ock--weighs 1,000,000
pounds. They are balanced by 800-ton concrete blocks and concrete
adjustment blocks. Their extreme length is 160 feet; the moving leaf
has a span of 117 feet.

With a 30-foot right of way for railroad tracks, 11 feet for vehicles
and trolley cars and four feet for pedestrians, they are designed to
meet traffic conditions of a great and growing city. They will support
50-ton street cars or 15-ton road rollers--New Orleans has nothing as
heavy as that now--and trains a great deal heavier than are now coming
to the city. No bridge in the South will support as heavy loads.

The tensile strength of the steel of which the bridges are constructed
is from 55,000 to 85,000 pounds to the square inch, and they will bear
a wind load of 20 pounds to the square inch of exposed surface.

They are operated by two 75-horse power electric motors, 440 volts,
60-cycle, 3-phase current, which is stepped down from 2,200 volts by
means of transformers. In addition, there is a 36-horse power gasoline
engine, to be used if the electrical equipment is out of order. To open
or close the bridges will require a minute and a half.

THE REMARKABLE LOCK.

Not only is the lock of the Industrial Canal one of the largest in the
United States, but its construction solved a soil problem that was
thought impossible. That of the Panama Canal is simple in comparison.
The design is unique in many respects. The lock is a monument to the
power of Man over the forces of Nature, and to the progress of a
community that will not say die.

Because of the great variation in the level of the river at low and
high water--a matter of twenty feet--it was necessary to make the
excavation, for building the lock, about fifty feet deep. In solid soil
this would be a simple matter. But this ground has been made by the
gradual deposit of Mississippi River silt upon what was originally the
sandy bed of the ocean, and through these deposits run strata of
water-bearing sand, or quicksand. This flows into a cut and causes the
banks to cave and slide into the excavation. Underneath there is a
pressure of marsh gas, which, with the pressure of the collapsing
banks, squeezes the deeper layers of quicksand upwards, creating boils
and blowing up the bottom.

New Orleans has had plenty of experiences with these flowing sands in
its shallow sewerage excavations. How, then, expect to make an
excavation fifty feet deep? asked the doubting Thomases. It c