Silent

Tess in a ruin at the Dorothea Quarry, Nantlle Valley, Snowdonia. 06-11-2010.

The Dorothea Quarry specialised in the production of blue and purple slates, mostly for roofing. Slate is a metamorphosed shale and that in Snowdonia is of Ordovician age. The quarry officially opened in 1829 though illegal quarrying in and around Nantlle had been active throughout the eighteenth century. Further investment was made in 1835 but production did not really get underway until the building boom of the latter nineteenth century. The quarry closed in 1970.

The Dorothea Quarry is five hundred feet deep and the last four hundred are in water. Around 1900 the company experimented with electric pumps to keep the quarry dewatered but was dissatisfied with them. Accordingly, in 1906 they installed a Cornish engine by Holman Brothers of Camborne, said to be the last ever built.

The engine pumped ten gallons per second from five hundred feet working in a shaft of 465 feet depth. Its two coal-fired Lancashire boilers fed steam to a sixty-inch diameter single cylinder that rocked a cast-steel beam of twenty-three tons. The engine worked until 1951 when it was replaced by a sixty horse-power electric pump. It did brief duty in 1956.

The engine and its house remain intact though the pump assembly has decayed and the boilers have been vandalised by copper thieves. Demonstrational steam is now raised by what looks like a small propane steam generator in an attached shed. The structure is Grade One Listed, the same as Caernarvon Castle, but its future remains in doubt.

In recent years the deep and frigid waters of the now flooded Dorothea Quarry have become the locus of illegal sport diving and there have been many fatalities, perhaps amounting to three a year. The nearest decompression chamber is in Liverpool and the only thing to do with a victim of narcosis is to send him back down if there is air enough, possibly to die of hypothermia. There are one or two moving memorials around the lake.