648 



.DYNAMICAL GEOLOGY. 



All wells and springs are tappings of these subterranean waters. 

 The large size of some of these under-ground rivers is proved by- 

 direct observation in caverns, where they have the variety of cas- 

 cades and quiet waters which characterizes the streams of the sur- 

 face. The Mammoth Cave of Kentucky, and the Adelsberg, twenty- 

 two miles northeast of Trieste, are examples. And, again, some- 

 times, as in the Jura Mountains of Switzerland, they come out of 

 the hills with sufficient force and volume to turn the wheel of a 

 large mill. 



The outward flow of the under-ground waters of a continent pre- 

 vents the in-flow of the salt water on sea-shores. Springs are com- 

 mon on shores ; occasionally their waters rise in large volume in a 

 harbor, or out at sea some miles distant from a coast. 



If subterranean streams have their rise in elevated regions, their 

 inferior portions beneath the plains of a country must be under 

 great hydrostatic pressure ; and this should appear, whenever a 

 boring is made to the waters, by their rising above the surface in a 

 jet. Borings of this kind have been made in many parts of Europe 

 and America with this effect. They were first attempted in France, 

 and are called Artesian wells, from the district of Artois, in France, 

 where they were early used. 



In fig. 943, let a b represent Fi S- 943 



an argillaceous stratum on 

 which the water descends, 

 and b c the boring ; bed is the 

 jet of water. The rise of the 

 jet falls far short of the height 

 of the source, because of the 

 great amount of friction along 

 the irregular rocky bed of the 

 stream, and also the resistance 

 of the air. 



It is possible that in some cases subterranean waters may be 

 under pressure from a stratum of gas over them, which is sufficient 

 to send them to the surface without other aid. 



Section illustrating the origin of Artesian wells. 



The Artesian well of Grenelle, near the Hotel des Invalides, in Paris, is 2000 

 feet deep. At 1800 feet, water was struck, and it darted out to a height above 

 the surface of 112 feet and at the rate of nearly one million of gallons a day. 

 The pressure indicated by the jet was equal to that of a column of water 2612 

 feet high, or 1160 pounds to the square inch. 



Another well, in Westphalia in Germany, is 2385 feet deep. 



An Artesian boring at St. Louis has been carried to a depth of 2200 feet; but 

 the water obtained is not pure. One at Louisville, Kentucky, 2086 feet deep, 



