Adapted from published geologic quadrangle maps ROCK UNITS TIME UNITS GEOLOGIC TIME SCALE Gravel Geologic Time Scale adapted from American Association of Petroleum Geologists, Stratigraphic Correlation Charts for Northern Appalachian and FORMATION, Crossbedded Midwestern Basin and Arches MEMBER, or BED sandstone Regions. PERIOD 3 million years Sandstone or sand Sandstone and shale Alluvium interbedded Interbedded shale and sandstone QUATERNARY Glacial deposits Shale and minor sandstone 3 million years Drift The following geologic units are absent because of either nondepos- tion or erosion: Tertiary, Cretaceous, Jurassic, Triassic, Permian, and part Silty shale of the Pennsylvanian. 320 million years Flint clay Carbonaceous shale Formations Lee and Breaathitt Clay shale PENNSYLVANIAN Olive Hill Clay Bed 330 million years Dolomitic shale Newman Limestone Interbedded shale and Nada Member limestone; shale dominant Interbedded limestone Cowbell Member and shale Interbedded limestone Nancy Member and shale; limestone dominant Borden Formation Farmers Member Nodular-bedded MISSISSIPPIAN limestone, minor shale Henley Shale Bed Cherty limestone Sunbury Shale Dolomitic limestone ? Berea Sandstone Silty to sandy dolomite Bedford Shale Soft-sediment deformation 365 million years DEVONIAN Unconformity Ohio Shale 415 million years Bisher Dolomite 420 million years Crab Orchard Formation SILURIAN Brassfield Formation 425 million years Drakes Formation Bull Fork Formation Grant Lake Limestone Fairview Formation ORDOVICIAN Upper Part of Ordovician Kope Formation Point Pleasant Tongue of Clays Ferry Formation Figure 3. Stratigraphy of rock units along the AA Highway and U.S. 23. 9.