l as a source of power.

=(A) Mining and preparation of coal.= Under this heading may be included
a large number of proposals which concern primarily the engineering
treatment of the coal underground and in the mine plants. Some of the
more important measures are:

1. Introduction of the long-wall system of mining in places where the
conditions allow it, in order to minimize the waste underground.

2. Modification of the room-and-pillar system of mining, by which larger
pillars are left while the mine advances, and are recovered in the
retreat,--thereby recovering a larger percentage of coal than under the
old system, where small, thin pillars were left, which failed and were
permanently lost.

It has been argued that the great loss of coal by leaving it in pillars
could be saved by using other material to support the roof; but an
elementary calculation of the cost of this procedure shows that it is
cheaper to use the coal. Chance[48] says:

The coal left as pillars to support the roof is thus utilized
and performs a necessary and useful function, yet the
principal part (perhaps two-thirds) of the 200,000,000 tons
our friends the conservationists claim is wilfully and
avoidably wasted every year is this coal that is left in
pillars to support the roof. I think we can safely claim that
this is not waste, but, on the contrary, is engineering
efficiency of the highest type, in that it utilizes the
cheapest and least valuable material available to support the
roof and saves the whole labor cost of building supports of
other materials. Investigation as to what becomes of that part
of the 200,000,000 tons claimed as wasted, which is not
utilized as pillars to support the roof, will disclose the
fact that a very large portion is coal that is left in mine
workings that are abandoned because the roof is unsafe and
because a continuance of operation would result in injuries or
loss of life. Coal left in the mines in order to conserve
human lives cannot be classed as avoidable waste. A small part
of the 200,000,000 tons is lost because it is intimately mixed
with refuse and because the labor cost of recovering it and
separating it from the refuse would be greater than its value.

3. Mining of shallow bituminous beds by means of the steam shovel.
Progress has been made along this line in the last few years, and
valuable