ORIGIN OF SOIL 87 



our work may take us, we still feel more or less the instinct 

 to go and work in the earth for our living, and find pleasure 

 in the following of that instinct. 



Formation of Soil. You have learned that all sub- 

 stances are either organic or inorganic; and the sciences 

 are often divided into those which treat of organic things 



FIG. 37. A section of the soil, showing its relation to the underlying rock. 



and those which treat of inorganic things. But soil, 

 more than anything else in the world, is a thing in which 

 the organic and inorganic meet and merge. It is composed 

 of mineral (inorganic) matter derived from the rocks 

 beneath, and of organic matter derived from the organ- 

 isms which live on and in it. So whether you are study- 

 ing geology, an inorganic science, or botany, an organic 

 science, in both you must study the soil. 



That soil is a mixture, a mixture in which organic and 

 inorganic materials "meet and merge," is quite evident 

 when we consider its origin, or look at it from top to bot- 

 tom (see Fig. 37). Where streams are eroding steep 



