"0 to 4m"@en . "Conformable with the Ceiswyn Formation; immediately overlain by rocks of the Glyn Gower Siltstones Member."@en . "Cefn Gwyn Tuff"@en . "Tuff. Stratified bedrock. Occurs onshore. Deposited during the Caradoc Series (Ordovician Period) (458.2-449.75 Ma BP)."@en . "CGTU"@en . "Cwm Clwyd Tuff Formation [Obsolete: use CGTU]"@en . . "Cefn Gwyn Tuff"@en . . "stable"@en . "458.2"^^ . . . . "Non-welded felsic ash-flow tuff."@en . "Cefn Gwyn Tuff Member [Obsolete: use CGTU]"@en . . . "449.75"^^ . . . . "Conformable with silty mudstones and siltstones of the Ceiswyn Formation."@en .