WThe Blakely Sandstone is a Middle 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 had initially named this unit the Caddo Shale at a 1907 Geological Society of America meeting, but later redefined and renamed the unit as the Ouachita Shale. He again renamed the unit to the Blakely Sandstone in a letter to Edward Oscar Ulrich, to which Ulrich used in a 1911 publication, becoming the first reference using this name. Ulrich assigned the Blakely Mountain in Garland 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.
WThe Bliss Formation is a geologic formation that is exposed in southern New Mexico, west Texas, and southeastern Arizona. It preserves fossils dating back to the late Cambrian to early Ordovician periods.
WThe Crystal Peak Dolomite is a geologic formation in the Wah Wah Mountains of western Utah. It preserves fossils dating from the Ordovician period.
WThe Cummingsville Formation is a geologic formation in Iowa and Minnesota. It preserves fossils dating back to the Ordovician period.
WThe El Paso Formation is a geologic formation that is exposed from the Permian Basin of New Mexico and Texas to southeastern Arizona. It preserves fossils dating back to the Ordovician period.
WThe Gull River Formation is a geological formation of Middle Ordovician age, which outcrops in Ontario, Canada. Lithologically, the formation is dominated by light grey to brown limestones and greenish gray dolomites with thin shale and sandstone interlayers.
WThe Kanosh Formation is a geologic formation in Utah and Nevada. It preserves fossils dating back to the Middle Ordovician period.
WThe Kimmswick Limestone is an Ordovician geologic formation in Arkansas, Illinois and Missouri. Fossils occurring in the Kimmswick include corals, bryozoans, brachiopods, conodonts, trilobites, crinoids and mollusks.
WThe Liberty Formation is a geologic formation in Ohio and Indiana. It preserves fossils dating back to the Ordovician period.
WThe Oneota Formation is a geologic formation in the upper Midwest including Minnesota, Illinois, Indiana and Wisconsin. It preserves marine fossils dating back to the Ordovician period.
WThe Platteville Limestone is the Ordovician limestone formation in the sedimentary sequence characteristic of the upper Midwestern United States. It is characterized by its gray color, rough texture, and numerous fossils. Its type locality is Platteville, Wisconsin. It was heavily used in the early decades of the building of Minneapolis–Saint Paul and Faribault, Minnesota.
WThe Queenston Formation is a geological formation of Upper Ordovician age, which outcrops in Ontario, Canada and New York, United States. A typical outcrop of the formation is exposed at Bronte Creek just south of the Queen Elizabeth Way. The formation is a part of the Queenston Delta clastic wedge, formed as an erosional response to the Taconic Orogeny. Lithologically, the formation is dominated by red and grey shales with thin siltstone, limestone and sandstone interlayers. As materials, comprising the clastic wedge, become coarser in close proximity to the Taconic source rocks, siltstone and sandstone layers are predominant in New York.
WThe Richmond Formation is a geologic formation in Michigan and Ohio. It preserves fossils dating back to the Ordovician period.
WThe Roubidoux Formation is a geologic formation in the Ozarks of Missouri and in Virginia. It preserves fossils dating back to the Ordovician period.
WThe Waynesville Formation is a geologic formation in Ohio and Indiana. It preserves fossils from the Late Ordovician period.
WThe Whitewater Formation is a geologic formation in Ohio and Indiana. It preserves fossils dating back to the Ordovician period.