ANALYSES OF SHALES AND CLAYS. 



891 



Probably the chief respect in which these shales differ in composition 

 from muds is that water is less abundant in them. To compare the above 

 analyses with the analyses of the original rocks, the water ought to be 

 omitted. Omitting the water, and increasing the other elements in propor- 

 tion, the analysis of shales would be as follows: 



Analysis of shales on basis of 100 per cent excluding the water. 



For comparison there is inserted the average of 12 analyses of clays 

 and soils from Illinois, Iowa, Minnesota, and Wisconsin. 



Average of 12 analyses of clays and soils. 0. 



« Clarke, F. W., Analyses of rocks, laboratory of the TJ. S. Geol. Survey, 1880-1899: Bull. D. S. 

 Geol. Survey No. 168, 1900, pp. 296-297. 



