In the cafie of less regular deposits, the workable area within
the above boundaries, that is, the proportion of this total area that



• See Trautivin^s Pocket Book^ p. i6o, and Treatises on Railroad Surveying.
I20 THE QUARTERLY.
can be profitably worked, must be more or less a matter of uncer-
tainty until the workings actually traverse the whole area. This,
in most cases, does not occur until the deposit is nearly exhausted
and the knowledge is of little practical value.
Sometimes, we can form an estimate of the relative areas of work-
able and unworkable ground from that portion of the deposit which
is exposed by the exploratory workings. A careful s.udy of these
developed portions of the mine will often reveal the laws govern-
ing the distribution of the useful mineral so that the future maybe
predicted with some con'idence. Estimates thus made may be
sufficiently trustworthy to be applied to the undeveloped portions
of the mine.
Variations in thickness and in richness or quality of the mineral
are often sudden and unexpected. Large barren or unworkable
areas are liable to occur, or the deposit may come to an abrupt
end. The estimates of mineral in undeveloped portions of the
mine and the values deduced therefrom are of necessity specula-
tive. This should be made very clear in the report on the prop-
erty. The value of an engineer's estimate of the speculative value
of the property, as opposed to the wild guesses of interested and
over-sanguine parties has been pointed out.
