A little further down is Mode Wheel, where are the locks that begin the process of descent, the fall at this point being 13 feet. Here the canal runs nearly west, and continues in this direction till it reaches the outskirts of Eccles, where it begins to run due west through a rock cutting that revealed in the exposed gravel, as the work was in progress, the trend of flowing water in historic times. Beyond are the Barton swing aqueduct and locks. The aqueduct which Brindley carried over the roadway here for the Bridgewater Canal was at the close of last century one of the wonders of the Manchester district. It had to be demolished to give place to a still greater wonder of the kind. Not only had a new aqueduct to be constructed to allow the ship-canal to pass underneath, but it had to be made in such a form that it could swing. This was done by forming the bridge portion of the aqueduct into a caisson, or trough, some 90 feet long by 19 feet wide, and 6 feet deep, and weighing some 1,400 tons. Ordinarily, of course, the water in the old canal is continuous, but when a ship is approaching on the larger canal, double sets of gates are closed at each end of the caisson, thus confining the water in the canal above and in the caisson itself. The caisson is then swung round on a central pier, on each side of which vessels may pass on the ship-canal. Below this engineering triumph are the Barton locks on the ship-canal, giving a fall of 15 feet. Here the new waterway takes a south-westerly turn, and continues thus till it gets to Warburton. About midway between Barton and the latter place, Irlam is reached, and here there are several interesting features of the canal to be seen. To begin with, there is another series of locks, giving a descent this time of 16 feet, with a set of sluice gates in addition, which have been constructed to carry off excess of water in times of flood--an expedient rendered necessary by the fact that just below Irlam the Mersey runs into the canal. Here also the Cheshire Railway lines cross the canal, and these had to be dealt with so as to give a clear waterway of 75 feet above water-level.