OF THE APPALACHIAN CHAIN. 501 



normal flexures in the great valley, in that part of the chain which 

 we have called the Potomac division. Some of the larger axes 

 are there prolonged, side by side, for nearly one hundred miles. 

 The same fact may be equally well seen in the great curving axes 

 of the Juniata division, and amongst those most remarkably per- 

 sistent flexures, which divide the parallel bituminous coal-fields 

 northwest of the Allegheny mountain, in Pennsylvania and Vir- 

 ginia. It is yet more strikingly displayed, perhaps, in the long 

 and singularly straight axes and faults of the Holston region, in 

 Virginia and Tennessee, where the lines, both of flexure and of 

 dislocation, maintain almost exactly the same distance from each 

 other for upwards of one hundred and fifty miles. This parallel- 

 ism, however, is after all but approximate, though, as many of the 

 adjacent axes of a group in a length of say fifty miles, observing a 

 mean distance of not more than two or three miles, seldom ap- 

 proach or recede more than a fourth of this space, we are justi- 

 fied in seeking for some theory ^vhich shall explain so conspicu- 

 ous a relation. 



6th. Of the great length of some of the axes. Perhaps nothing 

 astonishes the geological traveller in the Appalachian chain, so 

 much as the enormous length and persistency of many of the 

 axes. Tracing these Jines of flexure longitudinally, they will not 

 unfrequently be found to range for eighty or one hundred miles, 

 with but little deviation either from perfect straightness, or from 

 a uniform gradual curvature, parallel to the general inflection of 

 the division of the chain, in which they are included. This as- 

 tonishing regularity and length is, perhaps, best noticed in the 

 axes of the northwestern side of the belt, where they frequently 

 exhibit a steady curvature, for more than one hundred and fifty 

 miles. Whether the southeastern axes are less prolonged, or 

 whether their crowded condition often conceals the continuity of 

 their range, are points we do not at present undertake to decide. 

 Among the very numerous instances of long and regular axes of 

 the steep normal type, we must specify, in the Susquehanna re- 

 gion, the straight axis of Montour's ridge, which extends about 

 eighty miles ; in the Juniata division, the beautifully inflected axis 

 of Jack's mountain, continuous for more than ninety miles ; in 



