POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 23 



found not only in the laboratory, but also under natural conditions. The replace- 

 ment of sodium in silicates by the potassium of a dissolved salt takes place far more 

 readily than the reverse reaction. A similar reaction, although perhaps not quite so 

 marked, exists between magnesium and calcium silicates. The transformation of a 

 magnesium silicate by calcium chloride into calcium silicate is more difficult than 

 the reverse change." ^ 



The most significant fact of absorption phenomenon is the greater susceptibility of 

 potassium to be absorbed than any of the bases and the greater resistance of potassium 

 compounds to the action of percolating waters. The acid radicals, with the excep- 

 tion of carbonic, bicarbonic, and phosphoric, are unaffected in quantity. 



The restricted and irregular rainfall of the basin region would result in more con- 

 centrated solutions being received by the seepage zone, and would result, therefore, 

 in a greater relative amount of absorption than with the less concentrated solutions 

 of humid regions. 



A further fact must be kept in mind, and that is that a considerable part of the 

 basin area receives such a scanty rainfall that only on comparatively steep slopes 

 do the percolating waters reach ground-water levels and add their quota of soluble 

 material to underground circulating waters. The greater part of the intermountain 

 area acts like a sponge and receives and retains the waters and their dissolved salts. 

 Capillarity raises a part of the water, together with such soluble material as escapes 

 absorption. 



Vegetation also plays an important part. It is a well-known fact that plants absorb 

 potassium salts from the soil and seepage water. The amount of potassium removed 

 annually in this way from ground waters must be large. 



We are justified in the conclusions that in the basin region a large part of the soluble 

 salts is retained in the interstitial or pore spaces of the soil; a part of the soluble 

 material is changed to insoluble, and potassium is more likely to be retained and 

 in greater relative amount than any of the other bases; a precipitation of the 

 more insoluble carbonates, such as lime and magnesia, takes place in the upper part 

 of the soil; that the stronger acids, such as chlorine, sulphuric anhydride, nitric, 

 and boric (excepting sulphuric and boric in the presence of soluble lime salts) are 

 practically undiminished by absorption phenomena. Combined with various bases 

 they either remain in the soil or are leached away in the ground water. 



Soluble salts reach the sinks or lowest parts of the intermountain areas in two ways — 

 by underground waters which gravitate to the low points and by the run-off waters 

 which accumulate in the same places. It is evident that in the passage of the seepage 

 water to the sink absorption continues and only a final residuum, which maybe only 

 a small part of the original total of soluble salts, reaches the sink. The run-off waters 

 are diminished on their way to the sink by seepage waters with consequent loss of a 

 part of the dissolved salts. Figure 2 illustrates the various losses which we may 

 expect in the movement of a soluble salt from the weathering zone to the sink. I 

 have taken potassium as the base to best illustrate the point. The quantitative side 

 of the problem can not be determined and consequently the figure does not involve 

 this feature. 



The case for sodium would be simpler than for potassium. Little or none of this 

 base would be retained by plants or by chemical absorption, and the only loss would 

 be that portion retained and brought by capillarity to the surface or retained simply 

 by the soil. The greater part of the sodium, either as sulphate or chloride, would 

 eventually reach the sink. 



The case for lime and magnesia is also a simple one. Only that portion in the run-off 

 waters would reach the sink. The remainder would be found distributed from and 

 within the zone of weathering to the sink. The greatest part would be nearest the 

 belt of weathering. A nominal amount would reach the sink thro.ugh the agency of 

 ground waters.^ 



1 Bui. 312, U. S. Geol. Survey, p. 22. 



2 Calcareous hardpans are not infrequently found in the Great Basin. In the vicinity of Las Vegas, Nev., 

 there is an especially good illustration of the development of a thick layer of calcareous material. This 

 in some places forms the surface and in other places is covered by a thin soil. The rocks of the neighboring 

 mountains are sandstones and limestones. An analysis of this hardpan shows the following (analysis by 

 J. A. CuUen, Bureau of Soils): 



Per cent. 



Insoluble 7. 6 



Ferric oxide and alumina 46 



Lime 37. 20 



Magnesia 12. 65 



Total potash 30 



Total soda 39 



Sulphate radical 03 



I have also noted many instances where the material of gulch dumps in the basin mountains has been. 

 cemented together by calcium carbonate. 



In the alluvial fans it is not uncommon to find the material removed by the burrowing of small animals 

 to be coated by calcium carbonate. 



