es him his most effective and
distinctive tool in exploration. Many other phases of exploration work
may be picked up empirically by any one familiar with the local
conditions; but when the man without sound geologic training attempts to
go into this particular field, his lack of background and perspective
often leads to fantastic hypotheses which may vitiate the inferences on
which he plans his exploration.

The scientific investigator, while not accepting the fanciful theories
of the local observer, will make a mistake if he fails to recognize the
residuum of solid fact on which they are built. Many practical explorers
are shrewd observers of empirical facts, even though their explanations
may show a lack of comprehension of the processes involved. Any
assumption of superiority, intolerance, or lack of sympathy, on the part
of the geologist, toward the inadequate explanations and descriptions
given him by the practical man, is likely to indicate a weakness or
limitation in his own mental processes. The geologist's business is to
sift out the fact from the inference, and not to throw over the whole
structure because some of the inferences are faulty.

LAKE SUPERIOR IRON ORE EXPLORATION AS AN ILLUSTRATION

To illustrate the application of some of the methods of exploration of
the kinds described in this chapter, the writer selects an example from
his own experience in the Lake Superior iron fields.[40]

In this region, consideration of the economic aspects of the problem may
eliminate from the best explorable field certain Canadian portions which
are far from water transportation, because the conditions in these
sections would prevent the use of anything but an exceptionally large
and rich deposit. Economic conditions determine in advance also that it
is not worth while looking for ores of certain grades, either because
they are not usable on account of deleterious constituents or low
content of iron, or because these particular grades have already been
developed in excess of requirements. Having determined what ore is
desired, whether Bessemer or non-Bessemer, whether open-hearth or
foundry, further elimination of area is possible on the basis of past
experience.

Coming to the geologic phases of the problem, the first step is to
eliminate great areas of rock which are known never to contain iron ore,
like the granite areas and the quartzite and limestone areas. Within the
remaining areas, by examination of the