360

HISTORY OF ENGINEERING.

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Ferry 170 feet, and at Cuerdly Point 650 feet: from thence it rapidly widens to S500 feet;it is then narrowed at Runcorn Gap to 1200 feet, and at a short distance beyond itswidth is 4200 feet, after which it extends to nearly 2^miles, and is again diminished at Liverpool to 3300 feet.

The level of the highest tide intersects the bed of theriver at 'NVoolston, a distance, by the course of thechannel, of nearly 26 miles ; and the bod of the riverat Manchester is 49 feet above the bed of the river atWoolstan. At Warrington is the first weir, after whichthe distance to Manchester is divided into ten pools.

At Liverpool, the spring tides rise 33 feet, at Run-corn 16 feet 6 inches, and at Warrington 8 feet. Thelowest of the neap tides at Liverpool is 23 feet 6 inches,and the depth of water with a high spring tide is 89 feet; lbut the bed of the river rises so much that at 9.^ milesthere is only 33 feet.

Birkenhead , on the Mersey, nearly opposite to Liver-pool, on the Cheshire coast, is becoming a port of greatimportance; the formation of numerous docks, and therapid increase of its inhabitants, have occasioned a newmarket, a town hall, and various other public edificesto be erected. The area of the market is 430 feet inlength, and 130 feet in breadth; its roof is supportedby forty-six cast-iron columns, 25 feet in height.

Aberconway has a small port or dry harbour, and itsancient town of Conway, surrounded by high walls12 feet in thickness, with twenty-four circular and semi-circular towers, give us some idea of a Greek or Romancity. The walls and four gateways remain, now in-closing a wretched collection of dwellings. On theeastern side of the wall of the town is a quay of someextent; and here was a ferry of so much importancethat it formed the landing-place for those who returnedfrom Ireland . The spring tides rise about 12 feet, andat low water the river Conway is not more than 150 feetin breadth. The sandy bed of the river still producesthe pearl oyster or muscle, as it did in the time of theRomans, and the limestone in the neighbourhood aboundswith copper ore.

Bangor , so famous for its slate quarries, is situated atthe Menai Straits, which separate the Isle of Angleseafrom the main land.

Caernarvon , the Scgontium of the Romans, is highlyinteresting to the antiquary for the remains of the ancientcity, which occupies an oblong square, containing sevenacres at a short distance from the present town.

The port affords excellent anchorage in 10 or 12fathoms of water, although the Aber sand bank forms adangerous bar to vessels entering. The quay is of con-siderable extent on the side of the castle, and has latelybeen greatly improved.

Beaumaris , a port of the Isle of Anglesea, has con-siderable trade, and in the neighbourhood are rich andextensive copper mines.

Menai lighthouse, constructed on a sunken rock about200 yards from the coast of Anglesea, was designed byMessrs. Walker and Burgess, and its total cost is saidto have been 12,800/.

It resembles- a circular tower, 40 feet in diameter,

75 feet in height, and 20 feet 6 inches in diameter at top,where it is capped by a castellated parapet of Angleseamarble. The base of this tower is solid to the height of22 feet 6 inches, after which the walls diminish at regularsets-off, of 9 inches each, and at the level of high waterthe diameter is 22 feet.

I he interior is divided into six stories; all the stones are laid perfectly water-tight,and are each secured to the one below by a slate joggle, and two oak trenails passing