s of shaft or tunnel.
Case II. Vertical or horizontal deposits, the only practical
means of attaining which is by a vertical shaft.
Case III. Inclined deposits to be worked from near the surface.
There are in such instances the alternatives of either
a vertical or an inclined shaft.
Case IV. Inclined deposits which must be attacked in depth,
that is, deep-level projects. There are the alternatives
of a compound shaft or of a vertical shaft, and
in some cases of an incline from the surface.

MINES TO GREAT DEPTHS.

Case V. Vertical or horizontal deposits, the only way of reaching
which is by a vertical shaft.
Case VI. Inclined deposits. In such cases the alternatives are
a vertical or a compound shaft.

CASE I.--Although for logical arrangement tunnel entry has been
given first place, to save repetition it is proposed to consider
it later. With few exceptions, tunnels are a temporary expedient
in the mine, which must sooner or later be opened by a shaft.

CASE II. VERTICAL OR HORIZONTAL DEPOSITS.--These require no discussion
as to manner of entry. There is no justifiable alternative to a
vertical shaft (Fig. 4).

[Illustration: Fig. 4.--Cross-sections showing entry to vertical
or horizontal deposits. Case II.]

[Illustration: Fig. 5.--Cross-section showing alternative shafts
to inclined deposit to be worked from surface. Case III.]

CASE III. INCLINED DEPOSITS WHICH ARE INTENDED TO BE WORKED FROM
THE OUTCROP, OR FROM NEAR IT (Fig. 5).--The choice of inclined or
vertical shaft is dependent upon relative cost of construction,
subsequent operation, and the useful life of the shaft, and these
matters are largely governed by the degree of dip. Assuming a shaft
of the same size in either alternative, the comparative cost per
foot of sinking is dependent largely on the breaking facilities
of the rock under the different directions of attack. In this,
the angles of the bedding or joint planes to the direction of the
shaft outweigh other factors. The shaft which takes the greatest
advantage of such lines of breaking weakness will be the cheapest
per foot to sink. In South African experience, where inclined shafts
are sunk parallel to the bedding planes of hard quartzites, the cost
per foot appears to be in favor of the incline. On the other hand,
sinking shafts across tight schists seems to be more advantageous
than parallel to the bed