Ancient Monuments

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Cloddfa'r Lon Slate Quarry

A Scheduled Monument in Llanllyfni, Gwynedd

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Latitude: 53.0565 / 53°3'23"N

Longitude: -4.2357 / 4°14'8"W

OS Eastings: 250263

OS Northings: 353364

OS Grid: SH502533

Mapcode National: GBR 5K.CHKZ

Mapcode Global: WH43T.XF6N

Entry Name: Cloddfa'r Lon Slate Quarry

Scheduled Date: 24 June 1998

Source: Cadw

Source ID: 3962

Cadw Legacy ID: CN302

Schedule Class: Industrial

Category: Slate mill

Period: Post Medieval/Modern

County: Gwynedd

Community: Llanllyfni

Traditional County: Caernarfonshire


The monument consists of a core group of buildings from Cloddfa'r Lon Slate Quarry, including an important mill, chain incline, and two rows of slate quarrymen's cottages. Cloddfa'r Lon was the first major slate quarry on the floor of the Nantlle Valley, worked from 1808 by William Turner. It was the first quarry to be linked to the Nantlle Railway on its opening in 1828, and was a pioneer of steam up-haulage, introducing the Cornish chain incline to Wales in 1841. Substantial investment in the early 1880s developed this part of the quarry complex on an area of unworkable rock around an existing barracks and Pen y Bryn farm, until it fell out of use in 1892.

The mill was of radial type, built in 1884 to contain six De Winton saw tables, and was powered by a vertical single-cylinder steam engine by W.C. Mather which is now at the Welsh Slate Museum in Llanberis (the only slate mill steam engine to survive in Wales). The walls of the mill are complete to eaves height, and the substantial boilerhouse chimney is intact. The mill engine seems also to have driven a chain incline to the north, whereby waggons were raised from the quarry pit on an inclined chain. Another chain incline to the south of the complex is evidenced by a surviving engine house and strongpoint with landing platform for the raised waggons. The engine house contained a horizontal steam winding engine and a winding drum. The substantial abutments of a bridge carrying a tramway over the turnpike road to the Nantlle Railway survive with a weighbridge house to the south. The two rows of barracks consist of six cottages, thought to have been built c1866, complete to eaves height, with their garden plots and outbuildings.

The monument is a compact complex of signficant remains from a leading Nantlle pit quarry. It is of national importance for its potential to enhance our knowledge of 19th century slate production and industrial practices. It retains significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits. The structure itself may be expected to contain archaeological information concerning chronology and building techniques. A slate mill may be part of a larger cluster of monuments and their importance can be further enhanced by their group value.

The scheduled areas comprise the remains described and areas around them within which related evidence may be expected to survive.

Source: Cadw

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