Agriculture for Beginners | Page 4

great part of upper North America was a vast sheet of ice.
Whatever moisture fell from the sky fell as snow. No one knows what
made this long winter of snow, but we do know that snows piled on

snows until mountains of white were built up. The lower snow was by
the pressure of that above it packed into ice masses. By and by some
change of climate caused the masses of ice to break up somewhat and
to move south and west. These moving masses, carrying rock and
frozen earth, ground them to powder. King thus describes the stately
movement of these snow mountains: "Beneath the bottom of this
slowly moving sheet of ice, which with more or less difficulty kept
itself conformable with the face of the land over which it was riding,
the sharper outstanding points were cut away and the deeper river
cañons filled in. Desolate and rugged rocky wastes were thrown down
and spread over with rich soil."
The joint action of air, moisture, and frost was still another agent of
soil-making. This action is called weathering. Whenever you have
noticed the outside stones of a spring-house, you have noticed that tiny
bits are crumbling from the face of the stones, and adding little by little
to the soil. This is a slow way of making additions to the soil. It is
estimated that it would take 728,000 years to wear away limestone rock
to a depth of thirty-nine inches. But when you recall the countless years
through which the weather has striven against the rocks, you can
readily understand that its never-wearying activity has added
immensely to the soil.
In the rock soil formed in these various ways, and indeed on the rocks
themselves, tiny plants that live on food taken from the air began to
grow. They grew just as you now see mosses and lichens grow on the
surface of rocks. The decay of these plants added some fertility to the
newly formed soil. The life and death of each succeeding generation of
these lowly plants added to the soil matter accumulating on the rocks.
Slowly but unceasingly the soil increased in depth until higher
vegetable forms could flourish and add their dead bodies to it. This
vegetable addition to the soil is generally known as humus.
[Illustration: FIG. 2. GROUND ROCK AT END OF A GLACIER]
In due course of time low forms of animal life came to live on these
plants, and in turn by their work and their death to aid in making a soil
fit for the plowman.

Thus with a deliberation that fills man with awe, the powerful forces of
nature splintered the rocks, crumbled them, filled them with plant food,
and turned their flinty grains into a soft, snug home for vegetable life.
SECTION II. TILLAGE OF THE SOIL
A good many years ago a man by the name of Jethro Tull lived in
England. He was a farmer and a most successful man in every way. He
first taught the English people and the world the value of thorough
tillage of the soil. Before and during his time farmers did not till the
soil very intelligently. They simply prepared the seed-bed in a careless
manner, as a great many farmers do to-day, and when the crops were
gathered the yields were not large.
Jethro Tull centered attention on the important fact that careful and
thorough tillage increases the available plant food in the soil. He did
not know why his crops were better when the ground was frequently
and thoroughly tilled, but he knew that such tillage did increase his
yield. He explained the fact by saying, "Tillage is manure." We have
since learned the reason for the truth that Tull taught, and, while his
explanation was incorrect, the practice that he was following was
excellent. The stirring of the soil enables the air to circulate through it
freely, and permits a breaking down of the compounds that contain the
elements necessary to plant growth.
You have seen how the air helps to crumble the stone and brick in old
buildings. It does the same with soil if permitted to circulate freely
through it. The agent of the air that chiefly performs this work is called
carbonic acid gas, and this gas is one of the greatest helpers the farmer
has in carrying on his work. We must not forget that in soil preparation
the air is just as important as any of the tools and implements used in
cultivation.
[Illustration: FIG. 3. SLOPE TO WATER SHOWS SOIL
WEATHERED FROM FACE OF CLIFF]
If the soil is fertile and if deep plowing has always been done, good
crops will result, other conditions being favorable. If, however, the

tillage is poor, scanty harvests will always result. For most