704 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



Table XLV. — Comparison of average analyses; granite, basalt, diorite, and 



andesite. 





1 



2 



3 



4 



5 





A verage 



pre- 



Cambrian 



granite. 



Average 

 basalt. 



Mean 

 of land 2. 



A verage 

 diorite, in- 

 cluding 

 quartz dio- 

 rite. 



Average 



augite 



andesite. 





47 



198 





89 



33 



Number of Analyses. 







SiO 



71 



14 

 1 



1 



1 

 3 



4 



56 



48 



20 



47 



65 



18 



59 



98* 



26 



53 



10 



49-87 

 1-38 



15 96 

 5-47 

 647 

 32 

 627 

 9-09 

 316 

 1-55 

 •46 



60 71 



93 



15-08 



3-47 



4 06 

 •25 



3 43 



5 54 

 321 

 3 04 



•28 



59 



16 

 3 

 4 



3 



G 

 3 

 2 



19 

 81 

 51 

 02 

 17 

 13 

 93 

 47 

 39 

 12 

 26 



58 



17 

 3 

 3 



2 

 5 

 3 

 2 



65 



Ti0 2 



80 



AI2O3 



67 



Fe 2 3 



85 



FeO.... 



MnO 



69 

 22 



MgO 



CaO 



Na 2 



K2O.. 



90 

 92 

 60 

 40 



P 2 6 



30 





100-00 



100 00 



100 00 



100 00 



100 00 



\Ai I es -08% BaO and '02% SrO. 



It is further significant that the average composition of the ground-mass 

 of four typical augite andesites is nearly identical with the average pre-Cam- 

 brian granites, as it is with the average granite of all ages; these averages being 

 calculated as water-free. A second step in this far-flung guess as to the origin 

 of the acid shell is prompted by the facts illustrated in Table XL VI. Such a 

 glance at a hypothesis of origins cannot vitally affect the question as to the 

 existence of the acid earth-shell — here the essential point in the general theory 

 of the igneous rocks. 



