CHAPTER XXXIV 



SOIL AND ITS ORIGIN 



Since soil is so closely related to plant life and in- 

 directly to all life, we shall be interested to know something 

 about its origin and formation. 



In preparation for this lesson, have the pupils bring in 

 different kind of soil: gravel, sand, clay, or silt, obtained 

 from the excavations of a well or for a building; loam, the 

 ordinary soil of field or garden; and humus, thoroughly 

 decayed leaf mold, old logs, or stumps from the woods. 

 If the pupils cannot procure these, the teacher should get 

 together a collection of the different kinds of soil. To the 

 above should be added pieces of rock of various kinds. 



What is soil ? Lead the pupils to give their opinions. 

 We usually think of soil as the upper layer of earth capable 

 of supporting plant life. How thick is this true soil ? It 

 varies from a few inches to several feet. What is under 

 this ? If you have ever looked at the side of a freshly dug 

 ditch or well could you see a difference in the appearance 

 of the portion of the soil near the surface and that below ? 

 This lower, lighter colored portion is called subsoil. This 

 varies from a few inches to several hundred feet in thick- 

 ness. It varies also as to material. Sometimes it is sand, 

 sometimes gravel, sometimes very fine clay, sometimes 

 coarser clay or silt. Under this subsoil or mantle rock, as 

 it is sometimes called, is bedrock. Everyone who has ever 



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