The natural resources, to which the Conservation policy relates, may be divided into two classes: the minerals, which when used cannot be replaced, and things that grow from the soil, which admit of indefinitely augmented reproduction. At the head of the former category stands the supply of coal and iron. This factor in the nation's industry and commerce was being exhausted at a rate which made it certain that, long before the end of the century, the most important manufactures would be handicapped by a higher cost of production. The supply of merchantable timber was disappearing even more rapidly. But far more serious than all other forms of wastage was the reckless destruction of the natural fertility of the soil. The final result, according to Mr. Hill, must be that within a comparatively brief period--a period for which the present generation was bound to take thought--this veritable Land of Promise would be hard pressed to feed its own people, while the manufactured exports to pay for imported food would not be forthcoming. It should be added that this sensational forecast was no purposeless jeremiad. Mr. Hill told his hearers that the danger which threatened the future of the Nation would be averted only by the intelligence and industry of those who cultivated the farm lands, and that they had it in their power to provide a perfectly practicable and adequate remedy. This was to be found--if such a condensation be permissible--in the application of the physical sciences to the practice, and of economic science to the business, of farming.