380 



calcareous spar may owe its colour, in some instances, to bitumen, 

 must therefore be admitted : nor do I in the least doubt but inves- 

 tigation will discover, that the influence of bitumen is much more 

 extended, among the class of calcareous stones, than has been 

 hitherto supposed. 



The appearance which the above-mentioned fossil wood from 

 Oxfordshire yielded, previous to its exposure to the action of the 

 acid, was such as to lead me to suppose that it must have existed, 

 in a dry and withered state, at the time of its lapideous impregna- 

 tion, it being of a very pale colour, nearly resembling that of de- 

 cayed wood. But, on the removal of the stony matter, by the 

 action of the acid, it resumed the dark brown colour of bituminous 

 wood, which it retained, after it had been dried by the fire. The 

 light colour, which had thus deceived me, evidently proceeded from 

 the abundance of the white, spathose matter, with which it had 

 been penetrated ; and which had been in so considerable a propor- 

 tion, that, on its removal by the acid, the vegetable or bituminous 

 matter no longer held together, but subsided in a flocculent sedi- 

 ment to the bottom of the vessel. 



This kind of fossil wood is frequently found inclosed within the 

 solid lime-stone ; and it happens most frequently, that when suffi- 

 cient carbonate, in solution, has not percolated through the coarser 

 carbonate, or lime-stone, to impregnate the whole of the inclosed 

 wood, the latter remains soft and yielding, and exactly like bitu- 

 minious wood ; and what carbonate has entered, is formed into cry- 

 stalline septa, which, by intersecting each other, necessarily divide 

 the inclosed wood into small polygons: the whole yielding an ap- 

 pearance, which would not be badly represented by Fig. 5. in 

 Plate I. only substituting the brown bituminous wood, for the jet: 

 nor would a very dissimilar idea be formed of it, by conceiving its 

 divisions to resemble those of the Septarium, Ludus Helraontii, or 

 Waxen Vein. 



