The Sun.
London, England, 1864-09-08 00:00:00

ceiving the roughlyftsquared blocks of stone and
granite from Portland and Penbryn, and discharg-
ing all the finished blocks into the lighren, which

convey them, towed by steamtngs, to ttn works on

;Le Horse and Noman. The concrete blocks are

made from the shingle and sand of Sttkes Bay and

,he beat Portland cement. The total value of Mr,

Leather's plant, in connection with the Spithead

Fort Works, is estimated at over £40,000.
The site of one of the forts once definitely fixed
upon, the War Department first enter on posses•
sion, drive some dozen piles in a central position,
cover those with planking, erect a temporary light-
house, and begin to sink their cylinders, just after
the plan pursued in the construction of the Char.
ing•cross railway bridge. By means of these
cylinders an exact knowledge of the strata of the
earth below is obtained, and they also afford the
means of obtaining water at a moderate depth from
the surface if they reach a water•bearing strata. On
the Horse Sand the cylinder (in sections of Eft, dia.

Meter) has been sunk to a depth of 90ft, but no
water found, and it is now intended to make water-
tight by artificial means the bottom of the lowest

cylinder section, and then by boring it is calculated
water will be obtained on reaching the London clay,
about 500 ft from the surface. The same course will

be followed at the Noman. The London clay crops
ont, about 15ft below the surface, in the new No. 11

dock foundations bed now in course of construction

in Portsmouth dockyard. At the Horse and Noman
forts water is expected to be found in the stratum of
sand which intersects the London and plaster clay
beds. The foundation ground on the Noman and

Horse banks is everything that could have been

wished for the purpose. Of the Horse Shoal the sur■
face consists of 4ft 6in of fine gravel and sand, which

rest upon 2ft of natural concrete. Next comes a
stratum of 18ft of sand, containing shingle and
pieces of tree bark and branches. Eight feet of
clayey sand succeeds to the sand and shingle, and

contains remains of various marine substances. Next

comes a 5-feet stratum of sand shingle, followed by
15ft of a blue silty clay ; a stratum of sand, shells,
and shingle ; a thin stratum of stone ; and, lastly, a
conglomerate of flints, sand, and shingle. All this
is evidently a modern deposit. The cylinder on the
Horse Shoal has been sunk in the usual manner by
internal excavation. The cylinder on the Noman
Shoal has been sunk by a pneumatic process worked
up at last to an air pressure of 371 b to the inch until
in fact the vulcanised pipes could withstand the
pressure no longer, but gave way with a report like
a cannon shot. This was beyond endurance by the
human frame, and several men were incapacitated for
a time for further bodily exertion. It is a curious fact
that Sir Charles Fox, in his report to the War-office,
should have been entirely deceived in his conclu-

sions as to the under stratum of the Noman Shoal.
This he described as being composed of the Isle of
Wight limestone rock, which crops up on the shore
at the adjacent point of sea view, Nettlestone, as it is
marked on the charts. Contrary to this theory of Sir
Charles it is composed of sand and shingle intermixed
with ,large pieces of limestone, evidently washed
down from the island strata, and in coming across
these detached pieces of limestone Sir Charles, no
doubt, fell into the error of his theory. In these
cylinder excavations on the Noman the lower jaw
of a graminivorous animal was found 55ft below the
surface of the shoal. This was forwarded to Pro-
fessor Owen, who gave it as his opinion that it was
the jawbone of an ox or extinct species of deer.
How long had this jawbone been thus buried ?
We now come to the time when, the War Depart-
ment having erected its central staging, sunk its
cylinder, and examined the lower strata, the con-
tractor for the foundation of the forts comes upon
the scene and commences his operations for laying
the foundations of the forts comes upon the scene
and commences his operations for laying the foun-
dations of the forts. This he does by taking the
War Office staging as his base of operations, and
throwing out thence radial arms of timber, embrac-
ing the area required for the foundation, which are
supported on screw piles, and the superstructure is
formed of circular timber roadways, on which is
laid a line of railway, on which work powerful tra-
velling steam cranes, which lift the blocks of stone
from the lighters and drop them into their position,
in the water, where the divers below receive and
fix them according to their numbers and coloured
lines. This circular staging is divided into 25 sec.
Lions, and this arrangement, together with the
numbers and coloured lines on the stones, prevents
any possibility of a mistake in the final fixing of
the stones by the divers under water. Fifty men

are now employed on the Horse fort foundations, 12
of whom are divers, The foundations of this fort
are expected to be completed by the end of the pre.
sent year. The Noman and Horse foundations are
precisely similar in their structure, but differ-
ing in their height, the Noman requiring
from its greater depth of water nearly double
the depth of stonework from the shoal to that
necessary on: the Horse Shoal. Both founda-
tions are formed of rings of stonework, laid on the
levelled bed of the shoals, of 53ft. Gin. of base, and
42ft. Gin, at the upper course. The outer diameter
of the ring is 231tt. at low water mark, and 213 ft.
at the upper course. There is thus a considerable
area in the centre of this ring of stonework, which
can be filled up around the cylinder subsequently
by the Royal Engineering Department, into whose
charge !the foundations fall after their completion
by the contractor, according to their own ideas.
Five courses of stonework form this ring at the
Horse, and each succeeding course lessening its dias
meter from the base by 4ft Gin. gives the difference
in external diameter between the base and upper
course. The inner and outer diameters of the lower
courses are laid with the soft red Runcorn stone.
The same diameters of the upper tiers are laid with
Penhryn granite to bear the weight of the fort to be
constructed above. The heart of the work is filled
in with concrete blocks. The Noman foundations
are precisely similar in their five upper courses, but
they will have an additional four courses below of
Portland roach stone, having% vertical facing from
the shoal. The Noman Shoal is covered with 20ft.
of water at high water spring tides, and the Horse
Shoal with 15ft. Roustd the base of each founda-
tion on the shoals will be deposited sufficient rubble
to protect the stonework from any damage by the
tidal rush of the waters, or the break of the waves
in rough weather.
In executing a work in an exposed position in
tidal waters, the first danger (and sometimes it is
a continuous danger from first to last) the contrac-
tor has:to meet with is the action of the breaking
waves upon his piling in rough weather. This has
been provided for in the Spithead works by
Mr, Leather in the construction of a sys-
tem of piling that shall present the least re-
sistance to the sea, and at the same time
that possesses abundant strength to support
its superstructure. The best known illustra-
tions_ of the two systems of piling for submarine
works exist at Dover and Holyhead. At the former
Places he pilin and staging is a mere reed-like
structure that at first
sight appears far too frail to
maintain.
its
position in even a moderate breeze,
against the
„sees baits w!sh of the sea ; yet it in reality pos-
amount of soft ions arrangement an enormous
the attacks of the strongest strength, enabling it to defy
the contrary, the Sstrtongest gale. At Holyhead, on
there for the couipietai.t'ing that has been erected
time afternti°E the pierheadlhas been
swept away
bulk and consequent resinsliet' "lug
to its too great
to the sea. In the
great gale which, destroyed the
ottiteyal Charter the
piles and staging swept fro
Holyhead
,alongside the Great
pier wolks, drifted the end of the
fouling
Eastern, then anchored ia tLe
ai:djeobpyardy for
her paddles and screw, placed her
some considerable time.
With regard to the Spithead forts themselves
nothing definite appears as yet to :lave been arrive.
at. In the fiat place it w,ls intended to cereltrect the
forts entirely of iron. It was next proposed to con-
struct them of granite faced with iron, in the same
manner as the Cronstadt forts are now being Com-
pleted. It is said, however, that the authorities,
frightened at the cost of iron forts, and not knowing
where to turn for a good intermediate substance be-
tween the iron face and granite backing, intend to
construct the forts simpl y of granite, and leave their
coating outside for further consideration. If these
forts are to fi4ht iron ship, and that is what most
people believe must one day be their duty, they

must be constructed either of iron or clothed with
iron. If the latter course is adopted, there can be no
difficulty about the matter, for any thickness of
armour-plating can be fixed on the exterior of the
granite face by the aid of double T ended angle fram-
ing, and the interstices could be filled with sand to
prevent any damage to the granite by the blow of an
enemy's shot. This sand backing would also lessen
the vibration of the armour plate on being struck,
and would afford space for the removal of any
damaged armour plate, and the fixing of a sound
one in its place without disturbing the granite
frame of the fort. On the Noman the contractor's
circular staging has just been commenced. It will
be fully two years before the foundations of the fort
there can be completed.
There is one fort now just taken in hand by Mr
Leather, at no great distance from the Horse and
Noman, which, although it is included in the " Isle
of Wight Defences," is really a marine fort, and
must be looked upon as one in the group of the Spit.
head defences. This will be erected on the sandy
spit which runs out towards St. Helen's Roads, on
the south side of the entrance to the shallow har-
bour of Brading, the very spot where this fort will
stand being the silted-up sand and shingle which
covered up by tidal and wind action the works com-
menced by Sir Walter Raleigh for the protection
and extension of Brading Harbour. The fort will
be of an oval form, of 120 ft. in length, and about
190 ft. in breadth, and built of granite. A ring of
caissons will be sunk in the sand, after the manner
of those used in the formation of the Thames Em-
bankment, and within this ring will be formed the
foundation for the fort. The caissons will afterwards
be filled in with concrete and become a permanent
outer protective circle for the work.