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our ideas of elementary principles may be simpli- 
fied, it is impossible to say. We can only reason 
from facts. We cannot imitate the powers of com- 
position belonging to vegetable structures ; but at 
least we can understand them : and, as far as our 
researches have gone, it appears that in vegetation 
compound forms are uniformly produced from 
simpler ones ; and the elements in the soil, the atmo- 
sphere, and the earth, absorbed and made parts of 
beautiful and diversified structures. 
The views which have been just developed lead 
to correct ideas of the operation of these manures, 
which are not necessarily the result of decayed 
organised bodies, and which are not composed of 
different proportions of carbon, hydrogene, oxy- 
gene, and azote. — They must produce their effect, 
either by becoming a constituent part of the plant, 
or by acting upon its more essential food, so as to 
render it more fitted for the purposes of vegetable 
life. 
The only substances which can with propriety 
be called fossile manures, and which are found 
unmixed with the remains of any organised beings, 
are certain alkaline earths, or alkalies, and their 
combinations. 
The only alkaline earths which have been hitherto 
applied in this way, are lime and magnesia. Pot- 
assa and soda, the two fixed alkalies, are both 
used in certain of their chemical compounds. I 
shall state in succession such facts as have come to 
my knowledge respecting each of these bodies in 
their applications to the purposes of agriculture ; 
but I shall enlarge most upon the subject of lime ; 
