NORTH-CAROLINA GEOLOGICAL SURVEY. 119 



of remark, is useful ; and correct theory eminently useful. At the same 

 time, the fact may, and usually is, more important practically ; for the fact 

 leads to the right action, but it may fall short of the benefit it is calculated 

 to give, when fact and correct theory are conjoined, and go to the work 

 together. Theory and book learning are often ridiculed by the matter of 

 fact man, and yet observation often bears us out in the opinion that in most 

 instances there is not only a great want of facts, but that also when found 

 they are often greatly perverted. But we turn now to the subject more 

 immediately before us. What are the functions which the organic matter 

 performs in vegetation? Our belief is, that all terrestrial plants, if they 

 do not absolutely require it, are at least benefited by it. That it is not 

 taken into the plant in the condition of mould or humus, is proved from 

 the fact that it is not in this condition sufficiently soluble. If then it is 

 useful, it is necessary to maintain that it undergoes certain changes before 

 it becomes the food of plants. It may minister to the wants of vegetation 

 in several ways, without its becoming the food itself. It ministers to the 

 vegetable by its presence, procuring thereby an open state of the soil, by 

 which air is more freely conveyed to the roots. It ministers, also, to the 

 wants of vegetation by its absorbent and retentive powers. Indeed, in this 

 respect it is almost indispensable to vegetation. These, then, though not 

 all the uses which mould exercises in vegetation, still are sufficiently im- 

 portant to merit the attention of the agriculturist. In neither do we find 

 that the brown or black matter of soil becomes the nutriment of vegetables, 

 and yet its service is immense. To understand the nature of the changes 

 which take place in the organic matter of the soil, it is necessary to know 

 what agents exist there. A mixture of carbonate of lime and magnesia, 

 silex and alumine, and organic matter, would remain without change for- 

 ever, were there no other bodies of a more active kind, whose affinities be- 

 come a present and efficient cause for action. These powers or forces exist 

 in the atmosphere and in the water diffused through the soil, and it is 

 proper to make a distinction of the atmosphere within the soil, from that 

 above or without it. The atmosphere is composed of two elements, oxygen 

 and nitrogen, in the proportion of 79 nitrogen to 21 oxygen. The latter is 

 free and uncombined with the nitrogen, or is merely dissolved in it, just as 

 sugar or salt is dissolved in water. The consequences which follow from 

 this condition or state of the elements, is, that both are free to unite with 

 other bodies, that is, so far as attraction for each other is concerned there 

 is no hindrance or force to be overcome to bring about a separation. 

 Hence, in the respiration of animals, the oxygen of the atmosphere which 

 is inhaled combines readily with the carbon suspended in the return or 

 venous blood. So in the soil, there is the same independence; the oxygen 

 or nitrogen is not hindered from uniting with other bodies by any affinity 

 existing between themselves. The final end or cause of this is, the ulti- 

 mate union of the oxygen with certain bodies in the soil, especially with 

 the organic part. The other agent, water, undergoes chemical changes of 



