CHEMICAL ACTION OF WATEE 165 



of Massaelmsetts and of Maine, carved and facetted by the same 

 agencies.^ 



2. CHEMICAI, ACTION OF WATER 



Pure water, though an almost universal solvent, nevertheless 

 acts with such slowness upon the ordinary materials of the 

 earth's crust, that its results are scarcely appreciable to the 

 ordinary observer. But it by no means follows that its effects 

 are not worthy of our consideration. This is particularly true 

 when we reflect that the results being discussed are not merely 

 those of days and weeks, but of years even when counted 

 by the tens of thousands and millions. Moreover, absolutely 

 pure water, as a constituent of our sphere, presumably does not 

 exist. We have to consider its action when contammated with 

 sundry salts and acids which it has taken up in passing through 

 the atmosphere, and in jiltering through the overlying layer of 

 organic matter and decomposition products which cover so large 

 a portion of the surface of the land. It is when thus contami- 

 nated that are manifested the wonderful solvent and other chem- 

 ical reactions which have been instrumental in promoting rock 

 destruction, and it is here, then, that will be considered the com- 

 plex chemical processes commonly grouped under the head of 

 oxidation, deoxidation, hydration, and solution. 



(1) Oxidation. — Oxidation is perceptibly manifested only in 

 rocks carrying iron either as sulphide, protoxide carbonate, or 

 silicate. The sulphides, in presence of water and when not 

 fully protected from atmospheric influences, readily succumb, 

 producing sulphates which, being soluble, are removed in solu- 

 tion, or hydrated oxides, sulphuretted hydrogen, and perhaps 

 free sulphur. Such an oxidation is attended by an increase in 

 bulk, so that if nothing escapes by solution, there may be brought 

 to bear a physical agency to aid in disintegration. Weathered 

 rocks, containing iron sulphides, may not infrequently be found 

 with cubical cavities quite empty or partially jBlled with the 

 brownish, yellow, or red product of its oxidation in a more or 

 less powdery condition. Pyrites, though a wide-spread constitu- 

 ent, is, nevertheless, a less conspicuous agent in promoting rock 

 decomposition than the protoxide carbonates and silicates. In 



^ See "Waltliers, Denudation in der Wuste, Vol. 16, No. 3, 1891, of the 

 Abhand. Matli.-pTiys. CI. Konigl. Saehs. Gessell der Wiss. for details of 

 wind erosion in the Egyptian deserts. 



