60 



NORTH-CAROLINA GEOLOGICAL SURVEY. 



is finally resolved into new forms and conditions. Ammonia 

 and carbonic acid are the common products of change in all 

 these cases. Both are, however, compound bodies. The 

 first is a body recognized by its extremely pungent smell, 

 and commonly known as hartshorn, and is formed by the 

 union of two elements nitrogen and hydrogen. The latter 

 is the lightest substance known it is .069, the weight of air. 

 Carbonic acid is an air, also, or gas, and is heavier than at- 

 mospheric air, and hence is sometimes found in depressed 

 places, not, as is usually maintained, by falling down from 

 the atmosphere in consequence of its greater weight, but by 

 its escape from beneath, or from the soil or fissures of rocks. 

 Rain water and snow hold both ammonia and carbonic acid 

 in solution, and hence, as has been remarked, they are the 

 media from which growing plants derive these important 

 fertilizers. jSnow, particularly, is rich in ammonia. From 

 this material it may be obtained by evaporation. To this 

 substance, probably, the beautiful greenness of vegetation is 

 due, which appears on the melting of a March snow. 



These two substances, however, may be derived from any 

 organic matter in the earth, when it is undergoing decay ; 

 hence, most if not all bodies which have lived may furnish 

 them if buried in the soil and within reach of the roots of a 

 growing plant. There are, therefore, two modes by which 

 these fertilizers become subservient to nutrition 1, by w r ater 

 falling from the atmosphere and, 2, by water in the soil which 

 dissolves them out from particles of earth and organic matter. 



In the application of the first mode, husbandry has nothing 

 to do. It is a part of the machinery of nature, by which she 

 maintains the balance between the vegetable, animal and 

 mineral kingdoms. This machinery in its workings is per- 

 fectly competent to preserve this balance, to furnish food and 

 sustain in perpetual existence all the species which belong to 

 the present system. In a temperate climate, however, with- 

 out artificial aid, the cereals would cease to grow, or yield the 

 harvests they now T do, because of the exhaustion they bring 

 about in the progress of time and of cultivation. 



34. Fertilizers may be divided into kinds according to 



