22 4 DOUGLAS WILSON JOHNSON 



close of the long period of Tertiary baseleveling, confined for a num- 

 ber of miles in one part of its course (the present divide) by soft rock 

 monadnocks of considerable magnitude to a valley less than two miles 

 in width. This, however, is inconsistent with the accepted theories 

 of valley development. It is thus seen that the features of this present 

 divide are not such as would characterize a region of soft rocks occu- 

 pied for a long time by the middle course of a great river. On the 

 contrary, the frequent occurrence and large size of the unreduced 

 remnants contrast strongly with the portions of the present Tennessee 

 valley in the same rocks north and south of the gorge, but compare 

 favorably with other divides between the headwaters of small streams, 

 as, for example, that between East Chicamauga and east Armuchee 

 Creeks, on the opposite side of Taylor Ridge, where no large stream 

 is supposed to have ever held its course. When seen in the field, 

 this objection to the supposed former southward course of the Ten- 

 nessee across this divide is brought out even more strikingly than on 

 the maps; and one is forced to conclude that the river has held its 

 present course for a much greater period of time than since the Ter- 

 tiary, and that no great Appalachian River could have flowed south- 

 ward across this divide. 



It is possible that an appreciation of this difficulty led Dr. Hayes 

 to place the date of the diversion later than was done in the earlier 

 paper by himself and Mr. Campbell. In the original essay the 

 statement was made: "That the Appalachian drainage was diverted 

 to its present course before this uplift is quite certain, for no channels 

 are cut in the Tertiary peneplain across the Coosa-Tennessee divide" 

 (1894, p. 115). In the later paper Dr. Hayes says: 



The large axial stream in the Appalachian valley continued to flow southward 

 across the present divide for a short time after the uplift, but it was able to cut its 

 channel less than 100 feet in the peneplain before it was diverted to a westward 

 course (1899, p. 55). 



It will be seen that this latter interpretation, which regards the present 

 level of the divide as a channel cut below the peneplain instead of a 

 part of the peneplain itself, would mean a reduction of something 

 less than 100 feet in the heights of the monadnocks referred to, and 

 a decrease in their areal extent. But while this provides for a some- 

 what wider valley for the supposed Appalachian River, it does not 



