THE SOIL. 



63 



ter explained by the assistance of the following 

 table : 



The soil represented in the first and second columns 

 might still be fertile with less organic matter, or with 

 a larger proportion of clay (alumina), and less sand 

 (silicic acid). These affect its mechanical character ; 

 but, if we look down the columns, we notice that there 

 are small quantities of lime, magnesia and the other 

 constituents of the ashes of plants (except oxide of 

 manganese). It is not necessary that they should be 

 present in the soil in the exact quantity named above, 

 but not one must he entirely absent, or greatly reduced 

 in proportion. By referring to the third column, we 

 see that these ingredients are not all present, and the 

 soil is barren. Even if it were supplied with all but 

 one or two, potash and soda for instance, it could not 

 support a crop without the assistance of manures con- 



