e air is in use in any event and where
any mechanical system is at all justified. Any of the mechanical
systems where tonnage is sufficient in quantity to justify their
employment will handle material for from 1.5 to 4 cents per ton
mile.

TRACKS.--Tracks for hand, mule, or rope haulage are usually built
with from 12- to 16-pound rails, but when compressed-air or electrical
locomotives are to be used, less than 24-pound rails are impossible.
As to tracks in general, it may be said that careful laying out
with even grades and gentle curves repays itself many times over in
their subsequent operation. Further care in repair and lubrication
of cars will often make a difference of 75% in the track resistance.

TRANSPORT IN STOPES.--Owing to the even shorter life of individual
stopes than levels, the actual transport of ore or waste in them is
often a function of the aboriginal shovel plus gravity. As shoveling
is the most costly system of transport known, any means of stoping
that decreases the need for it has merit. Shrinkage-stoping eliminates
it altogether. In the other methods, gravity helps in proportion to
the steepness of the dip. When the underlie becomes too flat for
the ore to "run," transport can sometimes be helped by pitching
the ore-passes at a steeper angle than the dip (Fig. 36). In some
cases of flat deposits, crosscuts into the walls, or even levels
under the ore-body, are justifiable. The more numerous the ore-passes,
the less the lateral shoveling, but as passes cost money for
construction and for repair, there is a nice economic balance in
their frequency.

Mechanical haulage in stopes has been tried and finds a field under
some conditions. In dips under 25 deg. and possessing fairly sound
hanging-wall, where long-wall or flat-back cuts are employed, temporary
tracks can often be laid in the stopes and the ore run in cars to
the main passes. In such cases, the tracks are pushed up close
to the face after each cut. Further self-acting inclines to lower
cars to the levels can sometimes be installed to advantage. This
arrangement also permits greater intervals between levels and less
number of ore-passes. For dips between 25 deg. and 50 deg. where the mine
is worked without stope support or with occasional pillars, a very
useful contrivance is the sheet-iron trough--about eighteen inches
wide and six inches deep--made in sections ten or twelve feet long
and readily bolted together. In dips 35 deg. to 50