OXIDATION AND DEOXIDATION. 607 



circulating ground water. In many cases the major portion of the oxygen 

 is thus utilized. In so far as this takes place the process leaves no 

 direct evidence of itself by the existence of oxides. So far as suphuric acid 

 is formed the same is true. The carbonic acid and the sulphuric acid may 

 remain in part in the belt of cementation in carbonates and sulphates. So 

 far as this occurs the oxidized compounds remain in the belt, but not as 

 substances which we ordinarily think of as evidences of the process of 

 oxidation. 



After the oxygen of the waters of the belt of cementation is exhausted 

 organic and other compounds, such as sulphides, are likely to be taken into 

 solution, which renders the waters reducing, as explained on page 165. 

 The waters under impervious strata which take a long underground journey 

 are especially likely to be in this condition, for such a journey furnishes 

 ample time for the complete consumption of the oxygen contained in the 

 solutions. The above is illustrated by the deep artesian waters of many 

 parts of the world. Excellent cases are those furnished by the artesian 

 waters of the Potsdam sandstone of Wisconsin and the Dakota sandstone 

 of the James River Valley, Dakota. The waters which issue from the 

 Potsdam formation along Lake Michigan are of a reducing . character, 

 containing, as noted by Chamberlin, some hydrogen sulphide." 



Where the waters become reducing deoxidation of the compounds with 

 which they come into contact may take place. 



One form of deoxidation is of sufficient consequence to require men- 

 tion. While of no great quantitative importance, it is important from the 

 point of view of the metallic ores. It has been explained under "The belt 

 of weathering" (pp. 468-469) that the sulphides are continuously oxidized 

 to sulphites or sulphates. A part of the sulphurous and sulphuric acid 

 united with the original elements, or with other elements, joins the belt 

 of cementation. After the oxygen is exhausted and organic compounds are 

 present the sulphites and sulphates may be reduced to sulphides by the 

 direct action of the organic matter, or by these compounds after passing 

 into the solutions. 



The process of reduction, or deoxidation, of the sulphates involves 

 the oxidation of the organic material, and thus this reaction, from one point 

 of view only, is reduction. From the other point of view it is oxidation. 



o Chamberlin, T. C, The ore deposits of southwestern Wisconsin: Geol. of Wisconsin, vol. 4, 1882, 

 p. 547. 



