Geologic units in Madison county, Tennessee

Claiborne and Wilcox Formation (Tertiary) at surface, covers 44 % of this area

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.

Loess (Quaternary) at surface, covers 37 % of this area

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.)

Alluvial deposits (Quaternary) at surface, covers 11 % of this area

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.

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.