Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/357

344 migration of the Germanic types? And when we know that the Irish Sea is scooped out of the elevated bed of the sea of the glacial epoch, masses of which, of great extent and thickness, we find bounding its sides in England, the Isle of Man, and still more conspicuously in Ireland, and that on the great pleistocene plain lived the Cervus megaceros, can we doubt that over it the mass of Germanic types, forming the existing flora and fauna of Ireland migrated?—and that the migration of the species, less speedy of diffusion, which are now peculiar to England, was arrested by the breaking up of that land of passage—and thence the famous deficiencies of the Sister Isle, as for instance its freedom from reptiles, as, indeed, the excellent comparative Table of the Reptilia of Belgium, England, and Ireland, given by Mr. Thompson in his valuable Report on the Irish fauna, affords abundant proof.

On what did the difference (which is wholly numerical, and not specific) between the reptile population of Britain and Belgium, exhibited in this table, depend? On the same cause on which the difference between the flora and fauna of the east of England and Germany depends—on the breaking up of the upheaved bed of the Germanic Ocean of the glacial period, which possibly, indeed probably, was effected more slowly, and completed at a later time than the separation of Britain and Ireland.

But though the migration of animals and plants over the great Germanic plain will account for the major part of our British species which come from the west, we have in the mountain districts of Scotland, England, and Wales, a considerable flora, and a portion of our fauna, which cannot be traced to such a source, seeing that they are