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 hy 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 s€e 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 hyoena, 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 thoso 

 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 



