Noted in referenced WMS N/L as:

I was walking in the hills south of the Mawddach estuary in June and came across a short trial level (about 20 feet long and 8 feet high) with another level further up the hillside which I didn’t get to. The location is on the footpath across Dolgledr at approximately SH 687 174. Does anyone know of this and what was being searched for? Perhaps it was gold as on the north side of the estuary, or was it manganese? Mike Breakspear - [Harold Morris says that he thinks these were probably trials for iron. – Ed.]