The "Dérocheuse" (Plate II. fig. 12), constructed by Messrs Lobnitz & Co., is a good example of the dredger fitted with their patent rock cutters, as used on the Suez Canal. These rock cutters consist of stamps passing down through the bottom of the dredger, slightly in advance of the bucket chain, and are employed for breaking up rock in front of the bucket ladder so that it may be raised by buckets afterwards. This system of subaqueous rock cutting plant, on Messrs Lobnitz's patent system, was effectively employed in deepening the Manchester Ship Canal, and removed a considerable length of rock, increasing the depth of water from 26 ft. to 28 ft. at a cost of about 9d. per cub. yd. A full and illustrated description of this plant, and of a similar plant supplied to the Argentine Government, was published in _Engineering_ of August 17, 1906. An illustration of a bucket of 54 cub. ft. capacity constructed by Messrs Lobnitz & Co. is given (Plate II fig. 11), from which some idea of the size of dredging machinery as developed in recent practice may be obtained. In regard to the depth of water that can be obtained by dredging, it is interesting to note that the dredger "Diver," constructed by Messrs. Hunter & English for Mr Samuel Williams of London, is capable of working in 60 ft. of water. In this vessel an ingenious arrangement was devised by Mr Williams, by which part of the weight of the dredger was balanced while the ladder itself could be drawn up through the bucket well and placed upon the deck, enabling a long ladder to be used for a comparatively short vessel. The "Tilbury" dredger, also constructed by Messrs Hunter & English, was able to dredge to a depth of 45 ft. below the surface of the water. _Hopper Barges._--To receive the materials excavated by barge-loading dredgers, steam hopper barges are now generally employed, capable of carrying 500 tons or more of excavation and of steaming loaded at a speed of about 9 m. per hour. These hopper barges are made with hinged flaps in their bottoms, which can be opened when the place of deposit is reached and the dredgings easily and quickly discharged. Good examples of these vessels are the two steam hopper barges built for the Conservators of the river Thames in 1898. The dimensions are: length 190 ft., breadth 30 ft., depth 13 ft. 3 in., hopper capacity 900 tons. They are propelled by a set of triple expansion engines of 1200 i.h.p., with two return-tube boilers having a working pressure of 160 lb. Special appliances are provided to work the hopper doors by steam power from independent engines placed at the forward end of the hopper. A steam windlass is fixed forward and a steam capstan aft. The vessels are fitted with cabins for the officers and crew. On their trial trip, the hoppers having their full load, a speed of 11 knots was obtained, the coal consumption being 1.44 lb. per i.h.p.