Several beds of volcanic ash, now weathered to a clay called bentonite, are interbedded with Ordovician limestones in northwestern Georgia.
A volcanic island arc and possibly a small continent collided with North America in the Middle to Late Ordovician period, resulting in the formation of a large mountain range to the east.
Volcanic eruptions in eastern North America about 454 million years ago spread as as far south as Georgia, as far west as the Mississippi River, and eastward into Europe, which at that time was situated quite a bit closer to North America.
These provinces are known as the Coastal Plain, Piedmont, Blue Ridge, Valley and Ridge, and Appalachian Plateau.
The geologic history of each province is unique, but all the histories are interrelated.
Sea levels dropped worldwide at the end of the Ordovician period because of the buildup of glacial ice near the South Pole.
the Devonian period (416 to 359 million years ago), a large continent called Baltica (Europe) collided with northeastern North America, and a volcanic island arc called the Avalon terrane (or Carolina terrane) collided with eastern North America.