972 A TREATISE ON METAMORPHISM. 



atmosphere and the hydrosphere in carbon dioxide by carbonation is 

 compensated. 



In the early eras of the deposition of the sedimentary rocks, before 

 carbonates existed in important quantity, it is certain that carbonation far 

 outclassed silication; for before the latter process became important, 

 carbonates were necessarily formed in larg-e amounts and buried to a 

 considerable depth. The existence of the vast amounts of carbonates in 

 the sediments is evidence that carbonation has greatly exceeded silication. 



The further carbonation advances the more abundant become the 

 carbonate formations, many of which in due time are buried to a great 

 depth, and thus the more important becomes silication. And finally, in the 

 natural course of events, the two processes will approach each other in 

 quantitative value. The carbono-silicic cycle will approach a balance. 

 But that silication is now keeping pace with carbonation is not asserted. 

 Only conjecture can be offered on that point. While silication of car- 

 bonates may not yet equal carbonation in amount, it is believed that the 

 former process directly or indirectly returns to the atmosphere a large 

 percentage of the carbon dioxide abstracted from it by carbonation. 



Another obvious source of carbon dioxide for the atmosphere is the 

 oxidation of the carbonaceous materials of the earth. It has been pointed 

 out that nearly as fast as organisms are produced they are decomposed. 

 In so far as both processes occur there is neither loss nor gain of carbon 

 dioxide to the atmosphere. But continuously during a large part of geo- 

 logical time a residual portion of the organic material has not decomposed, 

 and thus the carbonaceous deposits have been built up, abstracting carbon 

 dioxide from the atmosphere. (See pp. 949, 966-967.) In so far as the 

 processes of the belt of katamorphism result in the storing of carbon in 

 the various hydrocarbons within the earth there is continuous depletion of 

 the carbon dioxide of the atmosphere, and during much of geological time 

 this has been a steady, cumulative process. But recently man has begun 

 artificially to oxidize these carbonaceous materials. Until the last half of 

 the nineteenth century this was unimportant, but in recent years the oxida- 

 tion of carbonaceous material once buried within the earth has been carried 

 on on an enormous scale. As calculated on page 464, the combustion of 

 1,000,000,000 metric tons of coal turns into the atmosphere 2,933,333,000 

 metric tons of carbon dioxide. Thus, at this annual rate of combustion of 



