The geographical distribution of animals, with a study of the relations ...

chap. VII.] MAMMALIA OF THE NEW WORLD. 131inhabited North America at a comparatively recent epoch, ismost remarkable. In Europe, we found a striking changein the fauna at the same period; but that consisted almostwholly in the presence of animals now inhabiting countriesimmediately to the north or south. Here we have the appearanceof two new assemblages of animals, the one now confinedto the Old World—horses, camels, and elephants ; theother exclusively of South American type—Hamas, tapirs,capybaras, Galera, and gigantic Edentata. The age of thevarious deposits in which these remains are found is somewhatuncertain, and probably extends over a considerable period oftime, inclusive of the Glacial epoch, and perhaps both anteriorand subsequent to it. We have here, as in Europe, the presenceand apparent co-existence in the same area, of Arctic andSouthern forms—the walrus and the manatee— the musksheepand the gigantic sloths. Unfortunately, as we shall see,the immediately preceding Pliocene depositsof North Americaare rather poor in organic remains ;yet it can hardly be owingto the imperfection of the record of this period,the South American types above numerated occursthat not one ofthere, whilea considerable number of Old World forms are represented.Neither in the preceding wonderfully rich Miocene or Eoceneperiods, does any one of these forms occur ;or, with the exceptionof Morotherium, from Pliocene deposits west of the RockyMountains, any apparent ancestor of them ! Wehave hereunmistakable evidence of an extensive immigration from Southinto North America, not very long before the beginning of theGlacial epoch. It was an immigration of types altogether newto the country, which spread over all the southern and centralportions of it, and established themselves sufficiently to leaveabundance of remains in the few detached localities where theyhave been discovered. How such large yet defenceless animalsas tapirs and great terrestrial sloths, could have made their wayinto a country abounding in large felines equal in size anddestructiveness to the lion and the tiger, with numerous wolvesand bears of the largest size, is a great mystery. But it isnevertheless certain that they did so ;and the fact that no such