So named to distinguish it from charcoal. The English did not use much sea-coal until c.1200. The sea-coal that was used came from the beaches of Northumberland and Durham having been washed ashore from seams exposed by the action of the sea. However, coals from Newcastle were arriving in London by c. 1225; exports to Flanders expanded throughout the 13c.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.