Volcanic rock, Two Lights State Park, Maine

The rock ledges exposed at Two Lights State Park represent the current stage of a very long and dynamic geologic history. The rock that makes up the ledges is classified as metamorphic rock, which means that at one time it was affected by heat and pressure inside the earth which has significantly changed its form. Before metamorphism it was sedimentary rock, which had formed originally by hardening of deep-sea sediment (sand and mud) into rock.

 

420 million years ago, Silurian Period: Sediment accumulated in a deep ocean basin. This basin lay between the edge of North America to the west, which at the time ran approximately from Flagstaff Lake to northern Moosehead Lake, and an ancient small continent to the east, the microcontinent called Avalon.

 

The layers of sediment that accumulated in that Silurian ocean are preserved in the rocks at Two Lights as light gray, massive quartzite and dark gray phyllite layers. The quartzite layers were originally sand or silt beds, and the phyllite layers were originally clay or mud beds. As the layers accumulated one on the other, some were deposited individually with sharp boundaries between them, and others were deposited as mixed masses in graded beds that change gradually from the bottom to the top of the layer.

 

All the rocks at Two Lights State Park belong to a single geologic formation. Geologists in the early 1900's referred to it as the Cape Elizabeth Formation, but geologists now think that these rocks are part of the Kittery Formation , which is found along the southern Maine coast and into New Hampshire.

 

Source: maine.gov

 

September 5, 2012, Cape Elizabeth, Maine, taken here.

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