Wonders of Earth, Sea and Sky | Page 9

whenever
that land has been under the sea; and this appears to have been the case,
at one or another past age, with the greater part of our present
continents. These fossil remains of sea-animals are discovered in all
quarters of the world, not only on the seashore but also far inland, not
only deep down underground but also high up on the tops of lofty
mountains--a plain proof that over the summits of those mountains the
ocean must once have rolled, and this not for a brief space only, but
through long periods of time. And not on the mountain-summit only are
these fossils known to abound, but sometimes in layer below layer of
the mountain, from top to bottom, through thousands of feet of rock.
[Illustration: FOSSIL SHELLS.]
This may well seem puzzling at first sight. Fossils of sea-creatures on a
mountain-top are startling enough; yet hardly so startling as the thought
of fossils inside that mountain. How could they have found their way
thither?
The difficulty soon vanishes, if once we clearly understand that all
these thousands of feet of rock were built up slowly, layer after layer,
when portions of the land lay deep under the sea. Thus each separate
layer of mud or sand or other material became in its turn the top layer,
and was for the time the floor of the ocean, until further droppings of
material out of the waters made a fresh layer, covering up the one

below.
While each layer was thus in succession the top layer of the building,
and at the same time the floor of the ocean, animals lived and died in
the ocean, and their remains sank to the bottom, resting upon the
sediment floor. Thousands of such dead remains disappeared,
crumbling into fine dust and mingling with the waters, but here and
there one was caught captive by the half-liquid mud, and was quickly
covered and preserved from decay. And still the building went on, and
still layer after layer was placed, till many fossils lay deep down
beneath the later-formed layers; and when at length, by slow or quick
upheaval of the ground, this sea-bottom became a mountain, the little
fossils were buried within the body of that mountain. So wondrously
the matter appears to have come about.
* * * * *
Another difficulty with respect to the stratified rocks has to be thought
of. All these layers or deposits of gravel, sand, or earth, on the floor of
the ocean, would naturally be horizontal--that is, would lie flat, one
upon another. In places the ocean-floor might slant, or a crevice or
valley or ridge might break the smoothness of the deposit. But though
the layers might partake of the slant, though the valley might have to be
filled, though the ridge might have to be surmounted, still the general
tendency of the waves would be to level the dropping deposits into flat
layers.
Then how is it that when we examine the strata of rocks in our
neighborhood, wherever that neighborhood may be, we do not find
them so arranged? Here, it is true, the lines for a space are nearly
horizontal, but there, a little way farther on, they are perpendicular;
here they are bent, and there curved; here they are slanting, and there
crushed and broken.
This only bears out what has been already said about the Book of
Geology. It has been bent and disturbed, crushed and broken.
Great powers have been at work in this crust of our earth. Continents
have been raised, mountains have been upheaved, vast masses of rock
have been scattered into fragments. Here or there we may find the
layers arranged as they were first laid down; but far more often we
discover signs of later disturbance, either slow or sudden, varying from
a mere quiet tilting to a violent overturn.

[Illustration: EXAMPLE OF DISTURBANCE OF THE EARTH'S
LAYERS.]
So the Book of Geology is a torn and disorganized volume, not easy to
read.
Yet, on the other hand, these very changes which have taken place are a
help to the geologist.
It may seem at first sight as if we should have an easier task, if the
strata were all left lying just as they were first formed, in smooth level
layers, one above another. But if it were so, we could know very little
about the lower layers.
We might indeed feel sure, as we do now, that the lowest layers were
the oldest and the top layers the newest, and that any fossils found in
the lower layers must belong to an age farther back than any fossils
found in the upper layers.
So much would be clear. And we might dig also and burrow a little
way down, through a few different