212 PARING AND BURNING. 



operations. All experience proves their great fertil- 

 izing power. Their whole action, mysterious as a 

 part of it may appear, depends for its success, upon 

 the formation of geine, salts, and silicates. And 

 first, — burning, in which is to be considered the 

 effects of simply burning the earthy parts of soils. 

 In the description of silicates, Chap. II, the frequent 

 occurrence of pyrites, or sulphuret of iron, was de- 

 scribed, and this is especially the case in all clays. 

 The effect of burning is, to disengage sulphurous acid, 

 and the red and seared appearance of the foliage in 

 the neighborhood of a brick kiln, which may be often 

 observed, is due to the disengagement of acid gases, 

 during the process of burning the bricks. This acid 

 gas being liberated, in the operation of burning soils, 

 hastens the formation of sulphates and salts. It di- 

 vides the silicates, and thus reduces them to a state 

 in which the carbonic acid of the air more easily de- 

 composes them. If we go one step further, and burn 

 the vegetable matter of the soil, a portion of geine is 

 lost, and ashes are formed, whose operation has been 

 already considered, Chap. III. They dissolve any 

 geine in soil, hence the practice of burning the par- 

 ings of a peat meadow, whose ashes, bring the bal- 

 ance into cultivation. The whole practice of burn- 

 ing vegetable soil for its ashes, is wasteful. The 



