Hence, if we consider the average rent per acre, or hectare, of the total cultivated land as is generally done in statistical works, in comparing either different countries in the same period, or different periods in the same country, we find that the average level of rent per acre, and consequently total rental, corresponds to a certain extent (although by no means identical, but rather a more rapidly increasing extent) to the absolute, not to the relative, fertility of the soil in a given country; that is, to the average amount of produce which it yields from the same area. For the larger the share of superior soils in the total cultivated area, the greater the output for equal capital investments on equally large areas of land; and the higher the average rent per acre. In the reverse case the opposite takes place. Thus, rent does not appear to be determined by the ratio of differential fertility, but by the absolute fertility, and the law of differential rent appears invalid. For this reason certain phenomena are disputed, or an attempt is made to explain them by non-existing differences in average prices of grain and in the differential fertility of cultivated land, whereas such phenomena are merely due to the fact that the ratio of total rental to total area of cultivated land or to total capital invested in the land — as long as the fertility of the rentless soil remains the same and therefore the prices of production, and the differences between the various kinds of soil remain unchanged — is determined not merely by the rent per acre or the rate of rent on capital, but quite as much by the relative number of acres of each type of soil in the total number of cultivated acres; or, what amounts to the same thing, by the distribution of the total invested capital among the various types of soil. Curiously enough, this fact has been completely overlooked thus far. At any rate, we see (and this is important for our further analysis) that the relative level of the average rent per acre, and the average rate of rent (or the ratio of the total rental to the total capital invested in the land), may rise or fall by merely extensively expanding cultivation, as long as prices remain the same, the differential fertilities of the various soils remain unaltered, and the rent per acre, or rate of rent for capital invested per acre in every type of soil actually yielding rent, i.e., for all capital actually yielding rent, remains unchanged.