302 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



and 2-628. These considerations suggest the possibility that this huge batholith, 

 including the Bayonne granodiorite, the Summit stock granites and, as we shall 

 see, the Lost Creek body, is stratified according to the law of density — biotite 

 granite above and granodiorite below. On this view, similar contrasts of 

 densities existed in the magmatic period and would find explanation in the 



ROOF 



2 Miles 



Horizontal and Vertical Scales. 



Figure 22.— Diagrammatic section showing relation of the summit stocks of Nelson Range 

 to the Bayonne batholith. 



differentiation of the magma through gravitative adjustment. On the other 

 hand, the smaller bodies may owe their lower density to their having been 

 specially acidified by the solution of the invaded quartzites; or, thirdly, the more 

 salic character of the satellitic stocks may be due to special concentration of 

 magmatic fluids in the smaller chambers, facilitating more extreme differentia- 

 tion in them than in the main Bayonne batholith. Probably all three causes 

 have operated. 



LOST CREEK GRANITE BODY. 



The peculiarly shaped mass of granite over which Lost creek flows is, 

 mineralogically, chemically, and genetically, akin to the granite of the Summit 

 stocks. The staple rock is alkaline, with microperthite and orthoclase as the 

 dominant feldspars. Oligoclase is the subordinate feldspar, biotite the only 

 femic essential; primary muscovite, magnetite, apatite, and zircon are the 

 accessories. In places the muscovite has the rank of a subordinate essential, so 

 that the rock varies from biotite granite to biotite-muscovite granite. The 

 average specific gravity is 2-617. 



Along all observed contacts this granite, for a distance of several score of 

 feet inward, is aplitic and poor in mica. The apophyses are generally composed 



