299 



petrified wood, 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, sili- 

 cified 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 specimens where, besides concentric layers, the me- 

 dullary prolongations are seen spreading from the centre to the cir- 

 cumference, 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 substance, retaining its form, texture, and di- 

 mensions, 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 de- 

 stroyed, 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 substitution 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 what- 

 ever 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, 



* Syst&ne des Comioissances Chimiques, torn. viii. p. 255. 



