Early coal extraction was small-scale, the coal lying either on the surface, or very close to it. Typical methods for extraction included drift mining and bell pits. As well as drift mines, small scale shaft mining was used. This took the form of a bell pit, the extraction working outward from a central shaft, or a technique called room and pillar in which 'rooms' of coal were extracted with pillars left to support the roofs. Both of these techniques however left considerable amount of usable coal behind.