We arrive through this at the third division, _Rent_. Under some circumstances the “Worth While of Labour” and the “Worth While of Capital” can just barely be earned, and no more. Under those circumstances production will take place, but under worse circumstances it will not. For instance, where there is very light, sandy soil near a heath a man finds that by putting a thousand pounds of capital on to a hundred acres of land he can get his bare subsistence and £50 worth of produce over: 5 per cent. on his capital. It is worth his while to cultivate that land, just barely worth his while. He also possesses land on a still more sandy part over the boundary of the heath itself. He calculates that if he were laboriously to save another £1,000 and take in 100 acres of the new, worse land, he would make the bare subsistence of the labour employed upon it, but only £10 extra, that is, only 1 per cent. on his new capital. He would say: “This is not worth while,” and the too-sandy bit of land would go uncultivated. When the conditions are such that the capital and labour applied to them _just_ get their worth while and no more, those conditions are said to be “_on the margin of production_,” which means that they are the worst conditions under which men in a particular society will consent to produce wealth at all. Put them on conditions still worse, and they will not produce. Now the existence of this Margin of Production creates the third division in Wealth, which is called =RENT=. _Rent is the surplus over and above the minimum required by labour and capital out of the total produce._ (We must be careful, as we saw in the case of “Interest” not to confuse true economic Rent with “Rent” in the conversational sense. Thus what is called “the rent” of a house is part of it true economic rent, but part of it interest on the accumulated or saved wealth, the _Capital_ of its bricks and mortar and building.) Take the case of a seam of coal, which at one end of its run crops out on the surface, a couple of miles on is only 1,000 feet below the surface, but dips down gradually until, within twenty miles, it is 10,000 feet below the surface. Under the conditions of the society in which the coal is being mined, and in the state which the science of mining has reached, it is found that, at a depth of 5,000 feet, this seam is _just_ worth while mining: that is, the capital which has to be accumulated for sinking the shafts and bringing the miners up and down from their work, and raising the coal to the surface, and providing subsistence for the miners at their work, _just barely_ gets the profit below which it would not be worth while to use it.