ch yield, unless it can
be _authentically_ connected with blocks of ore remaining, is not
necessarily a criterion of their contents. Except in the cases
mentioned, and as a check on other methods of determination, it
has little place in final conclusions.

TEST PARCELS.--Treatment on a considerable scale of sufficiently
regulated parcels, although theoretically the ideal method, is,
however, not often within the realm of things practical. In examination
on behalf of intending purchasers, the time, expense, or opportunity
to fraud are usually prohibitive, even where the plant and facilities
for such work exist. Even in cases where the engineer in management
of producing mines is desirous of determining the value of standing
ore, with the exception of deposits of the type mentioned above,
it is ordinarily done by actual sampling, because separate mining
and treatment of test lots is generally inconvenient and expensive.
As a result, the determination of the value of standing ore is,
in the great majority of cases, done by sampling and assaying.

SAMPLING.--The whole theory of sampling is based on the distribution
of metals through the ore-body with more or less regularity, so
that if small portions, that is samples, be taken from a sufficient
number of points, their average will represent fairly closely the
unit value of the ore. If the ore is of the extreme type of irregular
metal distribution mentioned under "previous yield," then sampling
has no place.

How frequently samples must be taken, the manner of taking them,
and the quantity that constitutes a fair sample, are matters that
vary with each mine. So much depends upon the proper performance
of this task that it is in fact the most critical feature of mine
examination. Ten samples properly taken are more valuable than
five hundred slovenly ones, like grab samples, for such a number
of bad ones would of a surety lead to wholly wrong conclusions.
Given a good sampling and a proper assay plan, the valuation of a
mine is two-thirds accomplished. It should be an inflexible principle
in examinations for purchase that every sample must be taken under
the personal supervision of the examining engineer or his trusted
assistants. Aside from throwing open the doors to fraud, the average
workman will not carry out the work in a proper manner, unless
under constant supervision, because of his lack of appreciation of
the issues involved. Sampling is hard, uncongenial, manual