equire more than usual protection. Three methods are
used: (_a_) timbering; (_b_) driving a sublevel in the ore above
the main roadway as a stoping-base, thus leaving a pillar of ore
over the roadway (Fig. 39); (_c_) by dry-walling the levels, as in
the Baltic mine, Michigan (Figs. 34 and 35). By the use of sublevels
the main roadways are sometimes driven in the walls (Fig. 38) and in
many cases all timbering is saved. To recover pillars left below
sublevels is a rather difficult task, especially if the old stope
above is caved or filled. The use of pillars in substitution for
timber, if the pillars are to be lost, is simply a matter of economics
as to whether the lost ore would repay the cost of other devices.

[Illustration: Fig. 38.--Cross-section of "shrinkage" stope.]

Frequent ore-chutes through the level timbers, or from the sublevels,
are necessary to prevent lodgment of broken ore between such passes,
because it is usually too dangerous for men to enter the emptying
stope to shovel out the lodged remnants. Where the ore-body is
wide, and in order that there may be no lodgment of ore, the timbers
over the level are set so as to form a trough along the level;
or where pillars are left, they are made "A"-shaped between the
chutes, as indicated in Figure 37.

[Illustration: Fig. 39.--Cross-section of "shrinkage" stope.]

The method of breaking the ore in conjunction with this means of
support in comparatively narrow deposits can be on the rill, in order
to have the advantage of down holes. Usually, however, flat-back
or horizontal cuts are desirable, as in such an arrangement it
is less troublesome to regulate the drawing of the ore so as to
provide proper head room. Where stopes are wide, ore is sometimes
cut arch-shaped from wall to wall to assure its standing. Where
this method of support is not of avail, short, sharply tapering
stulls are put in from the broken ore to the face (Fig. 39). When
the cut above these stulls is taken out, they are pulled up and
are used again.

This method of stoping is only applicable when:--

1. The deposit dips over 60 deg., and thus broken material will freely
settle downward to be drawn off from the bottom.

2. The ore is consistently payable in character. No selection can be
done in breaking, as all material broken must be drawn off together.

3. The hanging wall is strong, and will not crush or spall off waste
into the ore.

4. The ore-body is regular in size, else