aft is or is not in use for operating the
mine.
_b_. The breaking character of the rock.
_c_. The amount of water.

The delays incident to general carrying of ore and men are such that
the use of the main haulage engine for shaft-sinking is practically
impossible, except on mines with small tonnage output. Even with a
separate winch or auxiliary winding-engine, delays are unavoidable
in a working shaft, especially as it usually has more water to contend
with than one not in use for operating the mine. The writer's own
impression is that an average of 40 feet per month is the maximum
possibility for year in and out sinking under such conditions. In
fact, few going mines manage more than 400 feet a year. In cases
of clean shaft-sinking, where every energy is bent to speed, 150
feet per month have been averaged for many months. Special cases
have occurred where as much as 213 feet have been achieved in a
single month. With ordinary conditions, 1,200 feet in a year is
very good work. Rock awkward to break, and water especially, lowers
the rate of progress very materially. Further reference to speed
will be found in the chapter on "Drilling Methods."

TUNNEL ENTRY.--The alternative of entry to a mine by tunnel is
usually not a question of topography altogether, but, like everything
else in mining science, has to be tempered to meet the capital
available and the expenditure warranted by the value showing.

In the initial prospecting of a mine, tunnels are occasionally
overdone by prospectors. Often more would be proved by a few inclines.
As the pioneer has to rely upon his right arm for hoisting and
drainage, the tunnel offers great temptations, even when it is
long and gains but little depth. At a more advanced stage of
development, the saving of capital outlay on hoisting and pumping
equipment, at a time when capital is costly to secure, is often
sufficient justification for a tunnel entry. But at the stage where
the future working of ore below a tunnel-level must be contemplated,
other factors enter. For ore below tunnel-level a shaft becomes
necessary, and in cases where a tunnel enters a few hundred feet
below the outcrop the shaft should very often extend to the surface,
because internal shafts, winding from tunnel-level, require large
excavations to make room for the transfer of ore and for winding
gear. The latter must be operated by transmitted power, either
that of steam, water, electricity, or air. Where