South Yorkshire method.

The second great principle of working is that known as long-wall or
long-work, in which the coal is taken away either in broad faces from
roads about 40 or 50 yds. apart and parallel to each other, or along
curved faces between roads radiating from the pit bottom--the essential
feature in both cases being the removal of the whole of the coal at
once, without first sub-dividing it into pillars, to be taken away at a
second working. The roof is temporarily supported by wooden props or
pack walling of stone, for a sufficient breadth along the face to
protect the workmen, and allow them to work together behind. The general
character of a long-wall working is shown in fig. 7, which represents an
area of about 500 acres of the bottom hard steam coal at Shipley in
Derbyshire. The principal road extends from the shafts southward; and on
both sides of it the coal has been removed from the light-shaded area by
cutting it back perpendicularly towards the boundaries, along faces
about 50 yds. in length, those nearest to the shaft being kept in
advance of those farther away, producing a step-shaped outline to the
face of the whole coal. It will be seen that by this method the whole of
the seam, with the exception of the pillars left to protect the main
roadways, is removed. The roads for drawing the coal from the working
faces to the shaft are kept open by walling through the waste or goaf
produced by the fall of the unsupported roof. The straight roads are the
air-ways for carrying pure air from the down-cast shaft to the working
faces, while the return air passes along the faces and back to the
up-cast by the curved road. The above is the method of working long-wall
forward, i.e. taking the coal in advance from the pit towards the
boundary, with roads kept open through the gob. Another method consists
in driving towards the boundary, and taking the coal backward towards
the shafts, or working homeward, allowing the waste to close up without
roads having to be kept open through it. This is of course preferable,
but is only applicable where the owner of the mine can afford to expend
the capital required to reach the limit of the field in excess of that
necessary when the raising of coal proceeds _pari passu_ with the
extension of the main roads. Fig. 6 is substantially a modification of
this kind of long-wall work. Fig. 8 represents a method of working
practised in the South Yorkshire district, known as b