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Lower Devonian

Lower Devonian
State Illinois
Name Lower Devonian
Geologic age Devonian
Comments The lower Devonian includes the following formations: Clear Creek Chert, Backbone Limestone, Grassy Knob Chert, Bailey Limestone. Based on the statigraphic column on the 1967 paper map, these units collectively consist of about 60% limestone, 30% chert, and 10% dolomite.
Primary rock type limestone
Secondary rock type chert
Other rock types dolostone (dolomite)
Lithologic constituents
Major
Sedimentary > Carbonate > LimestoneThe lower Devonian includes the following formations: Clear Creek Chert, Backbone Limestone, Grassy Knob Chert, Bailey Limestone. Based on the statigraphic column on the 1967 paper map, these units collectively consist of about 60% limestone, 30% chert, and 10% dolomite.
Minor
Sedimentary > Carbonate > DolostoneThe lower Devonian includes the following formations: Clear Creek Chert, Backbone Limestone, Grassy Knob Chert, Bailey Limestone. Based on the statigraphic column on the 1967 paper map, these units collectively consist of about 60% limestone, 30% chert, and 10% dolomite.
Sedimentary > Chemical > ChertThe lower Devonian includes the following formations: Clear Creek Chert, Backbone Limestone, Grassy Knob Chert, Bailey Limestone. Based on the statigraphic column on the 1967 paper map, these units collectively consist of about 60% limestone, 30% chert, and 10% dolomite.
Map references
Willman, H.B., and others, (compilers), 1967, Geologic Map of Illinois: Illinois State Geological Survey, scale= 1:500,000, paper.
Unit references
Willman, H.B., and others, (compilers), 1967, Geologic Map of Illinois: Illinois State Geological Survey, scale= 1:500,000, paper.
Counties Alexander - Jackson - Pulaski - Union