LETTER XXI. 



THE PURER BITUMENS, THE RESULT OF THE SAME FERMENTA- 

 TION BY WHICH PEAT HAS-BEEN FORMED.. ..BITUMINOUS FER- 

 MENTATION IMITATES, IN ITS RESULTS, THE OPERATION OF 

 SECRETION. ...MINERAL TALLOW, PERHAPS OF ANIMAL ORIGIN 

 ....OTHER ARGUMENTS IN FAVOUR OF BITUMINOUS FERMENTA- 

 TION. 



JH.AVING 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 stag of a peculiar fermentation, 

 it is proper now to proceed to enquire 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 opera- 

 tion, can only be obtained. 



Every information which the best authorities have afforded, and 

 every conjecture which I have been induced to form, from a care- 

 ful 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 



