MOLECULAR VARIATION OF ELEOTRIG PEAK ROOKS. 



119 



varies irregularly, decreasing from the basic to the acid end of the series. 

 While each of the iron oxides is quite independent of the magnesia, it is 

 found upon reducing all the iron to the ferrous state that there is the 

 greatest accord between the iron and the magnesia, both varying in like 

 directions and to nearly the same extent. The magnesia drops rapidly at 

 first, and is very erratic in the more siliceous end of the series, where it 

 becomes very low. 



The most regular variation is in the lime, which decreases steadily from 

 the basic to the acid end of the series. It exhibits little or no connection 





Fig. 2.— Molecular variation of the rocks at Electric Peak. 



with the other constituents. The molecular proportions of the alumina, 

 though quite irregular between certain limits, maintain a uniformly high 

 position, and are much greater than those of any one of the other constitu- 

 ents except silica, At the extreme basic end of the scale, however, they 

 are equaled by those of both the magnesia and the lime. The alkilies are 

 most like the alumina in their variations, and remain very nearly uniform, 

 increasing somewhat toward the acid end of the series. The soda mole- 

 cules are more than twice as numerous as those of potash, which is one of 

 the most noticeable characteristics of the rocks of this locality. In the 

 basic end of the series the alkilies vary together in the same direction, 



