Meppen Limestone, Fern Glen Formation, and Burlington-Keokuk Limestone.
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.
Glen Park Formation, Hannibal Shale, Chouteau Limestone, McCraney Limestone, Prospect Hill Siltstone, and Starrs Cave Limestone.
New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone.
Baylis Formation (western Illinois).
Kimmswick (Trenton) Limestone and Decorah Formation in southern and western Illinois.
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.
Warsaw Formation and Salem Limestone in western Illinois.
Platteville Group, includes Pecatonica, Mifflin, Grand Detour, Nachusa, and Quimbys Mill Formations; includes Plattin Limestone in southwestern Illinois.
Alluvium - clay, silt, sand, and gravel.
St. Louis Limestone.
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.