Abercwmeiddaw Slate Quarry

Overview

A large slate quarry at Corris Uchaf, worked from the 1840s to 1938, notable for a pair of curious twin 'binocular' tunnels bored into the hillside in 1864 by one of the world's first mechanical tunnel-boring machines.

History

Quarrying at Abercwmeiddaw probably began in the 1840s, with the 1851 census already recording it as a large enterprise employing 80 workers. An 1871 report by John Imray described a well-developed concern, though it was not yet connected to the Upper Corris Tramway. The Abercwmeiddaw Slate Quarry Company was formed in 1876 under manager William Bright, acquiring the lease; by 1882 the quarry employed 188 men producing 4,173 tons of slate. Its most curious feature dates from 1864, when a newly-invented mechanical boring machine, designed by the Scottish engineer George Hunter, was tested at the quarry to bore a tunnel into the Broad Vein -- one of the world's first attempts at mechanised rock tunnelling. The machine worked but proved too difficult to steer and control; rather than abandon it outright, engineers moved it sideways once it had bored around 30 metres to cut a second, parallel bore, intending to keep the temperamental machine in constant use by shifting it between two intersecting cuts -- creating the twin 'binocular' tunnels that still survive. Output was carried out via the Corris Railway's Upper Corris Tramway to the Cambrian Railways at Machynlleth, material at first lowered by incline to the mill and later brought out on the level by a locomotive-worked tramway. The quarry continued working until 1938.

Geology

Hard slate slabs from the Broad Vein at Corris Uchaf — the vein a newly invented mechanical boring machine was set to drive into in 1864.

Workings

Hard slate slabs worked and lowered by incline (later a locomotive-worked level tramway) to a mill, connected onward via the Upper Corris Tramway and Corris Railway to the Cambrian Railways at Machynlleth; the curious twin 'binocular' tunnels, bored experimentally in 1864, survive reaching around 30 metres into the Broad Vein.

Closure

Worked until 1938.

What remains

Extensive remains survive across the site, including the machine-bored binocular tunnels, the original tramroad formation, a mill wheel pit, sections of the incline plane system, some former quarry buildings now in re-use, and fine large-scale drystone walling; a July 2021 exploration report confirms the tunnels and workings remain accessible and well preserved.

The binocular tunnels, tramroad formation, mill wheel pit, incline plane remains, re-used quarry buildings and drystone walling.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• By 1882 Abercwmeiddaw employed 188 men producing 4,173 tons of slate. ¹
• In 1864 a mechanical boring machine designed by the Scottish engineer George Hunter was tested at Abercwmeiddaw to bore into the Broad Vein; the machine worked but was too difficult to steer, so engineers moved it sideways after around 30 metres to cut a second, parallel bore, creating the twin 'binocular' tunnels that survive today. ²
• The quarry's binocular tunnels, tramroad formation, mill wheel pit and incline plane system all survive, along with some buildings now in re-use and notable drystone walling. ³
• The 1864 tunnel-boring machine trialled here was most likely supplied by John Dickinson Brunton, son of the engineer William Brunton; the twin-bore design let the machine be shifted to a second, intersecting face and kept continuously at work once the first bore was finished, though the machine proved too difficult to steer and the trial was abandoned. ¹

Photographs & further reading

Sources

1. (secondary) Abercwmeiddaw quarry — Wikipedia
2. (secondary) Inside the bizarre 'binoculars' tunnels cut by Victorian boring machines in North Wales — North Wales Live (Daily Post)
3. (secondary) Abercwmeiddaw Slate Quarry — People's Collection Wales

Record created: 30 August 2026 · Last researched: 30 August 2026