Tin on Dartmoor
(notes)

 

The importance of tin was that it ushered in the Bronze Age: it was added to copper to make bronze.  About 12% tin with copper produced a much harder metal, for tools, weapons, armour etc.  Before this, there was arsenic-bronze, but tin-bronze was more easily made.

Bronze Age: The Aegean Bronze Age began around 3200 BC, when civilizations first established a far-ranging trade network. This network imported tin and charcoal to Cyprus, where copper was mined and alloyed with the tin to produce bronze.  It started on Dartmoor around 2,150 BC - some 4,000 years ago. (DNPA Factsheet).  It was followed by the Iron Age.

Early tin deposits were probably found in streams where eroded cassiterite, tin dioxide (“black tin”) was deposited, particularly on bends in the water course;.  Extraction might have been by a forming of separation from unwanted tin gravels and debris by a form of gold-panning, i.e. separation by weight by swilling around on a flat object. 

The earliest documentary evidence for tin extraction on Dartmoor is in the Pipe Roll of 1156 (pp.46-48?), also Atti del IX Congresso Internazionale sulla Ceramica Medievale nel Mediterraneose (p.65). Alluvial tin was worked at this time at Sheepstor and Brisworthy.  This was early Medieval tin-streaming.  In Tudor and Elizabethan times, open cutting and adit mining came into use as well. In the 18th C and 19th C shaft mining was developed (Gill, p.100).

 

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The importance of tin on Dartmoor through the centuries .....

 

REDRAWN from Worth’s “Dartmoor” Fig. 87: Growth and decay of Dartmoor tin production, pp.286-288.  

The Golden Age was 1500-1550, the most successful year was 1524, with 252 tons.

White tin = smelted; black tin = output from tin mills i.e. un-smelted.

Good Stannary records for the Crown and The Duchy of Cornwall’s taxation purposes!  

1200s – incomplete records, but 1290-1299 inclusive, average annual production was 75,244 lbs = 33.6 tons. (= 336 tons)

1100s – much greater output, estimated that between 1171-1189, average annual output was 343 tons. (= 2,744 tons)

1400-1450     2,704 tons total in 50 years

1450-1500     5,196

1500-1550     9,944

1550-1600     4,655

1600-1650     1,250

Total recorded above: 26,829 TONS of white tin.

 It is likely that some tin was not recorded, meaning tax was not paid on it.

 

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From http://www.historic-cornwall.org.uk/flyingpast/streams.html

Cornwall: The boom years for tin streamers were the 1330’s when more than a million pounds (2,200 tonnes) of tin was produced annually. Although tin streaming declined in importance after the seventeenth century it continued as an industry up to the mid 1900s.

Streams of tin ………

Deposits of alluvial tin occur where tin-rich rocks have been broken away by erosion from their parent seam or ‘lode’, and have accumulated in the bottom of river valleys. These accumulations are known as tin streams.

After the formation of a tin stream, layers of sand and gravel settled on top of it. Over time they in turn were covered by accumulations of peat and leaf mould. These layers of overburden are frequently several metres deep. To reach the tin stream the tinners first had to remove the overburden. This was done by hand and dumps of unwanted overburden were produced alongside or downstream of the working areas.

The technique used to extract tin from these streams is known as tin streaming. Streamworkers took advantage of the fact that cassiterite (tin ore) is denser than the associated minerals which constitute granite. By diverting a stream of water over and through the tin stream, the lighter sands and silts could be washed away in suspension leaving behind the heavier gravels containing tin-rich rocks.

Ramped Workings .....

Streamers developed a range of methods to separate the cassiterite from the waste, depending on the nature of the tin stream and the elements constituting the overburden; each method produced its own distinctive type of earthwork remains.

Where large amounts of coarse overburden covered the tin stream the heavy wastes were systematically removed by wheelbarrow. This method of dumping waste produced a characteristic pattern of overlapping rectangular mounds or ramps. In cross section each mound is shaped like a wedge of cheese, with a shallow gradient leading to a steep scarp. The length of each ramp reflects a reasonable distance over which the waste could be barrowed. Once this distance was reached a new ramp was started; hence the overlapping ‘wedges’. The ground was exploited in strips in this way and the workings have scoured the landscape to a considerable depth.

Streams had to be temporarily diverted from the working areas to allow access to the tin gravels. As the whole width of a tin stream was worked numerous diversion channels were dug, sending the stream first one way, then another. As a result many streamworks have left deep cuttings gouged into the surrounding landscape. 

Parallel workings 

In situations where the overburden was shallow or comprised fine material, most of it could be simply washed away saving much heavy labour. 

In this type of streamworks water was brought through a channel into the working area and the overburden was washed into the river or a drain where it flowed downstream in suspension. The heavy stones and gravel left behind were piled up to form steep linear banks just downstream from the working area. By dumping waste on the area just worked, the streamers maintained a consistent width to their current working area. This would have been essential for maintaining a steady flow of water at the optimum velocity for the operation. Working upstream in a systematic way the streamers produced a regular pattern of parallel banks of spoil. 

Eluvial Workings
 
Eluvial tin streams are those where tin-rich rocks eroded from the parent lode are deposited in dry valleys or on hill slopes rather than washed into river valleys.

 From a tin streamer’s point of view the advantages of eluvial tin streams were that there was normally much less overburden to be dug away, there was no need to dig channels to divert the river (in some cases a major undertaking), and there was no problem with drainage in contrast to some low-lying alluvial workings. 

The great disadvantage was that water for washing away the waste material had to be brought to the site from available streams, often over long distances. This was done through a system of hand dug channels known as leats. Water brought via the leats was stored in purpose-made reservoirs until needed. 

For these reasons it is likely that eluvial streams were worked in winter when high rainfall meant water was plentiful. Conversely alluvial streamworks were probably worked in summer when river levels were lowest, making it easier to control the flow of diverted water and facilitating drainage.

 

FROM DNPA FACTSHEET …..

Dartmoor tin-working is documented from 1156 to its demise in 1930 when Golden Dagger, last working tin mine on Dartmoor closed. 

1195 – Stannary Courthouse and gaol built at Lydford.

1201 – Stannary Charter issued by King John.

1272 – Trowlesworthy rabbit warren set up.

 1305 – Ashburton, Chagford  and Tavistock become Stannary Towns.

1328 – Plympton becomes a Stannary Town.

 1494 – First recorded Great Tinners’ Court held at Crockern Tor.

1558 - 1603 - reign of Elizabeth I - German workers introduced the water-wheel in tin working, this was the period of the blowing houses.  Before the water-wheel and blowing houses, the main smelting site was Furnum Regis - King's Oven, mentioned in the 1240 Perambulation (S. Baring-Gould (1900). A Book of Dartmoor, 3rd facsimile 2002, Halsgrove, Tiverton, Devon, pages , p.120-122)

 

The results of tin streaming can be seen in many valley bottoms on Dartmoor, especially the River Plym and the River Erme. 

In the 1,400s, if not earlier, tinners began digging long open cast pits along tin lodes occurring near the surface., resulting in gullies some 200 x 20 x10 metres deep (“gerts”). On Dartmoor, the lodes align roughly E-W.  These were often called beamworks and the word Beam is often incorporated into their names.  

Most beamworks date to before 1650.

Vertical shafts and associated horizontal adits (for drainage) probably started to appear in the 1,400s, but the more easily recognised ones will before the 1,700 and 1,800s.

 

The mills 

Crushing only – knocking mills, after c. 1750, known as stamping mills – after that time, most tin was taken off the moor for smelting. Typified by mortar-stones. A rarity is the use of two flat stones for grinding ore, used like mill stones for grinding flour – these are crazing mills (one at Hexworthy / Gobbet mine).  

Smelting only – blowing mills – waterwheel drove a bellows to blow a blast furnace. Mould-stones often found.  Temperature had to reach 1150°C to melt the black  tin ore into a running liquid metal collected in a mould stone with a slope-sided oblong cut into it to form white tin ingots after cooling.

Norsworthy mill – no evidence of smelting – water wheel drove twin stamps.  

All mills had associated settling pits outside, buddles., for collecting the crushed tin as lighter material was separated off by running water.   

The last tin smelting on Dartmoor was at Eylesbarrow, 1822-1831, then sent to Cornwall e.g. Truro. 

In the late 1700s and 1800s. tin mines became more complex with machinery, waterwheels, cranks, flat rods etc.  for driving remote gear such as pumps.

The last working mine on Dartmoor was Golden Dagger, underground work finished by WW1, but surface work continued to re-process earlier waste until 1930s. The last man earning a living from this was a Mr Olver, who dies in France in WW2.  Tom Greeves (1986), Tin Mines and Miners of Dartmoor: A Photographic Record, Devon Books, Exeter, p.78.

 

                                                                                   

 

Deep Swincombe Blowing House - thought to be the oldest on Dartmoor. The mould-stone  is of cut elvan and different to any others, it has an early form of furnace. Later workers had a crazing mill there and stamps for re-smelting old slags that still had tin in them. "Until recentlythe Malays threw away their slags, which contained as much as 40% tin".  S. Baring-Gould (1900). A Book of Dartmoor, 3rd facsimile 2002, Halsgrove, Tiverton, Devon, pages 113-117

                                                                                   

 

Sources

http://ougs.org/southwest/event-reports/tin-extraction-on-dartmoor-145/

Streaming works are evident in nearly every Dartmoor valley and so prolific had this industry been during the 1500s that in 1598 Francis Drake, who was then Mayor of Plymouth, petitioned The Crown in London to levy further dues and impose tighter restrictions on the Tinners because the amount of silt being carried off the moor in the rivers threatened to choke the natural harbour of Plymouth Sound, home of the English Navy and vital for protection of the country from the traditional enemies of France and particularly at the time Spain. However, the industry was already in decline and by the early 1600s many alluvial cassiterite deposits on Dartmoor had been worked out. This was cited as one of the reasons for building Drake's (Plymouth) Leat (inaugurated April 1591), to flush Sutton Pool.

In the early 1600s two new mining technologies arrived in the UK. Black powder for blasting was first used in the south-west of England in the mines at Combe Martin around 1640 and could readily be used for creating open cast trenches. Controlled blasting on the other hand greatly facilitated the other new technology imported by miners from Germany; the driving of under ground tunnels known as 'levels' and 'adits' for the exploitation of the mineral veins deep underground by excavation of cavities known as 'stopes'. 

Even so by the early 1700s tin mining on Dartmoor had dwindled and effectively ceased; the new technologies were limited in their application because the abundant and ever present water (Dartmoor has more days of rain annually than anywhere else in the UK) caused persistent flooding and only a certain amount of draining of the underground works could be accomplished by running the water off through a drainage adit driven from low down on the side of a valley. 

 

http://classprojects.kenyon.edu/engl/exeter/Kenyon%20Web%20Site/Anna/mining%20insight%20pg.html

Dartmoor Productivity

In medieval times tin was still in great demand throughout England for its crucial role in making pewter, the alloy of tin and lead, which had become a highly desirable material for domestic house wares, such as cups, bowls, and utensils, (Newman, 6).  Tinning on Dartmoor reached its peak yield around between 1520 and 1530: in 1524 564,288 pounds of tin were extracted! (Worth 287-288).  There was a sharp decline in the tin mining for the next 70 odd years, and during the 1640s, a time of Civil War in England, tinning stopped almost entirely.  Thereafter, only smaller amounts of tin were dug in Dartmoor except for one year, 1706, in which 123,636 pounds were brought up, (Worth 287-288).  There was a slight increase during the Napoleonic Wars period, coupled with the approaching industrial aged, due to innovations of plating iron with tin, but tinning on Dartmoor continued to dwindle.  In the 19th century tin was required with the development of canning foods, but Dartmoor was by this time no longer a center for its production: smelting on the moor was finished by the beginning of the 19thcentury, and in 1838 an Act was passed which abolished the need to pay dues on coinage, (Harris, 44).  No tin has been mined in Devon since 1930, due to the cheaper cost of imports from other global mines in places such as Malaysia (Ibid). 

 

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 Long Ash Pits - early, possibly medieval or earlier, tin workings where tinners collected alluvial deposits along stream beds. The eroded tin ore could form quite pure tin gravel.  The early tinners "leated" water to a trench at the lower end of the ground, called a “tye”, and water was used to wash away the lighter “gangue” gravels. The method left banks of waste. The area is surrounded by a scarp that shows the original level of the land and the depth of the deposits. Tin streaming was often followed by open cast mining to go deeper, into big cuttings called "gerts", but this is not seen here. Wikipedia - Dartmoor tin-mining - Streaming link ......

 

Another view of the tin workings including Pila Brook. It was presumably this water source that was diverted and used for washing away the lighter sediments etc. so as to leave the heavier tin-bearing gravels and sands for smelting.  This would have been among the earliest tin-extraction methods.  This photograph also shows the scarp surrounding this area that suggests how much the early tinners changed the look of the landscape.

 

 Notes from Samuel Rowe (1848, facsimile 1985), A Perambulation of Dartmoor, Devon Books, Newton Abbot.

Richard Strode, MP for Plympton, inrpisoned by the stannators in Lydford Castle in 1512, for attempting to get Parliament to prevent the tinners from harming the harbours by their mining operations i.e. silting up. (p.224).

In 1466, King Edward IV granted the tinners of Cornwall rights of turbary (right to cut peat) and pasturage in Dartmoor Forest, after they ran out of timber in Cornwall for smelting and "coinage had fallen off three hundred marks and more"  i.e. the tax "take" was down! (pp. 300-301).

The earliest printed statutes of the Stannary Parliaments are from the reign of Henry VIII, passed at the Crockern Tor Parliament of Tinners, printed in Tavistock within the precincts of the abbey in 1510.  It was basically for the governance of tin works and blowing houses (pages 307-309).

 

Carbonarii  - persons licensed to dig turf (peat) on Dartmoor for the making of charcoal, for smelting tin?   33 in around 1350 to about 110 in around 1440. HSA Fox (1994), Medieval Dartmoor as seen through its account rolls. In: The Archaeology of Dartmoor: Perspectives from the 1990s, Devon Archaeological Society Proceedings No. 52, pp.149-172.

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Crazing mills - only three known on dartmoor: Gobbett, Outcombe and Yellowmead.

1750 - this is the date that it is considered that shaft mining started on Dartmoor. This is where shafts were sunk to ecploit deeper lodes where openworking and lodeback pits could not reach it. Adits were dug for drainage and for access. (p.184).

After 1750, most Dartmoor tin came from a relatively small number of mines, rather than the streamworks which seem to have become economically exhausted by this time (p.194)

Crushing and stamping was done close to the mine. After 1831, when Eyelborough closed (its furnace), all smelting was done off the moor (p.194).

 Dr Sandy Gerard (1994), The  Dartmoor industry: an Archaeological perspective. In: The Archaeology of Dartmoor: Perspectives from the 1990s, Devon Archaeological Society Proceedings No. 52, pp173-198.

Beamworks are invariably pre-1700    TAP Greeves & P Newman (1994), Tin working and land use in the Walkha, valley: a preliminary analysis. In: The Archaeology of Dartmoor: Perspectives from the 1990s, Devon Archaeological Society Proceedings No. 52, pp.199-219   (pp173-198)  p.204

Over Tor Brook / Over Tor Gert, reservoir above the track to Great Mis Tor. Likely to date to before 1.700. In Fig. 1 - Wheal Fortune (Merrivale Bridge Mine) across Walkham opposite the Over Tor Brookp.205-207.

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