SOME GEOCHEMICAL STATISTICS.^ 



By frank WIGGLESWORTH CLARKE. 



(Read April 20, igi2.) 



More than twenty years ago, in a paper on the relative abun 

 dance of the chemical elements,- the present writer compared a 

 number of averages of analyses of igneous rocks, representing dif- 

 ferent regions, and showed that they were essentially identical. 

 From these averages, combined into a general average, the mean 

 composition of the igneous part of the lithosphere was computed, 

 and the result obtained has since been confirmed by the study of 

 much larger masses of data than were originally attainable.^ Other 

 estimates, made by other computers upon similar lines, have since 

 served to check my own, thereby giving to my conclusions a high 

 degree of probability. The figures obtained have received a fairly 

 general acceptance, and have served as a basis for other computa- 

 tions of a fundamental character. 



This acceptance, however, has not been universal. The process 

 of averaging analyses is criticized by several writers,* who urge that 

 it is unphilosophical. An analysis of a dike rock is given the same 

 weight as that of a widespread and important formation, whereas 

 each rock should be weighted in accordance with its volume. But 

 we do not and probably cannot know these volumes, partly because 

 detailed surveys are lacking, and partly because a surface outcrop 

 fails to tell us what bulk of rock may lie below. If we try to esti- 

 mate the volumes of the many rocks represented in the average, or 



^ Published by permission of the Director of the U. S. Geological Survey. 



""Bull. Phil. Soc. Washington, 1889, Vol. 11, p. 131. Also in Bull. 78, 

 U. S. Geological Survey, 1891, p. 34. 



^ See Bull. 491, U. S. Geological Survey, " The Data of Geochemistry," 

 pp. 22-27. 



* See, for example, Daly, Proc. Amer. Acad., 1910, Vol. 45, p. 211; 

 Loewinsbn-Lessing, Geol. Mag., 191 1, p. 248; and Mennell, Geol. Mag., 1904, 

 p. 263, and 1909, p. 212. 



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