em are:--

_a_. It permits 25 to 40% greater load of material in
proportion to the dead weight of the vehicle.
_b_. The load can be confined within a smaller horizontal
space, thus the area of the shaft need not be so great
for large tonnages.
_c_. Loading and discharging are more rapid, and the latter
is automatic, thus permitting more trips per hour and
requiring less labor.
_d_. Skips must be loaded from bins underground, and by
providing in the bins storage capacity, shaft haulage is
rendered independent of the lateral transport in the
mine, and there are no delays to the engine awaiting
loads. The result is that ore-winding can be concentrated
into fewer hours, and indirect economies in labor
and power are thus effected.
_e_. Skips save the time of the men engaged in the lateral
haulage, as they have no delay waiting for the winding
engine.

Loads equivalent to those from skips are obtained in some mines
by double-decked cages; but, aside from waste weight of the cage,
this arrangement necessitates either stopping the engine to load the
lower deck, or a double-deck loading station. Double-deck loading
stations are as costly to install and more expensive to work than
skip-loading station ore-bins. Cages are also constructed large
enough to take as many as four trucks on one deck. This entails a
shaft compartment double the size required for skips of the same
capacity, and thus enormously increases shaft cost without gaining
anything.

Altogether the advantages of the skip are so certain and so important
that it is difficult to see the justification for the cage under
but a few conditions. These conditions are those which surround
mines of small output where rapidity of haulage is no object, where
the cost of station-bins can thus be evaded, and the convenience
of the cage for the men can still be preserved. The easy change
of the skip to the cage for hauling men removes the last objection
on larger mines. There occurs also the situation in which ore is
broken under contract at so much per truck, and where it is desirable
to inspect the contents of the truck when discharging it, but even
this objection to the skip can be obviated by contracting on a
cubic-foot basis.

Skips are constructed to carry loads of from two to seven tons,
the general tendency being toward larger loads every year. One
of the most fea