The Columbus Limestone is a significant carbonate unit in the Middle Devonian of central and northern Ohio. It's actually part of a much more widespread sheet of Devonian carbonates that extends from New York State to the Midwest. The Columbus Limestone represents deposition in a subtropical, shallow-water, carbonate platform environment. The rocks are principally micritic limestones, fossiliferous wackestones, and fossiliferous packstones. Some chert nodules are present in the unit. Fossils are typical Paleozoic shallow marine invertebrates - favositid corals, rugose corals, stromatoporoids brachiopods, crinoids, blastoids, bryozoans, trilobites, bivalves, gastropods, cephalopods, rostroconchs, and tentaculites. Microfossils include conodonts and charophyte oogonia. Other fossils in the Columbus Limestone include vertebrates (fish), land plants (rare), and trace fossils. Some fossil horizons in the Columbus Limestone are partially silicified.

Seen here is the Lafarge Kelleys Island Quarry near the end of its life. The site was formerly known as the South Side Quarry and the Kellstone Quarry. It was acquired by Lafarge in 2004 and shut down in 2007 - not long after this photo was taken. The quarry is now flooded. The bedrock here consists of Columbus Limestone. Crushed rock ("aggregate") was principally used in various construction projects on the mainland. The construction business sufficiently declined in 2007 to result in the cessation of activity here.

Stratigraphy: Columbus Limestone, Eifelian Stage, lower Middle Devonian