2 6 SCIENTIFIC AGRICULTURE. 



are most likely to be deficient, and in such cases 

 they must be supplied by the use of fertilizers or 

 manures. 



47. The great quantity of sand in most soils and 

 its presence in all have suggested the propriety of 

 classifying soils according to the amount of sand 

 they contain, as follows : 



1. Pure clay, from which no sand can be re- 

 moved by washing. 



2. Strong clay, when the soil contains from 5 

 to 20 per cent, of sand. 



3. Clay loam, when it contains from 20 to 40 

 per cent, of sand. 



4. Loam, from 40 to 70 per cent, of sand. 



5. Sandy loam, from 70 to 90 per cent, of 

 sand. 



6. Light sand, more than 90 per cent, of sand. 

 It is easy to classify soils in this way by merely 



washing out the sand and weighing it (25). 



48. When soils contain a large amount of calcium 

 carbonate, they are said to be calcareous, or marly ; 

 and, when a very large percentage of organic matter, 

 they are said to be peaty, or are called vegetable 

 mold. The presence of a large quantity of clay 

 makes a soil sticky when wet, and causes it to hold 

 moisture a long time, hence such soils are said lo be 

 heavy ; a large quantity of sand gives the opposite 

 property, that is, of not retaining moisture, and 

 hence these are said to be light. 



49. The soil proper is the surface layer down to 



