230 DOUGLAS WILSON JOHNSON 



this drainage may have persisted far enough into the beginning of 

 the Tertiary cycle to leave traces of its existence on portions of 

 Walden Ridge, is conceivable on the basis of either theory. 



In summing up the evidence which has been presented in favor 

 of the theory of a recent westward diversion of the Tennessee from a 

 former southward course, it has been pointed out that while the 

 facts noted in that connection admit of a rational interpretation on 

 the basis of the theory of capture, they are to be explained just as 

 readily and satisfactorily entirely independent of that theory. 



On the other hand, there are certain grave objections to the pro- 

 posed theory of capture, and certain lines of evidence which seem 

 to prove that the Tennessee River has held its present course through- 

 out Tertiary and more recent times. The winding character of the 

 gorge, on the basis of the theory of capture, necessitates a process 

 of diversion so involved and complicated that one is led to seek a 

 more simple explanation for the phenomenon. The conception of 

 meanders inherited from a former baseleveling period offers such an 

 explanation. The character of stream-dissection on the ridge both 

 north and south of the gorge is seen to bear strong evidence against 

 the theory of capture, but is wholly in accord with the alternative 

 theory. The complete breaching of the massive sandstone cap in 

 several places by small streams at a time when larger and more 

 powerful streams had scarcely begun that work, appears incredible. 

 The divide south of Chattanooga is seen to present features dis- 

 tinctly different from what we should expect had a large stream 

 flowed across it until the close of the Tertiary baseleveling period, 

 but well in accord with the features observed on other divides devel- 

 oped by small streams working under similar geological conditions. 

 In order to accept the theory of capture, we must admit that the 

 headwater portion of a comparatively small stream, having, apparently, 

 no marked advantage in regard to its length or the rocks over which 

 it flowed, was able to reduce its valley to a considerably lower level 

 than the middle portion of a great river near by — a thing which does 

 not seem possible. The supposed former difference in relative ele- 

 vation of the river-brought gravels above the Tennessee in the two 

 valleys — advanced in favor of the capture — is seen not to exist. The 



