If it shall be thought advisable to go to a greater depth than 3,200
feet, a station of large size will be made on the east side of the
present shaft, and in this station will be sunk a shaft of smaller
size. The reason why the work will be continued in this way is that in
a single hoist of 3,200 feet the weight of a steel wire cable of that
length is very great--so great that the loaded cage it brings up is a
mere trifle in comparison. In this secondary shaft the hoisting
apparatus and pumps will be run by means of compressed air. As it is
very expensive to make compressed air by steam power, the pressure
pipe will be tapped at the level of the Sutro tunnel, and a stream of
water taken out that will be used in running a turbine wheel of
sufficient capacity to drive three air compressors. As there will be a
vertical pressure upon the turbine at this depth of over 2,000 feet, a
large stream of water will not be required. The water used in driving
the wheel will flow out through the Sutro tunnel, and give no trouble
in the shaft.

By means of this great shaft and its powerful hydraulic and Cornish
pumps the crust of the earth will probably yet be penetrated to far
greater depth than in any other place in the world. It has been only a
little over ten years since the work of sinking it was begun, whereas
in the mines of the Old World they have been delving since "time
whereof the memory of man runneth not to the contrary." The work on
the Combination shaft has been by no means continuous. There have been
long stoppages aside from those required at such times as they were
engaged in running long drifts to the westward to tap the vein, and at
times for many months, when the several companies interested in the
shaft were engaged in prospecting the various levels it had opened up.