the blocks of the two
upper tiers were cramped together. Alter settlement on the mound had
ceased, a thick capping of mass concrete was laid all along the top of
the superstructure; and, finally, a mound of concrete blocks was
deposited at random on the mound in front of the sea face of the
superstructure to break the force of the waves and prevent
undermining. A similar wave-breaker, with blocks somewhat specially
arranged, was deposited in front of the sloping concrete-block
superstructure of the breakwater sheltering the Portuguese harbour of
Marmagao on the west coast of India, more particularly with the object
of preventing the undermining of the superstructure founded only 18
ft. below low water of spring tides, on a layer of rubble spread on
the muddy sea-bottom, the settlement in this case being occasioned by
the yielding of the soft clay bed. This breakwater having been
commenced in 1884, subsequently to the failure at Madras, the
superstructure, formed of concrete blocks weighing 28-1/2 to 37-1/2
tons was built in accordance with the design adopted for the
reconstructed outer arms at Madras, with the exceptions that the
separate sections were given a slope of 70 deg. instead of 76 deg.
shorewards to ensure greater stability, that the superstructure was
made 30 ft in width instead of 24 ft., that the top tier of blocks in
each section was secured to the next tier by two dowels, each formed
of a bundle of four rails, penetrating 3-1/2 ft. into each tier, so as
to enable the top courses to be more correctly aligned than with
tenons and mortises, and that the outer side of the continuous
concrete-in-mass capping was raised about 22 ft. above low water (fig.
11). The rise of spring tides at Marmagao is 6 ft.

[Illustration: FIG. 10.--Colombo North-West Breakwater with Titan
Crane.]

At Colombo the superstructures of both the south-west and north-west
breakwaters were built on the sloping-block system in sections 5-1/2
ft. thick, and built at an angle of 68 deg. shorewards (fig. 10); and
the blocks, from 16-1/2 to 31 tons in weight, were laid in bonded
courses across each section, with four tiers of blocks in the
south-west breakwater founded 20 ft. below low water on the rubble
mound, and six tiers of blocks in the north-west breakwater, founded
30-3/4 ft below low water. Five oblong grooves, moreover, were formed
in moulding the blocks, in