568 Proceedings of the British Association, 



The Appalachian Chain of North America is described by the authors 

 as consisting of a series of very numerous parallel ridges or anticlinal 

 lines, forming a mountain belt generally 100 miles in breadth and 

 nearly 1,200 miles in length, stretching from the South-eastern angle of 

 Lower Canada to Northern Alabama. 1. The strata which compose 

 this chain are the American representatives of the Silurian, Devonian, 

 and Carboniferous systems of Europe, united into one group of con- 

 formable deposits. The general direction of the chain being N.E. and 

 S.W., there is a remarkable predominance of S.E. dips throughout its 

 entire length, especially in the south-eastern or most disturbed side 

 of the belt. Proceeding north-westwards, or away from the quarter 

 of greatest disturbance, N.W. 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 S.E. 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 N.W. than on 

 S.E. of each anticlinal, amounting at length to a complete folding under 

 and inversion, especially on the S.E. side of the chain, where the 

 contortions are so closely packed as to present a uniform dip to the S.E. 

 These folds gradually open out, the N.W. side or inverted portion of 

 each flexure becomes vertical, or dips abruptly to the N.W. ; proceeding 

 further in this direction the dips gradually lessen, the anticlinals and 

 troughs becoming rounder and flatter, and the intervals between the 

 axes constantly increasing till they entirely subside at about 150 miles 

 from the region of gneiss and intrusive rocks. The authors express 

 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 simply a higher development 

 of the same general conditions. The passage of inverted flexure into 

 faults is stated to occur frequently, and invariably along the N.W. side 

 of the anticlinal or S.E. of the synclinal axes ; these dislocations, like 

 the axes maintain a remarkable parallelism. 3. The axes of the Appa- 

 lachian chain are distributed in natural groups, the members of each 

 1 group agreeing approximately in length, curvature, amount of flexure, 

 and distance apart. Nine principal groups are described, in five of 

 which the axes are straight, whilst the four which alternate with them 

 are curved ; in two of the curved divisions the line of strike is convex 

 to the N.W., in the other two it is convex to the S.E. In every part of 

 the chain the axes, whether curved or straight, maintain an ap- 

 proximate parallelism to those of their own division, and in the minor 



