i 9 6 DOUGLAS WILSON JOHNSON 



same time that the broad longitudinal valleys in softer rock were 

 being excavated. According to the other hypothesis, throughout the 

 Tertiary cycle the river flowed on southward in the longitudinal 

 valley east of the mountain, and so, by way of the Coosa and Alabama 

 Rivers, into the Gulf of Mexico, continuing in this course until the 

 present broad valleys both north and south from Chattanooga were 

 completed (Fig. 2); then, at the close of the Tertiary cycle, by a 

 process of stream capture, the Tennessee was tapped at a point near 

 Chattanooga by a branch of a stream occupying the valley west of 

 the mountain, and so diverted from the former course to its present 

 course through the gorge (Fig. 3). In recent years this latter theory 

 has been most strongly supported. Certain new evidence, now avail- 

 able, appears to afford good reasons for adopting the first of these 

 theories. It seems desirable, therefore, to review the previous con- 

 siderations of this problem, weighing carefully the evidence both for 

 and against each theory. 



LITERATURE 



In 1894 there appeared a paper by C. Willard Hayes and Marius 

 R. Campbell on The Geomorphology of the Southern Appalachians. 

 Their essay gives a somewhat detailed account of the physiographic 

 history of the region treated, and devotes a number of pages to the 

 Tennessee drainage problem. The results of their studies led them 

 to believe in the post-Tertiary diversion of the Tennessee from a 

 former southward course; hence they support the second of the 

 above hypotheses with a variety of evidence. This evidence is dis- 

 cussed in detail below. 



In a later paper, on The Physiography of the Chattanooga Dis- 

 trict, Dr. C. Willard Hayes discusses the physiographic develop- 

 ment of the region more fully than in the former paper by himself 

 and Mr. Campbell. Dr. Hayes traces the past history of stream- 

 adjustments throughout the region in great detail, offering a new 

 interpretation regarding one or two points in the Tennessee problem, 

 but supporting the main conclusion reached in the earlier report. 



In 1900 Mr. Charles T. Simpson published a paper on The 

 Evidence of the Unionidce Regarding the Former Courses of the 

 Tennessee and Other Southern Rivers. Working along entirely 



