236 



THE GEOLOGIST. 



throughout its entire length, especially in the south-eastern 

 or most disturbed side of the belt. Proceeding north-west- 

 wards or away from the quarter of greatest disturbance, 

 N.W. dips began 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 the 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 sub- 

 side at about 150 miles from the region of gneiss and intru- 

 sive 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 

 toivards the region of chief disturbance. The inverted 

 flexures are regarded by the authors as exhibiting simply a 

 higher developement 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 anti- 

 clinal or S.E. of the synclinal axes ; these dislocations, hke 

 the axes, maintain a remarkable parallelism. 



3. The axes of the Appalachian chain are distributed in 

 natural groups, the members of each group agreeing ap- 

 proximately 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 alter- 



