ediately on crossing
the dislocation seen in the figure it is changed and the deeper seam D
is found.

The evidence therefore of these bores (3 and 4) indicates some material
derangement, which is then proved by other bores, either towards the dip
or the outcrop, according to the judgment of the borer, so as to
ascertain the best position for sinking pits. (For the methods of boring
see BORING.)

Methods of working.

The working of coal may be conducted either by means of levels or
galleries driven from the outcrop in a valley, or by shafts or pits sunk
from the surface. In the early days of coal-mining, open working, or
quarrying from the outcrop of the seams, was practised to a considerable
extent; but there are now few if any places in England where this can be
done. In 1873 there could be seen, in the thick coal seams of Bengal,
near Raniganj, a seam about 50 ft. thick laid bare, over an area of
several acres, by stripping off a superficial covering varying from 10
to 30 ft., in order to remove the whole of the coal without loss by
pillars. Such a case, however, is quite exceptional. The operations by
which the coal is reached and laid out for removal are known as
"winning," the actual working or extraction of the coal being termed
"getting." In fig. 2 A B is a cross cut level, by which the seams of
coal 1 and 2 are won, and C D a vertical shaft by which the seams 1, 2
and 3 are won. When the field is won by the former method, the coal
lying above the level is said to be "level-free." The mode of winning by
level is of less general application than that by shafts, as the
capacity for production is less, owing to the smaller size of roadways
by which the coal must be brought to the surface, levels of large
section being expensive and difficult to keep open when the mine has
been for some time at work. Shafts, on the other hand, may be made of
almost any capacity, owing to the high speed in drawing which is
attainable with proper mechanism, and allow of the use of more perfect
arrangements at the surface than can usually be adopted at the mouth of
a level on a hill-side. A more cogent reason, however, is to be found in
the fact that the principal coalfields are in flat countries, where the
coal can only be reached by vertical sinking.

Sinking of shafts.

Tubbing.

The methods adopted in driving levels for collieries are generally
similar to those adopted in other mines. The ground is secured by
tim