Appalachian Plateau Geologic Province
At the base of the Mississippian-Pennsylvanian section is a distinctive black shale, the Chattanooga Shale, which dates to the Devonian. It is less than ten meters thick but forms a useful and distinctive marker for geologic mapping. Because of its weakness relative to the overlying limestones, low-angle thrust faults produced during folding commonly flattened out and propagated through the Chattanooga Shale. As a consequence, throughout the plateau country in Georgia, Mississippian and Pennsylvanian strata are detached from older strata by a major subhorizontal thrust fault.
The Mississippian rocks are dominantly limestones and house a famous labyrinth of caves that developed as a result of solution weathering by slightly acidic groundwater. The Pennsylvanian rocks, on the other hand, are mainly sandstones and shales. The resistant sandstones protect the high plateaus from erosion. The resulting topography is an exact reversal of the underlying rock structure; the upfolds form valleys, and the downfolds form the mountain plateaus.
Other mineral commodities mined in the area include limestone, still mined for cement and aggregate, and ironstone, long since exhausted. Thus the plateau country offered a similar combination of iron ore, coal fuel, and limestone flux to that found near Birmingham, Alabama. In the early 1900s there were thriving blast furnaces at Chattanooga, Tennessee; Gadsden, Alabama; and Rising Fawn, Georgia. However, although similar in age and origin, the iron seams in Georgia were much thinner than those in Alabama and were soon depleted.
A curious natural feature of the plateau country is the development of so-called "rock towns." The most famous is Rock City, Tennessee, but the crest of Pigeon Mountain in Georgia is another excellent example. In both cases a jumble of sandstone blocks is separated by a
For early settlers moving west into Tennessee and Kentucky, the Cumberland escarpment on the east side of the Appalachian Plateau formed a major obstacle. The southeast sides of Lookout and Pigeon mountains forms the equivalent feature in Georgia. However, in the southern Appalachians, the Tennessee and Coosa river valleys provide natural gaps and routes to the interior. Settlers utilized these gaps for access to rich farm lands in the limestone valleys (Lookout, Sequatchie, and Wills) and generally avoided the plateau country, where the soils were thin and acidic. Apart from a few old coal-mining communities, such as Durham in Walker County, most settlement occurred in such valleys as Trenton Valley in Dade County. This pattern continues to the present day but with increasing housing development along the scenic bluffs overlooking the valleys.
George W. Fisher, ed., Studies of Appalachian Geology: Central and Southern (New York: Interscience Publishers ).
Aurelius S. Furcron, "The Georgia Story (The Geological History of Georgia)," Georgia Mineral Newsletter 1-5 (1948-1952).
Keith I. McConnell and Charlotte E. Abrams, Geology of the Greater Atlanta Region, Georgia Geologic Survey Bulletin 96 (1984).
Timothy Chowns, University of West Georgia
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