Paleontology and geology
North Dakota was above sea level during the early Devonian, but shallow seas later flooded the land and covered the state for much of the rest of the period. The presence of some ancient soil deposits tells us that the shallow seas occasionally receded, exposing the land surface. Coral, brachiopod, cephalopod, gastropod, bivalve, sponge, and fish fossils have been found in the seafloor sediments. Devonian rocks are not exposed at the surface, but information about them comes from drill cores.