This earthwork watercourse is a former leat that took water from Llyn Cerrigllwydion Isaf for approximately 16km to feed Nant Methan and provide a head of water for the waterwheels at Cwm Elan mine (NPRN 34022). According to David Bick, the leat was dug over three months in 1876 by the New Cwm Elan mine company. It is orientated from east to west along the slope of Llethr Du and varies from 1 - 2m in width with a bank between 0.3 and 0.5m high with the ditch on the southern side. A section on Moelfryn, at SN8946966376 where it is taken across the level ridge top, is a cutting with pronounced banks either side.

Source: David Bick (1991) The Old Metal Mines of mid-Wales, Part 6, A Miscellany, page 21

J.J. Hall, Trysor, 11 December 2009