eastern Tennessee, shows on the west a part of the broad
Cumberland plateau. On the east is a roughened upland platform,
from which rise in the distance the peaks of the Great Smoky
Mountains. The plateau, consisting of strata but little changed
from their original flat-lying attitude, and the platform,
developed on rocks of disordered structure made crystalline by
heat and pressure, both stand at the common level of the line AB.
They are separated by the Appalachian valley, forty miles wide,
cut in strata which have been folded and broken into long narrow
blocks. The valley is traversed lengthwise by long, low ridges,
the outcropping edges of the harder strata, which rise to about
the same level,--that of the line cd. Between these ridges stretch
valley lowlands at the level ef excavated in the weaker rocks,
while somewhat below them lie the channels of the present streams
now busily engaged in deepening their beds.

THE VALLEY LOWLANDS. Were they planed by graded or ungraded
streams? Have the present streams reached grade? Why did the
streams cease widening the floors of the valley lowlands? How long
since? When will they begin anew the work of lateral planation?
What effect will this have on the ridges if the present cycle of
erosion continues long uninterrupted?

THE RIDGES OF THE APPALACHIAN VALLEY. Why do they stand above the
valley lowlands? Why do their summits lie in about the same plane?
Refilling the valleys intervening between these ridges with the
material removed by the streams, what is the nature of the surface
thus restored? Does this surface cd accord with the rock
structures on which' it has been developed? How may it have been
made? At what height did the land stand then, compared with its