Timeline

The chert types are aranged from oldest to youngest

Chert Type               Age                      Series                       Formation/Member ----------------------------------------------------------------------------------------------------------------            Grassy Knob             Devonian               Lower Devonian         Grassy Knob Chert            Clear Creek               Devonian               Lower Devonian         Clear Creek Chert            Chouteau                  Mississippian          Kinderhookian            Chouteau Limestone            Fern Glen                 Mississippian          Valmeyeran                 Fern Glen Limestone            Burlington                 Mississippian          Valmeyeran                Burlington Limestone                       Grime Hill                 Mississippian          Valmeyeran                Burlington Limestone            Cresent Hills              Mississippian          Valmeyeran                Burlington Limestone            Mill Creek                 Mississippian          Valmeyeran                Warsaw-Salem Formation            St. Louis                   Mississippian          Valmeyeran                St. Louis Limestone            Cobden/Dongola        Mississippian          Valmeyeran                St. Louis Limestone             Root Beer                 Mississippian          Genevievian               St. Genevieve Limestone             Old Blue                   Mississippian          Genevievian               St. Genevieve Limestone             Kaolin                      Chesterian              Elvirian                      Vienna  limestone or                                                                                                                  secondary deposit              Moline                      Pennsylvanian        Desmoinsian              Spoon Formation

Bibliography

Types