218 



GEOLOGY Oif TONOPAH MINING DISTRICT, NEVADA. 



Silica 

 Si0 2 



Potash 

 K,0 



2 _ 



4 I 



5 



6 



7 _ 



Alumina 

 AI 2 3 



Iron oxides 

 FeOand 



2 



3 



4 _ 



5 . 



6 . 



8 '. 



Magnesia 

 MgO 



i 



a 



4 ~ 



3 . 



6 . 



7 . 



8 . 



2 _ 



3 _ 



4 . 



6 . 



8' 



Soda 

 Na 2 



Lime 

 CaO 



1 



2 _ 



4 ~ 



6 . 



Scale-.. 01 (quotient figure) "^5 inch 



Fig. 73. Uiagrum to show changes in amounts of commoner elements during stages of alteration of earlier andeslte. 



