Parr V. Sect. i. § 1.) PLEISTOCENE. 891 
_ far as uncovered, was eventually clothed with vegetation. Hence the 
long glacial period must have been interrupted by episodes, probably 
of considerable duration, when a milder climate prevailed. Such an 
alternation of conditions is explained on the hypothesis discussed in 
previous pages (pp. 21-29). During these intervals the Arctic 
mammals—the hairy mammoth, rhinoceros, rein-deer, musk-sheep, 
Arctic fox, glutton, and lemming—peopled the lower grounds. The 
mammoth advanced at least as far south as the now extinct volcanoes 
_ of central Italy, which were then in full activity. The rein-deer 
migrated southwards into Switzerland, the glutton into Auvergne, 
while the musk sheep and Arctic fox travelled certainly as far as the 
Pyrenees. When the climate became less chilly and allowed the 
animals of a more southern type to advance into Europe, the regions 
from which the Arctic foxes now retreated were visited by the porcu- 
pine, leopard, African lynx, lion, striped and spotted hyznas, African 
elephant, and hippopotamus. 
Evidences of Submergence.—After the ice had attained 
its greatest development, some portions of north-western Europe 
which had perhaps stood at a higher level above the sea than they 
have done since, began to subside. The ice-fields were carried down 
below the sea-level, where they broke up and cumbered the sea with 
floating bergs. ‘he heaps of loose debris which had gathered under 
the ice, being now exposed to waves, ground-swell, and marine 
currents, were thereby more or less washed down and reassorted. 
Coast-ice, no doubt, still formed along the shores, and was broken 
up into moving floes, as happens every year now in northern Green- 
land. The proofs of this phase of the long glacial period are contained 
in the sands, gravels, erratic blocks, and stratified clays which overlie 
the coarse older till. It is difficult to determine the extent of the 
submergence, for when the land rose the more elevated portions 
continued to be the seats of glaciers, which, moving over the surface, 
‘destroyed the deposits that would otherwise have remained as 
witnesses of the presence of the sea, while at the same time the great 
bodies of water discharged from the retreating glaciers and snow- 
fields must have done much to reassort the detritus on the surface of 
the land. The most satisfactory evidence of submersion is un- 
doubtedly that supplied by beds of marine shells. From data of 
this kind we know that southern Scandinavia sank about 600 feet 
below its present level; while North Wales appears to have gone 
down at least 1350 feet. 
That ice continued to float about in these waters is shown by the 
striated stones contained in the fine ciays, and by the remarkably 
contorted structure which these clays occasionally display. Sections 
may be seen (as at Cromer) where, upon perfectly undisturbed 
1 Mere fragments of marine shells in a glacial deposit need not prove submergence 
under the sea; for they may have been pushed up from the sea-floor by moving ice, as 
in the ease of the shelly till of the west of Scotland, Caithness, Holderness, and Cromer, 
But beds of unbroken shells evidently assorted in water may be taken as good evidence 
of the former presence of the sea on their site. 
