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.
