ice-sheets, which locked away large quantities of water, and the weight of the ice in the north that caused the landmass to tilt. During the summers, partial melting of the ice created large rivers that washed enormous amounts of sand and gravel across the county, forming huge terraces in both the upland areas and valleys. These rivers cut down into the landscape as they made their way to the lower sea levels. This action caused many large-scale landslips, most notably around Shaftesbury and Abbotsbury. Landslips caused by marine erosion still occur today, with some of the largest taking place along the West Dorset Coast. Fossilised remains, including the teeth and tusks of elephants and mammoths dating back 500,000 years, are often exposed. Flint and chert tools from early human visitors have been retrieved from the river terraces around the Dorset and Devon border, although these may have been transported here with the other river deposits. Chesil Bank, a long barrier beach stretching from West Bay to Portland, was created 10,000 years ago, when sea levels rose at the end of the last ice age. Structure Structural development The Variscan orogeny is the oldest event for which evidence is found in Dorset, forming a major series of thrust faults in Carboniferous and older rocks. These thrusts trend west–east, dip moderately towards the south, and have controlled later basin development and subsequent phases of inversion. During the Permo-Triassic, the area was affected by a phase of rifting that reactivated the older thrusts in extension. These extensional faults were themselves reactivated during further rifting in Jurassic to early Cretaceous times. The area experienced the effects of the early stages of Alpine collision during the Late Cretaceous to Palaeogene, with reverse reactivation of many of the extensional faults, creating the most visible of the structures in the Dorset area, such as the Purbeck Monocline. Litton Cheney Fault The Litton Cheney Fault is a west–to-east-trending, south-dipping normal fault. The fault was active during deposition of the Lias Group and again during the late Jurassic to early Cretaceous. Some evidence exists of minor reversal on the fault during the late Cretaceous to Palaeogene inversion. Abbotsbury–Ridgeway Fault This major west–to-east-trending, south-dipping normal fault was mainly active during the late Jurassic to early Cretaceous, as shown by the local preservation of the Wealden in its hanging wall. It was reactivated as a reverse fault during the late Cretaceous