ct. Where associated with coal, the percentage of fixed carbon
in the coal may be a guide to the presence and nature of the oil (see
Chapter VIII).

The geological staff of the Netherlands East Indies estimated the tin
reserves of one of these islands by the use of a factor or coefficient,
based on the experience of another island.

In the Cobalt district of Canada a factor for future discoveries and
output, based on past experience, was similarly developed.

Hoover[39] made a statistical study of several hundred metal mines in
various parts of the world, and found that not 6 per cent of the mines
that yielded profits ever made them from ore mined below 2,000 feet; and
that of the mines that paid dividends, 80 per cent did not yield profit
below 1,500 feet, and most of them died above 500 feet.

Attempt has been made by a Swedish geologist to estimate the iron ore
resources of continents by the use of an iron coefficient. This
coefficient was obtained by dividing the known iron ore resources of the
comparatively well-investigated portions of the world by the number of
square miles in which they occurred, and was then multiplied into the
area of the continents whose resources were to be determined.

The application of quantitative methods of this kind has not yet become
very general, nor is it possible to use them in some cases; where
applied many of them have been very crude and others have been partly
disproved by experience. With increasing knowledge and experience, such
methods are becoming more accurate and useful, and are likely to have
wider use in the future.

ORIGIN OF MINERAL DEPOSITS AS A FACTOR IN EXPLORATION

In exploration, the geologist is keen to ascertain the origin of the
mineral deposit. This is often a source of wonder to the layman or
"practical" man, and the geologist may be charged with having let his
fondness for theory run away with him. A widespread fatalistic
conception is expressed in the Cornishman's dictum on ore, "Where it is,
there it is." Yet an understanding of the origin of any particular ore,
the "why" of it, is coming to be recognized as the most effective means
of reaching sound practical conclusions. By ascertaining the approximate
origin of the ore, it may be possible at once to infer a whole group of
practical considerations based on experience with ores of like origin in
other localities. The origin of the ore is the geologist's primary
interest, and it is this which giv