BRITISH ASSOCIATION. 



237 



nate 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 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 100 and sometimes 130 miles in 

 length, and they deviate very little from a rectihnear 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 extremities of 50^ in a distance of 90 miles, and the 

 rectilinear axes of different divisions vary in their line of 

 direction as much as 60o. As all the flexures were un- 

 doubtedly formed at one period, the authors consider these 

 facts at variance with M. Beaumont's hypothesis, that dis- 

 locations 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 N.W,, or away from the quarter of great- 

 est local disturbance, is considered important by the au- 

 thors in its bearing upon the subject of the elevation of 

 broad continental tracts. The authors next proceed to no- 

 tice memoirs, describing what they consider similar phe- 

 nomena in Europe. 



Theory of Flexure and Elevation of Strata,— Yxom the 

 consideration 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 oscillation and a tangential 

 pressure 3" — a purely vertical force exerted simultaneously 



