Types of the Cretaceous Peneplain. 71 
sank their channels to the second baselevel and almost com- 
pletely removed the intervening portions. Hence there are 
only a few widely separated outliers of the Cumberland plateau 
whose summits still mark the surface of the peneplain. One of 
the most typical of these outliers is Short mountain, in central 
Tennessee, which rises 1,000 feet above the surrounding level 
plain. It has about the same altitude and is capped by the same 
hard sandstone as the Cumberland plateau, 20 miles distant. 
The intervening low plain is underlain by inestane which, on 
the removal of the sandstone cap, offered comparatively little 
resistance to degradation, so that only a combination of favorable 
accidents has preserved this remnant of the old peneplain once 
continuous over the whole region. 
Plateau Type.—This is very different from the foregoing, chiefly 
in the degree and manner of its preservation. In the great Ap- 
palachian coal basin, south of Cumberland gap, the rocks are 
cqmparatively undisturbed. Along certain lines narrow anti- 
clinal folds have developed, leaving broad basins between. The 
anticlines have been eroded, and the synclinal basins, with their 
flat lying strata, constitute the mountains or more properly the 
plateaus of this region. The form of the level topped plateaus 
has been attributed to the attitude of the strata, especially where 
the surface is formed by the great Carboniferous conglomerate, 
as is the case over most of the region; but close study shows that 
this uniform surface does not always correspond to the geologic 
structure, but isa more or less perfect plain, regardless of the 
attitude of the strata. The few low knobs and ridges which rise 
above this common level are truly monadnocks,* standing out 
in striking contrast to the uniform surface below. They gen- 
erally bear no definite relation to the outcrop of the harder 
beds, but appear to be due rather to the accidents of erosion and 
remoteness from main drainage lines. These features prevail 
throughout the coal basin from central Alabama to Kentucky. 
The plain is well preserved in the southern portion, but becomes 
more deeply dissected toward the north, until near Cumberland 
gap there remain only a few narrow remnants of the once con- 
tinuous surface. The conditions for the study of, this plain are 
nearly ideal in the plateau region, where it was so perfectly 
*A term lately used by W. M. Davis to designate those isolated eleva- 
tions standing above a baseleveled plain as mount Monadnock stands 
above the surrounding plain. 
11—Narv. Geog. Maa., vou. VI, 1894, 
