In 1861, the quarry was restarted and a large mill was built just behind the Pentre-bont houses on the edge of Dolwyddelan.

The mill had a large waterwheel which was fed from the Llyn Cwm-penamnen reservoir about 1 mile (1.6 km) to the south.

Unusually, the incline was laid as standard gauge, allowing wagons from the London and North Western Railway to be taken up to the mill.

It was one of only four slate quarries in North Wales that had standard gauge railway laid directly to its mill.

[4] The quarry worked slate from the Nod Glas Formation, which outcrops along the Lledr Valley.