222 DOUGLAS WILSON JOHNSON 



into the ridge from the valley to the east. Such a process seems to 

 add to the difficulties of the case rather than to decrease them; the 

 disposal of the rainfall of a given area on the ridge by several streams 

 instead of by one must mean less powerful streams and decreased 

 cutting in each individual case. That such streams should have been 

 able completely to breach the thick sandstone cap of the ridge, even 

 at their headwater areas, by the close of the Tertiary period, whereas 

 their larger neighbors, with the additional advantage resulting from 

 250 feet of post-Tertiary incision of the main streams, have only 

 begun that process in their lower courses, seems wholly incredible. 

 (In this connection it must be borne in mind that such streams as 

 flow short distances down steep slopes directly into the present 

 Tennessee are not comparable with streams heading in the ridge, 

 but flowing some distance out across the open valley to join the main 

 stream, or its tributary, the Sequatchie. Thus, in the immediate 

 vicinity of the gorge, where the streams enter the main Tennessee 

 while it is still fairly within the limits of the Walden syncline, dissec- 

 tion of the ridge is very marked, as at points west of Brown's Ferry, 

 east of Kelley's Ferry, and along Running Creek just south of the 

 gorge. This local dissection, consequent in part upon the 250 feet 

 of post-Tertiary trenching of the main Tennessee, is wholly in accord 

 with the hypothesis that the Tennessee has held its present course 

 since Cretaceous times.) 



In order to account for the diversion of the upper Appalachian 

 independently of this process, which involves such great dissection 

 by obsequent streams, it has been suggested that the diversion may 

 have been accomplished by what has been termed "cavern capture." 

 This process involves a leakage from the Appalachian valley east of 

 the ridge into the Sequatchie valley to the west, whereby a system 

 of caverns was developed in the limestone below the massive sandstone 

 cap of Walden Ridge, resulting in a diversion of the Appalachian 

 River through this underground channel into the Sequatchie River, 

 with the subsequent falling in of the cavern roof. There are several 

 objections to this theory. It is difficult to conceive that the Sequatchie 

 valley could have been lower than the valley of a great river to the 

 east, as is pointed out more fully in a later paragraph, so as to admit 

 of such a leakage as this theory involves. The process would entail 



