_Coal._--The waste in the mining of coal must be reduced from 50 and 150 per cent of the amount taken out to 25, 15, or 10 per cent by the working of upper beds first, the utilization of slack, etc. [Footnote: Van Hise, pp. 26, 27.] The reckless waste of coal in the making of coke can be prevented by the use of the right sort of oven. It is estimated that there would be a saving of $50,000,000 per annum if such a substitution were made. [Footnote: Van Hise, p. 28. ] The tremendous loss of the power value, [Footnote: Van Hise, pp. 29, 30.] from 20 to 33 per cent, and of illuminating value [Footnote: Van Hise, p. 32.] (99 per cent) in coal because of its imperfect consumption can be greatly reduced by the employment of mechanical stokers and other devices. The use of the gas- engine in the place of the steam-engine, [Footnote: Van Hise, p. 31.] the use of power developed from water, and the diffused carbon dioxide in the air tempering the climate are also intimations of forces that may lengthen the life of the coal, 99 per cent of which still remains in the keeping of the valley. It is not too late. [Footnote: See "The Coal Resources of the World," International Geological Congress, 1913.] _Petroleum._--Its probable life may be lengthened beyond ninety years by its restriction to lubricating and illuminating uses only and by the prevention of its exportation. [Footnote: Van Hise, pp. 50-55.] _Natural Gas._--Its flame is ephemeral at best, but its light may be kept burning a little longer if the prodigious waste is prevented. During 1907 four hundred billion feet were consumed and almost as great an amount wasted through uncontrolled wells, leaky pipes, etc. [Footnote: Van Hise, p. 58.] _Iron (and, in less measure, gold, silver, and other metals)_, whose life does not, as coal and oil and gas, perish with the using, but some of whose value is lost in the transformation from one state of use to another, needs only to be more economically mined and used. [Footnote: Van Hise, p. 68.] Non-metallic, inexhaustible materials, as stone, clay, cement, should be employed in their stead when possible. [Footnote: I watched day by day for weeks the erection of a great building in Paris, and I noticed how little iron or steel was used as compared with that in such structures in New York. We shall undoubtedly come to that.] Every scrap of iron should be conserved, cry our constructive prophets, even as the Indians treasured it. We may not need it, but succeeding generations will. It may be recast to their use. We are but its trustees. [Footnote: See, "Iron Ore Resources of the World," International Geological Congress, 1910.]