SCHUYLKILL PERMANENT BRIDGE. 59 



cross beams, which were horizontally placed inside the 

 dam, to resist the pressure from without, as the belts 

 were calculated to sustain that of the puddle ; the whole 

 united together, like a floor of joists. The lower 

 belts and gratings were first sunk, as near the bed of 

 the river, as its inequalities would permit. The others, 

 to the number of five, or six, were sunk successively, 

 with the correspondent gratings, at proper heights or 

 distances from each other ; secured, at first, by anchors 

 and cables, and finally fixed by main piles driven by the 

 7'ajn, so as to form a skeleton of the whole dam ; which 

 Avas thereafter embodied, by driving the sheet piles, and 

 filling in the puddle. After the dam was completed, the 

 water contained in it was pumped out; and the pumps 

 continually kept at work, while leakages required. The 

 foundation was laid for the pier, as soon as the dam was 

 evacuated of most of its contents. But a long course of 

 labour, danger, and apprehension, occurred, before this 

 was accomplished. As soon as the masonry arrived at 

 the gratings, successively, the exact shape and size of 

 the pier were cut away. The parts of the beams, and 

 other timber of the gratings remaining, bearing against 

 the stone work had their full effect in supporting, and 

 keeping the dam in its place. 



The great desideratum, in such works, is to have some 

 pervious substance, as a yoofm^ for the piles, and suffici- 

 ently sound and tenacious, to prevent bottom leakages, 

 or blowing, which are often fatal. The advantages of 

 '^noh footing were denied, in many parts, by the bareness 

 of the rock, on which the pier is founded. Owing to 

 this untoward circumstance, under leakages constantly 

 annoyed and threatened. A well intended, but mis^ 



