964 A TREATISE ON METAMORPHISM. 



of carbon, the amount would still be small, certainly but a fraction of 1 

 per cent. 



Farrington's" analyses of meteorites show that carbon is present in 

 these bodies in various forms. As a solid it occurs as amorphous carbon, 

 as graphite, and as diamond. As solid hydrocarbons it is found as CH 2]1 , 

 as C 4 H 12 S 5 , and as C 9 H 8 2 . As gases included in the meteorites it occurs as 

 carbon monoxide (CO), carbon dioxide (C0 2 ), and carbureted hydrogen 

 (CH 4 ). The total quantity of all of these compounds in any one meteorite 

 is small, usually less than 1 per cent, and corresponds very well with the 

 amount in the outer 10 miles of the earth. 



The importance of carbon compounds to the lithosphere is out of all 

 proportion to the abundance of this element. As is well known, the carbon 

 compounds are the basis of all forms of life, and it has been seen that life 

 is one of the most potent factors concerned in the decomposition of rocks. 

 Hence the small percentage of carbon in the lithosphere, hydrosphere, and 

 atmosphere is of first importance among the elements concerned in the 

 metamorphism of rocks. 



SEGREGATION OF CARBON. 



It is evident from what has been said in considering the amount of 

 carbon in the lithosphere that this element has been segregated in various 

 ways. Carbon is segregated (1) by the process of carbonation, and (2) in 

 the carbonaceous deposits. It has been seen (pp. 473-474) that the carbon 

 now being segregated is directly derived from the carbon dioxide of the 

 atmosphere. The amount of C0 2 in the atmosphere, calculated upon the 

 basis of 0.045 per cent by weight, is 2,381,400,000,000 metric tons. This 

 figure is very close to that of Dittmar, who estimates the amount to be 

 2,277,000,000,000 metric tons.'' Each of the processes of segregation and 

 the sources of supply of carbon dioxide to the atmosphere will be considered. 



segregation by carbonation.^Many }^ears ago Hunt c stated "that the carbonic 

 acid absorbed in the process of rock-decay during the long geologic ages, 

 and now represented in the form of carbonates in the earth's crust, must 

 have equalled probabty two hundred times the entire volume of the present 



«Farrington, cit., pp. 395-408, 522-532. 



6 Dittmar, William, Narrative of the cruise of H.'M. S. Challenger, 1873-1876, vol. 1, pt. 2, 1885, pp. 

 954-955. 



c Hunt, T. Sterry, The geological relations of the atmosphere: Kept. British Assoc. Adv. Science, 

 1878, p. 544. 



