The Duke's Level
The Duke's Level is an adit built to drain the mines of Grassington Moor. Its entrance is in the Hebden township, on the west bank of Hebden Gill, about 800 metres from the Hole Bottom gate, and 200 metres above the Mossy Moor Reservoir outlet. Its most obvious feature when walking up the the miners' track is an outlet from a small stone and concrete water management tank cascading into the beck.
The productivity of the Grassington Moor Mines fell by half between the 1760s and the 1790s, largely because many of them had reached the water table, and drainage became too much of a problem for the relatively small-scale operators to overcome. The Duke of Devonshire (then William Cavendish, the 5th Duke) received a sixth share of the output of the mines, and his revenue was also declining. By the mid-1790s it had become obvious that something had to be done to ensure the future of his revenue. After a number of options were considered, the site in Hebden Gill was chosen to be the outlet of a drainage sough that would drain the mines of both Yarnbury and Grassington Moor.
About 34 acres of unenclosed land with their mineral rights were purchased from the Trust Lords of the Hebden Township in 1796, probably for about £360 which was distributed amongst the Trust Lords. This triangular area was enclosed by the Langholme Laithe wall to the south, Tinker's Lane to the west and north, and Hebden Beck to the east.
Cornelius Flint, the Duke of Devonshire's Mineral Agent, was responsible for the project. Originally he intended that the level should not just drain the mines, but should also be used to transport ore from the mines on small boats. With this in mind, the tunnel was to be nine feet wide with walkways on either side.
Thomas Bowdin was selected to oversee the operation. He was a successful mining agent in the Duke's Ecton Mines in Staffordshire. The Duke bought Hole Bottom and the land associated with it, in particular the land that stretched up the west side of Hebden Gill up to the tranche of common land just purchased. In doing so, he also procured 3.6% of the Manorial Rights, thus gaining a foothold in the township that the twelfth duke still has today. Thomas Bowdin and family moved into Hole Bottom in August 1796. The Bowdins were to play a major role in the village for the next 100 years.
Excavation of the adit was slow through the hard rock, Cockbur not being reached until 1811. In 1818 Thomas Taylor, the sixth Duke's newly appointed Mineral Agent reviewed the project with Thomas Bowdin. At this stage the level was 1520 metres long. It was realised that shipping ore through the level on boats, only for it to be hauled back up the hill to be processed, was not a viable proposition, so the decision was made to reduce its size to four foot wide by six and a half feet high, thus lowering the cost of construction considerably as well as speeding up the operation. It was also decided to sink an air shaft at Cupola Corner, which was just ahead of the end of the level, to provide ventilation and a shorter route to remove excavated material. Bowdin's Shaft on Yarnbury was reached by a branch passage called Black Drift by 1820, and then driven forward to drain the whole area. The main adit eventually reached Coalgrovebeck on Grassington Moor in 1830. The construction so far had taken 34 years, and cost over £27,000. Over the next twenty years it was extended, mainly via a set of cross-cuts, to drain most of the rest of the mines on the moor.
The Grassington Moor mines had all closed by 1882, and the Duke's Level was no longer required. In 1886 the seventh Duke sold Hole Bottom farm, including the land in which the Duke's Level lies, to David and Richard Joy. He did, however, retain all the associated mineral and manorial rights.
When Grassington Hospital was built in 1919, its water was supplied from the Duke's Level, pumped up to a concrete reservoir above the hospital and just below Edge Lane. Michael Lee of Chapel Lane, who died in 1982 aged 95, recalled how he helped dig the trenches up the hill. The water from the adit has a very high level of heavy metal contaminants, so the wisdom of using it as a water supply was questionable. The water was also used to augment the village water supply in times of drought in the 1960s and 1970s.
The Adit today
The level was inspected and recorded in 1947 by the British Speleological Association, and there has been no significant change since then, although the entrance was gated by the Craven Water Board in 1997. This resulted in considerable silt accumulations on the floor, hiding the walkways and making progress difficult. Behind the portal, the nine-foot wide adit is walled for the first thirty yards. From here, the adit is cut for a straight line for about 550 metres, passing out of Hebden into Grassington below Tinker's Lane. At the end of this section it used to be possible to see daylight through the entrance portal, until Yorkshire Water modified the entrance.
From this point the adit veers towards the north, passing through a short walled section, and continues in the same direction for just over 400 metres to where there is a step up into a side level on the left. This is Black Drift which leads to a flooded shaft after five metres. It was driven to drain the Yarnbury mines.
Back in the main tunnel, the tunnel is walled for the next 60 metres, with one section reinforced with metal hooping. At the end of this section, the passage veers to the east, and enters unstable shaley ground with an unstable roof, and a total blockage is encountered after a further 50 metres. This point is beneath Cockbur.
Survey of Duke's Level
This survey of Duke's Level was produced by members of the British Speleological Association in June 1941. It also shews its course relative to the surface features. The distance measurements were paced, so should be treated with a bit of caution.
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