954 A TREATISE ON METAMORPHISM. 



It might be supposed that in counting the oxygen consumed in the 

 oxidation of hydrogen to produce water, that formed by the decomposition 

 of water through the agency of ferrous oxide should be disregarded, since 

 the amount of oxygen required for the change of ferrous oxide to ferric 

 oxide in the change from the original to the altered sediments has already 

 been estimated. But the lavas are original igneous rocks and the ferric 

 oxide which they contain may be in part produced by the oxidation of 

 ferrous oxide through water in accordance with the equation above given, 

 and therefore the oxygen required to oxidize the ferrous oxide to the ferric 

 oxide as calculated (p. 951) does not include that required by the reaction 

 above. 



Since there is so little hydrogen in the air, it might be argued that the 

 oxidation of hydrogen has taken place upon the earth on a great scale, 

 and therefore that large quantities of oxygen have been thus consumed. 

 But Chamberlin has shown that it is doubtful if hydrogen can be per- 

 manently held in the atmosphere by the attraction of the earth." If free 

 hydrogen can escape from the earth it can not be assumed that the amount 

 of oxygen required to oxidize hydrogen is important, at least during later 

 geological time. 



Another way in which oxygen has been consumed by metamorphism 

 is in the oxidation of nitrogen. It has been explained (pp. 465-466) 

 that in various ways, but chiefly by means of the bacteria and leguminose 

 plants, free nitrogen is oxidized to nitric acid, and in consequence the 

 nitrates are formed. Since the nitrates are not known in the original 

 igneous rocks, nor in meteorites, it is to be presumed that all of the 

 nitrogen compounds upon the earth have been produced by the oxidation 

 of nitrogen. At the present time it is wholly impracticable to make any 

 estimate of the amount of nitrates upon the earth. In arid regions, as is 

 well known, there are large deposits of nitrates. (See p. 787.) In some 

 humid regions, as for instance at places in the Orinoco Basin of South 

 America, the nitrates compose a large percentage of the soil. As explained 

 (pp. 505-506), nitrates are essential constituents of all fertile soils. Hence, 

 while no quantitative statement can be made, the quantity of oxygen which, 

 must have been consumed in the oxidation of nitrogen must have been 

 very large. 



"Chamberlin, T. G, A group of hypotheses bearing on climatic changes: Jour. Geol., vol. 5, 

 1897, pp. 666-667. 



