58 Natural History of Volcanos and Earthquakes. 



Strata, and extending from B to D, and if, lastly, the new forma- 

 tion contain impervious strata, then the conditions will undergo 

 a change. The meteoric water, which penetrates at A, between 

 each separate portion, will now all issue in the form of rising 

 springs at B, between the elevated mountain and the new strat- 

 ified formation which lies at its side. Should any obstacle here 

 present itself to its exit, the water will even take a retrograde 

 course B D, and issue at D, in which case the water between the 

 last formed horizontal stratum and the impervious stratimi lying 

 under the newest raised ones will unite with it. We will not, 

 however, enter into farther particulars, as many circumstances 

 may be supposed to exist which modify the course of the springs ; 

 and still more complicated relations naturally arise, when, after 

 the deposition of the latest formed stratum, the elevation and 

 raising are repeated. It will be sufficient to have called atten- 

 tion to the circumstance, that rising springs can exist only when 

 the originally horizontal position of the stratified formations 

 has been destroyed by elevations ; and that the most copious 

 springs, and those which arise from the greatest dei)ths are found 

 precisely at the limits between the elevated masses and the raised 

 strata. 



Numerous instances can be cited in proof of this assertion. 

 The Pyrenees and Alps, present very characteristic circumstan- 

 ces. Thus Pallasou* shows, that not only are the majority of the 

 hot springs in the Pyrenees, situated in the great granitic district 

 at the eastern side, but also, that all the others issue only from 

 hollows of the newer formations, v/here the granite rises f 

 beneath, at the foot of the declivities. He shows also, that even 

 the degree of temperature of these springs depends on the greater 

 or less exposure of their source; for the thermal springs nearer 

 the principal granitic mass are warmer, while those more remote 

 are colder. 



Professor Forbes has likewise pointed out, in an interesting 

 memoir on the temperatures and geological relations of certain 

 hot springs, particularly those of the Pyrenees,^ that, in the 

 departments of the Arriege and the Pyrenees Orientates, where 

 granite formations preponderate, in almost every case which he 



ora 



* Mem. pour servir k I'Hist. Natur. des Pyrenees, 1815, p. 435, 459 

 t PhiloB. Transact, for 1836, p. 575. 



V™^ 



