934 



A TREATISE ON METAMORPHISM. 



compiled these and other analyses, with the purpose of obtaining an 

 approximate idea of the composition of the lithosphere. In his computa- 

 tions Clarke has considered only the "igneous and crystalline rocks." As 

 these terms are used there are excluded from consideration the unmeta- 

 morphosed sediments and the metamorphosed sediments so far as they are 

 recognized as sediments. In the following table are found the analyses of 

 various groups of 880 igneous and crystalline rocks, and the mean of the 

 whole : 



Analyses of igneous and crystalline rocks. a 



Kl.KMKXTAKY srBSTAXC'KS. 



« Clarke, F. W., The relative abundance of the chemical elements: Bull. U. S. Geol. Survey No. 7S 

 1891, pp. 36-37. 



