10 AGRICULTURE 



exist. It supplies a root-hold and home for plants. It is a store- 

 house for the water, air, and heat which they need. It is a manu- 

 factory, too, in which forces and organisms are at work changing 

 matter into forms that plants can use for food. 



Formation of Earth-crust. Have you ever considered how the 

 soil was formed ? We are told that long ago the earth was a fiery 

 mass of matter whirling through space. Gradually it cooled, and 

 as it cooled it hardened into a sphere, or round body. Its surface 

 was a crust of solid rock, surrounded by heavy acid vapors. 



Bare and lifeless as a ball of iron, it whirled through space. 

 There was no foothold for the tiniest plant, no home for the hum- 

 blest insect. Then God set His servants, the forces of nature, to 

 work to make the barren rock an abode for plants and animals. 

 Many agencies worked, singly and together. 



Heat and Cold. First, there were heat and cold. As you 

 know, heat causes most substances to expand, or grow larger, 

 and cold makes them contract, or grow smaller. As the earth- 

 surface cooled, the rock contracted, cracked, and broke, forming 

 elevations and depressions, or hills and valleys. The cold con- 

 densed the heavy acid vapors surrounding the earth and they de- 

 scended in rain. Continents rose, small at first, but increasing in 

 size as the earth-crust shrank and cracked. The waters flowed in 

 streams through narrow valleys and in deep ones formed lakes, 

 seas, and oceans. 



Atmosphere. The atmosphere, or air and gases and vapors 

 around the earth, worked slowly but constantly. It crumbled the 

 earth-surface and bore the rock-dust from one place to another. 



Water. The greatest part of the soil-making, however, was done 

 by water in its various forms vapor, rain, dew, frost, snow, and 

 ice. As a gas, a liquid, and a solid, it worked and is still working. 

 During those early days water was busy, rain and streams 



