Summerton slate quarry is located a short distance to the north-west of Puncheston. It was a substantial hillside working from about 1830, then deepened into a pit with cutting access which also drained the working. As the workings deepened a ropeway was used to haul out. There appears to have been a tramway leading to a water-powered mill. The underground workings are believed to be later trials for metal. Despite early investment there were probably less than half a dozen men employed by the early 1840s. The quarry closed in 1880.
Remains of the site are enigmatic. Two adits in the face of the pit are short. Pillars on either side of the pit are thought to be related to the ropeway. A causeway 250m long to the west appears to be a tramway leading to ruined buildings, including a structure that may have been the mounting for a water-powered sandsaw. Traces of more buildings and a wheelpit lie downhill. The nearby former leat system has been ploughed away.
Although shown as disused on early Ordnance Survey maps, the quarry is portrayed as a pit, about 80m north-east to south-west by 60m, set amid an area of spoil, about 180m by 200m.
The site is associated with an erect monolith (Nprn308794).
Sources:
OS County Series 25-inch map: sheet Pembrokeshire XVII.1, first edition 1889.
RCAHMW air photos: 965013/49-51
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.225.
A.J.Richards, The Slate Quarries of Pembrokeshire (1998), pp.66-9.

David Leighton & J.Wiles, RCAHMW, 11 March 2015