most no market for it, and if it were either in the roof or
bottom of the coal bed, it has been left unmined. If mixed with pure
coal, the low-grade coal was thrown into great heaps at the mouth of the
mine. This refuse coal is called culm. The amount varies from one-tenth
to one-half of the coal in nearly every coal bed, and would probably
average one-fourth in all the mines of the country.

This material is rich in carbon, and when used in gas-engines will
furnish more power than the best Pocahontas coal when steam-engines are
used. Thus one-fourth of all our coal is wasted at the mines simply
because steam-engines instead of gas-producer engines have been
employed. If in the future installation of power this fact is taken into
consideration, it will make the cost less to the user, and at the same
time utilize a large proportion of our impure coal and save the higher
grades for other purposes.

(2) In the mining of coal it was formerly the unfailing custom to leave
supporting pillars of coal for the over-lying rocks to rest upon, to
make suitable working-rooms, etc. These pillars, twelve to eighteen
inches square, and higher than a man's head, are scattered throughout
the entire mines and are usually of the highest grade coal. In many
mines, also, a roof of coal a foot or more in thickness must be left
because the material above the coal is not solid enough to prevent
cave-ins. When the mine is abandoned and closed these pillars and
roofings remain untouched, because removing them constitutes one of the
greatest dangers to life, and is one of the frequent causes of mine
accidents. It is improbable that the coal thus left in abandoned mines
will ever be reclaimed, because not enough is left to make it profitable
at present prices to re-open the mines; and frequently the rocks cave in
about these pillars and make the task almost impossible.

(3) By careless blasting an unnecessarily large amount of coal is blown
into powder,--the slack which has not been marketed at all until within
the last few years. Much of this slack, which is the best grade of coal
in a pulverized form, is left inside the mines. These wastes in
abandoned roofing, pillars, and small-sized coal, together make a total
which for all the mines in the country will average fully one-fourth
more of the coal that is in the ground.

It is to be noted, however, that conditions are changing for the better.
The most modern mines use fewer supporting pillars