Site of Cwmorthin slate mill, near Tanygrisiau

Site of Cwmorthin slate mill, near Tanygrisiau

The expanse of level ground across the river was the site of a large mill, where slate from the nearby Cwmorthin slate quarry was processed.

The quarry was mainly underground from the 1860s, when a narrow-gauge railway was opened to take finished slates down the hillside to the Ffestiniog Railway. The quarry had a mill building, which still stands, on the shore of the lake but needed a larger facility as output grew. Builders were invited to submit tenders for a new mill in 1873.

The new mill was erected on ground built up by tipping waste rock over the culverted river. The machinery was powered by water from a reservoir a little north west of the mill.

The long building, known as the London House mill, was orientated roughly north to south. Railway tracks entered at the north end. When the slate had been sawn, split and planed, the finished product was dispatched on a line which emerged from midway along the building. This line linked to the quarry’s exit railway, behind you as you look at the mill site. It crossed the river on the bridge you can see today.

Waste from slate processing was moved on a lower railway from the yard south of the mill to the tips you can see alongside the track on your left as you descend to Tanygrisiau.

The river’s channel was altered again for an early hydro-electricity power station.

Cwmorthin quarry was disused by 1949 but parts of it were worked sporadically until the 1980s, using road transport instead of narrow-gauge wagons.

In the 1990s the site of the mill was landscaped but there is no longer public access to it.

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