ALKALI SOILS. 



439 



below this, at 20 feet, there is a final very heavy increase, not only of 

 the total salts but especially of common salt, which evidently represents 

 the drainage toward the salt deposit. Above this level there is a very 

 remarkable predominance of Glauber's salt (sodium sulfate), also observ- 

 able elsewhere, e. g. near White Plains, Nev., whose name is derived 

 from the copious surface accumulation of the sulfate. It seems as 

 though this must have been formed in some way from the common 

 salt. 



Horizontal Distribution of Alkali Salts in Arid Lands. The 

 constant occurrence of " alkali spots " in arid lands shows at 

 once the great inequality of horizontal distribution of alkali 

 impregnation. This is as prominent in level lands as on slopes, 

 and in extremely arid regions it is mostly not possible to recog- 

 nize even very considerable differences without close examina- 

 tion. Thus in lands appearing exactly alike on the surface, 

 on the edge of the Salton basin in California, on the same forty 

 acre i.4 ( /r (56,000 pounds per acre) was found in the surface 

 four feet at one point, and a hundred yards away, i2.5'/r 

 (500,000 pounds). The mapping of alkali lands is therefore 

 somewhat precarious unless carried into great detail. More- 

 over, it has been found that the location of the salts changes 

 from year to year, especially in irrigated land, as might be ex- 

 pected. Those cultivating alkali lands have therefore to exer- 

 cise constant watchfulness, unless the salts have been defi- 

 nitively eliminated by underdrainage over a considerable area; 

 as merely local operations may be rendered ineffectual by the 

 migration of the salts from neighboring tracts not reclaimed. 



Alkuli in ffill Lands. As a rule, hill lands themselves are 

 remarkably free from alkali, even in the arid regions; except 

 when water is gathered in depressions, where strongly saline 

 waters may be found in \Vashington. Montana and elsewhere. 

 But on level plateau lands, where drainage is slow or imperfect, 

 alkali appears as freely as it does in the same regions in tiie 

 stream bottoms. In the latter the leachings and seepage ot the 

 uplands naturally causes a concentration of the salts, and thus 

 we find alkali salts incrusting the surface in the valleys of the 

 streams, as c. .. that of the Yellowstone. Musselshell. Judith. 

 Yakima and others in the north, and of (ireen river. I'latte. 

 Pecos, and Rio ("irande farther south; as well as in numerous 

 vallevs of central and southern California. 



