86 ANNUAL REPORT 
place and flattened out the bags were about 2% feet thick. The forms 
for the superstructure were of timber trussed with 11% inch iron rods, the 
sheeting being of 3 inch plank, with planed edges and surface. The con- 
crete was composed of 1 cement to 7 sand and gravel, except in quiet water - 
and unexposed places where.9 parts of sand and gravel were used. The 
average cost of the concrete in place was $5.50 per cubic yard. This work 
has withstood the wave action excellently and is not affected by salt water. 
Seu Wall, 
Fig. 31.—-Concrete Shore-Wall, Lincoln Park, Chicago, Ill. 
The timber breakwater constructed at Marquette, Mich., in 1870, be- 
came inadequate for the needs about 1888 and efforts were made to have 
the government extend it. These efforts finally succeeded in 1895, and the 
government proceeded to improve the harbor. The old breakwater was in 
bad condition above low water and it was decided to replace the timber 
top with a permanent one of concrete. 
The original structure was cut down to one foot below low water 
and the concrete superstructure with dimensions as shown in figure 32 
was added. Within this solid concrete mass on the harbor side a gallery 
2.83 feet wide and 6.25 feet high was built to give a passageway during 
heavy storms to the lighthouse at the end of the breakwater. The super- 
structure was made in 10 foot sections, alternate sections being constructed 
and allowed to set, then the intermediate blocks built between. The pro- 
portions of Portland concrete used in the base beneath water level was 1 
part cement, 24 parts sand, and 5 parts stone, and cost $6.35 per cubic 
