his system, in order to protect the
men, a pillar is often left under the level by driving a sublevel,
the pillar being easily recoverable later. The method of sublevels
is of advantage largely in avoiding the timbering of levels.

[Illustration: Fig. 23.--Longitudinal section of an underhand stope.]

OVERHAND STOPES.--By far the greatest bulk of ore is broken overhand,
that is broken upward from one level to the next above. There are
two general forms which such stopes are given,--"horizontal" and
"rill."

[Illustration: Fig. 24.--Horizontal-cut overhand stope--longitudinal
section.]

The horizontal "flat-back" or "long-wall" stope, as it is variously
called, shown in Figure 24, is operated by breaking the ore in slices
parallel with the levels. In rill-stoping the ore is cut back from
the winzes in such a way that a pyramid-shaped room is created,
with its apex in the winze and its base at the level (Figs. 25 and
26). Horizontal or flat-backed stopes can be applied to almost any
dip, while "rill-stoping" finds its most advantageous application
where the dip is such that the ore will "run," or where it can be
made to "run" with a little help. The particular application of
the two systems is dependent not only on the dip but on the method
of supporting the excavation and the ore. With rill-stoping, it is
possible to cut the breaking benches back horizontally from the
winzes (Fig. 25), or to stagger the cuts in such a manner as to
take the slices in a descending angle (Figs. 21 and 26).

[Illustration: Fig. 25.--Rill-cut overhand stope--longitudinal section.]

In the "rill" method of incline cuts, all the drill-holes are "down"
holes (Fig. 21), and can be drilled wet, while in horizontal cuts
or flat-backed stopes, at least part of the holes must be "uppers"
(Fig. 20). Aside from the easier and cheaper drilling and setting
up of machines with this kind of "cut," there is no drill dust,--a
great desideratum in these days of miners' phthisis. A further
advantage in the "rill" cut arises in cases where horizontal jointing
planes run through the ore of a sort from which unduly large masses
break away in "flat-back" stopes. By the descending cut of the
"rill" method these calamities can be in a measure avoided. In
cases of dips over 40 deg. the greatest advantage in "rill" stoping
arises from the possibility of pouring filling or timber into the
stope from above with less handling, because the ore and material
will ru