285 
substance would be formed, without disturbing the existing arrangement 
of those parts, on which the form and general appearance of the fossil 
would depend. To determine how far this opinion was correct, wood, 
petrified by flint, was subjected to simple distillation over a naked fire, 
when an oily sublimated film, possessing a strong empyreumatic smell, 
was obtained. It could not be expected, from the refractory nature of 
silica, that any thing more decisive could be obtained from any 
experiment on opaline wood ; since no agent could, perhaps, be employed 
for the removal of the earth which would not, at the same time, entirely 
decompose the bituminous substratum. 
But in calcareous fossil wood this objection did not exist, since by 
the employment of any dilute acid, the earth might be removed, and 
it might be clearly ascertained whether the presumed vegetable or 
bituminous matter was present or not. The experiment was made, 
and with complete success : the cai’bonate of lime was removed by 
diluted muriatic acid, and a dark brown, friable, but coherent mass 
remained, which bore every appearance of bituminous wood, and 
which, when brought into contact with the flame of a candle, directly 
burned with a small, bright, lambent flame, and yielded a strong 
bituminous odour. 
From this experiment, I conceived that I was warranted in con- 
cluding that, with respect to vegetables, the process of petrifac- 
tion is not merely, as Mr. Kirwan supposes, the substitution of stony 
or metallic bodies, in the place of the organic substance which has 
been destroyed by putrefaction nor, as is taught by Fourcroy, that 
the petrifying matter is deposited as in a mould : the complete de- 
struction of the vegetable matter and the disappearance of whatever 
constituted its elements taking place at the same time.-j- But that a 
part of the organic matter still remained, though somewhat changed ; 
and that the process of petrifaction was the impregnation of this sub- 
* Geological Essays, P. 137. 
f Systeme des Connoissances Chitniques, Tome VIII. P. 255. 
