ALKALI SOILS. 



453 



the latter causing a reversal of the formation of sodic carbonate 

 that had been induced by the former. 



Exceptional Conditions. While the phenomena of alkali 

 lands as outlined above probably represent the vastly predomi- 

 nant conditions on level lands, yet there are exceptions due to 

 surface conformation, and the local existence of sources of 

 alkali salts outside of the soil itself. Such is the case where 

 salts ooze out of strata cropping out on hillsides, as at some 

 points in the San Joaquin Valley in California, and in parts of 

 New Mexico, Colorado and Wyoming; also where, as in the 

 Hungarian plain, saline clays underlie within reach of surface 

 evaporation. 



Again, it not infrequently happens that in sloping valleys or 

 basins, where the central (lowest) portion receives the salts 

 leached out of the soils of the adjacent slopes, we find belts of 

 greater or less width in which the alkali impregnation may 

 reach to the depth of ten or twelve feet, usually within more or 

 less definite layers of calcareous hardpan, likewise the outcome 

 of the leaching of the valley slopes. Such areas, however, are 

 usually quite limited, and are at present scarcely reclaimable 

 without excessive expenditure ; the more as they are often un- 

 derlaid by saline bottom water. In these cases the predominant 

 saline ingredient is usually common salt, as might be expected 

 and as is exemplified in the Great Salt Lake of Utah, in the 

 Antelope and Ferris Valleys, and in Salton basin in California; 

 in the Yellowstone valley near Billings, Mont. 1 in the Aralo- 

 Caspian desert, and at many other points. 



Conclusions. Summing up the conclusions from the fore- 

 going facts and considerations, we find that 



1 i ) The amount of soluble salts in alkali lands is usually 

 limited ; they are not ordinarily supplied in indefinite quantities 

 from the bottom-water below. These salts have mostly been 

 formed by weathering in the soil-layer itself. 



(2) The salts move up and down within the upper four or 

 five feet of the soil and subsoil, following the movement of the 

 moisture; descending in the rainy season to the limit of the 

 annual moistening as a maximum, and then reascending or not, 

 according as surface evaporation may demand. At the end of 



