The wide bands of hard limestone exposed by the weathering cliffs at Kimmeridge Bay all have special names to distinguish them in their alternating sequence with the softer shales. The layers are inclined to the horizontal and their line can be traced gently sloping from one side of the bay to the other in the stacked strata of the cliff.
I believe this particular layer is called the Washing Ledge Dolostone Bed, which is part of the Aulacostephanus autissiordorensis Zone of the Lower Kimmeridge Clay from the Jurassic Period. It is a ferroan dolomite with a narrow, dark grey, central bituminous shale band (also called a central oil-shale parting). The limestone is stained yellow and red by the oxidation (rusting) of the iron minerals on the exposed surface of the rock. The colour contrasts dramatically with the grey shales around it.
West, Ian. Kimmeridge Bay, Dorset. Geology of the Wessex Coast of Southern England. An on-line information resource.
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