16 GEOLOGICAL SURVEY OF ALABAMA. 



channels, if not into new directions. B"ut admitting that the 

 direction of drainage has not been materially changed, it is 

 urged that the deep canon-like gorges, in which the streams 

 flow through the Sand Mountain, are apparently of more 

 recent origin than their channels on the other side of the 

 valley. The evidence of the apparently greater age of the 

 stream channels on the south-east side of the valley consists 

 in their greater general breadth, and in the considerable 

 amount of bottom lands that exists along them ; while on the 

 north-western side no bottom land exists along their narrow 

 channels from the edg3 of the valley till they reach the 

 synclinal. 



These facts are apparent, and would usually be persuasive, 

 if not conclusive of the subject. But here, with the changes 

 of levels produced by the rising fold, they may have originated 

 from other causes than difference in age. It has already 

 been stated that this Sand Mountain rim has been greatly 

 denuded. Before its elevation, the channels of the present 

 streams (if then existing) must have been several hundred 

 feet above their present beds! With the rising rim the an- 

 cient flood plains would be washed away, and the streams 

 would cut down their channels deeper and deeper, as eleva- 

 tion progressed. Hence, on the theory that the drainage 

 here was established before the fold began to rise, it does not 

 necessarily follow, from the observed facts, that the course 

 ol the streams was thereby materially changed. But it might 

 also be assumed that the rising of this fold, and the rising 

 of this region above the waters, and the establishment of its 

 drainage were all synchronous events, and that they pro- 

 ceeded and progressed pari passu. Upon this hypothesis 

 the deep narrow gorges cut by the streams through Sand 

 Mountain, would be accounted for by the greater depth they 

 had to be excavated. While above and below, the streams 

 were widening their flood plains ; here their whole force was 

 expended in cutting down their beds. Without endorsing 

 either hypothesis, it is sufficient for the present purpose to 

 present the facts as stated. 



Other topographical features being closely connected with 



