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Feock Trails - History Information

The Carnon Valley

Historical mineral workings

The shipping, which brought supplies to and from the great mining area of Gwennap, had always found access via Restronguet Creek and along the Carnon Valley, however progressive mining activities over the centuries have caused increasing quantities of waste and spoil to silt the valley. This gradually impeded navigation to its highest reaches. During the reign of King Henry VIII petitions were made to the king bringing attention to the activities of Tinners and the effect of their activities in reducing draught for vessels. As late as 1620 however boats up to 200 tons burden were still able to access the port of Bissoe.

The chimney of the Bissoe Arsenic Works

A report from the West Briton of the 25th May 1871 provides a fine summary of the situation in the 19th century:


"Carnon stream is remarkable for the vast amount of tin taken by streaming and by mining out of the silt and sand deposited in or near its junction with the tidal water of the Restronguet Creek, which is an arm of the Fal river. The tin taken from this deposit was washed down the valley from the mines in the Gwennap district from the backs of the innumerable lodes which it contains. Another remarkable circumstance connected with it is the Great Adit, alias the Poldice Adit or the County Adit which discharges its waters into this stream. It is said that this adit unwatered a greater number of mines than any other in the World. Its length (including branches) is about 33 miles, its depth 50 fathoms. It was commenced in 1768 by the grandfather of Sir William Williams, Bart., to unwater Poldice and other mines in the vicinity. It was afterwards at different times extended in many other directions. The following list will comprise the majority of the mines drained by it:-Clifford Amalgamated (Consols, United, Wheal Clifford, and Wheal Squire), Tingtang, Pennance Consols, Carharrack, East Damsel, West Damsel, Wheal Jewell, West Jewell, Wheal Pink, Trefula, Wheal Clinton, Wheal Gorland, Poldice, Wheal Unity, Wheal Unity Wood, Wheal Maid, Creegbrawes, Great Wheal Busy, Boscawen, Hallenbeagle, Wheal Chance, Treskerby, North Downs, North Treskerby, East Downs, New North Downs, Briggan, Cardrew, Wheal Harmony, &c. When all these mines were at work the volume of water issuing from the adit was very large. To utilise this water in working that portion of Clifford Amalgamated called Wheal Andrew, an adit was brought up from Carnon, a few fathoms deeper than the great adit, so that the water might pass over two water-wheels, to drain the Union mines (as Wheal Andrew and Nangiles were then called, 1822), and worked by Messrs. Williams and Co. Between the tail, or outlet, of the adit water there are numerous precipitate works, for taking the copper out of the adit water. This is accomplished by laying down scraps of iron in drains, which has the effect of taking out the copper held in solution in that water. The iron attracts the particles of copper, which after a few days or weeks is scraped off, and sold at a high price, being nearly pure copper."

The precipitate works mentioned in the article were a major aspect of the valley's landscape although they are already marked as disused on the ordnance survey maps of 1880. A large works was situated just above Dunstan's Bridge with smaller works above and below the viaduct. There were further works above and below Carnon Bridge and a vitriol (Sulphuric Acid ) plant in the area of the current industrial site downstream of Carnon Bridge. A major reason for the scale of this industry in the Valley was the presence of the County Adit, however it is also interesting to note a peculiarity of the Nangiles mine which is still a feature of the landscape a little above the Bissoe Bike Hire. Nangiles was a mine of ancient pedigree which in later years became subsumed into the Falmouth Consolided Mines and, later still, Wheal Jane. It was said of Nangiles that its waters were so acid that they could “rot a pair of boots off a man's feet in one day”. This would no doubt have contributed to the heavy metal content of the drainage waters which fed into the Carnon Valley and gave rise to the copper precipitation industry. 


Bissoe and the Carnon Valley was also an early home of the Arsenic industry in Cornwall. Arsenic is found as a contaminant in mined ores of tin and copper. Its presence causes the refined metals to be of poor quality and it must be removed in, or prior to, the smelting process. This was normally achieved by roasting the concentrated ore in a stream of air which caused oxidation of the arsenic minerals. This was normally undertaken at the mines in order to improve the price of their ore. The furnace in which the roasting took place was called a calciner.  The resulting asenious oxide was volatile and carried away in the fumes. This waste from the ore preparation process caused great contamination and pollution in the land surrounding the mines until the early 19th century when it was realised that a use could be found for arsenic. New processes were put in place to condense and collect the white asenious oxide dust and refine it for sale.

The first works to refine arsenic from mine wastes was set up near Perranwell by a Dr Edwards of Falmouth in around 1812. He joined with William Williams of Penryn and Wm. Gregory in purchasing the smelting house in Melingey Creek off Tarrandean Lane. Within papers of the Enys Estate at the time a report stated "The deposit in the chimneys of the tin burning houses was till within a few years entirely wasted, when Dr Edwards conceived the idea of extracting and separating the arsenic from it. This he accomplished and is able to manufacture a sufficiency for the supply of this whole Kingdom and a quality fully equal to the best".


The new industry was not without its pitfalls and when in 1840 Dr Edward's original works was taken over and expanded by Thomas Garland, local people were subjected to horrifying pollution which led to them taking action at the 1851 Assizes. It was stated that the works produced arsenic fumes "like a fog day and night" and objector Richard Thomas said that he had lost three cows and a horse and pony to the arsenic. The judge found the case proved, saying that "whilst it was undesireable that any man should be prohibited from carrying on a manufacture that is beneficial to himself and to the public; yet at he same time he must take care so as to conduct his work as not to injure other people."


There shortly followed a second refinery at Bissoe in 1835 owned by Messrs Henry Conn and Co and Bissoe was associated with arsenic production from this time until the outbreak of World War II. In latter years it was given a boost when in 1913 the Falmouth Consolidated Mines at Bissoe set up more advanced Humbolts calciners. This equipment was more effective and efficient in producing arsenic but also allowed better production of sulphur, the second product of the process. In the simple calciner process material deposited nearest the furnace was nearly pure arsenious oxide and furthest away sulphur. The sulphur was used to make sulphuric acid or vitriol as it was known.


Early uses for arsenic were within dyes and pigments, but its later use within insecticides became increasingly important. It was used in sheep dips at home and abroad and calcium arsenate was used to control the Colorado beetle that was ravaging the potato crop in America, and the Boll Weevil insect which was having a similar effect on the cotton crop.


It has been estimated that during the 1870s the greater part of the worlds production of arsenic came from the mines of Cornwall and Devon, however in the 1950s the last production stopped as major producers around the world made production in Cornwall uneconomic.

Written by Phil Allen



A fascinating account of arsenic production, which has greatly informed this account, may be found in “The Cornish Arsenic Industry" by Bryan Earl published by Penhellick Publications.

OS Map (1907) Precipitating Works at Bissoe

OS Map (1907) Precipitating Works at Bissoe

OS Map (1907) Vitriol Works at Bissoe

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