ix.] DANGERS ATTENDANT ON IRRIGATION 287 



canals pouring large volumes of water upon the land 

 may equally establish the capillary connection between 

 the subsoil salts and the surface. The following extract 

 from Bulletin No. 14, U.S. Dept. of Agric, Div. of Soils, 

 dealing with alkali soils in the Yellowstone Valley, 

 shows the evil effects of incautious irrigation : 



" Irrigation has been practised for twelve or fifteen 

 years. The water for the main ditch supplying the 

 valley is taken out of the river nearly 40 miles above 

 the town of Billings. When the country was first settled, 

 and indeed above the ditch at the present time, the 

 depth to standing water in the wells was from 20 to 50 

 feet, and there were no signs of alkali on the surface of 

 the ground. Under the common practice of irrigation, 

 however, an excessive amount of water has been applied 

 to the land, and seepage waters have accumulated to 

 such a degree that water is now secured in wells at a 

 depth of from 3 to 10 feet in the irrigated district, while 

 many once fertile tracts on the lower levels are already 

 flooded, and alkali has accumulated on them to such an 

 extent that they are mere bogs and swamps and alkali 

 flats, and the once fertile lands are thrown out as ruined 

 and abandoned tracts." 



Nor is it necessary that the subsoil be charged with 

 salts for irrigation to produce alkali land; the mere 

 continual evaporation of ordinary river or spring water 

 may cause such an accumulation of saline matter at the 

 surface as is harmful to vegetation. This is well seen in 

 Egypt, where perennial irrigation is practised with the 

 Nile water, and the following quotation from Willcock's 

 Egyptian Irrigation will explain the action that takes 

 place : 



"The introduction of perennial irrigation into any 

 tract in Egypt means a total change in crops, irrigation, 

 and indeed everything which affects the soil. Owing to 



