Ancient Monuments

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Porthgain Quarry and Harbour

A Scheduled Monument in Llanrhian, Pembrokeshire (Sir Benfro)

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Latitude: 51.9483 / 51°56'53"N

Longitude: -5.183 / 5°10'58"W

OS Eastings: 181350

OS Northings: 232544

OS Grid: SM813325

Mapcode National: GBR C9.MF1B

Mapcode Global: VH1QQ.39T8

Entry Name: Porthgain Quarry and Harbour

Scheduled Date: 1 August 1972

Source: Cadw

Source ID: 3644

Cadw Legacy ID: PE382

Schedule Class: Industrial

Category: Industrial building

Period: Post Medieval/Modern

County: Pembrokeshire (Sir Benfro)

Community: Llanrhian

Traditional County: Pembrokeshire


The monument consists of the remains of a harbour and associated industrial complex dating to dating to the 19th and 20th centuries. Porthgain harbour was constructed in 1851, its primary purpose being the export of slate from quarries in the surrounding area operating from at least 1800. Slate was brought to Porthgain both by horse drawn tramway then to the harbour by horse powered whims (winding engines) and by boat before being cut to size at a mill powered by a 7.3m diameter waterwheel. The industry was sporadic throughout the nineteenth century, undertaken by a series of companies with varying fortunes but by 1875 the mill had become steam powered and from 1889 slate waste from the quarry was being made into red bricks in a brickworks established on the south side of the harbour. To enable the waste to be brought directly to the brickworks a 137m long tunnel was driven from the St Bride’s Quarry immediately to the west through to the quayside. At around the same time an expanding market for roadstone opened up quarries for the hard dolerite rock of nearby coastal outcrops. Brought by tramways to Porthgain this was reduced and graded by steam powered crushers that were built on the slope above the harbour before being stored in giant hoppers constructed from the locally made brick. The harbour and quays were expanded in 1902-04 to cope with demand and by 1909 exports of roadstone in specially-built 350-ton coasters was totalling around 4000 tonnes per month. The inter-war depression led to a decline in trade and in 1930 the quay was shortened to allow ships of up to 660 tonnes to enter, this proved insufficient to allow economic recovery however and the crushing plant closed in 1931.

The monument is of national importance for its potential to enhance our knowledge of 19th and 20th century 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. An industrial monument may be part of a larger cluster of monuments and their importance can further enhanced by their group value.

The scheduled area comprises the harbour: pilot house, jetty and quays , the remains of crushing and grading plant, the bank of storage hoppers, a section of the tunnel from the quay to the quarry and the cutting of a former tramway and Blondin system above together with areas around them within which related evidence may be expected to survive.

Source: Cadw

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