"Glynllifon Trachydacite"@en . "About 350m"@en . . . "Trachydacite. Igneous intrusive bedrock. Occurs onshore. Emplaced during the Caradoc Series (Ordovician Period) (458.2-449.75 Ma BP)."@en . . "stable"@en . "458.2"^^ . . . . . "449.75"^^ . "Porphyritic trachydacite, with sodic andesine phenocrysts, glomeroporphyritic clots and mafic pseudomorphs, apetite and zircon in a weakly flow foliated microcrystalline groundmass."@en . . "GLTD"@en . "Glynllifon Trachydacite"@en .