As the latent power of any modern society depends in an intimate way upon the buried stores of solar energy in coal-beds, the large area and good quality of the American coal-fields are very important advantages, and are full of promise for the economic future of its people. Among the less important resources of the rocks in North America are the various classes of coal-oils which were first brought into commerce from its fields. Although these oils are not peculiar to North America, the small amount of disruption which its rocks have undergone have caused them to be retained in the subterranean store-houses; while in other countries, where the rocks have been more disturbed, these oils have been allowed to escape to the streams or the air. The areas where these oils occur on the continent are widely scattered. They are, however, principally confined to the Upper Ohio Valley; they are known to exist also in the Valley of the Cumberland River, in California, and in Western Canada north of Lake Erie. Besides these flowing oils there are immense areas of black shales, which yield large quantities of oil to distillation. These are not now of value, on account of the abundance of these flowing oils; but as in the immediate future these flowing wells are likely to cease their production, we may look to these shales for an almost indefinite supply of oil. In the Ohio Valley, extending eastward in Virginia into the valleys of the Atlantic streams, there is an area of over one hundred thousand square miles of this shale, which is on the average over one hundred and fifty feet thick, and yields about ten per cent of oil. In other words, it is equal to a lake of oil as large as New York and Pennsylvania, and fifteen feet deep,—a practically unlimited source of this material. It is important to note that the sources of supply of phosphate and alkaline marls are very large. As these substances are subject to a constant waste in agriculture, and are the most important of all materials to the growth of the standard crops, the soil of America promises on the whole to be as enduring as is that of Europe, though, owing to the larger rainfall, it tends to waste away more rapidly. The building stones of a country are of importance, inasmuch as they affect the constructions of a people; in such materials, suited for the purposes of simple strength and durability, the country is very well supplied, being quite as well off as Europe. On the other hand, the stones that lend themselves to the more decorative uses, the pure white or variegated marbles, are not nearly as rich as the countries about the Mediterranean, which is of all known regions the richest in decorative stones.