The method of working used throughout Cleveland is known at ‘Bord and Pillar’
The mine progresses forward by cutting a checkerboard of passages (bords) leaving pillars of ironstone about 20ft by 30ft supporting the roof.
When the limit of working is reached, which could be the edge of the mining royalty or the outcrop of the ironstone, then the miners start to retreat and extract the ironstone from the pillars (top right) When this happens the roof collapses and the ground surface above may subside, also that part of the mine can no longer be accessed.
When this happens it becomes known locally as “goaf”
In this plan of Skelton High Street the three distinct phases of mining are shown.
- The area under the Church (centre right) has not been mined, no passages have been dug. This happened under important buildings and reservoirs.
- The area under the High Street (centre left) has been undermined, but the pillars not extracted. Pillars were left under houses, roads and railways to support them.
- The shaded areas (top and bottom) have been goafed, these areas were open fields at the time, so any subsidence should not have damaged buildings.
Sometime the area under buildings was intentionally goafed and the buildings above allowed to collapse, this happened at Upleatham Hall which was destroyed around 1900.