The Iowa plain dealer. [volume] (New Oregon, Howard County, Iowa) 1867-1895, 1890-10-16
ABOUT PEBBLES.

Fairies still are lowering.
Elizabeth A. Davis. in Golden Days.
ABOUT PEBBLES.
How tho Bits OF Rock From which They
are Made are Shaped.
Is there q more common, every day
object in the world than pebble? How
can one find any thing to say about
thato Well, one can try. anyhow.
In tho first place. it is we'll to know
Just what We are talking about. What
il pebble? A rounded bit OF rock.
How did it get its shape? Why-but,
already.
Have you ever been in a quarry, or
noticed where street had been cut
through mass Of rock, as often hap
pens in the upper rart Of New York
City? You have? Very well, 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 obscrvant.
These cracks and seams ran in two
directions, SO rs to cross each other. In
some kinds of soft rocks, like sand
stones and states. they are principally
level. dividing the rock into layers, or
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 lon can easily
believe, therefore, my statement that
water pcEetrates 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 a moment and you will
see.
What is true of ouarrics and the rock
exposed in street or railway cuttings is
true of the cliffs which face the sea or
project from q mountain. since these,
like the face OF quarry, are only the
exposed edges OF the great mass of rock
elsewhere covered with earth; a 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, intcrsccting cracks, more
or less filed 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 a bottle chock full of water and
leave it out over cold winter night.
or put it into an icc-crcam freezer.
and see how quickly the bottle will
break. just tho same thing happens
when the water freezes in crevice in
the rocks. 1t swells and prizes of every
piece which can possibly be moved. One
vi tlOSC pItCcS, illus pE4Cu OAs JIG
the beginning Of a pebble.
There are various other ways, how
ever, in which rocks split to pieces.
Sometimes the dampness, working it's
way into the crevices. will rust the rock
and cat tiny cracks into large crevices,
and SO turn what was once q solid cliff
into heap Of loose and topping stones
ready to tumble headlong the first time
a lightning 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 of. One or the other or all
of these forces are at work all the time.
| SO that wherever you see a cliff there
you will find slope Of fallen fragments
| at its base.
If the fragments are large. they tend
| to break into smaller ones, and still
smaller, in the same way. If this cliff
is inland, tho stones will keep their
angular edges. and should you dig down
hundreds Of years afterward you would
find their shape tho same; but il the
| cliff is beside q stream, or fronts 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. II 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 dislodgc them.
This knocks their corners off-irst the
most prominent, then the less and sc
on until there are no more corners left.
] have heard this going on in the bot.
tom OF swift river in the Rocky mount
aims SO plainly that tho grinding made
muffled roar above the dashing o.
the waves
This river came from under a glacier
which is an enormous mass, a whole
valley full. OF slowly-moving ice. DowI
from the slopes Of the bordering mount
aims. fragments Of rocks were incessant
ly falling and sliding on to the back o
the glacier. This ice was full of cracks
| allowing many of the stones to fal
/ IL III "Hlls tuo IcSC NOThcu lItl
way under the edges As the ponder
Gus ice moved on, it rolled these stone
under its aw ul weight, turning then
over and over. G ushing the softer one
to powder, ana rounding the hard one
into 'cobblestones" and pebbles O
various sizes and shapes. Ages ago tn
whole northern third OF the globe wa
covered by glaciers, and it is believe'
that all the vast banks of gravel an,
| rounded stones which are sea,
tered over the Northern State
and Canada were made in thi
way under the leo. In man
cases it can he told, by the peculiar
ties Of the rock frcm which these pei
bles were made, that they must hav
i come frp2 particular range Of hill.