THE CHEMISTRY OF UNDERGROUND WATERS. 819 



faults, which descend to an indefinite depth, far below any point 

 which it is possible for us to reach. Generally, they serve only for 

 the direct descent of waters which, having been swallowed into them, 

 find a little farther down an outlet from which they issue still cold. 

 But it also happens, and the fact should be kept clearly in mind, that 

 a fault offers a return route to water which has been heated at great 

 depths. This is the case at Bourbonne-les-Bains. In the Alps, ac- 

 cording to M, Lory, the same fault feeds the thermal springs of Mo- 

 nestier, Briangon, Brides, and Salines near Montiers. The fault which 

 cuts and terminates the chain of the Alps near Vienna in Austria is 

 the emissary of a considerable number of spi'ings. Most of them are 

 cold ; but some hot springs, as those of Baden and Voslau, are ranged 

 along a distance of eleven kilometres. 



The return branch of these natural siphons is often filled up and 

 obstructed by incrustations which the water has formerly made, so as 

 to form metalliferous veins. If the obstruction is not complete, or if 

 it has been opened by raining excavations, these veins may be still 

 serving for a way of ascent. A passage pierced at Plombi^res some 

 thirty years ago in the granitic flank of the valley for the regulation 

 of the warm waters, cut several veins of quartz and fluor-spar, along 

 the sides of which springs gushed out forcibly. A similar incident 

 took place at Lamalon, in Herault, where it became necessary to stop 

 the working of the veins of copper and lead, in order not to compro- 

 mise the existence of the thermal establishment, the source of which 

 was only a few dozen metres away. In the Comstock lode torrents 

 of water having a temperature of 158° Fahr. gave out such heat that 

 the workmen had to use ice to cool their shafts ; and after twenty 

 years of most profitable operation the mines became the object of great 

 expenditures to obviate this difficulty. 



It is for the most part in the neighborhood of extinct volcanoes 

 and rocks of a volcanic nature that faults produce thermal spoutings. 

 While such springs are usually wanting in the greater portion of the 

 French central granitic plateau, they abound in those regions of the 

 same plateau which are traversed by volcanic rocks. 



There is no reason, therefore, to be surprised at finding the region 

 of active volcanoes itself rich in emanations of this kind. Puzzuoli, 

 BaijB, and the baths of Nero, are situated near the solfataza of Puz- 

 zuoli and the ancient craters of Agnano and Lake Avemus. On the 

 island of Ischia, as at Guadeloupe, the hot waters gush copiously 

 from the flanks of the volcanoes. 



We also observe near volcanoes boiling water violently projected 

 into the air by torrents of vapor. The noise they make, Avhich is like 

 that of a steam-boiler, has caused the name of " Steamboat Springs " to 

 be given to a group of this kind in the State of Nevada. Such springs 

 are in close analogy with others in which the water is forced up, in 

 the shape of a tall column, by intermittent eruptions. The latter have 



