290 



ELEMENTS OF GENERAL SCIENCE 



or clayey soil with but a slight amount of decayed organic 

 matter to peat in which there is little or no clay or sand. 

 In nature these soils are found in all possible mixtures. A 

 careful study of the table in section 290 will enable you to 

 learn a good deal about how soils may be mixed and also 

 about the size and percentages of the different parts of which 

 they may be composed. 



290. Size of soil particles. Careful measurements have 

 been made of the actual size of the particles of different 

 kinds of soils, also of the percentage of air space in these 

 soils. The following table presents the data for a few types : 



291. Plants and animals as soil-formers. In sand upon 

 which plants have grown for a year or more, magnification 

 will usually show, in addition to the sand, some of the re- 

 mains of plant roots, stems, or leaves, although these may 

 have decayed to an extent that makes it difficult to recognize 

 their origin. 



When peat is examined under magnification little or no, 

 sand is seen, but this soil consists of the more or less dis- 

 organized particles resulting from dead plant and animal 

 bodies. Peat is so nearly pure plant material that when dry 

 it makes a fuel of importance in some parts of the world ; 

 it is cut from the earth in brick form, dried, and then sold in 

 the markets. Sometimes peaty soils get afire and may burn 

 slowly for weeks or even months. 



