Cliff and talus communities are a system that includes cliff faces, ledges, cliff-top outcrops or cliff-edge, and the cliff base. The cliff face of some cliff types may be shear or vertical, they may be deeply recessed and cave-like (e.g. rockhouses), they may be very steeply sloping and with or without ledges. At the top of many Tennessee cliffs at the cliff edge there may be open glade-like outcrops. These are here considered and have been considered by others to be part of the overall cliff community. All cliff communities are subject to erosional forces. Water, wind, mass wasting, freeze-thaw processes are often the major forces responsible for maintaining cliff communities. These erosional processes result in much material be deposited at the base of the cliff. This jumbled mass of material--called talus and resulting in the formation of a talus slope--is often unstable and loose and is itself often subject to slope creep. Tennessee's cliffs are associated mostly with consolidated rock formations such as limestone, dolomite, shale, sandstone, and a variety of metamorphic types. In the Coastal Plain of West Tennessee there are also cliffs that are formed of unconsolidated materials such as gravel, clay, loess, and lignite. Below, the cliff types of Tennessee are classified by their geology and physiographic location.