492 OF THE PHYSICAL STRUCTURE 



In the Bvll Pasture mountain, which traverses Pendleton and 

 a portion of Bath counties, in a line southeast of the range above 

 described, we have an example of the retention of the normal 

 structure throughout the entire length of the axis, embracing a 

 distance of more than fifty miles. Here, also, we witness the 

 gradual steepening of the flexure, as lower and lower groups are 

 elevated to the surface, although the whole amount of the eleva- 

 tory movement, having, in this case, been less than in that of the 

 Knobly axis, it has nowhere produced an actual inversion of the 

 dip. 



The interesting relation here disclosed between the steepness 

 of the flexure, and the amount of actual rise of the rocks, at dif- 

 ferent points in the axis, extends to all the shorter, as well as the 

 most prolonged of these lines, and applies to every part of the 

 Appalachian chain, constituting a law of structure, connected in- 

 timately with the theory of the nature of the folding movement. 



Besides the above cases, we may cite, for Pennsylvania, the 

 great axis of Wills's Creek mountain, that of the Black Log an- 

 ticlinal valley, and the still more prolonged one of the Kishico- 

 quillas valley, and Jack's mountain, in all three of which the 

 normal type is preserved, while the relation between the degree 

 of developement of the axis and the steepness of the northwestern 

 dips, as already announced, is uniformly displayed. 



2nd. Inverted Flexures. As indicated in the general or ideal 

 Section of the chain, the flexm*es, accompanied by an inversion of 

 the strata on the northwestern side, are of most frequent occurrence 

 along the southeastern border of the Appalachian chain. In some 

 districts, however, these foldings extend, for a considerable distance, 

 across towards the middle of the belt, a fact well exemplified in 

 the general southeasterly dip of the Pottsville coal-field. The pas- 

 sage from the normal to the closely folded inverted curvature, as the 

 developement of the axis increases, is a phenomenon well ob- 

 served in a number of the principal anticlinal ranges in Pennsyl- 

 vania and Virginia, among which may be instanced the Bald 

 Eagle axis, in the former State, and the Jackson's mountain and 

 the Wolf creek axes, in the latter. 



The Bald Eagle axis, commencing some miles south of HoUi- 



