218 



CLARKE— SOME GEOCHEMICAL STATISTICS. [April 20, 



America, South America and Europe, South America being repre- 

 sented by the average of 82 analyses cited by Washington. The 

 weights assigned are stated under each column. 



J, N. America. 



Si02 . . 

 AI2O3 . . 

 Fe203. . 

 FeO. . , 

 MgO.. 

 CaO.. 

 Na20 . . 

 K2O. . , 

 Ti02.. 

 P2O5 . . , 

 MnO. . 



Weight 



61-47 



15.63 



2.67 



3.22 



4.02 



5-12 



3-62 



3.06 



.81 



.27 



.11 



P, S. America. 



61.13 



16.29 



3-76 



2-93 



3-18 



5-54 



4.01 



2.16 



.66 



.14 



.20 



O, Europe. 



59-89 



16.07 



4.18 



3-18 



59 

 30 

 70 



25 



51 



20 



13 



Q, General Mean. 



60.76 



15.87 

 3.40 

 3-19 

 3-78 



23 

 67 

 08 



67 

 23 



12 



100.00 



100.00 

 I 



100.00 



7 



100.00 



The last column may be taken as probably representing, with 

 certain obvious limitations, the average igneous rock of the entire 

 visible position of the lithosphere. The agreement between the pre- 

 ceding columns is so close as to suggest that similar averages from 

 other parts of the world are likely to be of the same general order. 

 It is hardly conceivable that analysts, dealing with rocks from such 

 diverse regions as Colorado, South America, Germany, Great 

 Britain, etc., s\\on\& select subsilicic and persilicic rocks or salic and 

 ferric rocks, in nearly identical proportions. The selection has been 

 made by nature itself, and although there are differences indicating 

 the existence of petrographic provinces, they are so slight as to leave 



