307 
"^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 con- 
version into stone. 
Thus, I 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 particles of 
earth have been deposited, will necessarily be the subjects of se- 
parate examinations. For although, in almost every case of vege- 
table petrifaction, the earthy particles appear to have been deposited 
chiefly in a crystalline form, it is not meant to deny, that this 
process may have been aided by the introduction, and deposition, 
