POTASH SALTS AND OTHEE SALINES IN THE GREAT BASIN REGION. 21 



These are all compounds of very low solubility, and, as practically all are present 

 abundantly in the zone of weathering, we may consider the solution as being saturated , 

 or nearly satm-ated, with respect to these compounds. With the more soluble com- 

 pounds it is unusual, except very locally, to have conditions in the zone of weathering 

 which would lead to saturation. 



Wind and water are the two agents concerned in the movement of the products 

 of the zone of weathering. Even though the basin region has a scanty rainfall, water 

 is by far the more important agent. Water dissolves the soluble constituents and car- 

 ries away in suspension the finely comminuted products of disintegration and decom- 

 position. Heavy rainstorms and cloudbiu:sts carry down from the mountains c^uan- 

 tities of comparatively coarse material to be deposited upon apron slopes or even in 

 the central portions of the playas. One has but to walk over the detrital fans in 

 Death Valley to appreciate the prodigious erosion that has been accomplished by 

 cloudbm-sts. Ravines and gullies are choked with coarse debris, which spreads 

 out in fan-like masses at then- mouths and resembles more than anything else the 

 piles of debris resulting from hydraulic mining. One has but to experience a dust 

 storm in Death Valley, or any portion of the basin region for that matter, to appre- 

 ciate the importance of wind as an agent of erosion and deposition. 



ABSORPTION PHENOMENA. 



In a previous section has been pointed out the importance of the seepage water and 

 the fact that only a small part of the rainfall is collected in streams and reaches the sinks 

 and lakes. This fact would indicate that under present climatic conditions only a 

 fraction of the soluble salts is collected by the run-off, while the greater part is carried 

 away by the seepage water to be in part permanently retained by the soil and in part 

 to be removed by underground waters. Certain reactions take place within the soil 

 and alluvial material and the soluble salts which are carried into the seepage zone 

 by percolating waters. These reactions are to a greater extent chemical and to 

 a less extent physical in nature. The net result is to withdraw a portion of the saline 

 material permanently. The reacting substances are silicates and the colloidal material 

 of soils, and in the solution, soluble salts of sodium, potassium, calcium, and magne- 

 sium. A solution of salts carrying more or less suspended material percolates into 

 alluvial material. The suspended material is quickly removed and is concentrated 

 in the upper layers of the soil. The phenomena attending the reaction between 

 soil constituents and solutions are much more complex. Cameron ^ shows that absorp- 

 tion accounts for the removal of a part, at least, of the soluble salts. He groups 

 under the term absorption the mechanical inclusion of solutions, the formation of 

 new compounds by double decomposition, and the condensation of dissolved sub- 

 stances on or about the surface of the absorbing medium. To the last the term absorp- 

 tion is given. E. C. Sullivan has summarized the literature dealing with adsorption, 

 and from this summary the facts of special interest to this inquiry are taken. 



The principal conclusions are embodied in the following quotations: 



"So far as the evidence goes the action of silicates, clay, and other constituents of 

 the earth's crust in solutions of such salts as do not dissolve in water with alkaline 

 reaction consists in an equivalent exchange of bases. The salt is uniformly dis- 

 tributed between the water of colloid silica and silicates and the water of the solution. 

 Any absorption of the salt as a whole by the solids mentioned is so slight as to have 

 escaped positive detection. As bearing upon the latter point, it should be said that 

 certain colloid substances, analogues to which are present in the earth's crust, do 

 take from solution both the acid and base of the salts mentioned. Ferric and alumi- 

 num oxides and metastannic and stannic acids, for instance, take potassium sulphate 

 from solution, while hydrated manganese dioxide takes up sulphate, chloride, or 

 nitrate of potassium. ^ 



"It may be observed that the base enters into reaction to approximately the same 

 extent, whether it is combined as sulphate, chloride, or nitrate. So far as there is a 

 difierence, more of the base is removed from sulphate solution than from the others. 

 On comparing chemically equivalent quantities, it is seen that ammonium is taken 

 from solution in greatest degree, followed in order by potassium, magnesium, sodium, 

 and calcium. As to the bases dissolved from the soil, Kiillenberg's conclusion is that 

 for the absorbed base nearly equivalent quantities of other bases, already present in 

 the soil, have been carried over into the solution.^ 



"When the solution is alkaline in reaction, containing a soluble hydroxide die- 

 solved as such or a salt made up of a strong base and a weak acid (as the carbonates, 

 silicates, and phosphates of sodium and potassium), which is hydrolyzed by water 

 with resulting formation of free alkali, its behavior with clay, soils, etc., is due largely 



1 The Soil Solution: Cameron, p. 59. 2 BuI. 312, U. S. Geol. Survey, p. 27. » Ibid., p. IG. 



