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have suifered an actual transmutation — a total change in its nature ; 
that which w^as ligneous having at least become bituminous. 
As the fossil wood, which appears to exist most abundantly, is 
that which has undergone a silicious impregnation, and as the for- 
mation of this species of fossil wood appears to be the most diffi- 
cult to be explained, we will take it first into consideration. But 
as its impregnation is here assumed to have been accomplished, by 
a solution of the silex, in some aqueous menstruum ; a circumstance 
of which no positive proof can, perhaps, be adduced ; it is neces- 
sary, previous to entering into a particular examination of this 
substance itself, to determine what degree of force is possessed, 
by that collateral evidence, to which we are necessitated to have 
recourse. 
So regularly does the earthy matter appear to have been diffused, 
through every part of the changed wood; and so intimate is the 
union which has taken place, that its deposition from a solution 
appears to be obvious. That it has chiefly been deposited in minute 
crystallizations, which, by their regular apposition to each other, 
have formed that continued silicious substance, of which these fossils 
are composed, may be inferred from the circumstance of most of 
these specimens having their surface invested with a crust of ex- 
tremely minute crystals ; and from a similar investiture, even, sur- 
rounding, in some specimens, every distinct compages of fibres, and 
lining the sides of every cavity, without obliterating them ; whilst, 
m other specimens, similar cavities, and fissures, proceeding from 
a deficiency of wood, or bituminous matter, are filled with a trans- 
parent quartzous mass. These circumstances are so plainly indica- 
tive of a slow deposition, from a solution in some aqueous men- 
struum, that here we might have rested our proof; if it had not 
been asserted, that all these effects might have been produced by 
the injection of silex, rendered fluid, hy simple fusion, hy heat This 
renders it, therefore, necessary, that we should first endeavour to 
