20 



CLARKE— STATISTICAL METHOD 



[April i8 



observation would probably modify that opinion, which, however, 

 is entitled to some weight. 



So far, my final average has only been partly given ; the minor 

 constituents of the rocks remain to be taken into account. In the 

 laboratory of the Geological Survey the analyses of igneous rocks 

 have been unusually elaborate, and many things have been deter- 

 mined which are too often ignored. The complete average is given 

 in the next table, with the number of determinations to which each 

 figure corresponds. In the elementary column, hygroscopic water 

 does not appear; but an allowance is made for a small amount of 

 iron which was reported in the analysis as FeSo. When a " trace " 

 of anything is recorded, it is arbitrarily reckoned as o.oi per cent., 

 and when a substance is known to be absent from a rock, by actual 

 determination of the fact, it is assigned zero value in making up the 



averages. 



SiO, 



ALO3 



Fe.Os 



FeO 



MgO 



CaO 1,215 



NaoO 1,268 



Number. 



1,358 

 912 

 961 

 962 



1,027 



Average. Reduced to 100. 



KoO .. 

 H2O — 

 H.O + 

 TiO, . 

 ZrOo . 

 COo .. 

 P2O5 . 

 S .... 

 CI ... 

 F .... 

 BaO .. 

 SrO .. 

 MnO . 

 NiO .. 

 Cr,03 . 



V,03 . 



U2O . 



1,265 

 770 

 832 

 870 

 185 

 469 

 884 

 575 

 234 



73 

 617 

 520 

 899 

 243 

 246 



40 

 550 



60.91 

 15.28 

 2.63 

 3-46 

 4.13 

 4.88 



3-45 

 2.98 

 .41 

 1.49 

 •73 

 .03 

 •53 

 .26 

 .11 



•07 

 .02 

 .11 

 .04 

 .10 

 .03 



.05 

 .03 

 .01 



59.87 



15.02 



2.58 



3-40 



4.06 



4-79 



3.39 



2.93 



.40 



1.46 



.72 



•03 

 .52 

 .26 

 .11 

 .07 

 .02 

 .11 

 .04 

 .10 

 •03 

 .05 

 .03 

 .01 



In Elementary Form 



O 47.09 



Si . 



Al 

 Fe 

 Mg 

 Ca 

 Na 

 K . 

 H . 

 Ti 

 Zr 

 C . 

 P . 

 S . 

 CI . 

 F . 

 Ba 

 Sr 

 Mn 

 Ni 

 Cr 

 V . 

 Li . 



28.23 



7.99 



4.46 



2.46 



3.43 



2.53 



2.44 



•17 



.43 



.026 



.14 



.11 



.11 



.07 



.02 



.089 



•034 

 .084 

 .023 



•034 

 .02 

 .01 

 100.000 



101.74 



100.00 



