304 
say, that I never yet saw one in which the line separating these two 
parts of the specimen was quite sharp and distinct, and different 
from what must have taken place, had the flinty matter been intro- 
duced into the body of the wood, by any fluid, in which it was dis- 
solved. On the contrary, in numerous specimens now before me, in 
which the fibres of the fossil wood are in some parts distinct, and in 
others lost, I seek in vain for any line of distinction, as to the pene- 
tration of the wood with silicious matter; but see, in all, no dif- 
ference whatever, in this respect, in that part where the structure is 
confused, or where it is distinct ; nor do I find the least reason to 
suppose, that the silex has not pervaded the whole, in the most 
uniform manner. 
‘‘ In those specimens of fossil wood that are partly penetrated by 
agate, and partly not penetrated at all,” the Professor says, ‘‘the 
same sharpness of termination may be remarked, and is an appear- 
ance highly characteristic of the fluidity produced by fusion.” Here 
I have again to lament the never having had the opportunity of seeing 
a specimen similar to those which are here alluded to. I possess 
several specimens of agatine, opaline, and jasperine woods, the 
appearance of the external parts of which very nearly resemble that 
of unchanged wood ; but examination soon shows that these parts 
have also been fully penetrated by the silex. That such specimens 
do not exist, it is not my intention to assert ; it is quite sufficient to 
remark, that such specimens would only prove that the petrifying 
matter had only been applied to one particular part of the wood : a 
circumstance of which there certainly exists no reason to prohibit 
the occurrence, in the case of the application of an aqueous solution 
of petrifying matter. 
Mr. Kirwan, indeed, quotes an account, that the Emperor of 
Germany, being desirous to know the length of time necessary to 
complete a petrifaction, obtained leave from the Sultan to take up, 
and examine, one of the timbers that had supported Trajan’s bridge 
