APPALACHIAN RIVER IN EASTERN TENNESSEE 37 



east of the Alabama River it is very calcareous and "inconspicu- 

 ous,"^ showing that these sandy sediments were brought down 

 from the west instead of from the north. Considering the nature 

 and disposition of these sediments, and the decided notch in the 

 Continental shelf nearly opposite Mobile Bay, and the tendency 

 of the Gulf current to carry sediments eastward in this region, 

 there seems no reason for believing that the Coosa-Alabama 

 River was ever larger than it is at present. 



Character of the gorge below Chattanooga. — It is claimed that 

 this gorge is too immature to have been the channel of the Ten- 

 nessee since Cretaceous time, or during the erosion of the upper 

 Tennessee valley. It is admitted that erosion has progressed 

 much more rapidly on the upturned strata of the valley, but it is 

 thought impossible that the river could make so wide a valley 

 along one part of its course and be held within such narrow limits 

 lower down. 



The rate of erosion in tilted soluble rocks, compared to that 

 in horizontal beds of the same nature, capped by heavy beds of 

 sandstone and conglomerate has never been definitely determined ; 

 but the contrast is undoubtedly strong. The Nashville basin 

 has been eroded in strata only slightly domed, while the streams 

 leading therefrom pass through gorges in horizontal strata hav- 

 ing only a slight siliceous covering. It is a notable fact, in this 

 connection, that the valley of the upper Tennessee is eroded 

 back toward the west only just to the beginning of the horizontal 

 strata, and where the horizontal strata have been reached the 

 slope is as steep and the distance cut into the horizontal beds is 

 no greater than in the Walden gorge; and moreover, the streams 

 that run from the Walden plateau east into the great valley have 

 proportionally as narrow gorges with as steep slopes as has the 

 Tennessee in its gorge. If the Appalachian River existed and 

 the valley is older than Walden gorge, these side gorges are 

 also older, and, according to this reasoning, should be wider; 

 for the streams, although small, apparently carry all the waste 

 brought to them. The wide coves on the eastern side of the 

 valley made by small streams on upturned dolomite, and prc- 



^Ibid., p. 148. 



