15. Relation of the Pleistocene Mammalia to the Glacial Period.
The relation of the Pleistocene mammalia to the Glacial age, or the age of maximum cold, must now be considered. Did they invade Northern and Central Europe during the first or the second Glacial period, before or after the marine submergence indicated by the "middle drift"? We might expect, à priori, that as the temperature became lowered, the northern mammalia would gradually invade the region occupied before by the Pliocene forms; and such a mingling of Pleistocene and Pliocene animals we find in the pre- glacial forest-bed. Traces of such an occupation would necessarily be very rare, since they would be exposed to the grinding action both of the advancing glacial sheet, and, subsequently, to that of the waves on the littoral zone during the depression and reelevation of the land. At the time also that the greater part of Great Britain was buried under an ice-sheet they could not have occupied that region, although they may have been, and most probably were, living in the districts further to the south, which were not covered with ice. The labours, however, of Dr. Bryce and others have proved that one at least of the characteristic Pleistocene mammalia, the mammoth, as well as the reindeer, lived in Scotldan before the deposit of the Lower Boulder-clay; while Mr. Jamieson has pointed out that these animals could not have occupied that area at the same time as the ice, and therefore must be referred to a still earlier date. Dr. Falconer has shown that the mammoth occurs in the Forest-bed; and his conclusion, which seemed to be doubtful, has been verified by fresh discoveries. The teeth and bones discovered in the ancient land-surface at Selsea also very probably indicate that the mammoth lived in Sussex before the glacial submergence, although they were never admitted by Dr. Falconer to be of the same age as the remains of Elephas antiquus from the same Preglacial horizon. On a careful reexamination of the whole evidence, I am compelled to believe with Mr. Godwin-Austen and Mr. Prestwich that the à priori argument that Pleistocene mammalia occupied Great Britain before the Glacial period is fully borne out by the few incontestable proofs that have been brought forward of the remains having been found in Preglacial deposits. And the scanty evidence on the point is just what might be expected from the rare accidents under which the bones in superficial deposits could have escaped the grinding of the ice-sheet, and the subsequent erosive action of the waves on the coast-line. The arrival of the northern and temperate Pleistocene mammalia in Britain in Preglacial times implies that they were living on the Continent before the low glacial temperature had set in. On the other hand the evidence is conclusive that they lived in Britain and on the Continent after the intense glacial cold had passed away, since their remains are found in deposits which rest on Boulder-clays. At Schussenried, for example, the reindeer, glutton, bear, and other animals were found by Prof. Fraas in a deposit which rested on the surface of the terminal moraine of the glacier of the
