70. Hayes and Campheli—Appalachian Geomorphology. 
rocks, and then, less perfectly, the harder rocks; the degree to 
which it was carried depending largely upon their location with 
reference to the margin of the sea or the larger streams. In this 
manner the greater. portion of the province was reduced to an 
almost featureless plain. The surface over hard and soft beds 
alike was smoothed until gentle slopes and low relief replaced 
the sharp declivities and high elevations which marked the early 
stages of the process. 
Following the period of quiescence above described came one of 
epeirogenic activity, and the process of baseleveling was brought 
to an end. The land was elevated and the streams began anew 
the rapid trenching of its surface; but the land was elevated 
unequally, and as it arose the surface was warped and twisted. 
Where the elevation was greatest the erosion was most active 
and quickly destroyed the symmetry of the surface, in some 
places producing a deeply cut mountain region, the summits 
alone marking the position of the former peneplain ; where the 
elevation was slight the surface remained practically unchanged ; 
andall gradations exist between these extremes—on the onehand, 
where the peneplain is wholly destroyed, and on the other, where 
it is perfectly preserved. 
Although the whole province, as stated above, had been re- 
duced to an almost featureless plain, the character of the under- 
lying rocks modified to a very slight extent the character of that 
plain. The soft rocks were somewhat more perfectly reduced 
than the hard rocks. Still the differences were not strongly 
marked. When, however, the nearly perfect plain was elevated 
and the activity of the streams was revived, differences in the 
underlying rocks became all important in determining the degree 
to which the plain would be preserved. Where the rocks were 
soft it was rapidly destroyed, and where they were hard it has 
retained in large measure its original form. Hence the peneplain, 
although originally quite uniform, now shows great diversity 
and presents several distinct types, depending jointly on the 
amount of elevation and the character of the underlying rocks. 
Western marginal Type:—In general around the margin of the 
province this peneplain has been almost entirely obliterated by 
later erosion. Especially is this true in central Tennessee and 
Kentucky, where limestone occupied the baseleveled surface or 
lay beneath a thin capping of sandstone. When erosion was 
revived upon the peneplain by its elevation the streams quickly 
