OLD OCEAN AS A BUILDER
“Grain by grain His Hand
Numbers the unmeasurable sand.”--C. G. ROSSETTI.
“... The ever changing strand
Of shifting and unstable sand
Which wastes beneath the steady chime
And beating of the waves.”--WHITTIER.
As a vast Cathedral is made of separate blocks of stone, laid one
upon another and cemented together, so a stratified rock is formed of
tiny particles of substance, placed one over another and pressed into
solidity.
Let us scoop up a little sand from the sea-shore, and look at it under
a magnifying-glass.
We shall find a number of loose yellow grains, not all alike in
shape, but all somewhat rounded. Most of them are characterised by a
glittering hardness, and probably some are transparent.
For the most part these grains are of a substance called _quartz_,
which may be almost any colour from white to black. Some beautiful
forms of it are known to us, such as amethyst, agate, and jasper. But
we have now to do with the humbler relatives of those aristocratic
gems; with the more commonplace kinds of quartz, such as sandstone.
Sandstone rock is chiefly made of grains of sand, firmly compacted
together. An especial interest belongs to the rounded shape of these
little grains. Like many voiceless things in the world of inanimate
Nature, it tells its own tale, if only we will pause to hear.
Why should grains of sand be rounded? Why not square, or pointed, or
angular?
That is just what they were, not very long ago. Each sand-speck,
when first detached from rock or stone, had its angles and corners.
But these have been gradually rubbed away; and by the very same
process which, in the course of years, rubs away angularities and
eccentricities from the characters of human beings.
The work has been done through contact with its neighbours--not by an
occasional rub, but by steady friction, long continued. Each grain of
sand, rubbing against and being rubbed by its companion-grains, has
been rounded, smoothed, polished, till it has grown into the finished
specimen, without any obtrusive points or disagreeable angles remaining.
An unpleasant discipline, perhaps; yet, in the case of sand-grains and
also of human beings, worth undergoing for the sake of results.
Looked upon from a geological point of view, this shape of the
sand-grains means merely the wearing and wasting away of substance,
with no pretty explanation attached, though with a very definite
underlying story of their past history.
“No workman ever manufactured a half-worn article, and the stones
were all worn.” So wrote Hugh Miller when describing his first boyish
experience of toil in a Scotch quarry twenty years earlier. Boy as he
then was, his keen eyes noted the stones, “rounded and water-worn,
as if they had been tossed in the sea or in the bed of a river for
hundreds of years.” Boy as he was, he knew that stones, broken off from
larger stones or rocks, have at first their irregular shapes, their
corners and jagged points, which can only be worked into smoothness
by the action of water. Boy as he was, he realised that these quarry
inland stones had once been rubbed and shaped by ocean-waves.
He made a mistake in his assertion. Some workmen do manufacture
articles, not indeed really half-worn, but with the look of being
half-worn though actually new, for mercantile purposes--to pass off
the new, as if it were old, when the old has greater value. But it may
safely and with confidence be declared that the Divine Architect of
Earth and Heaven never so puts forth His mighty power. When we see in
Nature a thing _worn_ in appearance we know that it has been worn in
reality.
In his first day of quarry work Hugh Miller saw more than this. He
noted surfaces of sandstone rock, laid bare by blasting, all “ridged
and furrowed, like a bank of sand that had been left by the tide an
hour before.” He had seen the latter hundreds of times when sailing
over shallows near the shore. But here the ridges and furrows were
petrified, changeless, and on dry land, where no ocean-waves could
reach. No wonder he was puzzled.
Such ripple-marked sandstone is far from uncommon. It gives a perfect
reproduction of the little sand-ripples or rounded ridges and hollows,
often to be found on a sandy shore, either visible through a thin layer
of water or left bare after the tide goes down. And it shows us how the
sandstone rock must originally have been put together, under water.
Soft undulations were made in the wet sand by one high tide, becoming
in a measure hardened before the next high tide, and so keeping their
shapes, while a fresh supply of sand was dropped upon them, partaking
of the same outlines.
As time passed, more and more sand would be thus deposited, the ground
probably sinking and the weight of sand increasing, until the lower
layers had stiffened into rock. In after days a slow upheaval of the
ground came about, and where ocean waters had flowed would be dry land.
By-and-by--who can say how long after?--the ripple-marked slabs of
sandstone, petrified memorials of the past, would be found; perhaps far
inland, if the country had risen much; perhaps in a quarry by a young
Scotch working-lad, to be marvelled over as a specimen of old Ocean’s
bygone work.
Another such token of the past is found in hardened raindrop traces,
impressed on solid sandstone.
The rain fell on a soft sandy shore, making tiny holes in the sand,
with splashed-up ridges round each small hole. Have we not all seen
this? If not, we might have used our eyes better. Before the coming
in of the next tide the surface hardened, like the sand-ridges already
described, and so, being covered over by new layers of sand and
gradually transformed into rock, it was later uplifted above the sea,
and the holes have lasted intact until now.
It may be objected that the time between one high tide and another is
hardly long enough for any such hardening process--even on the hottest
and driest of summer days.
Then the hardening may have taken place only on that slender belt of
sand, which is covered for a day or two by the spring tides, and is not
again reached by ocean-waves for nearly a fortnight.
In earlier chapters it was shown--first, how the Ocean is ever striving
to keep a level surface; and secondly, how the object sought is never
attained to.
Not only are the waters in ceaseless motion, heaving to and fro under
the influence of every passing breeze, borne hither and thither by
mighty streams, disturbed by innumerable storms. But also the powerful
attraction of the land, particularly of great mountain ranges, lifts
the sea-surface in some regions hundreds of feet higher than in others.
So that a ship, passing from the neighbourhood of a mountainous coast
to mid-ocean, may be actually sailing or steaming downhill, actually
descending a vast gentle watery slope.
Another question as to Ocean’s level has much exercised the minds of
men.
Throughout the world, remains of sea-creatures in countless multitudes
are found embedded in the substance of water-built rocks: sometimes the
very rocks being made up of them. This, not only on the tops of lesser
hills, but at the summits of mountains eight thousand feet high, twelve
thousand feet high, sixteen or eighteen thousand feet high.
Very ancient remains they often are, certainly many tens of thousands
of years old. But whatever their age may be, they echo and add to the
story which is told by the rocks themselves.
From the rocks we learn that, once upon a time, long ago, they were put
together, scrap by scrap, under water, not upon dry land. And from the
fossil remains in those rocks we learn with equal certainty that, once
upon a time, they lay under ocean-waters.
Fossil remains, buried in rocks, are of many kinds.
Not only relics of animals, or of parts of animals, such as teeth
and bones and shells. Not only relics of sea-weeds and other ocean
vegetation. Not merely the actual remains, hardened into stone; but
also the casts or shapes of all such remains, found impressed in the
substance of the rocks. The whole of these various records of the past
must be included under the term “fossils.”
Firmer substances, like shells and bones, have become often transformed
into actual solid stone. But softer living substances have more
frequently passed out of existence, leaving only an impress or _cast_,
which is filled up later by some other substance.
When upon high mountain-tops such fossils are found--the remains
of sea-weeds and sea-creatures embedded in rock--the question must
naturally arise, How could these ocean-inhabitants have found their way
to such a height?
That the sea must once have flowed over them cannot be doubted. But
how did it come about? Were those water-built heights under the sea,
because in those times the land lay lower, or because the sea-surface
stood higher?
That the earth-crust is restless, heaving, disposed to rise and sink,
to crumple into furrows, to fold into ravines and mountain ranges, we
now know. Yet this may not be the whole explanation of sea-shells upon
high summits. It may be also that the surface of the sea itself--the
general level of the ocean--has not been always the same. It too may
have risen and sunk; not once only, but many times.
Between one and two hundred years ago there was a theory that the
sea had as a whole sunk lower, on account of the enormous drying up
of its surface. Of course the surface does dry up very much and very
rapidly. Yet this deficit in ocean-waters being met by equally enormous
down-pourings of rain and gifts of river-water, evaporation will not
serve to account for a lowered ocean-level all over the earth. So the
notion had to be given up; and in later years it was looked upon as
certain that the land must have risen, and that the ocean-level must
have been changeless.
Until recently this was regarded as established; but in the curious
see-saw of scientific theories the pendulum has begun to swing back.
Not all the way. That the land has risen in parts, shaking its skirts
free from ocean-tides, is not doubted. Scientists are, however,
maintaining that while this is true, the other need not be untrue. They
hold that, while land in many places has undoubtedly risen and sunk,
the ocean-surface may have risen and sunk also.
The ocean could not, indeed, like the land have risen or sunk only
in parts. Except where it is forcibly held at a higher level by some
strong force of local attraction, this would be impossible. Yet causes
might exist which should affect the whole ocean-surface.
One such may be mentioned. The rising or sinking of great tracts of
land could not fail to affect the ocean-level.
That it must do so may be easily understood. Let us fill a basin with
water, to within an inch of the brim, and then slowly lower into
the water a ball, or any other solid body. As the ball enters, the
level of the water rises--_must_ rise. Then let us slowly lift the
ball out again; and as it leaves the water, the level of the latter
sinks--_must_ sink.
Precisely the same result would follow upon the rising or sinking of
some great continental mass. When it rises, the ocean contains less
land, and the water-level must go down. When it sinks, the ocean
contains more land, and the water-level must go up.
This question has been long under discussion. For many years, as with
other questions, each side looked upon its own view for the time being
as the only right one. But--as again with many difficult problems--the
fairer and wider view recognises the possibility of truth in both
explanations, and probably in the end both will prove to be in a
measure right.
Many other kinds of rock, as well as sandstone, have been built under
ocean-waters in past ages, constructed of minute particles, piled
together, and hardened. Some sorts, like sandstone, are only or chiefly
mineral; while others are only or chiefly “organic”--that is, are
mainly composed of the remains of “organised” or living beings. About
the latter much has to be said in future chapters.
A very few words in the close of this chapter, as to the classifying of
different kinds of Rocks, may not be amiss.
Ocean-deposits, or Ocean-buildings, are often roughly divided into
three groups.
In “Deep-Sea Deposits” are included all that lie beyond the
Hundred-fathom Line, or a depth of six hundred feet.
In “Shallow-water Deposits” are included all that lie between six
hundred feet deep and low-water mark.
In “Littoral Deposits”--the word coming from the Latin for
“shore”--are included all deposits that lie on shore-lines, between the
highest and the lowest tides.
At first sight the tide-deposits might seem to be but a small matter.
Not so small, really! Earth’s coast-lines reach to something like one
hundred and twenty-five thousand miles in length. Since the medium
breadth of ground affected by tides is about half-a-mile, the whole
tidal area amounts to over sixty thousand square miles.
No mean workshop this, under the auspices of crushing and grinding
billows. On shore-lines building takes place rapidly.
The “Shallow” zone is much more extensive, reaching to some ten
millions of square miles. Its principal deposits are much the same as
those of the tidal zone--muds, sands, gravels, pebbles. In parts of the
Earth they also include volcanic and coral muds.
Greater, far greater, far more widely reaching, are the regions of
“Deep-Sea Deposits,” which cover more than one-half of the whole
surface of our globe.
In those cold and dark and silent workshops, hidden from the eyes of
men, building goes on, very quietly, very slowly, through interminable
ages. In those workshops are deposited divers materials--Red Clay, Red
Mud, Blue Mud, Green Mud, Volcanic Mud, Diatom Ooze, Globigerina Ooze,
and many others, forming Ocean’s carpet.
Almost any of these muds and oozes may occasionally be found in the
second division, but they more generally belong to the “Deep Sea.”