2 FIELD AND LABOEATORY STUDIES OF SOILS 



Questions: 1. Does solid rock come to the surface 

 at- your home? 



2. Name a place where you know the depth at which 

 solid rock is found. 



3. Does your home well reach the rock? 



4. At what depth? 



5. Compare the shape of stones found in streams with 

 that of crushed stone. How do you account for any 

 difference? 



Discussion: Under the soil in any field is solid rock. 

 Sometimes this rock is very deep and again it may lie 

 but a few inches below the surface. The soil also was 

 once large rocks. It was made fine as we see it by natural 

 agencies working through millions of years. These agencies 

 are stiil at work and ma}^ often be observed. Water fills 

 the crack in a large stone, freezes and bursts the stone 

 apart. Exposed ledges of stone heated during the day 

 and cooled at night for several years finally crumble. The 

 roots of trees force themselves between the layers of rock 

 and split them apart. Every little stream rolls and wears 

 pebbles, grinding them finer and finer, finally forming soil. 



An examination of almost any soil shows that it con- 

 tains not only fine rock particles, but also plant and animal 

 remains. This organic matter may be found in the soil in 

 all stages of decay, and constitutes the most important 

 body of material present in the soil. It furnishes nitrogen, 

 which is an important plant nutrient, and enables the 

 soil to absorb and retain moisture. 



