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Generalized Geologic Map of the Conterminous United States
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  The North American Tapestry of Time and Terrain

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  Legend and Rock Ages
 

Mississippian Rocks - 360 to 325 million years ago

map of Mississippian rocks

 

The Mississippian is the first part of the time period geologists originally referred to as the Carboniferous (the second, later period is the Pennsylvanian) because of the presence of coal in similarly-aged rocks around the world. Mississipian rocks are well-exposed along the Mississippi River Valley (hence the period's name). They are mainly characterized as fossil-rich limestones formed in warm, shallow seas. The end of the Mississippian, however, saw a decrease in sea level, causing a marine extinction.

Mississippian rocks are found in the Ouachita Range and the Michigan Basin.