Whitby Mudstone Formation

This is a medium and dark grey fossiliferous mudstone and siltstone, laminated and bituminous in part, with thin siltstone and silty mudstone beds and rare fine-grained calcareous sandstone beds; dense, smooth argillaceous limestone nodules are very common at some horizons; phosphatic nodules at some levels. Nodular and fossiliferous limestones occur at the base in some areas.

In the Cleveland Basin around Staithes the base of the mudstone is resting upon the ooidal limestone or Sideritic nodules (Ironstone Doggers) of the Cleveland Ironstone Formation.