Each Physiographic Province is Underlain
By a Different Rock Type

The Cumberland Plateau is underlain by gently dipping Pennsylvanian sandstone and shale, some conglomerate, and coal. These rocks have a thickness of about 1,500 feet. The main coal seams in Pennsylvanian rocks are the Big Mary, Rock Spring, and Coal Creek. The Pennington Formation of Mississippian age is a transition from the basal Pennsylvanian sandstone and shale which overlie the Mississippian carbonate rocks. The Mississippian rocks are predominately limestone, calcareous shale, and siltstone, with a maximum thickness of about 1,000 feet. These rocks crop out along the escarpment formed by Walden Ridge. The Chattanooga Shale of Devonian age and the Rockwood Formation of Silurian age underlie the Mississippian rocks and crop out along the base of the escarpment. Gently east-dipping rocks underlying the plateau are warped upward along the escarpment and dip steeply to the northwest as a result of thrusting from the southeast (fig. 2.3-1).

Ordovician and Cambrian rocks that underlie the Ridge and Valley are predominately carbonate, siltstone, shale, and some sandstone. Northeast-trending ridges are formed by resistant formations such as the Cambrian Rome Formation. The valleys are underlain by less resistant formations such as the Cambrian Conasauga Shale and the Ordovician Chickamauga Limestone. The formations within the Ridge and Valley have been deformed by folding and intense faulting which occurred during the development of the Appalachian Mountains.

Karst topography formed by the solution of carbonate rocks occurs within both the Cumberland Plateau and the Ridge and Valley of Area 19. In the Cumberland Plateau, karst occurs along the Sequatchie anticline, just southwest of the Crab Orchard Mountains. The collapse of sinkholes in these areas contributes to the headward advance of the Sequatchie Valley. Karst is developed in those areas of the Ridge and Valley that are underlain by limestone. These areas are long narrow belts which trend to the northeast (fig. 2.3-2).