"Coal. Stratified bedrock. Occurs onshore. Deposited during the Bolsovian Substage (Carboniferous Period) (314.75-310 Ma BP)."@en . . . "314.75"^^ . "HTNC"@en . . "stable"@en . "310.0"^^ . . . "Houghton Thin Coal (South And West Yorkshire)"@en . "Coal."@en . . "Houghton Thin Coal (South And West Yorkshire)"@en . . .