Wonders of Earth, Sea and Sky | Page 7

far
out into the ocean, there dropping quietly the gravel, sand, and earth,
layer upon layer at the bottom of the sea. Thus pulling down and
building up go on ever side by side; and while land is the theatre
oftentimes of decay and loss, ocean is the theatre oftentimes of renewal
and gain.
Did you notice the word "sediment" used a few pages back about the
settlement at the bottom of a medicine-vial?
There is a second name given to the Stratified Rocks, of which the
earth's crust is so largely made up. They are called also Sedimentary
Rocks.
The reason is simply this. The Stratified Rocks of the present day were
once upon a time made up out of the sediment stolen first from land
and then allowed to settle down on the sea-bottom.
Long, long ago, the rivers, the streams, the ocean, were at work, as they
are now, carrying away rock and gravel, sand and earth. Then, as now,
all this material, borne upon the rivers, washed to and fro by the ocean,
settled down at the mouths of rivers or at the bottom of the sea, into a
sediment, one layer forming over another, gradually built up through
long ages. At first it was only a soft, loose, sandy or muddy sediment,

such as you may see on the seashore, or in a mud-bank. But as the
thickness of the sediment increased, the weight of the layers above
gradually pressed the lower layers into firm hard rocks; and still, as the
work of building went on, these layers were, in their turn, made solid
by the increasing weight over them. Certain chemical changes had also
a share in the transformation from soft mud to hard rock, which need
not be here considered.
All this has through thousands of years been going on. The land is
perpetually crumbling away; and fresh land under the sea is being
perpetually built up, from the very same materials which the sea and
the rivers have so mercilessly stolen from continents and islands. This
is the way, if geologists rightly judge, in which a very large part of the
enormous formations of Stratified or Sedimentary Rocks have been
made.
[Illustration: VIEW IN A CANON.]
So far is clear. But now we come to a difficulty.
The Stratified Rocks, of which a very large part of the continents is
made, appear to have been built up slowly, layer upon layer, out of the
gravel, sand, and mud, washed away from the land and dropped on the
shore of the ocean.
[Illustration: SEA CLIFFS SHOWING A SERIES OF STRATIFIED
ROCKS.]
You may see these layers for yourself as you walk out into the country.
Look at the first piece of bluff rock you come near, and observe the
clear pencil-like markings of layer above layer--not often indeed lying
flat, one over another, and this must be explained later, but however
irregularly slanting, still plainly visible. You can examine these lines of
stratification on the nearest cliff, the nearest quarry, the nearest bare
headland, in your neighborhood.
But how can this be? If all these stratified rocks are built on the floor of
the ocean out of material taken from the land, how can we by any
possibility find such rocks upon the land? In the beds of rivers we
might indeed expect to see them, but surely nowhere else save under
ocean waters.
Yet find them we do. Through England, through the two great
world-continents, they abound on every side. Thousands of miles in
unbroken succession are composed of such rocks.

Stand with me near the seashore, and let us look around. Those white
chalk cliffs--they, at least, are not formed of sand or earth. True, and
the lines of stratification are in them very indistinct, if seen at all; yet
they too are built up of sediment of a different kind, dropping upon
ocean's floor. See, however, in the rough sides of yonder bluff the
markings spoken of, fine lines running alongside of one another,
sometimes flat, sometimes bent or slanting, but always giving the
impression of layer piled upon layer. Yet how can one for a moment
suppose that the ocean-waters ever rose so high?
Stay a moment. Look again at yonder white chalk cliff, and observe a
little way below the top a singular band of shingles, squeezed into the
cliff, as it were, with chalk below and earth above.
That is believed to be an old sea-beach. Once upon a time the waters of
the sea are supposed to have washed those shingles, as now they wash
the shore near which we stand, and all the white cliff must have lain
then beneath the ocean.
Geologists were for a long while sorely puzzled to account for these old
sea-beaches, found