This coalfield is an outlier of Westphalian strata (Langsettian substage), about 5¾ miles long, under Malltreath Marsh, between Llangefni and the Cefni estuary. Of the seven seams present, two were greater than 78 inches thick.
There is documentary evidence for coal mining in the Malltraeth Marshes from the mid fifteenth century onwards, with Tyddyn Mawr colliery considered to be a good surviving seventeenth century example. There have been five small collieries, plus as many as twenty pits, and mining ended in the early 1880s with the closure of Pont Marquis colliery.
The Pentre Berw Colliery was opened around 1815 and worked mainly from shafts up to 130 yards deep. The Llangristiolus Burial Register for 1842 records the burial of Wm Williams killed underground, aged 12.Return to previous page