

if 





Ch. XVII.] 



AKTESIAN WELLS. 



391 



charge every twenty-four hours was at the rate of half a 

 million of gallons of limpid and warm water, the temperature 

 being 82° F. This implies an augmentation of 30° F. beyond 

 the average of springs in the latitude of Paris, making a rate 

 of increase of 1° F. for every 60 English feet of descent. 

 The depth at which the successive strata both tertiary and 

 cretaceous were encountered, agreed very closely with the 



most 



undertaking. 



Mr. Briggs, the British consul in Egypt, obtained water 



between Cairo and Suez, in a calcareous sand, at the depth 



of 30 feet; but it did not rise in the well.* But othei 



borings in the 



same 



depth, between 50 



and 300 feet, and which passed through alternations of sand, 

 play, and siliceous rock, yielded water at the surface. t 



The rise and overflow of the water in Artesian wells is 



same 



principle as the play of an artificial fountain. Let the porous 

 stratum or set of strata, a a, rest on the impermeable rock d, 



— r* # "IT i 



mass 



Fig. 27. 



mass a a may 



become 



may descend from 



and exposed parts — a hilly region to which clouds are at- 

 tracted, and where rain falls in abundance. Suppose that at 



some point, as at &, an opening be made, which gives a free 



passage upwards to the waters confined in a a, at so low a 

 level that they are subjected to the pressure of a considerable 

 column of water collected in the more elevated portion of 



s 



Boue" Resume des Prog, de la Geol. 

 en 1832, p. 184. 



f Seventh Rep. Brit. Ass. 1837, p. M. 



