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that it is therefore well fitted for the formation of substances, so 
abundant in carbon, as is coal, and every species of bitumen. Even 
the concurrent influence of air and water effects scarcely any 
change on it ; and it is said to resist, so absolutely, every known 
kind of fermentation, as to be supposed to be indestructible, except 
by insects. Reasoning, then, on the chemical nature of this sub- 
stance, we are led, by analogy, to conclude, that, as in every other 
case, so here, nature has appointed some agent, by which this ap- 
parently refractory substance shall be made to pass into new com- 
binations. Such an agent, the bituminous fermentation appears to 
be; and every observation warrants the conclusion, that it is the 
ligneous part of vegetables which is the chief substance susceptible 
of this peculiar change. 
Yours, &c. 
LETTER XXII. 
OP THE ORIGIN OF THE PURER BITUMENS NAPHTHA PETRO- 
I^EUM MINERAL TAB MINERAL PITCH ASPHALTUM 
AMBER MELLITE JET AND CANNEL COAL. 
T HAT the purer bitumens have had the same origin as peat that 
they have been produced from the same species of matter, and by 
the same natural process — and that they differ from it only in 
having been separated by percolation from the grosser parts, seem 
