priced at a sum so moderate as that
represented by the profit to be won from the ore in sight, and what
value should be assigned to this unknown portion of the deposit
admits of no certainty. No engineer can approach the prospective
value of a mine with optimism, yet the mining industry would be
non-existent to-day were it approached with pessimism. Any value
assessed must be a matter of judgment, and this judgment based on
geological evidence. Geology is not a mathematical science, and
to attach a money equivalence to forecasts based on such evidence
is the most difficult task set for the mining engineer. It is here
that his view of geology must differ from that of his financially
more irresponsible brother in the science. The geologist, contributing
to human knowledge in general, finds his most valuable field in the
examination of mines largely exhausted. The engineer's most valuable
work arises from his ability to anticipate in the youth of the mine
the symptoms of its old age. The work of our geologic friends is,
however, the very foundation on which we lay our forecasts.

Geologists have, as the result of long observation, propounded for
us certain hypotheses which, while still hypotheses, have proved
to account so widely for our underground experience that no engineer
can afford to lose sight of them. Although there is a lack of safety
in fixed theories as to ore deposition, and although such conclusions
cannot be translated into feet and metal value, they are nevertheless
useful weights on the scale where probabilities are to be weighed.

A method in vogue with many engineers is, where the bottom level
is good, to assume the value of the extension in depth as a sum
proportioned to the profit in sight, and thus evade the use of
geological evidence. The addition of various percentages to the
profit in sight has been used by engineers, and proposed in technical
publications, as varying from 25 to 50%. That is, they roughly
assess the extension in depth to be worth one-fifth to one-third
of the whole value of an equipped mine. While experience may have
sometimes demonstrated this to be a practical method, it certainly
has little foundation in either science or logic, and the writer's
experience is that such estimates are untrue in practice. The quantity
of ore which may be in sight is largely the result of managerial
policy. A small mill on a large mine, under rapid development,
will result in extensive ore-reserv