substance would be formed, without disturbing the existing arrange- 

 ment of those parts, on which the form and general appearance of the 

 fossil would depend. To determine how far this opinion was cor- 

 rect, wood petrified by flint, was subjected to simple distillation over 

 a naked fire, when an oily sublimated film, possessing a strong empy- 

 reumatic smell, was obtained. It could not be expected, from the re- 

 fractory nature of silica, that any thing more decisive could be ob- 

 tained, 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 carbonate 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 f. 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. 



t Systeme des Connoissances Chimiques, Tome VIII. p. 255, 



