108 AMERICAN MANURES. 



last four hundred years; although the soil 

 would cease to be fertile long before the last 

 particle of lime was removed. The supply of 

 magnesia is small in proportion to the other sub- 

 stances, and as most crops require more magnesia 

 than lime, this compound would be the first ex- 

 hausted in this soil. It will also be seen that 

 there are four and a half tons, or 90001bs. of 

 phosphoric acid. Supposing this to be in the 

 shape of bone phosphate of lime, or associated 

 with other bases in an insoluble form, and worth 

 four cents a pound, we have three hundred and 

 sixty dollars as the value of that article alone. 



It is very probable that this soil has been 

 cropped over a thousand years, and still contains 

 within itself sufficient of every fertilizing sub- 

 stance to last at least two hundred years or 

 more. Soils containing only a tenth in quantity 

 of these necessary elements may be equally 

 fertile, as only a given quantity can be assimi- 

 lated by each yearly crop, but the difference in 

 quantity should be an element in determining 

 the commercial value of the land. The time 

 must come, and is not very distant, when the 

 price of lands will be rated by their composition, 

 and not merely their present capacity for raising 

 crops. 



The following is an analysis of a remarkably 

 sterile soil : 



