341 



is formed by a thin cortical coat, exactly resembling that of the 

 inner cortical investment of recent wood. Another form, which, in 

 these instances, the external surface sometimes, bears, is that of ap- 

 parently dried, and withered wood, as at Plate II. Fig, 9. Both in 

 this, and in the other specimen the seeming cortical surfaces are per- 

 vaded by silex, but appear to be but little changed by bituminiza- 

 tion. This may assist, in accounting for their not possessing the re- 

 sinous lustre, which distinguishes the rest of the mass: numerous 

 observations seeming to point out, that the bark, and dry withered 

 wood, are not so susceptible of bituminous change, as those parts 

 in which the woody fibre was unimpoverished. 



Another circumstance, hitherto inexplicable, demands next to be 

 noticed. In many specimens of silicious fossil wood, are found 

 disposed, in and about it, distinct masses of a substance, bearing 

 so exactly the appearance of bitumen, as would leave no doubt of 

 its being of that nature, were it not that examination discovers it to 

 be a substance, containing a considerable proportion of silex. The 

 explanation of the formation of this mysterious substance is, un- 

 doubtedly, accompanied with considerable difficulty. After having 

 examined it in every point of view, I discover no mode of explain- 

 ing its formation, but by supposing it to have been actually a fluid 

 dark bitumen, which, by the medium of the water, we have already 

 seen it contains, has become impregnated by silicious earth. 



The general appearance of this seeming bituminous substance 

 appears strongly to point it out, as having existed in a soft state: 

 some pieces of it appearing as if their eminences had been rounded 

 off by slight friction. In the specimen figured at Plate II. Pig. 4. 

 which has very much the appearance of a piece of fossil deal wood, 

 this black bituminous-like matter almost covers one end, and pe- 

 netrates into the substance of the wood, as may be seen by the 

 section of the same specimen, at Fig. 5. of the same Plate: the 

 wood having split at the end, as if from dryness ; and the bitumen, 



