ys. Their
daily advance was often only from sixty to ninety centimeters (about 2
to 3 ft.), while with the "Derocheuse" it was possible to advance ten
times as rapidly in dredging to the same depth. The bottom upon which
the machine commenced its work was clean and of a true rocky nature.
It was soon perceived that this conglomerate, rich in gypsum,
possessed too great elasticity for the pointed battering rams to have
their proper effect upon it. Each blow made a hole of from fifteen to
sixty centimeters (6 in. to 2. ft.) in depth. A second blow, given
even very near to the first, formed a similar hole, leaving the bed of
the rock to all appearances intact between the two holes. This result,
due entirely to the special nature of the rock, led to the fear that
the action of the battering rams would be without effect. After some
experimentation it was found that the best results were obtained by
arranging the battering rams very near to the chain of buckets and by
working the dredge and battering rams simultaneously. The advance at
each oscillation was about 90 centimeters (about 3 ft.)

The results obtained were as follows: At first the quantity extracted
varied much from day to day; but at the end of some weeks, on account
of the greater experience of the crew, more regularity was obtained.
The nature of the conglomerate was essentially variable, sometimes
hard and tenacious, like malleable iron, then suddenly changing into
friable masses surrounded by portions more elastic and richer in
gypsum.

During the last five weeks at Port Tewfik, the expense, including the
repairs, was 8,850 francs ($1,770.00) for 1,600 cubic meters (2,093
cubic yards) extracted. This would make the cost 5.52 francs per cubic
meter, or $0.84 per cubic yard, not including the insurance, the
interest and the depreciation of the plant.

After some improvements in details, suggested by practice, the machine
was put in operation at Chalouf upon a hard rock, from 1.50 to 3
meters (4 ft. 11 in. to 9 ft. 10 in.) thick. The battering rams were
given a fall of 1.80 meters (5 ft. 11 in.). To break the rock into
fragments small enough not to be rejected by the buckets of the
dredge, the operations of dredging and of disintegration were carried
on separately, permitting the battering rams to work at a greater
distance from the wall face. The time consumed in thus pulverizing the
rock by repeated blows was naturally found to be increased. It was
found mo