Cincinnati Arch, geologic anticlinal (archlike) structure influential during the Paleozoic Era (542 million to 251 million years ago); it existed as a persistent low-lying land area flanked by seas covering a large part of the continent while connected with the ocean. The axis of the Cincinnati Arch extends southward from Ohio to Tennessee. Separated by a structural saddle, its southward extension is known as the Nashville Dome. On the north the Cincinnati Arch has two branches; one, trending west-northwest, is known as the Kankakee Arch. The other branch, trending north-northeast, is known as the Findlay Arch.
Ordovician rocks occur on the crest of the Cincinnati Arch, whereas Pennsylvanian strata can be found in the flanking basinal areas.
The Cincinnati Arch began to form during the Middle Ordovician (472 million to 461 million years ago) and was distinctive by the Silurian Period (444 million to 416 million years ago). Uplift occurred in Middle Devonian time (398 million to 385 million years ago), during which considerable erosion took place. Broad doming and uplift again occurred in post-Mississippian time, after which the arch was again submerged. Uplift once again affected the arch in post-Pennsylvanian time.