342 CONNECTION OF THERMAL SPRINGS IN VIRGINIA 



gi'eat Limestone Valley, and at other points, where the same 

 sti'ucture exists, many thermals have been detected, several of 

 which, from their marked elevation of temperature,' are included 

 in the preceding culalogue. 



These results are, I think, sufficiently explained by reverting 

 to the two conditions above specified, in connection with the 

 form of the surface, and the position of the strata in the vicinity 

 of these faults. In the first case, where For. II. rests upon the 

 overturned beds of For. XI, the strata composing the nan-owbelt 

 of the former, along the northwest base of the great range of Pe- 

 ters's and East River Mountain, and southeast of the line of fault, 

 as well as the rocks of these ridges, dip at a moderate angle 

 towards the southeast, and therefore aiuay from the fault. On 

 the opposite, or northwestern side of the fault, the country is 

 comparatively level, the Little Mountain, which formed the west- 

 ern boundary of the Sweet Spring Valley having been ingulfed 

 in the vast hiatus. Hence, though the rocks of XI, for a short 

 distance northwest of the dislocation, (through the breadth over 

 which this formation continues inverted,) actually dip towards 

 the fault, the flat topography on the northwest is not such as 

 naturally affords a hycbostatic column sufficient to raise the water 

 from a gi-eat depth to the surface, along the line of fracture. 

 Nor could we expect the heights of Peters's Mountain on the 

 southeast to furnish such a column, since the southeast dip of the 

 strata there would rather oppose than facilitate the passage of the 

 liquid towards the fault, and would most probably convey it to 

 subterranean tracts lying still further towards the southeast. There 

 is also another feature, to which, as I conceive, some influence 

 is to be ascribed in preventing the occurrence of thermals along 

 this line. The strata of For. XI, although overturned where they 

 are in contact with For. II, continue in this position across but a 

 narrow belt towards the northwest, and by a rapid curvature be- 

 low are soon brought into a very genfle northwest dip, or into a 

 horizontal attitude. Their upturned edges could receive du-ectly 

 from the atmosphere but small supplies, and these, most proba- 

 bly, in part at least, would be conveyed away towards the gi'ad- 

 ually declining level on the northwest. 



