undifferentiated rock units

Paleontology and geology

In Maine, the rocks of the Ordovician were derived from two very different and distant geographic areas. Some were originally deposited within an ocean along the North American margin, when Maine occupied a position approximately 15 degrees south of the equator. The other set was originally laid down offshore as volcanic islands situated somewhere within the Iapetus Ocean. Eventually, plate movements carried these volcanic islands northeast, where they collided with North America during a mountain-building event, the Taconic Orogeny. As a result, all fossil-bearing deposits in Maine were formed in the marine realm and represent habitats ranging from nearshore to deep-water basins. The nearshore faunas are dominated by brachiopods, but also contain snails, trilobites, corals, and clams. Graptolites and rare occurrences of brachiopods, trilobites and conodonts are found in the deeper water deposits.