ON THE CHEMICAL COMPOSITION OF AMERICAN 

 SHALES AND ROOFING SLATES. 



In the preceding paper the statemeut is made that the analyses 

 of the green slates at Slatington, Calif., "differ widely from 

 those of any normal clay slates." So little attention is paid to 

 the composition of sedimentary rocks, as compared with that of 

 igneous rocks, that the truth of this statement may not be 

 obvious to all readers. The present paper has been prepared 

 partly for this reason, but more largely because a summary of 

 our present knowledge of the subject seems desirable. 



Thirty-six analyses of American roofing slates have been 

 compared and used in the preparation of an average. These 

 analyses include all the published records noted by the writer in 

 the course of an examination of the literature, together with 

 several unpublished analyses obtained from the records of the 

 chemical laboratory of the U. S. Geological Survey. The 

 writer's acknowledgments are due to Dr. F. W. Clarke and Dr. 

 W. F. Hillebrand for aid in this work. 



Geographical distribution of the slates. — The thirty-six analyses 

 of slate discussed in this paper represent material from eleven 

 states, representing twelve distinct slate-producing districts. 

 While this geographic distribution is fairly representative of the 

 present condition of the slate industry in the United States, it is 

 by no means representative of the available supply of good 

 material ; for, of the twelve states from which analyses are on 

 file, ten are states of the Atlantic seaboard, or closely adjacent 

 thereto. Utah and California furnish the remaining analyses. 

 This distribution is due to purely commercial causes, which have 

 prevented the exploitation of equally good material located in 

 other states, but without transportation facilities or markets. To 

 this extent, therefore, the analyses are not as representative of a 

 given type of material as one might wish. 



Geologic distribution of the slates. — Owing in large part to the 

 geographic distribution of the analyses, the geologic distribution 



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