It was one of the most difficult works, we are told, which, up to that time, had been constructed in Great Britain. The engineer's resources were severely tested by the occurrence of rocks and quicksands: in some places the canal was carried over deep rivers, in others along embankments exceeding twenty feet in height. It traverses numerous roads and scores of rivulets; besides the streams of the Luggie (celebrated by the peasant-poet David Gray), and the Kelvin (immortalized by Burns). The bridge over the latter is 275 feet long and 68 feet high. The depth of the canal averages 8 feet. The total cost of the undertaking did not amount to £200,000. [Sidenote: The bridge at Coldstream.] Smeaton's next engagement was to construct a bridge across the Tweed at Coldstream. It consists of five principal arches, of which the central has a span of 60 feet 8 inches; the two lateral, of 60 feet 5 inches each; and the two land or side arches, 58 feet. It was completed at a total cost of about £6000; and opened in October 1766, having been upwards of three years in building. It will serve to show the great advance that has been made in engineering science since the days of Smeaton, when we state that a similar bridge could now be erected in nine months; though, owing to the rise in wages and in the price of materials, at a much greater cost. Smeaton also furnished the design for the bridge over the river Deveron, near Banff, in Scotland. It consists of seven arches, segments of circles, and measures 410 feet in length, and 20 feet in width. It resembles, in its leading features, the bridge at Perth; and its simple yet graceful aspect, added to the exceeding beauty of its position, renders it a much-admired object, and one of great pictorial interest. [Sidenote: The bridge at Hexham.] Smeaton built only one bridge in England, and, strange to say, it was his only failure. He was requested, in 1777, to furnish a design for a bridge to be erected across the Tyne at Hexham; and a very handsome structure, of nine arches, it proved to be. But it had scarcely been finished before a subsidence took place in the foundation of one of the piers; and an attempt was made to remedy the defect by "sheet-piling," and by filling up the cavities in the river's bed with rough rubble-stones. [Sidenote: A great misfortune.]