deposits are thus mined which can be mined profitably by no
other method.

4. New methods of filling mined-out spaces with sand, and new methods of
mine survey and design. According to Haas[49]

the greatest advance in the question of method was the system
of mine survey and design perfected in both the anthracite and
bituminous fields. The relatively new method of filling old
spaces with sand, etc., has also achieved success.

5. Use of methods by which coal is not left in the roof for the support
where the roof is weak, and by which coal of inferior quality is not
left in the roof.

6. Wider use of coal-cutting machines by which the wasting of thinner
beds may be avoided.

7. Where conditions allow it, the working of the upper beds before the
lower, in order not to destroy the upper ones by caving. The mining of a
lower coal seam has often so broken up the overlying strata as to render
it impossible to recover the upper coal seams contained therein. There
are certain difficulties, however, in the way of this conservational
measure. In some localities the seams are under separate ownership, and
there is a resulting conflict of interests. Also, if the better coal
seam happens to be below and the poorer seams above, market conditions
may require that the lower seam be mined regardless of the destruction
of the upper ones.

8. Elimination of coal barriers to mark the limits between properties.
This involves more cooperation.

9. Improvement of mining machinery, power drills, etc.

10. Centralization of power stations, rather than the use of many small
units.

11. Elimination of the wasting of slack or fine coal, through more
careful methods of mining, through limitations on the excessive use of
powder and larger use of wedges, through the abolition of laws for the
payment of miners on a run-of-mine basis, and in the case of anthracite
through recovery of the "silt" or dust caused by mining and sorting. It
has been argued that the excessive use of powder ("shooting from the
solid") means loss of coal, owing to the fact that it shatters the coal
and makes a relatively large amount of slack, besides being accompanied
by increased danger from fire and explosion and from weakening of the
roof. Although the excessive use of powder makes a large amount of
slack, it does not necessarily result in waste, for this fine coal is
carefully saved and for certain purposes is as valuable as the lump
coal.