544 A TREATISE ON METAMORPHISM. 



CONCENTRATION BY CIRCULATION MAINIiY CONFINED TO BELT OF WEATHERING. 



It has been seen (pp. 419-423) that of the water which enters the 

 belt of weathering' a considerable portion returns to the surface through 

 molecular attraction and vegetation and is evaporated. During the journey 

 of water downward and upward, in the outer belt of water circulation, it 

 takes material into solution. 



When the water, the circulation of which is wholly confined to the belt 

 of weathering, or which is derived from the belt of cementation by mole- 

 cular attraction, nears the surface evaporation begins, and finally a state 

 of saturation is reached. Ordinarily saturation occurs only within a few 

 inches of the surface, and especially in the outer inch or half inch. For 

 instance, in a case of segregation of saline incrustation at Washington, D. C, 

 Cameron states that practically all of the salt was in the surface inch, the 

 larger part of it being' in the top eighth inch. As a result of the above 

 processes the soluble materials in the outer part of the earth are taken into 

 solution in large quantities and brought near or to the surface and there 

 deposited. (See pp. 539-543.) 



It has been seen (pp. 417-419) that the downward movement of the 

 water is due both to gravity and to molecular attraction, and that the upward 

 movement is due largely to molecular attraction, working against gravity. 

 It is well known that the soil, even in humid regions, is relatively rich in 

 soluble constituents. This is undoubtedly in large part explained by the 

 fact that the soluble products are mainly produced by the process of decom- 

 position, and are more largely manufactured within the soil than elsewhere, 

 as so fully set forth on previous pages. The material there manufactured 

 is strongly held by the water of imbibition. But Means suggests in this 

 connection that the failure of the downward-moving water in humid regions 

 to remove the excess of soluble material is due to the fact that the down- 

 ward movement is mainly in large openings, the force being gravity, and 

 is therefore rapid, and consequently only a relatively small amount of 

 material is taken into solution, while the upward movements are in the 

 smaller openings, mainly under the influence of molecular attraction, and 

 consequentlv this upward-moving water is loaded with material. 6 



o Means, Thos. H., On the reason for the retention of salts near the surface of soils: Science, new 

 series, vol. 15, 1902, p. 33. 

 * Means, oit., pp. 33-35. 



