National Geographic : 1894 May 23
Types of the Cretaceous Peneplain. 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 limestone, 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 comparatively 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 is a 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-NAT. GEOa. MAG., VOL.VI, 1894.
1894 Jun 22
1894 Apr 25