Pennsylvanian Subperiod
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Pennsylvanian Subperiod
Second major interval of the Carboniferous Period, lasting from 318.1 to 299 million years ago. The Pennsylvanian is recognized as a time of significant advance and retreat by shallow seas. Many nonmarine areas near the Equator became coal swamps during the Pennsylvanian. These areas are mined for coal today.
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