210 Cofistr action of the Bridge and Causeway 



having in the first instance been disturbed by the process of 

 driving. In nearly all instances the depth of driving was 

 40 feet, and in some as much as 50 feet. 



The supports of the bridge consist of 20 piers 8 feet 

 broad, composed of 12 piles each in a double row, 10 

 of which carry the platform and 2 are for the purposes 

 of fender-piles — the intervals form 22 bays of 32 feet 

 span each ; of an abutment of 25 feet long on the southern 

 end adjoining the causeway of 25 piles : and of a pier 

 carrying the moving parts, or rolling bridge, of 100 feet 

 long, consisting of 98 piles. 



The total number of piles driven is 303. The roadway 

 is borne on longitudinal beams, 5 in breadth, carried 

 from end to end by the heading pieces secured on the 

 piles, and strengthened by a system of strutting between the 

 several bays or openings. 



At the third bay, from the northern shore, which has 

 been made 35 feet in the clear opening, the navigation 

 of the river is secured by the adoption of a moveable 

 j)latform, or rolling bridge, which is readily removed, 

 whenever occasion requires, to allow a vessel to pass 

 through. It opens in the following manner : — 



On the pier provided for the purpose are fixed a series of 

 large flange wheels carried on strong timber framing ; upon 

 these the moveable part of the bridge is run in or out, iron 

 rails being fixed on the under side of the longitudinal beams, 

 which traverse upon the wheels as they turn. 



The space which is thus occupied by the rolling bridge, 

 when run in, is filled up when it is run out, or across the 

 opening, by platforms upon wheels working laterally on 

 railways at each side, right and left. The breadth of the 

 roadway through these moving parts is considerably narrowed, 

 being only 12 feet, and admitting but of one vehicle to 

 pass at a time. 



The method adopted for moving this bridge is by powerful 



