Geologic units in Brown county, Ohio

Grant Lake Limestone and Fairview Formation, Undivided (Ordovician) at surface, covers 37 % of this area

Limestone and shale, interbedded; gray to bluish-gray weathers light gray to yellowish-gray; planar to lenticular, thin to medium bedded in lower half; wavy to irregular to nodular, thin to thick bedded in upper half; fossiliferous.

Preacherville Member of the Drakes Formation, Waynesville and Arnheim Formation, Undivided (Ordovician) at surface, covers 34 % of this area

Shale, limestone, and dolomite, interbedded; gray to maroon in upper part, weathers yellowish-gray to light-gray; planar to irregular to wavy to nodular, thin to thick bedded; shale increases upward.

Waynesville and Arnheim Formations, Undivided (Ordovician) at surface, covers 20 % of this area

Waynesville Formation, shale (70%) and limestone (30%) interbedded; gray to bluish gray weathers light gray; planar to irregular, thin to thick bedded; 90 to 120 feet thick. Arnheim formation, shale (60%) and limestone (40%) interbedded; gray to bluish gray weathers light gray; planar, wavy, irregular, to nodular (in upper portion), thin to thick bedded; 50 to 100 feet thick. Contains multiple sedimentary cycles consisting of the alternation of shale and limestone displaying planar to irregular bedding with limestone and shale exhibiting wavy to nodular bedding. Ranges from 140 to 220 feet. The Geological Survey of Ohio recognizes the Cincinnati Group proposed by Meek and Worthen (1865), but at this time retains it as an informal term. The unit will be formally reinstated as a lithostratigraphic term after revision of its lower boundary and minor lithologic redescription of its units are completed. The ten formations included in the group are the (ascending) Clays Ferry Formation, the Kope Formation, the Fairview Formation, the Miamitown Shale, the Grant Lake Limestone, the Arnheim Formation, the Waynesville Formation, the Liberty Formation, the Whitewater Formation, and the Drakes Formation. Six members have been identified in the course of field mapping: the Point Pleasant Tongue of the Clays Ferry, the informal Bellevue, Corryville, Mount Auburn, and Straight Creek members of the Grant Lake Limestone, and the Preachersville Member of the Drakes Formation. The Backbone Creek and Elk Creek beds are recognized as excellent stratigraphic marker beds (Shrake and others, 1988).

Kope Formation (Ordovician) at surface, covers 5 % of this area

Shale (75%) and limestone (25%) interbedded; gray to bluish gray weathers light gray to yellowish gray; planar, thin to thick bedded; 200 to 260 feet thick.

Point Pleasant Formation (Ordovician) at surface, covers 2 % of this area

Limestone (60%) and shale (40%) interbedded; gray to bluish gray weathers light gray; planar to lenticular, thin to medium bedded; 0 to 80 feet thick.

Drowning Creek Formation (Silurian) at surface, covers 1.0 % of this area

Limestone, and shale, interbedded; limestone, shades bluish, greenish, and yellowish gray to grayish-pink weathers light gray to shades of red; planar to irregular to nodular, thin to thick bedded; fine to very coarse grained; locally silty, dolomitic, cherty, glaconitic; moderate to abundant fossils. Shale, greenish-gray to bluish-gray weathers light gray, thin bedded; silty.

Drakes, Whitewater and Liberty Formations, Undivided (Ordovician) at surface, covers 0.7 % of this area

Drakes Formation; shale (90%) and limestone/dolomite (10%), interbedded; gray and maroon, weathers yellowish gray; planar to irregular, thin to thick bedded; 20 to 30 feet thick. Whitewater Formation, limestone (60%) and shale (40%) interbedded; gray weathers yellowish gray; irregular to wavy, thin to medium bedded; 20 to 80 feet thick. Liberty Formation, limestone (50%) and shale (50%), interbedded; gray weathers yellowish gray; planar to irregular, thin to medium bedded; 20 to 40 feet thick. Interval ranges from 60 to 150 feet in thickness. The Geological Survey of Ohio recognizes the Cincinnati Group proposed by Meek and Worthen (1865), but at this time retains it as an informal term. The unit will be formally reinstated as a lithostratigraphic term after revision of its lower boundary and minor lithologic redescription of its units are completed. The ten formations included in the group are the (ascending) Clays Ferry Formation, the Kope Formation, the Fairview Formation, the Miamitown Shale, the Grant Lake Limestone, the Arnheim Formation, the Waynesville Formation, the Liberty Formation, the Whitewater Formation, and the Drakes Formation. Six members have been identified in the course of field mapping: the Point Pleasant Tongue of the Clays Ferry, the informal Bellevue, Corryville, Mount Auburn, and Straight Creek members of the Grant Lake Limestone, and the Preachersville Member of the Drakes Formation. The Backbone Creek and Elk Creek beds are recognized as excellent stratigraphic marker beds (Shrake and others, 1988).

Estill Shale (Silurian) at surface, covers 0.2 % of this area

Shale and minor dolomite interbedded, reddish to greenish gray, weathers light gray, planar to irregular bedding, thin to thick bedded, 30 to 180 feet thick. Diagnostic features include dominance of shale and the units susceptibility to be unstable on slopes and cause landslides.

Salina Group (Silurian) at surface, covers < 0.1 % of this area

Dolomite, gray, yellow-gray to olive-gray, laminated to thin bedded; occasional thin bed and laminae of dark gray shale and anhydrite and/or gypsum; brecciated zones in part.