EXERCISE 3 

 A STUDY OF SOIL PARTICLES 



Object. To study the size, shape, color, and character 

 of the soil particles in different types of soil. 



Explanation. The earth is supposed at one time to have 

 been solid rock. The soil that now covers the earth was 

 formed by the breaking up of this rock material. Mixed 

 with the rock material of the soil is a small amount of plant 

 material or organic matter. 



In the beginning of soil formation the rocks that com- 

 posed the earth were undoubtedly not all of one kind ; some 

 were soft and others were hard. The soft rocks gave way 

 easily to the forces of nature and were soon ground into 

 very small particles. The hard rocks have resisted this 

 action, consequently they have been broken up very slowly, 

 and they form the larger particles of the soil. 



Some of these particles are so large that they hinder 

 plowing and cultivating. These are called stones. Other 

 particles smaller than these are called gravel, and still 

 smaller particles are called sand. Thus it is possible to 

 take a soil, and, by examining it closely, see that it is made 

 up of a countless number of particles of many different 

 sizes. These particles representing different sizes have been 

 given different names, as follows: 



8 



