in THE NATURE OF THE SOIL 27 



Take a little of this subsoil, dry it, and repeat the 

 preceding experiment. It does not smoke, and loses 

 very little in weight, showing that it consists almost 

 entirely of mineral, and not of vegetable, substances. 



If we dig deeper still, we shall find the rock by 

 the crumbling of which the soil was first formed. 



The Way the Soil has been Formed 



We can now understand how the soil has been 

 formed. We must imagine a hard surface of rock 

 where now there is soil. This rock has slowly 

 crumbled to powder, forming the mineral portion of 

 the soil (sand, clay, etc.). Plants sown by chance 

 seeds have sprung up, died, and decayed, forming the 

 vegetable portion of the soil. The mixture of the 

 two forming a soil suitable for future vegetable life. 



The crumbling of this rock to form the soil has 

 been caused partly by the action of air and rain, 

 but also by the freezing of water which has soaked 

 into the pores of the rock. 



When water freezes it expands slightly, and so 

 splits up the rock. When the thaw comes those 

 broken-off pieces fall apart. . 



This action of freezing water can be easily tested. 



Experiment 20 



Take a small narrow-necked glass flask, and fill 

 it with water, and place it in a vessel containing a 



