Geology

This is the largest and most important landslip area on the British coast, with fine exposures of Lias and Cretaceous rocks, a species-rich naturally-developed ashwood, and a rich grassland and cliff flora. The NNR is some 8 km long, aligned east-west along the South Devon coast. Its interest derives mainly from a massive 1839 landslip, when a large field became detached from the main cliff and moved seaward. Both the chasm and the cliffs, which rise to about 150m in altitude have largely become covered with woodland and scrub.

Because of its isolation, plant and animal communities have developed virtually untouched by man. In particular, a species-rich, ungrazed, coastal ashwood has developed. A continuing series of minor slips has produced an area of varied topography, as well as exposing fresh areas for geological study and for colonisation by wildlife. The climate is typically western Atlantic, and the frequent damp mists encourage a profuse and vigorous growth of ferns and climbers.

This is the most renowned area of landslipping in Great Britain. Although movements probably commenced towards the end of the pleistocene, the very large Bindon Landslip of 1839, to the west of the area, brought the site to public prominence. The features of the Bindon slip are now much obscured by vegetation, but the major topographic elements, for example to the chasm-bound block known as 'Goat Island', are clearly discernible from the air. The series of slides involved Chalk, Upper Greensand and Gault of the Cretaceous Period, with Jurassic and Triassic sediments beneath. Large-scale movements are infrequent, but smaller-scale movements continue to the present day, notably near the western fringes of Lyme Regis and in the Pinhay area. This is an historic site which has played an important part in the elucidation of landslip processes.

It is also the richest Lower Jurassic reptile site in Britain, and probably the world. The Lower Lias of this coast has yielded hundreds of extremely well preserved specimens of ichthyosaurs, plesiosaurs, pterosaurs and linosaurs, including type specimens of more than 15 species. Fossil reptiles have been collected here since the 18th century, and important finds are still being made as cliff erosion exposes fresh rock. Entire skeletons have been extracted from the Blue Lias and the 'Shales with beef'. The coast from Pinhay Bay eastwards into Dorset is an outstanding, internationally important, locality. It shows the most complete Lower Jurassic sequence in Europe. In Britain it is the only single section which provides exposures through the entire Lias, and thus practically constitutes the British standard section. The coast has been the subject of innumerable studies documented in an enormous body of literature spanning two centuries and dealing with all aspects of palaeontology and stratigraphy. Pinhay Bay itself is an important site for studying Rhaetian (Triassic) sediments showing a thick development of White Lias and their transition into the Jurassic strata above, affording unrivalled exposures for this rock interval. The White Lias section, eight metres in thickness, includes the 'Sun Bed' at its top. Above, these beds grade into the Pre-Planorbis Beds and overlying Hettangian Blue Lias.

The most extensive exposures of the most southerly British Rhaetic outcrops are seen at Culverhole, where an outstanding section of Rhaetian strata is overlain by the Albian (Cretaceous). A section from the Tea Green Marls to the White Lias is exposed here. At the base of the section, a highly fossiliferous bone bed is seen to penetrate the Tea Green Marls; this has yielded archosaur bones. Landscape marble occurs in the two metre Cotham section, beneath the white Lias.