Devonian rocks are exposed at the surface in the Knobs Region, which rings the Blue Grass Region. Devonian rocks are absent in the Blue Grass Region, but occur below the surface in other areas of Kentucky. During most of the Devonian, Kentucky was covered by shallow tropical seas, although some very low lands may have been emergent at times in central Kentucky. During the later part of the Devonian, deep seas covered Kentucky, and the water was poorly oxygenated at depth. Dark organic-rich muds were deposited, producing the Devonian black shales in Kentucky, which contain oil shales and are a potential source for a variety of fossil fuels. Much of the oil and gas found in Kentucky originally came from these Devonian black shales.
All the Devonian rocks found in Kentucky are marine and consequently all the fossils are marine (sea-dwelling) invertebrates and vertebrates. Common Devonian fossils found in Kentucky include sponges (Porifera), corals (Cnidaria), bryozoans, brachiopods, trilobites, snails (gastropods), clams (pelecypods), squid-like animals (cephalopods), crinoids (Echinoderms), and microscopic animals like ostracodes and conodonts. Probably the most common sponge fossils found in Kentucky are the stromatoporoids, or stroms for short. Stroms are calcareous sponges that form mounds 2 to 3 feet across on the sea floor. Stroms still exist today in moderately deep water. Devonian stroms can be seen at the Falls of the Ohio near Louisville (see below).
Fossil bones of giant arthrodires, sharks, and other fish have been found in the Devonian rocks in the Knobs Region of Kentucky. Some giant arthrodires, with sharp cutting beaks, grew to more than 20 feet in length and fed on sharks. A big arthrodire is shown chasing smaller fish in the Devonian scene above.
The most commonly found plant fossils in the Devonian black shales of Kentucky are silicified logs (called Callixylon) of the seed-fern tree, Archaeopteris. Several silicified fossil logs from these shales in Kentucky are on display at the Smithsonian Institution in Washington, D.C. Rarely, foliage from these and other plants is found in these Devonian shales
Perhaps the most famous fossil coral outcrop in the world is the Falls of the Ohio near Louisville. Many solitary and colonial coral fossils can be seen in the rocks exposed in this protected area. Access to the outcrop is best on the Indiana side of the Ohio River (through the Falls of the Ohio State Park), although the exposures are actually in Kentucky.