ding planes, and inclines following the
dip cost more per foot than vertical shafts.

An inclined shaft requires more footage to reach a given point
of depth, and therefore it would entail a greater total expense
than a vertical shaft, assuming they cost the same per foot. The
excess amount will be represented by the extra length, and this
will depend upon the flatness of the dip. With vertical shafts,
however, crosscuts to the deposit are necessary. In a comparative
view, therefore, the cost of the crosscuts must be included with
that of the vertical shaft, as they would be almost wholly saved
in an incline following near the ore.

The factor of useful life for the shaft enters in deciding as to
the advisability of vertical shafts on inclined deposits, from the
fact that at some depth one of two alternatives has to be chosen.
The vertical shaft, when it reaches a point below the deposit where
the crosscuts are too long (_C_, Fig. 5), either becomes useless,
or must be turned on an incline at the intersection with the ore
(_B_). The first alternative means ultimately a complete loss of
the shaft for working purposes. The latter has the disadvantage
that the bend interferes slightly with haulage.

The following table will indicate an hypothetical extreme case,--not
infrequently met. In it a vertical shaft 1,500 feet in depth is taken
as cutting the deposit at the depth of 750 feet, the most favored
position so far as aggregate length of crosscuts is concerned. The
cost of crosscutting is taken at $20 per foot and that of sinking
the vertical shaft at $75 per foot. The incline is assumed for two
cases at $75 and $100 per foot respectively. The stoping height
upon the ore between levels is counted at 125 feet.

Dip of | Depth of | Length of |No. of Crosscuts| Total Length
Deposit from | Vertical | Incline | Required from | of Crosscuts,
Horizontal | Shaft | Required | V Shaft | Feet
-------------|-------------|-------------|----------------|---------------
80 deg. | 1,500 | 1,522 | 11 | 859
70 deg. | 1,500 | 1,595 | 12 | 1,911
60 deg. | 1,500 | 1,732 | 13 | 3,247
50 deg. | 1,500 | 1,058 | 15 | 5,389
40 deg. | 1,500 | 2,334 | 18 | 8,038
30 deg. | 1,500 | 3,000 | 23 | 16,237
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