26 



B. Jasperine wood displays all the colours and appear- 

 ances belonging to common jasper, so disposed as to mark 

 the existence of ligneous texture, and frequently so varied 

 as to give the resemblance of different woods. It is usually 

 opaque, but sometimes translucent at the edges, and some- 

 times in patches, where it appears as jasper-agate. Its 

 fracture passes from conchoidal to flat and earthy : its in- 

 ternal lustre is generally dull, but sometimes approaching 

 to resinous ; its interstices are frequently set with minute 

 crystals. The texture of the wood is discoverable in some 

 very rare specimens of Heliotrope, or bloodstone. 



C. Opaline wood occurs in pieces of a yellowish or 

 yellowish-white colour, passing into different shades of 

 brown : surface generally marked by the ligneous structure, 

 and possessing a resinous lustre. The fracture more or less 

 approaching to perfect conchoidal, showing the ligneous 

 marking and a glistening lustre. Fragments -sharp-edged, 

 and somewhat translucent: the surface sometimes dull, 

 like wood, and the internal substance transparent. 



It is considered by Dr. Thompson as consisting of wood 

 penetrated by opal, and as being so intimately connected 

 with opal, that it would perhaps be better to unite them. 



D. Pitchstone wood. Specimens of fossil wood, evi- 

 dently showing its original texture, and answering to the 

 characters of pitchstone, are frequently seen : its colours 

 are yellow, brown, reddish brown, red, black, white, and 

 grey, with various intermediate shades ; fracture is flattish, 

 imperfectly large conchoidal ; lustre varying between dull, 

 vitreous and resinous. 



The woody texture is to be traced also in numerous la- 

 pideous substances bearing the intermingled characters of 

 pitchstone, opal, jasper, chalcedony, jasper-agate, &c. 



III. ALUMINOUS VEGETABLE FOSSILS. 



1. Bituminous slate, schistus, and shale, containing ve- 

 getable remains, are frequently met with in the neigh- 



