112 Hayes and Campbell—Appalachian Geomorphology. 
Tennessee-Georgia line to 0 where the two plains coincide in 
southern Alabama. <A careful estimate shows that the volume 
of material removed by the Alabama and all its tributaries dur- 
ing the Tertiary cycle is about 622 cubic miles. The great dis- 
parity between this and the volume of sediments laid down 
during. this cycle by a river occupying the position of the Ala- 
bama leads us to seek farther for the source of the great mass of 
material. Manifestly this source is in the Appalachian valley 
north of the Coosa basin and at present drained by the Tennessee 
toward the northwest. The volume of material remoyed from 
the Tennessee basin above Chattanooga during the Tertiary cycle 
combined with that removed from the Alabama basin is about 
2,500 cubic miles. Comparing this with the 2,340 cubic miles 
of sediments deposited during the Tertiary cycle by the Alabama 
river, the agreement is so close that the conclusion seems to be 
inevitable that the drainage of the Appalachian valley was south- 
ward until near the end of the Tertiary cycle. 
Evidence from the Character of the Gorge below Chattanooga.—A 
third line of evidence bearing on the date at which the Appa- 
lachian drainage was diverted to its present westward course is 
derived from an examination of the Tennessee gorge below Chat- 
tanooga and a comparison of this gorge with other portions of 
the Tennessee valley formed under analogous conditions. 
The winding course of the Tennessee river through Walden 
plateau has been considered as evidence that this portion of its 
course was determined during a. period of baseleveling when the 
present summit of the plateau stood near sealevel; that with 
subsequent uplift the river continued to flow in its sinuous 
course, acquired under baselevel conditions, cutting its present 
gorge below the surface of the old peneplain. If this explana- 
tion of its winding course is correct, it follows either that the 
Tennessee is here flowing in an antecedent course or that it was 
diverted some time before the close of the Cretaceous cycle; but 
this conclusion is at variance with that reached by the two lines 
of evidence given above, as well as by a consideration of the gorge 
itself. The character of the gorge is shown on plate 4. Its sides 
are extremely steep from the cliffs at the plateau summit to the 
water’s edge. In most places there is scarcely room for a wagon 
road between the abrupt slope and the river, and only a few 
narrow strips of flood-plain occur throughout its entire length. 
On the hypothesis of diversion in the Cretaceous cycle, the river 
