Grant County herald. [volume] (Lancaster, Wis.) 1850-1968, 1890-10-02
ABOUT PEBBLES.
How the Bits of Rock From which They
are Made are shaped.

How the Bits of Rock From which They
are Made are shaped.
Is there a more common, everyday
object in the world than pebble? How
can one find any thing to say about
that? Well, one can try, anyhow.
In the first place. it is well to know
Just what we are talking about What
is a pebble? A rounded bit of rock.
How did it getsit shape? Why-but
hello! we are on the track of story
already.
Have you ever been in quarry, or
noticed where street had been cut
through a mass of rock, as often hap
pens in the upper part of New York
City? You have? Very we'll, did you
not notice that the rock in the walls of
the quarry or in the exposed face of the
street cutting was full of cracks and
seams? Yes. Now let me tell you some
other things you saw, or might have
seen, If you were observant.
These cracks and seams ran in two
directions, so as to cross each other. In
some kinds of soft rocks, like sand
stones and States they are principally
strata, with only few upright cracks.
But the harder kinds, such as granite,
and the tough mica-schist which under
lies New York, and whitish, shining
rocks made up largely of coarse quartz
crystals, have cracks all through them
in all sorts of directions.
Some of these seams are quite large
and open, and you will often notice
water oozing out and trickling down to
the bottom of the quarry. Other
cracks are so fine you can not slide your
knife-blade into them, yet here, too,
dampness will appear. You can easily
believe, therefore, my statement that
Mater peEetrateS far into the center of
masses of rocks, and it is the escape of
this water into larger channels, which
lead it to the surface, that forms springs
and gradually fills with water mines,
quarries and deep wells.
But what has this to do with pebbles
you ask? Wait moment and you will
see.
What is true of quarries and the rock
exposed in street or railway cuttings is
true of the cliffs which face the sea or
like the face of a quarry, are only the
exposed edges of the great mass of rock
elsewhere covered with earth; mass
or hill of rock, similarly, is only the
part above ground of the mass under
meath. And not only these cliffs and
rock-hills but the masses underneath.
are all of fine. intersecting cracks, more
or less filled with moisture.
Now, when winter comes, the water
that has filtered into the cracks near
the surface will freeze solid. You know
what happens when water freezes in
confined space-it bursts the prison.
Fill bottle chock full of water and
leave it out over cold winter night.
or put it into an ice-cream freezer,
and see how quickly the bottle will
break. Just the same thing happens
when the water freezes in crevice in
the rocks 1t swells and prizes off every
piece which can possibly be moved. One
of those pieces, thus pried off, may be
the beginning of a pebble.
There are various other ways, how
ever, in which rocks split to pieces
Sometimes the dampness, working its
way into the crevices, will rust the rock
and eat tiny cracks into large crevices,
and so turn what was once solid cliff
into heap of loose and topping stones
ready to tumble headlong the first time
ligh Jning stroke, or little landslide,
or something else jars the earth enough
to give them start The action of
MONDAY heat and midnight cold, by
causing rocks to swell and shrink alter
nately, helps to separate them, until
piece-by piece the face and top of the
crags fall off. One or the other or all
of these forces are at work all the time.
so that wherever you see cliff there
you will find slope of fallen fragments
at its base.
II the fragments are large, they tend
to break into smaller ones, and still
smaller, in the same way. If this cliff
is inland, the stones will keep their
angular edges, and should you dig down
hundreds of years afterward you would
find their shape the same; but il the
cliff is beside stream, or ffonts the
waves, very different thing happens.
As fast as the pieces roll into the river
they are caught by the current and
moved about with more or less vio-
lence. If the river is very rapid, they
may be rolled over and over and pushed
and crowded along till they find rest
ing-place in some nook from which the
current can not easily dislodge them.
This knocks their corners of-frst the
Most prominent, then the less. and SO