Porthgain quarry is located on the north Pemrokeshire coast. A small pit working producing mainly slab, it opened in 1831 and developed into a self-contained community largely dependant on maritime communications. Material was carried down by incline to a water-powered mill near the harbour. As the pit deepened, steam was used to power an uphaulage incline, later replaced by a ropeway. Engines of 16hp and 20hp were recorded as in use though the purpose of the latter is inknown; it possibly replaced the 24-foot mill wheel. Wind power is said to have been tried on site. In 1898 only four men were recorded as working at the quarry.
By the start of the twentieth century the slate was deteriorating into shales which were used for brick making. Uphaulage from the pit was now avoided by means of a tunnel which ran below pit-bottom level allowing drams to be loaded by chutes. Further diversification occurred in the building of brick hoppers to load granite brought from a quarry on a nearby headland by a locomotive powered railway. No slate work was done after 1910. The production of crushed granite was carried out until the early 1930s when the enterprise closed.
The pit itself survives along with the port tunnel (now gated) and the incline to the mill of which little survives. Other visible structures (in 1991) include a fine slate leat, buildings in re-use (in particular the harbour office), dwellings still occupied, and the remains of brick kilns.

Sources:
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.223.
A.J.Richards, The Slate Quarries of Pembrokeshire (1998), pp.40-8.

RCAHMW, 28 May 2015