80 
SECOND BOOK. 
HOW SOILS ARE FORMED. 
1 . Have you ever tried to think how the soil, 
which is the standing-place for our plants and a 
storehouse for some of their food, was first formed, 
and whence it came? 
There was a time, ages ago, when there was no 
soil on the earth, but all was hard rock. What was 
it, then, that caused the great change? 
2 . The work of making and mixing the soil is 
still going on, and the chief workers are the air, the 
water, and the changes of temperature. 
Let us first notice what heat and cold can 
do. 
3. When the ground becomes greatly heated it 
cracks and splits, causing the particles to press 
against each other so much that they crumble and 
fall apart. In countries where it is cold enough 
for water to be frozen, the ice formed in the soil 
forces it to split and break up. 
4 . It seems strange that lands now in the warmest 
part of the world were covered with ice and snow 
long years ago, just as the Arctic regions are now. 
And the masses of ice, as they slowly slid down 
the mountains, ground down the rocks, and so took 
a share in making the soil. 
5. When by any means the rocks become cracked 
and broken they are laid open to the wearing-down 
work which is done by water. 
