PROPER MODE OF INVESTIGATION. 47 



manures, further inquiry will show us that these poor lands had 

 once been rich. 



The continued fertility of certain countries, for hundreds or even 

 thousands of years, does not prove that the land could not be, or 

 had not been, exhausted by cultivation; but only that it was slow 

 to exhaust and rapid in recovering; so that whatever repeated 

 changes may have occurred in each particular tract, the whole 

 country taken together always retained a high degree of productive- 

 ness. Still the same rule will apply to the richest and the poorest 

 soils to wit, that each exerts strongly a force to retain as much 

 fertility as nature gave to it and that when worn and reduced, 

 each kind may easily be restored to its original state, but cannot be 

 raised higher, with either durability or profit, by putrescent ma- 

 nures, whether applied by the bounty of nature, or the industry 

 of man. 



CHAPTER IV. 



EFFECTS OF THE PRESENCE OF CALCAREOUS EARTH IN SOILS. 



PROPOSITION 2. The natural sterility of the soils of lower Virginia 

 is caused by such soils being destitute of calcareous earth, and 

 their being injured by the presence and effects of vegetable acid. 



The means which would appear the most likely to lead to the 

 causes of the different capacities of soils for improvement is to 

 inquire whether any known ingredient or quality js-^always to be 

 found belonging to improvable soils, and never to the unim- 

 provable or which always accompanies the latter, and never the 

 former kind. If either of these results can be obtained, we will 

 have good ground for supposing that we have discovered the general 

 cause of fertility, in the one case, or of barrenness, in the other; 

 and it will follow that, if we can supply to barren soils the deficient 

 beneficial ingredient or can destroy that which is injurious to 

 them their incapacity for receiving improvement will be removed. 

 All the common ingredients of soils, as sand, clay, or gravel and 

 such qualities as moisture or dryness a level, or a hilly surface 

 however they may affect the value of soils, are each sometimes 

 found exhibited, in a remarkable degree, in both the fertile and the 

 sterile. The abundance of putrescent vegetable matter might well 

 be considered the cause of fertility, by one who judged only from 

 lands long under cultivation. But though vegetable matter in 

 sufficient quantity is essential to the existence of fertility, yet will 



