OF THE APPALACHIAN CHAIN. 503 



are, however, comparatively rare, and are confined chiefly to the 

 divisions of the chain in which the curvature is convex to the 

 northwest. A more common linear form among the longer 

 curving axes, if we except those, — the longest and most regular 

 of all, — which traverse the gi*eat northwestern coal region, is one 

 which embraces a partial discontinuity of the line, at one or several 

 points. This discontinuity is, in most cases, only partial, being of 

 the nature of a warp, the anticlinal arch embracing, generally on 

 its southeastern slope, another flexure, which either immediately, 

 or at a moderate distance, becomes the principal, and finally the 

 only, anticlinal crest, while the original summit, in its turn, sub- 

 sides upon the flank of the other. In such cases, where the two 

 closely overlapping flicxures are included within one general an- 

 ticlinal arch of about the same average breadth and height as the 

 parts which contain the flexure in its single state, and where the 

 relative depression embraced by the warp is comparatively trivial, 

 there seems no impropriety in considering the whole as one great 

 undulation, locally disturbed, from some inequality in the bend- 

 ing or resisting forces. The warp will, in fact, be found, in such 

 cases, to occur commonly near the central portion of the line, 

 where the maximum degi-ee of flexure and elevation, in all strictly 

 continuous axes, has been experienced, and exactly where we 

 would naturally look for the greatest in-egularities in the move- 

 ment of the strata. 



When the bearing of the various phenomena of curving axes 

 upon some of the most interesting questions of geological dynam- 

 ics is contemplated, the importance of a critical investigation of 

 all their modifications of form cannot fail to be recognized. Be- 

 sides demanding their proportion of attention, in any theory which 

 attempts to explain the origin of axes, generally, these curving 

 axes of our Appalachian region merit particular examination in 

 another light. They appear to contradict directly the well known 

 hypothesis of the disflnguished French geologist, M. Elie de 

 Beaumont, which supposes, that a constant relation subsists be- 

 tween the epoch of elevation, and the directions or strikes of the 

 lines of disturbance. These curving axes constitute so many in- 

 termediate links between the straight divisions of the chain, in 



