_Third Sort._--The third and last sort of rude produce, of which the price naturally rises in the progress of improvement, is that in which the efficacy of human industry, in augmenting the quantity, is either limited or uncertain. Though the real price of this sort of rude produce, therefore, naturally tends to rise in the progress of improvement, yet, according as different accidents happen to render the efforts of human industry more or less successful in augmenting the quantity, it may happen sometimes even to fall, sometimes to continue the same, in very different periods of improvement, and sometimes to rise more or less in the same period. There are some sorts of rude produce which nature has rendered a kind of appendages to other sorts; so that the quantity of the one which any country can afford, is necessarily limited by that of the other. The quantity of wool or of raw hides, for example, which any country can afford, is necessarily limited by the number of great and small cattle that are kept in it. The state of its improvement, and the nature of its agriculture, again necessarily determine this number. The same causes which, in the progress of improvement, gradually raise the price of butcher's meat, should have the same effect, it may be thought, upon the prices of wool and raw hides, and raise them, too, nearly in the same proportion. It probably would be so, if, in the rude beginnings of improvement, the market for the latter commodities was confined within as narrow bounds as that for the former. But the extent of their respective markets is commonly extremely different. The market for butcher's meat is almost everywhere confined to the country which produces it. Ireland, and some part of British America, indeed, carry on a considerable trade in salt provisions; but they are, I believe, the only countries in the commercial world which do so, or which export to other countries any considerable part of their butcher's meat. The market for wool and raw hides, on the contrary, is, in the rude beginnings of improvement, very seldom confined to the country which produces them. They can easily be transported to distant countries; wool without any preparation, and raw hides with very little; and as they are the materials of many manufactures, the industry of other countries may occasion a demand for them, though that of the country which produces them might not occasion any.