Sussex's natural resources have been used for thousands of years. The South Downs includes some of Britain's earliest mines, including Church Hill, Findon which dates from around 4200BC. while the Sussex Weald was historically the centre of England's iron industry, using iron ore in the form of siderite. The Wealden iron industry was established before the Roman invasion and was superseded in the 18th century by coal areas of Wales and northern England. There remains a long-established deep-mining operation centred on the High Weald village of Brightling, the country's largest resource of calcium sulphate or gypsum. Used primarily to make plaster, plasterboard and cement, gypsum has been excavated in the area since the 1880s.