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sits, in their places, the stony particles ; which are necessarily dis- 

 posed in the same order, and in the same form, with those of the 

 ligneous parts, which have been removed ; since they have been 

 distributed in the same points, and have been moulded in the same 

 cavities, which the molecules of the decayed wood have left. All 

 the substance of the wood is thus, by degrees, removed, and its 

 place exactly filled by a stony substance, bearing the exact appear- 

 ance of the wood itself. These stones, then, he says, are, in fact, 

 not petrifactions, but only stony depositions which have received 

 the impressions of different parts of the wood : and he concludes, 

 that there is no vegetable substance which can become petrified ; 

 and that petrifaction can only take place in animal substances, of 

 which a part already possesses a stony hardness. To prevent any 

 mistake on this subject, he observes, that petrified wood should 

 possess the distinctive character of wood, by possessing the medul- 

 lary productions. It is not sufficient to see concentric layers, it is 

 necessary there should be also lines traversing these annual layers ; 

 as they are beheld in the tranverse section of a tree, from the pith 

 to the bark, and in some trees, as the cork and the green oak, even 

 in the bark itself*. 



The opinion of Mons. Fourcroy, on this subject, very much 

 resembles that of Mons. Daubenton. The layers, he says, of fossil 

 wood, penetrated by water, lose a portion of their dissoluble, mu- 

 cilaginous, and extractive matter, with a part of the hydrogen, 

 which they contained. Hence they approach to the state of a pure 

 wooden skeleton : the external substance of the woody fibres being 

 even decomposed, and taking on the colour and appearance of 

 charcoal. It appears, he says, in fact, that, although still woody, 

 the fossil wood is approaching to destruction ; and that a still' 

 longer stay in the earth would destroy it entirely. With respect to 



* Legora Nonnales, torn, iii, Observations sur les Petrifications, 



