OF THE MORE DISTURBED ZONES OF THE EARTH'S CRUST. 437 



Others again are curved, some of these sweeping convexly towards the quarter 

 of chief crust dislocation and metamorphism, others curving convexly from it, 

 but we never find these two classes associated in the same group, and in the 

 Appalachians, never even in the same segment of the undulated zone. In some 

 districts of this and other chains, some of the principal curvilinear anticli- 

 nals and troughs are quite as extended in length as the great axes which are 

 straight. They appear to be independent waves generated from curvilinear frac- 

 tures of the crust, and not to be merely the bending terminations of adjacent 

 rectilinear flexures. One of the most interesting features belonging to some of 

 them is, their extent of curvature, and the graceful continuous smooth sweep which 

 their curving axes present, often without jog or hitch, from one extremity to the 

 other. This crescent-like form is developed in a high degree in those curving 

 sections of the Appalachian chain, where the waves are convex north-westward, 

 or from the quarter of maximum dislocation — the Atlantic slope. In the Juniata 

 division of the chain in Pennsylvania, some of the curving anticlinals, 80 and 

 100 miles in length, change their trend between their two extremities as much 

 as 40° ; and in the Delaware division of the same chain, which also bends with 

 a concave sweep to the north-west, the deflection in more than one great syn- 

 clinal trough, and anticlinal axis, is not less than 60". This fact of the curvi- 

 linear form of anticlinals and synclinals of great length in this was long ago 

 offered by us, as a phenomenon incompatible with the generalization of the 

 eminent French geologist M. Elie de Beaumont, who conceives that the lines 

 of elevation of the crust have been great circles of the sphere, and that those 

 of a given geological epoch have invariably observed one constant direction. 

 The whole of the Appalachian chain having been demonstrably corrugated into 

 its present undulations at one epoch, that of the end of the coal period, the simple 

 fact that its different groups of waves deviate as widely in direction from each other 

 as 60°, while those of each group are reciprocally parallel, — the whole chain in- 

 deed, if subdivided on this principle of direction, including not less than eleven 

 conspicuous segments, — is itself enough to show that no particular constancy of 

 relation can be established between the dates of elevations, and the mere direc- 

 tions of the lines or axes of the strata. But this other fact of so marked ach ange 

 of direction in one and the same axis, as displayed by these crescent-shaped waves, 

 is, if possible, in still more striking contradiction with that hypothesis. Another 

 fact connected with the groups of curving waves in the Appalachian chain is par- 

 ticularly deserving of mention in this place, from the bearing it appears to have 

 upon the question of the direction of the pulsatory or wave-like motion of the crust, 

 at the time of the permanent production of the flexures. It is this— the individual 

 waves in all the segments of the chain which are convex north-westward exhibit, 

 as already said, a continuous symmetrical crescent-like curvature ; those, on the 

 contrary, which are included in the other curvilinear districts, convex to the south- 



