are bolted with an oblique face resting on the main braces, an 11in. side uppermost and horizontal, and a 3in. side looking towards the coping, and covering by that much the next altar above. A series of continuous steps, ascending from floor to coping with 8in. rise and 11 in. tread, is thus formed around the entire body and head of the dock, admitting of convenient access at any point.

The entrance works differ somewhat in detail of construction from the body. Six lines of transverse sheet piling on each side run from the floors to the main outer line before referred to, one at the end of the apron, two at each sill, and one at the inner end of the inner abutment. The concrete foundation is carried 5 feet beyond the floors, and the sides or walls are backed by concrete 5 feet thick at the bottom and 2 feet thick at coping. The cross floor timbers and main braces are covered by two thicknesses of 6 in. timber breaking joint. Each course is thoroughly caulked with dry pine wedges.

The transverse floor timbers in the inner abutment are 10 in. higher than the corresponding body floor timbers. The rise from the main floor is formed by six large oak timbers, rabbetted and bolted together, and backed up by heavy oak knees, running back over and framed into the main floor timbers.

There are two positions for the gate 20 feet apart. At each sill four heavy pieces of oak, rabbetted and securely fastened together, form a step or offset, that runs across the floor and up the sides, and receives the weight and thrust of the gate when in position. The top courses of 6 in. timber are rabbetted into and are flush with the sill timber. There are no grooves, and the chances of troublesome obstructions are consequently much lessened. The offsets are fitted with stout rubber gaskets, against which the gate bears and forms a water-tight joint.

The apron is constructed on a concrete foundation in similar manner to the floors of the gate platforms, the timber being covered with an extra layer or facing of concrete. The apron proper extends 21 feet beyond the outer sill with a concrete toe carried 13 feet further.

Sheet piles are of spruce fitted with dry pine tongues or keys. Bearing piles are of the same timber. All are driven to the hard gravel on which the concrete foundations of the floors rest, so that the whole structure has a perfectly uniform bearing.

The excavation of the dock basin was made after most of the piles had been driven. The material excavated was alluvium, having but a small proportion of gravel, and was found to be impervious to water; hence no more was disturbed than was necessary for the setting of main braces and ties. As the altars were put on, all existing spaces

were filled with suitable material taken from the excavation, and thoroughly rammed. Very slight indications of leakage appeared at several points in the plane, dividing the more recent from the glacial drift. This was doubtless caused by the same plane having been cut in dredging a wet slip on the South side of the dock.

The area around the dock was filled with earth carted from the neighbouring hills, and was graded level with the top of the coping timber. Cross-caps and sheet-piles are thus covered by about two feet of ground.

The cofferdam was formed by driving three parallel rows of sheet piling about 5 feet apart, each row being re-inforced by round piles and braces. The intervening spaces were filled with earth. In plan its form was three sides of a rectangle, the two parallel sides being under the piers at each side of the dock entrance, and the third connecting them just outside the toe of the apron.

The dock is fitted with sliding bilge blocks, 28 on each side, operated from the coping by endless chains. Keel blocks are placed on each cross-floor timber. They are thus 4 ft. apart from centre to

centre.

Materials are sent to the working floor by means of six slides conveniently situated, three on each side of the dock.

The gate is a floating iron caisson. It is provided with a steam capstan, a 10 in. direct acting centrifugal ballast pump, and a boiler. The capstan stands on the upper or flush deck. The engines that operate it and all the other fittings are on a lower deck.

Eight pipes, or filling culverts 22 in. diameter, that pass athwart-ship through the gate, afford a means of filling the dock. They are fitted with valves controlled by hand-wheels on the lower deck.

The gate is moved into and out of position by the steam capstan and suitable warps. Raising and lowering are effected by the ballast pump and inlet valves.

The pumping installation is placed in a brick building a little to the back of the abutment on the north side. The pumps and engines were made by W. H. Allan & Co., of London, England. There are two thirty inch centrifugal pumps, each driven by an independent single engine. The discs are 5 ft. 6 in. in diameter, with curved arms similar to the Appold. The suction expands from 30 in. to 36 in. the size of the wrought iron suction pipe. The discharge expands from 30 in. to 48 in., at which size it delivers into a brick culvert 14 ft. 6 in. wide, 5 ft. 8 in. deep, and 60 ft. long. The suction is divided into two passages at the periphery of the pump, and water is drawn into the disc chamber from both sides

at the centre. Each pump is fitted with a steam ejector for priming. The engines are single, horizontal, variable cut-off, directly connected to the pump shafts having cylinders of 21 in. diameter; and 22 in, stroke, The drainage and leakage are removed by a 10 in. Heald and Cisco centrifugal, driven by a pair of vertical engines directly connected.

The engine pit is enclosed by sheet piling. For a foundation round piles were driven 3 ft. apart, all soft material was excavated to a depth of 2 ft. below floor level, and a quantity of loose stone thrown in. The piles were capped, and concrete laid on the loose stone was rammed round them and brought up level with the caps. A double floor of caulked 3 in. spruce was then laid, and another thickness of concrete placed on it. The pumps and engines were bedded on this foundation in concrete faced with brick. The walls of the engine house start from the same platform, the space between walls and sheet piling being filled to the surface with concrete.

There are two boilers of the marine type built of Siemens-Marten steel. They are 12 ft. 9 in. diameter and 11 ft. 6 in. long. Each hast hree furnaces 3 ft. inside diameter, 8 ft. 3 in. long, each furnace opening into a separate combustion chamber.

The contract stipulated that there should be pumping capacity sufficient to empty the dock when occupied by a 2,000 ton ship in two hours and a half. At an official trial under direction of the writer, the dock was emptied without a ship in it in two hours and twenty minutes. At every six inches fall of the water observations were taken of the time steam pressure in boilers, and speed of engines. The speed of the engines, though slightly increasing, was comparatively uniform. It so happened also that the depth of water was reduced at a uniform rate, that is to say, very nearly the same time elapsed between the observations, from which it will appear that the slip resulting from the increased depth of suction varies approximately as the contents of a layer or stratum of a given depth at varying depths in the dock.

On the south tide of the dock is a wooden freight shed 400 ft. × 40 ft., conveniently situated for a storage of cargo, either from ships in the channel dredged directly alongside or from ships in the dock.

On the opposite or north side a brick building 400 ft. x 35 ft. affords ample space for convenient office accommodation, stores and work shops. The shops are furnished with electric light plant, punch, shears, rolls, and other machinery suitable for repairs of wood and iron ships, and a stationary engine giving the necessary motive power.

Among the most prominent features in this dock are the entire absence on the working floor of discomfort or inconvenience from drain

age; the abundance of light and ventilation for workmen, resulting from the great top width; the readiness with which shores may be adjusted, owing to the small and numerous altars; and the facilities for expeditious construction.

The materials used were the very best of their respective kinds, and the workmanship most thorough throughout.

The only casualty that occurred during construction was a slight movement of the material on the South side of the entrance works, before the frames or concrete were put in. It was promptly stopped by a system of struts to the opposite side, and gave no further trouble.

The work of construction was commenced on 28th May, 1883, and was suspended for four months during the winter of 1883-4. On the 10th Dec., 1884, the dock was formally opened, and H. M. S. "Tenedos" was successfuly docked.

From the Drawings accompanying this paper Plate IX has been prepared.

DISCUSSION.

Mr.Collingwood For nearly two years the writer has acted as Company's engineer for a similar work built by Messrs. J. E. Simpson & Co., from their own plans at Newport News, Va. The two docks are so nearly identical in dimensions and structural details that in most respects the description of one is the same as of the other. While, in general, the floors are the same, the character of the site at Newport News, required piles to be used throughout, to which the longitudinal timbers were drift-bolted. The James River at that point is about five miles wide. The shores consist mostly of fine sand and loam, so that the bottom slopes very gradually, and 25 ft. depth was not reached until about 1,600 ft. from the shore line.

The plan adopted was to build an embankment 315 ft. wide at grade, cutting down the bluff behind for the purpose, and to continue the same each side of the dock nearly to the entrance.

On the South, a timber bulkhead, 200 ft. long, served to protect the outer end of the tank, and the pump and engine house, and on the North a similar one 100 ft. long was built. Beyond these, piers 250 ft. long built on piles were extended on each side of the entrance, the heads of the piers reaching to about 1,100 ft. from the shore line, and to a depth of 9 ft. of water at M.H.W. Sheet piling was driven around the exterior row of piling, exactly as described in the paper.

The cofferdam consisted of four rows of sheeting filled with material from the excavation.

The bottom consisted of a soft surface deposit, below which, to the full depth excavated, there was a kind of marl, made up of great quantities of shells, mixed with sand, etc., from the shores, the fine material resulting from the wear of the shells giving it a greyish appearance. It would stand up vertically under water, and was exceedingly hard to dredge, but after being disturbed, made a thin, sticky mud. The cofferdam was not closed until the pit had been dredged to about its depth, and on pumping out the water there were from one to four feet of mud covering the bottom. There can be but little doubt that such material may, by suitable appliances, be most economically excavated "in the day."

The winds from the North-west and South-west have a reach of at