of Overjlowing Wells. 161 



The springing of cold mineral gaseous waters may be assimi- 

 lated to that of the compression fountain. 



The circumstances of springs which flow out upon the decli- 

 vities of hills, nearly at a constant height in stratified countries, 

 and particularly in those composed of alternate layers of sand 

 and clay, establish and characterize that disposition of water 

 which we have said to be in sheets, and whose origin is due 

 either to subterranean effusions coming from higher countries, 

 or to infiltrations of snow and rain water arrested by these 

 claybeds. 



This sheet of water has been likened by Professor Hachette * 

 to a layer of ice of a similar form to a layer of clay, sand, or 

 chalk. If the water is considered as occurring there between 

 two curved surfaces, such as two sections or basins of different 

 diameters, whose upper edges are in a plane, or irregularly in- 

 dented, or partly closed, the liquidity of the water is the cause 

 of the pressure which the tube of the bored well measures ; but 

 if, in place of a sheet of fluid water, there be supposed a layer 

 of ice, the pressure would resist, and would not be indicated 

 by the tube, and it would be changed in its power of cohe- 

 sion. 



Whatever be the manner in which water spreads under 

 ground, in descending from higher to lower grounds, whether 

 in sheets or in veins, stripes or torrents, when it happens to 

 meet with an issue of any kind in the ground, it insinuates it- 

 self into it, and rises to a height corresponding to the level of 

 its point of departure, or rather to a height which balances the 

 pressure which the water exercises against the walls of the ca- 

 nal which contain it f . Hence arise the spouting fountains or 

 natural jets-d'eau, which occur in secondai'y formations. 



Whence it follows, that, to obtain a spouting fountain, we 

 must, 1st, Try, according to the nature of the ground, at a 

 greater or less depth, to reach a flow of water coming from 

 higher basins, and passing along, in the bosom of the earth, 



• M. Hachette, Considerations sur recoulcment des liquides. 

 f Memoir by M. Bairoi.s, on Bored Wells : Societc- ilcs Sciences de Lille, 

 1825. 



APRIL — JUNE 1830. L 



