in a fluid state, having apparently filled the rifts thus produced. 

 This section, being polished, serves also to show, that both of the 

 substances, which enter into the composition of this specimen, are 

 thoroughly penetrated by the silex : both having acquired the same 

 brilliant polish, from the lapidary's wheel. 



Another circumstance may be mentioned, in addition to those 

 which have been already adduced, in confirmation of the opaline 

 woods being 'formed, by the combination of bituminous wood and 

 silex ; which is, that they sometimes are marked by depressions, 

 evidently from pressure against contiguous bodies; which depres- 

 sions have every appearance of having been made, whilst the fossil 

 wood was about the firmness of wax, or of tallow. In a specimen 

 which I obtained, since the Plates intended for this Work were 

 finished, a circumstance occurs, which seems to prove irrefragably 

 thfe facility with which bitumen and silex may thus unite. One side 

 of this specimen presents the ordinary appearance of bituminous 

 wood, although the whole is well impregnated with silex. On the 

 other side, part of the wood had begun to suffer a change into jet, 

 and is also covered, in detached spots, with a substance possessing 

 that particular varnish-like lustre which has been so often mentioned, 

 but is of a jet black. Many parts of the specimen are sprinkled 

 with drusy crystals of quartz, which, in the neighbourhood of the 

 jetty part of the wood, are also of a jet black, evidently from the 

 intermixture of the fluid black bitumen with the silex, of which 

 the crystals are chiefly composed. 



As silicious, and even opaline wood, has been found in almost 

 every part of the world, and as mention has already been made of 

 many places where it is particularly abundant, all that remains ne- 

 cessary appears to be, to give a slight sketch of the differences 

 which have been remarked, in the silicious woods of various parts. 

 Silicized wood has been discovered in various parts of England, 

 but seldom any which displays any thing of the opaline lustre. A 



