bed

At Stair Hole, on the Durdle Promontory in Dorset, England, the sedimentary beds of Portland and Purbeck limestone have been folded into a step- or stair-like shape. This was the result of tectonic movements during the Alpine mountain-building period, 30 million years ago. The folding has also fractured the limestone, and the lines of weakness thus created were later exploited by marine erosion to form small arches in the limestone.

At Stair Hole in Dorset, England, the sedimentary beds of Portland and Purbeck limestone have been folded into a step- or stair-like shape, by tectonic movements during the Alpine mountain-building period, 30 million years ago. The folding has also fractured the limestone, and the lines of weakness thus created were later exploited by marine erosion, forming small arches in the limestone.

In geology, a single sedimentary rock unit with a distinct set of physical characteristics or contained fossils, readily distinguishable from those of beds above and below. Well-defined partings called bedding planes separate successive beds or strata.

The depth of a bed can vary from a fraction of a centimetre to several metres, and can extend over any area. The term is also used to indicate the floor beneath a body of water (lake bed), and a layer formed by a fall of particles (ash bed). Beds of Portland and Purbeck limestone are clearly shown at Stair Hole, next to Lulworth Cove, Dorset, England.