DAMS. 207 



It is obvious that the use of the rollers here suggested 

 is only applicable to the grain crops, and not for those 

 that are to be cultivated. 



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i A U 



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CHAPTER K V ALL. 



THE SUPPLY OF WATER. DAMS. PUMPS. RESERVOIRS. 

 ARTESIAN WELLS. 



DAMS. For extensive irrigation, the available supply 

 of water can be found only in permanent streams ; large 

 and copious wells, from which the water is raised by 

 pumps of great capacity, operated by steam, or in ex- 

 tensive reservoirs, in which the drainage of large areas 

 of mountain territory is collected. No dependence can 

 be placed upon artesian wells, though the contrary has 

 been erroneously taught by some writers having a limited 

 acquaintance with this subject. This expectation has 

 been shown in a previous chapter, to be delusive, both on 

 account of the limited supply of water that can be thus 

 obtained, and the costliness of the system. For excep- 

 tional cases, these wells may be employed with profit. 

 These cases will be found to exist where extensive water- 

 bearing strata are depressed in a basin shaped area, at a 

 moderate depth beneath the surface, so that a copious 

 and permanent supply can be procured at a moderate 

 cost, and where the area to be irrigated is small. The 

 futility of depending upon artesian wells, in other cases 

 than those above cited, will be evident when the principle 

 upon which they operate, is explained further on in this 

 chapter. 



For the present, and for many years to come the main 



