30 
ff 
INTERNATIONAL TRADE 
paths; and then once more it became a question what were the 
long sustained currents in the movement of goods from country to 
country. 
Mining industries present a peculiar case,! in international trade 
as well as in domestic. It is not easy to say whether they are to be 
regarded as analogous to agriculture or to manufactures. They 
are extractive industries, and therein like agriculture; but they 
are not subject to any “law” of diminishing return; at all events, 
to none of the same kind that bears on agriculture. It is true that 
in mining we find at any given period of time varying costs quite as 
sharply as in agriculture, and more sharply than in manufactures. 
But mining operations are not subject to the kind of pressure which 
appears when men cultivate the soil — when they use land as a 
means for yielding crops perennially. In mining there is a fixed 
store, not an instrument for transmuting matter. And the mines 
which are known and are in use at any one time, while they vary in 
richness, show no certain trend toward greater or less richness. All 
that we are sure of is that each and every single mine will sooner 
or later be exhausted; but it may continue to be unvarying in 
richness until it gives out. Still more uncertain is it whether new 
mines will be discovered, and whether they will prove worse or 
better than those previously worked. We have further to consider 
that while the variations between the costs at the several sources 
of supply are due to physical causes such as differences in richness 
and accessibility, their availability depends markedly on the same 
human factors which are outstanding in manufactures, the ability 
and venturesomeness of business leaders. All in all, it is doubt- 
ful whether we can speak in strictness of any tendency to con- 
stant returns or diminishing returns or increasing returns in mining. 
For the theory of international trade we must be satisfied with 
some general empirical results. The tangled forces that act in the 
mineral industries — the mysteries of the earth’s crust, unpredict- 
able new finds, the progress of science, the progress of business 
management and industrial organization — bring it about that at 
1 Ag was long ago pointed out by Ricardo (Principles, Ch. 3).