EXAMPLES OF WALL SECTIONS. 149 



the greatest difficulty, the large stones generally fracturing in 

 preference to the concrete. 



The concrete was made of 1 part, by measure, of Portland 

 cement to 7 parts of ballast dredged from the harbour. 



The sides and rear of each block were defined and kept 

 in shape by wooden panels which were removed when the 

 block was completed, and re-used for the same purpose. 



A block took from three to four weeks to build, and was 

 considered sufficiently consolidated to move after an interval of 

 ten weeks. 



The length of 12 feet was preserved for a width of 2 feet in 

 from the face. The block then tapered about 2 inches on each 

 side to the rear, in order to give some latitude for adjustment 

 at the time of setting, so as to ensure the range being accurately 

 maintained without having an open joint on the face. 



Vertical grooves (Fig. 130) 3 feet wide and 18 inches deep 

 were formed in the sides of the blocks. When, therefore, two 

 blocks were placed in position, a rectangular aperture 3 feet 

 square was formed, in which concrete was deposited which 

 acted as a dowel or key connecting the two blocks. This detail 

 was introduced as an element of safety rather than as an 

 essential, as no doubt the blocks would have acted satisfactorily 

 had the dowels been omitted. 



To provide for lifting, two cast-iron girders, weighing 11 

 cwt. each, were laid on the platform, and built into the bottom 

 of each block (Fig. 126). The girders acted as washers to 

 spread the local pressure of the suspension bars which 

 supported the block and connected it with the lifting chains. 



The suspension bars were of wrought iron 5 inches in 

 diameter, and 31 feet long, with T ends at both top and 

 bottom. Two rectangular holes were formed in each girder, 

 and over each hole a tube of boards was placed vertically, 

 round which the masonry was built so that there were four 

 rectangular apertures, each 20 inches broad by 11 inches wide, 

 passing vertically through the heart of the block. When 

 the block was ready for lifting, the suspending bars were 

 dropped down through the apertures and turned at right angles, 

 so that their "f ends caught in the girders below, and thus 

 took the bearing of the block. After the block had been set 

 in place, the suspending bars were turned round 90 degrees and 

 withdrawn, to be re-used for lifting other blocks. 



