Sedimentary rocks are composed of sediment particles deposited by wind or water, or organic products of living creatures, or residues deposited by inorganic chemical processes such as precipitation or evaporation.
Sedimentary rock occurs in two regions of Georgia: Ridge and Valley, and Coastal Plain. Sandstones, shales, limestones, and coal of the Ridge and Valley range in age from Cambrian to Pennsylvanian; they incorporate fossils of trilobite, brachiopod, crinoid, fern, and lepidodendron (scale tree). Younger, softer sandstones, limestones, and sediments of the Coastal Plain range in age from late Cretaceous to Holocene (recent); they include fossils of marine molluscs, Pleistocene megafauna (e.g. sloth), and shark teeth. Dinosaur fragments have been found in Coastal Plain rivers.
Ridge and Valley sediments were deposited 300-600 million years ago on the continental shelf of Proto-North America, beneath waters of the Iapetus Ocean. When movement of Earth's crust -- plate tectonics -- closed the Iapetus basin, collision of Proto-Africa with Proto-North America faulted and folded these sediments in parallel bands. 300 million years of erosion have shaped them into the Ridge and Valley provinces of Appalachia's western mountains.
About 100 million years ago, in mid-Cretaceous time, sea level stood hundreds of feet higher than today. Cretaceous shoreline erosion cut the Fall Line scarp in Georgia's surface. Below the Fall Line, shallow seas deposited Cretaceous and younger sediments of today's Coastal Plain. Sea level has fallen erratically since mid-Cretaceous, leaving progressively younger sediments toward the south and east. The Coastal Plain appropriately resembles a sea bed, with sandy soils and gentle slopes.