30? 



dered essentially different in its nature, it frequently happens, that 

 its form has undergone no change, and that the disposition of its 

 fibres has suffered hardly any alteration. The second is, that, when 

 found in wet situations, its substance is so thoroughly pervaded by 

 water, that it may be discharged from it as from a sponge. 



Reflection on these circumstances must show, that this wood is 

 in the exact state which fits it, for becoming a similar substance, 

 with that which most specimens of fossil wood present to our view. 

 The form and structure of the wood are curiously preserved ; water 

 pervades every part of it ; and its durability is such, as to ensure 

 its preservation until that event happens, on which its consolidation 

 appears to depend the saturation of the water, with which it is in 

 every part imbued, with earthy particles, in a state of solution. 

 These consolidating, by the formation of extremely minute crystal- 

 lizations, through the whole softened mass of bituminized wood, 

 give it a calcareous, or a silicious substance, without disturbing 

 the existing arrangement of its fibres. Thus appear to be formed 

 all those fossils, which really deserve the name of vegetable petri- 

 factions ; and thus, perhaps, can, alone, be explained that curious 

 phenomenon the exact preservation of even the minute fibres of 

 the wood ; still retaining their continuity, and their original charac- 

 teristic disposition, whilst their substance has undergone a conver- 

 sion into stone. 



Thus, 1 trust, may the petrifaction of, by far the greater part of, 

 vegetable fossils be explained. The several species, and varieties, 

 dependent, on the different substances which have been thus 

 changed, on the kind of earth, and on the state in which the par- 

 ticles of earth have been deposited, will necessarily be the subjects 

 of separate examinations. For although, in almost every case, of 

 vegetable petrifaction, the earthy particles appear to have been de- 

 posited chiefly in a crystalline form, it is not meant to deny, that 

 this process may have been aided by the introduction, and deposi- 



