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colour and general appearance of which manifests very plainly its 

 previous bituminization, the silicious impregnation, in those spe- 

 cimens which I possess, has been such as to have given to them suffi- 

 cient hardness to dispose to the conchoidal fracture, approaching 

 in some parts to the shivery ; and to occasion them to yield sparks, 

 by percussion with steel. Their external surface has sometimes the 

 whiteness of wood which has been long exposed to the air ; but a 

 section of them shows the internal substance to be of the colour of 

 dark brown bituminized wood. The character of this species of 

 fossil wood is, that although the silicious fluid has pervaded every 

 part of -it, it has entered into no other union with it, than that of 

 penetrating every fibre, and filling up every minute interstice, 

 without entering into such chemical union with the bitumen, as to 

 allow it to manifest the least trace of bitumen, in its lustre, transpa- 

 rency, or colour, in any of those parts where the silex has been 

 allowed to transude, and separate from the general mass of the im- 

 pregnated wood : the silicious matter assuming, generally, in those 

 situations, the mammillated surface, and that degree of transparency, 

 which is in general displayed by silicious matter, in that form which 

 is termed mammillated calcedony. In PL II. Fig. 10. is represented 

 a specimen, showing the whitened surface, beautifully invested with 

 transparent mammillated calcedony, appearing as if it had perco- 

 lated through the substance, and had hardened on the surface of 

 the wood. Plate VIII. Fig. 9- represents another specimen, in 

 which the circular cavities, which had been formed by the teredo 

 navalis, are filled up by the transudation of the uncoloured, pellucid 

 calcedony. At Plate II. Fig. 11. a specimen is depicted, which 

 appears to have suffered a higher degree of bituminization, in conse- 

 quence of which the filtered silicious matter, with which it is every 

 where beset, in the form of yellow semi-pellucid globules, appear to 

 have derived some slight tinge from the bitumen ; which, in conse- 

 quence of the more perfect state of bituminization, in which it had 



