n down the sides of the pyramid (Figs. 32 and 34). Thus
not only is there less shoveling required, but fewer ore-passes
and a less number of preliminary winzes are necessary, and a wider
level interval is possible. This matter will be gone into more
fully later.

[Illustration: Fig. 26.--Rill-cut overhand stope-longitudinal section.]

COMBINED STOPES.--A combined stope is made by the coincident working
of the underhand and "rill" method (Fig. 27). This order of stope
has the same limitations in general as the underhand kind. For
flat veins with strong walls, it has a great superiority in that
the stope is carried back more or less parallel with the winzes,
and thus broken ore after blasting lies in a line on the gradient
of the stope. It is, therefore, conveniently placed for mechanical
stope haulage. A further advantage is gained in that winzes may
be placed long distances apart, and that men are not required,
either when at work or passing to and from it, to be ever far from
the face, and they are thus in the safest ground, so that timber
and filling protection which may be otherwise necessary is not
required. This method is largely used in South Africa.

[Illustration: Fig. 27.--Longitudinal section of a combined stope.]

MINIMUM WIDTH OF STOPES.--The minimum stoping width which can be
consistently broken with hand-holes is about 30 inches, and this
only where there is considerable dip to the ore. This space is
so narrow that it is of doubtful advantage in any case, and 40
inches is more common in narrow mines, especially where worked
with white men. Where machine-drills are used about 4 feet is the
minimum width feasible.

RESUING.--In very narrow veins where a certain amount of wall-rock
must be broken to give working space, it pays under some circumstances
to advance the stope into the wall-rock ahead of the ore, thus
stripping the ore and enabling it to be broken separately. This
permits of cleaner selection of the ore; but it is a problem to
be worked out in each case, as to whether rough sorting of some
waste in the stopes, or further sorting at surface with inevitable
treatment of some waste rock, is more economical than separate
stoping cuts and inevitably wider stopes.

VALUING ORE IN COURSE OF BREAKING.--There are many ores whose payability
can be determined by inspection, but there are many of which it cannot.
Continuous assaying is in the latter cases absolutely necessary
to avoid the treatment of