360 Proceedings of the British Association. 



and invariably along the northwest side of the anticlinal or south- 

 east of the synclinal axes ; these dislocations, like the axes, main- 

 tain a remarkable parallelism. 3. The axes of the Appalachian 

 chain are distributed in natural groups, the members of each 

 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 al- 

 ternate with them are curved : in two of the curved divisions 

 the line of strike is convex to the northwest, in the other two it 

 is convex to the southeast. In every part of the chain the axes, 

 whether curved or straight, maintain an approximate parallelism 

 to those of their own division, and in the minor groups within 

 the large divisions the parallelism is still more exact. The axes 

 vary in length from insignificant flexures to lines frequently one 

 hundred and sometimes one hundred and fifty miles in length, 

 and they deviate very little from a rectilinear course, or, as the 

 case may be, from a uniform rate of curvature. Some of the 

 longer curved axes exhibit a difference of strike at their extremi- 

 ties of fifty miles in a distance of ninety miles, and the recti- 

 linear axes of different divisions vary in their line of direction as 

 much as 60°. As all the flexures were undoubtedly formed at 

 one period, the authors consider these facts at variance with M. 

 Beaumont's hypothesis, that dislocations of the same geological 

 age are parallel to one and the same meridian. 4. The general 

 declension in level of the Appalachian strata towards the north- 

 west or away from the quarter of greatest local disturbance, is 

 considered, by the authors, important in its bearing upon the 

 subject of the elevation of broad continental tracts. The authors 

 next proceed to notice memoirs, describing what they consider 

 similar phenomena in Europe. 



Theory of Flexure and Elevation of Strata. — From the con- 

 sideration of the preceding general facts, the authors have arrived 

 at a theory which they conceive applicable to the bending and 

 elevation of strata generally. They state that the oblique form 

 of all normal anticlinal and synclinal flexures " indicates that the 

 force producing the dips was compounded of a wave-like oscilla- 

 tion and a tangential pressure ;" — a purely vertical force exerted 

 simultaneously or successively along parallel lines could only 

 produce a series of symmetrical flexures, whilst tangential pres- 

 sure, unaccompanied by a vertical force, would result in irregular 



