Beyond the suggestions already given, it is difficult to generalize in the matter of rents from mines and similar returns, for each instance must be worked out for itself, the residual value being so variable. For example, deep mining does not affect the value of the land for agricultural purposes; while quarrying, clay working, and other varieties of open mines leave the land in such form as to render it useless for any subsequent purpose.

For an example of the consumption of growth on the land, consider the yellow pine forests of the Southern and Southwestern States. Here there are three distinct elements of value appealing to three distinct classes of investors, viz.:

1. The turpentine rights, which cover only the "boxing" of the timber and are useful only to naval stores operators.

2. The trees themselves, which, after having been

"boxed," retain their value for logging purposes.

3. The naked land, which in many cases is more valuable for agricultural purposes after the turpentine and logs are removed than it was before.

In such an instance, the total cost of the land may be apportioned to these three divisions without difficulty, for such land is almost invariably surveyed and examined by experts before purchase. If the rent obtained for turpentine rights exceeds the portion of the cost assigned to turpentine, such excess is profit; if it falls short, the deficit may be regarded as a loss, or, under some circumstances, may be added to the cost of the land and timber. The same principle is followed with the logging payments, and the naked land is left with its proper proportion of the cost.