Mendip Hills In some areas the limestone and the dolomitic conglomerate have been mineralised with lead and zinc ores. From the time of Roman Britain until 1908, the hills were an important source of lead. These areas were the centre of a major mining industry in the past and this is reflected in areas of contaminated rough ground known locally as "gruffy". The word "gruffy" is thought to derive from the grooves that were formed where the lead ore was extracted from veins near the surface. Other commodities obtained included calamine (zinc ore), manganese, iron, copper and baryte. The eastern area reaches
Schlangenberg Nature Reserve the surface where erosion removed large amounts. About 200 million years ago aqueous metal solutions filled the cavernous rocks. Primary ores were created mostly consisting of Sphalerite, Marcasite and Galena. The process continued and the ore close to the surface decomposed due to the influence of carbon dioxide and water. In this process as a secondary ore calamine ZnCO which is known as calamine developed. Presumably the Celts had been the first digging for the calamine in the region. Ancient Celtic and Roman coins dated between 100 BC and 92/93 AD as well as remains of a Roman settlement proved