If this list[237] of animals from the caves be compared with that of the river-deposits of Britain and the continent, it will be seen that the same fauna is present in both, and that they are therefore of the same geological age.[238] This was the conclusion to which Dr. Falconer was led by the examination of the caves of Gower, and it has been confirmed by every subsequent discovery.
The Pleistocene Coast-line of North-Western Europe.
The identity of the British pleistocene fauna with that of the continent, leads to the conclusion that in the pleistocene age Britain was connected with the adjacent countries by a bridge of land, over which the wild animals had free means of migration. And this might be brought about by a comparatively small elevation of the area. The soundings show that Britain and Ireland constitute merely the uplands of a plateau now submerged to the extent of about 100 fathoms, on the side of the Atlantic. On the east it extends at a depth of from twenty to fifty fathoms, in the direction of Belgium; and on the south it is only sunk from twenty to forty fathoms below the sea-level. Immediately to the westward of this line the sea deepens so suddenly, that there is scarcely any difference between the lines of 100 and of 200 fathoms, and the depth rapidly increases to 2,000. Were this plateau elevated above the sea to an extent of 100 fathoms, the tract shaded in the map ([Fig. 126]) would unite the British Isles to the continent, and the Thames and other rivers on the eastern coast would unite with the Elbe and the Rhine to form a river debouching on the North Sea, somewhat after the manner which I have represented by taking the deepest line of soundings. The Straits of Dover would then be the watershed between this valley of the German Ocean, as it may be termed, and that of the English Channel, in which the Seine and the Somme and other French rivers joined those of the south coast, and ultimately reached the Atlantic. Evidence that the latter river flowed in the course assigned to it in the map is afforded by the discovery of the fresh-water mussel (Unio pictorum), recorded by Mr. Godwin Austen[239] to have been dredged up by Captain White from a depth of from 50 to 100 fathoms, not very far from what I have taken to be its mouth. We are also indebted to Mr. Godwin Austen for the discovery near this spot of banks of shingle and littoral shells, which indicate the position of the ancient coast-line.
Fig. 126.—Physiography of Great Britain in Late Pleistocene Age.
Shaded area = land now submerged; dotted area = region occupied by animals;
plain area = region occupied by glaciers.
The view that the 100-fathom line marks the limit of the pleistocene land surface to the west, is held by Sir H. de la Bêche, Mr. Godwin Austen, Sir Charles Lyell, and other eminent geologists, and it is supported by many facts that can be explained in no other manner. To pass over the discovery of a fresh-water shell at the bottom of the English Channel, quoted above, the distribution of fossil mammalia at the bottom of the German Ocean (represented in [Fig. 126] by the dotted area) is analogous to that which we find in the river gravels and brick-earths on the land. The quantity of teeth and bones belonging to the mammoth, woolly rhinoceros, horse, reindeer, and spotted hyæna, and other animals, dredged up by the fishermen in the German Ocean is almost incredible. Mr. Owles, of Yarmouth, informed me in 1868 that off that place there is a bank on which the fishing nets are rarely cast without bringing up fossil remains. It seems most probable, that these accumulations have been formed under subaerial conditions near the drinking places, or below the fords, which were used for ages by the pleistocene animals. I might quote as an example of a similar deposit of fossils on the land, that discovered in 1866 by Captain Luard, R.E., in digging the foundations of the new cavalry barracks at Windsor, which consisted mainly of bones and antlers of reindeer, with a few carnivores, such as the brown bear and wolf, that usually follow reindeer in their migrations in Siberia.[240] Were this submerged it would be a case precisely similar to that off Yarmouth.
The ancient forest, exposed at low water under the cliffs on the Norfolk and Suffolk shores, flourished when the land stood higher than it does now. Traces of a similar forest, also at, and below, low-water mark, have been met with on the shore at Selsea, near Chichester, in Sussex; and remains of the mammoth have been dredged up in several places off the coast, as for example in Torbay and in Holyhead harbour, or found in gravel beds near low-water mark, as in the Isle of Wight, and on the north coast of Somerset at St. Audries, near Watchet, where a skull with gigantic tusks rested in the gravel. In all these facts we have ample proof that Britain stood at a higher level in the pleistocene age than at the present day.
The vast abundance also of the mammalia in the caves of South Wales and Somerset, and their presence in the Island of Caldy, and it may be added in Ireland, can only be accounted for by the elevation of the present sea-bottom, so as to allow of their migration over plains covered with abundant pasture. It seems, therefore, to me that the accompanying map, [Fig. 126], represents with tolerable accuracy the ancient coast-line of Britain, and of the adjacent parts of the continent in the pleistocene age. The fertile valleys of the English Channel, Bristol Channel, and the German Ocean, would afford sustenance to a large and varied fauna, and numerous herbivores, such as the reindeer, bison, and horse, would supply food to the palæolithic hunters, who followed them in their annual migrations. And it must be remarked on this hypothesis, that the valley of the Garonne would offer a free passage both to the animals and to the hunters of Auvergne down to the prairie, extending as far as the 100-fathom line off the French coast, and that the hunting grounds would reach to Devonshire and Somerset without any barrier except that offered by the rivers. It is therefore no wonder that the implements in the caves of Kent’s Hole, Wookey Hole, and the South of France, should be of the same type.