. "Overlain by volcaniclastic mudstones and tuff [Gwern Feifod Tuff]."@en . "GFL"@en . "Gwern Feifod Lava Member"@en . "457.35"^^ . "455.167"^^ . . . "stable"@en . "Felsite. Stratified bedrock. Occurs onshore. Deposited during the Costonian Substage - to - Harnagian Substage (Ordovician Period) (457.35-455.167 Ma BP)."@en . "Flow-foliated and brecciated, vesicular felsic lava."@en . "Gwern Feifod Lava Member"@en . . . "18m"@en . "Conformably overlies volcaniclastic blue-grey mudstone of the Llangynog Formation."@en . .