worked above and below the
intersection by incline, and the vertical shaft becomes simply a
more economical exit and an alternative to secure increased output.
The North Star mine at Grass Valley is an illustration in point. Such
a positive instance borders again on Case IV, deep-level projects.

In conclusion, it is the writer's belief that where mines are to
be worked from near the surface, coincidentally with sinking, and
where, therefore, crosscuts from a vertical shaft would need to be
installed frequently, inclines are warranted in all dips under 75 deg.
and over 30 deg. Beyond 75 deg. the best alternative is often
undeterminable. In the range under 30 deg. and over 15 deg., although
inclines are primarily necessary for actual delivery of ore from levels,
they can often be justifiably supplemented by a vertical shaft as a
relief to a long haul. In dips of less than 15 deg., as in those over
75 deg., the advantages again trend strongly in favor of the vertical
shaft. There arise, however, in mountainous countries, topographic
conditions such as the dip of deposits into the mountain, which preclude
any alternative on an incline at any angled dip.

CASE IV. INCLINED DEPOSITS WHICH MUST BE ATTACKED IN DEPTH (Fig.
7).--There are two principal conditions in which such properties
exist: first, mines being operated, or having been previously worked,
whose method of entry must be revised; second, those whose ore-bodies
to be attacked do not outcrop within the property.

The first situation may occur in mines of inadequate shaft capacity
or wrong location; in mines abandoned and resurrected; in mines
where a vertical shaft has reached its limit of useful extensions,
having passed the place of economical crosscutting; or in mines in
flat deposits with inclines whose haul has become too long to be
economical. Three alternatives present themselves in such cases: a
new incline from the surface (_A B F_, Fig. 7), or a vertical shaft
combined with incline extension (_C D F_), or a simple vertical
shaft (_H G_). A comparison can be first made between the simple
incline and the combined shaft. The construction of an incline from
the surface to the ore-body will be more costly than a combined
shaft, for until the horizon of the ore is reached (at _D_) no
crosscuts are required in the vertical section, while the incline
must be of greater length to reach the same horizon. The case arises,
however, where inclines can be sunk throu