OF THE APPALACHIAN CHAIN. 513 



on the side of the undulated district, which borders the region 

 where the rents and dykes occur, and to it we trace the far greater 

 variety which there occurs in the size of the flexures. 



In the progress of this bending and folciing of the strata, through- 

 out the undulated district, the continual introduction and consol- 

 idation in the fissured district, of fresh materials from the liquid 

 mass beneath, rising in intrusive dykes, and filling the wide inter- 

 stices of the broken strata. Would permanently retain the inflected 

 crust in the new attitudes into which it had been forced, and 

 compensate for the reduction of horizontal breadth arising from 

 the flexures. Permanent axes might even be produced without 

 the fracturing of the crust being in all cases apparent at the sur- 

 face, since innumerable fissures, of sufficient size to permit the 

 sudden escape of an enormous quantity of elastic vapor, could 

 temporarily form, and yet close again superficially, and still the 

 strata be braced and retained in their flexured state by the dis- 

 lodgement of fragments, and the intrusion and congelation of 

 much lava matter in the lower parts of the rents. 



This theory agrees strikingly with the singularly undisturbed 

 condition of the strata, northwest of om- great lines of fault. When 

 describing, under a preceding head, some of these enormous dis- 

 locations, especially those of southwestern Virghiia, an account 

 was given of the gradual transition of structm-e, from the normal 

 to the folded or inverted form, and thence, to a successive ingulf- 

 ing of certain groups of strata, into a line of fault, presenfing some- 

 times, for the distance of seventy miles, an actual inversion of the 

 lower Appalachian limestone or slate, upon either the carboniferous 

 limestone or the next inferior group. The commencement in all 

 cases of these faults, in the steeply folded synclinal part of the flex- 

 ure, immediately on the northwest of the finally inverted anticlinal 

 curve, would seem to prove conclusively, that the fracture has 

 been due to a profound folding in and inversion of the rocks, 

 carried to the extent of producing an actual snapping asunder of 

 the beds where most incurved, followed by a squeezing down- 

 ward of the opposite side of the trough, by the horizontal north- 

 westward thrust of the anticlinal portion, causing the lower strata 

 of the latter to lie direcfly upon geologically higher gi-oups. The 



