A very important inquiry, in relation to the statement that upon the products whose composition and history have just been described the fuel supply of the future will depend, consists in the question of the extent and duration of these natural gas and oil reservoirs.  If we are beginning to look forward to a time when our coal supply will have been worked out, it behooves us to ask whether or not the supply of natural gas and oil is practically illimitable.  The geologist will be able to give the coming man some degree of comfort on this point, by informing him that there seems to be no limit to the formation of the fuel of the future.

Natural gas is being manufactured to-day by nature on a big scale.  Wherever plant material has been entombed in the rock formations, and wherever its decomposition proceeds, as proceed it must, there natural gas is being made.  So that with the prospect of coal becoming as rare as the dodo itself, the world, we are told by scientists, may still regard with complacency the failure of our ordinary carbon supply.  The natural gases and oils of the world will provide the human race with combustible material for untold ages—­such at least is the opinion of those who are best informed on the subject.  For one thing, we are reminded that gas is found to be the most convenient and most economical of fuels.  Rock gas is being utilized abroad even now in manufacturing processes.  Dr. M’Gee says that even if the natural supply of rock gas were exhausted to-morrow, manufacturers of glass, certain grades of iron, and other products would substitute an artificial gas for the natural product rather than return to coal.  He adds that “enormous waste would thereby be prevented, the gas by which the air of whole counties in coke-burning regions is contaminated would be utilized, and the carbon of the dense smoke clouds by which manufacturing cities are overshadowed would be turned to good account.”  So that, as regards the latter point, even Mr. Ruskin with his horror of the black smoke of to-day and of the disfigurement of sky and air might become a warm ally of the fuel of the future.  The chemist in his laudation of rock gas and allied products is only re-echoing, when all is said and done, the modern eulogy pronounced on ordinary coal gas as a cooking and heating medium.

We are within the mark when we say that the past five years alone have witnessed a wonderful extension in the use of gas in the kitchen and elsewhere.  It would be singular, indeed, if we should happen to be already anticipating the fuel of the future by such a practice.  Whether or not this is the case, it is at least satisfactory for mankind to know that the mother earth will not fail him when he comes to demand a substitute for coal.  I may be too early even to think of the day of extinction; but we may regard that evil day with complacency in face of the stores of fuel husbanded for us within the rock foundations of our planet.—­Glasgow Herald.