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Geologic Map
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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
Rock Types
Political Boundaries

  Legend and Rock Ages

Ordovician Rocks - 505 to 440 million years ago

map of Ordovician rocks


One of the most important geological events of the Ordovician period is the Taconic Orogeny, a series of mountain building events located in what we now know to be the northeastern United States. At the end of the Ordovician, there was also a huge extinction of many forms of marine life due mainly to an increase of glaciation and subsequent decrease in sea level.

Ordovician rocks are more common in the northeastern parts of the continent. They are found in features such as the Appalachian Valley and Ridge Province, the Michigan Basin, and the exotic terranes of the northeast.