ARTESIAN WELLS. 463 



by deep boring appear to be primarily due to infiltration from 

 bighlands where tlie water is first collected in superficial or sub- 

 terranean reservoirs. By means of channels conforming to tbe 

 dip of the strata, these reservoirs communicate with the lower 

 basins, and exert upon them a fluid pressure sufficient to raise a 

 column to the surface, whenever an orifice is opened."* The 

 water delivered by an artesian well is, therefore, often derived 

 from distant sources, and may be wholly unaffected by geograph- 

 ical or meteorological changes in its immediate neighborhood, 

 while the same changes may quite dry up common wells and 

 springs which are fed only by the local infiltration of their own 

 narrow basins. 



In most cases, artesian wells have been bored for purely eco- 

 nomical or industrial purposes, such as to obtain good water for 

 domestic use or for driving hght machinery, to reach saline or 

 other mineral springs, and recently, in America, to open fount- 

 ains of petroleum or rock-oil. The geographical and geological 

 effects of such abstraction of fluids from the bowels of the earth 

 are too remote and uncertain to be here noticed ; f but artesian 



1864, p. 619 ; Stoppani, Corso di Oeologia, i., 281 ; Desor, Die Sahara, Basel, 

 1871, pp. 50, 51. 



* It is conceivable that in shallow subterranean basins superincumbent min- 

 eral strata may rest upon the water and be partly supported by it. In such 

 case the weight of such strata would be an additional, if not the sole, cause of 

 the ascent of the water through the tubes of artesian wells. 



The ascent of petroleum in the artesian oil-wells in Pennsylvania, and, in 

 many cases, of salt-water in similar tubes, can hardly be ascribed to hydro- 

 static pressure, and there is much difficulty in accounting for the rise of water 

 in artesian wells in many parts of the African desert on that principle. Per- 

 haps the elasticity of gases, which probably aids in forcing up petroleum and 

 saline waters, may be, not unfrequently, an agency in causing the flow of 

 water in common artesian borings. It is said that artesian wells lately bored 

 in Chicago, some to the depth of 1,600 feet, raise water to the height of 100 

 feet above the surface. What is the source of the pressure? 



f Many more or less probable conjectures have been made on this subject, 

 but thus far I am not aware that any of the apprehended results are 

 actually shown to have happened. In an article in the Annalea des Fonts et 

 Chaussees for July and August, 1839, p. 131, it was suggested that the sinking 

 of the piers of a bridge at Tours in France was occasioned by the abstraction 

 of water from the earth by artesian wells, and the consequent withdrawal of 

 the mechanical support it had previously given to the strata containing it 



