Source : Webster's Revised Unabridged Dictionary (1913)

Sea coal \Sea" coal`\
   Coal brought by sea; -- a name by which mineral coal was
   formerly designated in the south of England, in distinction
   from charcoal, which was brought by land.

   {Sea-coal facing} (Founding), facing consisting of pulverized
      bituminous coal.

Source : WordNet®

sea coal
     n : pulverized bituminous coal; used as a foundry facing