GENERAL OBSERVATIONS. 407 



5. They are in numerous ranges ; but, while some are of very 

 great length, there is in general a commingling of shorter flexures, 

 and often they are in groups of overlapping lines (fig. 624), as 

 explained, with reference to the arrangement of the parts of 

 mountains, on pp. 19 and 20. 



6. Although many of the folds were like mountains in dimen- 

 sions, they have been so worn and removed by denuding waters — 

 either those of the ocean or rivers, or of both — that the higher parts 

 of the folds do not generally form the summits of existing eleva- 

 tions. The fissures of the broken mountains would have been 

 deepest and most numerous in the axes of the folds ; and hence de- 

 nudation has been most destructive along the more elevated por- 

 tions. 



7. Over the more eastern part of the Appalachian region and the 

 Continental border the folds were generally so pressed over to the 

 northwest that their tops projected westward, and, consequently, 

 both the southeast and northwest sides have a common dip to the 

 southeast (fig. G23) ; and, as these regions have been since denuded, 

 nothing remains in many parts but a series of strata dipping all 

 alike to the southeast. (See p. 107.) 



A uniform series of southeast dips over such a region is evidence 

 that the strata correspond to a number of decapitated folds. 



2. Faults. — Besides the remarkable plication of the earth's crust 

 in this Appalachian revolution, numberless fractures and faults or 

 dislocations occurred over the whole region, as was natural under 

 the contortions and uplifts in progress. Some of the faultings were 

 of great extent, lifting the rocks on one side of the line of fracture 

 5000 or 10,000 feet above the level on the other side. The faults 

 mentioned on p. 198 are of this character, and part of the series 

 there alluded to was probably made at this time. There is one of 

 these great faults west of the Cumberland Mountains, in eastern 

 Tennessee, well shown in the map and sections by Safford. In 

 southwestern Virginia there are faults, according to Eogers, of seven 

 or eight thousand feet. One remarkable line of this kind extends 

 along the western margin of the Great Valley of Virginia, through- 

 out the chief part of its length, along by the ridge (on the north- 

 west side of the valley) named in its different parts the Little North 

 Mountain, North Mountain, and Brushy Eidge. In some parts the 

 Lower Silurian limestone is brought into conjunction with beds but 

 little below the Subcarboniferous limestone, so that there is a tran- 

 sition from the lower strata to the upper in simply crossing the 

 fault. In some places there is an inversion of the strata, so that 

 a bed of semibituminous coal of the upper beds is found under the 



