Croesor Quarry

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Croesor Quarry in 2007, showing the remains of the fan house by the main adit and the site of the mill

Final and most awkward crossing in the Croesor to Rhosydd through trip

Croesor Quarry is a large underground slate mine in north Wales which was served by Croesor Tramway. It has a single adit in the hillside and ceased operation after a hundred years in 1930 having produced 11,000 tonnes of finished slate annually at its peak.^[1]

1 Features
2 History
3 Current conditions
4 References

[edit] Features

Croesor Quarry is notable amongst Welsh slate quarries for being almost entirely underground, with no significant surface workings. It was rare in its extensive use of forced air ventilation instead of the more common natural ventilation used in most slate mines. It also generated relatively small external waste tips compared with the volume of finished slates produced; this was largely achieved by back-filling underground chambers with waste once they were exhausted. ^[2]

[edit] History

Croesor Quarry was initially worked from 1846 until 1878. From 1864 onwards, the quarry was connected to the slate wharfes at Porthmadog by an incline to the head of the Croesor Tramway. After a hiatus, it re-opened in 1895 and continued in production until 1930^[2].

In the 1960s the quarry was operated by Cookes Explosive, a local firm who used its underground chambers to store explosives. In the early 1970s it was purchased by the Ffestiniog Slate Company with a view to reopening it as a working slate quarry. Planning permission for this was not granted and in the later 1970s most of the remaining mine infrastructure was removed for use in the Oakeley Quarry, also owned by the Ffestiniog Slate Company.

[edit] Current conditions

The whole mine is largely shattered and not in particularly good condition. Chamber 1 East was possibly the biggest underground chamber in the slate industry, being several colossal chambers worked into one void – so big in fact the roof couldn’t support itself any longer and it collapsed. The top third of the chamber remains intact.^[1]

Croesor Quarry is connected to the nearby Rhosydd Quarry by a tunnel that was built to aid surveying and settle boundary disputes.^[1]

In spite of a series of collapses, the Croesor to Rhosydd through trip is still possible and has long been considered a classic trip for mine explorers.^[3]^[4]^[5] Fixed ropes, home-made suspension bridges, zip wires, and inflatable boats have been installed which make it possible to complete the journey in comfort although not necessarily in safety.