GEOLOGY OF THE SAN JOSE DISTRICT 295 



both, as do also the ferrous and ferric molecules, and in the 



same sense. 



The ratios for all the other rocks of the region, so far as 



analyses are available, are found to vary in a definite manner. 



Na O 

 They tend to fix themselves as multiplies of ^ for l^ and 



FeO , , . . . 



■ ^ ^ > and the variation is never more than .10, nor usually 

 FeP3 



so large. ^ l^ is constantly on the increase from left to right, 



FeO . . , 



between 1.98 and 3.73. ^ ^ varies in the opposite sense, 



constantly decreasing, excepting in III, where 1.20 is a great 



^ , ^ Na^O + Kp . ^ . ^ . ^ 



deal too low. — ^.^ — ^— is at the same time decreasing from 



S1O2 



left to ripfht as is also ^.^ - 



For the San Jose district, soda increases at the expense of 

 potash, as silica decreases with reference to the combined alka- 

 lies and to soda alone. At the same time ferric iron is gaining 

 over ferrous iron. 



Annals N. Y. Acad. Sci., XIV, March 22, 1904—20. 



