St. Peter Sandstone, Everton Formation
Decorah Group, Plattin Group
Alluvium - clay, silt, sand, and gravel.
Fine crystalline, silty, cherty dolomite, and oolitic chert with local sandstone beds.
Chattanooga Shale, Sylamore Sandstone, Fortune Formation, Holts Summit Sandstone, Snyder Creek Shale, Cedar Valley Limestone, Louisiana Limestone, Saverton Shale, Grassy Creek Shale, Turpin Sandstone, Bushberg Sandstone, Glen Park Limestone, St. Larent Limestone, Beauvais Sandstone, Grand Tower Limestone, Clear Creek Chert, Little Saline Limestone, Grassy Knob Chert, Bailey Formation.
Joachim Dolomite, Dutchtown Formation
Leemon Formation, Maquoketa Group including: (Girardeau Limestone, Orchard Creek Shale, Thebes Sandstone, Cape La Croix Shale), Cape Limestone, Kimmswick Limestone, Noix-Cyrene Limestone, Maquoketa Shale.
Joliet Limestone, Bowling Green Dolomite, Bryant Knob Formation, Bainbridge Formation, Sexton Creek Limestone.
Kimmswick (Trenton) Limestone and Decorah Formation in southern and western Illinois.
Tamms Group, includes Bailey Limestone, “Flat Gap Limestone”, Grassy Knob Chert, Backbone Limestone, and Clear Creek Formation.
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.
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.
Coarse - crystalline cherty dolomite with a basal Gunter Sandstone Member.