'An impressive group of ruined buildings located on gently sloping moorland at the head of Cwm Cregan. The remains comprise several outbuildings, yards and field walls clustered around the main farmhouse, which has been ruinous for at least 40 years. Old OS maps show a disused quarry and tramway nearby and the main building appears to have been modified for some purpose, possibly connected with the adjacent industrial ventures. Ton Mawr was originally a hearth-passage house, probably divided into a hall and narrow inner room, though all trace of a partition has vanished. There was a stone winding stair beside the main fireplace recess, which has the remains of an inserted brick oven at one side. The original entrance in the end gable was blocked at some stage, and a secondary entrance was formed and accessed from a lean-to porch at the front of the house. One original wide and deeply splayed window survives in the hall, though blocked up. The house has evidently been subject to much rebuilding and alteration, and the exact sequence is not clear, since few dateable features remain; however, the additions appear to include a lean-to dairy at the rear, and a heated room (a parlour?) at the lower end. A cowshed has been added to the uphill end, which was later modified by an inserted cross-wall. One narrow window opening remains, and the exterior walls have an offset just above ground level. No original timberwork survives, but the layout and thickness of the walls might point towards an early-seventeenth century date.'
Notes by Paul Davis, 1984
RCAHMW, January 2023