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South-central Tennessee and northeast .. Ma:bama are underlain by gently dipping rocks of Ordovician to Pennsylvanian age. Rock types and topographic forms are closely related. Resistant sandstones, interbedded with some shale and coal, underlie the Cumberland Plateau and form the caprock of the Cumberland Escarpment. The lower slopes are underlain by limestone, and the escarpment retreats as a result of sapping by solution. Sandstone blocks and colluvium collect on the slopes and are washed down to form extensive alluvial ·deposits in the coves that indent the escarpment. The stream channels in the coves are well graded in accordance with the coarseness of the alluvial material of the bed and banks. Size of this material decreases downstream as a result of selective transportation. The Highland Rim is a low plateau formed in cherty limestone of Missi.ssippian age. Its outer margin is a dissected hilly area capped by the Fort Payne ehert. The form of the stream channels depends on the materials which the streams cross. Stream profiles for a given discharge are gentlest at the inner margin of the Highland Rim where the rocks are less cherty than those nearer the NaShville Basin. According to one interpretation, the topography formed in three cycles of base leveling, each of which were followed by periods of uplift, when the peneplains were warped and then partially dissected. According to this idea the Cumberland Plateau, Highland Rim, and Nashville Basin still contain areas in which the old peneplains are preserved in areas of resistant rocks. This interpretation is difficult to criticize without attacking the basic assumptions through an analysis of the processes involved in downwasting. The multiple cycles, however, cannot be proved by geologic evidence. The alternative interpretation is that the forms of the present landscape are adjusted to processes now acting on them or that acted on them in the recent geologic past. The landscape could have formed by continuous lowering of the surface, a process that involves slope retreat on beds of different reSistance. This interpretation is the simpler of the two and is in ·accord with present conditions. It is supported by the di·stribution and Character of the surficial deposits, which are adjusted to the outcrop pattern of the rocks now exposed.

Interpretation of Cumberland Escarpment and Highland Rim, south-central Tennessee and northeast Alabama