<h2 class="nobreak" id="CHAPTER_V">CHAPTER V</h2>
<h3>RECORDS LEFT BY THE SEA</h3></div>
<p>We have already spoken of the story which the
sea writes in the annals of geology. It is a
story with two plots. In the first place, the sea
is always wearing away the land. In the second place, it
is arranging on its own bed the materials which it takes
from the land, either directly or indirectly. As a sequel
to both stories, the materials all neatly ranged, packed,
and folded are revealed when the sea subsides from them,
or when, in process of one of those great geological
changes, the origin of which we have already attempted
to account for, the sea bottom is raised to become the
land of a continent. The first part of the sea's belligerent
story is written so plainly for all eyes to see that one
scarcely need dwell on it. Every strip of coast around
these islands bears witness to it.</p>
<p>Off Shetland masses of rock twelve or thirteen tons in
weight have been cut out from the cliff seventy feet above
the smooth-water level. The sea's battering-rams are the
masses of shingle, gravel, and loose blocks of stone which
it carries with it; but it has subtler methods in the corrosive
action of its salts, for just as it rusts or wears away
<span class="pagenum" id="Page_60">-60-</span>
iron, so its salts and acids must eat their way into many
rocks.</p>
<p>But, after all, the coast-line of the world is a small
fraction of the whole land surface of the globe; and a
smaller fraction of the sea's own wide area. On that area
are flung all the records and treasures which the sea has
wrested from the land. The rivers, as we have already
several times repeated, are the chief carriers of deposits
to the sea. By their deltas they may be known. The
deltas of the Ganges and Brahmaputra cover an area as
large as that of England and Wales. The delta has been
bored through to a depth of nearly five hundred feet, and
has been found to consist of numerous alternations of fine
clays, marls, and sands or sandstones, with occasional
layers of gravel. In all this accumulation of sediment
there are no traces of marine animals; but land plants
and the plants and animals of the river and of the surrounding
land have been discovered in quantity. The sea
most often destroys land; but it sometimes deposits
beaches; and, we might almost say, silts up the land. At
Romney Marsh, for example, a tract of eighty square miles
which was marsh in Julius Cæsar's time is now dry land,
and has become so partly by the natural increase of
shingle thrown up by the waves. The coarsest shingle
usually accumulates towards the upper part of the beach,
and the rest arranges itself generally according to size
and weight, that which is finest being nearest to low-water
mark.</p>
<p>It is often long before the stuff brought down by the
rivers settles on the floor of the ocean. The finer particles
<span class="pagenum" id="Page_61">-61-</span>
may be carried out to sea for three hundred miles or more
before they settle. Within this three-hundred-mile zone
the land-derived materials are distributed over the floor
in orderly succession. Nearer the land we shall find
coarse gravel and sand. Beyond there will be tracts of
finer sand and silt, with patches of gravel here and there.
Still farther off will come fine blue and green muds, which
are made of the tiny particles of such materials as form
the ordinary rocks of the land. But when we are once
past this zone of land material we come upon deposits
which are the ocean's own freehold—materials which it
does not derive from the continents, but which may be
called oceanic in origin. First there are vast sheets of
exceedingly fine red and brown clay. Whence comes it?
It is by far the most common deposit in all the deeper
parts of the ocean. It may either be the dust of volcanic
fragments washed away from volcanic islands, or (which
is much more likely) it may be supplied by eruptions
under the sea. For it must be remembered that the sea
floor is two to five miles nearer the hot rocks that are in
the interior of the earth than the land surface is, and
that consequently the water coming into contact with
them may cause explosions arising from the action of
steam. This is a question we shall have to consider later,
and for the present we must ask the reader to accept the
fact—and read on.</p>
<p>There is one very curious thing about this red clay, and
it is that the accumulations of it appear to be built
up very slowly. Where it occurs farthest from land
great numbers of sharks' teeth with ear bones and other
<span class="pagenum" id="Page_62">-62-</span>
bones of whales have been dredged up from it. Some of
these relics are quite fresh; others are coated with a crust
of brown peroxide of manganese. Some are covered with
this material and hidden in it. One haul of an ocean
dredge will bring up the bones in all these states, so that
they must be lying side by side. The bones are probably
those of many generations of animals, and it must take a
long time to cover them with the manganese deposit.
But the clay is deposited even more slowly than the manganese,
so that it must fall very slowly indeed.</p>
<p>But besides these things the bottom of the sea receives
deposits of the remains of all kinds of shells, corals, and
all sorts of marine creatures, great and small. As the
countless myriads of the animals of the sea die, the shells
with which they are covered, or the bones which form
their framework, fall continually to the bottom of the
oceanic gulfs in which they dwell. Then the ocean floor
is covered with the remains of tiny animals incomparably
more numerous than the stars of the sky; and this grey
slimy ooze of organic matter hardens by pressure into
sedimentary rock. In the course of ages, when the slow
decline of the water lays it bare, it may become part of
the land on which men dwell. But it is always forming,
has always been forming, since life first appeared on the
earth. It is on this ocean floor that man to-day lays his
telegraph cables. Mr. Rudyard Kipling, in his verses
"The Deep Sea Cables," has drawn a vivid picture of
the bed of the deep ocean:—</p>
<div class="poetry-container">
<div class="poetry">
<div class="stanza">
<div class="verse indent0">The wrecks dissolve above us: their dust drops down from afar—</div>
<div class="verse indent0">Down to the dark, to the utter dark where the blind white sea-snakes are.</div>
<div class="verse indent0">There is no sound, no echo of sound, in the deserts of the deep,</div>
<div class="verse indent0">On the great grey level plains of ooze, where the shell-burred cables creep.</div>
</div></div>
</div>
<p><span class="pagenum" id="Page_63">-63-</span></p>
<p>It is in these silent depths that for uncounted and innumerable
years the crust of the earth has been forming
and has been growing outwards, while it has been slowly
hardening inwards above the fires of its unplumbed
interior.</p>
<p>It has been calculated that in a square mile of the
ocean down to a depth of one hundred fathoms there
exist more than sixteen tons of carbonate of lime in the
form of the bones or shells of living animals. A continual
fine "snow-storm" of dead chalky animals is therefore
falling on to the bottom. Here and there, especially
among volcanic islands, portions of the sea-bed have
been raised up into land and masses of modern limestone.
Though these rocks are full of the same kinds of shells
as are still living in the neighbouring sea, they have been
cemented into hard rock. This cementing is due to the
water which has penetrated and permeated the stone,
dissolving chalky matter from the outside shells, and
depositing it once more lower down and farther in, like a
fine mortar, so as to bind the mass together.</p>
<p>Every one has heard of coral reefs. They are one of
the best and most familiar examples of the way in which
great masses of solid rock can be built up by the dead
bodies of animals. In the warmer seas of the earth, and
notably in the track of the great ocean currents, various
kinds of coral polyps, as they are called, take root on the
edges and summits of submerged rocks and peaks, as well
<span class="pagenum" id="Page_64">-64-</span>
as on the shelving shores of islands. The coral polyp is
a jelly-like creature, but it has a hard chalky skeleton
inside its transparent body. It is a great colonist, with
no liking for a solitary life, but with, on the contrary,
a great fancy for its neighbours; in fact, the polyps grow
and thrive in clumps, and the clumps unite to form communities,
and the communities increase to colonies and
nations, till they unite to form what is called a reef. The
coral polyps are rather exigent in the choice of their residential
neighbourhoods. They cannot live at a greater
depth than fifteen or twenty fathoms, and in defiance of
the inclinations which rule human beings, they have the
strongest distaste for sun and air; in fact, they die when
exposed to it.</p>
<p>Now when the polyp dies its skeleton remains behind
it, and millions upon millions of these coral skeletons
make a layer of coral. These layers of coral
gradually lift the generations of polyps upwards to
the surface of the water. But as we have seen, the
living polyps die when they get so far, and consequently
the reef then spreads outwards. On the
outer edges of the reef the coral polyps flourish in
the most vigorous way. There they are as completely
provided for as in a County Council Utopia. The
breakers bring them the food on which they live; the
water and the climate suit them exactly. The only blot
on their lives are the occasional storms which break off
fragments of the coral foundation on which they live.
But even this, while it is disastrous to the individual
polyp, is for the good of the community, because these
<span class="pagenum" id="Page_65">-65-</span>
blocks as they roll down form a new foundation on which
new generations of polyps can grow and feed. Moreover,
it is better for the polyp to take the risks of these evictions
than to vegetate <i>inside</i> the reef, for there in the calmer
water he will not have enough to eat, and will dwindle
and die. Thus the tendency of all reefs must be to grow
seawards, and to increase in breadth. Perhaps their
breadth may tell us roughly how old they are. But
there is another possibility to be taken into consideration,
which is that while the polyps are building the sea
bottom or island foundation may be slowly sinking. In that
case it is quite likely that the coral builders might just
keep pace with the subsiding foundations of their home,
and build up a great thickness of coral rock during the
countless years of change.</p>
<p>Sir Archibald Geikie has called attention to the swiftness
with which the structure of the coral polyp's skeleton
is effaced from the foundation and a compact mass of
rock put in its place. The sea-water's chemical and
dissolving action, and the vast amount of mud and sand
produced by the breakers are chiefly responsible for this.
As the rock is being formed it is always being cemented.
On the portion of a reef laid dry at low water, the coral
rock looks in many places as solid and old as some of
the ancient white limestones and marbles of the land.
In pools where a current of water keeps the grains of
coral sand in motion, each grain may be seen to be
rounded. This is because on each particle of coral the
dissolved carbonate of lime in the water is always being
deposited (like the sediment in the bottom of a kettle).
<span class="pagenum" id="Page_66">-66-</span>
A mass of these rounded or egg-like grains all
gathered together in a lump is called <i>oolite</i>, from
the Greek word "oon" (Latin "ovum"), an egg. In
many limestones, now forming parts of agricultural
land, this <i>oolitic</i> structure is strikingly shown, and
there can be no doubt that in such cases it was produced
just as now coral reefs are being formed before
our eyes. In the coral tracts of the Pacific Ocean there
are nearly three hundred coral islands, besides extensive
reefs round volcanic islands. Others occur in the
Indian Ocean. Coral reefs abound in the West Indian
seas, where in many of the islands they have been upraised
into dry land—in Cuba to a height of 1100 feet
above the sea-level. The Great Barrier Reef that fronts
the north-eastern coast of Australia is 1250 miles long
and from ten to ninety miles broad.</p>
<p>It will thus be seen that, apart from any other consideration,
the animals of past ages leave permanent
records of their existence merely by the accumulation
of their dead bodies. Nevertheless, alike on land and
on sea, the proportions of organic remains thus sealed
and preserved is only a small part of the total population
of plants and animals living at any given time.</p>
<hr class="chap x-ebookmaker-drop" />
<p><span class="pagenum" id="Page_67">-67-</span></p>
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