I9I2.] CLARKE— SOME GEOCHEMICAL STATISTICS. 221 



alteration. The maximum for CO,, 0.49 per cent., may neverthe- 

 less be admitted in computing the composition of the entire litho- 

 sphere, as an allowance for carbonaceous matter which would other- 

 wise escape attention. Copper does not appear in the table, but it 

 is sometimes determined, and the order of its abundance is perhaps 

 about the same as that of lithium, say o.oi per cent. Boron, possibly, 

 ought also to be taken into account, but it is seldom estimated, and 

 no figure can be assigned to it. As for water, which up to this point 

 has been neglected, the average shown by the Survey analyses is 

 1.95 per cent. This figure, which is excessive so far as the unaltered 

 igneous rocks are concerned, may, however, be taken as including 

 the water enclosed in the lithosphere and not otherwise estimated. 

 The allowance is ample. 



Including the minor constitutents, the Survey analyses alone give 

 the subjoined mean composition for that portion of the lithosphere 

 which is represented by rocks of igneous origin. The total is re- 

 calculated to 100 per cent. 



SiO. 59.8s 



AI2O3 14.95 



FcsOs 2.59 



FeO 345 



MgO 3.85 



CaO 4.87 



Na^O 3.39 



K2O 2.99 



H=0 1.92 



TiO. 75 



CO2 48 



P2O5 27 



MnO 10 



Minor constituents 54 



100.00 



This differs from the general mean already given under column Q 

 in that it includes only the Survey data, and takes account also of 

 water, carbon dioxide, and the minor constituents of igneous rocks. 

 The important values, however, are all of the same order of magni- 

 tude in both estimates. The undetermined elements cannot aggre- 

 gate over 0.5 per cent., and represent minor corrections which may 



PROC. AMER. PHIL. SOC, LI. 205 L, PRINTED JULY 24, I9I2. 



