38 GEOLOGICAL SURVEY OF ALABAMA. 



pletje reversal ; while in the central portion of the valley 

 they have described an arc of 135 to 150, lacking only 30 

 to 45 of complete reversal. It is therefore reasonably con- 

 cluded, that with less yielding to the lateral pressure and 

 with less displacement in this portion of the fold, the absence 

 of the vertical wall lor a few miles may be considered as ex- 

 plained. 



The Horse Shoe Curve of the upper end of Red Mountain 

 is a striking and peculiar feature. It circles around the 

 upper end of Red Mountain Valley, making a cove of its 

 upper part, without materially diminishing its width. In 

 its outer circle it closely approximates the curve of the end 

 of the valley. 



This peculiar topographical structure resulted from the 

 effects of two distinct causes. 1st. A flexure in the main 

 fault at the upper end of Red Mountain Valley it there 

 suddenly deflects from an east north-east fco a north north- 

 west course in passing through Red Mountain; but beyond 

 that, again resumes its former course. Hebce, the denuding 

 waters were not aided by this fault in the excavation of this 

 sub-valley above the deflexion of the fault to the west. Hard 

 strata were encountered, and the further abrasion of this 

 sub-valley to the north-east was arrested. 



2d. Because the waters above and beyond this point 

 found outlets along each side of the valley. These waters 

 with their interlocking heads eroded the Red Mountain and 

 its curved upper ends, and its adjoining Chert ridges on the 

 outside, and were the main agencies in carving out its .present 

 form. But for the obstruction occasioned by the flexure in 

 the fault at this place, it is more than probable that the de- 

 nuding waters would have flowed down it, and eroded out 

 the Red M'ountain Valley to the head of the fold. The ends 

 of Red Mountain and the Chert ridge would then have been 

 left trending in the direction of the axis of fold, instead of 

 being united together. 



The end of the fold. The head of the valley is the end of 

 the fold to the north-east. All around its terminal rim the 



