40 IRRIGATION FARMING. 



depth to the earth's stratifications, through which thev 

 have percolated from higher sources, either open or hid- 

 den, and generally in either case at great distances from 

 the artesian channel proper. These waters are neces- 

 sarily not nearly so available as the more readily attained 

 surface supplies, and are to be developed only in urgent 

 cases and in the places where a surface supply is not 

 accessible. Underflow waters are sometimes brought to 

 the surface by the gravity process. This is possible in 

 the sandy beds of many Western streams a greater por- 

 tion of the year. Phreatic waters usually abound within 

 100 feet of the surface and are raised chiefly by pumps, 

 while the deep artesians have an invisible power, which 

 forces the water to the top in ever-flowing streams. 

 Later chapters in this work will bear upon these subter- 

 ranean waters more fully. 



Tunneling for Water. In California where fruit 

 crops form the main agricultural pursuits, the rather 

 expensive plan of tunneling the high mountains for 

 water supply has been successfully carried out in many 

 places. The work has been done mostly by organ- 

 ized companies with plenty of capital, the object being 

 to make salable the adjacent tracts of foothill land-. 

 which for several reasons are best adapted to fruit cul- 

 ture. These tunnels are opened by means of diamond 

 drills operated with the power of compressed uir sup- 

 plied by an air pump, at the opening of the drift. As a 

 rule the tunnels are less than 1000 feet in length, and arc 

 run in such a way as to tap the various shelving stratifi- 

 cations of formation, which carry more or less quantities 

 of pure water seeking its level from the higher mountains. 

 The plan is practicable in supplying a satisfactory head of 

 water to fill an ordinary ditch, but before such a heavy 

 undertaking is commenced the services of a geologist or 

 hydraulic engineer should be called to determine the 

 nature of the mountain's interior, especially as to the 



