PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 375 



by the same standards there is considerable, but not as yet conclusive, 

 evidence that both in Europe and North America the Quaternary exhibits 

 three faunal periods (I, II, III), the first of these subdividing into two, as 

 follows : 



Faunal Period I 



First fauna. Temperate fauna of Second fauna. Rich temperate 



late pre-glacial and early interglacial fauna of interglacial times. Intermin- 



times. Several sui'viving Pliocene types. gling of extinct and recent species. Large 



Species mostly now extinct. southern clement. 



Faunal Period II 



TJiird fauna. Entrance of an arctic or circumpolar fauna in the last glacial 

 stages. Arrival of new northern elements. Southern element greatly reduced. 

 Many existing species. 



Faunal Period III 



Fourth fauna. The prehistoric mammals. All existing species. A north 

 temperate fauna of modern forest and plains types. 



The secular climatic conditions in America were broadly contemporaneous 

 with those in Europe; it is thus natural to expect to discover a broad similarity 

 in the faunal succession, and it may be said that this expectation is realized. 

 Close similarity should not be anticipated, first because the animals at 

 the close of the Pliocene in the two countries contain many different ele- 

 ments (Europe including south-Asiatic and African, and America including 

 South American forms) ; second, because physiographic conditions in Amer- 

 ica were different. Below the southernmost ice limit of the United States 

 was a vast land area, whereas in Europe the Mediterranean closely bordered 

 the ice-clad regions on the south. 



There is little doubt that in both countries these four faunas broadly 

 correspond with the advance of Pleistocene or glacial time as follows : 



Fourth fauna, post-glacial and modern conditions. 



Third faima, maximum glacial, arctic conditions. 



Second fauna, mid-Pleistocene interglacial temperate conditions. 



First fauna, early Pleistocene temperate conditions. 



Time Divisions of the Quaternary 



The fluctuations of climate and of the animal and plant life of the 

 Pleistocene are so numerous, so widespread, and so profound that it seems 

 best to introduce the subject by a review of the great time divisions, together 

 with some discussion as to the period when we should consider that the 

 Quaternary proper begins. The reader will observe at once that these 

 time divisions are based on evidence of four kinds: 



