The shale layers that make up most of these cliffs are known as ‘black’ shales because of their dark colour. This comes from the large amount of organic material included in the sediment and tells us that the sea bed at the time must have been stagnant and had very little oxygen. The nature of the rocks and the fossils contained within them points to an ancient deep sea, populated mostly by swimming creatures like ammonites, belemnites, fish, Ichthyosaurs and plesiosaurs.
To the West of Lyme Regis the Undercliff stretches between the cliffs and the sea for eight miles. It has been formed over the centuries by the slippage of land over the cliff-tops. The most spectacular occurred on Christmas Eve 1839 when acres of cultivated land, including a wheat field and a turnip field, slid over the cliffs to form a new landscape of strange-looking gulleys and peaks. What caused this tumult was not known at the time. Was it a landslip, as many locals maintained? Was it an earthquake? Or a volcano? Or even a punishment from God? The arrival of visitors in thousands to see the devastation was soon turned to advantage by the quick-witted locals. Farmers charged sixpence for a visit and there was a gala reaping of the wheat field in its dislodged position.
In the past strips of this land were used for orchards and grazing but today it forms an unspoilt tree-clad wilderness sheltering a wide diversity of plants and animals. In 1959 it became one of the first of Britain’s National Nature Reserves. This area figures vividly in John Fowles’s novel, The French Lieutenant’s Woman, and the film made from it.