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Mineral Resources > Online Spatial Data > Geology > by state > Illinois Geology

Geologic units in Alexander county, Illinois

Lower Devonian (Devonian) at surface, covers 31 % of this area

Lower Devonian

Lithology: limestone; chert; dolostone (dolomite)

Silurian (Silurian) at surface, covers 6 % of this area

Silurian

Lithology: dolostone (dolomite); limestone; coral

Tertiary - Paleocene, Eocene (Tertiary) at surface, covers 24 % of this area

Tertiary - Paleocene, Eocene

Lithology: sandstone; clay or mud; gravel; silt

Galena-Platteville Groups (Ordovician) at surface, covers 6 % of this area

Galena-Platteville Groups

Lithology: limestone; dolostone (dolomite); shale

Upper Devonian (Devonian) at surface, covers 0.7 % of this area

Upper Devonian

Lithology: shale; black shale; limestone; sandstone

Cretaceous (Cretaceous) at surface, covers 19 % of this area

Cretaceous

Lithology: sandstone; clay or mud; gravel; siltstone

Middle Devonian (Devonian) at surface, covers 1 % of this area

Middle Devonian

Lithology: limestone; shale; dolostone (dolomite); sandstone; evaporite; sedimentary breccia;

HOLOCENE SERIES (Phanerozoic | Cenozoic | Quaternary | Holocene) at surface, covers 1 % of this area

HOLOCENE SERIES - Alluvium - clay, silt, sand, and gravel

Lithology: clay or mud; silt; sand; gravel

Maquoketa Group (Ordovician) at surface, covers 7 % of this area

Maquoketa Group

Lithology: shale; limestone; siltstone

Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series (Mississippian) at surface, covers 4 % of this area

Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series

Lithology: limestone; siltstone; shale