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Hrosion of the Peneplain. 91 
acter of the rocks. Where the uplift was considerable the streams 
cut narrow gorges in their rocky floors, but’ where the elevation 
was slight the valleys were widened and present more the ap- 
pearance of corrasion under baseleveling conditions. 
This broad dissection of the Tertiary peneplain is greatest in 
the southern portion of the province, for there the elevation was 
only sufficient for the streams to work upon the decayed rock 
and residual mantle which had accumuiated during the preced-, 
ing period. The streams were almost entirely occupied in broad- 
ening their valleys, so that in the Coosa-Alabama basin probably 
a third of the surface was removed during this period. After 
the Columbia depression this region was once more elevated 
and the streams have deeply trenched their broad valleys. In 
the vicinity of Chattanooga the Tennessee river has lowered its 
channel but 250 feet below the Tertiary peneplain, and this has 
been accomplished gradually, for the contours are generally 
flowing and well rounded, except where the river cuts some un- 
usually hard stratum. Throughout the basin of the Tennessee 
river northeast of Chattanooga the amount of cutting is variable, 
depending upon the amount of deformation of the peneplain. 
Streams located upon the axes of maximum elevation were 
stimulated to a high degree of activity, While those located be- 
tween such axes in areas of minimum uplift received only a 
moderate acceleration. The Clinch and Holston rivers show in 
a striking manner the effect of the warping on the erosion of 
the peneplain. The upper Clinch is located upon the axis K JL, 
plate 6,and has cut a canyon from 500 to 700 feet deep through 
the limestones and calcareous shales, with slopes as steep as such 
material will stand. In striking contrast with this is the broad 
open valley of the Holston, located in an area of minimum 
elevation between the axes K Land M N and about twenty miles 
southeastward of the Clinch river. 
The great gorges cut in the Tertiary peneplain in the New- 
Kanawha basin have been referred to. They indicate clearly 
that the conditions which prevailed here in post-Tertiary time 
have been different from those in any other portion of the 
province. The uplift which elevated the Tertiary peneplain to 
an altitude of 2,500 feet, as shown in plate 6, was confined almost 
entirely to the axis K L. This axis crosses the river in its lower 
course, but the river had sufficient volume to hold its antecedent 
position across the rising fold. In doing so it has cut a narrow, 
