is still in youth. Thus many peneplains which have been elevated
and dissected have been recognized by the remnants of their
ancient erosion surfaces, and the length of time which has elapsed
since their uplift has been measured by the stage to which the new
cycle has advanced.

THE PIEDMONT BELT. As an example of an ancient peneplain uplifted
and dissected we may cite the Piedmont Belt, a broad upland lying
between the Appalachian Mountains and the Atlantic coastal plain.
The surface of the Piedmont is gently rolling. The divides, which
are often smooth areas of considerable width, rise to a common
plane, and from them one sees in every direction an even sky line
except where in places some lone hill or ridge may lift itself
above the general level (Fig. 62). The surface is an ancient one,
for the mantle of residual waste lies deep upon it, soils are
reddened by long oxidation, and the rocks are rotted to a depth of
scores of feet.

At present, however, the waste mantle is not forming so rapidly as
it is being removed. The streams of the upland are actively
engaged in its destruction. They flow swiftly in narrow, rock-
walled valleys over rocky beds. This contrast between the young
streams and the aged surface which they are now so vigorously
dissecting can only be explained by the theory that the region
once stood lower than at present and has recently been upraised.
If now we imagine the valleys refilled with the waste which the
streams have swept away, and the upland lowered, we restore the
Piedmont region to the condition in which it stood before its
uplift and dissection,--a gently rolling plain, surmounted here
and there by isolated hills and ridges.