212 



WILLIAM H. EMMONS 



of the stock, south of the summit of Baboon Mountain (see Fig. 3) 

 is given below. 



SiO.. 



AI.O3 



Fe203 



FeO. 



MgO. 



CaO. 



ANALYSIS OF VARIETY C. GEO. STEIGER, ANALYST 



H2O+ 49 



TiOa .'90 



P.O5 43 



NiO trace 



MnO 12 



BaO 06 



SrO 02 



57-98 



.17.01 



■••■ 3-34 



3-34 



2 . 74 



7-35 



NajO 3.92 



K2O. 2.02 



H.O- 14 



The norm of C calculated 

 I of the table below, the mode 



I. Norm 



Quartz 10-38 



Orthoclase 11.68 



Albite 33 ■O'^ 



Anorthite 23 . 07 



Hypersthene 4.71 



Diopside 8 . 64 



Magnetite 4.87 



Ilmenite 1.67 



Apatite i.oi 



Water 0.63 



Total 99-72 



According to the quantitative classification this rock is a tona- 

 lose and its chemical composition very closely resembles that of a 

 hornblende -augite-andesite from the Wind River Plateau, Yellowstone 

 National Park, described by Hague and Jaggar,^ and a diorite from 

 Captains Bay, Unalaska Island, Alaska, described by G. F. Becker.^ 

 It is similar in composition to a large number of rocks from nearly 

 every continent, being one of the commonest types known. It is 

 very close to Clark's average rock for the United States, but exceeds 

 it slightly in alumina, lime, and titania, and contains a little less 

 magnesia and potash.^ 



1 Bulletin No. 168, U. S. Geological Survey, p. 96. 



2 Bulletin No. 148, U. S. Geological Survey, p. 232. 



3 Bulletin No. '/8, U. S. Geological Survey, p. 37. 



Total -. ..99.86 



from the analysis is given in column 

 in column II. 



II. Mode 



Quartz 12. i 



Orthoclase 9.7 



Albite 31.2 



Anorthite 20 . 8 



Pyroxene 13.5 



Biotite 6.7 



Magnetite and Ilmenite 4.9 



Apatite i . i 



Total 100 . o 



