Tin mill, tinwork and post-medieval farmstead at Outcombe, 260m east of eastern boundary of Roughtor Plantation

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. On Dartmoor, tin streamworks represent intermittent tin working activity dating from the medieval period to the 20th century. During this time previously abandoned works were often brought back into production, while some streamworks are still not exhausted, raising the possibility that they may become viable once again. Streamworks exploited tin deposits that had been detached from the parent lode and redeposited by streams and rivers within either alluvial deposits in valley bottoms or in eluvial deposits in shallow, steeper tributaries on hillsides. The technique involved large scale extraction (which has left major earthworks visible in the landscape) and the use of water to separate tin from the lighter clays and silts which contained it. The water derived either from canalised streams or reservoirs fed by specially constructed leats which can be seen running for several miles along the contours of many hillsides. The streamworks themselves survive as a series of spoil dumps, channels and disused work areas which indicate their character and development. Streamworking was particularly prevalent on Dartmoor, being by far the most numerous and extensive type of tinwork on the moor. Remains are to be found in most valley bottoms and on many hillsides, where they make a dominant contribution to landscape character as well as providing unusually detailed evidence for medieval industry. Streamworks on Dartmoor will be considered for scheduling where they are well preserved and representative of the industry in this area, or where there is a demonstrable relationship with medieval and later settlement and its associated remains.

During the medieval and early post-medieval 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, and appears to have been employed throughout much of the medieval period until the introduction of wet stamping in the 16th century. 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. Dressing involved separating the lighter waste material from the heavier cassiterite (tin oxide) using water. Much of this work was carried out in sloping rectangular or triangular shaped boxes called buddles where, to prevent premature sedimentation, shovels were used to agitate the contents. The original number of stampings mills of Dartmoor is unknown, but at least 60 survive. Those with associated dressing floors are relatively rare. All well preserved examples are considered to be of national importance. Despite afforestation, the tin mill and tinwork at Outcombe survive well and are an important resource for our understanding of tin extraction and processing. In particular, surviving crazing mills are known to be nationally very rare and this one may contain crucial information relating to the inter-relationship between stamping and crazing. The large number of mortar stones surviving within and around the mill indicates that this processing facility may have operated for a considerable time and therefore information relating to the development of techniques may also survive. The farmstead will also contain archaeological and architectural information but is of particular interest because of its direct spatial association with the adjacent tinwork.

Details

The monument includes a tin stamping and crazing mill, an openwork together with prospecting pits and shaft, an area of alluvial streamworking and a post-medieval farmstead situated on a north facing slope at Outcombe overlooking the Narrator Brook. The tin mill survives as an irregular shaped structure composed of large granite blocks standing up to 1.9m high. The interior measures up to 5m long by 4m wide and is strewn with large granite rocks, many of which are discarded mortar stones bearing one or more circular depressions formed by the hammering of the stamp head. A further group of at least ten mortar stones lies some 70m north west of the mill where they have been arranged to form a low wall. The power to operate the stamping machinery was supplied by a wheel which sat in a stone faced pit on the eastern side of the building. This wheelpit appears to have been served by at least two separate leats. The entrance to the mill survives as a narrow passage leading into the structure from the west. The mill building was also used at some stage for grinding ore between rotating horizontal mill stones. This type of mill is known as a crazing mill and although no crazing stones are currently visible, it is known that at least one existed at the site in the first part of the 20th century. The crushed ore from these mills would have been dressed in nearby buddles. Two relatively steep sided hollows to the north of the mill may represent the site of this dressing activity. Much of the ore crushed at this mill would have been mined from the nearby openwork. This survives as a substantial elongated hollow measuring up to about 30m wide and 15m deep. This openwork was documented in 1577 as Oldebeame, otherwise Outhombeame or Liteltorsworke. Within the base of the openwork is a shaft through which deep tin ore would have been extracted. Within the vicinity of the openwork are some of the prospecting pits employed to find the lode. In the valley bottom below the mill are a group of earthworks which represent the remains of alluvial tin streamworking which is probably earlier than the tin mill. The post-medieval farmstead within the monument survives as a series of rectangular buildings and structures linked to each other by field walling. The farmstead is situated on raised ground to the east of the openwork and at least seven distinct structures survive, all of which are composed of drystone walls.

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

Legacy

The contents of this record have been generated from a legacy data system.

Legacy System number:

34437

Legacy System:

RSM

Sources

Books and journals
Castle, P, P, , Gill, M, Giles, N, DTRG Newsletter in Outcombe Tin Mill in Sheepstor Parish: A Survey of the Field Etc, Vol. 3, (1992), 11
Newman, P, Rep. Trans. Devon. As. Advnt. Sci. in The Moorland Meavy - A Tinners' Landscape, Vol. 119, (1987), 225

Other
Devon County Sites and Monuments Register, SX56NE122, (1985)
Devon County Sites and Monuments Register, SX56NE228, (1985)
MPP fieldwork by S. Gerrard, Gerrard. S., (2000)
MPP fieldwork by S. Gerrard, Gerrard, S., (2000)
Plate 67B, Worth, R H, Worth's Dartmoor, (1967)

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