the walls three feet apart, from center to center, and the caps or joists passing overhead are timbers of the same size.  The timber used is mountain spruce.  Not one of these huge stations has thus far cost one dollar for repairs.  The station at the 2,400 level has been in use five years, that at the 2,600 three years, and the one at the 3,000 level eight months.  Room for ventilation is left behind the timbers, and all are still sound.  Timbers of the same kind are used in the shaft, and all are sound.  The shaft has cost nothing for repairs.  Being in hard andesite rock from top to bottom, the ground does not swell and crowd upon the timbers.

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.

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REMARKABLE WELLS AND CAVERNS.

Yucatan is one of the most interesting States of Mexico, owing to the splendid ancient palaces and temples of once grand cities, now hidden in the forests.  That country also presents great attractions for geologists and botanists, as well as naturalists, who there find rare and beautiful birds, insects, and reptiles.