LETTER XIX. 



FOSSIL TREES, IMBEDDED IN PEAT, HAVE UNDERGONE THE BITU- 

 MINOUS FERMENTATION. ...THE CHANGES WHICH MOW-BURNT 

 HAY UNDERGOES, SOMEWHAT SIMILAR TO THAT PRODUCED BY 

 THE BITUMINOUS FERMENTATION. 



1 HE fossil trees which are so frequently found imbedded in peat, 

 may also be considered as vegetable fossils ; and as they appear to 

 have undergone exactly the same kind, and the same degree of 

 mineralization with peat, their consideration along with that sub- 

 stance seems most eligible* 



These trees, as appears by the accounts already given, are almost 

 always found to have preserved their original form and structure so 

 exactly, as frequently to render it easy to discover what species of 

 trees they are, even in this their mineralized state. When first found, 

 these trees are generally of a dark brown colour, manifesting, as 

 has been already mentioned, the exact form of the original tree ; 

 but so soft, as to be capable of being deeply cut into by the stroke 

 of a spade ; and also of so spungy a texture, as to allow a very 

 considerable quantity of water to be squeezed from them, even by 

 a moderate degree of pressure. So tenacious are they of the water 

 they have thus imbibed, as still to retain a- very large portion of it, 

 even where great pains have been taken to procure its expulsion. 



But when, after long exposure to the air, this water has been 

 evaporated, the substance of these fossil trees assumes different de- 

 grees of solidity, dependent on the state in which the wood existed 

 at the time of its exposure to the bituminous fermentation, and cm 



