Geologic units in Starke county, Indiana

Antrim Shale (Devonian) at surface, covers 73 % of this area

Black shale; gray shale and limestone in lower part

Muscatatuck Group (Devonian) at surface, covers 17 % of this area

Limestone and dolomite

Ellsworth Shale (Devonian-Mississippian) at surface, covers 10 % of this area

Green shale; some black shale in lower part