From Runcorn the ship-canal forms the southern side of the Mersey. The outer wall of protection follows the course of the river, bending with it round what may be called the Runcorn headland, and crossing the mouth of the river Weaver. The Weaver being navigable up to Northwich, the construction of the canal across its opening into the Mersey was a work of considerable ingenuity and difficulty. In the first instance, provision had to be made by special locks to give entrance to the tributary before the point of junction with the Mersey could be interfered with; and when the canal itself was carried over the tributary, a series of great sluices had to be constructed to regulate the flow of the waters into the Mersey. Since then the Weaver has not been subjected to the inconvenience of low tide. Another result of the change has been the formation of a new town on its west bank, known as Saltport, with wharves and other arrangements specially adapted for the cargoes of salt that come down the Weaver for shipment elsewhere. In the case of a smaller stream further on, the Gowy, the water had to be carried under the canal by means of syphons strong enough and large enough to withstand tidal influences. From the Gowy the line of the canal follows the northward sweep of the estuary, and continues thus past Ellesmere Port, where is the outlet for the Shropshire Union system of canals. It then passes onward to what may be called the grand entrance to this commercial undertaking, namely, the Eastham Locks. These locks are in sets of varying sizes, according to the vessels that come and go, this arrangement being necessary to avoid waste of water from the canal. From Eastham the distance by the Mersey to Liverpool is six miles, and to the lightship at the bar nineteen miles.