PALEONTOLOGY SINCE CUVIER. 69 



' The whole surface of the earth of the Old World 

 during the Tertiary, as far as is known, formed one 

 single natural domain for the mammal fauna ; it 

 was more extensive, but the same as that which had 

 previously sustained the animal world of the Eocene 

 formation.' From here the primeval Mammalia 

 proceeded not only southward into Africa, but had 

 also, as it seems, found their way into the New World 

 by an isthmus of land connecting Europe with 

 North America ; partly also as is shown by the 

 fossil elephants of Japan from Northern Asia in 

 the direction of the Aleutian Islands. The fauna of 

 North America, the principal portion of which, to 

 all appearances, was not indigenous to the country, 

 then wandered southwards, following the course of 

 the principal mountain ranges, where they met 

 members of a foreign fauna coming northwards 

 from the south, and which in the more recent 

 periods even crossed the isthmus. At all events, 

 the Mammalian fauna of North America appeared 

 as inferior and dependent upon that of the East, 

 and immigration from the New to the Old World 

 seems a doubtful matter and even a question of 

 secondary importance. As Eiitimeyer goes on to 

 say: ' The Miocene fauna of Nebraska is the offspring 



of the Eocene formation of the Old World. The 



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