But a novel situation did develop; a condition that would
have sent the cost sky-rocketing if an Orleanian had not met the
difficulty.

Louisiana is what geologists call a region of subsidence. The gulf of
Mexico formerly reached to where Cairo, Ill., now is. Washings from the
land, during the slow-moving centuries, pushed the shoreline ever
outward; the humus of decaying vegetation raised the ground surface
still higher. This section of Louisiana, built by the silt of the
Mississippi, was of course the most recent formation.

Twenty thousand years ago, say the geologists, there were great forests
where Louisiana now is. Among these mighty trees roamed the glyptodont;
the 16-foot armadillo with a tail like the morning-star of the old
crusaders, monstrously magnified; the giraffe camel; the titanothere;
the Columbian elephant, about the size of a trolley car and with
15-foot tusks; the giant sloth which could look into a second-story
window; here the saber-toothed tiger fought with the megatherium;
mighty rhinoceroses sloshed their clumsy way, and huge and grotesque
birds filled the air with their flappings.

As the subsoil packed more solidly, this wilderness in time sunk
beneath the waters. The Mississippi built up its sandbars again, storms
shaped them above the waves, marsh grass raised the surface with its
humus, and another forest grew. This, in turn, sunk. And so the process
was repeated, time after time.

At different depths below the surface of the ground the remains of
these forests are found today, the wood perfectly preserved by the
dampness. And through this tangled mass the dredges had to fight their
way.

It was a task too great for the ordinary type of 20 or 22-inch suction
dredge, even with the strength of 1,000 horses behind it. When they met
these giant stumps and trunks they just stopped.

A. B. Wood, of the sewerage and water department, had already designed
and patented a centrifugal pump impeller adapted to the handling of
sewerage containing trash. Learning of this, W. J. White,
superintendent of dredging on the Canal, asked him to design a special
impeller, along similar lines, for the dredge Texas.

Results from the invention were remarkable. During the thirty days
immediately preceding the installation the dredge had suffered delays
from clogged suction which totalled 130-3/4 hours. During the thirty
days immediately succeeding installation the total of delays for the
same reason was