Map of United States in the Middle Pennsylvanian Time

By Water Availability and Use Science Program 1969 (approx.)

Map of the U.S. where most areas of the Nation are covered by sea and swamps.

Original Thumbnail Medium

Detailed Description

Map of United States in Middle Pennsylvanian Time (about 300 million years ago). Source: USGS Bulletin 1291.

Sources/Usage

Public Domain.