DISTRIBUTION OF ANIMALS IN AMERICA. 243 



is confined to the extinction of many Pachydermata, a 

 displacement of the rhinoceros, elephant, tapir, and 

 hippopotamus, and an extremely abundant development 

 of the true ruminants and the cattle which proceeded 

 from them with an exaggerated form of head. Bears 

 and canine species occupy the territory where viverridae 

 and hyenas once predominated ; but as "numerous locally 

 and historically limited species, a large number among 

 the smaller fauna a majority of Miocene races remain in 

 possession of the ancient and probably constantly increas- 

 ing habitat." (R.) " In this gradual change of things, 

 no one will be able to discern aught but phenomena of 

 the same order of which we are still the witnesses." (R.) 

 How circumstances occurred in America has been 

 described in a masterly style by Riitimeyer as follows : 

 " America affords a basis for the distribution of animals 

 completely different from that of the Old World. 

 In the latter, ridges, open only in places, divide the 

 entire continent into mountainous zones, and corres- 

 pond to the distribution of temperature. Thus in a 

 twofold manner they prescribe a definite range east 

 and west to the extension of animals ; while a migra- 

 tion from north to south is impeded less by the height 

 of the mountains than that on their summit the north 

 comes into contact with the scorching south. Behind 

 this wall, moreover, in the expanse from the Caspian 

 Sea to China, there is a zone of steppes and deserts 

 which fences in the animals more effectually than the 

 mountain chains. In America, not beasts of prey alone, 

 but graminivora also, may advance without hindrance 

 from the regions of the lichen on the Mackenzie River, 

 through the pine forests of Lake Superior, to the land of 

 17 



