"486.5"^^ . . . "Blaen-Y-Glyn Formation"@en . "Stratified bedrock. Occurs onshore. Deposited during the Tremadoc Series (Ordovician Period) (486.5-477.1 Ma BP)."@en . . . "stable"@en . "477.1"^^ . . "Blaen-Y-Glyn Formation"@en . . "BYG"@en . .