Geologic units in Madison county, Tennessee

Loess (Quaternary) at surface, covers 37 % of this area: Loess - Clayey and sandy silt, gray to brown, massive. Maximum thickness about 100 feet along bluffs of Mississippi River; thins eastward. (Minimum mapped thickness 4 feet.)
Lithology: silt
Alluvial deposits (Quaternary) at surface, covers 11 % of this area: Alluvial Deposits - Sand, silt, clay, and gravel. In flood plain of Mississippi River more than 100 feet thick; in smaller streams generally less than 20 feet thick.
Lithology: sand; silt; clay or mud; gravel
Midway Group including Porters Creek Clay and Clayton Formation (Tertiary) at surface, covers 8 % of this area: Midway Group - includes Porters Creek Clay - Pale-brown to brownish-gray, massive, blocky clay; locally contains glauconitic sand. Thickness 130 to 170 feet. Also includes Clayton Formation- Glauconitic sand, argillaceous and locally fossiliferous; at base in Hardeman County is an impure fossiliferous limestone. Thickness 30 to 70 feet.
Lithology: clay or mud; sand; limestone
Claiborne and Wilcox Formation (Tertiary) at surface, covers 44 % of this area: Claiborne and Wilcox Formations -- Irregularly bedded sand, locally interbedded with lenses and beds of gray to white clay, silty clay, lignitic clay, and lignite. Thickness more than 400 feet.
Lithology: sand; clay or mud; lignite