Chapter XIX: Part 19

The superstructures at Holyhead and Portland, being built on the old
weak system of a sea wall and a harbour wall, with rubble filling
between, are protected on the sea side by raising the rubble against
them from low water up to high water of spring tides; whereas the
superstructure of Cherbourg breakwater, being built solid and less
exposed, is only protected on the sea side by large rubble and some
concrete blocks, forming an apron raised slightly above low water.
These three breakwaters are provided with a quay sheltered by a raised
wall or promenade on the sea side; but as the mound on the harbour
side is raised up to, or a little above low water, the quay is only
accessible for vessels near high water. This, however, is of
comparatively little importance, since these quays, though very useful
for access to the end of the breakwater in fairly calm weather, are
inaccessible in exposed situations with a rough sea; and quays for the
accommodation of vessels are better provided well within the sheltered
harbour.

The outer portions of the main breakwaters at Genoa and at Naples
(fig. 6), extending into depths of about 75 ft. and 110 ft.
respectively, have been provided with superstructures, similar in
type, but more solid than the superstructure at Marseilles; and the
sorted rubble mounds upon which the superstructures rest are protected
on the sea slope by stepped courses of concrete blocks from a depth of
26 ft. below sea-level, covered over at the top by a masonry apron
forming a prolongation of the superstructure. The outer extension of
the main breakwater at Civita Vecchia furnishes an interesting example
of a composite form of breakwater, in which the rubble mound has been
protected, and greatly reduced in volume and extent in deep water, by
stepped courses of concrete blocks carried up from near the bottom of
the mound (fig. 7).

The breakwaters in front of Havre, constructed in 1896-1907, for
sheltering the altered entrance to the port, were formed of a sorted
rubble mound, protected on the sea slope by concrete blocks, and
raised a little above low water of spring tides, upon which large
blocks of masonry, built on land, were deposited with their upper
surfaces about 18 in. above low water of neap tides. As soon as
settlement of the mound under the action of the sea appeared to have
ceased, these masonry blocks were connected together by filling the
spaces between them with masonry; and a solid masonry superstructure
was built during low tide on this foundation layer, as shown in fig.
8.

The breakwaters constructed for forming harbours on the sea coast of
the United States are almost all rubble-mound breakwaters. The two old
detached breakwaters sheltering Delaware Harbour near the
south-eastern extremity of Delaware Bay, were formed of simple rubble
mounds raised about 13 ft. above low water; but in closing the gap
between them towards the close of the 19th century, the rubble mound
was stopped at low water, and a sort of superstructure, consisting of
stepped courses of large rectangular blocks of stone on the sea and
harbour sides, with tightly packed rubble between them and capped
across the top for a width of 20 ft. with a course of large blocks,
was raised to 14 ft. above low water, resembling, on a small scale,
the upper part of the Civita Vecchia mound (fig. 7). A similar
construction was adopted for the new breakwater formed in 1897-1901
for providing a harbour of refuge at the mouth of Delaware Bay; but in
this instance the mound was made considerably wider at the top, and
had to be protected along the toe of the superstructure on the sea
side by large stones. The same form of superstructure, also, on a
narrower base, was resorted to for a breakwater in deeper water at San
Pedro in California with satisfactory results. When, however, a
breakwater of the Delaware type was in progress for forming a harbour
of refuge in Sandy Bay, Massachusetts, in front of Rockport to the
north of Boston, the upper 13 ft. of the 600 ft. of completed
superstructure were carried away during a severe storm in 1898 leaving
only a portion about 5 ft. in height above low water, the average rise
of tide there being 8-3/5 ft. The design was, accordingly, modified in
1902, by commencing the stepped courses of large stones at 12 ft.
below mean low water on each slope, instead of at low water raising
this kind of superstructure to 22 ft. above low water in place of 18
ft., and capping the stepped courses at the top by large blocks of
stone, 20 ft. long and 5 ft. deep, laid across the breakwater, which
thus presented a marked resemblance to the upper section of the mound
at Civita Vecchia.

Superstructure below low-water level.

The breakwater at Sandy Bay just referred to, and the one at Civita
Vecchia, which it somewhat resembles, approximate to that class of
breakwater which has a superstructure founded below low-water level,
so far as stepped courses of blocks can be regarded as forming part of
a superstructure; but as the protection afforded by these courses
differs only in the arrangement of the blocks from that obtained by
blocks deposited at random, it appears expedient to restrict this
class to the more solid structures, resembling upright-wall
breakwaters, founded on a mound at some depth below low water As the
main object of this class of breakwater is to keep the mound below the
zone of disturbance by waves in severe storms, it is evident that the
depth at which the superstructure is founded should vary directly with
the exposure of the site, and inversely with the size of the materials
forming the mound.

The depth at which waves striking against a superstructure may affect
a rubble mound near its toe by the recoil, has been only very
gradually realized. Thus, in 1847, the Alderney breakwater, though
fully exposed to the Atlantic Ocean, was begun with a superstructure
founded at low water of spring tides upon a rubble mound; but within
two years the foundations had to be carried down 12 it. below low
water, and this was adhered to till close to the head, though the
breakwater, completed in 1864, extended 4700 ft. from the shore into a
depth of 130 ft. at low tide, the rise of springs being 17 ft. The
great recoil of the waves in storms from the promenade wall on the sea
side of the superstructure, raised 33 ft. above low water, disturbed
the sea slope of the mound along the outer portion, situated in depths
of 80 to 130 ft. at low water, out to a distance of 90 ft. from the
superstructure and to a depth of 20 ft.; whilst the outer toe of the
superstructure was only preserved from being undermined by frequent
deposits of stone along the sea face.

The south-west breakwater at Colombo Harbour, constructed in
1876-1884, facing the seas raised by the south-west monsoon, extends
into a depth of 39 ft. at low water, where the rise of tide is only 2
ft. at springs, and was built with a superstructure founded upon a
rubble mound at a depth of 20 ft. below low water, but raised only 12
ft. above this level without any parapet, and protected along its sea
face by an apron of concrete in bags. In this case, not only was the
depth of the sea much less than at Alderney, but the small elevation
of the superstructure above low water enabled a portion of the waves
in storms to pass over it without materially impairing the shelter
inside. These circumstances reduced the shock and recoil of the waves;
and the greater depth of the foundations and the protection of the toe
of the superstructure greatly diminished the danger of undermining.
Consequently, the Colombo breakwater has been preserved from the
injuries to which the outer part of the Alderney breakwater succumbed.
Nevertheless, in subsequently constructing the north-west detached
breakwater, less exposed to the south-west monsoon, but in somewhat
deeper water (see COLOMBO), the experience of the action of the sea on
the south-west breakwater led to the laying of the foundations of the
superstructure on the rubble mound at 30-3/4 ft. below low water (fig.
9).

The breakwater for sheltering Peterhead Bay, where the rise of springs
is 11-1/4 ft., was begun in 1888, and designed to extend into a depth
of 9-1/2 fathoms at low water (see HARBOUR). It was built as an
upright wall upon the rocky bottom for 1000 ft. from the shore; but
owing to the increase in depth it was decided to construct the outer
portion with a rubble base, surmounted by a superstructure originally
designed to be founded 30 ft. below low water. As, however, during a
storm in October 1898, the recoil of the waves from the breakwater,
which is provided with a promenade wall rising about 35 ft. above low
water, disturbed rubble to a depth of 36-1/2 ft., the superstructure
has been founded 43 ft. below low water on the rubble base; and its
outer toe is protected from being undermined by two rows of concrete
blocks on the rubble mound.

Construction of the superstructure.

Formerly, in constructing a large superstructure upon a rubble mound,
it was a common practice to build a sea wall and a harbour wall
several feet apart, and to fill up the intermediate,. space between
them with rubble, so as economically to form a wide structure on the
top of the mound, and provide an adequate width for a quay along the
top. A sheltering wall was also generally erected on the sea side.
This, for instance, was the system of construction adopted for the
superstructures, founded at low water, of Holyhead breakwater,
Portland inner breakwater, and St Catherine's, Jersey, breakwater.
Alderney breakwater, the Tyne breakwaters and Colombo south-west
breakwater were also commenced with a precisely similar method of
construction. The system, however, possesses a Very serious defect for
exposed situations, namely, that if once the sea can force a small
opening through the sea wall, the scooping out of the rubble filling,
and the overthrow of the thinner harbour wall are rapidly accomplished
if the storm continues or recurs before repairs can be effected.
Experience soon proved at Alderney and Tynemouth the unsuitability of
the system for very exposed situations; and the intermediate rubble
filling was replaced by solid hearting down to a certain depth. At
Colombo, after the first 1326 ft. of the south-west breakwater had
been built with two walls and intermediate rubble for the
superstructure, as the exposure proved greater than had been
anticipated, and a slight displacement of part of the sea wall, 24 ft.
wide, had occurred, the rubble filling was discontinued, and the two
walls were united into a solid superstructure 34 ft. in width.

sloping block system.

A difficulty experienced in constructing a solid superstructure on the
top of a rubble mound consists in the settlement of the mound which
takes place when the weight of the superstructure comes on it, in
spite of the consolidation of the rubble under the action of the sea
for one or two years before the erection of the superstructure on it
is undertaken. When the superstructure is carried out in long
stepped-forward courses, irregular settlement is particularly liable
to occur, as the weight is progressively imposed in an uneven manner
on the yielding rubble, in proportion to the height of the rubble base
and its deficiency in compactness. The open joints between the blocks
laid below low water enable the air to penetrate, on the recoil of the
waves at low tide, into any internal fissures resulting from
settlement; and the following wave, on striking the superstructure,
compresses the air inside, which, on its expansion when the wave
recedes, forces out any unconnected face stones. The hole thus formed
is rapidly enlarged by the sea if the storm continues; and a breach is
eventually formed. The sloping-block system was, accordingly devised
to provide against the dislocation of superstructures by the
inevitable irregular settlement, by forming them of a series of
sloping sections, composed of concrete blocks laid at an angle, free
to settle independently on the mound, as shown in fig. 10. In the
first superstructure thus constructed, in 1869-1874, at the entrance
to Karachi harbour, founded 15 ft. below low water on a rubble mound
and 24 ft. high, the blocks in each section, consisting of two rows of
three superposed blocks laid at an inclination of 76 deg. shorewards,
were entirely unconnected; and, consequently, though the
superstructure offered as little opposition as practicable to the
waves by having its top slightly below high water, the waves in a
storm forcing their way into the vertical joint between the two rows,
threw some of the top 27-ton blocks of the inner row down on the
harbour slope of the mound. This cause of damage was obviated in
effecting the repairs, by connecting the top blocks with the next ones
by stone dowels. The superstructures of the breakwaters forming Madras
harbour, commenced in 1876, were similarly constructed in sloping,
independent sections, 4-1/2 ft. thick, composed of two distinct rows
of four tiers of blocks founded upon a rubble mound 22 ft. below low
water (the rise of tide at springs being 3-1/3 ft.), and raised 3-1/2
ft. above high water. The blocks in each row were connected by a
tenon, projecting at the top of each block, fitting into a mortise in
the block above it. The retention of the vertical joint however,
between the two rows led to the overthrow of the greater part of the
superstructures of the outer arms at Madras, situated in a depth of 45
ft. and facing the Indian Ocean, during a cyclone of 1881. In the
reconstruction of these superstructures, bond was introduced in the
successive tiers of each sloping section; and 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.

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 the adjacent faces of each sloping section,
extending from top to bottom of the sections. These, when settlement
on the mound had ceased, were filled with concrete in bags which not
only connected the tiers of blocks in each section together, but also
joined the several sections to one another, and effectually closed
the transverse joints between the successive sections, which were
further connected together by a continuous capping of concrete-in-mass
along the whole length of the breakwater.

These sloping blocks are laid by powerful overhanging, block-setting
cranes, called Titans (see CRANES), which travel along the completed
portion of the breakwater, and lay the blocks in advance on the mound
levelled by divers, as shown in fig. 10. The earlier Titans, employed
for the sloping-block superstructures at Karachi and Madras, were
constructed to travel only backwards and forwards on the completed
work, with sufficient sideways movement of the little trolley
travelling along the overhanging arm, from which the block is
suspended at the proper angle, to lay the blocks for each side of the
superstructure. In later forms, however, such for instance as the
Titan laying the 14-ton blocks at Peterhead breakwater in horizontal
courses, the overhanging arm is supported centrally on a ring of
rollers, placed on the top of the truck on which the Titan travels, so
that it can revolve and deposit blocks at the side of the
superstructure for protecting the mound, as well as in advance of the
finished work. These Titans possess the important advantage over the
timber staging formerly employed for such breakwaters, that, in
exposed situations, they can be moved back into shelter on the
approach of a storm, or for the winter or stormy months, instead of,
as in the case of staging, remaining out exposed to the danger of
being carried away during stormy weather, or necessitating loss of
time in erection at the beginning of the working season.

Though composite breakwaters are still occasionally constructed with a
superstructure founded on a rubble mound at, or above, low-water
level, these breakwaters are now almost always constructed with the
superstructure founded at some depth below low water, even at harbours
on the continent of Europe, where formerly broad quays founded at
sea-level, protected by a parapet wall and outer concrete blocks, were
the regular form of superstructure adopted. The breakwater for the
extension of the harbour at Naples provides an interesting example of
this change of design. A solid superstructure, formed of large
concrete blocks capped with masonry, about 50 ft. wide at the base, is
laid on a high rubble mound at a depth of 31 ft. below mean sea-level,
and provides a quay on the top, 24-1/2 ft. wide, protected on the sea
side by a promenade wall, 10 ft. high and 12-1/2 ft. wide at the top,
raised 19-2/3 ft. above sea-level (fig. 12). In view of the increased
depth at which superstructures are now founded upon rubble mounds,
causing the breakwaters to approximate more and more to the
upright-wall type, it might seem at first sight that the rubble base
might be dispensed with, and the superstructure founded directly on
the bed of the sea. Two circumstances, however, still render the
composite form of breakwater indispensable in certain cases: (1) the
great depth into which breakwaters have sometimes to extend, reaching
about 56 ft. below low water at Peterhead, and 102 ft. below mean
sea-level at Naples; and (2) the necessity, where the sea-bottom is
soft or liable: to be eroded by scour, of interposing a wide base
between the upright superstructure and the bed of the sea.

The injuries to which composite breakwaters appear to have been
specially subject must be attributed to the greater exposure and depth
of the sites in which they have been frequently constructed, as
compared with rubble mounds or upright walls. The latter types,
indeed, are not well suited for erection in deep water, in the first
case, on account of the very large quantity of materials required for
a high mound with flat slopes, and in the second, owing to the
increased pressure of air under which divers have to work in laying
blocks for an upright wall in deep water. The ample depth in which
superstructures are founded, the due protection afforded to their
outer toe, the adoption of the sloping-block system for their
construction, and the dispensing in most cases with a high sheltering
wall on the sea side of the superstructure, render modern
superstructures as stable as upright-wall breakwaters of similar
height. Nevertheless, superstructures require to be given a greater
thickness than similar upright walls, because the greater depth of
water in which such composite breakwaters are built causes them to be
exposed to larger waves under similar conditions.

The superstructures of composite breakwaters erected by the United
States for harbours on the shores of Lake Superior were formerly in
some cases composed of timber cribs floated into position and sunk by
filling them with rubble stone. On account of the cheapness of timber
several years ago in those regions, this simple mode of construction
was also economical, even though the rapid decay of the timber in the
portions of the cribs where it was alternately wet and dry involved
its renewal about every fifteen years on the average. Owing, however,
to the fact that the price of timber has increased considerably,
whilst that of Portland cement has been reduced, durable concrete
superstructures are beginning to be substituted for the rapidly
decaying cribwork structures.

With the exception perhaps of the Alderney breakwater, which, owing to
its exceptional exposure and the unparalleled depth into which it
extended, had its superstructure so often breached by the sea that,
owing to the cost of maintenance, the inner portion only has been kept
in repair, the composite breakwater of Bilbao harbour has probably
proved the most difficult to construct on account of its great
exposure. The original design consisted of a wide rubble mound up to
about 16-1/2 ft. below low water, a mound of large concrete blocks up
to low water of equinoctial spring tides, and a solid masonry
superstructure well protected at its outer toe by a projection of
masonry, and raised several feet above high water, forming a quay
sheltered by a promenade wall. The rise of equinoctial spring tides at
the mouth of the river Nervion is 14-3/4 ft. In carrying out the work,
however, the superstructure built in the summer months was for the
most part destroyed by the following winter storms; and, accordingly,
the superstructure was eventually constructed on a widened rubble
base, so as to be sheltered to some extent by the outlying
concrete-block mound already deposited, a system subsequently adopted
in rebuilding the damaged portion of the North Pier at Tynemouth under
shelter of the ruins of the previous work. The modified superstructure
of the Bilbao breakwater was founded on the extended rubble mound at a
depth of 16-1/4 ft. below low water, and formed of iron caissons
partially filled with concrete and floated out, sunk in position, and
filled up with concrete blocks and concrete. It thus consists of a
continuous row of concrete blocks, each of them being 42-2/3 ft. in
width across the breakwater, 23 ft. in length along the line of the
breakwater, 23 ft. high, and weighing 1400 tons. These caisson blocks,
raised 6-3/4 ft. above low water, form the base of the superstructure,
upon which the upper part was built of concrete blocks on each face
with mass concrete filling between them, forming a continuous quay, 24
ft. wide, raised 8 ft. above high tide, and slightly sheltered by a
curved parapet block only 5 ft. high. The outer toe of the caisson
blocks is protected from being undermined by two tiers of large
concrete blocks laid flat on the rubble mound. This superstructure has
successfully resisted the attacks of the Atlantic waves rolling into
the bay. At this breakwater and at Tynemouth advantage has been taken
of the protection unintentionally provided by previous failures, by
which the waves are broken before reaching the superstructure and pier
respectively; but instead of introducing a wave-breaker of concrete
blocks, for a protection to the superstructure, as arranged at
Marmagao (fig. 11) and the outer arms at Madras, it would appear
preferable to increase the width of the solid superstructure, if
necessary, as carried out at Naples (fig. 12). and to dispense with a
parapet and keep the superstructure low, as being unsuitable for a
quay in exposed situations, according to the plan adopted at Colombo
(fig. 9).

3. _Upright-Wall Breakwaters._--The third type of breakwater consists
of a solid structure founded directly on the sea-bottom, in the form
of an upright wall, with only a moderate batter on each face. This
form of breakwater is strictly limited to sites where the bed of the
sea consists of rock, chalk, boulders, or other hard bottom not
subject to erosion by scour, and where the depth does not exceed about
40 to 50 ft. If a solid breakwater were erected on a soft yielding
bottom, it would be exposed to dislocation from irregular settlement;
and such a structure, by obstructing or diverting the existing
currents, tends to create a scour along its base; whilst the waves in
recoiling from its sea face are very liable to produce erosion of the
sea-bottom along its 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. With a
rise of tide at springs of 18-3/4 ft., the average depth is thus
approximately 66 ft. at high tide, necessitating a pressure of 29 lb.
on the square inch, which is the limit at which men can work without
inconvenience in the diving-bells. The breakwaters are raised about 11
ft. above high water of springs. The detached southern breakwater was
finished off at this level; but the extended western breakwater, or
Admiralty pier, is provided with a promenade parapet on its exposed
side, rising 13 ft. above the quay; and the eastern breakwater also
has a parapet on its exposed eastern side, raised, however, only 9 ft.
above its quay. The breakwaters are protected from scour along their
outer toe by an apron of concrete blocks, extending 25 ft. out from
their sea face.

FIG. 13. South Breakwater.

FIG. 14. Admiralty Pier Extension.]

Concrete bag foundations.

The levelling of the foundations for laying the courses of an
upright-wall breakwater is costly and tedious, even in chalk; and the
expense and delay are considerably enhanced where the bottom is hard
rock. Accordingly, in constructing two breakwaters at the entrance to
Aberdeen harbour on a bottom of granite in 1870-1877, concrete bags
were laid on the sea-bed; and these bags, by adapting themselves to
the rocky irregularities, obviated levelling the bottom. They formed
the foundation for the concrete blocks in the south breakwater; and by
the deposit of successive layers of 50-ton concrete bags till they
rose above low water, they constituted the whole of the submerged
portion of the north breakwater. The 50-ton bags were deposited from
hopper barges towed out to the site; and the portions of both
breakwaters above low water were carried up with mass concrete.
Subsequently, the breakwater at Newhaven was constructed on a
foundation of chalk, with lop-ton concrete bags up to low water, and
mass concrete above. Still later, the two breakwaters sheltering the
approach to the river Wear (see HARBOUR) and the Sunderland docks were
built with a foundation mound of concrete in bags, 56 to 116 tons in
weight, on the uneven sea-bottom, raised slightly above low water of
spring tides, on which a solid upright wall was erected, formed of
concrete blocks on each side faced with granite, filled in the centre
and capped on the top with mass concrete. The most exposed northern
Roker breakwater, raised about 11 ft. above high water of springs
where the rise is 14 ft. 5 in., is devoid of a parapet; but a subway
formed near the top in each breakwater gives access to the light on
the pierhead in stormy weather (fig. 15). These concrete bags are made
by lining the hopper of the barge with jute canvas, which receives the
concrete and is sewn up to form a bag whilst the barge is being towed
to the site. The concrete is thus deposited unset, and readily
accommodates itself to the irregularities of the bottom or of the
mound of bags; and sufficient liquid grout oozes out of the canvas
when the bag is compressed, to unite the bags into a solid mass, so
that with the mass concrete on the top, the breakwater forms a
monolith. This system has been extended to the portion of the
superstructure of the eastern, little-exposed breakwater of Bilbao
harbour below low water, where the rubble mound is of moderate height;
but this application of the system appears less satisfactory, as
settlement of the superstructure on the mound would produce cracks in
the set concrete in the bags.

Foundations with large blocks.

Foundation blocks of 2500 to 3000 tons have been deposited for raising
the walls on each side of the wide portion of the Zeebrugge breakwater
(fig. 16) from the sea-bottom to above low water, and also 4400-ton
blocks along the narrow outer portion (see HARBOUR), by building iron
caissons, open at the top, in the dry bed of the Bruges ship-canal,
lining them with concrete, and after the canal was filled with water,
floating them out one by one in calm weather, sinking them in position
by admitting water, and then filling them with concrete under water
from closed skips which open at the bottom directly they begin to be
raised. The firm sea-bed is levelled by small rubble for receiving the
large blocks, whose outer toe is protected from undermining by a layer
of big blocks of stone extending out for a width of 50 ft.; and then
the breakwater walls are raised above high water by 55-ton concrete
blocks, set in cement at low tide; and the upper portions are
completed by concrete-in-mass within framing.

Concrete monoliths.

Sometimes funds are not available for a large plant; and in such cases
small upright-wall breakwaters may be constructed in a moderate depth
of water on a hard bottom of rock, chalk or boulders, by erecting
timber framing in suitable lengths, lining it inside with jute cloth,
and then depositing concrete below low water in closed hopper skips
lowered to the bottom before releasing the concrete, which must be
effected with great care to avoid allowing the concrete to fall
through the water. The portion of the breakwater above low water is
then raised by tide-work with mass concrete within frames, in which
large blocks of stone may be bedded, provided they do not touch one
another and are kept away from the face, which should be formed with
concrete containing a larger proportion of cement. As long continuous
lengths of concrete crack across under variations in temperature, it
is advisable to form fine straight divisions across the upper part of
a concrete breakwater in construction, as substitutes for irregular
cracks.

Upright-wall breakwaters should not be formed with two narrow walls
and intermediate filling, as the safety of such a breakwater depends
entirely on the sea-wall being maintained intact. A warning of the
danger of this system of construction, combined with a high parapet,
was furnished by the south breakwater of Newcastle harbour in Dundrum
Bay, Ireland, which was breached by a storm in 1868, and eventually
almost wholly destroyed; whilst its ruins for many years filled up the
harbour which it had been erected to protect. In designing its
reconstruction in 1897, it was found possible to provide a solid
upright wall of suitable strength with the materials scattered over
the harbour, together with an extension needed for providing proper
protection at the entrance. This work was completed in 1906.

Upright-wall breakwaters and superstructures are generally made of the
same thickness throughout, irrespective of the differences in depth
and exposure which are often met with in different parts of the same
breakwater. This may be accounted for by the general custom of
regarding the top of an upright wall or superstructure as a quay,
which should naturally be given a uniform width; and this view has
also led to the very general practice of sheltering the top of these
structures with a parapet. Generally the width is proportioned to the
most exposed part, so that the only result is an excess of
expenditure in the inner portion to secure uniformity. When, however,
as at Madras, the width of the structure is reduced to a minimum, the
action of the sea demonstrates that the strength of the structure must
be proportioned to the depth and exposure. In small fishery piers,
where great economy is essential to obtain the maximum shelter at
limited expense, it appears expedient to make the width of the
breakwater proportionate to the depth. This was done in Babbacombe
Bay; and in reconstructing the southern breakwater at Newcastle,
Ireland, advantage was taken of a change in direction of the outer
half to introduce an addition to the width, so as to make the strength
of the breakwater proportionate to the increase in depth and exposure.
In large structures, however, uniformity of design may be desirable
for each straight length of breakwater; though where two or more
breakwaters or outer arms enclose a harbour, the design should
obviously be modified to suit the depth and exposure. At Colombo
harbour, the superstructure of the less exposed north-west breakwater
has been made slightly narrower than that of the south-west
breakwater; and a simple rubble mound shelters the harbour from the
moderate north-east monsoon. In special cases, where a breakwater has
to serve as a quay, like the Admiralty pier at Dover, a high parapet
wall is essential; but in most cases, where a parapet merely enables
the breakwater to be more readily accessible in moderate weather, it
would be advisable to keep it very low, or to dispense with it
altogether, as at the southern Dover breakwater, the northern
breakwater at Sunderland, and the Colombo western breakwaters. This
course is particularly expedient in very exposed sites, as a high
parapet intensifies the shock of the waves against a breakwater and
their erosive recoil. Moreover, when a light has to be attended to at
the end of a breakwater, sheltered access can be provided by a subway,
as at Sunderland.

Structures in the sea almost always require works of maintenance; and
when a severe storm has caused any injury, it is most important to
carry out the repairs at the earliest available moment, as the waves
rapidly enlarge any holes that they may have formed in weak places.
(L. F. V.-H.)

BREAL, MICHEL JULES ALFRED (1832- ), French philologist, was born on the 26th of March 1832, at Landau in Rhenish Bavaria, of French parents. After studying at Weissenburg, Metz and Paris, he entered the Ecole Normale in 1852. In 1857 he went to Berlin, where he studied Sanskrit under Bopp and Weber. On his return to France he obtained an appointment in the department of oriental MSS. at the Bibliotheque Imperiale. In 1864 he became professor of comparative grammar at the College de France, in 1875 member of the Academie des Inscriptions et Belles-lettres, in 1879 _inspecteur-general_ of public instruction for higher schools until the abolition of the office in 1888. In 1890 he was made commander of the Legion of Honour. Among his works, which deal mainly with mythological and philological subjects, may be mentioned: _L'Etude des origines de la religion Zoroastrienne_ (1862), for which a prize was awarded him by the Academie des Inscriptions; _Hercule et Cacus_ (1863), in which he disputes the principles of the symbolic school in the interpretation of myths; _Le Mythe d'Oedipe_ (1864); _Les Tables Eugubines_ (1875); _Melanges de mythologie et de linguistique_ (2nd. ed., 1882); _Lecons de mots_ (1882,1886), _Dictionnaire etymologique latin_ (1885) and _Grammaire latine_ (1890). His _Essai de Semantique_ (1897), on the signification of words, has been translated into English by Mrs H. Cust with preface by J.P. Postgate. His translation of Bopp's _Comparative Grammar_ (1866-1874), with introductions, is highly valued. He has also written pamphlets on education in France, the teaching of ancient languages, and the reform of French orthography. In 1906 he published _Pour mieux connaitre Homere_.

BREAM (_Abramis_), a fish of the Cyprinid family, characterized by a deep, strongly compressed body, with short dorsal and long anal fins, the latter with more than sixteen branched rays, and the small inferior mouth. There are two species in the British Isles, the common bream, _A. brama_, reaching a length of 2 ft. and a weight of 12 lb., and the white bream or bream flat, _A. blicca_, a smaller and, in most places, rarer species. Both occur in slow-running rivers, canals, ponds and reservoirs. Bream are usually despised for the table in England, but fish from large lakes, if well prepared, are by no means deserving of ostracism. In the days of medieval abbeys, when the provident Cistercian monks attached great importance to pond culture, they gave the first place to the tench and bream, the carp still being unknown in the greater part of Europe. At the present day, the poorer Jews in large English cities make a great consumption of bream--and other Cyprinids, most of them being imported alive from Holland and sold in the Jewish fish markets. In America the name bream is commonly given to the golden shiner minnow (_Abramis chrysoleucus_), to the pumpkin-seed sunfish (_Eupomotis gibbosus_), and to some kinds of porgy (_Sparidae_).

BREAST (a word common to Teutonic languages, of the Ger. _Brust_, possibly connected with an O. Sax. _brustian_, to bud), the term properly confined to the external projecting parts of the thorax in females, which contain the mammary glands (for anatomy, and diseases, see MAMMARY GLAND); more generally it is used of the external part of the thorax in animals, including man, lying between the neck and the abdomen.

BREAUTE, FALKES DE (d. 1226), one of the foreign mercenaries of King John of England, from whom he received in marriage the heiress of the earldom of Devon. On the outbreak of the Barons' War (1215) the king gave him the sheriffdoms of six midland shires and the custody of many castles. He fulfilled his military duties with as much skill as cruelty. The royalists owed to his daring the decisive victory of Lincoln (1217). But after the death of William Marshal, earl of Pembroke, Falkes joined the feudal opposition in conspiring against Hubert de Burgh. Deprived in 1223 of most of his honours, he was drawn into a rebellion by the imprudence of his brother, who captured a royal justice and threw him into prison (1224). Falkes was allowed to go into exile after his submission, and endeavoured to obtain a pardon through the mediation of Pope Honorius III. But this was refused, and Falkes died at St Cyriac in 1226.

See Shirley, _Royal Letters_, vol. i.; the _Patent_ and _Close Rolls_;
Pauli, _Geschichte von England_, vol. i. pp. 540-545. (H. W. C. D.)

BRECCIA, in petrology, the name given to rocks consisting of angular fragments embedded in a matrix. They may be composed of volcanic rocks, limestones, siliceous charts, sandstones, in fact of any kind of material, and the matrix, which usually corresponds to some extent to the fragments it encloses, may be siliceous, calcareous, argillaceous, &c. The distinctive character of the group is the sharp-edged and unworn shapes of the fragments; in conglomerates the pebbles are rounded and water-worn, having been transported by waves and currents from some distance. There are many ways in which breccias may originate. Some are formed by ordinary processes of atmospheric erosion; frost, rain and gravity break up exposed surfaces of rock and detach pieces of all sizes; in this way screes are formed at the bases of cliffs, and barren mountain-tops are covered with broken debris. If such accumulations gather and are changed into hard rock by pressure and other indurating agencies they make typical breccias. Conglomerates often pass into rocks of this type, the difference being merely that the fragments are of purely local origin, and are unworn because they have not been transported. In caves breccias of limestone are produced by the collapse of part of the roof, covering the floor with broken masses. Coral reefs often contain extensive areas of limestone breccia, formed of detached pieces of rock which have been dislodged from the surface and have been carried down the steep external slopes of the reef. Volcanic breccias are very common near active or extinct craters, as sudden outbursts of steam bear fragments from the older rocks and scatter them over the ground.

Another group of breccias is due to crushing; these are produced in fissures, faults and veins, below the surface, and maybe described as "crush-breccias" and "friction-breccias." Very important and well-known examples of this class occur as veinstones, which may be metalliferous or not. A fissure is formed, probably by slight crustal movements, and is subsequently filled with material deposited from solution (quartz, calcite, barytes, &c.). Very often displacement of the walls again takes place, and the infilling or "veinstone" is torn apart and brecciated. It may then be cemented together by a further introduction of mineral matter, which may be the same as that first deposited or quite different. In important veins this process is often repeated several times: detached pieces of the country rock are mingled with the shattered veinstone, and generally experience alteration by the percolating mineral solutions. Other crush-breccias occurring on a much larger scale are due to the folding of strata which have unequal plasticities. If, for example, shales and sandstones are bent into a series of arches, the sandstones being harder and more resistant will tend to crack, while the shales, which are soft and flow under great pressures, are injected into the crevices and separate the broken pieces from one another. Continued movement will give the brecciated fragments of sandstone a rounded form by rubbing them against one another, and, in this way, a crush-conglomerate is produced. Great masses of limestone in the Alps, Scottish Highlands, and all regions of intense folding are thus converted into breccias. Cherts frequently also show this structure; igneous rocks less commonly do so; but it is perhaps most common where there have been thin bedded alternations of rocks of different character, such as limestone and dolerite, limestone and quartzite, shale or phyllite and sandstone. Fault-breccias closely resemble vein-breccias, except that usually their fragments consist principally of the rocks which adjoin the fault and not of mineral deposits introduced in solution; but many veins occupy faults, and hence no hard and fast line can be drawn between these types of breccia.

A third group of breccias is due to movement in a partly consolidated igneous rock, and may be called "fluxion-breccias." Lava streams, especially when they consist of rhyolite, dacite and some kinds of andesite, may rapidly solidify, and then become exceedingly brittle. If any part of the mass is still liquid, it may break up the solid crust by pressure from within and the angular fragments are enveloped by the fluid lava. When the whole comes to rest and cools, it forms a typical "volcanic-fluxion-breccia." The same phenomena are sometimes exemplified in intrusive sills and sheets. The fissures which are occupied by igneous dikes may be the seat of repeated injections following one another at longer or shorter intervals; and the latter may shatter the earlier dike rocks, catching up the fragments. Among the older formations, especially when decomposition has gone on extensively, these fluxion and injection-breccias are often very hard to distinguish from the commoner volcanic-breccias and ash-beds, which have been produced by weathering, or by the explosive power of superheated steam. (J. S. F.)

BRECHIN, a royal, municipal and police burgh of Forfarshire, Scotland. Pop. (1901) 8941. It lies on the left bank of the South Esk, 7-3/4 m. west of Montrose, and has a station on the loop line of the Caledonian railway from Forfar to Bridge of Dun. Brechin is a prosperous town, of great antiquity, having been the site of a Culdee abbey. The Danes are said to have burned the town in 1012. David I. erected it into a bishopric in 1150, and it is still a see of the Episcopal Church of Scotland. In 1452 the earl of Huntly crushed the insurrection led by the earl of Crawford at the battle of Brechin Muir, and in 1645 the town and castle were harried by the marquis of Montrose. James VI. gave a grant for founding a hospital in the burgh, which yet supplies the council with funds for charity. No trace remains of the old walls and gates of the town, but the river is crossed by a two-arched stone bridge of very early date. The cathedral church of the Holy Trinity belongs to the 13th century. It is in the Pointed style, but suffered maltreatment in 1806 at the hands of restorers, whose work, however, disappeared during the restoration completed in 1902. The western gable with its flamboyant window and Gothic door and the massive square tower are all that is left of the original edifice. The modern stained glass in the chancel is reckoned amongst the finest in Scotland. Immediately adjoining the cathedral to the south-west stands the Round Tower, built about 1000. It is 86-3/4 ft. high, has at the base a circumference of 50 ft. and a diameter of 16 ft., and is capped with a hexagonal spire of 18 ft., which was added in the 15th century. This type of structure is somewhat common in Ireland, but the only Scottish examples are those at Brechin, Abernethy in Perthshire, and Egilshay in the Orkneys. Brechin Castle played a prominent part in the Scottish War of Independence. In 1303 it withstood for twenty days a siege in force by the English under Edward I., surrendering only when its governor, Sir Thomas Maule, had been slain. From the Maule family it descended to the Dalhousies. Its library contains many important MSS., among them Burns's correspondence with George Thomson, and several cartularies including those of St Andrews and Brechin. In the Vennel (alley or small street) some ruins remain of the _maison dieu_, or _hospitium_, founded in 1256 by William of Brechin. Besides these historical buildings the principal public structures include Smith's school, the municipal buildings, the free library, the episcopal library (founded by Bishop Forbes, who, as well as Bishop Abernethy-Drummond, presented a large number of volumes). The principal industries include manufactures of linen and sailcloth, bleaching, rope-making, brewing, distilling, paper-making, in addition to nurseries and freestone quarries. Brechin--which is controlled by a provost, bailies and council--unites with Arbroath, Forfar, Inverbervie and Montrose to return one member to parliament.

Edzell (pronounced Edyell, and, locally, Aigle) lies about 6 m. north of Brechin, with which it is connected by rail. It is situated on the North Esk and near the West Water, which falls into the Esk 2 m. south-west. Edzell is on the threshold of romantic Highland scenery. The picturesque ruins of Edzell Castle lie a mile to the west of the town. Once the seat of the Lindsays the estate now belongs to the earl of Dalhousie. The church of the parish of Farnell, 3-1/2 m. south-east of Brechin, was erected in 1806 after the model, so it is stated, of the famous Holy House (Casa Santa) of Loreto in Italy. It was here that the old sculptured stone giving a version of the Fall was found. Between Farnell and Brechin lies Kinnaird Castle, the seat of the earl of Southesk.

BRECKINRIDGE, JOHN CABELL (1821-1875), American soldier and political leader, was born near Lexington, Kentucky, on the 21st of January 1821. He was a member of a family prominent in the public life of Kentucky and the nation. His grandfather, John Breckinridge (1760-1806), who revised Jefferson's draft of the "Kentucky Resolutions" of 1798, was a United States senator from Kentucky in 1801-1805 and attorney-general in President Jefferson's cabinet in 1805-1806. His uncles, John Breckinridge (1797-1841), professor of pastoral theology in the Princeton Theological Seminary in 1836-1838 and for many years after secretary of the Presbyterian Board of Foreign Missions, and Robert Jefferson Breckinridge (1800-1871), for several years superintendent of public instruction in Kentucky, an important factor in the organization of the public school system of the state, a professor from 1853 to 1871 in the Danville Presbyterian Theological Seminary at Danville, Kentucky, and the temporary chairman of the national Republican convention of 1864, were both prominent clergymen of the Presbyterian Church. His cousin, William Campbell Preston Breckinridge (1837-1904), was a Democratic representative in Congress from 1885 to 1893. Another cousin, Joseph Cabell Breckinridge (1842- ), served on the Union side in the Civil War, was a major-general of volunteers during the Spanish-American War (1898), became a major-general in the regular United States army in 1903, and was inspector-general of the United States army from 1899 until his retirement from active service in 1904.