380 
calcareous spar may owe its colour, in some instances, to bitumen, 
must therefore be admitted : nor do I in the least doubt but in- 
vestigation 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 impreg- 
nation, it being of a very pale colour, nearly resembling that of 
decayed 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 proportion, 
that, on its removal by the acid, the vegetable or bituminous matter 
no longer held together, but subsided in a flocculent sediment 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- 
minous wood ; and what carbonate has entered, is formed into crys- 
talline 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 Helmontii, or 
Waxen Vein. 
