84 NATURE AND PROPERTIES OF SOILS 



sists in an examination of the soil as to color, an estimation of 

 its organic content, and, especially, a testing of the ' ' feel ' ' of 

 the soil in order to decide as to the class name. Probably as 

 much can be judged as to the texture and class of a soil merely 

 by rubbing it between the thumb and the fingers or in the 

 palm of the hand as by any other superficial means. This 

 method is used in all field operations, especially in soil survey 

 work. It really consists in sufficiently recognizing the textural 

 composition of a soil that the class name may be determined. 1 



The accuracy of such a determination depends largely on 

 experience. Inaccuracies are likely to occur in distinguishing 

 between the various finer grades of soil ; for this reason, more 

 nearly exact methods are necessary at times, especially in 

 checking soil survey work or in carrying out investigations in 

 which absolute accuracy is required. 



As a mechanical analysis of a soil is really a percentage 

 expression of texture, it presents an exact method for class 

 determination. For detailed work, somewhat complicated 

 tables 2 have been arranged; but the following diagram 



1 Key for the practical classification of mineral soils : 



I. Soils possessing the properties of one size of 

 particle largely. 



1. Particles very large Gravel 



2. Particles apparent to eye; feel gritty and 

 non-plastic Sands 



3. Particles very small ; soil very plastic when 



wet, hard when dry Clay or 



Sandy Clay 



II. Soils possessing the properties of a number of 

 sizes of particles — a mixture. 



1. A fairly equal exhibit of sandy and 

 clayey properties Loam 



2. A mixture but with sand predominating . . . Sandy Loam 



3. A mixture but with silty character dom- 

 inant. The soil has a floury or talc feel 



and is quite plastic when wet Silt Loam 



4. A mixture but with clayey characters very 

 apparent. Soil is very plastic and ap- 

 proaches a clay in character Clay Loam 



2 Bur. of Soils, Soils Survey Field Boole, p. 17; U. S. Dept. Agr., Bur. 

 Soils, 1906. Also, Bur. Soils, Bui. 78, p. 12, 1911. 



