| Reference | Title | Date |
| RHP146000 | National Coal Board Inspectorate plans of workings | 1957- |
| RHP146000/177 | Plans of workings at Ordnance Survey National Grid Reference NS 26/5426 Hillhead, Sorn Castle, Dalgain Mine, Sorn, Woodhead, Beechgrove and Smiddyshaw noted on these plans. | 1953 |