Drive up Arkengarthdale and look up onto the rocky slopes. The old lead mine workings are easy to spot, they are the bits where little grows.
During the eighteenth and nineteenth centuries the dales which formed the catchment area for the River Swale produced more than half a million tons of lead, one of the most productive areas in the country.
Robert White, the senior conservation archaeologist for the Yorkshire Dales National Park, says what little is left is far from being a blot on the landscape. "They are quite a tourist draw if you like, archaeology's strange in that sense. Nineteenth century remains which are, to some extent, built out of traditional materials, and are now slightly picturesque ruins, are quite attractive features in the landscape to many people's eyes."
There is a lot of social history here too. The workers set up some of the first public subscription libraries in the country. But this was brutal industry. As well as dust affecting the lungs - a condition known as "black spit" – there were the hazards of working in dark and wet conditions and the impact of the smelting process where fumes were given off. No wonder many of the workers died young. About 40 per cent of the Yorkshire Dales National Park was once mined for lead, particularly around Arkengarthdale and Swaledale, and there's still plenty to see. "Places like Gunnerside Gill have some of the finest mining landscapes in Northern England, if not the country," says Mr White
This landscape has often been shaped by the way that the lead ore, or galena, was extracted. Sometimes this was done by driving horizontal tunnels into the hillside, on occasions miles into the rock, leaving large spoil heaps at the open end of these shafts. Little vegetation grows on them, even today. Another technique was "hushing". This used the power of water to clear away the topsoil to expose the rock. The idea was to dam streams above the area to be worked. The water behind it was then released in torrential force over the section of the hillside containing the lead deposits. Once the rock-face had been exposed, miners chiselled and hacked at what was left.
"People should look out for a large linear quarry or gorge without much of a stream running through it," says Robert White. "Mainly dry, but 100 or 150 feet deep sometimes." Heavy metals which remain in the soil tend to be toxic to most plants. Some flowers which can tolerate the lead ore, and even thrive on it, although according to Robert White these plant colonies can take decades or even hundreds of years to grow. Spring Sandwort is one example, and some of the places are Sites of Special Scientific Interest, SSSIs. One such is the Ballowfields Local Nature Reserve near Carperby in Wensleydale, which is rich in these lead tolerant plants, known as metallophytes. Dr Paul Evans, regional biodiversity coordinator for Natural England, the body responsible for designating SSSIs, says: "The common one we think of in the Dales is the Spring Sandwort, also known as the Leadwort, which is extremely common on these old spoil heaps right across Northern England, but they are quite scarce in Britain as a whole."
Other lead loving species include Moonwort, a small fern, as well as a plant called the Thrift. There are also SSSIs based on old lead workings at Pikedaw Calamine Caverns close to Malham Tarn.
These old lead mineworkings may be good for the archaeologists,
the tourist trade and botanists. But they can cause problems for farmers with animals which graze around the old spoil heaps. "After you turned out your ewes with their lambs in May, you had to go regularly to the moor to see that they were all right," says Raymond Alderson, a retired farmer from Low Row in Swaledale. For him the legacy of this once massive industry could be a nightmare, especially for his lambs.
"They used to go stiff, they wouldn't walk far, they went stiff on their hind legs and they'd lie down."
He blames the residues of lead from the spoil heaps. "It didn't come every season, every year. If it was a wet spring it wasn't so bad. If it was dry then that was the trouble." Mr. Alderson suspects there was more dust around when it was dry, and this allowed more of the lead to get into the animals.
Scientists who have studied lead deposits on farmland think that heavy rainfall may cause problems further down the hill in the flood plains and valley bottoms. Dr Peter Abrahams from the Institute of Geography and Earth Sciences at the University of Aberystwyth has just completed a study which looks at how much lead sheep could potentially ingest from grass growing on land affected by the run-off of old lead mines.
"What I was interested in was the flood plain soils, because you have sediments being transported down the surface drainage systems, through rivers and streams," says Dr Abrahams.
He says his studies show sheep in these pastures take in lead through soil that they also eat alongside the grass, especially when the grass is short and sheep have to bite closer to the roots. "As much as 44 per cent of the dry matter intake for the sheep was soil." says Dr Abrahams.
Some of the soil samples studied by the team showed as much as 2,000 parts of lead per million. The average in normal soil is 40 parts per million. By comparing the amount of lead residue in the soil with what came out in sheep droppings, the team was able to work out just how much the animals were taking in.
"Lead concentration in the faeces was very high," says Dr Abrahams.
Some of these metals are showing up in analysis for blood and wool from the animals, so some of it must be absorbed. He would like to carry out further sampling – on offal and other meat from lambs raised in these "lead rich" pastures – to try to find out how much might be getting into our food.
Dr Abrahams is sceptical about these lead residues causing health problems and adds says that there is very little we could potentially do about it. "If you think about mineralisation and mining in England and Wales, you're looking at hundreds and thousands of square kilometres of land which are enriched in a variety of elements, such as lead, copper, arsenic, zinc and
Although lead mining died out early in the twentieth century, a victim of cheap imports from South America, it will take a lot longer to kill off its remains. The parts of our landscape which have been rendered largely lifeless by the lead ore will stay that way for many years to come, and Dr Paul Evans from Natural England thinks this is important.
"We often just value the natural world in terms of natural features, and natural plant communities," he says.
"But there's a whole range of man-made habitats, ex-industrial sites, roadside verges, which all harbour their own specific mixtures of plants. As a botanist, the reasons those grow together are incredibly important. We have a lot to learn."