. . . "461.25"^^ . . "Bryn Brith Grits [Obsolete: use BYN]"@en . "Mafic tuff and tuffite with subsidiary tuffaceous-sandstone and trace mudstone. Stratified bedrock. Occurs onshore. Deposited during the Abereiddian Stage (Ordovician Period) (468-461.25 Ma BP)."@en . . "Bryn Brith Member"@en . "BYN"@en . "Massive lenticular beds of disturbed mafic tuff, tuffite and tuffaceous sandstone, with subordinate thin mudstones."@en . "Bryn Brith Beds [Obsolete: use BYN]"@en . . . "Conformable on the felsic ash-flow tuffs of the Offrwm Volcanic Formation or within the lowermost mudstones of the Cregennen Formation."@en . . "To 65m, and might be locally up to 150m."@en . . "stable"@en . "Conformable within the mudstones of the Cregennen Formation."@en . "468.0"^^ . . "Bryn Brith Member"@en .