Ordovician [units] including Richmond Group (which includes Mannie Shale - Olive-gray shale. Thickness 0 to 20 feet; Fernvale Limestone - Massive, coarsely crystalline, gray limestone with varicolored grains. Thickness 0 to 50 feet; Sequatchie Formation - Olive-gray and greenish-gray shale, mudstone, and argillaceous limestone; dolomitic, laminated, and sandy. Thickness 0 to 100 feet; and Arnheim Formation Nodular, shaly, gray limestone. Thickness 0 to 20 feet; the Maysville Group (which includes Leipers Formation - Nodular, shaly limestone; fine- to coarse-grained limestone; and phosphatic calcarenite locally. Thickness 0 to 150 feet); the Eden Group (which includes the Inman Formation - Thin-bedded to laminated, fine-grained, gray limestone with shale partings. Thickness 0 to 50 feet); and the Nashville Group (which includes Catheys Formation - Nodular, shaly limestone; fine- to coarse-grained limestone; phosphatic calcarenite; and light-gray cryptograined limestone. Thickness 50 to 175 feet.)
Fort Payne Formation - Bedded chert; calcareous and dolomitic silicastone; minor limestone and shale; scattered lenses of crinoidal limestone. Thin green shale (Maury) at base. Average thickness about 250 feet (475 in Wells Creek area); and Chattanooga Shale - Black carbonaceous shale, fissile. Thickness 0 to 70 feet; average about 20 feet. (Mapped as MDc on East-Central and East sheets)
Nashville Group - Bigby-Cannon Limestone - Brownish-gray phosphatic calcarenite and light-gray to brownish-gray, cryptograined to medium- grained, even-bedded limestone. Thickness 50 to 125 feet; and Hermitage Formation - Thin-bedded to laminated, sandy and argillaceous limestone with shale; nodular shaly limestone; coquina; and phosphatic calcarenite. Thickness 50 to 100 feet.
St. Louis Limestone - Fine-grained, brownish-gray limestone, dolomitic and cherty. Thickness 100 to 280 feet; and Warsaw Limestone - Coarse-grained, gray, crossbedded limestone; somewhat shaly in the northeast. Thickness 40 to 150 feet.
St. Louis Limestone - Fine-grained, brownish-gray limestone, dolomitic and cherty. Thickness 80 to 160 feet.; and Warsaw Limestone - Mainly medium- to coarse-grained, gray limestone, crossbedded. Includes much calcareous sandstone and shale to the north. Thickness 100 to 130 feet.