Drainage Adjustments about Chattanooga. 107 
an anticlinal and synclinal fold—Lookout valley and moun- 
tain—of which the latter was probably not reduced entirely to 
the Cretaceous baselevel, and hence afforded a protecting bul- 
wark against erosion upon the eastern side of Sand mountain. 
North of the present Tennessee gorge the conditions were exactly 
reversed. The western side of the plateau was protected from 
erosion by the Sequatchie anticline, the eastern limb of which, 
composed of heavy conglomerate, had probably remained some- 
what above the Cretaceous baselevel, turning the drainage east- 
ward to the Appalachian rivers, whose valleys were rapidly 
lowered upon soft rocks early in the Tertiary cycle. These 
streams cut deep notches in the eastern side of the plateau as far 
south as Chattanooga, beyond which the eastern side was pro- 
tected by the Lookout mountain syncline of hard sandstone, as 
already explained. As a result of these peculiar conditions the 
plateau was attacked by streams on both its eastern and western 
sides only within a strip a few miles broad, where the Tennessee 
river now crosses. Here deep notches were cut on opposite sides 
of the plateau and the capping sandstone removed on several 
lines entirely across. So long as the uplift on the axis O P con- 
tinued the divide was held stationary and neither set of streams 
encroached upon the territory of the other, but the cols were 
reduced nearly to the valley level on either side, and the way 
thus prepared for the diversion of the Appalachian river, later 
in the cycle. The uplift along this axis probably continued 
with diminishing force through the first half of the Tertiary 
cycle or possibly longer. During the same period variable 
amounts of uplift occurred in other portions of the province, 
which was thus brought to an altitude from 109 to 1,000 feet 
higher than that held at the close of the Cretaceous cycle. — Prob- 
ably other stream adjustments similar to those described in the 
Chattanooga district were brought about by this unequal uplift ; 
but in general the streams simply sank their channels below the 
surface of the peneplain, following the same courses as in the 
preceding cycle. Wherever these courses were located upon 
soft rocks the rivers were quickly lowered to the newly estab- 
lished baselevel and began to widen their channels, forming a 
second peneplain. 
Condition of Drainage prior to the Lafayette Depression—Thus 
toward the close of the Tertiary cycle the streams flowing west- 
