological story unfinished by leaving out the culmination of it all in man. In the higher gravels--the Plateau Gravels--no remains of man are found; but in the lower--the Valley Gravels,--of the South of England is found abundant evidence of the presence of man. Large numbers of flint implements have been collected from the Thames valley and over the whole area of the rivers which have gravel terraces along their course. Over a large sheet of gravel at Southampton, whenever a large gravel pit is dug, implements are found at the base of the gravel. The occurrence of the mammoth and other arctic creatures in the gravels shows that in the Glacial Period man was contemporary with these animals. Remains in caves tell the same story. In limestone caverns in Devon, Derbyshire, and Yorkshire, implements made by man are found in company with remains of the cave bear, cave hyaena, lion, hippopotamus, rhinoceros, and other animals either extinct or no longer inhabitants of this country--remains which have been preserved under floors of stalagmite deposited in the caves. In caves of central France men have left carvings on bone and ivory, representing the wild animals of that day--carvings which show a remarkable artistic sense, and a keen observation of animal life. Among them is a drawing of the mammoth on a piece of mammoth ivory, showing admirably the appearance of the animal, with his long hair, as he has been found preserved in ice to the present day near the mouths of Siberian rivers. Drawings of the reindeer, true to life, are frequent.

Till recently very few Palaeolithic implements had been recorded as found in the Isle of Wight. In the Memoir of the Geological Survey only one such is recorded, found in a patch of brick earth near Howgate Farm, Bembridge. A few more implements, which almost certainly came from this brick-earth, have been found on the shore since. In recent years a large number of Palaeolithic implements have been found at Priory Bay near St. Helen's. They were first observed on the beach by Prof. E. B. Poulton, F.R.S., in 1886, and were traced to their source in the gravel in the cliff by Miss Moseley in 1902. From that time, and especially from 1904 onwards, many have been found by Prof. Poulton, by R. W. Poulton . Up to 1909 about 150 implements had been found, and there have been more finds since.

The most important finds, besides those at Priory Bay, have been those of Mr. S. Hazzledine Warren at Freshwater, especially in trial borings in loam and clay below the surface soil in a depression of the High Downs, south of Headon Hill, at a level of about 360 ft. O.D., in which a number of Palaeolithic tools, flakes, and cores were found. Isolated implements have been found in recent years in various localities in the Island. There are references to finds of implements at different times in the past, but the descriptions are generally too vague to conclude certainly to what date they belong. Much of the gravel used in the Island comes from the angular gravel on St. Boniface Down, or the high Plateau Gravel of St. George's Down; but in the lower gravels and associated brick earth, it is highly probable that more remains of Palaeolithic man will yet be found in the Island, and quite possible that such have been found in the past, but for want of accurate descriptions of the circumstances of the finds are lost to us.

When Neolithic man appeared the land stood higher than at present, though not so high as during great part of the Pleistocene. Britain was divided from the Continent, but the shores were a good way out into what is now sea round the coasts, and forests clothed these further shores. Remains of these, known as submerged forest, are found below the tide mark round many parts of our coast. Peat as at Southampton Docks, is found under the estuarine mud off Netley. The wells at the Spithead Forts show an old land surface with peat more than 50 feet below the tide level. The old bed of the Solent river lies much lower still--124 feet below high tide at Noman's Land Fort; this channel was probably an estuary after the subsidence of the land till it silted up with marine deposits to the level on which the submerged forest grew.

The remains of Neolithic man are not only found in submerged forests, but over the present surface of the land, or buried in recent deposits. He has left us the tombs of his chiefs, known as long barrows--great mounds of earth covering a row of chambers made of flat stones, such as the mounds of New Grange in Ireland, and the cromlechs or dolmens still standing in Wales and Cornwall. These consist of a large flat or curved stone--it may be 14 feet in length,--supported on three or four others. Originally a great mound of earth or stones was piled on top. These have generally been removed since by the hand of later man. The stones have been taken for road metal, the earth to lay on the land. The great cromlech at Lanyon in Cornwall was uncovered by a farmer, who had removed 100 cart loads of earth to lay on his stony land before he had any idea that it was not a natural mound. Then he came on the great cromlech underneath. Another form of monument was the great standing stone or menhir, one of which, the Longstone on the Down above Mottistone still stands to mark the tomb of some chieftain of, it may be, 4,000 years ago.

The implements of Neolithic man are found all over England, the smooth polished axe head, commonly called a celt , the chipped arrow head, the flaked flint worked by secondary chipping on the edge into a knife, or a scraper for skins; and much more common than the implement, even of the simplest description, are the waste flakes struck off in the making. Very few stone celts have been found in the Isle of Wight. The flakes are extremely numerous, and a scraper or knife may often be found. They are turned up by the plough on the surface of the fields, in the earth of which they have been preserved from rubbing and weathering. They have however, acquired a remarkable polish, or "patina"--how is not clearly explained--which distinguishes their surface from the waxy appearance of newly-broken flint. In places the ground is so covered with flakes that we can have no doubt that these are the sites of settlements. The implements were made from the black flints fresh out of the chalk, and we can locate the Neolithic flint workings. In our northern range of downs where the strata are vertical the layers of flint in the Upper Chalk run out on the top of the downs, only covered with a thin surface soil. In places where this soil has been removed--as in digging a quarry--the chalk is seen to be covered with flakes similar to those found on the lower ground, save that they are weathered white from lying exposed on the hard chalk, instead of on soft soil into which they would gradually sink by the burrowing of worms. It is probable that these flakes would be found more or less along the range of downs under the surface soil.

In places on the Undercliff have been found what are known as Kitchen Middens--heaps of shells which have accumulated near the huts of tribes of coast dwellers, who lived on shellfish. One such was formerly exposed in the stream below the old church at Bonchurch, and is believed to extend below the foundations of the Church.

After a long duration of neolithic times a great step in civilisation took place with the introduction of bronze. Bronze implements were introduced into this country probably some time about B.C. 1800-1500; and bronze continued to be the best material of manufacture till the introduction of iron some two or three centuries before the visit of Julius Caesar to these Islands. To the early bronze age belong the graves of ancient chieftains known as round barrows, of which many are to be seen on the Island downs. Funeral urns and other remains have been found in these, some of which are now in the museum at Carisbrooke Castle. Belonging to later times are the remains of the Roman villa at Brading and smaller remains of villas in other places; and cemeteries of Anglo-Saxon date, rich in weapons and ornaments, which have been excavated on Chessil and Bowcombe Downs. But the study of the remains of ancient man forms a science in itself--Archaeology. In studying the periods of Palaeolithic and Neolithic man we have stood on the borderland where Geology and Archaeology meet. We have seen that vast geological changes have taken place since man appeared on earth. We must remember that the geological record is still in process of being written. It is not the record of a time sundered from the present day, but continuous with our own times; and it is by the study of processes still in operation that we are able to read the story of the past.

THE SCENERY OF THE ISLAND--Conclusion.

After studying the various geological formations that enter into the composition of the Isle of Wight, and learning how the Island was made, it will be interesting to take a general view of the scenery, and see how its varied character is due to the nature of its geology. It would hardly be possible to find anywhere an area so small as this little Island with such a variety of geological formations. The result is a remarkable variety in the scenery.

The main feature of the Island is the range of chalk downs running east and west, and terminating in the bold cliffs of white chalk at Freshwater and the Culvers. Here we have vertical cliffs of great height, their white softened to grey by weathering and the soft haze through which they are often seen. In striking contrast of colour are the Red Cliff of Lower Greensand adjoining the Culvers, and the many-coloured sands of Alum Bay joining on to the chalk of Freshwater. The summits of the chalk downs have a characteristic softly rounded form, and the chalk is covered with close short herbage suited to the sheep which frequently dot the green surface. Where sheets of flint gravel cap the downs, as on St. Boniface, they are covered by furze and heather, producing a charming variation from the smooth turf where the surface is chalk. The Lower Greensand forms most of the undulating country between the two ranges of downs; while the Upper Greensand, though occupying a smaller area, produces one of the most conspicuous features of the scenery--the walls of escarpment that form the inland cliffs between Shanklin and Wroxall, Gat Cliff above Appuldurcombe, the fine wall of Gore Cliff above Rocken End, and the line of cliffs above the Undercliff. To the Gault Clay is due the formation of the Undercliff--the terrace of tumbled strata running for miles well above the sea, but sheltered by an upper cliff on the north, and in parts overgrown with picturesque woods. The impervious Gault clay throws out springs around the downs, which form the headwaters of the various Island streams. The upper division of the Lower Greensand, the Sandrock, forms picturesque undulating foothills, often wooded, as at Apsecastle, and at Appuldurcombe and Godshill Park. On a spur of the Sandrock stands Godshill Church, a landmark visible for miles around. At Atherfield we have a fine line of cliffs of Lower Greensand, while the Wealden Strata on to Brook form lower and softer cliffs.

To the north of the central downs the Tertiary sands and clays, often covered by Plateau gravel, form an extended slope towards the Solent shore, much of it well wooded, and presenting a charming landscape seen from the tops of the downs. This slope of Tertiary strata is deeply cut into by streams, which form ravines and picturesque creeks, as Wootton Creek, 200 feet below the level of the surrounding country. While much of the Island coast is a line of vertical cliff, the northern shores are of gentler aspect, wooded slopes reaching to the water's edge, or meadow land sloping gradually to the sea level. Opposite the mouths of streams are banks of shingle and sand dunes, forming the spits locally known as "dovers." Some of these, in particular, St. Helen's Spit, afford interesting hunting grounds for the botanist.

The great variety of soil and situation renders the Isle of Wight a place of interest to the botanist. We have the plants of chalk downs, of the sea cliff and shore, of the woods and meadows, of lane and hedgerow, and of the marshes. The old villages of the Island, often occupying very picturesque situations--as Godshill on a spur of the southern downs, Newchurch on a bluff overlooking the Yar valley, Shorwell nestling among trees in a south-looking hollow of the downs, Brighstone with its old church cottages and farmhouses among trees and meadows between down and sea--the old and interesting churches, the thatched cottages, the old manor houses of Elizabethan or Jacobean date, now mostly farm houses, for which the Island is famous, add to the varied natural beauty.

The cause of these chines seems to be the same in all cases. It may be noticed that Shanklin and Luccombe chines are cut in the floors of open combes,--wide valleys with gently sloping floors; and at each side of these chines is to be seen the gravel spread over the floor of the old valley. It can scarcely be doubted that these combes are the heads of the valleys of the old streams, which flowed down a gradual slope till they joined the old branch of the Yar, flowing over land extending far over what is now Sandown Bay. When the sea encroached, and cut into the course of this old river, and on till it made a section of what had been the left slope of the valley, the old tributaries of the Yar now fell over a line of cliff into the sea. They thus gained new erosive power, and cut back at a much greater rate new and deeper channels; with the result that narrow trenches were cut in the floors of the old gently sloping valleys. The chines on the S.W. coast are to be explained in a similar way. They have been cut back with vertical sides, because the encroachment of the sea caused the streams to flow over cliffs, and so gave then power to cut back ravines at so fast a rate that the weathering down of the sides could not keep pace with it. The remarkable wind-erosion of these bare south-westerly cliffs by a sort of sand-blast driven before the gales to which that stretch of coast is exposed has already been referred to.

A few words in conclusion to the reader. I have tried to show you something of the interest and wonder of the story written in the rocks. We have seen something of the world's making, and of the many and varied forms of life which have succeeded each other on its surface. We have had a glimpse of great and deep problems suggested, which are gradually receiving an answer. Geology has the advantage that it can be studied by all who take walks in the country, and especially by those who visit any part of the sea coast, without the need of elaborate and costly scientific instruments and apparatus. Any country walk will suggest problems for solution. I have tried to lead you to observe nature accurately, to think for yourselves, to draw your own conclusions. I have shown you how to try to solve the questions of geology by looking around you at what is taking place to-day, and by applying this knowledge to explain the records which have reached us of what has happened in the past. You are not asked to accept the facts of the geological story on the word of the writer, or on the authority of others, but to think for yourselves, to learn to weigh evidence, to seek only to find out the truth, whether it be geology you are studying or any other subject, and to follow the truth whithersoever it leads.

TABLE OF STRATA

Recent. Peat and River Alluvium.

Pleistocene. Plateau Gravels: Valley Gravels and Brick-Earth.

Absent from the Isle of Wight.

Barton Sand. Barton Clay. { { { Eocene { Bracklesham Beds. { { Bagshot Sands { { London Clay { { Plastic Clay

{ { White { Upper Chalk { { Chalk { Middle Chalk { { { { { A. plenus Marls { Upper { Lower { Grey Chalk { Cretaceous { Chalk { Chalk Marl { { { Chloritic Marl { { { { { Upper { Chert Beds { { Selbornian { Greensand { Sandstone and { { { Rag Beds Mesozoic { { Gault or { Secondary{ { Carstone { { Lower { Sandrock and Clays { { Greensand { Ferruginious Sands { { { Atherfield Clay { Lower { { Perna Bed { Cretaceous { { { { Shales { { Wealden { Variegated Marls

FOR FURTHER STUDY.

Norman's "Guide to the Geology of the Isle of Wight," 1887, still to be obtained of Booksellers in the Island. Gives details of strata, and lists of fossils, with pencil drawings of fossils.

Other books bearing on the subject have been mentioned in the text and foot-notes.

An excellent geological map of the Island, printed in colour, scale 1 in. to the mile, full of geological information, is published by the Survey at 3s.

A good collection of fossils and specimens of rocks from the various strata of the Isle of Wight has recently been arranged at the Sandown Free Library, and should be visited by all interested in the Geology of the Island. It should prove a most valuable aid to all who take up the study, and a great assistance in identifying any specimens they may themselves find.

GEOLOGICAL MAP OF THE ISLE OF WIGHT

INDEX

Words in Italics refer to a page where the meaning of a term is given.

Agates, 22, 41, 50

Alum Bay, 56-62

Ammonites, 32, 34, 39, 44

Astronomical Theory of Ice Age, 83, 85

Atherfeld, 29

Avon River, 94

Barrows, 102, 104

Barton, 61

Belemnites, 33

Bembridge Limestone, 65 -- shingle at, 95

Benettites, 27

"Blue Slipper," 15

Bonchurch, 50, 103

Bos primigenius, 101, 102

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