A‘r‘rwmx. xv 
     
    
   
   
    
     AGRICULTURAL GEOLOGY. 
     
    
   
   
    
         
     
       
     
       
     
         
     
         
     
         
     
         
     
       
     
       
     
         
     
        
     
       
     
         
     
         
     
        
     
        
     
         
     
       
     
        
     
    
   
   
    
     The Science of Geology embraces the facts ascers 
     
     tained in regard to the Physical and Chemical struc— 
     
     ture of the earth. Extending to the soil, it contri- 
     
     butes aid to practical agriculture, and by explaining 
     
     :the causes to which the covering of the earth owes 
     
     its origin, it points to improvement in the production 
     
     :of plants. 
     
    
   
   
    
     The chief parts cfall the stratified rocks, are sand 
     
     stones, limestones and clays, under diflerent degrees 
     
     of hardness. Ifthese rocks, and even those of vol- 
     
     canic origin, are exposed to the operations of frost, 
     
     rain and atmosphere, a soil results. The soils 
     
     produced by the disintegration of the solid masses 
     
     ofthe crust of the earth, brought forth the plants 
     
    
   
   
    
     found in a fossil state, and therefore partake of the 
     
     .‘character oftho rocks from which they had been de- 
     
    
   
   
    
     rived. The surface of a bed of diluvial gravel soon 
     
     forms a soil, after its covering is removed, and the 
     
     plants that grow upon it, soon deposit a quantity of 
     
     vegetable matter, which adds fertility. Very fre- 
     
     quently rocks are covered with a soil that has result- 
     
     ed frnm dilapidation, and it has been already shewn 
     
     that diluvial matter had been transported from one 
     
     place to another, over great distances, and being in- 
     
     ermixed with the native covering of other districts, 
     
     a diversity of soils has followed, recognised by 
     
     ‘eology. The sotls of granitic and trappean moun- 
     
     ains are peculiar in themselves. In gypseous dis- 
     
     ricts the soil frequently contains so much sulphate of 
     
     ime that it is sterile, and in tracts of limestone the 
     
     and is sometimes barren from a superabundance ’of 
     
     carbonate of lime. It is by the mixture of mineral 
     
     ingredients ofthe earth that the surface is fruitful, to 
     
     produce which many powerful natural agenciea are 
     
     mployed by a ruling Providence. 
     
     B32