Carnglaze Slate Caverns, near St Neot, are Cornwall’s only underground slate quarry. It has been worked for over 500 years. Guided tours are available. St Neot,is in the valley of the River Loveny, a tributary of the River Fowey about half-way from the A38 trunk road and St Neot village. North of A38, 3km south-east of St Neot, between Liskeard and Bodmin.
The caverns are the result of slate quarrying and mining in the 18th and 19th century. Most of the slate was used for roofing and flooring in buildings and the headstones in the churchyard are made of slate. Slate was transported by packhorse to quays on the River Fowey at St. Winnow, near Lostwithiel. Another route lead to Polperro and Looe. On the return journey packhorses brought lime for neutralising the acid soil on the moors.
Carnglaze slate is blue in colour, noticeably different from the greyer slates of North Cornwall which have been quarried at Delbole. There the heat from the cooling granite has altered the slate making it distinctly pink and soft. Further away from the granite at Carnglaze the slate is hard, blue and well cleaved slate beds enable it to be split into very thin slices making a durable and light material which is ideal for roofing.
Just inside the entrance to the caverns are the foundations of an engine mounting. Which was used in 1937 to haul up loads of building stone. A long flight of steps to the first chamber, 90 m long by 15 m wide and up to 6 m high. It is occasionally used for concerts and can seat 300 people. At one point is a pool of clear water which is 2 m deep. In the next chamber is the underground lake called The Blue Grotto of Capri, which is 9 m deep. Splashes of colour, red, orange and yellow, these are from the iron oxides in the rock. There are some small straw stalactites.
The road from St. Neot to Twowatersfoot past Carnglaze was built in 1837 and, the road through the Glynn Valley was made only a short time later.
The slate quarry ceased production of roofing slates in 1903 but supplied building stone for another three decades.
A few of the quarry men employed at the Carnglaze Caverns are recorded in 19th century census. Other trades people of St. Neot at this time a butcher, grocer, mason, miller, blacksmith, carpenter, tailor, saddle and harness maker, boot and shoe maker and draper.
1603 slate quarry began on the surface.
1800 underground working commenced.
1833 first written reference in Parochial History of St Neot.
1903 underground working finished.
1937 the dumps inside the mine were turned over in search of building stone.
1939-1945 used as storage for vast quantities of rum for the Royal Navy. Bats left the mines as they could not tolerate the strong fumes given off by the rum barrels.
1973 opened to the public as a tourist attraction.
Carnglaze Slate Caverns web site
Slate Mines and Quarries in Cornwall