|Geologic age||Middle Devonian (Eifelian to Givetian)|
Sedimentary > Carbonate > Limestone (Bed)Limestone can be sandy, silty, shaly or argillaceous, or cherty.
Sedimentary > Clastic > Mudstone > Claystone > Bentonite (Bed)K-bentonite
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Carbonate > Dolostone (Bed)Dolomite can be sandy or silty.
|Comments||Thickness from stratigraphic columns: Grand Tower Ls (0-230’), St. Laurent (Alto and Lingle) Fm (0-200’) in southern Illinois (south of 40 degrees north latitude); Detroit River Fm (0-30’), Wapsipinicon Ls (0-100’), and Cedar Valley Ls (0-100’) in northern Illinois (north of 40 degrees north latitude). In southern Illinois, the units (from oldest to youngest) are the Grand Tower Limestone and St. Laurent (Alto and Lingle) Formation: the Grand Tower Ls includes, from oldest to youngest, the Dutch Creek Sandstone, Geneva Dolomite, and Tioga K-bentonite Bed; and the St. Laurent (Alto and Lingle) Fm includes "Hoing" and "Hibbard". In northern Illinois, the the Detroit River Fm and Wapsipinicon Ls (equivalents) are overlaid by the Cedar Valley Ls: the Hoing Ss occurs at the base of the Cedar Valley Ls. [Oil well drillers' terms shown in quotation marks.]|
|Stratigraphic units||Dutch Creek Sandstone, Geneva Dolomite, Tioga K-bentonite Bed, "Hoing", "Hibbard", Hoing Sandstone|
Kolata, D.R., comp., 2005, Bedrock Geology of Illinois: Champaign, Ill., Illinois State Geological Survey, Illinois Map Series 14, scale 1:500,000.
|Counties||Adams - Alexander - Calhoun - Champaign - Cook - Douglas - Ford - Greene - Henderson - Henry - Iroquois - Jackson - Jersey - Mercer - Pike - Pulaski - Rock Island - Union - Warren|