National Geographic : 1894 May 23
Nature of the Deformation. 79 of the present valley ridges, while the present wind-gaps repre sent the former baseleveled intervals between the monadnocks. In the plateau region south of the Crab Orchard mountains no areas of sufficient extent to be represented on the map remained unreduced. The peneplain in this portion of the province was less perfect than in some others and occasional slight elevations remain clearly above its general level. These are sometimes due to the attitude of unusually resistant beds, but more often to the accidents of erosion acting on tolerably homogeneous material. DEFORMATION OF THE CRETACEOUS PENEPLAIN. One of the most important conclusions contained in the pres ent paper, in its bearings upon geomorphology, is the recognition of the nature of the deformation found recorded in the present attitude of the baselevel peneplains. It is that these deforma tions have. been mainly produced by true orogenic movements affecting comparatively narrow areas along certain well defined axes; that they were not epeirogenic or continental uplifts such as would preserve a peneplain in approximately its original hori zontal position; nor even, as suggested by Willis,* uplifts which broadly arched the surface across the whole expanse of the pro vince; also that orogenic activity has not been continuous along any one axis nor always in the same direction, though the total effect of the intermittent motion has been to elevate the whole province. Deformations of the baselevel peneplains have been recognized in this and adjacent regions by other writers, especially Davis and McGee. Thus Davis has shown that the Cretaceous pene plain in Pennsylvania, New Jersey and portions of New England is tilted seaward, but he has not located its axis of elevation; also McGee has shown that in the southern Appalachians every subsidence has been greatest at the sea margin and every eleva tion greatest in the interior, which implies a cumulative seaward tilting. The class of facts from which he derived his evidence did not enable him to locate the main axes of uplift, though he clearly recognized the transverse Memphis-Charleston axis, which will be more fully described on a subsequent page. *Topography and Structure of the Bays Mountains, Tennessee, by Bailey Willis: School of Mines Quarterly, vol. viii, 1887, p. 252. 12-NAT. GEOG. MAO., VOL. VI, 1894.
1894 Jun 22
1894 Apr 25