rd the bottom. The rock in which the
channel must be cut at this point is partly serpentine greenstone,
partly chrome iron ore, and is intensely hard. In the section of the
Iron Gate, the work to be done consists in "canalizing" the river for
a distance of a mile and a half, by building a wall on each side, and
excavating the bed of the river between. The channel between the walls
will be two hundred and fifty feet wide. It is estimated that nearly
three million cubic feet of rock will have to be excavated here, all
of which will be used to fill in behind the embankment walls. Of
course, the greater part of the rock will be removed by means of
blasting with high explosives, but some of it is to be attacked with a
novel instrument, which was first tried, on a small scale, on the
Panama Canal, and is to be used for serious work here. This
instrument, as it is to be employed on the Danube, consists of an
enormous steel drill, thirty-three feet long, and weighing ten tons.
By means of a machine like a pile driver, this monstrous tool is
raised to a height of about fifty feet, and allowed to drop, point
first. So heavy a mass of metal, falling from a considerable height,
meets with comparatively little resistance from the water, and the
point shatters and grinds up the rock on which it strikes. Fifty or
sixty blows per minute can be struck with a tool of this kind, and ten
thousand blows in all can be inflicted before the tool is so worn as
to be past service. Several of these drills will be at work at the
same time, and to remove the fragments of rock which they break off, a
huge dredge of three hundred and fifty horse power is to be employed.
For excavating by means of explosives, arrangements have been made for
drilling the holes for the cartridges with the greatest possible
rapidity, as on this depends the celerity with which the work can be
pushed forward. Much of the work will be done by means of diamond
drills, which are mounted on boats. Five of these boats have been
provided, each with seven diamond drills, arranged so as to work
perfectly in twenty feet of water. Other boats are fitted with
pneumatic drills, which are operated by means of air, compressed to a
tension of seven hundred and fifty pounds to the square inch. The
pressure of the compressed air is transmitted by means of water to the
drills, which act by percussion, and work very rapidly. These drills
are curiously automatic in their operation. After borin