He sometimes demands rent for what is altogether incapable of human improvements. Kelp is a species of sea-weed, which, when burnt, yields an alkaline salt, useful for making glass, soap, and for several other purposes. It grows in several parts of Great Britain, particularly in Scotland, upon such rocks only as lie within the high-water mark, which are twice every day covered with the sea, and of which the produce, therefore, was never augmented by human industry. The landlord, however, whose estate is bounded by a kelp shore of this kind, demands a rent for it as much as for his corn-fields. The sea in the neighbourhood of the islands of Shetland is more than commonly abundant in fish, which makes a great part of the subsistence of their inhabitants. But, in order to profit by the produce of the water, they must have a habitation upon the neighbouring land. The rent of the landlord is in proportion, not to what the farmer can make by the land, but to what he can make both by the land and the water. It is partly paid in sea-fish; and one of the very few instances in which rent makes a part of the price of that commodity, is to be found in that country. The rent of land, therefore, considered as the price paid for the use of the land, is naturally a monopoly price. It is not at all proportioned to what the landlord may have laid out upon the improvement of the land, or to what he can afford to take, but to what the farmer can afford to give. Such parts only of the produce of land can commonly be brought to market, of which the ordinary price is sufficient to replace the stock which must be employed in bringing them thither, together with its ordinary profits. If the ordinary price is more than this, the surplus part of it will naturally go to the rent of the land. If it is not more, though the commodity may be brought to market, it can afford no rent to the landlord. Whether the price is, or is not more, depends upon the demand. There are some parts of the produce of land, for which the demand must always be such as to afford a greater price than what is sufficient to bring them to market; and there are others for which it either may or may not be such as to afford this greater price. The former must always afford a rent to the landlord. The latter sometimes may and sometimes may not, according to different circumstances.