Excavations at the Coleorton open-cast mine site uncovered several oak boards and runners with iron strips attached. These had been 'corf' sledges with upright poles of wood at one end. A corf was a basket used to measure and carry coal. The pole was probably used to pull the sled along and support the basket.
The corf sled would have been filled at the coalface with around 63kg of coal. The iron-clad runners would then allow the sled to be dragged along the mine tunnels to the main shaft where it would be winched out of the pit. During the late medieval and early post medieval periods coal was generally sold by the 'rook' of 18 corves, what would today be around 1.1 metric tonnes.