their action is the greatest on those which are landward. There are
other wreckers of the coast; for the heat of the sun, the winter’s
frost, the rain, and the chemical action of the air, one and all
crumble and break off pieces of rock or earth. These fall on to the
tidal shore, and are rolled here and there, and up and down, to be
turned into mud, sand, and pebbles. The cliffs and bold headlands are
worn year by year, and during centuries they lose much, and retire
landward. Needles and “no man’s lands” stand out on the shore, or out
at sea, testifying to the former extension of the land; and shore
exists where there was once high solid rock. The shore consists
of the worn surface of the old land, rock, or earth, and this is
usually hidden by stone or stuff which has fallen from the cliffs,
and by sand, or mud, or pebble and stone, which the tide has swept
along. But often the jagged or rounded remains of the former rock
project out of the sand, mud, and stone on the shore, and they may
be bare, or covered with sea-weed. In other spots, the hard rock is
hollowed out into places which let the water stand in them like so
many puddles, pools, and ponds, when the tide has gone down. These
are often crowded with marine plants and animals of the shore. The
rolling stones, the wash of the tide, and the rush and drawback of
the waves, are ever wearing off the surface of the shore and grooving
it, or planing it flat, and in some places where the stones do not
collect, this is very evident; but where they form great masses of
pebbles or shingle, it can not be readily seen.
There are many shores around Great Britain, where the rock is hard,
which are rarely covered with pebbles, bowlders, and sand; and the
sea-weed grows on them and protects them against the sea. But usually
the rock is only exposed here and there, and the stones which collect
and cover much of it come from a distance, and are on the move at
every tide. In some places, where the coast is composed of clay or
soft sandstone, the shore is muddy, soft, and may be uncovered or
covered by stones.
The wear of the sea is but little seen in such places as this, and
still less so where the coast is low and flat, and the shore is very
extensive and the water is shallow for a long distance. In fact,
on many of these flat shores, instead of erosion taking place, the
sea is adding to the land by depositing. This is particularly the
case at the entrance of great, and of many small rivers. Their mud
collects in the shallows at their mouths, and is added to by sand
and shingle, so that land grows seaward, instead of the reverse. The
seashore is then, usually, uninviting and often consists of large
mud flats. Again, in some localities, where much sand collects on
the surface of the rock forming the seashore, it may be “quick” in
many places. The rising tide gets under the sand, which suddenly
becomes like so much sand and water, and the falling tide leaves it
hard for a while. The ordinary condition of a sandy shore is either
that of a number of very slightly rounded stretches of sand, with
drainage-streams between them, or it is pretty hard, readily dug
into, and marked on the surface by ripples. The ripple-mark on sand
always strikes the observer; it represents little ripple-like waves,
wonderfully regular, and each has a ridge and a valley. They are very
lasting, but disappear on the slightest movement of the wet sand as
the tide comes in. These little ridges and valleys are not found
when the water covers the sand at a considerable depth, but they are
especially seen between high and low spring-tide limit. Such marks
can be made, artificially, with sand, for instance, on the bottom
of a large basin. If some sand is placed on the bottom, and water
be poured in, and the edge of the basin be pushed, a to-and-fro
movement of the water will occur, and it will be continued down to
the sand. As the motion ceases, the sand will be seen to collect
in ridges, side by side, and they will be perfect when the motion
stops. Motion of the sea-water in one direction over soft sand will
not produce ripple-mark well, but a slight to-and-fro movement will
do it to perfection. Infinitely more wonderful than these ripples
are the pebble beaches, for they often extend for many miles, and
have a very considerable thickness. Worn, in the first instance,
from distant rocks, born of huge bowlders, which the mighty waves
laden with rolling stones have broken down, the pebble is formed
by rolling against others, and the result of its wear and tear is
carried off in the form of sand. They travel miles and miles along
the coast with the tide, and therefore it is very common to find one
kind of rock forming the coast-line, and the shore close by having
pebbles made up of stone which is not known to be near at hand. Thus,
on the coast of South Devon, the red rocks form the coast-line;
they are sandy, and are covered in some places by a beautiful green
vegetation. The sea is often of the brightest blue, or gray, when the
sky is not much tinted with color. But the sea covering the shore at
high tide looks whitish, and this is produced by the white and light
slate-colored pebbles which reach up close to the red rocks. They are
not made up of red sand; on the contrary, they are of gray and bluish
limestone, and come from rocks which are situated miles to the west.
Further east, the Chesil Bank is seen, and it is an enormous shore
of pebbles, which have been carried along the coast and have found
an uncertain resting-place there. Every tide makes more sand out of
the hardest pebbles, as they knock one against the other and wear
away, and the sand already made scrubs them as it is hurried hither
and thither by the waves. In some places where the sea is giving up
rather than taking off land, the sand which is cast up may be the
result of the wear of distant pebble-making, or it may be composed of
myriads of broken tiny shells which once lived in shallow water.
It has been already stated that the sea is encroaching on the land
in some parts of England, and that it does not do so in others,
while it appears to be giving place to land elsewhere. In the first
instance, the seashore must grow, as it were, must increase landward,
and it really does so at different rates, in different parts of the
country. In some parts of the coast a yard is lost every year and the
sea comes in on the land so much the more. But all the space once
occupied by cliff and rock is soon worn by the sea and is covered
gradually by the tide, and after years have elapsed this _fore-shore_
is deepened seaward by the rolling stone and rushing waves, so that
the visible beach or shore diminishes in size, unless a corresponding
landward extension takes place. Although the cliffs and rocks fall,
and their remains are swept away from the level of the shore, by
currents, tides, and waves; yet, as has already been noticed, much
of the ruined surface, leveled down as it has been, is covered up by
relics of their wear and tear or by stone brought from a distance. It
is only after some severe gale of wind, accompanied by a very high
tide, that these stones and covering-up relics are swept away and the
old rock-surface comes in view. All these matters are of importance,
for the living creatures of the seashore depend upon the state of
things, in each of the zones, for their ability to exist and flourish.
Where the coast has been low and the sea has gradually encroached,
the remains of stumps of trees are often exposed after a gale. Then
what is called part of a submarine forest is opened to the sight.
There are many of them around England and especially on the coast of
Norfolk and Essex, on the east; in many places on the south coast
as far as Torbay; and on the west they are found in the Bristol
Channel, and about Holyhead and the river Mersey. Sometimes it
appears that the sunken forest has not been altogether produced by
the encroachment of the sea on the land, and that sinking of the
coast, or slipping of part of it, has caused the event. When the sea
comes in on the land, it wears everything before it, and any forest
land would in most instances be completely wrecked and the roots of
the great trees would be worn and torn out of the soft earth and
carried off to sea by the waves, tides, and currents. On looking at
some smaller forests which are laid bare at very low tides, it is
found that they consist of stumps of trees of great size, whose roots
are still in the clay in which they grew, and a quantity of mud and
sand is between the stumps and protects them from the usual action of
water on submerged land. It appears that some movement of the earth’s
crust had caused the coast to sink down, and then the sea invaded
without wearing off the land. The trees were ruined by the sea-water,
and broken off, and the mud, sand, and stone collected around the
stumps.
It is not uncommon to see collections of stone and shells high up on
the face of a rock or cliff, and when they are carefully examined
they are found to resemble a bit of a shore or a piece of the beach,
hoisted up many feet above the present line of the waves and tides.
They are called raised beaches, and they were formed by an upheaval
of part of the coast with its shore during movements in the crust of
the globe. There was a shore and a cliff, as there may be now, and
the whole was pushed up some twenty, thirty, or more than a hundred
feet beyond the reach of the highest tides and waves. In years past
the waves broke upon the cliff beneath the upraised portion, and wore
it away bit by bit; and then the air and sun acted with the rain in
wearing it, and now only a portion remains.
Every coast-line is subject to these sinkings-down and upheavals,
and of course a seashore is produced rapidly, and is made broad and
shallow during the first kind of occurrence, and is stopped and has
to be formed afresh during the last. As these remarkable movements
of the outside of the globe are not universal, and affect some parts
of a coast more than others, they will tend to give great variety
to the seashores of a country. Together with the varying action of
the tides, waves, and currents upon cliffs and rocks of different
stones and earths, and of many hardnesses, these movements have made
the shores of Great Britain very curiously varied in their size and
character.
It must be remembered that as new shores are formed, or old ones
are extended, the zones are kept within their bounds, and that as
one zone creeps in on the land, those to the seaward move up also;
so that where there was once a between-tide zone there may now be
deep water. This change in the position of zones is very important;
for certain animals and plants of the shore only live in certain
zones, and their increase or decrease in numbers depends upon the
corresponding state of their special locality.
III.--THE ATMOSPHERE
THE OCEAN OF AIR
--AGNES GIBERNE
Our earth has many robes. Closely-fitting garments come first, of
brown soil or gray rock and green grass, with wide liquid underskirts
of deep blue filling up the spaces between. Outside these are
coverings more wonderful still; fragile, yet strong, transparent,
almost invisible, folded around layer upon layer, or, as one
might say, veil upon veil, each more gossamer-like than the last.
These form earth’s surrounding atmosphere--a substance pervading
everything, found everywhere. One may travel from the equator to the
poles, one may journey by sea or by land, one may soar high in a
balloon or descend deep into a mine, but one can never in this world
go to a place where the atmosphere is not.
A substance--for air can be felt; air has weight; air occupies space;
air, like any other body, can be made hot or cold; air is composed of
particles of substantial matter. Air has a faint bluish tint, which
on a sunshiny day becomes in the sky a very pure and deep blue. This
tint is not believed to be the natural color of the atmosphere. Were
it so, the air would merely act the part of a blue pane of glass,
rendering the white light of the sun blue as it reaches our eyes;
but the blue of the atmosphere is known to be a reflected blue.
If reflected, there must be something in the atmosphere to reflect
it; and such indeed is the case. Perfectly pure air would doubtless
be without color, but perfectly pure air we do not find. The whole
atmosphere is full of multitudinous minute specks, so small as to be
in themselves invisible, so light as to remain aloft. To the presence
of these the blue tint is believed to be due. They scatter the light
of the sun, and produce the blue effect.
A beam of strong white light, caused to pass through a liquid which
contains a large supply of minute floating particles, is affected
by them in a like manner. The short blue waves are more abundantly
reflected than the long red waves; and so the water seems to be blue.
This explanation serves for the deep-blue color of the ocean, as well
as for the blue of the atmosphere.
The whole earth is surrounded by this marvelous air-ocean; an
ocean of gaseous matter, at least one hundred times as deep as the
water-ocean. At the bottom of the gaseous ocean we small human
creatures crawl about, commonly on flat lower levels--the ocean
bottom, in fact. Sometimes, with much toil and trouble, we climb the
little ridges and mounds called “mountains”; little compared with the
depth of the atmosphere, though not little compared with ourselves.
The highest mountain-peaks of even the vast Himalayas lie low down
near the bottom of the ocean of air.
But the very extent of the ocean of air adds to our difficulty
in studying its nature. All observations that we can make must be
limited by the state of the atmosphere just around ourselves. We
can never get out of and beyond the atmosphere, so as to see it as
a whole. At any time a slight local fog is enough to put a stop
altogether to such observations, beyond the unpleasant experience of
the fog itself.
It used to be supposed that the atmosphere reached only to a height
of about fifty miles above earth’s surface. Of late years the opinion
has gained ground that the atmosphere reaches to a height certainly
of two or three hundred miles, probably of four or five hundred,
possibly a good deal more. But the condition of the air far above is
different from that of the air in lower levels, where we live and
breathe. The higher we ascend, the more thin or “rare” becomes the
air. A less quantity fills a certain space up there than down here.
The particles float further apart one from another.
This difference in the density of the air is chiefly due to
attraction. Each separate air-particle is drawn steadily earthward by
the force of gravitation, and that force is stronger on the surface
of earth than at a distance. The closer to earth, the heavier the
pull; the further from earth, the less the pull. Besides the actual
attraction of the earth drawing the air-particles downward, there is
the great weight of the whole atmosphere above, caused by the same
attraction. Miles and miles of air overhead press mightily downward,
packing tightly together the lower layers of air near to earth’s
surface.
Without this pressure of the overlying atmosphere, the air down
here would not be nearly so dense as it is; and, indeed, would not
be fitted to support life. A man ascending a mountain or rising in a
balloon leaves heavy layers of air below, and has an ever-lightening
weight above, so that the atmosphere around him becomes constantly
more thin, more difficult to breathe.
In the beginning of the last century Humboldt made a vigorous attempt
to scale Chimborazo, one of the loftiest of the Andes. He and his
party suffered severely from sickness, giddiness, and difficulty in
breathing, and the attempt proved a failure. Not till over seventy
years later was the ascent actually accomplished by Mr. Whymper.
Carried upward passively in a balloon, without effort, men have risen
higher than the highest mountains. Mr. Coxwell and Mr. Glaisher in
their celebrated aerial voyage of 1862 are believed to have mounted
seven miles above the sea. No little peril and suffering were
involved, alike from the extreme thinness of the air, and from the
bitter cold.
The voyagers suffered from severe “sea-sickness,” though not from
bleeding of the nose or singing in the ears, popularly expected on
such occasions. They had enough to bear without these additions.
Mr. Glaisher held manfully to his task, observing and noting down
the state of the atmosphere minute by minute, despite sickness,
brain-pressure, violent headache, and a pulse at 108 per minute, all
due to the rarity of the air.
In those lofty regions of the air-ocean no living creatures exist.
The voyagers passed through boundless silent solitudes--silent
except for the hurried beating of their own hearts, the sound of
their own panting breath, the sharp ticking of their watches, and the
“clang of the valve door.”
On leaving earth the thermometer stood at 59°. Soon afterward the
balloon passed through masses of cloud, thousands of feet in depth,
then came out into dazzling sunshine, with deep-blue sky above and
countless mountain masses of billowy cloud below.
As they rose, they released at intervals a captive pigeon. One set
free at a height of nearly five miles “fell downward like a stone.”
Of two others taken higher, one died of the cold and the other
was stupefied. When they reached five miles above the sea, the
temperature was below zero.
Still upward, further upward, rose the resolute pair. Then blinding
darkness and insensibility seized Mr. Glaisher. Had he been alone, he
could never have revived. With no one to open the valve, the balloon
must have carried him onward into yet higher and deathlier regions,
where for lack of air he would have perished. Even then Mr. Coxwell
did not at once give in; but he was strictly on the watch. At the
seven miles’ level, a tremendous height, he too felt signs of failing
consciousness. In a few minutes more all would have been over with
them both, and at last he yielded. It was indeed time that he should.
His hands were powerless to act, but he seized the valve rope in his
teeth and pulled. The gas rushed out; the balloon steadily sank. Both
lives were saved, and a mighty feat had been accomplished.
Yes, a mighty feat, and a tremendous height--in consideration of
human powers! Seven miles high would seem to be the outside limit at
which animals generally can exist for even a short time. Birds may
be to some extent an exception. Certain birds are believed to soar
occasionally two or three miles higher still.
But what are seven miles--what are even ten miles--compared with the
four or five hundred miles of atmosphere-depth? With all our utmost
efforts, we and the birds still find ourselves only able to creep and
flutter on or near the floor of the ocean of air.
What earth would be without her surrounding ocean of air, we can
scarcely imagine. The atmosphere plays so extraordinary and essential
a part in all around, that to picture its entire absence is not easy.
We see faintly on the moon something of what an airless world must
be. Yet since we only “see” from a distance of two hundred and forty
thousand miles, that does not mean much. Imagination has to come in,
and imagination is apt to play us curious tricks when running after
affairs which lie outside the range of human experience.
Without air, man and beast can not breathe. Without air, plants and
trees can not grow. Without air, life as we know it--the lower animal
life common to man and beast--is a thing impossible. Without air, our
world would be, as we suppose the moon to be, a world of lifelessness.
Air is earth’s outer robe, “for use and for beauty”--for use in modes
uncountable; for beauty, not so much in itself as in the softening,
the diffusing, the controlling effects of its presence. Air is a
mighty ocean, in which all things living must dwell. Even the living
things of the sea are not exceptions to this rule, for water itself
is pervaded by air. A man, going into and under water, does not get
beyond the touch of air; only, not being provided, like fishes,
with breathing gills, he can not make use of what is there--he can
not separate the air from the water, and so keep himself alive by
breathing it.
Some animals living in the water-ocean are as dependent upon the
air-ocean as man himself for “the breath of life.” Whales are a
remarkable example of this. They are not fishes, though often
mistakenly called so, but belong to the same “family” of creatures as
men and land-quadrupeds generally. A whale is warm-blooded, has no
gills, and breathes atmospheric air, coming to the surface for it.
A whale kept forcibly for a long while under water would be drowned
exactly as a man would be. If a whale is thrown upon the shore, it
does not die of suffocation, but of inanition. A fish’s gills are
no more fitted to breathe air in bulk than a man’s lungs are fitted
to breathe air diffused in minute particles through water. The fish
out of water is suffocated by getting air too rapidly: the man under
water by exactly the reverse. A whale breathes like a man, and on
land it simply starves fast from lack of the incessant food required
by such a huge carcass.
There is a difference certainly between man and whale in the matter
of breathing. A man has to take in fresh supplies of air constantly,
and if he is beyond reach of air for more than a few minutes he dies.
A whale comes to the surface for about ten minutes, spouting out
enormous supplies of used-up air and taking in enormous supplies of
fresh air, after which it can remain under water for half an hour or
more: some say an hour. Then a fresh bout of noisy breathing becomes
an absolute necessity. This, however, is merely a matter of internal
arrangement. The whale has an immense reservoir of blood, which,
being thoroughly purified by the air during ten minutes of vigorous
breathing, serves slowly to supply the creature’s requirements while
below. But the need for air, and the effect of that air upon the
blood, are much the same in man and whale.
Small creatures, as well as big ones, spending much time under water,
and yet breathing air, have to come regularly to the surface.
If our world had no ocean of air, there could be on earth no men, no
quadrupeds, no whales or fishes, no birds or insects, no forms of
life.
Like the ocean of water, the ocean of air knows no repose or
stagnation. What we call stillness on the most sultry of summer days
does not mean absolute stillness. Though not enough wind may stir
to lift a feather, yet the air is in ceaseless motion, to and fro,
hither and thither. The whole atmosphere is a vast and complicated
system of air-currents, and each lesser portion of air has its own
lesser circulation. You can not lift your hand without causing a tiny
breeze; you can not turn a wheel without making a minute whirlwind;
and every separate air-movement draws other movements in its train.
There is water enough on earth for all needed purposes; but we
should find ourselves in direful straits if the whole water-carrying
from lakes and rivers for men and animals had to be performed by
human agencies.
Far from this, a mighty apparatus is provided. The scanty aid that
man can give only shows how little he is capable of. The entire
atmosphere is a tremendous pumping engine, an enormous watering
machine, always at work; always receiving supplies of liquid from the
ocean, from seas, lakes, rivers; always showering this water down
again upon the land, as needful drink for plants and animals, as
needful cleansing for all things.
Air, the great carrier of water, in its wonderful strength and
restlessness, bears vast layers of cloud to and fro, wafts away
superfluous damp, drenches the dry and thirsty earth, fills ponds and
lakes, feeds--nay, actually makes--the rivers, never flags in its
ceaseless energy. If clouds hang low or fogs arise, we are glad of
the moving air which sweeps them elsewhere. If the soil is caked and
plants droop, we are glad of the moving air which brings rain. Thus
our wants are supplied, and the wide water circulation of earth is
carried on. Without circulation, without motion, stir, change, there
can not be life. Stagnation must mean death. Our earth, without her
ocean of moving air, would be a world of death.