Mr. Chavatte’s great anxiety was to know whether he should succeed in causing the first section of tubbing to traverse the four feet of gravel; for in case it did not pass, he would be obliged to employ a second section of smaller diameter, thus increasing the expense.  He was persuaded that the coarse gravel remaining in the side of the shaft would greatly retard the descent of the tubbing.  So he had decided to remove such obstructions at the proper moment through divers or a diving bell.  Then an idea occurred to him that dispensed with all that trouble, and allowed him to continue with the first section.  This was to place upon the dredge two claw-bars, T (Pl. 2, Fig. 3), which effected the operation of widening with wonderful ease.  To do this it was only necessary to turn up the bags, and revolve the apparatus during its descent.  The claw at the extremity of the bar pulled out everything within its reach, and thus made an absolutely free passage for the tubbing.

The sands and gravels were passed by means of a single section of tubbing 31 feet in length, which was not stopped until it had penetrated a stratum of white chalk to a depth of two yards.  This chalk had no consistency, although it contained thin plates of quite large dimensions.  These were cut, as if with a punch, by means of the teeth of the extirpator.

It now remains to say a few words concerning the sinking of the shaft, which, after the operation of the dredge, was continued by the process called “natural level” The work was not easy until a depth of 111 feet had been reached.  Up to this point it had been necessary to proceed with great prudence, and retain the shifting earth by means of four iron plate tubes weighing 54 tons.  Before finding a means of widening the work already done by the dredge, Mr. Chavatte was certain that he would have to use two sections of tubbing, and so had given the first section a diameter of 161/2 feet.  He could then greatly reduce the diameter, and bring it to 153/4 feet as soon as the ground auger was used.

After two yards of soil had been removed from beneath the edge of the tubbing, the earth began to give way.  Seeing this, Mr. Chavatte let down a tube 13 feet in length and 15.4 in diameter.  The exterior of this was provided with 12 oak guides, which sliding over the surface of the tubbing had the effect of causing the tube to descend vertically.  And this was necessary, because this tube had to be driven down every time an excavation of half a yard had been made.

Afterward, a diameter of 15.35 feet was proceeded with, and the small central shaft of 41/4 feet diameter was begun.  This latter had not as yet been sunk, for fear of causing a fall of the earth.

Next, the earth was excavated to a depth of 8.2 feet, and a tube 16.4 feet in length was inserted; then a further excavation of 8.2 feet was made, and the tube driven home.

After this an excavation of 261/4 feet was made, and a tube of the same length and 141/2 feet in diameter was driven down.  Finally, the shifting soil was finished with a fourth tube 191/2 feet in length and 14 feet in diameter.