Geologic units in Logan county, Illinois

Shelburn-Patoka Formations undivided (Pennsylvanian (Kasimovian)) at surface, covers 46 % of this area

Shelburn-Patoka Formations undivided.

Bond Formation (Pennsylvanian (Kasimovian)) at surface, covers 31 % of this area

Bond Formation

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 23 % of this area

Carbondale Formation.

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers < 0.1 % of this area

Tradewater Formation