Proceedings of the British Association. 359 



Sect. C. Geology and Physical Geography. 



On the Physical Structure of the Appalachian Chain, as ex- 

 emplifying the laws which have regulated the elevation of great 

 mountain chains generally ; by Professors H. D. Rogers and W. 

 B. Rogers. — The Appalachian chain of North America is de- 

 scribed by the authors as consisting of a series of very numerous 

 parallel ridges or anticlinal lines, forming a mountain belt gene- 

 rally one hundred miles in breadth, and nearly one thousand two 

 hundred miles in length, stretching from the southeast angle of 

 Lower Canada to Northern Alabama. 1. The strata which com- 

 pose this chain are the American representatives of the Silurian, 

 Devonian, and Carboniferous systems of Europe, united into one 

 group of conformable deposits. The general direction of the 

 chain being northeast and southwest, there is a remarkable pre- 

 dominance of southeast dips throughout its entire length, espe- 

 cially in the southeast or most disturbed side of the belt. Pro- 

 ceeding northwest, or away from the quarter of greatest disturb- 

 ance, northwest dips begin to appear ; at first few and very steep, 

 afterwards frequent and gradually less inclined. 2. The authors 

 consider the frequency of dips to the southeast or towards the 

 region of intrusive rocks, accounted for by the nature of the 

 flexures, which are not symmetric, the strata being more inclined 

 on the northwest than on the southeast of each anticlinal, amount- 

 ing at length to a complete folding under and inversion, especially 

 on the southeast side of the chain, where the contortions are 

 so closely packed as to present a uniform dip to the southeast. 

 These folds gradually open out, the northwest side or inverted 

 portion of each flexure becomes vertical, or dips abruptly to the 

 northwest ; proceeding further in this direction, the dips gradu- 

 ally lessen, the anticlinals and troughs becoming rounder and 

 flatter, and the intervals between the axes constantly increasing 

 till they entirely subside at about one hundred and fifty miles 

 from the region of gneiss and intrusive rocks. The authors ex- 

 press their belief that a similar obliquity of the anticlinal axes 

 will be found to obtain in all great mountain chains, their planes 

 always dipping towards the region of chief disturbance. The 

 inverted flexures are regarded by the authors as exhibiting sim- 

 ply a higher development of the same general conditions. The 

 passage of inverted flexure into faults is stated to occur frequently, 



