The seam was from six to eight inches (0.15 to 0.2m) thick where worked around Coalgrovebeck on Grassington Moor, whereas it was five inches (0.13m) thick where seen in workings at Hebden Gill, and nine inches (0.27m) thick in Old Prosperous Level at Gateup Gill.
Gill, M.C. “Great Dales Coalfield, Eastern Areas” British Mining No.86 (2008), pp.68-108
Gill, M.C. The Grassington Mines (British Mining No.46, 1993)