150 DISTRIBUTION OF EXTINCT ANIMALS. [part n. 



time since these changes took place is, geologically, minute. 

 The time of the whole of the Post-Pliocene period, as measured 

 by the amount of physical and general organic change known to 

 have taken place, is exceedingly small when compared with the 

 duration of the Pliocene period, and still smaller, probably, as 

 compared with the Miocene. Yet during these two periods we 

 meet with no such break in the continuity of the forms of life, no 

 such radical change in the character of the fauna (though the 

 number of specific and generic changes may be as great) as we 

 find in passing from the Post-Pliocene to recent times. For 

 example, in Central Europe numerous hyaenas, rhinoceroses, and 

 antelopes, with the great Machairodus, continued from Miocene 

 all through Pliocene into Post-Pliocene times ; while hippo- 

 potami and elephants continued to live through a good part of 

 the Pliocene and Post-Pliocene periods, — and then all suddenly 

 became extinct or left the country. In North America there has 

 been more movement of the fauna in all the periods ; but we 

 have similar great felines, horses, mastodons, and elephants, in 

 the Pliocene and Post-Pliocene periods, while Rhinoceros is com- 

 mon to the Miocene and Pliocene, and camels range continuously 

 from Miocene, through Pliocene, to Post-Pliocene times ; — when 

 all alike became extinct. Even in South America the evidence is, 

 as far as it goes, all the same way. We find Machairodus, Equus, 

 Mastodon, Megatherium, Scelidothcrnim, Megalonyx, and numerous 

 gigantic armadillos, alike in the caves and in the stratified 

 tertiary deposits of the Pampas ; — yet all have since passed away. 

 It is clear, therefore, that we are now in an altogether 

 exceptional period of the earth's history. We live in a zoologi- 

 cally impoverished world, from which all the hugest, and fiercest, 

 and strangest forms have recently disappeared ; and it is, no 

 doubt, a much better world for us now they have gone. Yet it 

 is surely a marvellous fact, and one that has hardly been suffi- 

 ciently dwelt upon, this sudden dying out of so many large 

 mammalia, not in one place only but over half the land surface 

 of the globe. We cannot but believe that there must have been 

 some physical cause for this great change ; and it must have 

 been a cause capable of acting almost simultaneously over large 



