62 A STATISTICAL ACCOUNT OF THE 



The dam could always be pumped out, as low as 30 

 or 33 feet, with ease. Probably^ the column of air, 

 equal to the area of the dam in its base, assisted the sub- 

 stiinces remaining in the dam, to balance and resist the 

 exterior pressure; which could not be overcome to a 

 greater depth by any eftbrts, until the puddle, and the 

 outward barrier of stone and saml (hereafter mentioned) 



ing the artificial foundation, but proved, incontestibly, the 

 unavoidable necessity of the step. And this was a point of 

 no small importance, in a work which depended so much on 

 public opinion, to induce farther advances for its prosecution. 



The dam was so pressed, and became so critically debili- 

 tated, towards the last stages of the evacuation of the mud 

 and silt, that the breaking of a single cross beam, had nearly 

 wrecked it. This beam broomed and splintered ; and in its 

 dlruption, with a loud and violent explosion, shook the dam 

 throughout. Another beam which resisted the pressure on the 

 failure of this, had been fortunately saved from being cut, to 

 admit a pump. The w^eakening, or cutting this, would have 

 gone far to compleat the destruction. Thus perilously uncer- 

 tain are coffer dams, on the best construction, in deep water, 

 and with little, or partial footing for piles. 



These circumstances are detailed, to shew the true state of 

 things, with which many Stockholders were unacquaint- 

 ed ; and were, in consequence, dissatisfied, because the first 

 course of masonry of the western pier, was not laid on the 

 rock. They supposed, though experience has proved the con- 

 trary, that the artificial foundation would be found incom- 

 petent: and some yet concei\'e, the rock could have been 

 bared without danger. 



The statement will also serve as a caution, to all who In 

 futiu-e engage in such difficult tasks, to avoid, however desi- 

 rable the object, the ruinous consequences of doing too much. 



