218 



University of California Publications. 



[Geology 



Eelative Age of Virgin Valley and Thousand Creek Faunas, Accord- 

 ing to General Correspondence and Stage op Evolution 



Middle 





Blanco 



Pliocene 







Lower 



Thousand Creek 





Pliocene 





Snake Creek 



Upper 

 Miocene 





Santa Fe 

 and 



Madison Valley 



Middle 

 Miocene 



Virgin Valley 



Maseall, Deep Eiver, 



and 

 Pawnee Creek 



Relation of Thousand Creek Fauna to its Environment. — 

 The deposits formed during the Thousand Creek epoch are not 

 characterized by lignitic beds or carbonaceous shales as in the 

 Virgin Valley section, nor have water-laid deposits containing 

 abundant plant remains been recognized. The deposits do, how- 

 ever, contain scattered bones of small fishes in at least one 

 locality examined," and were evidently in some part formed in 

 standing water. Some of the material is volcanic ash which 

 accumulated rapidly. Another portion is made up of beds which 

 resemble soil accumulations, to which additions may have been 

 made by dust or fine ash deposits. 



From the character of the Thousand Creek Beds taken by 

 themselves there is little to indicate the nature of the climatic 

 conditions that obtained in this region while they were being 

 deposited. So far as the evidence at hand may be interpreted, 

 there seems no reason for presuming that the conditions at that 

 time differed far from the possible range of environment within 

 the Basin region at the present time. The degree of humidity 

 may have been slightly higher than to-day, but the evidence 

 favoring this view is derived mainly from the character of the 

 fauna. Presumption is in favor of the view that the degree of 

 humidity was less than during the deposition of the principal 

 mammal beds in Virgin Valley. 



The distribution and stratigraphic relations of the Thousand 



