490 OF THE PHYSICAL STRUCTURE 



sent to the two concave belts, where the axes are shorter and less 

 parallel. 



9. Alabama Division. This disturbed tract, progressively di- 

 minishing in breadth, from its commencement in Tennessee to its 

 termination in Alabama, displays the usual inversion of the lower 

 rocks, and the other signs of the presence of oblique flexures, and 

 of that species of dislocation, which results from them, and would 

 seem, from the best information we can collect, to preserve these 

 features of structure without abatement to its extreme southwest- 

 ern end, where it is finally overspread by the newer secondary 

 and tertiary strata. 



Thus, every section of the Appalachian chain, whatever its di- 

 rection or curvature, offers the same remarkable and beautiful 

 features and gradations in its axes, implying, that the cause 

 of these phenomena was some grand and simple energy, coex- 

 tensive with the whole margin of the Appalachian Sea, from 

 Canada to Alabama. 



Exemplification of the several Modes of Structure. 



1st. Normal Flexures. Having presented a general outline 

 of the different divisions of the chain, we shall next enter into a 

 description of the several varieties of sti'ucture, which distinguish 

 the different parts of it. Flexures of the normal character, con- 

 stitute, as we have seen, the predominant curvatures of the strata, 

 throughout almost the entire length of this mountain zone, the 

 obliquely folded, or inverted axes, being principally limited to a 

 belt of variable width, along the southeastern side. Of the nu- 

 merous parallel anticlinal and synclinal ranges, which sti'ikingly 

 exhibit this normal configuration, we shall cite a few examples 

 from Pennsylvania and Virginia, and refer to the engraved Sec- 

 tions accompanying this paper, for details of the dip in each re- 

 spective portion of the chain. In the Knobly mountain, the most 

 westerly of the great anticlinal flexures, situated to the southeast 

 of the coal region, the normal character is maintained, with great 

 uniformity, throughout a distance of upwards of fifty miles. It 

 commences with the first appearance of the axis, in the immediate 



