2.30 



University of California Publications. [Geology 



There does not, however, seem to be anything in the physical 

 evidence to indicate whether the deposition occurred in early 

 or in late Pliocene time. 



The only suggestion bearing upon the question as to the 

 division of the Pliocene represented by the Rattlesnake Beds is 

 offered by the fauna. The few species thus far found at the 

 Rattlesnake exposures are unfortunately only poorly represented, 

 and in a large percentage of eases the occurrence is not known 

 exactly. Following is the list of species referred to this forma- 

 tion : 



Neohipparion occidentale (Leidy). 

 Neohipparion sinclairi (Wortman). 

 Platygonus rex Marsh. 

 Plioliippus supremus (Leidy). 

 Canis(^) davisi Merriam! 

 Clemmys hesperia Hay. 

 Rhinoceros, indet. 

 Camel, large, indet. 

 Camel, small, indet. 

 Suilline, large, indet. 



Of the above forms the rhinoceros seems quite certainly not 

 later than the earlier Pliocene, so that taking all evidence into 

 consideration an approximation of the age of the Rattlesnake as. 

 early Pliocene seems justified. 



Judging the age of the Thousand Creek and Rattlesnake 

 Beds separately on the basis of available information both seem 

 to fall within the Lower Pliocene. The meagre Rattlesnake 

 fauna offers so little for comparison that faunal similarity be- 

 tween the two is not evident. The only parallels indicated are 

 shown in the occurrence in both of rhinoceroses and large camels, 

 together with horses having an advanced type of tooth structure.. 

 An additional suggestion appears in the presence in the Thous- 

 and Creek Beds of the can id species, Cams I !) davisi, which 

 seems to be identical with a species doubtfully derived from the 

 Rattlesnake at Rattlesnake Creek, Oregon. 



Id the region where the Thousand Creek Beds are exposed 

 there are fortunately two important factors in the geologic 

 sequence which seem to be almost identical with the physical 

 factors which check the possible upper and lower limits of age 

 of the Rattlesnake Beds in the John Day Valley: these factors 



