SOILS. 2 



Per cent. 



Potassium oxide 0.2 



Sodium oxide 0.4 



Calcium oxide, or lime 5.9 



Magnesium oxide, or magnesia o.8j 



Iron oxide, or ferric oxide 6.1 



Aluminium oxide, or alumina 5.7 



Manganese oxide o.i 



Silicon oxide (silica) 64.8 



Sulphuric acid, or sulphur trioxide 0.2 



Phosphoric acid, or phosphorus pentoxide 0.4^ 



Carbonic acid, or carbon dioxide 4.0 



Chlorine 0.2 



Organic matter 9.7 



Loss 1.4 



Total 100.0 



The proportion of some important constituents, 

 as potassium oxide, phosphoric acid, etc., is very 

 small, but the smallest would amount to several tons 

 per acre. 



46. Silica, or sand, is the chief substance in a great 

 many soils. Clay, a compound of silica and alumina 

 with small quantities of other elements, is also abun- 

 dant in most soils ; so are lime and iron oxide. The 

 amount of organic matter is quite variable. In some 

 soils it reaches 15 or 20 per cent, while in others it 

 is less than i per cent. The total absence of any 

 of the constituents mentioned above, except perhaps 

 aluminium oxide and manganese, would render the 

 soil unproductive for ordinary crops. Those in least 

 abundance, as potassium oxide and phosphoric acid, 



