surface and emptied into cars.

The dredge was set in motion by four oak levers (Figs. 5 and 6). Two
of these were manned by workmen stationed upon the surface flooring,
and the other two by workmen upon the flooring in the tubbing. The
axis was elongated, in measure as the apparatus descended, by rods of
the same dimensions fastened together by cast iron sleeves and bolts
(Fig. 7).

The steel plates were not capable of acting alone, even in cases where
they operated in pure moving sand containing no pebbles, for the sand
was too compact to be easily scraped up by the steel, and so it had to
be previously divided. For this purpose Mr. Chavatte used rakes which
were in form exactly like those of the extirpators, U and V, of Figs.
1, 2, and 3, of Pl. 2, except that the dividers carried teeth that
were not so strong as those of the extirpators, and that were set
closer together. These rakes were let down and drawn up at will. They
were maneuvered as follows:

The dredge descended with the extirpators pointing upward. When their
heads reached the level of the upper floor, the tools were removed.
Then the dredge was raised again. In this way the extirpators lay upon
the floor, and, if the lifting was continued, they placed themselves
in their working position, in which they were fixed by the bolts A" B"
C" (Fig. 1). After this, the apparatus was let down and revolved. The
rakes divided the earth, the scrapers collected it, and the bags
pocketed it.

The great difficulty was to cause the tubbing to descend vertically,
and also to overcome the enormous lateral pressure exerted upon it by