Geologic units in Lake county, Indiana

Wabash Formation (Silurian) at surface, covers 39 % of this area

Limestone, dolomite, and argillaceous dolomite

Muscatatuck Group (Devonian) at surface, covers 33 % of this area

Limestone and dolomite

Antrim Shale (Devonian) at surface, covers 23 % of this area

Black shale; gray shale and limestone in lower part

Ellsworth Shale (Devonian-Mississippian) at surface, covers 5 % of this area

Green shale; some black shale in lower part

Silurian System undivided (Silurian (Llandovery to Pridoli)) at surface, covers 0.1 % of this area

Silurian System undivided, includes Sexton Creek Limestone, St. Clair Limestone, and Moccasin Springs Formation in southern Illinois; includes Wilhelmi Formation, Elwood Dolomite, Kankakee Dolomite, Joliet Dolomite, Sugar Run Dolomite, and Racine Dolomite in northeastern Illinois; includes Mosalem, Tete des Morts, Blanding, Sweeney, Marcus, and Racine Dolomites in northwestern Illinois.