Construction of the Bridge and Causeway, dc. 215 



a structure of high utility and advantage to the Colony, and 

 likely to answer its purpose of public convenience for many 

 years to come. 



The bottom of the river across its whole width is composed 

 of mud, varying from 5 to 15 feet deep, and under it is a 

 bed of soft clay of unascertained thickness. 



The depth of water in the channel, or deepest part of the 

 river, is from 20 to 25 feet. 



The rate of the current in the summer time, when the 

 stream is lowest, is not more than from ]|- to 2 knots per 

 hour ; and in times of a flood it rarely exceeds 4 knots. 



From the above data it will be seen that no difl&culty was 

 to be anticipated in driving piles of any required length : 

 the points upon which any doubt existed were, whether they 

 could be so driven and secured together as mutually to 

 assist each other in rendering the whole structure stable, and 

 made sufficiently secure for carrying the superstructure and 

 for resisting the pressure of the current in times of flood, — 

 for it had long been contended that piles, when driven into 

 so soft a stratum as the river's bed, would not be found to 

 be equal to the required purposes. 



Consequently, the contractors bound themselves to drive 

 piles which, at the last or trial strokes, should not be 

 depressed at each stroke more than 1 inch. This con- 

 dition, however, was not fulfilled, and, apparently, could 

 not be — no pile being driven which did not exhibit at the 

 last stroke a depression of 3 or 4 inches. 



The piles, which were from 05 to 90 feet long, could 

 therefore have been driven with ease much further into the 

 bed of the river had their length permitted ; and they were 

 not so firmly fixed immediately after driving but that they 

 could be readily made to move or shift in their places from 

 side to side. But it was found, after the duration of a month 

 or so, that they became much firmer and stifter, the clay 

 bed in which they were placed adhering closer to them, — it 



