Britannia Tuicer•-62 feet by 52 feet 5 inches at the base, and reduced by the batter to 55 feet by 45 feet 5 inches at the height of 102 feet above high-water line, at which level the tubes pass through it. A plinth extends round the base of this and the other towers ; and the height of this tower above level is 200 feet, or nearly.:( feet from the bottom of the foundation on the rock. The stone used for the external parts of this, and the other towers and abutments, is a limestone of hard and durable quality, known as Anglesea marble.' It is quarried at Pennmen, on the shore, and near the north-eastern extremity of the island, and is pa' in stones of great size, sonic of them weighing 10 to 14 tons. The interior of this, and the other masonry, is constructed of red sandstone, which is a soft stone, and therefore easily worked. It is quarried at Runcorn, in Cheshire, and is durable for inside work. The solid contents of this tower. if solid, would exceed 575,000 cubic feet, but it is ettnstrneted with hollow spaces or chambers within it, and the quantity of stone said to be actually used in it is 146,625 cubic feet of the limestone, and 144,025 cubic feet of sandstone. The total weight of the masonry in this tower is about 20,000 tons, and about 367 tons of east iron in beams and girders are built in it.
Time foundatlims were laid, and the work np to the level of high-water was constructed, during the intervals of tide. no Mier-dam being emphtyed. and thus some !mlti); were occupied in laying the first Coarse, commenced in May, 1610. The scttMirIliug used for this and the other parts of the work, was of whole timbers or [talks. Ian., together with iron straps and bolts where required. and braced with diagonal half-balks connecting the upright posts. Parallel timbers were laid horizontally on the tops of the posts, and rails lived upon them, and upon those rails travelling crabs or • jennies,' were enabled to pass in both directions, to pick up the stones from the ships. raise them to the required height, and deposit them exactly in their intended places. The stones in the whole of the masonry are left:with the quarry or rough thee, except at the angles, where they are dressed to a square arris, and in the recesses and top entab lature, where they are dressed to a fitir thee all over." "Anglesea and Ca•narvon Towers.—The same dimensions at the base as the Blitatmia tower, viz., 62 that by 52 feet 5 inches, reduced by the batter to 55 feet by 32 feet at the level of the bottom of the tubes; height from level of high water 190 feet, or 10 feet less than the Britannia tower. In architectural design and general appearance these towers exactly resemble the Britannia tower, and they are said to contain 210 tons of cast-iron in beams and girders." "Anolesea and Carnanon ..lbutinents.—These are also battered similar to the towers, and are 176 feet in length, and of width corresponding to the towers, viz., 55 that at the level of the bottom of the tubes. The raised part of the abutments, in which the ends of the tubes are supported, are continuous across the railway, forming in l'act complete towers, of smaller height than. but otherwise similar to, the
towers already described. The remainder of the abutments are built of stone-work externally. but built up internally with longitudinal and cross walls, and intermediate arches of brick-work. Over the two parallel spaces formed between the longitudinal walls, corresponding with the two lines of railway, cast-iron girders are fixed, to support the roadway. The continuations of the abutments are surmounted with parapet-walls of solid masonry and considerable height, each of which terminates at the extremity of the bridge with a projecting pedestal, on which a conchant lion, in the Egyp tian style, and of colossal dimensions, faces the approaching visitor, and seems to guard the entrance to the iron wonder behind. Each of these lions is composed of eleven pieces of limestone, and measures 25 feet in length and 12 in height., weighing about 30 tons. Repose and dignity' are skilfully blended in the expression, and these lions are pro bably, in more than one respect, among the greatest of the works which the talented chisel of Mr. Thomas is destined to produce.
'`The four spaces between the Britannia tower and the towers, and between these towers and the abutments, are, as already described, of two dimensions, viz., two of 460 feet, and two of 230 feet. These four spaces have therefore to be spanned by the iron tubes; and as each tube serves for one line of rails only, S tubes are required, 4 of 400 feet net length, and 4 of 230 feet net length: the 4 longer ones being across the water, the 4 shorter ones over the land." In the completion of the work, however, these several tubes are united together, and (with the short lengths also constructed within the towers, and joined to the other lengths) forming two lines of tube parallel to each other, each of the length of 1,313 feet, and each line carrying its respective line at' rails. The process of building and placing these tubes was conducted as follows : The land tubes were constructed in their proper positions, on scatlblding of enormous strength erected for that purpose. The portions of tube intended to occupy the Anglesea and Carnarvon towers, after being completed on the scaffolding at either end, were launched forward to meet the main tubes; while these again were built on the land, floated to the proper place, and then raised by hydraulic presses of immense power, to their destined situation. The method of floating these tubes from the building-stages to the base of the towers, was thus accomplished. Several large pon toons having been provided, they were placed at low-water under the tube to be floated, in such a manner that each end of the tube rested on four of these pontoons. As the tide rose lifting the pontoons, the tube Lorne by them was also lifted, and safely floated to its proper position, ready to be raised by the hydraulle presses.