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The Genesis Of Soil
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Soil primarily had its beginning from rock together with animal
and vegetable decay, if you can imagine long stretches or periods
of time when great rock masses were crumbling and breaking up.
Heat, water action, and friction were largely responsible for
this. By friction here is meant the rubbing and grinding of rock
mass against rock mass. Think of the huge rocks, a perfect chaos
of them, bumping, scraping, settling against one another. What
would be the result? Well, I am sure you all could work that out.
This is what happened: bits of rock were worn off, a great deal of
heat was produced, pieces of rock were pressed together to form
new rock masses, some portions becoming dissolved in water. Why, I
myself, almost feel the stress and strain of it all. Can you?
Then, too, there were great changes in temperature. First
everything was heated to a high temperature, then gradually became
cool. Just think of the cracking, the crumbling, the upheavals,
that such changes must have caused! You know some of the effects
in winter of sudden freezes and thaws. But the little examples of
bursting water pipes and broken pitchers are as nothing to what
was happening in the world during those days. The water and the
gases in the atmosphere helped along this crumbling work.
From all this action of rubbing, which action we call mechanical,
it is easy enough to understand how sand was formed. This
represents one of the great divisions of soil sandy soil. The sea
shores are great masses of pure sand. If soil were nothing but
broken rock masses then indeed it would be very poor and
unproductive. But the early forms of animal and vegetable life
decaying became a part of the rock mass and a better soil
resulted. So the soils we speak of as sandy soils have mixed with
the sand other matter, sometimes clay, sometimes vegetable matter
or humus, and often animal waste.
Clay brings us right to another class of soils clayey soils. It
happens that certain portions of rock masses became dissolved when
water trickled over them and heat was plenty and abundant. This
dissolution took place largely because there is in the air a
certain gas called carbon dioxide or carbonic acid gas. This gas
attacks and changes certain substances in rocks. Sometimes you see
great rocks with portions sticking up looking as if they had been
eaten away. Carbonic acid did this. It changed this eaten part
into something else which we call clay. A change like this is not
mechanical but chemical. The difference in the two kinds of change
is just this: in the one case of sand, where a mechanical change
went on, you still have just what you started with, save that the
size of the mass is smaller. You started with a big rock, and
ended with little particles of sand. But you had no different kind
of rock in the end. Mechanical action might be illustrated with a
piece of lump sugar. Let the sugar represent a big mass of rock.
Break up the sugar, and even the smallest bit is sugar. It is just
so with the rock mass; but in the case of a chemical change you
start with one thing and end with another. You started with a big
mass of rock which had in it a portion that became changed by the
acid acting on it. It ended in being an entirely different thing
which we call clay. So in the case of chemical change a certain
something is started with and in the end we have an entirely
different thing. The clay soils are often called mud soils because
of the amount of water used in their formation.
The third sort of soil which we farm people have to deal with is
lime soil. Remember we are thinking of soils from the farm point
of view. This soil of course ordinarily was formed from limestone.
Just as soon as one thing is mentioned about which we know
nothing, another comes up of which we are just as ignorant. And so
a whole chain of questions follows. Now you are probably saying
within yourselves, how was limestone first formed?
At one time ages ago the lower animal and plant forms picked from
the water particles of lime. With the lime they formed skeletons
or houses about themselves as protection from larger animals.
Coral is representative of this class of skeleton-forming animal.
As the animal died the skeleton remained. Great masses of this
living matter pressed all together, after ages, formed limestone.
Some limestones are still in such shape that the shelly formation
is still visible. Marble, another limestone, is somewhat
crystalline in character. Another well-known limestone is chalk.
Perhaps you'd like to know a way of always being able to tell
limestone. Drop a little of this acid on some lime. See how it
bubbles and fizzles. Then drop some on this chalk and on the
marble, too. The same bubbling takes place. So lime must be in
these three structures. One does not have to buy a special acid
for this work, for even the household acids like vinegar will
cause the same result.
Then these are the three types of soil with which the farmer has
to deal, and which we wish to understand. For one may learn to
know his garden soil by studying it, just as one learns a lesson
by study.
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