low the difficulties of
ventilation and lowering the ore down to the shaft, which brings
expenses to much the same thing as operating through crosscuts.

The advantages of combined over simple vertical shafts are earlier
production, saving of either rises or crosscuts, and the ultimate
utility of the shaft to any depth. The disadvantages are the cost
of the extra length of the inclined section, slower winding, and
greater wear and tear within the inclined section and especially
around the bend. All these factors are of variable import, depending
upon the dip. On very steep dips,--over 70 deg.,--the net result is in
favor of the simple vertical shaft. On other dips it is in favor
of the combined shaft.

CASES V AND VI. MINES TO BE WORKED TO GREAT DEPTHS,--OVER 3,000
FEET.--In Case V, with vertical or horizontal deposits, there is
obviously no desirable alternative to vertical shafts.

In Case VI, with inclined deposits, there are the alternatives
of a combined or of a simple vertical shaft. A vertical shaft in
locations (_H_, Fig. 7) such as would not necessitate extension in
depth by an incline, would, as in Case IV, compel either crosscuts
to the ore or inclines up from the horizon of intersection (_E_).
Apart from delay in coming to production and the consequent loss of
interest on capital, the ventilation problems with this arrangement
would be appalling. Moreover, the combined shaft, entering the deposit
near its shallowest point, offers the possibility of a separate
haulage system on the inclined and on the vertical sections, and
such separate haulage is usually advisable at great depths. In
such instances, the output to be handled is large, for no mine of
small output is likely to be contemplated at such depth. Several
moderate-sized inclines from the horizon of intersection have been
suggested (_EF_, _DG_, _CH_, Fig. 8) to feed a large primary shaft
(_AB_), which thus becomes the trunk road. This program would cheapen
lateral haulage underground, as mechanical traction can be used
in the main level, (_EC_), and horizontal haulage costs can be
reduced on the lower levels. Moreover, separate winding engines
on the two sections increase the capacity, for the effect is that
of two trains instead of one running on a single track.

SHAFT LOCATION.--Although the prime purpose in locating a shaft
is obviously to gain access to the largest volume of ore within
the shortest haulage distance, other conditions also ente