lt that on an average it may be predicted for any
district, in an exploration of sufficient magnitude, how much ore is
likely to be cut in either vertical or horizontal dimension. Thirteen
per cent of the productive area of the Mesabi iron formation is iron
ore. For the remainder of the Lake Superior region five or six per cent
is the factor. These figures mean that, if a person could explore a
broad enough area of iron formation, any miscellaneous group of drill
holes or underground openings would tend to yield these percentage
results. Such percentages are amply sufficient to pay a large profit on
the exploration. The question may be raised why the application of
geology is required, if such average results can be secured from
miscellaneous undirected work. The answer is that seldom is it possible
to conduct an exploration on a sufficiently large scale to be sure of
approximating this average, and that geologic study has made it possible
in many cases to secure a better percentage result. If the geologist is
able to raise the percentage ever so little, the expenditure is amply
justified. He is not expected to have 100 per cent success; but he is
expected to better the average returns, and in this on the whole he has
not failed.

Applying this method specifically to the Gogebic Range, it appears that
up to January 1, 1918, exploration and development had covered 3,650
acres of iron formation, measured along the dip in the plane of the
footwall, within the limits of the area in which the formation is in
such condition as to allow concentration of the ore. The total area of
the footwall to a depth of 3,000 feet is approximately 9,650 acres. The
range, therefore, was 38 per cent developed to this depth. In the
developed area, 160,000,000 tons of ore had been found, or approximately
one ton per square foot of footwall area, or 43,800 per acre of
footwall explored. The total area of ore measured on the footwall was
785 acres. The ratio of ore area to total explored area, measured in the
plane of the footwall, was 21-1/2 per cent. This may be taken in a rough
way to indicate the average exploring possibilities in new ground, where
local conditions to the contrary do not exist. This means that over the
whole range about one drill hole or cross-cut in five will strike ore on
an average. Or, looked at in another way, about 200 feet of drifting in
every 1,000 on the footwall will be in ore. Applying this factor to the
unexplored