260 THE WORLD OF LIFE 



and four genera of tlie wonderful terrestrial slotlis, ranged 

 over the whole country as far north as Oregon and the Great 

 Lakes in quite recent times; while four genera of the great 

 ground-sloths have been found as far north as Pennsylvania. 



This remarkable assemblage of large Mammalia at a period 

 so recent as to be coeval with that of man, is most extraor- 

 dinary; while that the whole series should have disappeared 

 before historical times is considered by most geologists to be 

 almost mysterious. At an earlier period, especially during 

 the Miocene (Middle Tertiary), Xorth America was also 

 wonderfully rich in Mammalia, including not only the ancestors 

 of existing types, but many now quite extinct. At this time 

 there were several kinds of monkevs allied to South American 

 forms; numerous extinct Carnivora, including the great sabre- 

 toothed tiger, Machserodus; several ancestral horses, includ- 

 ing the European Anchitherium ; several ancestral rhinoceroses, 

 the huge horned Brontotheriidae, the Oreodontidse, and many 

 ancestral swine. Almost all these became extinct at the end 

 of the Miocene age. "^ 



In Europe we find very similar phenomena. During the 

 Pleistocene age, the great Irish elk, the cave-lion and the 

 sabre-toothed tiger, cave-bears and hyaenas, rhinoceroses, 

 hippopotami and elephants, extinct species of deer, antelopes, 

 sheep and cattle, were abundant over a large part of Europe 

 (many even reaching our own country), and rapidly became 

 extinct; and what renders this more difficult to explain is, 

 that all of these and many others, with numerous ancestral 

 forms, had inhabited Europe throughout the Pliocene and 

 some even in Miocene times. 



These very interesting changes in the northern hemisphere 

 are paralleled and completed in far-distant Australia. In 

 caves and surface deposits of recent formation a whole series 

 of fossil remains have been found, all of the marsupial order, 

 and most of them of extinct species and even extinct genera. 

 But what is more extraordinarv is, that several of them were 

 larger than any now living, while some were as gigantic as 



