Between the Mersey and the Trent there were considerable elevations which formed very difficult country for water transport. These elevations had to be overcome by the gradual rising of the canal, by means of locks, to a certain height, by the construction, at that point, of a tunnel through the hills, and by a fresh series of locks on the other side, to allow of a lower level being reached again. The rise of the Trent and Mersey Canal from the Mersey to the summit at Harecastle, near the Staffordshire Potteries, was 395 ft., a final climb of 316 ft. being made by means of a flight of thirty-five locks. Through Harecastle Hill there was driven a tunnel a mile and two-thirds in length, with a height of 12 ft. and a breadth of 9 ft. 4 in.[25] South of this tunnel the canal descended to the level of the Trent, a fall of 288 ft., by means of forty locks. In addition to this the canal, in its course of 90 miles, had to pass through four other tunnels and be carried across the river Dove by an aqueduct of twenty-three arches and at four points over windings of the Trent, which it followed to its junction therewith at Wilden Ferry. These engineering difficulties were successfully overcome by Brindley, and the canal was opened for traffic in 1777. The benefits it conferred on industry and commerce, having in view the unsatisfactory alternative means of transport, were beyond all question. English traders saw established across the island, from the Mersey to the Humber, a line of inland navigation which, apart from the long and tedious voyage round the coast, and, also, from the scarcely passable roads, was the first connecting link in our national history between the ports of Liverpool and Hull. But of even greater importance were the facilities for making use of either or both of these ports--the one on the west coast, and the other on the east coast--which were opened up to {175}manufacturers and traders in the midland districts, and especially when the Trent and Mersey Canal was supplemented by the Wolverhampton (now the Staffordshire and Worcestershire) Canal, connecting the Trent with the Severn; the Birmingham Canal; the Coventry Canal (which gave through navigation from the Trent via Lichfield and Oxford, to the Thames); and others.