SOURCES OF SEGREGATED CARBON. 969 



The igneous rocks containing- the carbon compounds may flow out in 

 the belt of weathering, or, if deep seated, may reach it by denudation. 

 In either case, under favorable conditions, oxygen may slowly oxidize the 

 amorphous carbon, graphite and diamond, carbon monoxide, and the carbon 

 of methane, to carbon dioxide. If the theory be correct which regards 

 high temperature and volcanism as much more prevalent in the early stages 

 of the earth than at the present time, the oxidation of these compounds 

 may have gone on more rapidly than at present, but even now when lavas 

 containing carbon compounds are poured out over the surface their high 

 temperature in the belt of weathering affords conditions very favorable for 

 the oxidation of the carbon. 



In this connection it should be recalled that carbon dioxide is given 

 off in great quantities by volcanoes. "Cotopaxi, according to Boussingault, 

 evolves more carbonic anhydride annually than a whole city like Paris." " 

 Cotopaxi is, of course, only a single volcano, and many other volcanoes 

 are giving off large amounts. Moreover, at times of regional volcanism 

 it is to be presumed that vastly more carbon dioxide is given off than at 

 times of local volcanism like the present. It is probable that some, perhaps 

 much, or even a large part of the carbon dioxide extruded by volcanoes 

 is that resulting from the oxidation of the various carbon compounds 

 present in the original magmas, although a part of it may be occluded 

 carbon dioxide and some or much of it may be derived from carbonate 

 formations representing previous segregations. 



It is to the oxidation of the carbon of the original rocks that we must 

 look for one important primal source of carbon dioxide. 



Tilden found that in a number of rocks, including gneiss, granite, 

 gabbro, and basalt, the volume of occluded gases varied from one to 

 eighteen times the volume of the rock, and of these gases carbon dioxide 

 was the most abundant, varying in five cases from 23 to 78 per cent, but in 

 one case being as low as 5.5 per cent. 6 Occlusions occur even to a greater 

 extent in the sedimentary rocks which have been metamorphosed under 

 deep-seated conditions by the process of silication of the carbonates. 

 When the rocks occluding carbon dioxide are disintegrated and decom- 



« Letts, E. A., and Blake, R. F., The carbonic anhydride of the atmosphere: Sci. Proc. .Royal 

 Dublin Society, vol. 9, new series, pt. 2, 1900, p. 159. 



6 Tilden, W. A., On the gases inclosed in crystalline rocks and minerals: The Chemical News, 

 vol. 75, 1897, pp. 169-170. 



