PLATE I.--SINKING A MINE SHAFT.]

It was first raised to a height of fifteen feet, so as to cause it to
enter the sand by virtue of its own gravity. It thus penetrated to a
depth of about twenty inches. After this the workmen were ordered to
man the windlasses and hoist out some of the sand. This caused the
tubbing to descend about eight inches more, when it came to a
standstill. It was now loaded with 17,000 pounds of pig iron, but in
vain, for it refused to budge. Mr. Chavatte therefore had recourse to
a dredge with vertical axis, constructed as follows:

Upon a square axis, A B (Pl. 2, Figs. 1, 2, and 3), provided with
double cross braces, C D, and strengthened by diagonals, were riveted,
by their upper extremities, two cheeks, G H, whose lower extremities
held the steel plates, I J I' J', which, in turn, were fastened to the
axis, A B, by their other extremities. These plates were so inclined
as to scrape the surface of the ground over which they were moved.
They each carried two bags made of coarse canvas and strengthened by
five strong leather straps (Figs. 2 and 4). To the steel plates were
riveted two plates of iron containing numerous apertures, through
which passed leather straps designed for fastening thereto the lower
part of the mouth of the bags. That portion of the mouth of the latter
that was to remain open was fastened in the same way to two other
plates, X Y, X¹ Y¹ (Fig. 1), held between the lower cross-braces.

When the apparatus was revolved, the plates scraped the earth to be
removed, and descended in measure as the latter entered the bags.
These bags, when full, were hooked, by means of the five rings which
they carried, to the device shown in Fig. 8 (Pl. 2), and raised to the