d as flint.

The hydraulic pump now working at the 3,000 foot level of the shaft is
the deepest in the world. In Europe the deepest is in a mine in the
Hartz Mountains, Germany, which is working at the depth of 2,700 feet.
It is, however, a small pump not half the size of the one in the
Combination shaft. Although these pumps were first used in Europe,
those in operation here are far superior in size, and in every other
respect, to those of the Old World, several valuable improvements
having been made in them by the machinists of the Pacific coast.

The capacity of the two Cornish pumps, which lift the water from the
2,900 foot level to the Sutro drain tunnel (at the 1,600 level), is
about 1,000,000 gallons in twenty-four hours, and the capacity of the
present hydraulic pumps is 3,500,000 gallons in the same time. They
are now daily pumping, with both hydraulic and Cornish pumps, about
4,000,000 gallons, but could pump at least 500,000 gallons more in
twenty-four hours than they are now doing. The daily capacity with the
hydraulic pump now coming, and which will be set up as mate to that
now in operation at the 3,000 foot level, will be 5,200,000 gallons.

The water which feeds the pressure pipe of the three sets of hydraulic
pumps is brought from near Lake Tahoe, in the Sierra Nevada Mountains.
The distance is about thirty miles, and the greater part of the way
the water flows through iron pipes, which at one point cross a
depression 1,720 feet in depth. The pressure pipe takes this water
from a tank situated on the eastern slope of Mount Davidson, 3,500
feet west of the shaft. At the tank this pipe is twelve inches in
diameter, but is only eight inches where it enters the top of the
shaft. The tank whence the water is taken is 426 feet higher than the
top of the shaft, therefore the vertical pressure upon the hydraulic
pump at the 3,000 foot level is 3,426 feet. The pressure pipe is of
ordinary galvanized iron where it receives the water at the tank, but
gradually grows thicker and stronger, and at the 3,000 level it is
constructed of cast iron, and is 21/2 inches in thickness. The pressure
at this point is 1,500 pounds to the square inch.

In the early days of hydraulic mining in California the miners thought
that with a vertical pressure of 300 feet they could almost tear the
world to pieces, and not a man among them could have been made to
believe that any pipe could be constructed that would withstand a
vertic