301 



wood, with the vascular structure, perfectly in its natural state and 

 situation, but if it had been by aqueous solution that the. wood 

 had been penetrated and consolidated, all the parts of that body 

 would be found in the same natural shape and situation. This, 

 however, is far from being the case ; for while, in some parts, the 

 vascular structure is preserved entire, it is also evident, that, in 

 general, the woody structure is variously broken and dissolved by 

 the fusion and crystallization of the flint*/' 



The first proposition which the Doctor lays down, and with regard 

 to which, he says, there cannot be a doubt, is that " with whatever 

 different substances the woody body shall be supposed to have been pene- 

 trated, in a state of solution by water, the regular structure of the 

 plant would still have remained, with its vacuities, variously filled with 

 the petrifying substances, separated from the aqueous menstruum, and 

 deposited in the vascular structure of the wood." The test which the 

 Doctor has here proposed for ascertaining, whether the petrifaction 

 of wood is, or is not, an operation dependent on aqueous solution, 

 is certainly the best adapted of any that could .be devised ; for, as 

 is implied in the Doctor's statement, if the regular structure of the 

 plant remain, with its vacuities, variously filled with the petrifying 

 substances, separated from the aqueous menstruum, and deposited 

 in the vascular structure of the wood ; then the change cannot have 

 b*een effected by any other means, but an aqueous solution of the 

 impregnating matter. Now not to dwell on the general evidence, 

 which, 1 think, is yielded by almost every specimen of silicious 

 wood ; I will urge the more direct evidence which is afforded 

 by a particular specimen I possess. In this specimen, impregnated 

 with silex, either by gradual decay, or by the mechanical action of 

 water, the fasciculi of longitudinal fibres, which appear to have 

 retained their natural colour, seem to have been so loosened in their 

 attachments, as to have hardly adhered together, previous to their 



* Theory of the Earth, vol. i. p. 61. 



