Galena Group (Trenton Limestone), includes Decorah, Dunleith, Wise Lake and Dubuque Formations in northern Illinois.
Platteville Group, includes Pecatonica, Mifflin, Grand Detour, Nachusa, and Quimbys Mill Formations; includes Plattin Limestone in southwestern Illinois.
Ancell Group, includes St. Peter Sandstone, Dutchtown Limestone, Joachim Dolomite, and Glenwood Formation; includes Prairie du Chien Group in Jo Daviess County of northwestern Illinois.
Dolomite with some limestone and shale; includes Galena, Decorah, and Platteville Formations
Orthoquartzitic sandstone with minor limestone, shale and conglomerate; includes Glenwood and St. Peter Formations
Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations
Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations