undifferentiated rock units

Paleontology and geology

During the Precambrian, Maine did not yet exist. The first parts of Maine were not assembled until the Ordovician, when ancient landmasses were accreted to North America during a mountain-building event. Preserved within one of these terranes is a Late Precambrian to Early Cambrian aged deposit known as the Grand Pitch Formation. The sediments of the Grand Pitch were likely deposited in a deep-water, marine basin with limited oxygen. The trace fossil Oldhamia smithi has been preserved within this rock unit. The organisms that made these traces were never natives of Maine. Instead, they lived out their lives somewhere else, died and became fossilized before becoming part of Maine later in the Ordovician. The fossiliferous rocks of the Grand Pitch Formation are located in northern Maine, but do not show on this map. There are other Precambrian deposits in Maine, including those shown here to the west, but they do not contain fossils.