Nant y Pistyll Gwyn is a small slate quarry (nprn 419110) marked on the 1891 OS map, by which time it appears to have been abandoned. A machine base is comprised of at least 5 large stones, averaging 0.8m square, each with a sheared off iron bolt set into the top and sealed with lead. There are 3 in a line between the flooded pit (NPRN536734) and the stream, oriented NE-SW, and a 4th downhill to the SE. They are 1.75 - 2.5m apart. A 5th block was seen in the stream. Below the bolts along the streamside, is a low stone wall, with a possible opening for an outflow. These holding down bolts probably supported a crane or pump connected with the quarry pit.
Recorded as part of RCAHMW Uplands Initiative Project, W B Horton, H & H, 09/01/2014.
