THE MORE COMMON ELEMENTS AND COMPOUNDS 13 



upon the recent computations of. Professor F. W. Clarke of the 

 United States Geological Survey for the average composition of 

 the ocean and of the earth's crust 1 to a depth of ten miles, essen- 

 tially upon Sir William Ramsay's recent estimate for the average 

 composition of air, and upon the author's compilations and com- 

 putations for the average composition of shelled corn (maize). 



TABLE 2. THE MORE IMPORTANT ELEMENTS 



1 United States Geological Survey Bulletin 330 (1908). The data for phos- 

 phorus and potassium include analyses of 1671 and 2110 different samples, re- 

 spectively, of representative rocks, some of which were kindly furnished to the author 

 by Doctor Clarke since Bulletin 330 was published. 



2 About sixty other elements (most of them very rare) must account for this 

 deficiency. 



3 Constant traces of helium, neon, krypton, and xenon are also found in the air, 

 of which they may constitute five parts per million. Varying amounts of moisture, 

 compounds of nitrogen, sulfur, chlorin, and more or less dust, also exist in the air. 



