The Trenton Formation is a geologic formation in Canada and Michigan, Ohio, and Indiana in the United States. It preserves fossils dating back to the Ordovician period.
The Waynesville Formation is a geologic formation in Ohio and Indiana. It preserves fossils from the Late Ordovician period.
The Saluda Formation is a geologic formation in Ohio and Indiana. It preserves fossils dating back to the Ordovician period.
The Liberty Formation is a geologic formation in Ohio and Indiana. It preserves fossils dating back to the Ordovician period.
The Grant Lake Formation is a geologic formation in Ohio and Kentucky. It preserves fossils dating back to the Ordovician period.
The Bull Fork Formation is a geologic formation in north central Kentucky and southwestern Ohio. It preserves fossils dating back to the Ordovician period.
The Breathitt Formation is a geologic formation in Ohio and Kentucky. It preserves fossils dating back to the Pennsylvanian period.
The Cincinnati Group is a geologic group in Kentucky, Ohio and Indiana. It is Upper Ordovician.
The Harrodsburg Limestone is a geologic formation, a member of the Sanders Group of Indiana Limestone, of Mississippian age. It was named for Harrodsburg in southern Monroe County, Indiana by T. C. Hopkins and C. E. Siebenthal. It is made up primarily of calcarenite and calcirudite. It also may include some beds of dolomite and shale.
The Salem Formation is a geologic formation in Illinois, Indiana, Kentucky, and Missouri. It preserves fossils dating back to the Mississippian subperiod.
The Davis Formation is a geologic formation in Indiana and Missouri. It preserves fossils dating back to the Cambrian period.
The Osgood Formation, also known as the Osgood Shale is a geologic formation in Indiana, Kentucky, and Ohio. It preserves fossils dating back to the Silurian period.
The Otterdale Formation is a geologic formation in Virginia. It preserves fossils dating back to the Triassic period.
The Fernvale Limestone is a geologic formation in Alabama, Arkansas, Illinois, Missouri, Oklahoma, and Tennessee. It preserves fossils dating back to the Ordovician period.
The Franconia Formation is a geologic formation in the upper mid-western United States, with outcroppings found in Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, and Wisconsin. It preserves fossils dating back to the Cambrian period. It was named the Franconia Formation due to the first published documentation of exposures in vicinity of Franconia, Minnesota in the 1897 Ph.D. dissertation by Charles P. Berkley at the University of Minnesota titled Geology of the St. Croix Dalles. The Franconian stratigraphic stage was named after this formation.
The St. Clair Limestone is a geologic formation in Arkansas, Indiana, Missouri, and Oklahoma. It preserves fossils dating back to the Silurian period. This high density, high magnesium dolomitic limestone was originally classified as a marble in Oklahoma due to the fact that it would hold a high polish, hence Marble City.
The Fern Glen Formation is a geologic formation in eastern and southeastern Missouri. It preserves fossils dating back to the Osagean Series of the Mississippian subperiod.
The Minturn Formation is a geologic formation in Colorado. It preserves fossils dating back to the Carboniferous period. Among the fossils preserved are of crinoids, spiriferid brachiopods, gastropods, and the spines and teeth of numerous sharks such as Petalodus
The Huntersville Chert or Huntersville Formation is a Devonian geologic formation in the Appalachian region of the United States. It is primarily composed of mottled white, yellow, and dark grey chert, and is separated from the underlying Oriskany Sandstone by an unconformity. The Huntersville Chert is laterally equivalent to the Needmore Shale, which lies north of the New River. It is also laterally equivalent to a sandy limestone unit which is often equated with the Onondaga Limestone. These formations are placed in the Onesquethaw Stage of Appalachian chronostratigraphy, roughly equivalent to the Emsian and Eifelian stages of the broader Devonian system.
