The Geology of Ohio--the Ordovician

To geologists, the Ordovician System of Ohio is probably the most famous of the state's Paleozoic rock systems. The alternating shales and limestones of the upper part of this system crop out in southwestern Ohio in the Cincinnati region and yield an incredible abundance and diversity of well-preserved fossils. Representatives of this fauna reside in museums and private collections throughout the world. Indeed, fossils from Ohio's Ordovician rocks define life of this geologic period, and the rocks of this region, the Cincinnatian Series, serve as the North American Upper Ordovician Standard. Furthermore, in the late 1800's, Ordovician rocks in the subsurface in northwestern Ohio were the source of the first giant oil and gas field in the country.