The absolute necessity for returning to the land the manure yielded by its products is so generally admitted that it would appear scarcely necessary to do more than state the fact; for every land-owner knows that when he grants the lease of a farm, one of the conditions he desires to insert is, that all the hay that is made shall be fed upon the land, and that manure shall be purchased to supply the waste resulting from the sale of corn or flax from off the land. In order, however, that it may be so supplied, it is indispensable that the place of consumption shall not be far distant from the place of production, as otherwise the cost of transportation will be greater than the value of the manure. In a recent work on the agriculture of Mecklenburgh, it is stated that a quantity of grain that would be worth close to market fifteen hundred dollars would be worth nothing at a distance of fifty German, or about two hundred English miles, from it, as the whole value would be absorbed in the cost of transporting the grain to market and the manure from market--and that the manure which close to the town would be worth five dollars to the farmer, would be worth nothing at a distance of 4-3/4 German, or 19 English miles from it--and that thus the whole question of the value of land and the wealth of its owner was dependent upon its distance from the place at which its products could be exchanged. At a greater distance than 28 German, or 112 English miles, in Mecklenburgh, the land ceases to yield rent, because it cannot be cultivated without loss. As we approach the place of exchange the value of land increases, from the simultaneous action of two causes: First, a greater variety of commodities can be cultivated, and the advantage resulting from a rotation of crops is well known. At a distance, the farmer can raise only those of which the earth yields but little, and which are valuable in proportion to their little bulk--as, for instance, wheat or cotton; but near the place of exchange he may raise potatoes, turnips, cabbages, and hay, of which the bulk is great in proportion to the value. Second, the cost of returning the manure to the land increases as the value of the products of land diminishes with the increase of distance; and from the combination of these two causes, land in Mecklenburgh that would be worth, if close to the town or city, an annual rent of 29,808 dollars, would be worth at a distance of but 4 German, or 16 English, miles, only 7,467 dollars.