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we know that their removal from a soil destroys its fertility, 
which may be restored and increased by a new supply. 
Is it possible, after so many decisive investigations into the 
origin of animals and vegetables, the use of the alkalies, of lime, 
and the phosphates, any doubt can exist as to the principles 
upon which a rational agriculture depends ? Can the art of 
agriculture be based upon anything but the restitution of 
a disturbed equilibrium ? Can it be imagined that any country 
however rich and fertile, with a flourishing commerce, which 
for centuries exports its produce in the shape of grain and 
cattle, will maintain its fertility, if the same commerce does not 
restore, in some form of manure, those elements which have 
been removed from the soil, and which cannot be replaced by 
the atmosphere ? Must not the same fate await every such 
country which has actually befallen the once prolific soil of 
Virginia, now, in many parts, unable to grow its former staple 
productions — wheat and tobacco. ? 
In the large towns of England the produce both of English 
and foreign agriculture is largely consumed ; elements of the 
soil indispensable to plants do not return to the fields — contri- 
vances resulting from the manners and customs of English 
people, and peculiar to them, render it difiicult, perhaps impos- 
sible, to collect the enormous quantity of the phosphates which 
are daily, as solid and liquid excrements, carried into the rivers. 
These phosphates, although present in the soil in the smallest 
quantity, are its most important mineral constituents. It was 
observed that many English fields, exhausted in that manner, 
immediately doubled their produce, as if by miracle, when 
dressed with bone earth imported from the continent. But if 
the export of bones from Germany is continued to the extent it 
has hitherto reached, the soil of Germany must be gradually 
exhausted, and the extent of loss may be estimated, by con- 
sidering that one pound of bones contains as much phosphoric 
acid as a hundred-weight of grain. 
A field in which we cultivate the same plant for several suc- 
cessive years becomes barren for that plant in a period varying 
with the nature of the soil; in one field it nill be in three, in 
another in seven, in a third in twenty, in a fourth in a hundred 
years. One field bears wheat, and no peas; another beans or 
turnips, but no tobacco ; a third gives a plentiful crop of 
