Location: SE 02631 64796
Dukes Level was a drainage adit driven from Hebden Gill and was approximately 1.5 miles in length. The level provided drainage for most of the deeper workings across Grassington Moor, reaching both Yarnbury and the Out Moor. Work started in 1792 and it was first designed as an underground boat level where ore and waste material could be transported out of the connecting mines, as well as to provide the vital function of drainage. Initially the level was constructed five feet wide by nine feet high, however in 1818, the new mining agent John Taylor instructed that the dimensions of the level were to be reduced down to four feet by six feet and six inches above the rails. Taylor’s reasoning for doing this was due to the cost of driving the level and the fact that once the ore was extracted by the boats it would need to be hauled back up to the mines to be dressed and smelted. As there was no room for a dressing floor and smelt mill at the levels portal from 1818, work was continued only to provide a drainage adit for the mines across the moor. Dukes Level took 20 years to reach the mines at Yarnbury and only reached Coalgrovebeck Engine Shaft on the Out Moor by 1830.
The level was explored by members of the Grassington Mines Appreciation Group on the 5th of March 2020 where it was followed to a distance of around 1300m at which point the passage was completely collapsed. This measurement is not entirely accurate as the team members did not have any form of measuring device and so was calculated by pacing. The passage itself is filled with waist height water and liquid mud that makes it difficult to progress.
The first 10 metres of passage consists of a well line arch, however at the end is a collapse and care needs to be taken passing by it. After this point, the main passage has no stopes holding the roof up and is nice and solid.
The passage has no notable features apart from a couple of stacks of deads and one large piece of wood wedged above head height, however there are numerous shot holes and what looks to be candle holders at certain points along the level. Eventually you come to a point where the passage angles off to the right and after following this for a few minutes, an arch of deads forms the passage roof. Off to the left is the only deviation in the level where a passage can be followed for around 5 metres before reaching a blue coloured sump. From looking at the underground map of the area in British Mining 46, It is believed this is the sump which connects to Beever, mine and the rest of the mines around Yarnbury to provide drainage.
The main passage continues and a number of steel bands are incorporated into the dry stone arching in order to support it. From here, the passage becomes less stable and large sections of the roof have collapsed. The rock seems to be some sort of shale, with layers that peel off from the roof and walls. You can still walk along the passage but there are sections where you have to stoop.
Continuing near to the end of the adit, there is a short left hand passage to the left leading immediately to a collapse. Here inscribed on the wall are the letters EPC 86 written in mud. As of April 2020, it was discovered that the individual who inscribed this note on the wall was John Southworth a longstanding member of the Earby Pothole Club.
Finally, you reach the end of the passage where another arch of deads lines the roof. Here there is a large collapse which has filled most of the floor and only leaving around a foot between the floor and the top of the arch. Behind this, there is a total collapse, but a large amount of water flows through the boulders.
The passage angles to the right 3 times before you reach the collapse. Looking at the British Mining 46 survey, taking into consideration these changes in angle, the distance and including the sump connecting to Beever Mine, It is believed that the limit of exploration is just before Cockbur Mine.
Credit: British Mining 46 - Northern Mine Research Society