the intensive development and use of our mineral resources is in its
infancy, and is in many respects in an experimental stage.

As nations have awakened to their need of mineral raw materials and to
the recent rapid depletion of these materials, they have been naturally
led to inquire how long the reserves may last, and to consider
prevention of waste and the more efficient use of materials, with a view
to planning more prudently for future national supplies. The first
inquiries seemed to reveal such shortage of mineral supplies as to call
for immediate and almost drastic steps to prevent waste, and possibly
even to limit the use of certain minerals in the interests of posterity.

More careful study of the problem, as might be expected, revealed new
factors and greater complexity. The conservational idea has a wide
sentimental appeal, but the formulation and application of specific
plans meet many difficulties. In its practical aspects the problem is
now a live one, the solution of which is requiring the attention of
mining men, engineers, geologists, economists, and public officials. It
is a question which is coming more and more into the field of actual
professional practice of the economic geologist.

It is our purpose to indicate the general nature of the conservation
problem. We may assume agreement to the desirability of preventing
waste, of making a wise present use of mineral products, and of striking
a proper balance between the present and future in their use. Nature has
taken many long geologic periods to build up these reserves. We, of the
present generation, in a sense hold them in trust; they are entailed to
our successors. With this general thought in mind, how shall we proceed
to formulate definite plans for conservation?

An initial step is obviously a careful taking of stock. With increasing
knowledge of mineral resources, it is becoming apparent that early
estimates of supplies were too low. Many of these estimates failed to
take into account mining to great depths, and wide use of low-grade
ores, rendered possible by improved methods; and especially they failed
to put sufficient emphasis on the probabilities of new discoveries to
replace exhausted supplies. Early predictions have already been upset in
regard to a number of mineral resources. The recognition of the general
fact that the world is far from explored in two dimensions, to say
nothing of three, of the fact that known geologic condition