CHAP. VII.] MAMMALIA OF THE NEW WORLD. 131 



iiiliabited North America at a comparatively recent epoch, is 

 most remarkable. In Europe, we found a striking change 

 in the fauna at the same period ; Ijut that consisted, almost 

 wholly in the presence of animals now inhabiting countries 

 immediately to the north or south. Here we have the appear- 

 ance of two new assemblages of animals, the one now con- 

 fined to the Old World — horses, camels, and elephants ; the 

 other exclusively of South American type — llamas, tapirs, 

 eapybaras, Galcra, and gigantic Edentata. The age of the 

 various deposits in which these remains are found is somewhat 

 uncertain, and probably extends over a considerable period of 

 time, inclusive of the Glacial epoch, and perhaps both anterior 

 and subsequent to it. We have here, as in Europe, the presence 

 and apparent co-existence in the same area, of Arctic and 

 Southern forms — the walrus and the manatee — the musk- 

 sheep and the gigantic sloths. Unfortunately, as we shall see, 

 the immediately preceding Pliocene deposits of ISTorth America 

 are rather poor in organic remains ; yet it can hardly be owing 

 to the imperfection of the record of this period, that not one of 

 the South American types above numerated occurs there, while 

 a considerable number of Old World forms are represented. 

 Neither in the preceding wonderfully rich ]\Iiocene or Eocene 

 periods, does any one of these forms occur ; or, with the exception 

 of Morothenum, from Pliocene deposits ivest of the Rocky 

 Mountains, any apparent ancestor of them ! We have here 

 unmistakaljle evidence of an extensive immigration from South 

 into North America, not very long before the beginning of the 

 Glacial epoch. It was an immigration of types altogether new 

 to the country, which spread over all the southern and central 

 portions of it, and established themselves sufficiently to leave 

 abundance of remains in the few detached localities where they 

 have been discovered. How such large yet defenceless animals 

 as tapirs and great terrestrial sloths, could have made their way 

 into a country abounding in large felines equal in size and 

 destructiveness to the lion and the tiger, with numerous wolves 

 and bears of the largest size, is a great mystery. But it is 

 nevertheless certain that they did so ; and the fact that no such 



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