posits, their occurrence, structure, and origin. The basic information
thus acquired is useful in estimating reserves and life of mineral
deposits. This leads naturally to considerations of valuation. Because
valuation plays such a large part in any tax program, the geologist is
being used by tax boards of the federal and state governments.

Both in the formulation of laws relating to mineral resources, and in
the litigation growing out of the infraction of these laws, the economic
geologist plays a part.

One cannot go very far with the study of mineral resources without
consideration of the question of conservation. Geologists are called on
not only for broad surveys of the mineral reserves, but for the
formulation of general principles of conservation and their application
to specific mines and minerals.

The geologist's familiarity with the distribution and nature of mineral
resources has given him a part in coping with broad questions of
international use of natural resources. War conditions made it necessary
to use new sources of supply, new channels of distribution, and new
methods of utilization. The economic geologist came into touch with
questions of international trade, tariffs, and shipping.

But economic geology is not solely confined to mineral resources. In
relation to engineering enterprises of the greatest variety--canals,
aqueducts, tunnels, dams, building excavations, foundations,
etc.--geology now figures largely, both in war and in peace.

The nature, amount, and distribution of underground water supplies are
so involved with geologic considerations that a considerable number of
geologists give up their time wholly to this phase of the subject.

It might seem from this list of activities that geology is spreading too
far into the fields of engineering and commerce, but there are equally
rapid extensions of other fields of knowledge toward geology. The
organization of these intermediate fields is required both in the
interest of science and in the interest of better adaptation of the race
to its environment. The geologist is required to do his part in these
new fields, but not to abandon his traditional field.

It is proposed in this volume to discuss the economic aspects of geology
without exhaustive discussion of the principles of geology which are
involved. Practically the whole range of geologic science has some sort
of economic application, and it would be futile to attempt in one volume