In the cataract section, at Jucz, a channel two hundred feet wide, and more than half a mile long, is to be blasted out of the rock, and a breakwater built, to moderate the suddenness of the fall.  This breakwater is to be about two miles long, and ten feet thick at the top, increasing in thickness toward 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 boring the holes to the allotted depth, the machine automatically sets in each a tube, washes out the dust, inserts a dynamite cartridge, withdraws the tube, and connects the wire of the electric fuse in the cartridge with the battery wire in the boat.