Agriculture for Beginners | Page 3

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AGRICULTURE FOR BEGINNERS
CHAPTER I
THE SOIL
SECTION I. ORIGIN OF THE SOIL
The word soil occurs many times in this little book. In agriculture this
word is used to describe the thin layer of surface earth that, like some

great blanket, is tucked around the wrinkled and age-beaten form of our
globe. The harder and colder earth under this surface layer is called the
subsoil. It should be noted, however, that in waterless and sun-dried
regions there seems little difference between the soil and the subsoil.
Plants, insects, birds, beasts, men,--all alike are fed on what grows in
this thin layer of soil. If some wild flood in sudden wrath could sweep
into the ocean this earth-wrapping soil, food would soon become as
scarce as it was in Samaria when mothers ate their sons. The face of the
earth as we now see it, daintily robed in grass, or uplifting waving acres
of corn, or even naked, water-scarred, and disfigured by man's neglect,
is very different from what it was in its earliest days. How was it then?
How was the soil formed?
Learned men think that at first the surface of the earth was solid rock.
How was this rock changed into workable soil? Occasionally a curious
boy picks up a rotten stone, squeezes it, and finds his hands filled with
dirt, or soil. Now, just as the boy crumbled with his fingers this single
stone, the great forces of nature with boundless patience crumbled, or,
as it is called, disintegrated, the early rock mass. The simple but
giant-strong agents that beat the rocks into powder with a clublike force
a millionfold more powerful than the club force of Hercules were
chiefly (1) heat and cold; (2) water, frost, and ice; (3) a very low form
of vegetable life; and (4) tiny animals--if such minute bodies can be
called animals. In some cases these forces acted singly; in others, all
acted together to rend and crumble the unbroken stretch of rock. Let us
glance at some of the methods used by these skilled soil-makers.
Heat and cold are working partners. You already know that most hot
bodies shrink, or contract, on cooling. The early rocks were hot. As the
outside shell of rock cooled from exposure to air and moisture it
contracted. This shrinkage of the rigid rim of course broke many of the
rocks, and here and there left cracks, or fissures. In these fissures water
collected and froze. As freezing water expands with irresistible power,
the expansion still further broke the rocks to pieces. The smaller pieces
again, in the same way, were acted on by frost and ice and again
crumbled. This process is still a means of soil-formation.

Running water was another giant soil-former. If you would understand
its action, observe some usually sparkling stream just after a washing
rain. The clear waters are discolored by mud washed in from the
surrounding hills. As though disliking their muddy burden, the waters
strive to throw it off. Here, as low banks offer chance, they run out into
shallows and drop some of it. Here, as they pass a quiet pool, they
deposit more. At last they reach the still water at the mouth of the
stream, and there they leave behind the last of their mud load, and often
form of it little three-sided islands called deltas. In the same way
mighty rivers like the Amazon, the Mississippi, and the Hudson, when
they are swollen by rain, bear great quantities of soil in their sweep to
the seas. Some of the soil they scatter over the lowlands as they whirl
seaward; the rest they deposit in deltas at their mouths. It is estimated
that the Mississippi carries to the ocean each year enough soil to cover
a square mile of surface to a depth of two hundred and sixty-eight feet.
[Illustration: FIG. 1. ROCK MARKED BY THE SCRAPING OF A
GLACIER OVER IT]
The early brooks and rivers, instead of bearing mud, ran oceanward
either bearing ground stone that they themselves had worn from the
rocks by ceaseless fretting, or bearing stones that other forces had
already dislodged. The large pieces were whirled from side to side and
beaten against one another or against bedrock until they were ground
into smaller and smaller pieces. The rivers distributed this rock soil just
as the later rivers distribute muddy soil. For ages the moving waters
ground against the rocks. Vast were the waters; vast the number of
years; vast the results.
Glaciers were another soil-producing agent. Glaciers are streams
"frozen and moving slowly but irresistibly onwards, down well-defined
valleys, grinding and pulverizing the rock masses detached by the force
and weight of their attack." Where and how were these glaciers
formed?
Once a