FOR GREAT BRITAIN AND IRELAND. 95 



matter, or rock of a quality likely to crumble on exposure. 

 Very large boulders should not be admitted, unless after 

 being broken up. In no case, unless the pier^be of great 

 width, should the stones be tipped in, without being after- 

 wards assembled with the hand. T/te rubble of break- 

 waters is generally of a much larger size than for ordinary 

 commercial piers. The ratio of voids in a cubic yard of 

 rubble, after being deposited, depends of course on the 

 kind of materials, and varies from about 4 to about 7 cubic 

 feet in each yard." 



EDGE WORK IN PIER OR QUAY BUILDING. 



On this method Mr. T. Stevenson quotes the views of 

 the late Mr. Bremner of Wick, as follows : 



" If the walls are constructed on a (horizontal) angle of 

 25 to the sea, and the materials built on edge with 3 inches 

 of slope to the foot perpendicular, they cannot retain any 

 air ; and the sea, running along a small portion of the 

 building at one time, actually assists in forcing together 

 the edge building." Mr. Stevenson speaks very highly 

 of this method, and particularly refers to it at St. 

 Andrews and Prestonpans, as evincing greatly superior 

 strength in these ancient works. He condemns the 

 assemblage of stones together in any other way, in exposed 

 positions, but he adds, " care must be taken, however, not 

 to adopt this plan where there is any risk of heavy seas 

 coming in a wrong direction, so as to strike the masonry 

 on the overhanging side." 



Treenailing. " This is a method of securing each stone 

 to its neighbour by iron bolts or wooden pins let into the 

 lying beds or into both beds and joints. At the Eddystone 

 and Bell Rock lighthouses the stones were not only secured 



