5 s THE IMPROVEMENT OF RIVERS. 



were narrow and incumbered with off-sets of masonry, never afforded in high water 

 more than one arch practicable for navigation, and that one could be used only with 

 difficulty. The later construction of submerged sills below sufficiently distributed 

 the fall so that the same boats were able without serious difficulty to pass the arches 

 which before they had not been able to approach." 



