[Illustration: THE ROCKS TELLING THEIR STORY.]
Not long ago I saw some men at work in a stone quarry on Second Avenue,
at the corner of Seventieth Street, New York. In this part of the city
there are many empty lots not yet built upon. These vacant squares are
in some places covered with great masses of rough rocks, that must be
cleared away before the houses can be built. So it happens there are
stone quarries right in the midst of the city. In talking to you about
the sea, you may remember I told you the world is like a great
picture-book. Here is one of the leaves lying wide open, where we may
read a strange old story. Those of you who live in New York can go up to
Seventieth Street and see it; but the men are busy tearing it down, and
before you get there, there may be nothing left but a fine row of
cellars or a block of houses. Many of you can not visit New York, so I
carried my camera to the place, and took a photograph of the rocky wall.
The engraver has made a picture from my photograph, and here you can
see it. At the left you can look down Seventieth Street, and see part of
the rocky hill on the next block. On top is an old shanty, a tree or
two, and a tumble-down fence. Directly in front is the solid wall of
stone, just as it has lain there for perhaps tens of thousands of years.
In the foreground are the broken fragments of rock that have been torn
down by the blasts. One of the quarry-men looked up from his work just
as I set up my camera, and got nicely caught in the picture.
You must study these rocks. See how they are split into thin sheets and
layers. The rocky wall is full of horizontal seams. It looks as if made
of thin layers laid one over the other. The middle part of the rock,
that is in the shadow of the overhanging layers, is divided into very
fine layers, so close together it is hard to tell them apart, yet you
can see by the broken edge against the sky that all the rocky pile is in
sheets and layers one above the other.
I carried some of the small pieces home, and rubbed them together over a
sheet of paper, and soon had a small heap of black and white dust. Here
we have two things about these rocks. The picture shows you the rock is
arranged in layers. Rubbing the pieces together showed that it was made
up of fine dust that when wet would resemble mud or wet sand. These
things plainly point to the water. The rock must have come from the sea.
The rain and the frost may have begun the work. The rain wet some old
rocks, and the cold turned the water to ice, and the ice worked its thin
fingers into every crack, and broke off millions of small pieces. The
spring torrents swept this dust into the streams, and these carried it
to the sea that then covered all this part of the country. Perhaps it
was the surf beating on some ancient shore that ground up the rocks; but
of this we can not be so sure as we may be concerning some other rocks
we shall see presently. One thing is pretty plain. The loose dust or mud
was swept hither and thither by the tides and currents. Very likely the
moon arranged all these sheets of stone. The tides rose and fell as the
moon swung round the world. Each tide carried up some of the soft
glittering and silvery mud, and left it on the shore to dry in the sun.
The next tide brought a little more, and laid it over the first sheet.
In this way, for perhaps hundreds of years, the moon bid the sea spread
carpets of mud and soft sand one over the other upon its floor. Under
the shadow of the overhanging part of the rock it seems to be of quite a
different kind. Something happened, and the tides and currents brought a
different kind of material.
In time the soft mud became pressed together into solid rock, and was
lifted above the sea. Perhaps not suddenly, but so slowly that a
thousand years passed before it was all dry. Then terrible days came.
The rock was bent and twisted by strains and heavings as the earth
moved. None of these layers as we see them to-day are level. All are
tilted up toward the northeast. Hot rocks, liquid, like melted lead,
burst up and filled the cracks with new kinds of stone. The old rocks
were frightfully burned, and changed so much that in looking at some of
the pieces we can not be quite sure whether they came from the sea or
not. For this reason they are sometimes called the changed rocks.
However, much of the rock to be found in this part of the city clearly
came from the sea; and perhaps the whole of it, except that which has
been melted, was born in the ocean.
Afterward the pile of rocks was buried deep under solid ice, that ground
and crushed over it as it moved toward the south. To-day you can see
where the ice tore off great pieces, and scratched and polished the low
hills into their present curious shapes.
I have chosen these rocks on Second Avenue because they tell so much.
They show you how to read the great picture-book of the world. How do we
know all these things happened? Because we see such things going on
to-day all about us. The sea, the ice, the wind, the tides, and the rain
are ever at work tearing down and building up. We can see the sea making
sand and mud that will one day be solid rock and dry land. Surely these
things are worth studying, and you must look about for other rocks, and
try to read their story.
Everywhere in New York city, and in many other Eastern cities, you will
see a rock that you may be very sure came from the sea. A smooth and
beautiful stone that is like a story-book telling of old beaches where
the surf beat with terrible fury in great storms, where the tides kept
time with the moon, and of long summer days when the sea was smooth, and
gentle waves fell on the white sand glistening in the sun. This is the
brown stone used in building houses. It is a real sandstone.
Upon the beach you saw the sand arranged in wavy lines and curves by the
water. Each creamy wave that ran up the beach left a trace showing just
how far it went. The smaller and lighter particles of sand swept along
by the water were dropped just at the place where the water stopped for
an instant before it turned back. As the wave retreated, you remember
the larger grains of sand were to be seen sorted out along the lower
edge of the beach.
Look at these blocks of sandstone. Here are the same markings. Look
carefully and you will soon find a piece where the sand is arranged in
horizontal layers just as the water left it. Perhaps you can count a
hundred layers in a single piece of stone. Some will be thick, and full
of large grains of sand. There must have been a high tide that day, or
perhaps there was a bad storm. Some of them will be thin, and of about
the same thickness for several inches. It must have been pleasant
weather then, when the sea was smooth, and each tide brought up about as
much sand one day as another.
The masons in getting out the stone from the quarry cut across the
layers in every direction, so that these marks are not everywhere
equally plain. Yet with a little search you can soon find a perfect
picture of that old, old beach. Each piece bears the finger-marks of the
sea, the tracings of the moon and tides, the very handwriting of the
waves. Afterward the white sand was stained with iron rust. The water
bearing the iron left it mixed with the sand, and when it became dry,
and was lifted above the water, the iron bound all the sand firmly
together into this beautiful red sandstone, this story-book of the sea.
[Illustration: THE CAPTURED MOUSE.]