increasing quantity of food, or with the growing improvement and cultivation of the lands; and as the nature of their business admits of the utmost subdivisions of labour, the quantity of materials which they can work up, increases in a much greater proportion than their numbers. Hence arises a demand for every sort of material which human invention can employ, either usefully or ornamentally, in building, dress, equipage, or household furniture; for the fossils and minerals contained in the bowels of the earth, the precious metals, and the precious stones. Food is, in this manner, not only the original source of rent, but every other part of the produce of land which afterwards affords rent, derives that part of its value from the improvement of the powers of labour in producing food, by means of the improvement and cultivation of land. Those other parts of the produce of land, however, which afterwards afford rent, do not afford it always. Even in improved and cultivated countries, the demand for them is not always such as to afford a greater price than what is sufficient to pay the labour, and replace, together with its ordinary profits, the stock which must be employed in bringing them to market. Whether it is or is not such, depends upon different circumstances. Whether a coal mine, for example, can afford any rent, depends partly upon its fertility, and partly upon its situation. A mine of any kind may be said to be either fertile or barren, according as the quantity of mineral which can be brought from it by a certain quantity of labour, is greater or less than what can be brought by an equal quantity from the greater part of other mines of the same kind. Some coal mines, advantageously situated, cannot be wrought on account of their barrenness. The produce does not pay the expense. They can afford neither profit nor rent. There are some, of which the produce is barely sufficient to pay the labour, and replace, together with its ordinary profits, the stock employed in working them. They afford some profit to the undertaker of the work, but no rent to the landlord. They can be wrought advantageously by nobody but the landlord, who, being himself the undertaker of the work, gets the ordinary profit of the capital which he employs in it. Many coal mines in Scotland are wrought in this manner, and can be wrought in no other. The landlord will allow nobody else to work them without paying some rent, and nobody can afford to pay any.