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DOUGLAS WILSON JOHNSON 



sluggish courses. The completion of this peneplain marked the 

 close of the first physiographic cycle of which we have satisfactory 

 evidence in the district. With the elevation of the region above sea- 

 level at the beginning of the Tertiary, the second cycle commenced, 

 during which the streams, flowing over weak rocks, were able to 

 excavate broad valleys nearly to their headwaters, developing in these 

 valleys a second plain of denudation, the Tertiary peneplain, while 

 hard rock regions remained unreduced, preserving the Cretaceous 

 peneplain over broad areas. This Tertiary cycle was followed by 

 depressions and elevations, the final result of which has been to leave 



Fig. 2. — Supposed former course of Tennessee (as Appalachian). 



the Tertiary peneplain well elevated and to allow the streams to cut 

 their valleys some distance below its level. The elevations and 

 depressions were accompanied by distinct warping, and the warping 

 is correlated with certain drainage modifications (1894). 



Dr. Hayes, in his report on the physiography of the Chattanooga 

 district, gives specific names to the different peneplains, the Creta- 

 ceous peneplain being known as the Cumberland, the Tertiary as 

 the Highland Rim, and a still later level, near the present beds of 

 the streams, as the Coosa peneplain. We are not here concerned 

 with the more exact ages ascribed to the several peneplains, nor with 

 the last formed of the three, the Coosa. And since we are dealing 

 with a particular problem, which is more fully discussed in the 

 earlier paper by Hayes and Campbell, we will, for sake of conven- 

 ience, employ the more general terms used in that essay. 



In the accompanying figures (Figs. 2 and 3) the flat top of Walden 

 Ridge, continued southward as Sand Mountain, represents a remnant 



