The Pennsylvanian Period
in West-central Illinois
North America, during the Pennsylvanian period (325 million to 280 million years ago), was locationed on the equator. As the super continent of Pangaea was being formed, North America was colliding with Europe and Africa. During this time Illinois was part of a vast lowland that extended for hundreds of miles, interrupted only by a few areas of low hills. As this great lowland subsided, Illinois became covered by a shallow, tropical sea. During this time great beds of limestone, with many fossils of marine plants and animals, were formed. At other times, the Illinoian lowlands were covered by vast tropical, swamp forests. Seed ferns, true ferns and giant horsetails and club mosses lived long side primitive insects, amphibians and reptiles in these great swamp forests. As the plants died and fell into the swampy water, their remains formed thick layers of peat. As time continued on the great peat beds would be transformed into large deposits of bituminous coal.