442 University of California Publications in Geology [Vol. 10 



CORRELATION WITH OLD WORLD FAUNAS 

 Certain elements found in American Pliocene mammal faunas so 

 closely resemble characteristic genera and even species of the Old 

 World that little doubt exists concerning their common origin. Such 

 types as Hipparion, Teleoceras, Tragocerus, Hyaenarctos, Ischyro- 

 smilus, Pseudaelurus, and Dipoides appear even in similar specific garb 

 at various localities in the Pliocene of America, Asia, and Europe. 

 It is worthy of note that the forms appearing in America and in the 

 Old World are also generally widely spread on each of these two areas, 

 indicating their tendency to range widely. It is also worthy of note 

 that some of these forms have a long antecedent history in one area 

 and appear suddenly in the Pliocene of the adjacent region, while 

 within approximately the same periods other groups originating in the 

 second region extended their range to the first area. These arguments, 

 taken with the facts relating to corresponding amount of organic evo- 

 lution and corresponding amount of crustal movement in both regions, 

 leave little room for doubt that we have here an unusually well founded 

 case of correlation in which contemporaneity is indicated, at least 

 within the limits of half of a geological period. 



There is good reason to believe that the earlier American Pliocene 

 faunas as the Alachua, Snake Creek, Ricardo, Rattlesnake, and Thou- 

 sand Creek are approximately contemporaneous with Old World 

 faunas of Schansi in China, Dhok Pathan of India, Maragha of Persia, 

 and Pikermi of Greece. It is not yet possible to give an exact com- 

 parison of the relative stages of the early Pliocene represented by 

 these faunas. For the later Pliocene less evidence of contemporaneity 

 of American and Old World faunas is available, but there is good 

 reason for looking carefully into the question of relative stage of the 

 Idaho and the Boulder Conglomerate of India, both possibly in part 

 Pleistocene, and both containing primitive forms of Equus. 



Future work will largely illuminate the field of investigation cov- 

 ering Pliocene life, upon which we have as yet made only a beginning ; 

 and later years of study hold in store much of that unequalled pleasure 

 found in difficult scientific quest, and in the discoveries which so 

 frequently reward intensive investigation. 



