On the hillside above the cleared site of Marine Colliery (nprn 33571) is a squat circular brick ventilation chimney and shaft, measuring approximately 4.2m diameter and 5.66m high, built in the 1840s or 1850s and disused by 1876. It is the only example of this once common pre-fan type of shaft ventilation known to survive in Wales. The shaft is connected to a stone-lined level of similar date (nprn 85054), entering the hill from the riverbank below.
B.A.Malaws, RCAHMW, 30 October 2009.