TERTIARY HISTORY OF THE TENNESSEE RIVER 205 



would seem, at first sight, more than all others, to have been deposited by this 

 river; but a study of the whole area shows that this formation increases in thick- 

 ness and coarseness toward the west, in western Alabama and in Mississippi; 

 while east of the Alabama River it is very calcareous and inconspicuous, showing 

 that these sandy sediments were brought down from the west instead of from 

 the north (p. 36). 



In view of the considerations stated above, it is not believed that 

 any argument in favor of the supposed capture of the Appalachian 

 River by a branch of the Sequatchie can be properly based on a 

 comparison of the sediments opposite the mouth of the Alabama 

 River with the amount of material eroded during Tertiary times 

 from the basin of the Alabama or other rivers. So far as such evi- 

 dence goes, there seems to be no reason for supposing that the Coosa- 

 Alabama River was ever any larger than it is now. 



Evidence from the character 0} the gorge below Chattanooga. — The 

 third line of evidence developed by Hayes and Campbell in favor of 

 the diversion of a southward-flowing Appalachian River by a branch 

 of the Sequatchie River to the west, is based on the youthful character 

 of the transverse gorge west of Chattanooga. They recognize the 

 fact that the course of the river through a ridge capped by hard sand- 

 stone several hundred feet in thickness would necessitate, on the 

 basis of either theory, a valley of younger expression at this point 

 than east or west of it where the river follows weak rocks. Their 

 argument is that the degree of youthfulness is too great to be accounted 

 for on any other theory than that of a comparatively recent diversion 

 of the river to that course by a process of stream- capture. This is a 

 point which does not readily admit of demonstrable proof, and the 

 best evidence is to be secured from a comparison with other valleys 

 of known age and formed under similar conditions. Hayes and 

 Campbell, therefore, compare the gorge of the Tennessee through 

 Walden Ridge with a valley southwest of Scottsboro, Alabama, in 

 the following words : 



While a direct comparison cannot be made between the Walden gorge and 

 the upper Tennessee valley on account of difference in conditions, such a com- 

 parison can be made between the gorge and a valley in northern Alabama, extend- 

 ing from Scottsboro southwestward to the mouth of Flint River It is 



nowhere less than six miles broad, and its floor is very regular, forming a portion 

 of the Tertiary peneplain. The age of this valley is easily determined; it is 

 carved in the Cretaceous peneplain; therefore it is more recent than the Cretaceous; 



