"Coralville Member" "County Line (Alburnett) silt" "Covel Conglomerate Bed" "Coxville Sandstone Member" "Cramer Limestone Member" "Crane Member" "Creal Springs Limestone Member" "Cretaceous System" "Croixan Series" "Crowleys Ridge Silt" "Curlew Limestone Member" "Cypress Sandstone" "Dane Member" "Danville Coal Member" "Davenport Member" "Davis Coal Member" "Davis Member" "Daysville Dolomite Member" "De Graff Coal Member" "De Long Coal Member"