938 



A TREATISE ON METAMORPHISM. 



sedimentary rocks, in which 1,545 rocks were taken into consideration. 

 The table below gives his results. 



Composite analyses of sedimentary rocks. " 



A. Composite analysis of 27 Mesozoic and Cenozoic^ shales. Each individual shale was taken 

 in amount roughly proportional to the mass of the formation which it represented. 



B. Composite analysis of 51 Paleozoic shales, weighted as in the former case. 



C. General average of A and B, giving them respectively weights as 3 to 5. This average 

 represents 78 rocks. 



D. Composite analysis of 253 sandstones, about 1 gram of each being taken in preparing the 

 average sample. 



E. Composite analysis of 371 sandstones used for building purposes, equal weights taken. 



F. Average of D and E, total of 624 sandstones. The sandstones selected at random and those 

 used for building purposes are given equal weights. 



G. Composite analysis of 345 limestones, equal weights being taken. 



H. Composite analysis of 49S limestones used for building purposes, equal weights taken. 

 I. Average of G and H, total of 843 limestones. The limestones selected at random and those 

 used for building purposes are given equal weights. 



"Clarke, F. W., Analyses of rocks, laboratory of the U. S. Geol. Survey, 1880-1899: Bull. U. S. 

 Geol. Survey No. 168, 1900, pp. 16-17. 



5 Includes organic matter. '-' Of organic origin. 



