CLAYS, SHALES, AND SLATES. 



357 



Shales. 



It has been noted above that shales are simply clays which have 

 been hardened by pressure. This statement, while approximately 

 correct, requires some restriction. For the shales were formed almost 

 entirely from extensive deposits of clays of marine origin, and, there- 

 fore, do not show the same irregularities of composition, etc., that modern 

 clays exhibit. Shales, for example, rarely are so full of coarse sand 

 and gravel as the glacial clays of Michigan and other Northern States. 



TABLE 162. 

 ANALYSES OF NORMAL SHALES USED IN AMERICAN CEMENT-PLANTS. 



1. Western P. C. Co., Yankton, S. D. Mineral Industry, vol. 6, p. 97. 



2. Crescent P. C. Co., Wampum, Pa. 



3. Wellston P. C. Co., Wellston, Ohio. W. S. Trueblood, analyst. 

 4-7. Ironton P. C. Co., Ironton, Ohio. C. D. Quick, analyst. 



8-11. Diamond P. C. Co., Middle Branch, Ohio. E. Davidson, analyst. 

 12-14. Hudson P. C. Co., Hudson, N. Y. Heiberg and Honey, analysts. 



15. Alpena P. C. Co., Alpena, Mich. Vol. 8, pt. 3, Reports Mich. Geol. Survey, p. 227. 



16. Wolverine P. C. Co., Coldwater, Mich. 



17. Michigan P. C. Co., Coldwater, Mich. Cement Industry, p. 78. 



18. Lehigh P. C. Co., Mitchell, Ind. 26th Ann. Rep. Indiana Dept. Geology, p. 276. 



19. Bronson P. C. Co., Brqnson, Mich. Mineral Industry, vol. 6, p. 99. 



20. Peerless P. C. Co., Union City, Mich. Lundteigen, analyst. 

 22-25. Cayuga P. C. Co., Portland Point, N. Y. J. H. McGuire, analyst. 



