Geological History of the Atmosphere. 93 



form an approximate estimate of the quantity of carbonic 

 acid annually removed from the atmosphere in this way. 

 even though it is comparatively easy to form an estimate of 



the total quantity of carbonate of lime and other carbonates 

 that are annually carried into the sea by rivers, the difficulty 

 being in estimating the proportion of these carbonates that is 

 derived from limestone and other carbonates already present 

 in the soil and rocks subject to denudation, and the proportion 

 that is formed through the decomposition of silicates by water 

 and carbonic acid. However, it can be easily shown that the 

 quantity of carbonic acid removed in this w ay must be very 

 much smaller than the quantity annually removed by the 

 growth of vegetation. Prof. Dittmar (article on Sea Water 

 in Encyc. Britt.) estimated that the total carbonate of lime 

 introduced into the ocean annually by all rivers amounts to 

 1*34 X 10° tons (or the x n/o o u P art °* tne carbonate of lime 

 already present in the ocean, which he estimated at 160 x 10 12 

 tons). The amount of carbonic acid present in 1*34 x 10 9 tons 

 carbonate of lime is 590 X 10 6 tons, a quantity which is equal 

 to about -gQ of the quantity annually decomposed by vege- 

 tation as calculated above. A certain amount of carbonate 

 of lime is no doubt also formed by the direct action of the 

 sea on rocks containing silicates, and the free carbonic acid 

 which takes part in this reaction may be regarded as being- 

 removed from the atmosphere since the sea and the atmo- 

 sphere react on each other : but the quantity removed in this 

 way is probably not so great as is required to form the car- 

 bonates annually carried into the sea by rivers. Also, as 

 already remarked, it is only a portion of the carbonic acid 

 present in the carbonates carried into the sea by rivers that 

 can be regarded as having been derived directly from the 

 atmosphere ; and therefore we are entitled to infer that the 

 total quantity of carbonic acid which is removed from the 

 atmosphere through the weathering of rocks is very much 

 less than the quantity which is decomposed through the 

 growth of vegetation. 



Of the agencies which produce or evolve carbonic acid the 

 most important, as already stated, is the oxidation of vegetable 

 and other organic remains. This oxidation takes place in 

 one or other of three different ways : (1) by animal respi- 

 ration, (2) by active combustion with evolution of light and 

 heat, and (3j by eremacausis or slow decay. All of these are 

 important as methods in which carbonic acid is produced in 

 larg^ quantities, and as a result of the total oxidation effected 

 in these ways, by far the greatest proportion of vegetable and 

 animal remains is oxidized to water and carbonic acid. Still it 



