SOILS 



287 



The richness of the soil will first depend upon the com- 

 position of the underlying rock and next upon the action 

 of the plants which yield the organic matter. 



U. S. Geological Survey. 

 FIG. 247. Erratic Bowlders. 



These bowlders have been deposited by the glacial stream. 



In most soils the rock particles predominate, making up 

 from 60 per cent to 95 per cent of the total weight. From 

 two to five per cent 

 is organic matter, 

 and most of the re- 

 mainder is water. 



Experiment 73. - 



Shake a quantity of 

 soil with water in a 

 bottle (Figure 248), 

 until all the particles 

 of the soil are broken FIG. 248. 



medium 

 sand 



