Iconic images of cliff-top engine houses perched in dramatic locations have come to symbolise Cornish mining and Cornwall as a whole. But these buildings are more than just photo opportunities; those in west Cornwall are the surface evidence of pioneering submarine mines that stretch far out under the sea.
The engine houses of Cornwall’s coastal mines are positioned so dramatically because the mine shafts needed to be sunk as close as possible to the productive mineral lodes. Locating the shafts part way down the cliff also reduced the time and money required to sink the shaft. Positioning the pumping engines nearer sea level also reduced the distance the water had to be lifted before being discharged into the sea. In some mines the productive ore is known to have extended over a kilometre out under the sea bed.
Levant and Geevor Mines
This group of mines along the coast near St Just form the greatest concentration of submarine tin and copper mines in the world. Surface and shallow mining dates back to at least the mid-1500s in this area. All along the coast are many ‘zawns’ – a local term to describe a distinctively narrow and usually steep-sided cove carved out of the cliffs by nature along the weaknesses of the mineral lodes. In some instances these helped miners identify where to mine.
Throughout the 18th and 19th centuries, technologies were developed which enabled shafts to be sunk deeper and workings to be extended further out to sea. Levant reached its deepest point – the 350 fathoms (640 metres) level – in 1904. Level is the name for the horizontal, underground tunnels cut to follow
During storms, miners working under the sea often heard the eerie rumble of boulders moving above them on the seabed.
the lodes; driven at approximately 100ft (30m) apart vertically. In order to reach the lowest level at Levant, two vertical shafts were sunk out under the sea – Old Submarine Shaft, connecting the 210 to the 302 fathom level, and New Submarine Shaft, connecting the 260 to the 350 fathom level.
It was said that during storms miners often heard the eerie rumble of boulders moving above their heads, especially in the notorious ‘40 backs’ - a level that ran dangerously close to the sea floor. The sea never broke in when the mine was working but it did eventually find its way in after Levant had closed in 1930. In 1969 nearby Geevor Mine, which had bought Levant some years earlier, sealed the breach and pumped the mine dry again, to exploit the remaining submarine riches.
The Crowns engine houses are precariously sited on a promontory just above the sea, further south along the coast from Levant. Their dramatic setting has inspired generations of writers, artists and photographers.
There is great technical interest in the inclined Boscawen Diagonal Shaft (sunk 1858-62) that runs at an angle of 32.5 degrees out under the seabed to a distance of 800m from the cliffs. It reaches a total vertical depth of 250 fathoms (450m) below the adit.
Wheal Trewavas and Wheal Prosper
Situated on the clifftop a few miles west of Porthleven at the southern tip of the granite outcrop known as the Godolphin-Tregonning granite, Wheal Trewavas was a short-lived but productive mine working in the mid to late 19th century.
Wheal Trewavas exploited four copper lodes and one bearing tin, trending south-east and north-west across the coastline. Its underground levels extend under the sea, where rich copper ore could be found. It closed in 1846 when, so it's believed, the workings beneath the sea became flooded. The engine houses at Wheal Trewavas and nearby Wheal Prosper have now been consolidated by the National Trust and provide an insight into what mining at the edge of the land must have been like.
Having perhaps the most famous collection of Cornish engine houses, Wheal Coates near Chapel Porth was in operation from 1802 and worked intermittently until 1889, with a reworking from 1911-13. The site is notable for its trio of engine houses, which were used for winding, pumping and stamping. All three perch on or near the cliff edge, 200ft above the sea.