CORRELATION OF THE C EN O ZOIC 261 



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 o\erlie 

 certain true Lower Pliocene molluscs. The mammals of these clays 

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

 are consequently 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 w^estern 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 

 the mammalian life of Casino, which is very sharply demarkated 

 from that of Pikermi. 



Middle. — The Astian, or Middle Pliocene, life of France, typified 

 at Roussillon and Montpellier, is broadly comparable with the Blanco 

 of Texas, where we enter the sixth faunal phase, marked by the inva- 

 sion of South American armored edentates, or glyptodonts, into the 

 southern United States. These deposits are accordingly known as 

 the Glyptotherium Zone. They mark a great advance upon those of 

 the Republican River. 



