COMPOSITION OF THE LITHORPHERE. 935 



A. The mean of 82 analyses of volcanic rocks from the Western Territories of the United States, 

 published in Clarence King's Survey of the Fortieth Parallel. 



B. 64 analyses of rocks from the Yellowstone Park, taken from the laboratory records of the 

 United States Geological Survey. 



C. 54 analyses of volcanic rocks collected in northern California; also from the Survey records. 



D. 39 analyses of eruptive rocks from various localities in the Western United States, taken from 

 the Survey records. 



E. 80 crystalline and Archean rocks from all parts of the United States. Of these analyses 50 

 were taken from the Survey records, 23 from the Fortieth Parallel Report, and 7 from the report of 

 the New Hampshire Survey, vol. 3. 



F. 75 analyses of European volcanic and crystalline rocks, taken at random from five recent 

 volumes of the Neues Jahrbuch. 



G. 486 miscellaneous plutonic rocks, analyzed between 1879 and 1883, and collected by Roth in 

 his "Beitrage zur Petrographie der plutonischen Gesteine." 



H. The mean of the foregoing 880 analyses. 



Clarke remarks that the columns A to F are remarkably accordant, and 

 further says: "The thesis that the crust of the earth is fairly homogeneous 

 in composition is thus sustained by positive evidence. The variations in the 

 foregoing table are as small as could reasonably be expected."" 



Clarke, in 1891, made an estimate of the composition of the lithosphere, 

 of the ocean, and of the mean of the lithosphere, ocean, and air, but many of 

 the analyses upon which this first estimate of the composition of the litho- 

 sphere was based were "incomplete regarded from a modern point of view." 

 In 1900 Clarke therefore reestimated the composition of the lithosphere, 

 basing the estimate upon 830 complete analyses of rocks and 400 partial 

 analyses. Also, he computed the ten most important elements as oxides both 

 for his first and second estimates of the lithosphere. His results are given 

 in the following tables. 



a Clarke, eit, p. 37. 



