In the 14th century the bailiff of Gateshead combined the post with that of steward of the bishop's coal mines. The earliest explicit reference to coal mining in Gateshead is in 1344 when coal was conveyed from coal workings by pack horse to the riverside and tipped into keels for shipment. Evidence for earlier mining activity is provided by the streetname "Colyercher" in a deed probably of the late 12th century. This states that staiths were built at Pipewellgate (HER 4385) in 1349, timber from the bishop's park was used to build pits and watergates for the coal mines in 1364 and in 1367 proprietors of coal mines in Gateshead were obliged to ship their coal across the river to Newcastle. Evidence for medieval mining was found in Robson's Yard on the east side of Oakwellgate in 1999. Two circular pits, 3 metres in diameter were interpreted as mine shafts. The infill contained 12th century and 13th century pottery. In this area the uppermost coal seams are relatively shallow, c5 metres below ground level, and such seams would have been easily winnable by means of bell (or crop) pits.