Geologic units in Bienville Parish, Louisiana

Sparta Formation (Eocene) at surface, covers 34 % of this area

White to light gray massive sands with interbedded clays; some thin beds of lignite or lignitic sands and shales.

Alluvium (Holocene) at surface, covers 21 % of this area

Gray to brownish gray clay and silty clay, reddish brown in the Red River Valley, some sand and gravel locally.

Cook Mountain Formation (Eocene) at surface, covers 15 % of this area

Greenish gray sideritic clay in upper part may weather to brown ironstone; yellow to brown clays and fossiliferous marl in lower part may weather to black soil. Ironstone concretions near base.

High Terraces (Pleistocene) at surface, covers 8 % of this area

Tan to orange clay, silt, and sand with a large amount of basal gravels.

Intermediate Terraces (Pleistocene) at surface, covers 7 % of this area

Light gray to orange-brown clay, sandy clay, and silt; much sand and gravel locally.

Prairie Terraces (Pleistocene) at surface, covers 5 % of this area

Light gray to light brown clay, sandy clay, silt, sand, and some gravels.

Cane River Formation (Eocene) at surface, covers 4 % of this area

Brown silty clay with basal glauconitic, fossiliferous silts which may weather to ironstone locally.

Wilcox Group (undifferentiated) (Paleocene) at surface, covers 4 % of this area

Gray to brown lignitic sands and silty to sandy lignitic clays, many seams of lignite; some limestone and glauconite.

Cockfield Formation (Eocene) at surface, covers 1 % of this area

Brown lignitic clays, silts and sands; some sideritic glauconite may weather to brown ironstone in lower part.

Natural Levees (Holocene) at surface, covers 0.2 % of this area

Gray and brown silt, silty clay, some very fine sand, reddish brown along the Red River.

Midway Group (undifferentiated) (Paleocene) at surface, covers < 0.1 % of this area

Dark gray to black shale

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

Fossiliferous limestone and marl