342 
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 
the 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 
necessary 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 
