A tin mill in the Erme Valley at Stony Bottom.
Reasons for Designation
Dartmoor is the largest expanse of open moorland in southern Britain and, because of exceptional conditions of preservation, it is also one of the most complete examples of an upland relict landscape in the whole country. The great wealth and diversity of archaeological remains provide direct evidence for human exploitation of the Moor from the early prehistoric period onwards. The well-preserved and often visible relationship between settlement sites, major land boundaries, trackways, ceremonial and funerary monuments as well as later industrial remains, gives significant insights into successive changes in the pattern of land use through time.
Blowing mills (also known as blowing houses) survive as rectangular drystone buildings served by one or more leats and are characterised by the presence of granite blocks with moulds cut into them - bevelled rectangular troughs known as mould stones - and on occasion by the square or rectangular stone built base of the furnace itself. During the medieval and early post-medieval period, black tin (cassiterite) extracted from streamworks and mines, was taken to blowing mills to be smelted. Once the tin had become molten, it flowed from the furnace into a float stone and was ladled into the mould stone, in which it cooled to form an ingot of white tin. The original number of blowing mills on Dartmoor is unknown, but at least 26 are believed to survive, whilst a further 41 are known only from stray finds and documentary sources.
During the same period, tin ore extracted from mines was taken to stamping mills to be crushed, using heavy iron-shod stamps attached to the lower end of vertical wooden posts called lifters, which were raised using a water-driven rotating axle. Thus raised, the stamps fell under gravity onto the ore, crushing it between the stamp's head and a hard slab of rock called the mortar stone. There were two types of stamping machinery. The first, known as dry stamps, involved the crushing of the ore without use of water, the second, wet stamping utilised a constant flow of water to carry the tin crushed by the stamps through a fine grate into a channel, to be carried in suspension to a settling pit from where it could be collected for dressing. The original number of stamping mills on Dartmoor is unknown, but at least 60 survive.
Despite its tumbled appearance the tin mill in the Erme Valley at Stony Bottom survives comparatively well and is closely associated with an extensive area of tin streamworkings throughout the Erme Valley. It will contain archaeological and environmental evidence relating to its construction, use, longevity and overall landscape context.
This record was the subject of a minor enhancement on 11 November 2015. This record has been generated from an "old county number" (OCN) scheduling record. These are monuments that were not reviewed under the Monuments Protection Programme and are some of our oldest designation records.
The monument includes a tin mill situated in the upper Erme Valley just north of the confluence between the Hook Lake and River Erme. The tin mill survives as a rectangular drystone structure measuring 6.3m long by 3.8m wide internally with walls of up to 0.7m wide and 1.5m high. Inside there is a section of narrower cross walling which appears to be a later addition. The entrance is in the southern wall at its western end. Internally, there is a large stone which has a rectangular depression thought to be a mould stone, a long slot and two axle bearings on one edge. The presence of this mould stone suggests a possible function as a blowing mill for smelting tin. There is a wheel pit at the western end of the north side of the building which measures up to 4.5m in length and is largely in-filled with tumbled stone. Above this is a leat embankment which connects to a long leat leading back to the River Erme. A nearby place name of Knackersmill Gulf might also imply the tin mill was used as a stamping mill for crushing cassiterite.
The tin mill is located in an area rich with tin streamworkings and other archaeological remains, some of these are scheduled whilst others are not because they have not been formally assessed.