CHAP, VII.] MAMMALIA OF THE NEW WORLD. 131 
inhabited North America at a comparatively recent epoch, is 
most remarkable. In Europe, we found a striking change 
in the fauna at the same period; but 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, 
capybaras, Galera, 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 North 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 Miocene or Eocene 
periods, does any one of these forms ovcur ; or, with the exception 
of Morotherium, from Pliocene deposits west of the Rocky 
Mountains, any apparent ancestor of them! We have here 
unmistakable 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 
