About a mile below the weir at Irlam the canal widens out at the bottom to 250 feet, to form the Partington coal-basin, thus allowing barges and other vessels to be moored at the side, leaving the regulation stretch of the canal for ordinary traffic. Elaborate arrangements are made here to deal with the shipment of coal from both the Lancashire and Yorkshire fields. Just below are the Cadis Head viaducts, carrying the Cheshire lines over the canal, a work that involved much labour to secure the desired gradients and the 75 feet above water-level. At Warburton the roadway has been carried over a high level bridge, on the cantilever principle. The town, which lies to the south of the canal, is of some antiquity, and was the site of a Premonstratensian Priory. Some little distance down, the river Bollin, coming northwards from the neighbourhood of Macclesfield, falls into the canal on one side; on the other, the Mersey is liberated, being now at the same level as the canal itself. Here the Mersey begins to assume its most tortuous course. It twists, bends, and doubles upon itself in a perplexing way, affording a great contrast to the canal, which now runs straight as an arrow all the way to Runcorn. In the course of its meanderings the river comes down to the canal again at Thelwall Ferry, where it had to be deviated for a short distance and made into a straight line. At the end of the deviation it resumes its serpentine character, and here and there accommodation canals run through it to give short cuts. In another of its great bends the Mersey comes down to the canal again at the point where Warrington is brought into touch with the new waterway.