Two stamping mills 200m and 175m north of Norsworthy Bridge

Reasons for Designation

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 minerals 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 stamping mills on 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 natural importance.

The two stamping mills 200m and 175m north of Norsworthy Bridge survive well and together contain a rich array of archaeological evidence relating to the crushing and processing of tin ore. The mill 175m north of Norsworthy Bridge contains a variety of worked stones, which together illustrate that this mill functioned for a considerable time. By contrast, the mill 200m north of Norsworthy Bridge may have been relatively short lived, but unusually for Dartmoor, a triple head of stamps was employed.

Details

The monument, which falls into two areas of protection, includes two stamping mills together with their leats, a dressing floor and part of a tinwork situated on either side of the River Meavy. The northern stamping mill includes a sub-rectangular building measuring 7.3m long by 3.7m wide denoted by a substantial drystone wall standing up to 1.7m high. Within the mill are at least six mortar stones, one of which has been reused at least four times as an axle bearing stone. Some of the mortar stones have more than two hollows indicating that they have been reused. The pattern of hollows on the stones indicates that double stamps were used within this mill. Two stones within the building have rectangular sockets cut into one side, whilst a third stone has a complete rectangular slot cut into its upper face. These types of stone are known from grist and crazing mills, where they are considered to have formed part of the support for the machinery. It is therefore possible that this building was also at one time used for crushing tin using horizontally rotating stones. The water supply to power the machinery within the mill was provided by a leat carrying water from the nearby River Meavy and this can be traced leading 90m northward from the building. The floor where the crushed tin was dressed lies south of the mill, and within this area four rectangular hollows probably represent the remains of buddles. The southern mill lies on the western side of the River Meavy and survives as a 4.6m long by 3m wide rectangular building denoted by drystone walling. The wheelpit is attached to the northern side of the building and measures 4m long by 0.94m wide. The wheelpit wall is up to 1.2m high adjacent to the mill and 2.5m high on the eastern side. A single mortar stone with three hollows on one face sits on top of the slope east of the mill and indicates that a triple head of stamps were employed. The leat carrying water from the nearby river survives as an earthwork measuring up to 1m wide and 0.35m deep, with the associated bank thrown up during its construction being up to 3m wide and 0.7m high. A short distance west of the mill is a rectangular earthwork which may represent the site of a broadly contemporary building. The interior of this structure measures 5m long by 2.5m wide and is denoted by a rubble bank standing up to 1.8m wide and 0.8m high. This building and the mill sit within a 3.5m deep gully formed by earlier tinworking at this location.

MAP EXTRACT The site of the monument is shown on the attached map extract. It includes a 2 metre boundary around the archaeological features, considered to be essential for the monument's support and preservation.

Legacy

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

Legacy System number:

22400

Legacy System:

RSM

Sources

Books and journals
Greeves, T A P, Robinson, R, Norsworthy Left Bank Stamping Mill, (1984)

Other
MPP fieldwork by S. Gerrard, Gerrard, S., (2000)
MPP fieldwork by S. Gerrard, Gerrard, S., (2000)

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