SANDSTONE PETRIFACTIONS. 161 



round a piece of wood, or other organized matter, 

 we cannot possibly see how the inner part of it 

 should be petrified. But when we inspect the pe- 

 trifactions of which I am speaking, we find the in- 

 ner parts of them equally solid, and equally con- 

 verted into stone with the exterior : — nay, if any 

 difference, more so. It also appears to me, to be 

 difficult to apprehend how the particles of sand 

 should penetrate the lower parts of the wood equal- 

 ly with the upper, contrary to the law of gravity ; 

 though, perhaps, the principle of pressure may help 

 us out here. 



But if we reject the opinion of sandstone being 

 a mechanical deposit, and conceive it to be a chemi- 

 cal precipitate, in the same way as some other stony 

 substances undoubtedly are, then, I think, the ex- 

 planation of sandstone petrifactions, though by no 

 means divested of difficulty, will be very much fa- 

 cilitated. For, on the supposition that the quartzy 

 or siliceous matter of which the particles of sand- 

 stone are composed, were dissolved in a fluid, then 

 we can more readily form an idea of the manner in 

 which this solution, havingpenetrated the wood, might 

 there precipitate its contents, and so produce the 

 appearances we observe. And though even here a 

 difficulty presents itself, (for what becomes of the car- 

 bon and other indestructible parts of the vegetable ?) 

 yet the difficulty is not, I think, so great as when we 

 suppose the mechanical formation of the sandstone. 

 We know that all the different parts of wood ex- 



VOL. III. L 



