"Glascoed Mudstone Formation"@en . . . "Coalbrookdale Formation"@en . . "At least 220 m thick."@en . . . "Calcareous silty mudstones and siltstones, with limestone nodules, localised thin bentonitic clays, and very fossiliferous containing a diverse shelly fauna, mainly of brachiopods."@en . . "Wenlock Shales [Obsolete: use GLMD, NYG]"@en . "stable"@en . "Mudstone and siltstone with subsidiary clay and limestone. Stratified bedrock. Occurs onshore. Deposited during the Wenlock Epoch (Silurian Period) (432.9-426.7 Ma BP)."@en . "Glascoed Mudstone Formation"@en . "432.9"^^ . . "GLMD"@en . . "At the base of sandstone-dominated beds of the Ton Siltstone Formation."@en . "426.7"^^ . . "Not seen."@en .