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HER Number:162291
Name:BOSTRAZE AND TREGASEAL - Post Medieval mine


The working on Bostraze Moor is probably medieval in origin, and was at work in the late C18. Bostraze was reworked 1822-43, and 1889-1913.

Grid Reference:SW 3911 3211
Parish:St Just, Penwith, Cornwall
Map:Show location on Streetmap

Protected Status: None recorded

Other References/Statuses

  • Cornwall PROJECT ID: WH
  • National Mapping Programme (Morph No.): 325.7.1-5
  • Primary Record No. (1985-2009): 162291

Monument Type(s):

  • MINE (Post Medieval - 1540 AD to 1900 AD)

Full description

The working on Bostraze Moor is probably medieval in origin, and was at work in the late C18. Bostraze was reworked 1822-43, and 1889-1913. Tin. Lodes: unknown, most material probably alluvial.
Streaming has an exceptionally long pedigree in the Cot Valley and its side valleys. Hal Golour was certainly at work in 1782 when it was located by Moody, though men had probably been working the valley alluvials for 500 years before that. Noall (b2) noted that work was being carried on at Bostraze Moor Streamworks between 1822-43. In the last decades of the C19 a shallow shaft was sunk in the former streamworks (as West Bostraze) and small-scale floors established to dress the tin. In 1893 the mine was known as Bostraze and Tregaseal, and there are intermittent records of output from this site until 1913.
There were probably tin stamps and water-powered sites along the sides of the Tregaseal stream since mining first began in the district - such a potent source of water power would have been impossible to ignore. Even in the late 1800's, when steam engines had been at work in the district for three quarters of a century and most large mines had mechanised dressing floors, there was still work for these small businesses, and most were mapped at work by the Ordnance Survey in the late 1870's. With the closure of these mines, however, they quickly fell into disuse, and by 1908 all but one (at Lower Bostraze) was idle and ruinous. Even this last mill could not have lasted long into this century.
Site surveyed by Sharpe in 1992 (b1). Although slight traces of streamworking can be found in the Tregaseal Valley along much of its length, by far the best evidence in the St Just mining district occupies a large area on Bostraze moor -now marshy and hummocky, and an important and specialised wetland habitat. The indications of pre-C19 streaming activity have been overlain near the river, but must have stretched over a broad triangular tongue of land stretching into the shallow hollow of these moors, from SW 390 320 up to SW 392 324, as well as to the east beyond the Bog Inn. The edge scarps of the streamed area have become blurred, and the interior is a marshy wilderness, almost impossible to cross in safety - a patchwork of extensive marshy hollows, leats and channels filled with soupy peat and faintly visible linear banks of upcast. The area covered is about 1000 metres square. This must have been worked as an eluvial working (requiring impounded water for the washing process), since the streams in this area consist of little more than a general seepage than a flow. No traces of dressing floors associated with these early phases of working were found - they probably lie under the sites of the stamping mills further downstream. This area requires further survey to see whether the remains of any structures can be located within it. There are some hints at the western edge of the streamwork that there may have been early (prehistoric, perhaps medieval) fields in this area of the moorland - a few scraps of low stone and earth bank were noted in places.
The later streamworks and mining operations were centred around a small shaft at SW 3917 3206. The shaft stands within a large dump of upcast; its throat has now run in, and part of a cross-country course built by the nearby riding stable runs across the shaft hollow! The streamworks excavations and upcast run along the side of the watercourse north of the fields of Higher Bostraze. They consist of a series of deep water-filled hatches (the excavated areas) at SW 3906 3206, SW 3906 3210, SW 3910 3201, SW 3915 3213, SW 3920 3205, SW 3927 3205 and SW 3930 3202 accompanied by cuesta dumps - shaped like wedges of cheese laid on their sides, the thinner end of the wedge pointing into the hatch from which the waste was barrowed. These dumps flank the stream, which in this section has been canalised to act as the main drainage channel for the streamworks, and run from SW 390 320 to SW 393 321 (very large and rather amorphous dumps, some dug into), north to SW 392 322 (smaller, well defined cuesta dumps). Drainage channels separate the dumps and link the hatches. A further extensive area of streamworking of apparently similar character formerly existed to the east (in the region of SW 393 319), but moorland improvement, drainage and the straightening of the stream channel has almost totally obliterated this evidence. On the north-western fringes of the streamed area can be seen two possible dams (probably associated with the later mine and streamworking) at SW 3908 3204 and at SW 3914 3214. A pond at SW 3905 3224 is probably a modern creation. A very large earthwork dam at SW 3985 3190 may have impounded water for the Bostraze Bog streamworks.
To the east again (SW 3903 3222), the ground is boggy and hummocky, but this is more likely to be the result of peat cutting than streamworking. Such activity must also have been carried out over much of the moorland to the north. A ruinous smallholding at SW 3891 3231 is typical of many that were established through the C19 on the fringes of the moorland. Traces of its paddocks can still be made out, as well as one or two stretches of walling, but most of its remains have been demolished, and the site is returning to the moor. At SW 3920 3197 are the remains of the Bog Inn - reputed to have been an un-licensed beer shop and haunt of smugglers, which is likely to have started life as another similar smallholding. The structure has recently been consolidated. The remains of the mine are visible on aerial photographs (p1) and were plotted as part of the NMP. (See also record 53143).

<p1> PMB, 1973, FSL 7330/1/196 (Photographic Record). SCO15687.

<1> Sharpe, A, 1992, St Just, an Archaeological Survey of the Mining District Vol 2, 73-76 (Bibliographic reference). SCO4373.

<2> Noall, C, 1973, The St Just Mining District, Monograph on Mining History No 5, 177 (Bibliographic reference). SCO3998.

<p2> NMR, 1977, SW 3932/2/983 (Photographic Record). SCO16082.

Sources / Further Reading

[p1]SCO15687 - Photographic Record: PMB. 1973. FSL 7330/1/196. ABP.
[1]SCO4373 - Bibliographic reference: Sharpe, A. 1992. St Just, an Archaeological Survey of the Mining District Vol 2. 73-76.
[p2]SCO16082 - Photographic Record: NMR. 1977. SW 3932/2/983. ABP.
[2]SCO3998 - Bibliographic reference: Noall, C. 1973. The St Just Mining District, Monograph on Mining History No 5. 177.

Associated Finds: none recorded

Associated Events

  • ECO1489 - Cornish Mining World Heritage Site Bid
  • ECO1781 - CM World Heritage Bid: Devon Great Consols
  • ECO2465 - Cornish Mining World Heritage Site Bid
  • ECO2466 - Cornish Mining World Heritage Site

Related records: none recorded