DISTRIBUTION OF DISSOLVED MATERIAL. 543 



attributed to the excrement of bats." But, as already said, the preponderant 

 precipitates of the belt of weathering form in the soil. 



The accumulation of particles at and near the surface in the soil is a 

 matter of great geological and agricultural importance, and therefore this 

 case will be especially considered. 



CONCENTRATION AT AND NEAR THE SURFACE. 



The abundance of alkalies throughout the soils of the semiarid regions 

 of the United States and other parts of the world is well known. The soil 

 for large areas is impregnated with considerable amounts of alkaline salts. 

 Of these salts sodium and potassium chlorides, carbonates, and sulphates 

 are the most important, Where the amount of alkaline carbonates and sul- 

 phates in the soil exceeds one-half of 1 per cent crops can not be grown. 6 

 Where more than one-tenth of 1 per cent is as carbonate or as "black 

 alkali" crops can not be grown. But locally in arid regions, as, for 

 instance, at places near Salt Lake, the amount of sodium carbonate is as 

 much as 10 per cent. In some regions nitrates of the alkalies are not less 

 important than the chlorides, sulphates, and carbonates. The country 

 most noted for abundance of nitrates is Chile, where there are extensive 

 deposits. Muntz and Marcano believe that these nitrates were produced 

 by the action of nitrifying- bacteria in the humid regions, that the salts have 

 been transported by water to the area where now found, and that the 

 evaporation of this water has resulted in the deposition of the nitrates. d 



The concentration of soluble products in the soil is accomplished both 

 by underground and by overground circulations. 



CONCENTRATION BY UNDERGROUND CIRCULATION. 



The concentration of considerable quantities of soluble material at and 

 near the surface may be accomplished by the circulation of the ground 

 water. This circulation may be confined to the belt of weathering or may 

 include the circulation in the belt of cementation. 



«Hess, Wm. H., Origin of nitrates in cavern earths: Jour. Geol., vol. 8, 1900, pp. 129-134. 

 Nichols, H. W., Nitrates in cave earths: Jour. Geol., vol. 9, 1901, pp. 236-2-13. 



* Means, T. H., and Gardner, F. D., A soil survey in the Pecos Valley, New Mexico: Kept. Div. 

 of Soils, U. S. Dept. Agric, No. 64, 1899, pp. 53, 74. 



<' Gardner, F. D., and Stewart, John, A soil survey in Salt Lake Valley, Utah: op. cit., p. 113. 



d Cornptes rendus Acad. Sci., Paris, vol. 101, 1885, pp. 65-68. See, also, Merrill, George P., Rocks, 

 rock- weathering, and soils, Macmillan Co., New York, 1897, pp. 372-373. 



