Whatever may be the price of wood, if that of coals is such that the expense of a coal fire is nearly equal to that of a wood one, we may be assured, that at that place, and in these circumstances, the price of coals is as high as it can be. It seems to be so in some of the inland parts of England, particularly in Oxfordshire, where it is usual, even in the fires of the common people, to mix coals and wood together, and where the difference in the expense of those two sorts of fuel cannot, therefore, be very great. Coals, in the coal countries, are everywhere much below this highest price. If they were not, they could not bear the expense of a distant carriage, either by land or by water. A small quantity only could be sold; and the coal masters and the coal proprietors find it more for their interest to sell a great quantity at a price somewhat above the lowest, than a small quantity at the highest. The most fertile coal mine, too, regulates the price of coals at all the other mines in its neighbourhood. Both the proprietor and the undertaker of the work find, the one that he can get a greater rent, the other that he can get a greater profit, by somewhat underselling all their neighbours. Their neighbours are soon obliged to sell at the same price, though they cannot so well afford it, and though it always diminishes, and sometimes takes away altogether, both their rent and their profit. Some works are abandoned altogether; others can afford no rent, and can be wrought only by the proprietor. The lowest price at which coals can be sold for any considerable time, is, like that of all other commodities, the price which is barely sufficient to replace, together with its ordinary profits, the stock which must be employed in bringing them to market. At a coal mine for which the landlord can get no rent, but which he must either work himself or let it alone altogether, the price of coals must generally be nearly about this price. Rent, even where coals afford one, has generally a smaller share in their price than in that of most other parts of the rude produce of land. The rent of an estate above ground, commonly amounts to what is supposed to be a third of the gross produce; and it is generally a rent certain and independent of the occasional variations in the crop. In coal mines, a fifth of the gross produce is a very great rent, a tenth the common rent; and it is seldom a rent certain, but depends upon the occasional variations in the produce. These are so great, that in a country where thirty years purchase is considered as a moderate price for the property of a landed estate, ten years purchase is regarded as a good price for that of a coal mine.