LA VAS IN THE GREAT BASIN REGION 



637 



TABULATION 



The relative age of the different members of the volcanic 

 section, therefore, may be roughly outlined in the following 

 table. It must be remembered that this is only, approximate. 



The age of the members of volcanic succession being deter- 

 mined, we can sometimes apply this determination in cases where 

 the age of the lavas cannot be independently ascertained, and 

 use them roughly as time markers. 



Epochs of sedimentation 



Eocene-Miocene Lakes < 



Shooshne Lake 



Lake Lahontan 

 Walker Lake, etc. 



Standard time divisions 



End of Cretaceous 



Eocene 



Miocene 



riiocene 



Pleistocene 



Epochs of vulcanism 



No. i. Acid (type, biotite 

 rhyolite) 



J>No. 



^No. 



i 



Y J No. 4. 



Medium intermediate 

 (type, hornblende- 

 mica-pyroxene ande- 

 site) 



Acid (type, biotite 

 rhyolite) 



Basic intermediate 

 (types, pyroxene, 

 andesite, etc.) 



Y No. 5. Basic and acid (basalts 

 and occasional rhyo- 

 lites) 



