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CAVING
Exploring Mendip’s minerals
FOR more than a thousand years the Mendip Hills have been known as a rich source of various minerals. Lead ore or galena was exploited by the indigenous Iron Age people and the mines were quickly exploited by the Roman invaders, who most likely used the local miners as slave labour. The only nonWith PHILIP metallic mineral, coal, was mined on eastern HENDY Mendip, from Nettlebridge north to Bristol and Gloucestershire. The mines are of little interest to cavers. Lead was the commonest mineral, being largely found in the carboniferous limestone. Mines were opened all over central Mendip and much ore was extracted close to the surface. The extensive trenches or “gruffs” at Charterhouse testify to the scale of the operation. After the Roman occupation, the heyday of lead mining was from the medieval period onwards, tailing off towards the end of the 19th century, although working of ancient lead-rich slag continued into the early 20th century. Processing the ore into lead ingots requires water and there were four “Mineries”; two at Priddy, The Waldegrave and St. Cuthbert’s works at Charterhouse, and also on Smitham Hill. Independent miners took their lead to these works to be processed and paid a tithe of “lot lead” for the privilege. It is thought that over the years in excess of 180,000 tons of lead was extracted from the mines. The metal was used for roofing and for holding the pieces of glass in stained glass windows. As an alloy with tin or copper, it makes pewter, for tableware. Associated with the lead were two other valuable metals, silver and arsenic. The Romans knew about the silver, which was present in the galena at about 0.009%. It was originally extracted by cupellation, by which the lead was heated and oxidised, leaving metallic silver. By the late 19th century, however, the Pattinson process was developed, which was much more efficient. Although it is thought that the Romans exploited the best silver-bearing ores, it is estimated that the Pattinson plant at Charterhouse was producing up to 100 pounds weight of silver annually between 1858 and 1878. The value of arsenic was not at first realised; in fact it was a dangerous nuisance. Carried aloft in the smoke from the lead smelting process, it was known to poison the surrounding land, causing illness and death in livestock and people. Long flues were built to cool the “flight”, allowing the arsenic to condense on the walls. Periodically it was scraped off and sold. The use of arsenic as a poison is well-known, but other uses included herbicides, wood preservatives, and, until the danger was realised, as a cosmetic. Second only to lead was zinc, mined all over Mendip as the carbonate, calamine, in the dolomitic conglomerate. The main area was around Shipham, where evidence still abounds in the numerous spoil heaps. One of Mendip’s longest mines, Singing River Mine, was originally excavated in the search for calamine. There are also mines around Sandford and in Harptree Combe. Around 100,000 tonnes of zinc were extracted from the hills, much being used to make brass in mills along the valley of the Bristol Avon. Iron was also mined at various places across Mendip. This ore
Charterhouse rakes
came in two main forms; the hard haematite, smelted to make metallic iron, and the softer red or yellow ochre. The metallic iron was used to make tools and other implements, the Fussell’s edgetool works in the Wadbury valley being particularly well-known, exporting its products across the world as well as throughout the UK. Each region has its own preferences regarding edge tools and Fussells willingly catered for these idiosyncrasies. Yellow ochre was found across the hills, notably around Sandford and Banwell and on Axbridge Hill. Some was extracted close to the surface, but there are deeper mines, rediscovered by cavers, which are more extensive. One such is Shute Shelve Cavern, while higher on the hill Axbridge Hill Cavern still has substantial amounts of yellow ochre and some mining artefacts. Winford Red, from mines around that village, was famous; the deep red colour could be enhanced by roasting the rock. Red ochre was also dug at Compton Martin Ochre Mine, now a protected bat roost. Ochre was not usually smelted to obtain metallic iron. Its main use was in paint manufacture and a thriving Bristol industry grew around it, remember Valspar? It was also used in the linoleum industry. This was a widely-used hard-wearing and waterproof flooring material before the invention of vinyl. There were a small number of manganese mines, most notably at Higher Pitts, south of Priddy. Manganese oxide, or Wad, is soft and dull black. It is a powerful oxidising agent, although the main uses were for clarifying glass and giving a black appearance to pottery. Barytes, or barium sulphate, is often found in conjunction with other ores. It is a dense mineral and the use of the barium meal when X-raying the intestinal tract is well-known. Usually, the barytes was not worth harvesting, although it was sufficiently plentiful at Banwell to be mined for making white paint and quality paper. Strontium, as the sulphate or celestine, is used to give a red colour to fireworks and has been used in Germany for refining sugar beet. Some was mined between Dinder and Westbury-subMendip, but the main mines were further north, at Yate and Chipping Sodbury. Mining and the reworking of slags ended around a hundred years ago and many sites have been lost, due to land reclamation and for safety reasons. The industry has been well-documented over the years and enough mines can still be explored to give us an idea of what it was like to have been a Mendip miner.
Phil has been caving for more than 50 years and is a member of the Wessex Cave Club. He has been involved in producing several caving publications and until his retirement was a caving instructor at Cheddar. His main interest is digging for new caves
PAGE 90 • MENDIP TIMES • NOVEMBER 2021
(Photograph by Phil Hendy)
MENDIP TIMES
