37 ; 
earth; but was unable to adduce any direct and positive evidence, 
in favour of this opinion, owing to the refractory nature of the silex, 
which demanded such agents to effect its separation, as would not 
fail to occasion a decomposition of the vegetable, or bituminous 
matter, with which it was combined. In calcareous fossil wood, 
which I suppose to differ from the former, merely in the nature of 
the earth thus introduced, the same difficulty does not exist ; since it 
will yield to the action of less destructive agents, and will allow of 
the complete separation of the superadded, from the original matter. 
Thus, by the addition of the mineral acids in a state of dilution, it 
might be expected that the carbonate of lime Avould be decomposed, 
and that the interposed particles of earth might in this manner be 
removed, leaving the vegetable or bituminous matter, in that state in 
which it existed, when its particles were first, perhaps some thousands 
of years since, involved in this stony mass. The result of such an 
experiment might also afford some elucidation of the question, re- 
specting the formation of silicious wood ; since if the original matter 
could be plainly made out, in the case of calcareous fossil wood, the 
inference would undoubtedly be admitted, that it was the same in the 
silicious fossil wood, and that in both cases the lapidifying change 
had been effected by impregnation, and not by substitution. 
A piece of the light-coloured fossil wood of Oxfordshire, already 
described, was immerged in nitric acid, diluted with about four times 
its bulk of water ; a considerable degree of effervescence ensued, 
which lasted several hours ; at the end of which time, the carbonate 
of lime being completely decomposed, the original matter of the 
wood had fallen to the bottom, in the form of a dark, fine, umber- 
coloured, flocculent sediment ; the carbonate of lime having been so 
thoroughly diffused between these light particles, as to have been 
their only bond of connection. A portion of this sediment, after 
having been washed and dried, was placed on a red-hot iron, when it 
directly inflamed, and was quickly consumed. 
VOL. I. 3 c 
