WITH ANTICLINAL AXES AND FAULTS. 325 



well-known fountains of the Sweet Spring Valley, which rise in a 

 region whose average is about fifty-one degrees. 



Admitting that the elevated temperature, observed in mines 

 and Artesian wells, is dependent upon a generally diffused inter- 

 nal heat, increasing with the depth, and not upon chemical or 

 volcanic agencies of local operation, the class of thermal waters, 

 as above described, ought to include a large proportion of such 

 springs as are not of superficial origin. Indeed, under any view 

 of the sources of their temperature, all springs ought to be in- 

 cluded in this class whose heat is invariable, or when liable to 

 change never sinks below the atmospheric mean of the place.* 

 Some decidedly thermal springs, as, for example, the White Sul- 

 phur Springs of Virginia, display considerable variations of tem- 

 perature with the change of seasons or of weather. It would, 

 therefore, not be correct to assume permanency of heat as the 

 criterion of thermal character, however completely, in the ordinary 

 circumstances of springs, such permanency would seem to prove 

 that the waters in which it is observed belong to the thermal class. 

 It may be fairly assumed in general, that a spring presenting a 

 uniform temperature, or one which, in its fluctuations, never 

 descends below the atmospheric mean, cannot be dependent for 

 its heat upon the atmosphere and superficial strata. Hence the 

 general dissemination of such springs over a widely extended 

 region, furnishes the strongest evidence for the existence of a pe- 

 rennial source of heat within the earth. 



As remarked by Bischoff, the coldest springs of uniform tem- 

 perature, provided they do not derive their waters from a neigh- 

 boring mountain, will exhibit the nearest approximation to the 

 average temperatm-e of the country ; but will always be a little, 

 though it may be a very little higher. Guided by these views, 

 he has shown, from extensive observations in Gerinany and other 

 parts of Europe, that thermal springs are of far more frequent 

 occurrence than had been supposed, and, indeed, that nearly all 

 the copious mineral springs there, and probably, by inference, in 



* Of course, this is intended to include springs originating in glaciers or near the tops 

 of high mountains. 



