The Cincinnati Arch is a broad structural uplift between the Illinois Basin to the west, the Michigan Basin to the northwest and the Appalachian Basin and Black Warrior Basin to the east and southeast. It existed as a positive topographic area during Late Ordovician through the Devonian Period which stretched from northern Alabama northeastward to the southeastern tip of Ontario. Fossils from the Ordovician Period are commonplace in the geologic formations which make up the Cincinnati Arch, and are commonly studied along man made roadcuts. The Nashville Dome of Tennessee and the Jessamine Dome or Lexington Dome of central Kentucky make up the central portion of the Arch. In the northern part, north of Cincinnati, Ohio, the Cincinnati Arch branches to form the Findlay and Kankakee arches. The Findlay plunges under Ontario and reappears as the Algonquin Arch further north.
The Medina Group is a geologic group in New York. It preserves fossils dating back to the Silurian period. The group includes the Whirlpool Sandstone, Power Glen Shale, Devils Hole Sandstone, Grimsby Formation, Thorold Sandstone, Cambria Shale and Kodak Sandstone.
The Power Glen Shale is a geologic formation in New York. It preserves fossils dating back to the Silurian period.
The Gaptank Formation is a geologic formation in Texas. It preserves fossils dating back to the Carboniferous period.
The Pogonip Group is an Ordovician period geologic group located in southern Nevada and in Utah.
The Campito Formation is a geologic formation in Nevada. It preserves fossils dating back to the Cambrian period.
The Deep Spring Formation is a geologic formation in Nevada. It preserves fossils dating back to the Cambrian period.
The Diamond Peak Formation is a geologic formation in Nevada. It preserves fossils dating back to the Carboniferous period.
The Vinini Formation is a marine, deep-water, sedimentary deposit of Ordovician to Early Silurian age in Nevada, U.S.A. It is notable for its highly varied, mainly siliceous composition, its mineral deposits, and controversies surrounding both its depositional environment and structural history. The formation was named by Merriam and Anderson for an occurrence along Vinini Creek in the Roberts Mountains of central Nevada and that name is now used extensively in the State.
The Windfall Formation is a geologic formation in northeastern and southern Nevada.
The Johnson Spring Formation is a geologic formation in California. It preserves fossils dating back to the Ordovician period.
The Al Rose Formation is a geologic formation in California. It consists mostly of siltstone, mudstone and shale, with some chert and occasional limestone. In it are found graptolite and trilobite fossils dating back to the Ordovician period.
The Antelope Valley Limestone is a limestone geologic formation of the Pogonip Group in southern Nevada.
The Buelna Formation is a geologic formation in Mexico. It preserves fossils dating back to the Cambrian period.
The Puerto Blanco Formation is a geologic formation in Mexico. It preserves fossils dating back to the Cambrian period.
The La Ciénega Formation is a geologic formation in Mexico. It preserves fossils dating back to the Carboniferous period.
The Clemente Formation is a geologic formation in Mexico. It preserves fossils dating back to the Ediacaran period.
The Gamuza Formation is a geologic formation in Mexico. It preserves fossils dating back to the Ediacaran period.
The Papalote Formation is a geologic formation in Mexico. It preserves fossils dating back to the Ediacaran period.
The Bigfork Chert is a Middle to Late Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned the town of Big Fork in Montgomery County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated. The Bigfork Chert is known to produce planerite, turquoise, variscite, and wavellite minerals.
