AMOUNT OF CARBON IN LITHOSPHERE. 963 



Reckoned as an oxide, 0.12 and 0.22 per cent of carbon would corre- 

 spond to 0.4-1 and 0.81 per cent of carbon dioxide, respectively. This 

 places carbon dioxide tenth among the oxides, and carbon eleventh in 

 abundance, making it less plentiful than either hydrogen or titanium. In 

 Clarke's estimate of 1900 the carbon in limestones is excluded from con- 

 sideration.' 1 In his estimate for 1891 is included the carbon in a layer of 

 limestone 528 feet thick enveloping the globe, the amount of limestone 

 estimated by Reade.' 



When Clarke made his estimate in 1891 he thought the analyses of 

 volcanic and crystalline rocks probably showed too high a percentage of 

 carbon dioxide, since the rocks analyzed were not perfectly fresh. But he 

 regards this error as offset by the undeterminable amount of carbon in coals, 

 shales, and petroleums, which were not considered. 6 He thinks his resultant 

 estimate, 0.22 per cent for the lithosphere, can hardly be too low. However, 

 it is possible that this estimate is too small, since it is practically impossible 

 to make more than the roughest sort of a guess as to the amount of carbon 

 contained as graphite, anthracite, and hydrocarbons in the crust of the 

 earth. The quantity of carbon in the coal of the earth has never been esti- 

 mated, and doubtless the quantity present in workable beds is less than 

 that present in nonworkable, widely extended, small, and thin seams. Fur- 

 thermore, in the carbonaceous shales associated with the coals there is a 

 vast amount of carbon, possibly more than in the coals. Shales as old as 

 the Algoiikian in some places contain nearly 20 per cent carbon. Graphitic 

 gneisses have a widespread occurrence among the older metamorphosed 

 sediments. It seems to me that the carbon present in the above forms in 

 the lithosphere is likely to much more than compensate for the excess of 

 carbon dioxide due to alteration in the igneous and crystalline rocks 

 analyzed, since rocks which are as fresh as can be obtained are always 

 selected for analysis. But, on the other hand, the estimated amount of 

 carbon in limestone is probably too high, for it is very probable that Reade's 

 estimate of the quantity of limestone is too great. While it is possible that 

 the amount of carbon in the lithosphere is somewhat greater than the larger 

 amount estimated by Clarke, even interpreting all doubtful points in favor 



« Clarke, F. W., Bull. TJ. S. Geol. Survey, No. 168, p. 15. 

 6 Clarke, Bull. TJ. S. Geol. Survey, No. 78, p. 3S. 



