Incomparably more important in the economic valuation of a piece of land is its capacity for cultivation, because this depends much less on the good or bad quality of the husbandman’s art. I mean here the so-called physical constitution of the vegetable soil; its water-holding power, its consistency (light or heavy soil) on which the difficulty of working it depends; its ability to dry, in a shorter or longer time, and its accompanying diminution in volume; its ability to draw moisture from the atmosphere and to absorb the various kinds of gases; its heat-absorbing and heat-containing power (hot, warm and cold soils).(215) Much depends here on the depth of the vegetable soil and on the constitution of the sub-soil, which, for instance, when it is very permeable, improves a very moist soil, but in the form of meadow iron-ore (_Wiesenerz_), works great injury. The vertical form of the land is also a very important element in estimating the natural fertility of the soil. In mountainous districts, the quantity of land which can be used (and with what labor!) is wont to be relatively smaller than in low lands. Hence it is, that the former become too small for their inhabitants; who, therefore, swarm over the plains lying before them either as settlers or conquerors.(216) In the eastern hemisphere, the northern slopes of mountain regions are most unfavorably situated, although the southern slopes are frequently subjected to more trying and more sudden variations of thawing and freezing weather.(217) But all these more special qualities of the soil must be distinguished from their general basis, the bearing or carrying capacity which land possesses as a mere superficies, and which the most naked rock (Malta!), and the bed of a flowing stream (the floating gardens of China!) possess to some extent, since there is a possibility of establishing a plant-feeding surface on them. This bearing capacity, which in most instances is given only by nature, and which can be added to only to a very limited extent and at great outlay, is wont, when the population is very dense, to acquire considerable exchange value in the vicinity.(218)(219) Section XXXVI. External Nature.—Further Divisions Of Nature’s Gifts.