Science Dictionary
Pennsylvanian   (pěn'səl-vān'yən)  Pronunciation Key 
The sixth period of the Paleozoic Era, from about 320 to 286 million years ago. Rock deposits from this period of time alternate between being marine and terrestrial in origin, and are rich in coal. Reptiles first appeared in the Pennsylvanian Period. See Chart at geologic time.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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