Carboniferous Period

Eon: Phanerozoic

Era: Paleozoic

Followed by: Permian Period

Preceded by: Devonian Period

Formation: Llewellyn

Range: Central and Western Pennsylvania

Fossil Types: Plants, especially ferns and trees

Description: The Carboniferous Period is formally divided into two major subdivisions—the Mississippian (358.9 to 323.2 million years ago) and the Pennsylvanian (323.2 to 298.9 million years ago) subperiods. The Pennsylvanian Subperiod is recognized as a time of significant advance and retreat by shallow seas. Many non-marine areas near the Equator became coal swamps during the Pennsylvanian. Ferns and Lycopod tree remains became fossilized during this period and are plentiful in the Llewellyn Formation.