Blowing mill and vermin trap 350m north east of Merrivale Bridge

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. At the blowing mill the cassiterite may have been washed a final time before being put into the furnace together with charcoal. To smelt tin the temperature within the furnace had to reach 1150 degrees C. This was achieved by blowing air through the furnace using water powered bellows. 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. All examples with a clearly identifiable surviving structure are therefore considered to be of national importance.

The blowing mill 350m north east of Merrivale Bridge is considered to be the best preserved example on the Moor. In particular, the furnace, float stone and mould stone remain in their original positions within a drystone building, which does not appear to have been damaged or altered subsequently. The vermin trap next to the blowing mill is a significant component of the nationally important Merrivale Warren.

Details

The monument includes a blowing mill, a short length of associated leat and a vermin trap situated on a steep west facing slope adjacent to the River Walkham. The blowing mill is of drystone construction with the wall standing up to 2m high. The interior of the mill, which is covered in tumble, measures 10m by up to 5.3m and access to it was through a clearly defined doorway in the western wall. A mould stone, into which molten tin was poured to form an ingot, sits next to the doorway. Close by is a large sloping granite block with a shallow linear trough cut into its upper face. This is the float stone in which the molten tin issuing from the adjacent furnace collected. The furnace itself survives as a 1.06m high by 0.55m wide and 0.6m deep stone lined chamber. In this chamber, tin and charcoal were smelted using bellows to provide a powerful draft of air. The bellows would have originally been sited to the north of the furnace and were operated by a waterwheel served by water carried in a leat which can still be traced leading northward from the building. A 14m length of this leat is included in the scheduling. Overlying the leat is a `V'-shaped arrangement of rocks which represents a vermin trap built to serve the Merrivale Warren. The vermin trap includes two lengths of drystone wall forming a `V'-shaped trap pointing towards the north eastern corner of the blowing mill. The position of the trap suggests that the blowing mill was intended to help encourage the vermin into the trapping area, which was originally sited at the point where the two lengths of walling converge. Vermin approaching their quarry tend to seek a route that provides visual cover and the purpose of a trap was to funnel predators along ditches or beside walls to a central point where they could be trapped. This vermin trap forms part of Merrivale Warren, which includes at least 27 pillow mounds and two vermin traps scattered along the lower slopes of Great Mis Tor, Little Mis Tor and Over Tor, and which are the subject of separate schedulings. It has been suggested that many of the pillow mounds within the Merrivale Warren may be of medieval date because of their unusual oval shape and association with a nearby medieval settlement. Most of the pillow mounds lie within the Merrivale Newtake, but some lie on open moorland just outside the intake wall.

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:

22379

Legacy System:

RSM

Sources

Books and journals
Greeves, T A P, Newman, P, The Archaeology of Dartmoor - Perspectives from the 1990's in Tin Working And Land-Use In The Walkham Valley, Vol. 52, (1994), 211

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