THE SAND AND PEBBLES OF THE SEASHORE
THE "beach" on our English coast is an accumulation of pebbles or of
sand, or of both, often accompanied by dead shells and other fragments
thrown up by the sea. Very generally it slopes rapidly from above
high-water mark to about half-tide limit, and then merges into a more
horizontal expanse of fine, compact sand. This last is not "a beach"
thrown up by waves, but a sediment or deposit. It forms a flat, often
ripple-marked plain (much has been written as to how those ripple-marks
are produced), which is exposed at low water, the sea retreating for
a quarter or even half a mile or more over it, on some level shores.
Sometimes, though rarely, the sea rises and falls against a hard, rocky
cliff without forming any beach or exposing any "shore" even at low
tide. This occurs on parts of the Cornish coast, where the Atlantic
beats against adamantine cliffs, which even at low tide rise sheer from
the water. Again, it sometimes happens that the shore is simply formed
of a terrace of sloping hard rock, without any "beach." But on the
coast of England generally there is a good beach of sand or pebbles, or
both, overlying the native rock or clay, and sometimes it is growing
every year, so as to extend the land surface seawards and add new acres
to the possessions of the landlord.
On other parts of the coast the beach "travels," being driven along
the underlying solid shore by the prevailing direction of the tidal
currents and by the waves. The sea-waves break close to the soft
cliffs of clay, sand, and sandstone. These are continually crumbling
away owing to the action of land water, which soaks from the surface
down to the layers of clay and forms subterranean springs and streams.
They undermine the face of the cliff and cause the upper parts to
topple. When there is a big, broad, growing beach in front of such
a cliff, the breaking down or "toppling" of its face only leads to
the formation of a slope (at the "angle of rest"), and things remain
but little changed for ages. But if the beach is not being piled up
and added to and growing out seawards year by year, and is, on the
contrary, a travelling beach, then the sea comes close up to the cliff,
and when masses of it topple on to the beach the sea washes them away,
and no "slope of repose" is formed. The cliff keeps on toppling as it
is undermined by springs of land water. Its natural buttress against
further breakage--namely, its own fallen material--instead of resting
against it as a great sloping, protective bank, is washed away by the
sea as fast as it falls, and is carried down the coast by the tidal
currents. This is the story of "coast erosion" about which there has
recently been a Government inquiry. Where the combined action of
prevailing winds and sea currents is throwing up and adding to the
beach there is no coast erosion. The causes of the sea currents on
our coasts are not easy to determine, as they are connected with the
general contour of the land and the currents in large tracts of sea,
such as the Channel and the North Sea. Coast erosion is a serious
thing. Large parts of the coast of Suffolk and Norfolk are being thus
washed away. It can be prevented by "holding" the beach with piles and
boarding, but this costs too much to make it worth doing unless the
land so preserved has a special value for the erection of houses.
At Felixstowe, where I am writing, the sea has swept away most of the
flat--the "dunes," or "deans"--covered with grass, which it had itself
built up by a contrary accumulating action before the time of the
Romans. On this flat the ancient Roman town was built. Why the sea has
reversed its action is very difficult to say. But within my knowledge
of this place high-water mark has advanced as much as 300 yards
nearer than it was to the old roadway and to old houses. The great
town of Dunwich, which in the Middle Ages had eleven churches, strong
fortifications, and a flourishing trade, stood on the flat grass-land
in front of the cliff on the Suffolk coast. Its site is now under the
sea, not far from here. The breaking away of the cliff (on to which
part of the town extended) is still going on there. A few years ago I
saw a great bricked well lying like a fallen chimney on the shore. It
had been exposed by the crumbling of the cliff, and at last fell out
of it. Once that well supplied fresh water to the monastery, part of
the walls of which are still standing, and were formerly three-quarters
of a mile distant from the seashore. The prehistoric cliffs to which
the sea came before it formed the flats or links which it is now again
eating away, are often traceable a mile or two inland. On the other
hand, on parts of the Lincolnshire coast the sea has piled up sand and
shingle and added valuable land to the extent of hundreds of acres to
the property of those whose estates were bounded by the shore line,
and is still doing so. Perhaps the action of the north wind in blowing
back and piling up sand out of the reach of the tide is influential in
producing this increase of shore-lands, which face northwards. Blown
sand forms hills 30 feet and more in height on such flat lands as those
of the Sandwich and Deal "links," which have been thrown up by the sea
since St. Augustine landed at Richborough, then a seaport, now a couple
of miles from the sea. On the French coast near Boulogne the sand has
been blown inland so as to form stratified deposits on the low hill
country as far as 3 or 4 miles from the sea, and the neighbouring port
of Ambleteuse, which five hundred years ago had the chief trade with
England--is now nothing but a vast stratified "dune" of blown sand. The
great Napoleon made some attempt to reopen the harbour, but gave it up
as a bad job; the blowing of sand inwards from the enormous tract of
flat, sandy shore was too much for his engineers.
The "erosion" and the contrary process of the "extension" of the
coast by the action of the waves and currents of the sea must be kept
apart and distinguished from a process leading to similar but not
identical results, namely, the actual "crumpling" or "buckling" of
the earth's crust, leading to the rising of the land surface in some
parts of the globe relatively to the sea-level, and on the other hand
to the sinking of the land beneath the sea in other regions. This
change of the actual level of the land has continually gone on in the
past, and is continually going on to-day. What are called "raised
beaches" are seen on many parts of the coast. These are lines of
ancient beach, consisting of sea-worn pebbles, fragments of shell,
etc., forming terraces along the face of the rocks which rise from the
present seashore--terraces which are now 15, 30, or more feet above
the sea-level, although they must at no very distant period have been
at the level of the sea. The land has risen and carried them up out
of reach of the waves. Such a raised beach is seen along the rocks
bordering Plymouth Sound, at a height of some 15 feet (so far as I can,
at this moment, remember) above high-water mark. Owing to the fact
that the rock is limestone, and is dissolved and redeposited by rain
water, as a rock of sugar might be, the pebbles and shells of the old
beach are all stuck together or "petrified" by redeposited limestone
(carbonate of lime). Lumps of it can be carried away as specimens.
Geological deposits of much older date than these comparatively recent
raised beaches tell us of the rising of great masses of land. Thus,
for instance, marine shells in a deposit not quite so old as our chalk
cliffs and downs, are present at a height of 10,000 feet, forming part
of the Alps. At one time that very spot was the bottom of the ocean,
whilst other tracts of the earth's surface, now sunk hundreds of
fathoms below the sea-level, stood out as continents, with hills and
valleys well raised above the waters. Direct evidence of the recent
sinking of the coast as distinct from its erosion is not familiar to
us in England. The evidence of it is naturally obliterated, as the
sinking goes on, whereas on a rising coast the evidence is as naturally
preserved. But on the shores of the Mediterranean near Naples the
evidence of sinking is well preserved, and has been carefully studied
and recorded. The ancient Roman road is still sunk beneath the water,
though the celebrated temple of Puteoli, which was formerly submerged
by the sinking of the land, has reappeared by a subsequent elevation of
the same area. This has not brought the site to so high a level as it
had when the temple was built, as appears from the fact that the Roman
paved roadway close by is still some 15 feet below the surface of the
sea.
A beach is built up of water-worn pebbles, consisting usually of bits
of the rock of the immediate vicinity, which have become rounded and
shaped by continually rolling and knocking against one another as the
waves of the sea throw them up or drag them down the sloping heap of
like pebbles which is accumulated near high-water line. At Dover and
such places, under chalk cliffs, the beach consists of chalk pebbles
oval in shape, often of 8 or 9 inches in length, with a large number
of well-rounded flint pebbles as big as your fist interspersed, or
outnumbering the chalk pebbles. At Tenby, in South Wales, the beach
consists of assorted sizes of limestone pebbles, well-worn bits of
the limestone cliffs of the neighbourhood. Large numbers of them are
literally "worm-eaten," being bored into, hard and dense as they are,
by a little marine worm (known as Polydora), which may be sometimes
found alive and at work in these limestone pebbles lying between tide
limits, or more easily at other places in similarly placed chalk blocks
or pebbles. On a coast bounded by granite cliffs you get a beach of
granite pebbles; where there are cliffs of slate or of sandstone,
pebbles of slate or of sandstone.
But there are some beaches which, as remarked above, are continually
travelling along the coast. That on the English shores of the North
Sea, for instance, is always moving southwards, except where it is held
by piles and breakwaters, locally called "shies." Moreover, the land of
the East Coast, especially the Suffolk and Norfolk coast, in the course
of its erosion, has given back to the sea old deposits of the glacial
and post-glacial period, consisting of gravels and "drift," made up of
flint pebbles and fragments of rocks from the more northern regions
over which the great European ice-cap of the glacial epoch extended,
and from which it ground and tore the surface rock and carried large
and small masses--boulders and incredible millions of tons of broken
up fragments--and spread them over East Anglia (where they form the
so-called "glacial drift"), and over regions still submerged in the
North Sea. Consequently the beach on the Suffolk seashore has a
specially variegated assortment of pebbles from all sorts of more
northerly situated rocks--though small flint pebbles, derived directly
from glacial drift and by the drift from the chalk land-surface (the
chalk itself not now reaching the shore-line of East Anglia), are
greatly predominant. It is in the chalk that flint takes its origin,
being found there as large irregular nodules and sheets.