CHAPTER IV 

 TEXTURE AND STRUCTURE OF SOILS 



As a result of the grinding to which rock is subjected in 

 the process of soil formation, there are to be found in soils 

 particles of all sizes, from gravel and coarse sand down to 

 particles so minute that they cannot be seen with the highest 

 power microscope, to say nothing of the unassisted eye. 

 In all but very sandy soils, particles are generally gathered 

 into clusters or granules. Texture is a term used in refer- 

 ence to the size of the particles in a soil ; the term struc- 

 ture refers to the arrangement of particles into granules. 



29. Shape of particles. — There is no universal shape 

 for soil particles. They vary from spherical to angular, 

 and are sometimes rather elongated, but the occurrence of 

 anything like needle shape is not common. Soils formed 

 by erosion and wave action are likely to have rounded 

 particles, as are also soils formed from limestone. 



30. Space occupied by particles. — The number of par- 

 ticles in a given volume of soil can only be estimated, their 

 minute size precludes an actual enumeration. It has been 

 estimated that the number of particles in a gram of soil 

 of certain different kinds is as follows : 



Early truck 1,955,000,000 



Truck and small fruit ....... 3,955,000,000 



Tobacco 6,786,000,000 



Wheat 10,228,000,000 



Grass and wheat 14,735,000,000 



Limestone 19,638,000,000 



30 



