Aug. 13, I9I7 Origin of Alkali 333 



little way down into the subsoil, from which they rise to the surface by the evaporation 

 of the water, and are thus accumulated at, and close to, the very top of the soil, often 

 in the form of crusts or crystals. It is right there that nearly all the damage is done; 

 the water in the depths of the soil is very rarely strong enough to hurt the roots of 

 plants, directly. 



These direct quotations probably will represent the teachings of Hilgard 

 regarding the origin of the alkali of arid soils. 



Hilgard also emphasized the necessity of care in the use of saline 

 irrigation waters (6, p. 41), which may intensify the alkali condition of 

 the soil. 



Many of the Experiment Stations of the West have published bulletins 

 and reports dealing with the alkali question, but they have simply 

 adopted Hilgard 's conception of the origin of alkali and present no new 

 views on the question. 



A notable exception is found in the work of Buffum, v/ho suggests a 

 different origin (2, p. 219). He says: 



In the Wheatland district, although the rainfall is too small to produce crops, and 

 all farms are irrigated, no injurious alkali has appeared upon any of the uplands under 

 cultivation. The soil of the uplands here is colluvial and derived from earlier geological 

 formations which do not supply the alkali salts. 



This view was further advocated by Slosson (8, p. 40) : 



The principal source of the alkali is not, however, the water used in irrigation, but 

 the beds of soluble salts that are deep in the soil. As soon as water is put on the land 

 these salts are drawn to the surface by evaporation. 



Soon after the organization of the Bureau of Soils of the United States 

 Department of Agriculture its attention was directed to the alkali prob- 

 lems of the West. Regarding the origin of alkali in certain soils at 

 Billings, Mont., Whitney and Means (11, p. 35) say: 



The results of these investigations show that the ultimate source of the alkali is in 

 the sandstone, and particularly in the shale or slate rocks from which the soils have 

 been derived. 



It is, however, not clear as to the condition in which they occur or the 

 manner of the transfer to the soils. Fortunately in a later publication 

 (4, p. 10) of the Bureau additional information is furnished upon this 

 point. 



In a few cases the genesis of alkali can be clearly traced. For instance, in the 

 Billings area, Montana, * * * it seems obvious that the source of the material is 

 found in the sulphides of iron prevalent in the Fort Benton shales, which on expostu-e 

 to the air oxidize to the sulphates and then on contact with water hydrolyze, forming 

 sulphuric acid and ultimately the sulphates of the alkalies and alkaline earths. 



Various other theories are also discussed regarding the origin of alkali, 

 such as deposition from wind-blown spray and Cameron's (4, p. n) con- 

 ception of the derivation of alkalies by means of hydrochloric and sul- 

 phuric acid resulting from the weathering of the original rock, which, as 

 Clarke shows (3, p. 17), contains an average of 0.07 per cent of chlorin 

 100303°— 17 2 



