84 Hayes and Campbhell—Appalachian Geomorphology. 
distance between the two peneplains. The uplift attained its 
maximum of about 2,600 feet in. northern Virginia and West 
Virginia, and was apparently continuous from the close of one 
period of baseleveling to the inauguration of the other. Asa 
direct consequence of this steady uprising of the land we find 
in this portion of the province the Cretaceous peneplain almost 
completely dissected, and it is extremely doubtful if any of the 
level surface is still preserved. From this maximum the eleva- 
tion decreased in an irregular manner toward the margin of the 
province, where the earlier and later baselevels coincide. 
The period of Cretaceous baseleveling was a very long one—so 
long that over much of the province the rocks, hard and soft 
alike, were reduced nearly or quite to the same level. The period 
of Tertiary baseleveling, on the other hand, was comparatively 
short when measured by geologic standards. Ifsufficed for the 
complete removal of the previous peneplain only about the mar- 
gin of the province, where conditions of erosion were exception- 
ally favorable, and for the cutting of broad valleys upon the soft 
rocks of the interior. Since only the softer rocks were reduced 
to baselevel, there is less diversity in the Tertiary than in the 
Cretaceous peneplain, but when the surrounding erosion slopes 
are considered in connection with the plain, as they must neces- 
sarily be, there is found a great variety of topographic forms, de- 
pending jointly on the kind of rocks, location with reference to 
the margin of the sea or large drainage channels, and amount of 
pre-Tertiary elevation. This peneplain, like the Cretaceous, has 
been greatly modified by late erosion, but even in this the three 
elements named above are the controlling ones and mainly re- 
sponsible for the forms produced. 
Marginal Types.—In the western portion of the province con- 
ditions were favorable for the production of an extensive base- 
level peneplain during this period. The very perfect Cretaceous 
plain was elevated from a few feet at the margin of the Tertiary 
sea to about 1,000 feet at the western line of the Cumberland 
escarpment. The greater part of the rocks thus raised above 
baselevel were limestones, in which the streams quickly lowered 
their channels and by lateral corrasion entirely removed the 
intermediate highlands, with the exception of a few isolated 
monadnocks, of which Short mountain, already described, is the 
type. Owing to the coincidence throughout central Tennessee 
