58 THE SOIL. 



The soil is a great chemical compound, and its 

 chemical character is ascertained (as in the case of 

 plants) by analyzing it, or taking it apart. 



"We first learn that fertile soils contain both at- 

 mospheric and earthy matter ; but, unlike the plant, 

 they usually possess much more of the latter than of 

 the former. 



In the plant, the atmospheric matter constitutes 

 the most considerable portion of the whole. In the 

 soil, on the contrary, it usually exists in very small 

 quantities, while the earthy parts constitute nearly 

 the whole bulk. 



The atmospheric or organic part of soils consists of 

 the same materials that constitute the atmospheric 

 part of the plants, and is in reality decayed vegetable 

 and animal matter. It is not necessary that this 

 organic part of the soil should form any particular 

 proportion of the whole, and indeed we find it vary- 

 ing from one and a half to fifty, and sometimes, in 

 peaty soils, to over seventy per cent. All fertile soils 

 contain some organic matter, although it seems to 

 make but little difference in fertility, whether it be 

 five or fifty per cent. 



The earthy part of soils is derived from the 

 crumbling of rocks. Some rocks (such as the slates 

 in Central New York) decompose, and crumble rap- 

 idly on being exposed to the weather ; while granite, 

 marble, and other rocks, will last for a long time 

 without perceptible change. The causes of this 

 crumbling are various, and are important to be un- 

 derstood by the agriculturist, as by the same process- 



