474 FOSSIL INVERTEBRATED ANIMALS. 



author, if the stony molecules had taken the place of the lig- 

 neous molecules, all the petrified mass would be of an uniform 

 colour, since the same stony matter would have successively 

 filled all the places left empty by the retirement of the ligneous 

 particles. 



To this observation we may answer, that it is easy to conceive 

 that each fibre of the wood has had its parts replaced succes- 

 sively, in such a manner that its general form and direction 

 have been in nowise altered ; and that the number of fibres of 

 a piece of petrified wood may be found equal to that of the 

 fibres of a piece of living wood of the same volume. As to the 

 colours, it appears to us that the observation respecting them 

 is more just ; nevertheless, there are many specimens of petrified 

 Avoods, all of which have the same tint. 



M. Patrin also refuses to admit the preliminary decomposi- 

 tion of the petrified wood ; and, on this subject, he instances 

 many specimens of petrified woods which contain holes made 

 by worms, and even the worms themselves, and their eggs, 

 changed into agate. From this he concludes that, if the fluid, 

 charged with siliceous matter, had deposited this matter, it 

 would also have filled the vacant spaces which we have just 

 mentioned. To this, again, may be plausibly opposed, that 

 the siliceous matter may have been deposited by an affinity 

 near the molecules of wood, without being deposited elsewhere ; 

 and thus the vacancies would have been preserved. 



According to M. Patrin, the decomposition took place sud- 

 denly ; for, from the moment in which substances so soft as 

 worms had experienced putrefaction, they would have been so 

 much deformed that not the least distinguishable appearance 

 of them would have remained. 



To this, once more, we may reply, that the fluid, which dis- 

 solved the siliceous matter, might have possessed a conserva- 

 tive property for the worms; and that, also, the change of the 

 latter into silex may have been more prompt than that of the 

 wood. Moreover, it would be desirable that the existence of 



