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



227 



of the patches of sedimentary deposits extending through Nevada 

 and into California' will enable us to arrive at an approximate 

 correlation of these formtaions. 



As a few mammalian remains are found in the deposits of 

 Tertiary age within the Great Valley of California it is hoped 

 that correlation of these beds with the continental deposits of the 

 Basin region may ultimately be possible. When this is accom- 

 plished we can determine the relationship of the continental beds 

 to the well-known marine series of the Pacific Coast region. 



The relation of the Columbia Lava series to the marine beds 

 of Western Oregon should also furnish important information 

 in any effort which may be made to correlate the continental 

 formations with the marine series. 



Relation of Virgin Valley Beds to Faulting Movements of 

 Basin Region. — As nearly as can be determined, the Virgin Val- 

 ley Beds rest unconformably upon the Canon Rhyolite in Virgin 

 Valley. There is reason to believe that these rhyolites represent 

 the upper portion of the igneous series of Pueblo Range, and 

 any disturbance which affected the rhyolites must have dis- 

 turbed this basalt series. It is evident that considerable fault- 

 ing movements have effected the basaltic series in comparatively 

 late time, and other movements may have occurred between the 

 Virgin Valley and Thousand Creek epochs. The amount and 

 nature of these movements cannot be determined until the rela- 

 tion of the Virgin Valley and Thousand Creek Beds to each 

 other is certainly known. If the Thousand Creek Beds were 

 formed in post-Mesa-Basalt time and all of the beds below the 

 Mesa Basalt are to be referred to one epoch, the Virgin Valley, 

 there must have been profound movements in pre- Virgin Valley 

 time, as the sediments below the Mesa Basalt have filled around 

 prominent points consisting of the older igneous rocks. If the 

 beds immediately below the Mesa Basalt are the equivalent of 

 the Thousand Creek series, it is possible that considerable move- 

 ments occurred after the deposition of the Virgin Valley and 

 previous to the deposition of the uppermost beds. The presence 

 of a marked unconformity below the rhyolitic gravels, which 

 possibly separate upper and lower Virgin Valley divisions, is 

 in favor of such a view. On the other hand, excepting at the 



