The remains of a cupola lead smelt mill built by the Duke of Devonshire to serve the lead mines on Grassington Moor in 1792. At the height of production the smelt mill contained two coal-fired reverberatory (‘cupola’) furnaces, a roasting furnace and a slag hearth. The mill is associated with an elaborate flue (nearly 1600 metres long) with two condensers in its course, terminating in an 18 metres high chimney. The chimney was saved by the Earby Mines Research Group which undertook major repairs to it in 1966 and 1971. The extended flue was built in the 1850s in order to collect lead from the waste gases called ‘fume’ drawn off the furnaces. The lead condensed out on the sides of the flue and on brushwood loaded into the two condensers along its course. The flue was regularly scraped and washed out and the contents led into settling ponds lying just above the smelt mill.