He first put down two beams, A B (Pl. 1, Figs. 2, 3, and 9), each 82 feet in length and of 20x20 inch section in the center, and upon these placed two others, E F, of 16x16 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 11/2 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.

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.