. "Gras Uchaf Coal (South Wales)"@en . . . "GUCO"@en . "318.0"^^ . "Gras Uchaf Coal (South Wales)"@en . . . . "stable"@en . "Coal. Stratified bedrock. Occurs onshore. Deposited during the Duckmantian Substage (Carboniferous Period) (318-314.75 Ma BP)."@en . . "314.75"^^ . "Coal."@en . .