So great a part of the circulating capital being continually withdrawn from it, in order to be placed in the other two branches of the general stock of the society, it must in its turn require continual supplies without which it would soon cease to exist. These supplies are principally drawn from three sources; the produce of land, of mines, and of fisheries. These afford continual supplies of provisions and materials, of which part is afterwards wrought up into finished work and by which are replaced the provisions, materials, and finished work, continually withdrawn from the circulating capital. From mines, too, is drawn what is necessary for maintaining and augmenting that part of it which consists in money. For though, in the ordinary course of business, this part is not, like the other three, necessarily withdrawn from it, in order to be placed in the other two branches of the general stock of the society, it must, however, like all other things, be wasted and worn out at last, and sometimes, too, be either lost or sent abroad, and must, therefore, require continual, though no doubt much smaller supplies. Land, mines, and fisheries, require all both a fixed and circulating capital to cultivate them; and their produce replaces, with a profit not only those capitals, but all the others in the society. Thus the farmer annually replaces to the manufacturer the provisions which he had consumed, and the materials which he had wrought up the year before; and the manufacturer replaces to the farmer the finished work which he had wasted and worn out in the same time. This is the real exchange that is annually made between those two orders of people, though it seldom happens that the rude produce of the one, and the manufactured produce of the other, are directly bartered for one another; because it seldom happens that the farmer sells his corn and his cattle, his flax and his wool, to the very same person of whom he chuses to purchase the clothes, furniture, and instruments of trade, which he wants. He sells, therefore, his rude produce for money, with which he can purchase, wherever it is to be had, the manufactured produce he has occasion for. Land even replaces, in part at least, the capitals with which fisheries and mines are cultivated. It is the produce of land which draws the fish from the waters; and it is the produce of the surface of the earth which extracts the minerals from its bowels. The produce of land, mines, and fisheries, when their natural fertility is equal, is in proportion to the extent and proper application of the capitals employed about them. When the capitals are equal, and equally well applied, it is in proportion to their natural fertility.