Pen-y-bryn slate quarries are located on the north-west side of Nantlle. A pit working opened here in 1770. It developed during the nineteenth century and by 1882 was employing 240 men producing 5083 tons. Eventually it consisted of four pits with haulages up to a mill area, with locomotive tramway layout. At one time two waterwheels were used for pumping and winding. In 1830 pioneer use was made of chain inclines, and a Blondin carriage system was in use until the 1930s. Product was transported to the Nantlle railway via an incline. After 1836 the quarry was owned by Dorothea , and some tipping was done on Dorothea property. The quarry substantially closed in the late 1890s but small scale intermittent use continued until the 1940s. The Dorothea company made a late bid to re-open it and began to construct a road access.
Much of the eastern part of the site (Hen Dwll) has been obscured by debris from Pen yr Orsedd, and the Twll Mawr and Twll Balast parts of the site are partly filled with water and rubbish. On the older, southern extent there are ruins (in 1991) of several buildings some of which may be of eighteenth-century date (Pen y Bryn farm here dates from the fifteenth century). The later, northerly mills area includes remains of a long mill, barracks and the chimney of a winding engine house. Also still visible are remains of incline formations, drumhouse (with some gear), and some railway formations, including the final Nantlle route - a clear formation - along with the diversion from its original route.
Source: extract from A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.54.

RCAHMW, 21 May 2015