TERTIARY. 427 



thus intermediate in character between the Pliocene and the 

 Pleistocene ; and a similar mingling of forms has been observed 

 in certain local deposits both in France and Italy. 



Pleistocene. 



The Pleistocene mammalian fauna of Europe is very remark- 

 able. It does not include many forms which have subsequently 

 become extinct ; but throughout the central and north-central 

 parts of the continent there is a curious mingling of northern, 

 eastern, and southern types which it seems difficult to explain. 

 The remains of this fauna are met with in the surface deposits 

 and caverns of Britain, so far north as Yorkshire, quite as 

 abundantly as on the continent ; so that the bed of the North 

 Sea and the Straits of Dover must still have been an open 

 valley, and our island remained part of the mainland. The 

 northern animals include the reindeer and musk-ox, which 

 wandered as far south as the Pyrenees; the typically eastern 

 animals comprise the saiga antelope, the jerboa, the tailless 

 hare, and Myogale moschata ; while among the numerous 

 southern types may be mentioned the lion, leopard, hya?na, 

 and hippopotamus. The principal forms which have since 

 become extinct are Machcerodus latidens, Ursits spelceus, Cervus 

 giganteus, Trogontherium cuvieri, Elephas primigenius, E. 

 antiqiius, Rhinoceros antiquitatis, and the great remarkable 

 Russian rhinoceros, Elasmotherium, sibiricum. Of these latter, 

 the so-called Irish deer (Cervus giganteus) is the only one which 

 seems to have survived until the dawn of historic times. 



The Pleistocene deposits of North America yield much 

 fewer mammals than those of Europe ; but there is a similar 

 mingling of northern and southern types in the central region. 

 It is also interesting to note that one of the commonest skele- 

 tons represents the latest known species of Mastodon (M. ameri- 

 canus). The mammoth, musk-ox, reindeer, elk, and bison are 

 present ; bears have now arrived, and the lion may also perhaps 

 be represented; but Equus has already become extinct, and 

 there are no traces' of the woolly rhinoceros (R. antiquitatis), 

 the cave bear, or the hyaena. In the surface deposits of the 

 southern United States, some of the typically South American 



