"Mudstone and trace sandstone. Stratified bedrock. Occurs onshore. Deposited during the Aeronian Age - to - Telychian Age (Silurian Period) (440.5-432.9 Ma BP)."@en . "stable"@en . . "Either disconformable on earlier Llandovery or Ashgill or conformable with Henfryn Formation. In latter case junction is gradational but taken at the base of the first thick mudstone bed above the pebbly mudstones, conglomerates and sandstones of the Henfryn Formation."@en . . . "440.5"^^ . . "Cerig Formation"@en . . "Either at the base of the incoming of thinly interbedded laminated and burrowed mudstones of the Dolfawr Mudstones, or at the base of the incoming of pervasively laminated mudstones of the Builth Mudstones."@en . "CER"@en . . "15 - 480m"@en . "Grey to green mudstones with dark burrow mottles. Units of dark laminated hemipelagite common in lower half of formation in slope settings, rare to absent on shelf. Sparse thin sandstones. NOTE: At Llandovey (type area) it is underlain by either the Derwyddon Formation or the Wormwood Formation and overlain by the Gwernfelen Formation. In the Rhayader district it overlies the Henfryn Formation or rests disconformably on earlier Formations. It is overlain by either the Dolfawr Mudstones or the Builth Mudstones."@en . . "Tarannon Pale Shales [Obsolete: use CER]"@en . "Pale Shales [Obsolete: use CER, DOL]"@en . "432.9"^^ . "Cerig Formation"@en . . "Bryn Bedwen Formation [Obsolete: use CER]"@en . . . .