The Sun.
London, England, 1853-05-09 00:00:00

THE SUN, LONDON, MONDAY EVENING, MAY 9, 1858.

LNSTITUTION OF CIVIL KVGINEERS.—May 3

The paper read was " A Description of the Chesil Bank
(Portland)," by Mr. J. Coode, M. Inst. C.E.
The author, in his position of the Resident Eng;neer of
the " Portland Breakwater Works," now in course of exe-
cution under Mr. J. M. Rendel. President Inst. C.E., had
for a long time directed his attention to the extraordinary
accumulation of shingle, called the Chesil Bank, one of
the most remarkable features of the south-east coast of
England.
It consisted of a vast mound of shingle, in the form of a
narrow isthmus, lying upon the western sea-board of Dor-
setshiro, between Abbotsbury and Portland ; its length
was 10 miles in a south-east direction, and is breadth at
the base, or level of low water of ordinary spring tides was
170 yards near Abbotsbury, and 200 yards at Portland.
Along a portion of its course, south of Wyke, the bark
acted as a natural breakwater to the anchorage of " Poi L.
land Roads," affording shelter from the westerly and south.
west gales. The height increased from the north-west, but
the inclination of the crest was not uniform throughout ;
the rise between Abbotsbury and Wyke being at the rate
of 1 in 8,150, whilst that between Wyke and Portland was
1 in 880.

In a transverse direction, one general slope appeared to
exist, from the summit down to a depth of 3A to 4i fathoms
below low water ; the rate of inclination varying only
from linsitol in 7. In the next depth of 2 fathoms,
the slope was 1 in 8 to 1 in 11; outside this, the slope was
about 1 in 30, to a depth varying from 6 to 8 fathoms, at
which point the shingle ceased entirely, and was succeeded
by fine sand.
It had been generally supposed, that the nucleus of the
bank was formed of a mound of clay ; repeated trials, by
boring, had, however, shown that the bed on which the
shingle rested, on the east, was the edge of the Ki mine-
ridge Clay of the East Bay ; and it was only on that side
that it could be reached by boring tools. The bank con-
sisted in reality of shingle, mixed in places with sand, and
so compact, as to prevent the percolation of water, except
during heavy gales from the south-west, notwitstanding
that at certain times the tide rose nearly 3 feet higher on
the west than on the east side of the bank, and in
heavy gales the waves ran up the slope as much as 10 feet
vertically.
The largest shingle was generally- found to " leeward," or
farthest from the point whence the heaviest seas pro-
ceeded ; and so clearly was this defined, that a Portland
fisherman was popularly said to be able to distinguish, in
the darkest night, any precise spot of the beach, by the
size of the peebles."

The shingle composing the bank, consisted chiefly of
chalk flints, with a small admixture of pebbles from other
formation, and in an interesting geological examination of
the coast, the author traced the principal supply of shingle
to have been derived from the chalk cliffs to the westward,
between Lyme and Sidmonth, and from the vicinity of
Beer Head. Other shingle, of distinct character, proceeded
from Budleigh Salterton, and other pebbles from Aylesbere
Hill, inland, being brought down to the coast by the River
Otter.

The question was next discussed as to the power by
which shingle was conveyed from a distance of between
40 and 50 miles, and deposited in the form of a high
mound. The action of tidal currents was carefully
examined, and after admitting that they did sometimes
modify the extent and form of accumulations of shingle,
and referring to the late Mr. H. R. Palmer's paper " On
the motion of Shingle Beaches," additional reasons
were given, against the sufficiency of this tidal action,
to produce such results. Instances were then cited
of shingle travelling in opposition to the prevailing
current of tide, and having shown, that the progress of the
shingle could not be attributed to the action of the tidal
currents, the effect of the wind waves was attentively con-
sidered. The prevalence of west and south-west winds,
on that coast, was demonstrated, from the observations
made at Plymouth with Whewell and Osler's anemometers,
by Sir W. Snow Harris, for the British Association and it
was shown, that lines drawn across the Bay, in the direction
of the heaviest and prevailing winds, would intersect the
points, whence the shingle had evidently been derived ; it
was shown also, that the seas driving along the west
side of Portland, sufficed to arre^t the progress of the
shingle, and the evidence adduced led irresistibly to the
conclusion, that the ultimate movement of shingle was
always found to be in the direction of, and never against,
the drift of the heaviest seas ; but frequently in opposition
to the prevailing tidal current.
It appeared evident, that neither the action of the stream
at Abbotsbury, nor the flow of the tide in the Fleet, could
have moved the mass, or piled up the mound of shingle
composing the bank. The sudde' depth of 8 fathoms of
water, at a cable's length from the shore, was a peculiar
feature, and permitted the heaviest seas to fall. in with
great violence, and without the retardation and loss of
force usually experienced on long shelving beaches.
Evidence was then adduced, that shingle was moved at
a much greater depth than was usually supposed ; the
author, in his researches, found that, at one time, the
pebbles, down to the edge of the sand, were incrusted with
barnacles, " balanus balanoides," and subsequently, after
continuance of heavy gales from the south-west, th
shingle, down to the lowest point, was found to be com-
pletely freed from incrustation ; demonstrating that there
had been considerable motion of the pebbles, at a depth of
eight fathoms below low water of spring tides.
The formation of the gullies, or " cans," in the face of
the bank, caused by the partial percolation, was then no-
ticed, as tending in some degree to produce the flat slope
on the east side. _ _ _ _ _

The author considered the cause of the largest shingle
being found to " leeward," was that large pebbles were
more easily moved than those of small size, inasmuch as
the former were generally of exceptional dimensions, were
usually found on the surface, and offered nearly the whole
of their surface to the. action of the waves, whereas the
latter, forming the bulk of the mass, were more uniform
in size, were closely embedded together and exposed little
more than their upper surfaces, over which the waves had
a tendency to travel, rather than to lift them from their
bed. Thus the larger stones were rolled about by every
wave, whilst the small pebbles were only moved in a mass,
and received their abrasion whilst settling down again to
form the even uniform surface of the beach.

Specimens were exhibited of shingle obtained from below
the low water mark, by means of dredging and (living, in
order to demonstrate, by the character and form of the
pebbles, the passage of the shingle from west to east, and
referring to remarks made by the author at a previous
meeting of the Institution, it was contended that the pre-
sent specimens confirmed the opinion then given, that the
smallest pebbles were generally found at the top of the
Chesil Bank ; the opinion expresEed by the majority of
speakers at that meeting was just the reverse, and the
error most probably arose from comparing the Chesil Bank
with the case of a beach terminating against a cliff or a
wall, about the level of high-water ; in such a case (and
then only after the prevalence of off-shore winds,) the
largest shingle would be found at the level of the previous
higk water, and therefore at the top ; this however
would not be the case upon the Chesil Bank, or upon
any other beach similarly situated, where the shingle was
free to assume a sectional form, unaffected by the recoil of
the water, striking against a vertical, or nearly vertical
face. _ _

After a heavy gale and a ground swell, the large shingle
was entirely scoured away.
The small shingle was thrown up to the crest, or top of
the bank during the height of heavy gales, out of the reach
of ordinary waves, or the clawing action of receding water.
By sections of the profile of the bank, taken after a
heavy gale from the south-west, at right angles to the
direction of the bank, the general form was shown to be
nearly that of a true parabola ; with the axis inclined to a
level line, to the extent of 1 foot in 90 feet.
Mr. Palmer's views as to the "accumulative" and the "de-
structive action of waves, were then examined, the au-
thor's observations inducing him to fix other limits ; the
rule, so,far as one could be formed, being, in his opinion,
that seven, or any less number of waves per minute, in-
duced the ' destructive' action, and nine, or any greater
number, in the same time, the accumulative' action; it
being admitted, that shingle always accumulated with off-
shore winds, and was scoured off during on-shore winds,
and especially by the subsequent ground-swell ; bearing
in mind, however, in watching the course of the crest of
the wave, after breaking, that if it fell upon the water
of the preceding wave, then returning down the slope
of the beach (as was the case when waves followed
in quick succession), the " accumulative" action was going
on ; but if the water descended directly on the pebbles (as
when the waves broke at longer intervals), the " destruc-
tive" action was progressing.
The rapidity with which the water ran off, or was ab-
sorbed, would influence the resalt, and that was to some
extent contingent on the slope of the beach, and also on the
nature and degree of compactness of the material of which
it was composed.
The paper concluded with some instances of the effects
produced on the Chesil Bank, by heavy gales from the
south-west, and it was stated that on such occasions it was
not an uncommon occurrence (when the advancing wave
met the receding water of the wave immediately preceding
it) to see an enormous mass of broken water and spray rise
vertically to the height of 60 feet or 70 feet. This force
had on several occasions crushed inwards the decks of ves-
sels, stranded on the beach.
During the gale of the 27th December, 1852, the quan-
tity of shingle scoured away between Abbotsbury and
Portland, was 3,763,300 tons ; and the quantity thrown in,
within the next eighteen days, was 2,671,500 tons.
On the 23d November, 1852, a heavy ground swell, con-
sequent on half a gale of only four hours' duration from
the South-West, scoured away within eighteen hours
4,553,1)0 tons, and in five days afterwards 3,554,200 tons
of shingle were found to have been thrown in again.
These quantities were derived from careful admeasurement
of the profile of the bank.
The paper was illustrated by a large series of diagrams,
of the sectional profiles of the bank, and the outlines of
the shores exhibiting the geological features of the coast,
with the bearings of the prevalent winds, &c. ; together
with a collection of specimens of the shingle, taken at
four different points along the bank, and at various levels,
from the top down to a depth of eight fathoms below low-
water of spring tides.
It was announced that the discussion on the paper would
be renewed at the meeting of Tuesday, May 10th, when,
if time permitted, the following papers would be read :
"On the Conversion of Heat into Mechanical Effect," by
Mr. C. W. Siemens ; " On Stirling"s Air Engine," by Mr.
J. Leslie, M. Inst., C.E. ; and " On the Caloric Engine,"
by Mr. C. Manby, M. Inst., C.E.

SHIPPING INTELLIGENCE.

CUSTOM-HOUSE, MAT 7.

ENTERED INWARDS.—The Soho, from Havre ; Marie
and Christina, Altona • Fameliens, Sannesund ; Newton,
Dantvic ; Engelina, Leer ; Sylph, Barbadoes ; William
Henry Angus Gothenburg ; Dorothea Fredericke, Struer ;
Colonist, Schien ; Panther, Ostend ; Wilhelmina, Doner
Nodde ; Patriot, do. ; Juno, Constantinople ; Hero,
Melbourne ; Wilhelm, Ebeltoft; Marie, Odense ; Wilber-
force, Hamburgh ; Sundscupminde, Sannesund ; Helene,
Sonderburg ; Salacia, Callao ; Maria Sollenta, Havannah ;
Bucephalus, Calcutta ; Sver, Buenos Ayres ; Christopher,
Sligo ; Hans Gorgensen, Aalborg ; .Mathilde, Borul ;
Herottoz, Whitstable ; Sir Edward Parry, Sydney, New
South Wales ; Georgians, Dunkirk Holdegard von
Schwartzer, Stralsund ; Wave, Memel ; Christianshaab,
Kioge.
ENTERED OUTWARDS FOR LOADING.—The Moderen
for Stavenger ; Europa, Calcutta ; Clifton, do. ; Lugstor.
Frederiksverk ; Fayaway, Melbourne ; Gesina, Hamburgh ;
Bucephalus, Trinidad and Calcutta.

CLEARED OUTWARDS WITH CARGO.—The Fanny Gann,
for Melbourne ; Florencia, Bilboa ; Lavinia, Hamburgh ;
Santos Segunda, Oporto ; Lydia, Elsinore, &c. • Avenir,
Rouen ; Hempsyke, Port Philip ; Swarthmo.ie, Bombay ;
Harriette, Valparaiso ; Empiresa, Santander ; Neptune,
St. Pei,ersburgh ; Sarah, St. Kitt's • Eclipse, Madeira ;
Jautina, St. retersbursh ; Mehemet Ali, Ceylon.