BLACKBALL DOCK. 



181 



Ft. in. 

 16 

 4 



8 

 15 



Made ground 



Peat 



Sand and silty clay 



Ballast and running 

 sand 



Making the mean 

 level of the clay 

 below coping level 43 



In carrying out 

 the work, the excava- 

 tions over the whole 

 area were taken down 

 by tide-work from the 

 surface to about 12 

 feet below high-water 

 level, and the mate- 

 rial barged away to 

 places of deposit. 



The coffer-dam was 

 then erected, and the 

 water excluded from 

 the site/ 



After the water 

 was shut out, trenches 

 were sunk, as shown 

 by Fig. 166, along each 

 side of the excava- 

 tion, in order to get 

 in the foundations for 

 the side walls. The 

 sides of the trenches 

 were timbered with 

 pole boarding for = 

 about 15 feet down 

 from the top, and be- 

 low that level with 

 9-inch by 3-inch run- 

 ners. The struts or 

 shores were spaced 3 

 feet vertically and 12 

 feet horizontally, both 

 walings and shores 

 being 12 inches square. 



