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.
