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 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 the earth that was being traversed.  Water put into the shaft helped somewhat, but the great stress to be exerted had to be effected by means of powerful jack screws.  These were placed directly upon the tubbing, and bore against strong beams whose extremities were inserted into the masonry.

As a usual thing it is not easy to use more than four or six such jacks, since the number of beams that can be employed is limited, owing to the danger of obstructing the mouth of the shaft.  Yet twelve were used by Mr. Chavatte, and this number might have been doubled had it been necessary.  As we have seen, the frame, K K (Pl. 1, Fig. 3), was provided with an oak circle traversed by 32 bolts.  The length of these latter was two inches and a quarter longer than they needed to have been, or they were provided with wooden collars of that thickness.  Later on, these collars were replaced with iron bars that held the wood against which the jacks bore in order to press the tubbing downward (Pl. 1, Figs. 10, 11, 12, and 13).