SILICA PERCENTAGES OF ELECTEIC PEAK ROCKS. 

 Table X. — Silica percentages of rocks from Electric Peal; — Continued. 



117 



Sheet 

 rocks. 



Dike and stuck rocks. 



Si0 2 . 



I. 



Ila. 



lib. 



Tic. 



III. 







60.56 









60. 56 

 60.89 

 61.50 

 61. 85 

 63.01 

 63.78 

 64.85 

 65.11 

 65.48 

 65.60 

 65.80 

 65.94 

 65.97 

 66. 05 

 67.54 

 69.24 





60.89 









61.50 











61.85 

















63.01 

 63.78 

 64.85 

 65.11 











































65.48 











65.60 











65.80 











65.94 













65.97 



1 









66.05 

 67.54 





















69.24 













Fig. 1. — Variation or silica percentages of rocks from Electric Peak. 



The silica percentages of a number of varieties of these rocks were 

 determined and are given in Table X, together with those from the complete 

 analyses. In a measure they supplement these analyses and demonstrate 

 what is evident from the microscopical study of the thin sections, namely, 

 that the diorites and porphyries pass through all possible gradations from 

 one extreme to the other. The character of this transition is shown by the 

 diagram, fig. 1, in which each determination is given the same weight. The 

 series is arranged according to the increase of silica, and the silica percent- 

 ages are plotted as ordinates. 



