CHAP. VII.] 
THE GLACIAL EPOCH. 
119 
glacial epoch when it was continually increasing in severity 
hardly a trace has been preserved, because each succeeding ex- 
tension of the ice being greater and thicker than the last, de- 
stroyed what had gone before it till the maximum was reached. 
Migrations and Extinction of Organisms caused by the Glacial 
Epoch . — Our last glacial epoch was accompanied by at least two 
considerable submergences and elevations of the land, and there 
is some reason to think, as we have already explained, that 
the two classes of phenomena are connected as cause and effect. 
We can easily see how such repeated submergences and eleva- 
tions would increase and aggravate the migrations and extinc- 
tions that a glacial epoch is calculated to produce. We can 
therefore hardly fail to be right in attributing the wonderful 
changes in animal and vegetable life that have occurred in 
Europe and N. America between the Miocene Period and the 
present day, in part at least, to the two or more cold epochs 
that have probably intervened. These changes consist, first, in 
the extinction of a whole host of the higher animal forms, and 
secondly, in a complete change of types due to extinction and 
emigration, leading to a much greater difference between the 
vegetable and animal forms of the eastern and western hemis- 
phere than before existed. Many large and powerful mammalia 
lived in ourown country in Pliocene times and apparently survived 
a part of the glacial epoch ; but when it finally passed away 
they too had disappeared, some having become altogether 
extinct while others continued to exist in more southern lands. 
Among the first class are the sabre-toothed tiger, the extinct 
Siberian camel (Merycotherium), three species of elephant, two 
of rhinoceros, a hippopotamus, two bears, five species of deer, and 
the gigantic beaver ; among the latter are the hyaena, bear, and 
lion, which are considered to be only varieties of those which 
once inhabited Britain. Down to Pliocene times the flora of 
Europe was very similar to that which now prevails in Eastern 
Asia and Eastern North America. Hundreds of species of 
trees and shrubs of peculiar genera which still flourish in those 
countries are now completely wanting in Europe, and we have 
good reason to believe that these were exterminated during the 
glacial period, being cut off from a southern migration, first by 
