INTRUSIVE SHEETS IN GALLATIN MOUNTAINS. 



81 



CHEMICAL COMPOSITION. 



Of the rocks belonging- to this intrusive mass and its outlying sheets 

 three have been analyzed chemically, and their analyses are given in the 

 accompanying table. No. 1 is from a sheet on the ridge southwest of the 

 summit of Electric Peak (182), and is hornblende-andesite-porphyry. No. 

 2 is the rock forming the thick sheet between Fan Creek and Cinnabar 

 Creek (164), and is hornblende-mica-andesite-porphyry. No. 3 is from the 

 southern slope of Cray Mountain, and is part of the great intrusive mass 

 (146); this also is hornblende-mica-andesite-porphyry. 



Analyses of rocks from vicinity of Electric Peal; Fan Creelc, and Gray Mountain. 



[Analyst, J. E. Whitfield.] 



Constituent. 



1. 



2. 



3. 



SiOo 



58.49 



65 63 



65 64 



TiOo 



1 71 







AlaOs 



16.70 



17. 00 



17.29 



Fe,0 3 



3.85 



2.55 



3.07 



FeO 



2.37 



1.19 



1.29 



MnO 



.24 





Trace. 



MgO 



3.12 



2 03 



1 78 



CaO 



5.90 



3.48 



1.98 



Li 2 



.01 



.04 



.04 





3.47 



• 4.42 



5.77 



KjO 



1.59 



1.64 



2.44 





Trace. 



.07 



.23 



SO; 



.63 





Trace 



CO 





27 





H.0 



Total 



2.44 



2.00 



1.03 



100. 52 



100. 32 



100. 73 





From these analyses it is seen that the hornblende-andesite-porphyiy 

 has 3 per cent less silica than the hornblende-mica rock of the Indian Creek 

 laccolith with nearly the same alkalies, and that the former has more mag- 

 nesia and considerable titanium oxide. The hornblende-mica-andesite- 

 porphyries of the Gray Mountain system which were analyzed have more 

 silica than the Indian Creek laccolith, and somewhat more alkalies and less 

 lime. Chemically and mineralogically they are near dacites, and might be 

 classed with them. Some of the rocks contain abundant idiomorphic quartz 



MON XXXII, PT II G 



