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 16½ feet. He could then greatly reduce the
diameter, and bring it to 15¾ 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.