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became much more susceptible 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 offered 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 of 

 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 

 tortoiseshell, 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 grains, 

 was added to an ounce and an half of water slightly acidulated with 

 nitric acid. During the effervescence, several small fragments, evi- 

 dently of bituminous wood, were detached ; and, on the subsiding 

 of the effervescence, these sunk to the bottom, leaving the fluid still 

 turbid, and of a dark brown colour: but, in about twelve hours, 

 the liquid became clear ; the less completely changed wood sunk to 

 the bottom, and a light bituminous matter swam at the top. That 



