From the stackyards outside Level 9 Mill (NPRN 408866) an 800 metre-long tramway traversed Bwlch y Rhosydd and passed across the precipitous head of Cwm Croesor on a shelf part-cut from the rock and part-supported on drystone walls, to the head of the steepest quarry incline in Wales. It was built in 1864, before which date slates were carried by pack animals down Cwmorthin to the Festiniog Railway at Tanygrisiau.
The incline was designed with a catenary profile by Charles Spooner of the Festiniog Railway, and fell 205 metres over a horizontal distance of 381 metres, an average gradient of 1 in 1.85. But the steepest part at the top had a gradient of 1 in 0.97, or 46 degrees. It was worked by gravity, one full waggon pulling up one empty one. Upward loads were balanced by waggons of slate waste which was dumped at the incline foot. The site of the incline top was so restricted that the rope drum had to be placed some 17 metres higher than the incline brow, with the brake controlled by cables and a ship's wheel at the brow. The given NGR is situated at the incline brow. At the bottom the tramway continued a further 120 metres to a junction with the Croesor Tramway (NPRN 34993), itself completed in 1864.
W J Crompton, RCAHMW, 6 May 2009.