Slag, slimes and gruffy ground: a brief history of Mendip lead mining


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In my previous video on the Somerset Coal Canal, I remarked that Somerset is generally not considered as an ‘industrial’ county, nor much associated with mining in the modern popular consciousness. However, the region actually has an extensive history of mining, not just for coal, but also for lead, zinc, copper, and other metals - a history which is both ancient and extremely important.

To first quantify the ‘ancient’ part: evidence of human habitation on the Mendip Hills goes back about as far as anywhere in Britain, with Cheddar Man, the oldest complete skeleton in the country at over 9000 years old, being found in a cave in Cheddar gorge. Some evidence of lead mining here is found from the late bronze age, and by the Iron age it seems apparent this was happening on a pretty big scale (by pre-industrial standards).

Big enough, in fact, to attract the attention of the dominant civilisation of the time, the Romans - which leads me to the ‘extremely important’ claim. British history would look pretty different with no Roman invasion, and while it would of course be highly remiss of me to imply anything as oversimplified as “Romans conquered Britain to get Mendip lead”, because for starters there were other major lead mines in Derbyshire, Yorkshire and elsewhere, not to mention Cornish tin, Welsh gold, and the multitude of factors not relating to metal extraction at all - it is undoubtedly true that the presence of these resources drove Roman engagement with Southern Britain even before the conquest, and was an important motivator of their invasion.

True to the stereotype of the Roman civilisation as technologically advanced and heavy on infrastructure and engineering, they promptly took lead mining to another level. Here at Charterhouse there is evidence of Roman occupation and mining from as early as 49CE, just six years after the invasion and only a couple years after this part of Britain was secured. This speed suggests they took over and ramped up an existing industry rather than prospected from scratch.

The Romans built a fort here to defend the mine, with a small town and an amphitheatre to boot. At least, that’s the story - unfortunately, there’s almost nothing to see in terms of Roman remains, and much as I love Time Team, my budget does not stretch to geophysics teams or helicopter LIDAR surveys, so you’ll pretty much have to take my word for the fact the Roman fort was… er… somewhere over there. In fact, at least one paper has questioned whether the ‘fort’ structure would have any much military value, positing it could have been more like a head office for the mines. And at least one archaeologist has suggested that the supposed Roman amphitheatre is actually a neolithic enclosure, and given the generous sprinkling of neolithic tumuli, earthworks and monuments in the region, this strikes me as entirely plausible, but I’m in no way qualified to confirm.

Roman ingots of lead now in the X museum are stamped with BRIT. EX. ARG. VEB, meaning "British (lead) from the VEB... silver works", suggesting the Roman name for this Charterhouse settlement began with Veb. Someone has reconstructed Vebriacum, but by what means, or how credible this is, I do not know.

The reference to silver works is interesting. Lead here is found in an ore called galena which is also generally an important source of silver. Although it only contains half a percent silver at most, this often ends up being worth more than the lead. Therefore it was long assumed that the Romans were at least equally interested in getting at the silver as the lead, via a process called cupellation, intending to use it to pay the locally stationed armies. Some have even framed the lead output as a mere by-product of silver mining.

However, recent research indicates “that silver was not a desired material during most of the Iron Age and was therefore not extracted from [Mendip] lead even where the levels in the ore would have made it worthwhile to do so. This appears to have been a cultural choice and not a technological limitation”. The author further asserts that there is remarkably little evidence that the Romans significantly changed matters in this regard. Pointing to a lack of archaeological evidence of cupellation facilities, and analysis of local lead artefacts suggesting the lead had usually not undergone de-silvering processes, Matthew Ponting concludes it is likely that in fact silver was more of a bonus by-product of the lead mining than vice versa, and a sporadic and small-scale one at that.

The Romans certainly had plenty of uses for the lead, with Charterhouse lead being used to line the baths at Bath, and being found as far afield as Pompeii.

The methods used to extract the lead created this distinctive post-industrial landscape, which locals call ‘gruffy ground’. The visible impact on the landscape was large because this mining mostly occurred near the surface.

Veins of lead ore were found at a rather shallow depth and were excavated in horizontal channels known as ‘rakes’. The Romans did also sink some vertical shafts to try and find deeper veins, but without much success, so excavation focused on these horizontal trenches near the surface.. In person, some of these feel like quite dramatic mini gorges, although I fear on camera, this doesn’t entirely come across. This rake, for example, is the largest here at several hundred metres long, about 20m wide and 5m deep, and today the exposed mini ‘cliffs’ of limestone are a popular venue for bouldering. With Cheddar Gorge just a couple of miles from here, you could be forgiven for thinking these miniature canyons are a natural formation. [ but no… ]

While most of the excavation would have been done by hand, the Romans also engaged in a form of hydraulic mining - that is, using water, in a process known as hushing. They built dams to create reservoirs of water, and then demolished these dams, so that the resultant wave of water flooding down the valley would scour away soil and vegetation, leaving the bedrock exposed, with any veins of ore therein hopefully visible.

As usual, I am paranoid of accidentally misleading or oversimplifying, so I should note that while we do know Romans used the hushing technique, in general, there isn’t definite evidence that they did so here - and even if they did, the reservoirs I’m showing here to illustrate it are definitely not Roman, nor for hushing. These were constructed to supply water for processing and washing.

Washing was the first step in processing the galena to extract the lead, taking place in a series of buddle pits, circular depressions about half a metre deep and 8 to 11m in diameter. I thought at the time this might be an example of a buddle pit, but it’s a lot smaller than 8m across, so with hindsight, perhaps not. You can see them quite clearly on satellite mode of your favourite online mapping service, though.

After washing, the ore could be smelted. For smelting, you need to heat up your ore, and also add a material known as a flux; the chemistry is beyond me, but it’s basically an additive which helps separate the good stuff from the useless stuff. The lead industry here would have benefited enormously from the fact that both requirements could be amply supplied locally: the Somerset coalfield, just a few miles east, provided the fuel for furnaces, while Mendip is literally made of limestone, which serves as a decent flux when smelting lead or iron.

In the post-Roman period the lead mining seems to have declined, although continued on a smaller scale. Around the 12th(??) and 13th centuries, documents show mining rights were owned by the church. By the 17th century it was more of a free-for-all, with any man discovering a vein able to stake a claim and mine there, and this seems to have driven production to perhaps its highest level, or at least the highest since the Romans, with 70 tons produced in 1610.

In fact, production was so voracious in the 1600s that by the turn of the century the accessible veins had been completely exhausted. Mining technology in the early 18th century was not up to the challenge of accessing deeper veins, especially with regards to drainage, so activity more or less ceased. But by the end of the 18th century, the industrial revolution was brewing, and with the aid of steam engines for pumping water, among various other technological advances, Cornish miners were, quite literally, taking mining to a whole new level.

It was therefore not long before hopeful land-owners and investors hired in this renowned Cornish expertise, convinced that further rich veins of lead would be found deep beneath the Roman and medieval workings. In 1844 a firm by the name of Mendip Hills Mining Company began operating at Charterhouse and their Cornish miners sank shafts up to 100m in depth. Unfortunately, the simple geological fact of the matter was that galena only existed in any significant quantities near the surface, petering out entirely by 50m down.

After three years of expensive digging and not a single worthwhile vein to show for it, the company turned their attention to another tactic: reprocessing the immense piles of slag left behind by their Iron Age, Roman and medieval predecessors. As these earlier generations had lacked blast furnaces and other such technology, their waste heaps still contained significant amounts of retrievable lead.

Specifically, the company found the slag to contain about 17% lead, whereas the “slimes” - a mixture of clay with the watery run-off from previous refinement processes - contained easily twice that; in some cases, incredibly, up to 57% lead. The layer of slag and slimes was several metres deep across a huge area, in places up to 7 metres deep, so this represented a serious amount of lead.

To cash in on this, the company built extensive infrastructure, obliterating most of the Roman archaeology in the process. Here for example we see the remains of the condensing flues. These were a series of 100m long tunnels which drew through the fumes from the blast furnaces, with some further lead being deposited on the bricks, from where it could be scraped off.

Perhaps the biggest infrastructure, though, was the system of water provision, with the large reservoir I showed you earlier, and a complex series of troughs and leats to supply this wherever needed for washing ore, powering waterwheels and so forth.

In 1848 this system was wrecked by a gathering of “40 or 50” rioters from Cheddar, and although the mining company won a legal case against them, with historical hindsight it’s hard not to be on the side of the rioters. See, the reason they were keen to destroy the company’s operations was that they were severely polluting Cheddar’s water supply. It was common practice for the toxic run-off from the buddle pits to be diverted into the nearest convenient swallet, or sink-hole. Unfortunately, the karst geology of the Mendips means that this doesn’t just disappear in the bowels of the earth. Rather, the huge cave systems in the limestone form giant river systems, and in this case, the polluted water emptied into Cheddar’s fish ponds. One of the company’s own staff later admitted that he had tested the water in those ponds and found up to 8% lead contamination.

It was a similar story elsewhere - in the 1860s, the owners of the Wookey Hole paper mill suspected the lead works near Priddy to be responsible for polluting their water, and proved it by dying the water entering St Cuthbert’s Swallet, thus establishing for the first time that this was a source of the River Axe. Intriguingly, cavers still haven’t figured out which swallet near Charterhouse links up to Cheddar…or at least, they hadn’t in 1984, when my source was written.

Pollution woes didn’t stop there. In 1855 the Mendip Hills Mining Company were obliged to buy a neighbouring farm for £8330, after the courts adjudged their smelter fumes to have rendered it unfit for livestock. To this day, the high levels of lead result in this site, and other lead mining locations such as Smitham Hill shown here, supporting rare lead-tolerant species like Spring Sandwort, Dwarf Mouse-Ear and Lead Moss. Unfortunately I lacked both the time and the expertise to find any examples of these species, so I’m just giving you generic shots of the plant life, and you’ll have to imagine these are exciting rarities.

Still, since when have we let environmental destruction stand in the way of hearty profits? These incidents didn’t cripple the company: on the contrary, the 1850s was a high point for the company, with over 300 employees at the Charterhouse operation producing somewhere between 10 and 100 tons a month, depending on which source you ask and which year you’re talking about.

Unsurprisingly, this success prompted entrepreneurs to exploit the slags and slimes of other ancient lead mining venues in similar fashion. Here at Smitham Hill, a few miles away, a group of Cornish miners built smelting works in 1867 to re-process waste. This was initially successful, with some sources claiming it produced 1000 tons a year by 1870, although I’m a teeny bit sceptical as that figure far outstrips even the most optimistic numbers floating around for the much bigger operation at Charterhouse.

At any rate, while initially successful, the Smitham Hill venture was short-lived. By 1875 the facility had closed, and all the buildings except the chimney were demolished. Operations at Charterhouse survived a decade longer, but dwindling reserves of material to reprocess and a fall in the price of lead meant it, too, was forced to close in 1885. The buildings there were demolished soon after, leaving this chimney as the last major standing remnant of an industry that had existed here for at least 2000 years.

Renovated in 1914, it was threatened with demolition in the 70s, before the Mendip Society secured its survival and renovated it once more in 1973. In 1987 it became a grade II listed building and today sits in the midst of a Forestry Commission woodland.

That’s all for this video. If I have somehow failed to sate your desire for lead-related content, you could check out my video on the world's first shot tower, in nearby Bristol, alternatively I have a few videos on other historical curiosities of Somerset, too. Thanks as usual to everyone whose work I built on in making this video, and special thanks to my Mum who discovered the chimney and thereby put me onto this topic in the first place. If you enjoyed the video please give it a like, and subscribe in case I make any more.