60 AGRICULTURE 



is wet because their tracks make clods, just as plow- 

 ing does. 



EXERCISE. Find what curious kinds of tiny plants are growing on 

 the bare rock in some shaded spot. 



Dig into several fields to learn how deep is the mellow soil. What 

 differences do you find between the soil and the harder subsoil ? Do 

 annual crop plants send their roots deep into most kinds of subsoil ? 

 Find a tree that has been blown down, or from around the roots of 

 which the earth has been washed away, and see how deep its roots went 

 into the subsoil. 



NOTE TO THE TEACHER. Samples of several soils, as clay, sandy 

 loam, and woods' earth, each on a separate newspaper, where they can 

 be moistened and worked into mud pies, will impress the varying de- 

 grees of adhesiveness, grittiness, fineness, and their probable relation 

 to (i) ease of plowing, (2) drainage, and (3) wear on implements 

 during plowing. 



FIG. 41. A GOOD SCHOOL EXERCISE 

 Two kinds of soil that have been wet and then dried. 

 The loamy soil remains loose and capable of growing 

 plants ; the clay soil below has baked and cracked. 



