"DRE"@en . "Greater than 600m in the type area."@en . "The upper boundary is taken at the top of the Mydrim Shales Formation. The boundary is not exposed, but in the type area is defined by a faulted contact with pale grey burrow-mottled mudstones of the Nantmel Mudstones Formation of Ashgill age."@en . . "The lower boundary of the Group is taken at the base of the Felin Wen Formation. The boundary is not exposed, but the incoming of the Formation was previously described by Strahan et al. (1909), from outcrop in a road bank opposite the corn mill in the village of Felin Wen, which yielded Didymograptus murchisoni graptolites."@en . "Mudstone with subsidiary calcareous mudstone, limestone, tuff and tuffaceous-sandstone. Stratified bedrock. Occurs onshore. Deposited during the Llanvirn Series - to - Caradoc Series (Ordovician Period) (468-449.75 Ma BP)."@en . "The Drefach Group comprises mudstones, limestones and tuffs of Llanvirn to Caradoc age exposed on the southwestern margin of the Lower Palaeozoic Welsh Basin. In its type area, south of the village of Drefach, Carmarthenshire, the Drefach Group comprises a lower Felin Wen Formation (formally the Didymograptus murchisoni Beds) overlain by the Asaphus Ash Formation. This is succeeded in turn by the Hendre Shales Formation, Mydrim Limestone Formation and Mydrim Shales Formation (eg Strahan et al. 1909)."@en . . "Drefach Group"@en . "468.0"^^ . . . . "stable"@en . "449.75"^^ . "Drefach Group"@en .