Geologic units in Henry county, Illinois

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 48 % of this area

Tradewater Formation

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 36 % of this area

Carbondale Formation.

Silurian System undivided (Silurian (Llandovery to Pridoli)) at surface, covers 7 % 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.

Shelburn-Patoka Formations undivided (Pennsylvanian (Kasimovian)) at surface, covers 7 % of this area

Shelburn-Patoka Formations undivided.

Muscatatuck Group (Middle Devonian (Eifelian to Givetian)) at surface, covers 2 % of this area

Muscatatuck Group, includes Grand Tower Limestone and St. Laurent (Alto and Lingle) Formation in southern Illinois; includes Detroit River Formation, Wapsipinicon Limestone, and Cedar Valley Limestone in northern and western Illinois.

New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone (Middle Devonian (Givetian) to Upper Devonian (Fammenian)) at surface, covers 0.3 % of this area

New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone.