Fig. 165.—Shows the general position of the main drainage lines in the southern Appalachians at the close of the Cretaceous cycle of erosion. The lower part of stream b is made to follow the course of a portion of the present Tennessee.
Fig. 166.—Shows the general position of the main drainage lines in the southern Appalachians, after the capture of the westerly tributaries of the Appalachian River by stream b. Compare [Fig. 165].
Fig. 167.—A stage later than that shown in [Fig. 166]. The sea is represented as having withdrawn from a considerable area which was submerged at earlier stages (Figs. [165], [166]).
Fig. 168.—Shows the final change which resulted in the present course of the Tennessee. The land is represented as somewhat higher than now.[68]
Still later there was further deformation which caused additional changes in the drainage. The whole region was uplifted, relatively if not absolutely, but the uplift was differential, being greatest along the axis represented by AB, [Fig. 167]. The effect of the deformation was to stimulate the tributaries of the Ohio flowing north from this axis. Their growth was further accelerated by the weakness of the strata over which they ran. At the same time, the uplift to the south led the southwesterly flowing stream (b, [Fig. 167]) to discover relatively hard beds of rock in its lower course, and these beds retarded its down-cutting. The result was that a tributary of the Ohio (a, [Fig. 167]) finally tapped the main stream flowing to the southwest (b, [Fig. 167]) and carried its upper part over to the Ohio ([Fig. 168]). This was the beginning of the present Tennessee.