INTEODUCTION 



15 



plants. Its presence in a soil, however, in anything more than very 

 minute traces, is injurious to plant growth. 



Barium. According to Failyer, 1 most of the soils of the United 

 States contain this element. Analyses of about 100 soils from Colorado 

 and Kansas showed them to contain from 0*01 to O'll per cent of 

 barium. The element could also be detected in various plants grown 

 on these soils. 



Arsenic. According to Headden, 2 this element is present in the 

 virgin soils of Colorado, to the extent of from 2-5 to 5'0 parts per 

 million, while the subsoils are generally richer, the amount of arsenic 

 reaching from 4 to 15 parts per million. 



Relative Abundance of the Elements. F. W. Clarke, 3 of the 

 U.S.A. Geological Survey, has estimated very carefully the relative 

 proportions of the more common elements constituting the earth's 

 crust to a depth of ten miles from the surface. He estimates that 

 of this 



93 per cent is composed of solid rock, etc. 

 1 per cent water and air 



the latter only amounting to about '03 per cent. 



The following table gives the relative abundance by weight of the 

 elements named : 



These numbers, it must be remembered, are merely estimated, and 

 can only claim to be approximations. They have been deduced from 



l. 72, 1910, U.S. Dept. of Agric., Bureau Soils. 

 2 Proc. Colorado Sci. Soc., 1910, 9, 345; Jour. Chem. Soc., 1910, Abstracts, 

 a. 890. 



3 BulL Philos. Soc., Washington, xi. 227. 



