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 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 coöperation.
9. Improvement of mining machinery, power drills, etc.
10. Centralization of power stations, rather than the use of many small units.