feet in length and of 20×20 inch section in the center, and upon these
placed two others, E F, of 16×16 inch section. Beneath the two first
were inserted six joists, _c c c c c c_, about 82 feet in length and
of 14 or 16 inch section in the center. Finally these were
strengthened at their extremities with two others, _d d_, about 82
feet in length. All these timbers, having been connected by tie bands
and bolts, constituted a rigid structure that covered a surface of
nearly seven hundred square yards.

From the beams, A B and E F, there was suspended a red fir frame by
means of thirty-four iron rods.

Upon this frame, which was entirely immersed in the moving sand, there
was established brick masonry (Figs. 1, 2, and 3). As the ends of the
timbers entered the latter, and were connected by 1½ inch bolts, they
concurred in making the entire affair perfectly solid. The frame, K K,
was provided with an oaken ring, which was affixed to it with bolts.

After this, a cast iron tubbing, having a cutting edge, and being
composed of rings 3.28 feet wide and made of six segments, was
lowered. This tubbing was perfectly tight, all the surfaces of the
joints having been made even and provided with strips of lead
one-tenth of an inch thick. It weighed 4,000 pounds to the running
foot.

[Illustration: FIG. 1.--Section through A B. FIG. 2.--Plan. FIG.
3.--Section through C D. FIG. 5.--Section through E F of Fig. 4. FIGS.
6 AND 7.--Work Prepared and finished. FIG. 10.--Section through A B
and C D of Fig. 12. FIGS. 11 6 AND 12.--Arrangement of jack-screw.
FIG. 13.--Section through A B and C D of Fig. 11.