area, amounting to 6,000 acres, the range had an expectation
on January 1, 1918, to a depth of 3,000 feet, over and above ores
already discovered, of approximately 262,800,000 tons. This was
sufficient to extend the life of the range by about forty-four years.
Knowing the average cost of development of ore per foot in the past, and
knowing the annual output and its rate of acceleration, it is possible
to figure with some accuracy how much expenditure should be planned for
annually in the future in order to maintain a safe margin of reserves
against output.

Such quantitative considerations in the Lake Superior region serve not
only to guide the general conduct of the exploration and development
work, but in some cases as a basis for valuation both for commercial and
taxation purposes.

DEVELOPMENT AND EXPLOITATION OF MINERAL DEPOSITS

The search for new ore bodies is closely related to the development,
extension, and mining of ore bodies already found. In this field the
geologist finds wide application of his science. Here he may not be so
much concerned with the economic factors or with the broader methods of
geologic elimination; his study is more likely to be based mainly on the
local geologic conditions.

Some of the larger and more successful mining companies, perhaps the
greater number of them these days, have geologists whose business it is
to follow closely the underground operations, with a view to advising on
the conduct of the development work. This requires the most precise and
intensive study. For instance, the Anaconda Copper Mining Company has a
staff of several geologists, who follow the underground work in the
utmost detail and whose approval must be obtained by the operating
department in the formulation of any development plan. The complexity
and fault relations of the veins in this company's mines are such that
the application of these methods has abundantly justified itself on the
cost sheet.

Too often mining companies leave the planning and execution of the
underground development work to the local management, commonly to the
underground mining captain, without geologic consultation. This
procedure does not eliminate the economic geologist; for when the
development fails at any point, or new and unexpected conditions are
met, the geologist is likely to be called in. In such cases the practice
of a geologist is like that of the ordinary medical practitioner; he is
called in only when his p