THE GLACIAL EPOCH 123 



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 migration, leading to a much greater 

 difference between the vegetable and animal forms of the 

 eastern and western hemisphere than before existed. 

 Many large and powerful mammalia lived in our own 

 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 ex- 

 tinct 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, two bears, five species of 

 deer, and the gigantic beaver ; among the latter are the 

 hyaena, bear, aud 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. The late Professor Asa Gray has pointed out 

 that hundreds of species of trees and shrubs of peculiar 

 genera which still flourish in those countries are now coqi- 

 pletely Avanting in Europe, and there is good reason to 

 believe that these were exterminated during the glacial 

 period, being cut off from a southern migration, first by 

 the Alps, and then by the Mediterranean ; whereas in 

 eastern America and Asia the mountain chains run in a 

 north and south direction, and there is nothing to prevent 

 the flora from having been preserved by a southward 

 migration into a milder region.^ 



Our next two chapters will be devoted to a discussion 

 of the causes which brought about the glacial epoch, and 

 that still more extraordinary climatic phenomenon — the 



^ This subject is admirably discussed in Professor Asa Gray's Lecture on 

 "Forest Geography and Archaeology" in the American Journal of Science 

 and Arts, Vol. XVI. 1878. 



