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DYNAMICAL GEOLOGY. 



the grander uplifts have been produced by lateral movements of 

 the crust, and generally a pushing up of the formations into folds. 

 In the region of southern Virginia and northern Alabama there 

 is a series of great Appalachian faults, and successive portions of 

 the crust have been pushed up along sloping faults, bringing the 

 Lower Silurian limestones to a level with beds of the Carboniferous 



Fig. 978. 



Section of the Palaeozoic formations of the Appalachians in southern Virginia, between 

 Walker's Mt. and the Peak Hills (near Peak Creek Valley) : F, fault ; a, Lower Silurian 

 limestone; b, Upper Silurian; c, Devonian; d, Subcarboniferous, with coal beds. 



age (Subcarboniferous period) ; and plications are a minor feature 

 of the region. But more to the north, in middle and northern 

 Virginia, and in Pennsylvania, there are great folds, or synclinal 

 and anticlinal axes, with fewer great faults. 



Lesley, after explaining the relations of the eastern or Blue Ridge, the 

 Great Valley next west, the Appalachian or middle chain, and the Alleghany or 

 western, and mentioning that the eastern escarpment of the last, " overlooking 

 the Appalachian ranges with their narrow parallel interval-valleys, is the so- 

 called Backbone Alleghany Mountain," and separates the head-waters of 

 nearly all the Atlantic and Western rivers, observes that New River, in 

 southern Virginia, divides the northern region of plications from the southern 

 of great faults ; and this river is remarkable for cutting through the Appalachians, 

 and taking its rise even as far east as the Blue Ridge. He adds concerning this 

 southern district, " The Palaeozoic zone included between the Great Valley and 

 the Backbone escarpment is occupied by as many pairs of parallel mountains 

 as there are great parallel faults; and, as these faults range in straight lines at 

 nearly equal distances from each other, these mountains run with remarkable 

 uniformity side by side for a hundred or two hundred miles, and are finally cut 

 off either by short cross-faults, or by slight angular changes in the courses of 

 the great faults." This strip of country is thirty to forty miles wide, and the 

 intervals between the fractures or faults are from five to six miles wide. All 

 have a southeast dip ; a portion of the Carboniferous formation forms the south- 

 eastern brow of each, overlooking to the southeast Lower Silurian limestone, 

 and resting on Devonian and Silurian, which come into view to the northwest. 



According to the Professors Rogers, these faults in southwestern Virginia, 

 which were early described by them, occur along the axes of plications, instead 

 of in monoclinal strata. (Trans. Amer. Assoc. Geol. Nat., p. 494) 



2. The facts in accordance with the supposed origin. — The Professors 

 Rogers have referred to waves in the earth's liquid interior for an 



