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oxide of the metal fill up the interstices, and involves the whole in a 
confused mass, as may be seen in the bog-iron of Shropshire, and 
many other parts. 
But, even admitting these instances of variation, I trust you will 
perceive that the grand agent in the mineralization of vegetables, 
is the process of bituminization ; which readily melts down the lig- 
neous substance — that substance which yields to hardly any other 
process, natural or artificial, and which resists almost every power, 
but that of fire. The examination of the vast variety which vege- 
table fossils yield, and the attempt to explain the circumstances, 
on which their different appearances depend, will best serve to show 
the degree of solidity possessed by this theory, which thus sup- 
poses the process of bituminization, to be the basis, as it were, of 
the petrifactive process by which the greater part of vegetable fossils 
have been formed. 
The earths which are most frequently found to be the chief con- 
stituents of vegetable fossils are silex, lime, and alumine ; and, ac- 
cording to the preponderance of either of these earths, may the fossil 
be distinguished by the term silicious, calcareous, or aluminous. 
Unwilling to take liberties with the mode of expression which com- 
mon usage has authorized, unless able to demonstrate a positive 
superiority, in the mode which is proposed to supersede that which 
is already adopted, I will not urge the adoption of such expressions, 
as pyritified wood, silicified wood, &c. which point out the circum- 
stance, of the substance having been once wood, but having now 
assumed an entirely different nature. I cannot, however, omit to 
observe here, that such words as do imply a real transmutation, 
may frequently be employed, without meriting that degree of cen- 
sure, which we have already seen is bestowed on them, by M. 
Daubenton ; since, although the stony nature of such substances is 
admitted to be merely the result of an earthy impregnation, the 
substances thus impregnated will, I believe, in general, be found to 
