Terrace

A stepped, roughly level working platform cut into an open quarry's hillside face, one of a stacked sequence rising up the slope, each carrying its own working gallery, rubble tips and processing sheds.

Historical usage

A feature of open hard-rock and slate quarrying wherever a quarry was cut back up a hillside rather than down into a single pit -- most fully developed in the Welsh slate industry from the late 18th century, where Penrhyn Quarry eventually rose in over 20 stacked terraces, and later copied at smaller quarries including Gorseddau.

How it worked

Rather than deepening one working face, a quarry's terraces stepped upward (or, worked in the opposite direction, cut downward) one above another, each terrace between roughly 9 and 21 metres deep at Penrhyn. Every terrace carried its own gallery where the rock face was actually worked, together with its own spoil/rubble tips and, in slate quarries, its own trimming or dressing sheds; a system of inclines linked the terraces to each other and down to the mills or railway at the base, so worked stone did not have to be hauled by hand from level to level.

Why it was used

Terracing let a quarry expose and work far more rock face simultaneously than a single pit ever could, while keeping each level's spoil and processing separate and giving every terrace its own safe, roughly level working surface rather than an unstable single deep face.

Risks & limitations

Each terrace was still an exposed, open working edge -- men worked roped to the rock on many of these terraces well into the 20th century, and a terrace's spoil tips and structures had to be actively managed so they did not slip or encroach on the terrace or terraces below.

Regional variation

The term applies to open quarrying generally, not only slate -- but it is in the Welsh slate industry that it reached its most developed, most extensively documented form, and the stepped terraced hillsides of that industry are now protected as part of the Slate Landscape of Northwest Wales UNESCO World Heritage Site.

Mines associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis — not every mine where this might plausibly apply.

• Glenariff Iron Ore Mines — County Antrim (well documented example)
  Named twice in this record, first in the current condition: “…pier foundations in the sea at Red Bay, a former workers' housing terrace beside the coast road, ruined engine-shed remains, and traces of the…”
• Bigrigg Mine — Cumbria (well documented example)
  Named twice in this record, first in the history: “…at nearby Cleator Moor, but still enough to support its own miners' terrace, Springfield Terrace, locally nicknamed 'Skid Row'. Street names…”
• Cwmorthin Slate Mine — Gwynedd (well documented example)
  Named in this record’s surface remains: “…steam-powered Lake Mill near the lake and part of its slate-built terrace, the decaying Tiberias Chapel, a Pelton wheel and generator beside a…”
• Rubislaw Quarry — Aberdeenshire (well documented example)
  Named in this record’s history: “…well beyond Aberdeen too, used on London's Waterloo Bridge, the terrace of the Palace of Westminster, and the Forth Bridge. The quarry…”

Sources

1. (secondary) Penrhyn quarry — Wikipedia
2. (secondary) The Slate Industry of North and Mid Wales: Penrhyn Quarry — Penmorfa (Slate Industry of North and Mid Wales)

Record created: 31 August 2026 · Last researched: 31 August 2026