Geologic units in Clay county, Mississippi

Demopolis chalk (Upper Cretaceous) at surface, covers 47 % of this area

(Selma group), Chalk and marly chalk containing fewer impurities than underlying and overlying formations.

Mooreville chalk (Upper Cretaceous) at surface, covers 13 % of this area

(Selma group), Marly chalk and calcareous clay.

Ripley formation (Upper Cretaceous) at surface, covers 12 % of this area

(Selma group), Gray to greenish-gray fine glauconitic sand, clay, and sandy limestone; south of Oktibbeha County is very sandy micaceous chalk.

Prairie Bluff chalk and Owl Creek formation (Upper Cretaceous) at surface, covers 10 % of this area

(Selma group), Prairie Bluff chalk, compact brittle chalk, sandy chalk, and calcareous clay; at base contains many phosphatic molds of fossils; in Ponotoc and Union Counties merges northward into Owl Creek formation, tough blue glauconitic sandy clay.

Clayton formation (Paleocene) at surface, covers 8 % of this area

(Midway group), Upper part, greenish-gray coarsely glauconitic sandy clay and marl; lower part, crystalline sandy limestone and loose sand, represented south of Houston by a discontinuous bed of indurated calcareous sandstone.

Eutaw formation (Tombigbee sand member) (Late Cretaceous) at surface, covers 6 % of this area

Massive fine glauconitic sand.

Porters Creek formation (Paleocene) at surface, covers 5 % of this area

(Midway group), Dark-gray clay, north of Clay County contains slightly glauconitic, micaceous sand lenses.

Eutaw formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

More or less cross-bedded and thinly laminated glauconitic sand and clay; basal part includes the McShan formation, greenish-gray, micaceous, locally very glauconitic, very fine-grained sand and thin-bedded light-gray clay, small chert gravels may be present in basal beds, not recognized in northern Tishomingo County.