outer toe. Moreover, when the foundations for an
upright-wall breakwater have to be levelled by divers, and the blocks
laid under water by their help, the extension of such a breakwater
into a considerable depth is undesirable on account of the increased
pressure imposed upon diving operations.

The Admiralty pier at Dover was begun about the middle of the 19th
century, and furnishes an early and notable example of an upright-wall
breakwater resting upon a hard chalk bottom; and it was subsequently
extended to a depth of about 42 ft. at low tide, in connexion with
the works for forming a closed naval harbour at Dover. This
breakwater, the Prince of Wales pier of the commercial harbour, and
the eastern breakwater and detached south breakwater for the naval
harbour, were all founded on a levelled bottom, carried down to the
hard chalk underlying the surface layer, by means of men in
diving-bells. The extension of the Admiralty pier and the other
breakwaters of Dover harbour consist of bonded courses of concrete
blocks, from 26 to 40 tons in weight, as shown in figs. 13 and 14, the
outer blocks above low water being formed on their exposed side with a
facing of granite rubble. The blocks, composed of six parts of sand
and stones to one part of Portland cement, moulded in frames, and left
to set thoroughly in the block-yard before being used, are all joggled
together, and above low-water level are bedded in cement and the
joints filled with cement grout. The blocks were laid by Goliath
travelling cranes running on temporary staging supported at intervals
of 50-1/4 ft. by clusters of iron piles carried down into the chalk
bottom. On each line of staging there were four Goliaths, preceded by
a stage-erecting machine. The front Goliath was used for working a
grab for excavating the surface layer of chalk, which was finally
levelled by divers, the second for carrying the diving-bell, the third
for laying the blocks below low water, and the fourth for setting the
blocks above low water. This succession of Goliaths enabled more rapid
progress to be made than with a single Titan at the end of a
breakwater; but it involved a considerable increase in the cost of the
plant, owing to the temporary staging required. The foundations were
carried down from 4 to 6 ft. into the chalk bottom, the deepest being
53 ft. below low water of spring tides, and the average 47 ft.