Eroded liassic limestone cliffs. Heavily-eroded limestone, shale and sandstone cliffs. Rockfalls (centre and left) are caused by wind, rain and wave erosion. Limestone is a sedimentary rock formed from calcium minerals such as calcium carbonate, from the shells of marine organisms accumulating on the bed of an ancient sea millions of years ago. The strata (layers) of sediment are clearly seen in the cliff face. The limestone dates from the Carboniferous period (360-300 million years ago) and early Jurassic period (the Lias, 200-176 million years ago). This is one of the best examples of liassic limestone cliffs in the world. Photographed near Southerndown, on the Glamorgan coastline, South Wales.