. "Comprises thick bits of coarse-grained green-grey massive sandstone, and interbedded mudstone, which is locally manganiferous, and local conglomerates."@en . "Bronllwyd Grit Formation"@en . "500m"@en . . "BGR"@en . "Bronllwyd Grit Formation"@en . "stable"@en . "486.9"^^ . . "Sharply defined but generally conformable base of coarse conglomeratic sandstone overlying the mudstones of the Llanberis Slates Formation."@en . . "Sandstone with subsidiary conglomerate and mudstone. Stratified bedrock. Occurs onshore. Deposited during the Comley Series - to - Merioneth Series (Cambrian Period) (526-486.9 Ma BP)."@en . "526.0"^^ . . . "Gradational into basal mudstones of the Marchlyn Formation."@en .