Geologic units in Hillsdale county, Michigan

Coldwater Shale (Mississippian) at surface, covers 66 % of this area

Coldwater Shale

Marshall Sandstone (Mississippian) at surface, covers 34 % of this area

Marshall Sandstone

Coldwater Shale (Mississippian) at surface, covers < 0.1 % of this area

Mostly gray shale

Coldwater Shale (Mississippian) at surface, covers < 0.1 % of this area

Shale; gray; clayey thin bedded; siderite nodules common; as much as 150 feet thick.