[105] Take the dates of a few important bridges in Lancashire. Time of King John, Lancaster Bridge; 1225, Preston; 1305, Warrington; 1365, Salford; 1372, Stockport; and 1490, Garstang Bridge. The first Lancashire bridges were but narrow structures for foot and horse. Some had very high single arches, and those with from four to six spans were steep and lofty; they seemed to fly away from spates. [106] On the other hand, there is a good social picture, showing that workmen in those days fed very well, though they could not afford to subscribe to the building of a bridge:-- Wives went out to wite [know] how they wrought; Five score in a flock, it was a fayre syght. In broad clothes bright white bread they brought, Cheese and chickens clerelych a dyght [prepared]. [107] Cofferdams are embankments which surround the site so as to exclude water from it. “They are formed in general by driving two rows of piles round the site so as to enclose between them a watertight wall of clay puddle; in depths of less than three or four feet, where there is little current, a simple clay dam may be used. In greater depths, the timber walls consist of guide piles at intervals, with some form of sheet piling between them; in extreme depths the timber walls may be composed of stout piles driven in side by side all round. The dam must be sufficiently strong to bear the pressure of the water against the outside when the space enclosed has been pumped dry.... The ‘Cours de Ponts,’ at the School of the Ponts et Chaussées, states that a cofferdam need never be made of greater thickness than from four to six feet, as the interior can always be sufficiently stayed inside. This method of founding is now seldom practised; it is costly and causes great obstruction in the stream.”--Professor Fleeming Jenkin. [108] A metre = 1·093633 yards, or 39·37079 inches; a centimetre = 0·39371 inch. [109] Professor Fleeming Jenkin, Ninth Edition of the “Encyclopædia Britannica.” [110] The centre arch has a span of 152 ft., and rises 29 ft. 6 in. above Trinity highwater mark; the arches on each side of the centre have a span of 140 ft., and the abutment arches 130 ft. Total length, 1005 ft.; width from outside to outside, 56 ft.; height above low water, 60 ft. Centre piers, 24 ft. thick. Materials: the exterior stones are granite, the interior, half Bramley Fall and half from Painshaw, Derbyshire.