RELATIONS OF OXIDATION AND DEOXIDATION. 471 



the iron being in the ferrous form." This is a region of less humidity 

 than the eastern region, and here dry seasons alternate with very Avet 

 seasons. According to Hayes, during the dry season each year the soil 

 cracks deeply, and a large amount of organic material falls into these cracks. 

 During the wet season the soil swells and fills the cracks, and the organic 

 matter becomes incorporated with the soil. This material acts as a reduc- 

 ing agent and prevents the further oxidation of the iron, or reduces any 

 part of the iron oxide which has become ferric oxide to the ferrous state. 



While this explanation is plausible, it seems incomplete. In the east- 

 ern division the soil is . continuously in contact with numerous dead and 

 dying- roots of the abundant vegetation, and the question naturally arises 

 .whether the difference is not due to saturation of the soil of the western 

 division, as explained below, the cracks being utilized hy the water. 



Deoxidation of the iron may occur in regions where the water of 

 the soil is so abundant as to approach saturation, and plants are abundant. 

 Under such conditions the large amount of oxygen required to decompose 

 the plants is not able to enter from the air with sufficient rapidity, and 

 hence the oxidation of the plants abstracts oxygen from ferric oxide*, and 

 this reduces the iron to the ferrous condition. This reduction of ferric salts 

 results from the demands of the abundant oxidizing bacteria for oxygen 

 where organic matter is being rapidly decomposed. Consequently the 

 process of deoxidation of iron compounds commonly takes place only by 

 the oxidation of organic constituents. So far as the inorganic constituent is 

 concerned, there is absolute loss of oxygen by the process. 



Examples of deoxidation of iron compounds are furnished by the 

 so-called cumulous deposits, where abundant vegetation near the water level 

 accumulates and does not completely decay. Instances of such deposits 

 are the sphagnum mosses of marshes,, bogs, lakes, and the margin of the 

 ocean, which result in the accumulation of peat; and the swamps, for 

 example, cedar, spruce, mangrove, etc. Probably the same conditions 

 obtained in the past, especially at the coal-forming periods, for the under- 

 clays of coal beds are almost always gray or white, the iron having been 

 almost completely reduced to the ferrous form. 



The iron reduced to the ferrous condition and that already in the 

 ferrous condition in the silicates is in the most favorable form to unite 



a Hayes, cit., pp. 130-132. 



