This is the site of the Fortitude Pit of the Old Hartley Colliery. This was dug or 'sunk' in the 1780s. It also finished working in the 1780s. The colliery was sunk and operated by the Delaval family who owned a number of other small collieries in the area. The coal, brought to the surface in baskets, was transported to the coast and export by the wagonway earlier constructed for the nearby Chatham Pit.