The abutments on either side of the Straits are huge piles of masonry. That on the Anglesey side is 143 feet high, and 173 feet long. The wing walls of both terminate in splendid pedestals, and on each are two colossal lions, of Egyptian design; each being 25 feet long, 12 feet high though crouched, 9 feet abaft the body, and each paw 2 feet 1 inches. Each weighs 30 tons. The towers for supporting the tube are of a like magnitude with the entire work. The great Britannia Tower, in the centre of the Straits, is 62 feet by 52 feet at its base; its total height from the bottom, 230 feet; it contains 148,625 cubic feet of limestone, and 144,625 of sandstone; it weighs 20,000 tons; and there are 387 tons of cast iron built into it in the shape of beams and girders. It sustains the four ends of the four long iron tubes which span the Straits from shore to shore. The total quantity of stone contained in the bridge is 1,500,000 cubic feet. The side towers stand at a clear distance of 460 feet from the great central tower; and, again, the abutments stand at a distance from the side towers of 230 feet, giving the entire bridge a total length of 1849 feet, corresponding with the date of the year of its construction. The side or land towers are each 62 feet by 52 feet at the base, and 190 feet high; they contain 210 tons of cast iron. [Illustration: CONWAY CASTLE AND TUBULAR BRIDGE.] The length of the great tube is exactly 470 feet, being 12 feet longer than the clear space between the towers, and the greatest span ever yet attempted. The greatest height of the tube is in the centre--30 feet, and diminishing towards the end to 22 feet. Each tube consists of sides, top and bottom, all formed of long, narrow wrought-iron plates, varying in length from 12 feet downward. These plates are of the same manufacture as those for making boilers, varying in thickness from three-eighths to three-fourths of an inch. Some of them weigh nearly 7 cwt., and are amongst the largest it is possible to roll with any existing machinery. The connexion between top, bottom, and sides is made much more substantial by triangular pieces of thick plate, riveted in across the corners, to enable the tube to resist the cross or twisting strain to which it will be exposed from the heavy and long-continued gales of wind that, sweeping up the Channel, will assail it in its lofty and unprotected position. The rivets, of which there are 2,000,000--each tube containing 327,000--are more than an inch in diameter. They are placed in rows, and were put in the holes red hot, and beaten with heavy hammers. In cooling, they contracted strongly, and drew the plates together so powerfully that it required a force of from 1 to 6 tons to each rivet, to cause the plates to slide over each other. The weight of wrought iron in the great tube is 1600 tons.