"Foel Grach Basalt Formation"@en . . . . "458.2"^^ . . "Rests on part of the Nant Ffrancon Subgroup and locally on the Braich Tu Du Volcanic Formation."@en . "Foel Grach Basalt Formation"@en . . . . "stable"@en . "400m in north; c.180m to the south."@en . "Basalt and volcaniclastic-breccia. Stratified bedrock. Occurs onshore. Deposited during the Caradoc Series (Ordovician Period) (458.2-449.75 Ma BP)."@en . "449.75"^^ . "Basalt and basalt breccias."@en . . "FGB"@en . "Overlain by outflow of the Foel Fras Volcanic Complex and by part of the Nant Ffrancon Subgroup."@en .