254 Scientific Intelligence. 



treated quantitatively rather than with the belief that the calcu- 

 lations given even approach accuracy. Indeed this chapter is no 

 more than an attempt to blaze a trail in the wilderness." 



The author then considers the average composition of the 

 lithosphere, the sedimentary rocks, the hydrosphere and atmos- 

 sphere, using the work of F. W. Clarke, Dittmar and Farrington. 

 The sedimentary rocks with certain portions of the hydrosphere 

 and atmosphere, if recombined should give the average compo- 

 sition of the igneous rocks from which they were originally 

 derived, and as a first approximation the shales are estimated at 

 0*65, the sandstones 0*30, and the limestones 0*05 of the sedimen- 

 tary rocks ; and the average thickness of the latter upon the sur- 

 face of the continents which have always remained within the zone 

 of katamorphism is estimated at two kilometers, this being less 

 than has usually been estimated. 



The results indicate that this relative proportion of the sedi- 

 ments must be in the neighborhood of the truth. In regard to 

 the thickness of the sediments, however, Van Hise is inclined to 

 think that even the moderate estimate of two kilometers may be 

 too great. By assuming a smaller thickness, however, the char- 

 acter of the results would not be changed but only the absolute 

 amounts of the surpluses and deficiencies. From these data some 

 surprising results are obtained. To oxidize the ferrous iron of 

 the igneous recks to the ferric state in which it is usually found 

 in the sediments would require 35 per cent of the oxygen now in 

 the atmosphere. The further oxidation of the metals and the 

 sulphur united as sulphides in the original rocks would require 

 twice the oxygen now in the atmosphere. Further quantities 

 have been consumed in the formation of nitrates. " In summary 

 it appears that the chief certain source of oxygen for the atmos- 

 phere is the reduction of carbon dioxide by vegetation and the 

 burial of a part of this vegetation in the earth. This source is 

 vast in amount. On the other hand . . . the oxygen consumed 

 during geological time . . . has been enormous. It probably 

 vastly exceeds the amount which has been liberated to the atmos- 

 phere by the reduction of carbonic acid through plants." 



" If this conclusion be correct, such wild guesses as those of 

 Koene and Phipson, that the carbon dioxide of the original atmos- 

 phere greatly exceeded the oxygen and that the proportions of 

 these elements have been reversed in consequence of the reduc- 

 tion of carbon dioxide by organic matter, are wholly unwar- 

 ranted." 



Under sulphur, it is shown that the proportion of sulphur in 

 the secondary rocks and ocean is more than four times as great 

 as in the original igneous rocks. It is thought highly probable 

 that the discrepancy is largely explained by the actual escape of 

 much sulphur as a gas during periods of volcanism, the igneous 

 rocks containing only the residual sulphur which separated as a 

 sulphide when the magma crystallized. The same explanation 

 probably applies to a similar excess of carbon and chlorine. 



