CHAP. VI DUKE'S CANAL TO RUNOORN. 383 



the enihankinent was raised to the point necessary to 

 enable the canal to he carried forward to the next 

 length. Arthur Young was of opinion that the saving 

 effected l.y constructing the Stretford embankment in 

 tin's way, instead of by carting* the stuff, was equivalent 

 to not less than five thousand per cent. ! The materials of 

 the caissons employed in executing tin's part of the work 

 were afterwards used in forming temporary locks across 

 the valley of the Bollin, whilst the embankment was 

 he ing constructed at that point by a process almost the 

 very reverse, but of like ingenuity. 



BBINDLET'S BALLAST BOATS. 



In the same valley of the Mersey the canal had to be 

 carried over a large brook subject to heavy floods, by 

 means of a strong bridge of two arches, adjoining which 

 was a third, affording provision for a road. Further on, 

 the canal was carried over the Mersey itself upon a 

 bridge with one arch of seventy feet span. Westward 

 of this river lay a very difficult part of the work, occa- 

 sioned by the carrying of the navigation over the Sale 

 Moor Moss. Many thought this an altogether imprac- 

 ti cable thing ; as not only had the hollow trunk of earth 

 in which the canal lay to be made water-tight, but to 

 I reserve the level of the water-way it must necessarily be 

 raised considerably above the level of the Moor across 

 which it was to be laid. Brindley overcame the difficulty 

 in the following manner. He made a strong casing of 

 timber-work outside the intended line of embankment on 

 ( -it her side of the canal, by placing deal balks in an erect 

 position, hacking and supporting them on the outside 

 with other balks laid in rows, and fast screwed together ; 

 and on the front side of this woodwork he had his earth- 



