HOW THE SOIL IS MADE.
How is the soil made? Where does it come from? We can learn something about the soil if we watch the men who are grading a road through the hill. Some of the men are driving horses hitched to great shovels on wheels. The horses pull the shovels over the ground and scrape off the soft dirt. This top dirt we call the soil. It is dark in color and full of grass roots and pieces of leaves and stems of plants.
• Below the dark soil the men find the ground harder. Some of them are using picks to loosen it. A little deeper the ground becomes so hard that they can no longer pick it.
Then they bring long iron rods called drills, and make holes in this hard ground. They put powder into the holes and explode it. The ground is blown into pieces which can be shoveled up and drawn away.
This hard ground is called rock. Soil is made from rock. We have already seen that where the men are working the soil forms only a thin layer on the top of the ground. As they dig deeper the soil soon disappears and rock takes its place. If you dig a hole in the ground anywhere you will at last come to rock. In some places the soil is very deep.
Here is a piece of rock which the men have blasted out. How bright and clean it is! There are sharp corners upon it which may scratch your fingers. How strange it is that rock like this can change to soil! We will take a piece of the rock and pound it to dust. Why cannot we call this pounded rock, soil? It does not look like the dark soil which the men found on the top of the ground.
Let us plant some seeds in a pot of the dust which we made by pounding the piece of rock. We will also plant some in a pot of the dark soil. In this way we can learn how our pounded rock differs from the soil which Nature made.
In a few days the seeds sprout, and for a time the tiny blades in one pot look just like those in the other. Then a change comes. The little plants in the pot of rock dust almost cease to grow. They lose their bright green color. The plants in the other pot keep on growing. This is because the dark soil is full of food all ready for the plant to use, while the rock dust has but little food ready for the little roots to take up.
We have discovered now that the soil is some thing more than rock dust. Nature makes the soil from the rock in a very different way.
A long time ago there was no soil covering the rocks. Do you think we could have lived upon the earth then? For many years the sun shone upon the rocks, and every day they became quite warm. At night when the sun was gone they grew cold. The little grains of which the rocks are made became larger when they were warm and crowded each other. When it was cold they shrank away from each other. In this way little cracks were made.
Rain fell upon the rocks and ran into the cracks At last the rocks began to soften and crumble into little pieces. In this way a layer of soil commenced. Little plants sent their roots into the soil as well as the tiny cracks. The soil was poor and did not give the plant much food, but after a long time things were different. When the pieces of rock had crum bled very fine and pieces of leaves and plant stems became mixed with it, and many little animals had made their homes in it, there was formed the dark rich soil.
Our picture shows another way in which soil is formed. In it you can see the bank of a stream. Perhaps you have visited one just like it.
The bank is made of pebbles and sand. These were washed here by the water a long time ago. At the top of the bank you can see a dark layer of soil.
You can also see the roots of the plants reaching down into the soil. The dark layer at the top is rich in plant food. The sand and pebbles below can furnish very little food.
There are many animals which help form the soil. The ground squirrels burrow in the earth and make it loose. There are also the earthworms who work the ground over and make it richer.
In every pinch of soil there are still other little living things. They are so small that you cannot see them. Each one is doing what it can to change the little grains of rock into soil.
Now we have seen how Nature makes the soil.