so well known, thus describes the relation of contemporary mammalia to glacial phenomena:—
"As the climate in Europe changed, the Pleiocene species yielded place to those which were better adapted to the new conditions, either retreating southwards or becoming extinct. The first division of the Asiatic invaders is composed of the animals forming the temperate group above mentioned; they are found in the early Pleistocene strata, in Britain and in France, side by side with the survivals from the Pleiocene Age. No arctic mammalia had as yet arrived. The next stage in the migration is that in which the temperate group of animals had for the most part replaced the Pleiocene survivals, in Britain and in France, and the arctic mammalia began to appear, but only in small numbers. This constitutes the middle Pleistocene division. The third stage in the migration is indicated by the presence in full force of the arctic species in the area north of the Alps and Pyrenees. They are not, however, met with south of this boundary, and therefore this classification does not apply to the deposits of Spain, or the other portions of the Southern Zone." (Early Man, p. 122.)
In his recent Huxley Memorial Lecture (Journ. Anth. Inst., vol. xl.) the same author has categorically tabulated the successive migrations of the Pleistocene mammalia into Britain, and the fate of extinction which has befallen many of them.
The entire series of phenomena incidental to the varying phases of the glacial epoch are so complicated that it is difficult to realise the exact conditions which led to the intermingling of such different animals as are included in the lists of northern and southern faunas. On the supposition that the Ice Age was one climatic interlude, presenting a gradual extension of local glaciers until they culminated in a mer de glace, with of course a corresponding period for their retreat, as advocated by de Mortillet, the association of these different animals in Central Europe would be more readily understood. The following explanation of the problem from the standpoint of those who maintain that the Pleistocene comprised a series of successive ice ages, with warm interglacial periods, comes from the pen of Professor James Geikie:—
