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Approximately 10,000 lead industry sites are estimated to survive in England, spanning nearly three millennia of mining history from the later Bronze Age (c.1000 BC) until the present day, though before the Roman period it is likely to have been on a small scale. Two hundred and fifty one lead industry sites, representing approximately 2.5% of the estimated national archaeological resource for the industry, have been identified as being of national importance. This selection of nationally important monuments, compiled and assessed through a comprehensive survey of the lead industry, is designed to represent the industry's chronological depth, technological breadth and regional diversity. Ore hearth smelt mills were introduced in the 16th century and continued to develop until the late 19th century. They were the normal type of lead smelter until the 18th century, when they were partially replaced by the reverberatory smelt mill. The ore hearth itself consisted of a low open hearth, in which lead ore was mixed with fuel (initially dried wood, later a mixture of peat and coal). An air blast was supplied by bellows, normally operated by a waterwheel; more sophisticated arrangements were used at some 19th century sites. The slags from the ore hearth still contained some lead. This was extracted by resmelting the slags at a higher temperature using charcoal or (later) coke fuel, normally in a separate slag hearth. This was typically within the ore hearth smelt mill, though separate slag mills are known. Early sites were typically small and simple buildings with one or two hearths, whereas late 18th and 19th century smelt mills were often large complexes containing several ore and slag hearths, roasting furnaces for preparing the ore, refining furnaces for extracting silver from the lead by a process known as cupellation, and reducing furnaces for recovering lead from the residue or litharge produced by cupellation, together with sometimes complex systems of flues, condensers and chimneys for recovering lead from the fumes given off by the various hearths and furnaces. The ore hearth smelt mill site will also contain fuel stores and other ancillary buildings. Ore hearth smelt mills have existed in and near all the lead mining fields of England, though late 18th and 19th century examples were virtually confined to the Pennines from Yorkshire northwards (and surviving evidence is strongly concentrated in North Yorkshire). It is believed that several hundred examples existed nationally. The sample identified as meriting protection includes: all sites with surviving evidence of hearths; sites with intact slag tips of importance for understanding the development of smelting technology; all 16th- 17th century sites with appreciable standing structural remains; 16th-17th century sites with well preserved earthwork remains; and a more selective sample of 18th and 19th century sites to include the best surviving evidence for smelt mill structures, and flue/condenser/chimney systems.

The smeltmills and related features at Langley represent a complex lead works of two separate, but interdependent smeltmills. These mills, which were individually large and elaborate, were focussed on a small area and have a complex history spanning over a century. The site is well documented in contemporary accounts and all the major mining companies in the North Pennine lead industry were involved in the site at various times: Greenwich Hospital, the London Lead Company, WB Lead and the Hudgill Mining Company. The changing fortunes of the lead industry left a series of distinct impressions on the site, and the monument is a very good example of how economic, technological and social factors shaped industrial sites in the late 18th and 19th centuries. The entire layout of Langley Mill survives as earthworks which will retain evidence for the development of the site and the technologies employed. Langley was also an important early site for zinc smelting and archaeological remains related to this process are also believed to survive. The standing and earthwork remains of ancillary buildings will all add to the understanding of the working of the site. The flue, which was extended and modified several times, retains rare surviving evidence of a steam powered condenser together with features related to the washing and lead recovering system.

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The monument is situated towards the top of the hillside rising from the South Tyne up to Stublick Moor. It includes the buried remains of a closely associated pair of smeltmills, with the standing and earthwork remains of a shared flue system which leads to an intact chimney. The estates of the Earl of Derwentwater were forfeited to the Crown after his part in the 1715 Jacobite Rebellion. These lands, which included the mineral rich area of Alston Moor, were assigned to the Greenwich Hospital in 1735. The London Lead Company took most of the mineral leases and paid Greenwich Hospital a rent in the form of duty ore. Initially this ore was sold back to the London Lead Company who smelted it at their smeltmill at Nenthead, but in 1768 Greenwich Hospital built their own smeltmill at Langley and started smelting the ore themselves. The mill was further expanded in the 1770s and the mill, in addition to the ore hearths, included two refining furnaces (for extracting silver from the lead ore), a reducing furnace (used to convert the lead litharge, which was left after the silver had been extracted, into metallic lead), and a slag hearth (for resmelting the waste slag from the ore hearths). In the 1780s the Greenwich Hospital built a second smeltmill next to, and downhill from Langley Mill which was leased to one of the smaller mining companies. This mill, known as Blagill Mill, used the tailrace water from Langley Mill and later shared the same flue system. In 1801-1803, the first section of horizontal flue was constructed, which extended 70m to 75m uphill from Langley Mill. By 1805, each had three ore hearths, a double refining furnace, a slag hearth, and roasting and reducing furnaces. The complexes each had a water powered stamp mill (for breaking the slag into smaller pieces prior to reprocessing), in addition to a number of store rooms for the different sorts of fuel used by the various processes and for lead at various stages in production. By around 1817 zinc was also being smelted at Langley. This was initially very successful, but due to competition from Germany, the zinc works closed around 1822. By this date, Langley Mill had increased to seven ore hearths and the Blagill Mill was leased by another company, the Hudgill Burn Mining Company. Between 1845 and 1860 the flue system was extended further by approximately 580m with a steam powered condenser installed before 1865. From cartographic evidence most of Blagill Mill had been demolished c.1860, leaving the reducing and refining house which was then converted into cottages. The last 500m section of flue leading to the chimney was built after the first edition 25 inch Ordnance Survey map and was complete by 1882. The mills finally closed in 1887 and much of the remaining works had been demolished by 1896. The building range known as Sawmill Cottages, which includes a two storey house at the east end of a row of three cottages, is excluded from the scheduling, although the ground beneath it and the flue which exits the building through the south wall are included. The 1805 plan of Blagill Mill shows this range of buildings to be the reducing and refining house. Across the trackway to the west of the cottage conversions there is another range of buildings, mostly surviving as wall footings with the easternmost single storey lean-to building still roofed and used as a garage. This building range is considered to have comprised ancillary buildings (such as store-rooms and workshops) and will retain buried deposits that will allow the identification of their functions. The remains of the range of buildings is included within the scheduling. To the east of the cottages there are a series of small gardens belonging to the currently occupied terrace. The revetment wall to the south of the gardens is thought to contain features from the original smeltmill or even to have once been part of it. To the south of this wall and the trackway that runs along the north side of the cottages, the land surface rises to a trackway that runs along the foot of the reservoir's dam. This area contains a number of terraces that include earthworks up to 0.75m high which are the remains of Langley Mill with associated ancillary buildings related to both mills. The entire layout of Langley Mill is believed to survive with in situ deposits of process residues which will retain important technological information about lead smelting from 1770 onwards as well as early 19th century zinc smelting. One nearly complete building survives at the east end of the area, 60m east of the cottages, which has been interpreted as a coal and lime house dating to before 1805. This twin celled, two storey stone building built into the rising ground, retains some flooring and more than half of its stone slab roofing. Across the trackway behind this building there is the approximately 2m high earthwork dam for the reservoir (which still holds water). This reservoir was part of a complex water management system which supplied water to both mills. The original reservoir was extended eastwards sometime after 1805 to triple the size shown on the 1805 plan. It was supplied from a second larger reservoir (Langley Dam) built around 1805, 0.4km to the south west. The embankment of the dam adjacent to the smeltmills has been altered in places to provide platforms for anglers and the north eastern end of the dam is not included in the scheduling. The section of dam included in the scheduling retains at least three different construction styles. The southern end of the dam incorporates the earliest section of the flue built in 1805. In front of the section of walling is an in situ iron valve assembly which is interpreted as part of the water control mechanism for the smeltmills. To the west of the dam are the foundations of another building dating to before 1860 with further earthworks to the rear standing up to 0.2m high which, from cartographic evidence, are thought to be early bingsteads (storage bays for unsmelted ore). Remains of further bingsteads are thought to survive along the flue where it forms part of the dam. The flue was extended after 1805 and zig zags up the hillside. It is thought to have been constructed as a stone lined trench about 1.5m wide which was arched over with a single thickness of pitched stones and then covered with the earth excavated from the trench, thus stabilising the construction. For most of its length the flue survives as an earthwork averaging 1m high and 6m- 7m wide with a hollow running along its top where the stone arching has collapsed. The flue was modified in the 1860s to allow the construction of the Hexham to Allendale railway, with a stone bridge being built to carry the flue across the railway cutting. Langley Mill actively tried to recover lead from the fumes of the furnaces and the earthwork remains of the steam powered condenser and associated features such as low mounds of boiler waste, are included in the scheduling. Just downhill from these earthworks on either side of the flue are the earthworks of a pair of small reservoirs. One is thought to have provided water for the steam engine's boiler which powered the fan in the condensor, but both are thought to have been part of the washing system for the flue. It is thought that periodically workmen entered the flue (via a number of access points along its length) to scrape the deposited material off the walls. Water was then allowed into the flue to wash the material down its length and into settling tanks where the water was allowed to evaporate off, leaving a lead rich mud which was then resmelted. Maintenance access points can be identified at several points along the flue's length retaining its side walling through the bank of the flue, the others as earthwork features considered to retain buried walling. A third small reservoir is located immediately on the west side of flue between these two of the access points. Three settling tanks have also been identified. The first (NY 8334 6230) is a 1.5m deep depression located at the bottom of the steepest section of flue whilst the second is approximately 120m to the south west. The last lies on the south side of the disused railway line, measures 8m by 8m with a 1m high embankment, with another level area served by a trackway immediately to the east. All of these features identified as being part of the washing system for the flue are included within the scheduling. In the 1860s the flue was extended an additional 0.5km beyond the steam powered condensor to end at a chimney on Stublick Moor. This section of flue was slightly wider and, for most of its length, was buried deeper. A small collapsed section, just north of the road, shows that it was 2m wide and 2m high internally, with an arched roof formed by a single thickness of pitched stone. The top of the arch was level with the surrounding land surface and was covered by 0.5m of earth forming the 6m to 7m wide mound that can be seen running across the fields. It is thought that the flue is intact underneath the B6305, and so this section has also been included in the scheduling. At the end of the flue is the chimney which is mostly built in rough ashlar masonry, with the upper third in brick. A number of features are excluded from the scheduling; these are the surface foundations of the B6305 road, modern metalled trackways, the small modern concrete building at NY 8294 6149, Sawmill Cottages, the building west of the dam and all fencing and drystone walls; although the ground beneath all these features is included.

MAP EXTRACT The site of the monument is shown on the attached map extract.