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tible of the action of fire ; or, in a word, acquired, a bituminous 
nature : in which state it now presents itself on being freed from 
its stony impregnation. 
One circumstance, however, was wanting to render the analogy 
between silicious and calcareous wood complete. In that species 
of silicious wood, which has been distinguished by the term opa- 
lized wood, appearances were observable, which seemed to warrant 
the conclusion, that some of the bituminous wood had existed, at 
the time of its impregnation with silex, in a softened, and, perhaps, 
fluid bituminous state ; and that the waxy lustre, which this species 
of wood displays, proceeded from the intimate union of the silex 
and bitumen, whilst each was in a fluid state : but no analogous 
appearance to this had olfered itself to my observation, in any 
specimen of calcareous wood. It happened, however, that, a few 
days before this sheet was sent to the press, I met with a piece ot 
calcareous spar, imbedded in blue lime-stone, which, at its fracture, 
displayed somewhat of the resinous lustre; and on its polished 
surface, exhibited a beautifully clouded appearance, resembling 
tortoise’-shell, yielding, in fact, exactly such an appearance as might 
be expected from the intermixture of petroleum and spar. By the 
aid of a magnifying glass, somewhat of a fibrous texture, like that 
of wood, was observable in the lighter-coloured parts, but not in 
the least in the dark, apparently bituminous parts, which had just 
so much transparency as to allow the transmission of light at its 
edges A small portion of this spathose matter, about 50 grams, 
was added to an ounce and an half of water slightly acidulated with 
nitric acid. During the effervescence, several small fragments, 
evidently of bituminous wood, were detached; and, on the subsiding 
of the effervescence, these sunk to the bottom, leaving the fluid sti 
turbid, and of a dark brown colour ; but in about twelve hours, 
the liquid became clear ; the less completely changed wood ® 
the bottom, and a light bituminous matter swam at the top. at 
