334 CONNECTION OF THERMAL SPRINGS IN VIRGINIA 



our For. VI, nearly equivalent to the Pentamerus limestone of 

 New York. 



The same conditions accompany the group of thermals marked 

 on Section IV. The strata here are more slightly inverted on the 

 northwest, and their curvature is so well preserved, even in the 

 massive beds of sandstone, (For. IV, Shawangunk grit of New 

 York,) as to present, in the gi*and exposure at Clifton forge, a vast 

 rocky arch of more than half a mile in span. 



The thermal at the southeastern extremity of Section I, is asso- 

 ciated with a different structure. The limestone (For. II) of the 

 gTeat valley is here, as in most places near the foot of the Little 

 North Mountain, thrown over upon For. III. This inversion, due 

 to a folded axis lying parallel to and southeast of that ridge, though 

 it often extends entirely through the mountain, at this point ceases 

 with the eastern outcrop of the lower beds of For. IV. At the 

 junction of Formations II and III, the latter is much crushed, and 

 a slight fault occurs. It is near this spot, in the limestone, that 

 the warm waters make their escape. The thermal, mai-ked at the 

 southeastern extremity of Section X, occurs under precisely the 

 same conditions, rising in the same rocks, thrown into the same 

 inverted attitude. 



Section V. Across the Sweet Spring Valley. 



The structure of this valley, like that of the Warm Springs, 

 is due to a great anticlinal axis. Commencing at a point south- 

 westward of the termination of the latter, this valley extends for 

 about fifteen miles in a nearly west-southwest direction, bounded 

 by the Sweet Spring or Peters's Mountain on the southeast, and 

 by the Snake Run or Little Mountain on the opposite side. Where 

 the limestone. For. II, begins to be exposed by the opening of a 

 great anticlinal range of For. Ill and IV, and for a short dis- 

 tance towards the southwest, the strata have a normal flexure, 

 those on the northwest side of the axis dipping steeply towards 

 the northwest. But as we procepd towards the southwest, the 

 flexure increasing, causes an inversion of the strata oit the north- 

 west side, accompanied by an occasional crushing and partial 

 concealment of the slate rocks of For. III. These conditions, 



