338 



not in the least, in its appearance, from the knot in a piece of 

 recent wood, but is perfectly impregnated with silicious matter* 

 Is it possible, that the change, which this knot has suffered, could 

 have been effected, by an abstraction of the greater part, or, of the 

 whole, of its original constituent parts, and a substitution of par- 

 ticles of a totally different nature ? Its hardness,- and its closeness 

 of texture, must oppose an insuperable bar to the supposition; 

 whilst the mysteriousness of the change is entirely dispelled, by 

 admitting the 7 softening operation of bituminization, and the conse- 

 quent admission of silicious matter. 



But another circumstance, peculiar to this species of fossil wood, 

 requires a particular inquiry ; the result of which cannot but affect 

 the opinion just noticed. This circumstance is the peculiar lustre 

 which this species of wood displays : its fracture, in general, exactly 

 resembles that of newly-broken resin; and, generally, the lustre of 

 its external surface approaches, as near as possible to that which 

 would have been produced by pouring over it a thin coat of melted 

 resin, or of fine varnish. 



In the specimen of a petrified root, represented in PI. II. Fig. 2. 

 this kind of coating, thinly spread, covers and softens down all the 

 asperities of its surface : and in Fig. 3. of the same Plate, the larger 

 pores seem to have been diminished, and some of them obliterated, 

 by the diffusion of this matter. The rough edge of the specimen, 

 Fig. 4. of the same Plate, also derives a bright gloss from this seem- 

 ing resinous varnish. 



Struck by this appearance, the celebrated Hauy terms it, as we 

 have seen, quartz resinite xyloide*; and Mr. Walch's attention was 

 particularly excited by this peculiar resinous or waxy gloss, which he 

 endeavoured to account for, by supposing that this petrified wood 

 had. been impregnated by a peculiar spathose matter; which had 



* Trait6 de Mineralogie, torn. ii. p. 139. 



