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or other vegetable matter, he remarks, it is a great error to consider 
it, as a conversion of vegetable matter into silex, as the term seems 
to imply. There exists, he says, to be sure, silicified fossil matters, 
which present to our view, not only the texture of wood, in general, 
but that even of particular kinds of wood : but the greater part of 
such specimens are, he thinks, merely pieces of jasper, the fibrous 
appearance of which imitates that of wood. Even in those speci- 
mens where, besides concentric layers, the medullary prolongations 
are seen spreading from the centre to the circumference, and which 
is, he thinks, the only incontestible proof of the specimen having 
been wood, it is not to be imagined that the original woody sub- 
stance, retaining its form, texture, and dimensions, is converted into 
silicious matter : it is necessary, he says, to conceive otherwise of 
fossil bodies, bearing these marks of organization. Wood, leaves, 
fruit, and all other kinds of vegetable matter, improperly said to be 
petrified, have been gradually destroyed, almost atom by atom, 
within the wet earth, where it has left a hollow mould, which becomes 
exactly filled by the silicious earth which the water has conveyed 
thither. Thus it really is not a petrified wood, but only a substitu- 
tion of silicious matter, mixed with other earths and metallic oxides, 
in the place of the wood. This species of silification is then, he 
adds, a proof of the complete destruction of the vegetable matter, and 
of the disappearance of whatever constituted its elements*. 
Innumerable objections oppose themselves to the attempt, of 
accounting for the lapidification of vegetable substances, by this 
process of substitution. In what manner can it be supposed that a 
line, smaller than a hair, extending from the centre of a piece of 
wood to its circumference, can have its original component parts 
taken away, and their places so exactly filled by earthy particles, 
merely deposited from water, as to preserve its continuity unbroken ? 
* Systeme des Connoissances Chimiques, tom. viii. p. 255. 
