The main engine is 10 × 24, operating, by bevel gearing and a 3½ in. vertical shaft, a 4 sided upper tumbler with 21 in. sides. This engine works also a gypsy shaft for swinging, and the conveyer that carries the mud ashore. A steam hoist with 6 × 11 engines raises and lowers the bucket ladder. The buckets, at 4 foot centers, have a struck capacity of 5 cubic feet, and are speeded to deliver from 18 to 20 a minute, according to the character of the material being handled. They are of boiler iron, with a 5 in. steel nosing. The links are of wrought iron, with cast bushings. The lower tumbler is hexagonal, on a 4 in. shaft. The conveyer, projecting 72 ft. from the center of the boat, consists of a 5 ply rubber belt 36 in. wide; running over iron drums at each end and intermediate iron friction rollers at 3 foot centers. Ratchet and pinion on each side of conveyer ladder give means for taking up the slack of the belt and adjusting the drums to maintain them parallel. This conveyer is the important feature of the dredge. It is entirely satisfactory in its working and delivers its material, as nearly as may be, in a dry state upon the levee. It was feared the rubber belt would be shortlived, but a 4 ply belt ran continuously for over two years on the Roberts Island dredge before it needed replacing. The boiler is of the marine type, 52 in. by 10 ft. 6 in., with 3 in. tubes and 14 in. flues; and burns about 1,400 lb. of steam coal in a day of 12 hours. There are three pumps aboard--a hand force pump for washing boiler, a plunger pump for boiler feed, and an Evans steam pump to throw a jet of water into the delivery hopper when digging in any very tenacious material. All three are connected with the boiler. Water tanks below deck serve to trim the boat and furnish a supply for the boiler. The dredger cuts by swinging on a center spud 16 in. in diameter, and moves forward from 8 to 10 ft. at each fleet. The Roberts Island dredger, of which the Ajax is an improved copy, handles steadily 700 yards per day of 12 hours, in the stiffest and most tenacious clay in which it has been worked; and ranges from that average to 1,500 yards per day in soft, peaty mud. The Ajax was built by Farrington, Hyatt & Co., of the Stockton Iron Works. This type of dredger can be built for about $12,500, and we are informed can be relied on for a monthly average of 26,000 yards in any material met with in the overflowed lands near Stockton, delivered 50 ft. ashore, at a height of 10 or 12 ft. above the ground line.--_Min. and Sci. Press_. * * * * * THE FLEXIBLE GIRDER TRAMWAY. This is an ingenious proposition for utilizing a modification of the wire tramway system for overcoming obstacles (while retaining the ordinary wire tramway or any light railway on other parts of the line), made by Mr. Charles Ball, of London.