undifferentiated rock units

Paleontology and geology

Shallow, warm marine waters covered Vermont during the Ordovician. The tropical seas were rich in marine life, including the first tabulate corals as well as bryozoans, brachiopods, cephalopods, gastropods, sponges, and trilobites. The shallow waters soon gave way to progressively deepening seas as a subduction zone developed to the east. Volcanoes rose and eroded, shedding sediments back toward the continent. In central Vermont, the Green Mountains, part of the Appalachian Mountain chain, rose to lofty heights as plates collided. This map indicates the presence of Ordovician rocks along the western margin of the state.