the ore." Small temporary
inclines following the deposit, even though they are eventually
useless; are nine times out of ten justified.

In prospecting deep-level projects, it is usually necessary to
layout work which can be subsequently used in operating the mine,
because the depth involves works of such considerable scale, even
for prospecting, that the initial outlay does not warrant any
anticipation of revision. Such works have to be located and designed
after a study of the general geology as disclosed in adjoining mines.
Practically the only method of supplementing such information is
by the use of churn- and diamond-drills.

DRILLING.--Churn-drills are applicable only to comparatively shallow
deposits of large volume. They have an advantage over the diamond
drill in exposing a larger section and in their application to
loose material; but inability to determine the exact horizon of
the spoil does not lend them to narrow deposits, and in any event
results are likely to be misleading from the finely ground state of
the spoil. They are, however, of very great value for preliminary
prospecting to shallow horizons.

Two facts in diamond-drilling have to be borne in mind: the indication
of values is liable to be misleading, and the deflection of the drill
is likely to carry it far away from its anticipated destination.
A diamond-drill secures a small section which is sufficiently large
to reveal the geology, but the values disclosed in metal mines must
be accepted with reservations. The core amounts to but a little
sample out of possibly large amounts of ore, which is always of
variable character, and the core is most unlikely to represent
the average of the deposit. Two diamond-drill holes on the Oroya
Brownhill mine both passed through the ore-body. One apparently
disclosed unpayable values, the other seemingly showed ore forty
feet in width assaying $80 per ton. Neither was right. On the other
hand, the predetermination of the location of the ore-body justified
expenditure. A recent experiment at Johannesburg of placing a copper
wedge in the hole at a point above the ore-body and deflecting
the drill on reintroducing it, was successful in giving a second
section of the ore at small expense.

The deflection of diamond-drill holes from the starting angle is
almost universal. It often amounts to a considerable wandering
from the intended course. The amount of such deflection varies
with no seeming rule, but it i