82 NATURE AND PROPEETIES OF SOILS 



The loam class is rather difficult to explain. In mechan- 

 ical composition it is more or less midway between sand and 

 clay. A loam may be defined as such a mixture of sand, silt, 

 and clay particles as to exhibit sandy and clayey properties 

 in about equal proportions. It is a half and half mixture 

 on the basis of properties, although the sum of the sands and 

 the sum of the silt and clay are g-enerally near 50 per cent., 

 respectively. (See Fig. 16 ) Because of the marked inter- 

 mixture of coarse, medium, and fine particles, loams are 

 usually soils of good physical character. They generally pos- 

 sess the desirable qualities both of sand and clay without 

 exhibiting those undesirable properties, such as extreme loose- 

 ness and low water capacity on the one hand and stickiness, 

 compactness, and slow air and water drainage on the other. 

 Most of the better soils are some type of loam. 



It is obvious that in the field not only various kinds of 

 gravelly, sandy, loamy, and clayey soils must occur, but the 

 groups must grade into each other, thus giving rise to a con- 

 siderable number of field names. (See Fig. 16.) These field 

 names are listed below : 



Common Class Names 



1. Gravel 9. Very fine sandy loam 



2. Coarse sand 10. Loam 



3. Medium sand. 11. Silt loam 



4. Fine sand 12. Silty clay loam 



5. Very fine sana 13. Clay loam 



6. Coarse sandy loam 14. Clay 



7. Sandy loam 15. Heavy clay 



8. Fine sandy loam 16. Sandy clay 



The meaning of these names should be clear except possibly 

 those into which the loam group is divided. Loam, as already 

 explained, refers to a soil possessing in about equal amounts 

 the properties imparted by the various separates. If, how- 

 ever, we have practically the same condition but with one 



