Geologic units in Clark county, Illinois

Bond Formation (Pennsylvanian (Kasimovian)) at surface, covers 37 % of this area

Bond Formation

Mattoon Formation (Pennsylvanian (Kasimovian)) at surface, covers 36 % of this area

Mattoon Formation.

Shelburn-Patoka Formations undivided (Pennsylvanian (Kasimovian)) at surface, covers 26 % of this area

Shelburn-Patoka Formations undivided.

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 2 % of this area

Carbondale Formation.

Patoka and Shelburn Formations (Pennsylvanian) at surface, covers 0.2 % of this area

Mostly shale and sandstone; also includes thin beds of limestone and coal. WF, top of West Franklin member

Bond Formation (Pennsylvanian) at surface, covers < 0.1 % of this area

Mostly shale and sandstone; also includes thin beds of limestone and coal