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The Redcar Formation is a grey, fossiliferous mudstone and siltstone with subordinate thin beds of shelly limestone below, and fine-grained carbonate cemented sandstone above; argillaceous limestone concretions occur throughout.
The upper boundary is gradational with the overlying Staithes Sandstone Formation, but is taken for consistency at the base of the "Oyster Bed", a fossiliferous calcareous and ferruginous sandstone packed with the bivalves Gryphea gigantea, Oxytoma inaequivalvis and Pseudopecten aequivalvis. This layer appears to persist as a continuous horizon throughout the Cleveland Basin.

Argillaceous limestone concretions in the Redcar Mudstone