21 ti 



University of California Publications. 



| Geology 



sand Creek .seems to be generically different from the only 

 remains found in Virgin Valley referable to the Suidae in the 

 wider sense. The large camels, which are among the most com- 

 mon fossils at Thousand Creek, seem not to be represented at 

 Virgin Valley. Ilingoceros, the peculiar twisted-horned antelope 

 of Thousand Creek, and Sphenophalos, the Antilocapra-like form 

 occurring with it, have not been discovered in any of the Virgin 

 Valley collections. 



The difference between the faunas of Virgin Valley and 

 Thousand Creek is so wide that a very considerable period must 

 have elapsed between the times of deposition of these two sets 

 of beds. It seems scarcely possible that the changes here indi- 

 cated, could be quantitatively less than those which took place 

 between the Middle Miocene and the Pliocene of well-known 

 regions, or that the time period represented could be less than 

 that occupied by the Upper Miocene stage of evolution of the 

 mammalia. 



General Relationships of Thousand Greek Fauna. — Among 

 the various assemblages of mammalian forms known in America 

 the fauna of Thousand Creek is unique. Its closest relationships 

 are apparently with Pliocene faunas as represented by the mam- 

 malia of the Snake Creek and Blanco, but to neither of these does 

 it correspond closely. 



As has already appeared, only a limited number of the 

 Thousand Creek generic types, and a smaller number of the 

 species occur in the Middle Miocene fauna of Virgin Valley, 

 while the presence of such ancient genera as Tephrocyon, Myla- 

 gaulus, and Teleoecras excludes the possibility of referring the 

 Thousand Creek fauna to a period as late as even the earliest 

 Pleistocene. 



The number of Thousand Creek species appearing in the 

 Snake Creek fauna is slightly larger than that found in any 

 other known assemblage of mammalian forms in America. The 

 list of forms common to the two includes the types Tephrocyon, 

 Mustela, Felis, Mylagaulus, Dipoides, Pliohippus, and presum- 

 ably Teleoecras. The camels and mastodons are also not improb- 

 ably closely related. These two faunas are the only ones in 



