Bwlch-Glas (which translates as ‘Blue Gap’) mine was worked between 1889 and 1923. On the surface is a concrete mill and dressing buildings dating from around 1909. At its maximum output in 1910, 154 tons of lead and 1250 ounces of silver were produced. At this time the workforce totalled 135 underground and as many as 169 surface workers.
No 1 adit was driven to cross-cut two parallel lodes. A shaft from within this adit descends to deep adit, with levels at 10, 20 and 35 metres.