94 TllK SOIL AND ITS IMPROVEMENT 



Not only does the soil supply the materials out of 

 which we build our bodies, but it also produces the sub- 

 stances with which we clothe our bodies, cotton, linen, 

 silk, and wool. Even such articles of commerce as lumber 

 are gifts of the soil to man. Many articles, too, which are 

 dug out of the earth (not, however, from the "soil," as 

 the farmer uses the term) are useful to us. Iron, coal, 

 paint, building stones, cement are either rocks or their 



RELATIVE SIZES OF SOIL PARTICLES. 

 From left to right : clay, silt, sand, gravel. 



products. And rocks, as we shall learn, come in time to 

 form the bulk of the soil. Truly, " the earth is the mother 

 of us all." 



55. What Soil Is. The term soil is used frequently in 

 this book. What is soil? It may be defined as the loose 

 surface material that covers the land and in which plants 

 usually grow. Pick up a handful of soil and examine it. 

 It is made up of many different substances, little stones, 

 gravel, sand, and, if allowed to dry, of a fine powder. Bits 

 of partly decayed plants and parts of insects may also be 

 noticed if we use a microscope. If we examine the dust 

 with a magnifying glass, it is seen to be composed of par- 



