Vol. 6] 



JHerriam: Virgin Valley and Thousand ('reek. 



217 



America known to include antelopes suggesting close relation- 

 ship with the typical Old World forms. In spite of a partial 

 resemblance, the Thousand Creek fauna differs distinctly from 

 that of Snake Creek in the absence of all representatives of 

 Hypohippus, Parahippics, Merychippus, Merychyus, Blast o- 

 meryx, and Merycodus, the horses being represented by Pliohip- 

 pus, possibly accompanied by Equus, and the booid artiodactyls 

 by previously unknown types of antelopes. There seems no 

 question but that the Thousand Creek fauna is younger than 

 that of Snake Creek, though evidently as near to the Snake 

 Creek stage as to any other recognized horizon in America. 



The Blanco Pliocene fauna of Texas resembles that of Thous- 

 and Creek in the absence of horses below the stage of Protohip- 

 pus and Neohipparion. Unfortunately the Thousand Creek 

 camels and mastodons are not well enough known for a thor- 

 oughly satisfactory comparison. In the disappearance of 

 rhinoceroses, mylagaulids and tephrocyons, and in the appear- 

 ance of several southern types of edentates the Blanco stage is 

 more advanced than that of Thousand Creek. 



In so far as correlation with the American mammalian 

 faunas is concerned the Thousand Creek fauna would seem 

 necessarily to take a place later than that of the Snake Creek 

 and earlier than that of the Blanco. With this arrangement it 

 seems probable that the Snake Creek fauna can hardly be con- 

 sidered as later than early Lower Pliocene, verging on the 

 Miocene. The Thousand Creek fauna may be included in the 

 lower Pliocene, but must represent a late stage of this division. 

 The Blanco fauna is presumably considerably later than that of 

 Thousand Creek. Though the variation may lie due in part 

 to geographic and climatic differences, it is hardly probable that 

 if the Thousand Creek fauna represents the late Lower Pliocene 

 the Blanco can represent a horizon as early as the earliest 

 Middle Pliocene. 



