SOILS xlND MANURES 



AVERAGE CHEMICAL COMPOSITION OF THE CRUST OF THE EARTH. 



AS ELEMENTS. 



Oxygen 

 Silicon 

 Aluminium 



Iron . 



Calcium . 



Magnesium 



Potassium . 



Sodium 



Titanium . 



Carbon 



Hydrogen . 



Phosphorus 



All other elements 



OXYGEN COMBINED. 



100-0 



100-0 



EOCKS. 



Bocks may be primarily classified as igneous, aqueous 

 and organic, according to their origin. 



Igneous Rocks. Igneous rocks consist of minerals which 

 have been apparently reduced to a state of flux by intense 

 heat and solidified in the crystalline form when cooled down. 

 In rocks which have cooled slowly, e.g., granite, the 

 crystals are large and can be seen with the naked eye. In 

 those which have cooled rapidly the crystals are smaller 

 and often can only be distinguished by microscopic ex- 

 amination. In obsidian the minerals are not crystalline, 

 and the rock presents the appearance of a vitreous glassy 

 mass. 



Aqueous Rocks. Aqueous rocks were probably formed, 

 in the first instance, out of the debris resulting from the 

 disintegration of igneous rocks of which, according to the 

 nebular hypothesis, the original crust of the earth entirely 



