Vol. 6] Merriam: Virgin Valley and Thousand Creek. 



221 



Thousand Creek collections, though a few of the Virgin Valley 

 species are present. In the horse group the presence of Pliohip- 

 pus and the absence of the Virgin Valley Hypohippus, Parahip- 

 pus, and Merychippus seem to exclude the Middle Miocene, the 

 Pleistocene, and probably also the Upper Miocene. Among the 

 booid artiodactyls, the presence of the peculiar antelope forms 

 Ilingoceros and Sphenophalos, not known in the Virgin Valley 

 Beds, and unknown in the abundantly represented Pleistocene 

 faunas of the Pacific Coast region, together with the absence of 

 Dromomeryx, Blast omery.r, and Merycodus, again indicates that 

 the Thousand Creek Beds represent a stage distinctly later than 

 the Middle Miocene and earlier than Pleistocene. 



The physiographic history of the Thousand Creek region as 

 indicated in the terrace levels bordering the valley, leads one to 

 suspect that Pleistocene deposits might be present, and that 

 mammalian remains derived from them could be mingled with 

 those from the underlying Pliocene beds. As has been indicated 

 in the preceding discussions, no definite suggestion as to such 

 mingling has been offered, excepting in the case of a few speci- 

 mens, especially certain remains of an Equus-like form obtained 

 from some of the terraces. The same form occurs, however, at* 

 another locality where rhinoceros remains seemed to be present 

 with it. 



It will not be surprising if future observations show that 

 a Pleistocene fauna is represented at Thousand Creek. With 

 the evidence at hand it does not appear that the question as to 

 the age of the extensive exposures recognized as the Thousand 

 Creek Beds, and containing a fauna including Protohippus, and 

 rhinoceroses is seriously complicated by such remains as are 

 doubtfully Pleistocene. 



As was indicated in the discussion of the physical history of 

 the Virgin Valley and Thousand Creek region in Part I of this 

 paper the possibilities as to age of the Thousand Creek Beds 

 with relation to the Virgin Valley Beds appear to lie as follows. 

 The Thousand Creek Beds may be : 



( 1 ) Upper Virgin Valley Beds, faulted down. 



(2) Post-Virgin Valley and p re-Mesa-Basalt, faulted down. 



