Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/407

394 is impossible to determine, but judging from the effect of the sea in destroying the portions which remain, we may suppose that it was rapidly effected in some places, and at certain times.

That the climatal conditions of the area thus converted from sea into land, were not suddenly but gradually altered, is shown by fair evidence. In the beautiful volume on the history of our Fossil Mammalia and Birds, by Professor Owen, we have an immense mass of invaluable information on the distribution "of our ancient land-animals brought together. If we select from this treasury of palæontological knowledge the portions which concern the area and epoch under discussion, and lay down on our map the ranges of those of our quadrupeds which distinctly inhabited Britain after the Glacial epoch,—and in this category I would include most of the cave-animals,—we shall see distinct indications of climatal conditions prevailing over a great portion of that area very different from those now existing. The position of the remains of the Cervus megaceros in basins of freshwater marls, containing existing testacea, resting in depressions of the upheaved glacial sea-bed (as in Ireland and the Isle of Man), gives a clue to the prevailing condition during the earliest post-glacial times. We cannot suppose that the limited tract of drift forming the northern extremity of the Isle of Man, in which there are numerous freshwater basins, containing entire skeletons of the Megaceros, was other than portion of a larger region inhabited by that remarkable deer. Now these basins are distinctly, both in the Isle of Man and Ireland, overlaid by the peat, with its ancient included forests.

[Diagram showing the relations of the freshwater marls (b) to the glacial marine beds (a), and overlying peat with included forests (c), in the Isle of Man (d), represents the old slates.]

The epoch of the Megaceros was anterior to the epoch of the Forests which aided in the formation of the great peat bogs, so frequently resting on the northern drift. This, too, was probably the time when the reindeer ranged in our country nearly to the 52° parallel. Also the beaver and the Bos primigenius, both of which survived their companions, and lived on for a time during the succeeding age of great forests. The Bos longifrons, the Cervus elaphus, the Elaphus primigenius, the horse, the wolf, and probably the bear, ranged over a great part of the British area during the intermediate time, and had become generally distributed before the breaking-up of the great central plain, occupying the position of the existing Irish Sea. When the land became covered