Tamms Group, includes Bailey Limestone, “Flat Gap Limestone”, Grassy Knob Chert, Backbone Limestone, and Clear Creek Formation.
Upper Pope Group (Tar Springs Sandstone through Kinkaid Limestone).
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.
Lower Pope Group (Aux Vases Sandstone through Glen Dean Limestone).
Ullin and Salem Limestones in southern Illinois.
Ste. Genevieve Limestone.
St. Louis Limestone.
Tertiary and Cretaceous undivided.
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.
Meppen Limestone, Fern Glen Formation, and Burlington-Keokuk Limestone.
Ft. Payne Formation, includes Springville Shale and Chouteau Limestone in southern Illinois.
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.
Warsaw Formation and Salem Limestone in western Illinois.
Alluvium - clay, silt, sand, and gravel.
Cretaceous undivided, includes Post Creek (Tuscaloosa), McNairy, and Owl Creek Formations (southern Illinois).