26 ON SOILS. 



Soil is the general name applied to the sur- 

 face of all sorts of land. It consists of the fine 

 powdery material formed by the chemical and 

 mechanical action of the air, water, and differ- 

 ent degrees of temperature, from the primitive 

 rocks of the earth, incorporated with each other 

 in an endless variety of proportions, and mixed 

 with decayed and other vegetable matter in 

 every stage of decomposition. 



The soil thus formed affords a place for ve- 

 getable life, by enabling the seed and plant 

 there to fix itself mechanically to one spot, and 

 by its peculiar properties of affording moisture 

 and the other ingredients necessary for the de- 

 velopment of plants in all their stages, to arrive 

 at maturity and thus furnish a supply of food 

 to man and animals. 



The various ingredients necessary for vege- 

 table life all exist in the primitive rocks of the 

 earth, and by their destruction these ingredi- 

 ents are rendered available for plants, and as 

 farther this disintegration is constantly, going 

 on, it must as a matter of necessity arrive that 

 a greater power daily exists for the support of 

 the vegetable creation. 



The substances produced by the decompo- 

 sition of the various strata of the original rock 

 are potash, soda, phosphoric acid, magnesia, 

 lime, and silex. Hereafter, in the consideration 

 of these various substances, their specific mode 

 of action on plants, and the immediate sources 

 of their supply, will be described — here they 

 are only noticed as being set free by the disin- 

 tegration of the original rock of the earth. 



