220 



WILLIAM H. EMMONS 



other oxides except silica and lime and magnesia, at the basic end of 

 the diagram. Ferrous and ferric iron are in a measure inversely 

 proportional to each other, an increase in one usuaUy being accom- 

 panied by a decrease in the other. The total amount of iron decreases 

 irregularly to the more siliceous end of the series. Magnesia also 

 decreases rapidly as the silica increases and this decrease more 

 nearly agrees with that of the ferrous than of the ferric iron. Lime, 



^ ^ 



7ff8 ^^S3 



Fig.' 2. — Chemical variation of types of the Haystack stock. 



like magnesia, decreases steadily from the less siliceous toward the 

 more siliceous end of the series, but increases slightly in the grano- 

 diorite at the extreme end. The soda, low in F, increases gradually 

 and steadily to B, and falls slightly in A. Potash increases very 

 irregularly to the more siliceous end of the diagram. The alkalies 

 vary neither directly nor reciprocally with each other, though both 

 increase with silica. 



Mr. H. S. Washington,' in discussing the differentiated complex 

 at Magnet Cove, Ark., ranges six analyses in order of ascending 

 silica. In his diagram with but one exception the oxides increase 



I Bulletin of the Geological Society of America, Vol. XI, p. 404. 



