THE CONSTITUENTS OF A SEABEACH
I ONCE went down to Aldeburgh, on the Suffolk coast, with a party of
friends, which included an American writer, himself as delightful and
charming as his stories. Why should I not give his name? It was Cable,
the author of "Old Creole Days." We walked through the little town
to the sea-front, and came upon the immense beach spreading out for
miles towards Orford Ness. "Well, I never!" said he to me; "I suppose
the hotel people have put those stones there to make a promenade for
the visitors. It's a big thing." It took me some time to persuade him
that they were brought there by the sea and spread out by it alone.
It was his first visit to Europe, but he had seen the seashore on the
other side, and there was nothing like this over there, he declared. A
similar readiness to ascribe Nature's handiwork to the enterprise of
hotel-keepers led a visitor to the Bel Alp, in the Rhone Valley, when
he looked down from that high-placed hostelry on to the great Aletsch
glacier, with its central "moraine" of huge rock masses and debris,
to exclaim, "I see the proprietor has spread a cinder-path along the
glacier to prevent us from slipping. It's a convenience, no doubt, but
gives a nasty dirty look to the snow." Mr. Cable, when he once realized
that the great Aldeburgh beach was a natural production, did what a
true poet and naturalist must do--he fell in love with it, and spent
hours in filling his pockets with strange-looking pebbles of all kinds
until he was brought into the house to dinner by main force, when he
spread his collection on the table, and demanded an explanation of
"what, whence, and why" in regard to each pebble. Our companions--a
great lawyer, a military hero, a politician, and two "learned
men"--regarded him as eccentric, not to say childish. But I entirely
sympathized with him, and when next day we sailed down to Orford and
stood in front of the old Norman fortress, he further established
himself in my regard by deeply sighing and exclaiming, "So that is a
real English castle!" whilst several large tears quietly streamed down
his undisturbed countenance.
To give an idea of what various rocks from far-distant localities may
be brought together on an East Coast beach, take that of Felixstowe
as an example. What is true of the East Coast is to some extent also
true of the South Coast, and, indeed, wherever the sea makes the
pebbles of a modern beach from the materials furnished by the breaking
up of old deposits, which were in their day brought by ice-flows or
torrential currents from remote regions. The most abundant kind of
pebbles on the Felixstowe beach are small, rounded, somewhat flat
pieces of flint, derived not directly from the chalk which is the
"stratum" or "bed" in which flint is originally formed, but from
the Red Crag capping the clay cliffs (London clay or early Eocene),
and also from surface washings and "gravels" (of later age than the
crag) farther north, whence they have travelled southward with many
other constituents of the beach. All these flints are stained ruddy
brown or yellow by iron--a process they underwent when lying in the
gravels or in the crag in which they were deposited as pebbles,
broken, washed, and rolled ages ago from the chalk. The iron is in
a high state of oxidation, and stains not only flint pebbles but
the sands of the Red Crag and later gravels a bright orange-red, or
sometimes a less ruddy yellow. The iron comes originally from very
ancient igneous rocks in which it is black and usually combined with
silica. The chalk flints are always, owing, it seems, to minute
quantities of carbon, quite black in the mass, but thin, translucent
splinters have a yellowish-brown tint. The flints are free from iron
stain when taken direct from the chalk. The commonest pebble next to
flint is milky quartz, or opaque white quartz. This is derived from
some far northern source, where there are igneous rocks traversed
by veins of this substance (perhaps Norway). Quartz, like flint, is
pure silica, the oxide of the element silicon. It appears in another
form as rock-crystal, and also as chalcedony and agate. Opal also
is pure silica, but differs from quartz and its varieties in being
non-crystalline or amorphous, and in being less hard and of less
specific gravity than quartz. Opal is soluble in alkaline water
containing free carbonic acid, such as are many natural waters and the
sea! But quartz is not so. The siliceous "spicules" and skeletons of
many microscopic animals and plants are "opal." The gem known as "opal"
is a variety owing its beauty to minute fissures in its substance which
break up light into the prismatic colours.
A great deal rarer than the milky quartz, but well known on the East
Coast on account of their beauty, and often sought for to be cut
and polished, are the small rolled bits or pebbles of chalcedony or
agate, which have been bedded before their appearance on the beach
in some of the pre-glacial or post-glacial gravels, together with
the flints, and in consequence are often stained of a fine red. Such
clear red-stained chalcedony is called "carnelian"; if the banded
agate structure shows, it is called agate rather than carnelian. It is
wonderful how many beautiful pieces of both carnelian and agate are
picked up on the Felixstowe beach, rarely, however, bigger than a hazel
nut. The original source of these carnelians and agates is the East of
Scotland. At Montrose you may see the igneous rock containing pale,
lavender-coloured agate nodules as big as a potato, the breaking and
rolling of which by the sea into small bits has furnished our Suffolk
carnelians. Quartzite--more or less translucent, sandy-looking pebbles,
colourless or yellow: jasper, black or green with red veining: a fine
wine-red or purple stone often veined with quartz--are all more or
less common, and come from northern igneous rocks--possibly some from
Scandinavia and some from the breaking up of an ancient "breccia" of
the Triassic age, which still exists northwards of East Anglia.
Other pebbles very common on this shore are those formed in a curious
way by the sea-water from the clay cliffs and sea bottom which are here
present, and are of that special geologic age and character known as
the London clay. The sea at this moment is continually converting the
clay of our Suffolk shore into "cement-stone" by a definite chemical
process. The clay and many other things submerged in the sea, as
Shakespeare knew, "undergo a sea-change." The cement-stone used to be
dredged up from the sea bottom and ground to make cement at Harwich.
Great rock-like slabs of it pave the shore at low water, and pebbles
of it are abundant. The curious thing is that ages ago--geological
ages, I mean--when the sea was throwing up here the old shell-banks
and sand-banks known nowadays as "the Red and Coralline Crags," the
London clay cliffs and clay sea bottom were in existence just as they
are now. But in that period there existed here enormous quantities
of bones of whales of kinds now extinct, which had lived a little
earlier in the sea of this area, and were deposited in vast quantity
as a sort of first layer of beach or shallow water sea-drift. Bones
consist largely of phosphate of lime, and are used as manure. In that
old crag sea the phosphate of lime was dissolved from the deposit of
bones, and as we find occurring in the case of other clays and other
bones elsewhere--was chemically taken up by the clay--the same kind of
clay which to-day is being converted into "cement-stone." It was thus,
at that remote period, converted into "clay phosphorite," owing to the
presence of the immense deposit of whales' bones, and it has been known
for sixty years as Suffolk "coprolite," owing to a mistaken notion
that it was the petrified dung of extinct animals. It has been dug up
by the ton from below the crag all over this part of Suffolk, where it
forms, together with bones, teeth, flints, and box-stones, a bed of
small nodules, a foot or so thick separating the London clay from the
shelly "crag." This bed is called the Suffolk bone-bed or nodule-bed.
The phosphorite, or "coprolite," occurs in the form of bits of clay,
hardened by phosphate of lime, and of the colour of chocolate, and
hundreds of tons of it have been used by manufacturers of the manure
known as "superphosphate." Henslow, of Cambridge, Darwin's friend and
teacher, was the first to point out its value. Bits of it, as well
as box-stones, and fragments of bone, teeth of whales, of sharks, of
mastodon, rhinoceros, tapir, and other extinct animals--all fallen from
the bone-bed in the cliff--are found mixed with the pebbles of the
Suffolk beach by those who lie on that beach in the sunshine, and, for
want of something better to do, turn over handful after handful of its
varied material. And, besides all the stones I have already mentioned,
they find amber, washed here by some mysterious currents from the
Baltic, wonderful fossil shells out of the crag, the cameo shell, and
the great volute,--shells which are as friable as the best pastry
when dug out of the Red Crag, but here on the shore become hardened
by definite chemical action of the sea-water, so as to be as firm as
steel. Here, too, the "chiffonier" of the seashore finds recent shells,
recent bones (slowly dissolving and wearing away), well-rounded bits
of glass, jet drifted down from Whitby, Roman coins, bits of Samian
ware (!), mediaeval keys, bits of coal, burnt flints (from steamers'
furnaces), and box-stones.
A very important and interesting thing about "beaches" is the way in
which the pebbles of which they consist are assorted in sizes. Suppose
that one prepares a trough some two or three yards long and twelve
inches deep, and lets it fill with water from a constantly running tap,
tilting it slightly so that the water will overflow and run away at the
end farthest from the tap. Then if one drops into the trough near the
tap handful after handful of coarse sand and small stones of varied
sizes, they will be carried along by the stream, and the more rapid and
voluminous the stream the farther they will be carried. But they will
eventually sink to the bottom of the trough, the bigger pieces first,
then the medium-sized, then the small, and the smaller in order, as the
current carries them along, so that one gets a separation and sorting
of the solid particles according to size, a very fine sediment being
deposited last of all at the far end of the trough. The waves of the
sea are continually stirring up and assorting the constituents of the
beach in this way. Usually the largest pebbles are thrown up farthest
by the advancing waves, and dropped soonest by the backward suck of
the retreating water, so that one generally finds a predominance of
big pebbles at the top of the beach. But on the flat shore of firm
ripple-marked sand lying lower down than the sloping "beach" and only
exposed at quite "low tide," one often finds very big pebbles of eight
or nine pounds weight scattered here and there and little rubbed or
rounded. They have gradually moved down the sloping beach and are too
heavy to be thrown back again by the waves of the shallow sea which
flows over the flat shores characteristic of much of our south-eastern
and southern coast. On some parts of the coast huge banks, consisting
exclusively of enormous pebbles as big as a quartern loaf, are piled
up by the waves, forming a great ridge often miles in length, as at
the celebrated Chesil pebble bank near Weymouth, and at Westward Ho!
in North Devon. The presence of these specially large pebbles is due
to the special character of the rocks which are broken up by the sea
to form them, and to the specially powerful wave-compelling winds and
tidal currents at the parts of the coast where they are produced.
One generally finds a selected accumulation of moderate-sized pebbles
lower down the beach as the tide recedes, and then still lower down
patches of sand alternating with patches or tracts of quite small
pebbles not much bigger than a dried pea. They are always assorted in
sizes, but the extent of each tract of a given size of pebble varies
greatly on different beaches along the coast, and even from day to day
on the same shore. The greater or less violence of the waves, and of
the currents caused by wind and tide, is the cause of this variation
and local difference. The pebbles of the "beach" are, of course, always
being worn away, rounded and rubbed down by their daily movement upon
one another, caused by the waves as the tide mounts and again descends
over the shore. Even the biggest stones, excepting those which lie
in deeper water beyond the beach, are eventually rubbed down, and
become quite small; but a point is reached when, the weight of the
pebbles being very small, they have but little effect in rubbing down
each other, and consequently where the pebbles consist of very hard
material--like flints--the smallest ones are not so much rounded, but
are angular and irregular in shape.
Whilst a perfect gradation in size can be found from the largest flint
pebbles some 6 inches or 7 inches long to the smallest, usually not
bigger than a split pea (though sometimes a patch of even smaller
constituents may be found), there is a real break or gap between
"pebbles" and "sand." I am referring now to what is commonly known as
"sand" on the southern part of the East Coast, much of the South Coast,
and the shores of Holland, Belgium, and France. There are "sands" of
softer material (limestone and coral sand), but the sands in question
are almost entirely siliceous, made up of tiny fragments of flint, of
quartz, agate, and hard, igneous rock. They are often called "sharp"
sand. The particles forming this sand are sorted out by the action of
moving water, and form large tracts between tide-marks looking like
brown sugar, for which baby visitors have been known to mistake them,
and accordingly to swallow small handfuls. The strong wind from the
sea blows the sand thus exposed, as it dries, inland out of reach of
the tide, to form sand-dunes, and it is also deposited, together with
still finer particles (those called "mud"), on the shallower parts
of the sea bottom. The curious thing about the particles of "sharp"
sand is that they are angular, and for the most part without rounded
edges. If you examine them under a microscope you will see that they
do not look like pebbles--in fact, they are not pebbles, for they are
so small and have so little weight, or, rather, mass, that they do not
rub each other to any effect when moved about in water. They look like,
and, in fact, are, for the most part broken bits of silica, unworn
and sharp-edged splinters and chips, glass-like in their transparency
and most of them colourless, a few only iron-stained and yellow.
Amongst these are a few rounded, almost spherical pieces, which are no
doubt of the nature of minute water-worn pebbles. Although these few
minute pebbles exist among the sharp, chiplike particles of "sand,"
it is clear that we must broadly distinguish "pebbles" of all sizes
down to the smallest--from the much smaller "sand particles." There
is no intermediate quality of material between "sand" and the finest
"shingle."