Abstract The Pennsylvanian section on the southern Cumberland Plateau in the Sewanee and Tracy City area is composed of the Gizzard Group (Raccoon Mountain Formation, Warren Point Sandstone, and Signal Point Shale) and the lower portion of the Crab Orchard Mountains Group (Sewanee Conglomerate and Whitwell Shale). The hydrogeologic setting of the area controlled the founding and development of the town of Sewanee and University of the South. Water use initially relied upon a system of perennial springs, soil seeps, shallow wells, and a failed method of dam construction. Later, reservoirs with earthen dams across first-order drainages set the stage for growth of the community. Deformation associated with the Alleghanian Cumberland overthrust on the University Domain (more than 10,000 acres owned by the university) is subtle and confined to Bon Air coals in the Raccoon Mountain Formation, but a well-developed system of thrusts and folds in nearby Fiery Gizzard documents a consistent northwest tectonic transport direction. Deformation ranges from centimeter scale in Raccoon Mountain Formation mudstones to tens of meters of Warren Point Sandstone cut by northeast-striking thrusts. Deformation in Fiery Gizzard is locally related to two décollement surfaces above (intensely sheared Raccoon Mountain sandstone) and below (sheared Raccoon Mountain mudstones and coals) Sycamore Falls. Fourteen kilometers to the southeast, these overthrust structures are thought to connect to the Sequatchie thrust.

The stratigraphy of the Pennington Formation (Upper Mississippian) and the Gizzard (Mississippian and Pennsylvanian) and Crab Orchard Mountains Groups (Lower Pennsylvanian) reflects a suite of littoral sedimentary environments which prograded west and south into the southern Cumberland Plateau of Tennessee from the central Appalachians. Because rock-stratigraphic nomenclature in southern Tennessee evolved separately from nomenclature in Kentucky and Virginia, and because stratigraphic relations are complex, different classification schemes and formational boundaries are used in different places for similar sequences of strata. In the southern Cumberland Plateau of Tennessee, distribution of Gizzard depositional environments seems to be in part tectonically controlled, with barrier sandstones along the more stable shelf and with lagoon and marsh deposits in adjacent sedimentary basins.

The Pennsylvanian strata of western Virginia, southeastern Kentucky, Tennessee, and northwestern Georgia consist of shales, sandstones, siltstones, numerous coals, several conglomerates, some thin bands of ironstone, and a few limestones. There is a maximum thickness of nearly 6000 feet near Big Stone Gap, Wise County, Virginia. The strata are of early Pennsylvanian age, equivalent to the Pottsville and the lower part of the Allegheny of Pennsylvania. The region is divided by anticlines, thrust faults and state boundaries into six or more segments where the strata have been differently named and classified. The coals of minable thickness have been named in the many mining districts in the area, and some massive cliff- or bench-forming sand-stones or conglomerates, a few thick shales, and some marine limestones have been named; most of the other lithologic units are unnamed. Field studies permitted the correlation of many of the coals and other named beds or formations between separated areas and a general classification of the strata for the area of this report was made, as follows: Strata of Kanawha and Lower Allegheny age Anderson formation, 560–950 feet Scott formation, 475–880 feet Jellico formation, 330–630 feet Briceville formation, 500–1800 feet Strata of Lee (New River) age Corbin sandstone, 10–150 feet Duskin Creek shale, 50–300 feet Rockcastle sandstone, 40–220 feet Vandever shale, 30–270 feet Newton sandstone, 0–100 feet Eastland shale, 0–700? feet Herbert sandstone, 0–100 feet Whitwell shale, 10–200 feet Sewanee conglomerate 0–150 feet Gizzard formation, 0–615 feet It is not proposed that these names, most of which are derived from Tennessee localities, should supplant the systems of nomenclature already in use in Kentucky, Virginia, and Georgia. However they serve better as a basis for comparing the successions of the several areas than do the other classifications. It was found that there are marked changes in lithology and thicknesses of stratigraphic intervals on opposite sides of major structures such as the Sequatchie Valley anticline and the Pine Mountain thrust fault, suggesting that these structures developed along belts which suffered differential movements during early Pennsylvanian sedimentation. The strata exhibit a type of cyclical sedimentation, but details of lithology vary more between nearby localities than in the Eastern Interior and Mid-continent areas where the Pennsylvanian is classified into cyclothems which can be traced for long distances. The subdivision of this succession into cyclothems seems inadvisable at present. The sediments are all of aqueous deposition, and probably record piedmont, delta, marsh, lake, and shallow sea-floor environments. Marine fossils are found in only about one per cent of the strata, while fossil plant remains are much more widely distributed. This suggests that the waters in which deposition took place were fresh a large part of the time. Neither marine invertebrates nor fossil plants have yet been used as a basis for fine subdivision of the stratigraphic column, although both offer promise of some usefulness for this purpose. Spores isolated from coal by maceration are also being investigated as aids in correlation. The source of sediment would seem to lie to the southeast in the old land Appalachia, because thicknesses of stratigraphic units increase and the sediments generally become coarser-grained in that direction. There is, however, some evidence suggesting the derivation of sediment from the Canadian shield to the north, the greater thickness in the southeast in that case resulting from greater downwarping rather than proximity to the source of sediment. The paper includes descriptions of 37 stratigraphic sections representing the formational subdivisions in the several districts in which different systems of nomenclature are used. It is illustrated with 20 cross-section diagrams, showing the nature of stratigraphic variation between outcrops along selected lines paralleling and transverse to the regional strike.