SOURCE OF CARBON DIOXIDE FOR CARBONATION. 609 



It has been fully explained on pages 473-475 that carbon dioxide is 

 produced in large quantities in regions of abundant vegetation, where 

 the process of oxidation of carbon goes on on a great scale in the belt of 

 weathering. Therefore, the conditions for abundant carbonic acid in the 

 waters joining the belt of cementation are those of luxuriant vegetation. 

 It has just been explained that the conditions favorable for the transporta- 

 tion of abundant oxygen to the belt of cementation are those of open soil 

 and lack of vegetation. Hence, the waters which carry carbonic acid 

 plentifully to the belt of cementation are not likely to carry oxygen plen- 

 tifully. Where one is abundant the other is likely to be deficient It has 

 just been explained that the process of oxidation may take place upon 

 carbonates. Also, by oxidation of organic matter which has been so deeply 

 buried as to be within the belt of cementation, carbon dioxide is formed. 

 In so far as these occur carbon dioxide is produced by the reactions within 

 the belt of cementation itself, and thus is added to the ground solutions. 

 It thus appears that the occurrence of one of the chemical processes 

 within the belt of cementation, that of oxidation, by its very action 

 produces another active agent, carbon dioxide, and therefore promotes 

 the second of the important reactions of the belt of cementation, that of 

 carbonation. 



The third source of carbon dioxide for the belt of cementation, as is 

 fully explained in the following chapter (pp. 677-679), is the process of 

 silication, with simultaneous decarbonation as a prominent and often a 

 dominant reaction. Some of the liberated carbon dioxide is permanently 

 retained in the zone of anamorphism as occluded gas and liquid. (See 

 p. 678.) But the temperatures of the zone of anamorphism are above the 

 critical temperature of carbon dioxide. This compound is therefore origi- 

 nally a gas, and is capable of making its way through very small openings. 

 Doubtless a considerable amount of it escapes from the zone of anamor- 

 phism and enters the belt of cementation. Thus is largely explained the 

 abundant carbonic acid which is frequently found in the waters of deep 

 mines rising from a still deeper source. 



It therefore appears that the waters of the belt of cementation have 



four important sources of carbon dioxide — from the belt of weathering, 



from the decomposition of carbonates of the belt of cementation through 



oxidation, from the oxidation of organic material within the belt of cemen- 



mon xlvii — 04 39 



