d lined
with masonry or brick-work, so as to afford room for handling the wagons
or trams of coal brought from the working faces. In this portion of the
pit are generally placed the furnaces for ventilation, and the boilers
required for working steam engines underground, as well as the stables
and lamp cabin.

Method of working coal.

Pillar working.

The removal of the coal after the roads have been driven may be effected
in many different ways, according to the custom of the district. These
may, however, all be considered as modifications of two systems, viz.
pillar work and long-wall work. In the former which is also known as
"post and stall" or "bord and pillar" in the north of England, "pillar
and stall" in South Wales, and "stoop and room" in Scotland, the field
is divided into strips by numerous openings driven parallel to the main
rise headings, called "bords" or "bord gates," which are again divided
by cutting through them at intervals, so as to leave a series of pillars
arranged chequer-wise over the entire area. These pillars are left for
the support of the roof as the workings advance, so as to keep the mine
open and free from waste. In the oldest form of this class of working,
where the size of the pillar is equal to the width of the stall or
excavation, about 3/4 of the whole seam will be removed, the remainder
being left in the pillars. A portion of this may be got by the process
known as robbing the pillars, but the coal so obtained is liable to be
very much crushed from the pressure of the superincumbent strata. This
crushing may take place either from above or below, producing what are
known as "creeps" or "sits."

[Illustration: FIG 3.--"Creeps" in Coal-Mines.]

A coal seam with a soft pavement and a hard roof is the most subject to
a "creep." The first indication is a dull hollow sound heard when
treading on the pavement or floor, probably occasioned by some of the
individual layers parting from each other as shown at a fig. 3; the
succeeding stages of creep are shown at b, c, d, f, and g, in the same
figure; the last being the final stage, when the coal begins to sustain
the pressure from the overlying strata, in common with the disturbed
pavement.

[Illustration: FIG. 4.--"Sits" in Mines.]

"Sits" are the reverse of creeps; in the one case the pavement is forced
up, and in the other the roof is forced or falls down, for want of
proper support or tenacity in itself. This accident gene