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
Calamine brass company (within whose monopoly it was) to build a brass works at Isleworth. However a decade later the company obstructed the owners from mining calamine. A plaque at Tintern Abbey claims that the well-known brassworks at this site began in 1568. New brass works were built by Jacob Momma, a German immigrant in 1649 at Esher, probably using Swedish copper. After the passing of the Mines Royal Act in 1689, further works were built near Bristol, where brass production became a major industry in the 18th century. Later brass production sites in England included Cheadle and Birmingham. Calamine brass was