301 
tion; 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 
penetrated, in a state of solution by water, the regular structure of 
the plant would still have remained, with its vacuities, variously 
filed 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 been effected by any other means, but an aqueous 
solution of the impregnating matter. Now not to dwell on the 
general evidence, which, I think, is yielded by almost every specimen 
of silicious wood j I will urge the more direct evidence which is 
afforded by a particular specimen I possess. In this specimen, im- 
pregnated 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 
* Theory of the Earth, vol. i- p- 61' 
