Afterward, a diameter of 15.35 feet was proceeded with, and the small
central shaft of 4¼ 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 26¼ feet was made, and a tube of the same
length and 14½ feet in diameter was driven down. Finally, the shifting
soil was finished with a fourth tube 19½ feet in length and 14 feet in
diameter.

A depth of 111 feet had now been reached, and the material encountered
was solid white chalk. From this point the work proceeded with a
diameter of 13.9 feet to a depth of 450 feet. The small shaft had been
sunk directly to a depth of 475 feet. At 450 feet the diameter was
diminished by three inches. Then an advance of a foot was made, and
the diameter reduced by one and a half inch.

The reason for this reduction in the diameter and change in the mode
of deepening was as follows:

The Chaudron moss-box, when it chances to reach its seat intact, and
can consequently operate well, undoubtedly makes a good wedging. But
how many times does it not happen that it gets injured before reaching
its destination? Besides, as it often rests upon earth that has caved
in upon its seat during the descent of the tubbing, it gets askew, and
later on has to be raised on one side by means of jacks or other