Definition of Avalonia
: a tectonic plate that was an independent continent about 500 million years ago and is currently divided between southwestern Great Britain and eastern North America A strip of the Maine coast south of Bangor is part of Avalonia. So too is eastern Massachusetts and all of Rhode Island. … Fossil trilobites found in outcrops at Braintree, Massachusetts, are also found in the Carolinas, the Canadian Maritime Provinces, southern Ireland, and parts of England and Wales—but nowhere else on Earth. — Chet Raymo and Maureen E. Raymo, Boston Globe, 11 Dec. 1988
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