gh old stopes, and thus
more cheaply constructed than vertical shafts through solid rock;
and also the case of mountainous topographic conditions mentioned
above.

[Illustration: Fig. 7.--Cross-section of inclined deposit which
must be attacked in depth.]

From an operating point of view, the bend in combined shafts (at
_D_) gives rise to a good deal of wear and tear on ropes and gear.
The possible speed of winding through a combined shaft is, however,
greater than a simple incline, for although haulage speed through
the incline section (_D F_) and around the bend of the combined
shaft is about the same as throughout a simple incline (_A F_), the
speed can be accelerated in the vertical portion (_D C_) above that
feasible did the incline extend to the surface. There is therefore an
advantage in this regard in the combined shaft. The net advantages
of the combined over the inclined shaft depend on the comparative
length of the two alternative routes from the intersection (_D_)
to the surface. Certainly it is not advisable to sink a combined
shaft to cut a deposit at 300 feet in depth if a simple incline
can be had to the surface. On the other hand, a combined shaft
cutting the deposit at 1,000 feet will be more advisable than a
simple incline 2,000 feet long to reach the same point. The matter
is one for direct calculation in each special case. In general, there
are few instances of really deep-level projects where a complete
incline from the surface is warranted.

In most situations of this sort, and in all of the second type
(where the outcrop is outside the property), actual choice usually
lies between combined shafts (_C D F_) and entire vertical shafts (_H
G_). The difference between a combined shaft and a direct vertical
shaft can be reduced to a comparison of the combined shaft below
the point of intersection (_D_) with that portion of a vertical
shaft which would cover the same horizon. The question then becomes
identical with that of inclined _versus_ verticals, as stated in Case
III, with the offsetting disadvantage of the bend in the combined
shaft. If it is desired to reach production at the earliest date,
the lower section of a simple vertical shaft must have crosscuts
to reach the ore lying above the horizon of its intersection (_E_).
If production does not press, the ore above the intersection (_EB_)
can be worked by rises from the horizon of intersection (_E_).
In the use of rises, however, there fol