302 
their impregnation ; and in some parts very considerable vacuities 
have been formed. In its present state, exceedingly small silicious 
crystals invest every fasciculus, and line every interstice and cavity, 
but without proceeding so far as to entirely obliterate them, or in 
the least to alter the regular structure of the wood ; all the remaining 
parts of which appearing to retain their natural shape and situation. 
That such an investiture of crystallization, spreading almost over 
the whole surface, could have been thus regularly disposed, from an 
injection of flint rendered fluid by heat, without obliterating the 
small cavities, and interstices of the wood, by the introduction of 
e melted matter and without affecting the regular structure, or 
even the colour of the wood, is hardly to be conceived; whilst the 
supposition of the silicious matter having been gradually applied, 
from an aqueous menstruum, offers us, comparatively, no difKculties 
to encounter. 
In the concluding part of the Doctor’s observations, two positions 
are laid down ; first, that if it had been by an 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 ; 
secondly, that the woody structure is variously broken and dissolved 
by the fusion and crystallization of the flint. With respect to the 
first of these positions, it certainly does appear to be untenable, 
since many specimens of fossil wood bear the strongest marks of 
having suffered much from decay previous to their impregnation; 
and surely, from long maceration and agitation in water, the pres- 
surrounding hard bodies, and the numerous accidents to 
which this wood may have been exposed, previous to its impreg- 
nation, It would not be surprising, if, after its consolidation, by the 
means of an aqueous menstruum, all its parts were not found in 
their natural shape and situation. On the other hand, specimens 
are frequent m which the natural shape and situation of the parts 
are preserved throughout, even to fibres, distinguishable only by the 
I 
