Geologic units in Bureau county, Illinois

Silurian System undivided (Silurian (Llandovery to Pridoli)) at surface, covers 36 % 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 25 % of this area

Shelburn-Patoka Formations undivided.

Carbondale Formation (Pennsylvanian (Moscovian to Kasimovian)) at surface, covers 20 % of this area

Carbondale Formation.

Tradewater Formation (Pennsylvanian (Bashkirian to Moscovian)) at surface, covers 14 % of this area

Tradewater Formation

Mattoon Formation (Pennsylvanian (Kasimovian)) at surface, covers 3 % of this area

Mattoon Formation.

Maquoketa Formation or Group (Upper Ordovician (Stage 6 to Hirnatian)) at surface, covers 0.8 % of this area

Maquoketa Formation or Group, includes Cape Limestone, Cape La Croix Shale, Thebes Sandstone, Orchard Creek Shale, Girardeau Limestone, and Leemon Formation in southern Illinois; includes Scales Shale, Fort Atkinson Limestone, Brainard Shale, and Neda Formation in northern Illinois; includes Noix Oolite in western Illinois.

Bond Formation (Pennsylvanian (Kasimovian)) at surface, covers 0.8 % of this area

Bond Formation

Galena Group (Trenton Limestone) (Upper Ordovician (Stage 5 to Stage 6)) at surface, covers 0.4 % of this area

Galena Group (Trenton Limestone), includes Decorah, Dunleith, Wise Lake and Dubuque Formations in northern Illinois.

Platteville Group (Upper Ordovician (Stage 5)) at surface, covers < 0.1 % of this area

Platteville Group, includes Pecatonica, Mifflin, Grand Detour, Nachusa, and Quimbys Mill Formations; includes Plattin Limestone in southwestern Illinois.