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.
