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LETTER XXL 
THE PURER BITUMENS, THE RESULT OF THE SAME FERMENTATION 
BY WHICH PEAT HAS BEEN FORMED BITUMINOUS FERMENTA- 
TION IMITATES, IN ITS RESULTS, THE OPERATION OF SECRETION 
.'.....MINERAL TALLOW, PERHAPS OF ANIMAL ORIGIN OTHER 
ARGUMENTS IN FAVOUR OF BITUMINOUS FERMENTATION. 
Having seen reason to conclude, after examining the subject in 
various points of view, that peat is the result of the changes effected 
on vegetable matter, during the first stage of a peculiar fermentation, 
it is proper now to proceed to inquire what is the product of that 
fermentation in a more advanced stage. But here I must be allowed 
to avail myself of the same indulgence, which 'I was obliged to 
crave, whilst endeavouring to ascertain the' origin of the former 
substance. Here, also, are the same impediments to the obtaining 
of positive proofs of the nature of the operation which nature has 
decreed to take place ; for here, as in the former case, where the 
process is carried on where the eye cannot reach, circumstantial 
evidence, respecting the particulars, and the products, of the ope- 
ration, can only be obtained. 
Every information which the best authorities have afforded, and 
every conjecture which I have been induced to form, from a careful 
attention to analogy, have led to the conclusion, that the purer 
bitumens, such as naphtha, amber, petroleum, asphaltum, &c. are 
the products of the same bituminous fermentation, only in a more 
advanced stage, as that on which the formation of peat depends. 
A considerable weight of evidence is undoubtedly furnished by 
the similarity of the products furnished by a chemical analysis of 
the peat and the bitumens. That their products by distillation agree 
