CORRELATION OF THE CENOZOIC 211 



the researches of Scott and Matthew. Here we enter the fifth faunal 

 phase, marked by fresh migrations and the first undoubted appear- 

 ance of the proboscideans and short-limbed rhinoceroses in America, 

 both arrivals from the Old World. Physiographic changes are 

 indicated in evidence of increasing summer droughts, numerical 

 increase of animals adapted to plains-living and the semi-arid con- 

 ditions, in the disappearance of most of the browsing types. The 

 correlation is, however, by no means close at present, because the life 

 of Europe and the great American plains is of different local habitat. 

 Upper. — In the Upper Miocene, however, we are again somewhat 

 more confident in correlating our Hipparion and Procamelus Zone, 

 the "Loup Fork" of early writers, with the Pontian or Pikermi stage 

 of Europe typified by the wonderful advent of the plains fauna of 

 Asia which spreads all over southern Europe, probably into Africa and 

 the far East of southern Asia and China. 



PLIOCENE 



It is difficult again to demarkate the close of our Miocene and the 

 beginning of our Pliocene. For the first time in American Tertiary 

 history an invertebrate paleontologist (Dall) comes to our aid through 

 discovering that the mammals of the Alachua Clays of Florida overlie 

 certain true Lower Pliocene molluscs. The mammals of these clays 

 are comparable to those of the Republican River of Kansas, and we 

 are consecjuently disposed to place the latter in the Lower Pliocene. 

 It is at least a more recent phase than the "Loup Fork," and is hence 

 distinguished as the Peraceras Zone, from the presence of a number 

 of broad-skulled hornless rhinoceroses. 



Lower. — Of undoubted Lower Pliocene age is the recently dis- 

 covered Snake River deposit of western Nebraska, the Neotragocerus 

 Zone, and the Virgin Valley and Thousand Creek of Nevada. The 

 arrival at this time of true Old World tragocerine and hippotragine 

 antelopes from Asia, as identified by Matthew and Merriam, is one 

 of the most noteworthy discoveries in recent paleontology. These 

 antelopes may prove to demarkate our Lower Pliocene, in which case 

 the Republican River will be pushed back into the close of th 

 Miocene because it certainly does not contain these Old World forms. 



The Lower Pliocene, or Plaisancian, of Europe is represented by 



