348 M. Beudant on the Opals of Hungary. 
owing to the infiltration of siliceous matter, is, that this is in 
some measure pure, and is found disengaged from extraneous 
matter as by a filter. The greater part also of the opalized 
wood which I have collected, has a more or less determinate 
translucidity ; the matter is commonly harder, and whatever 
the colour may be, the powder does not stain the fingers like 
that of the ferruginous opal-jaspers. Sometimes perfectly trans- 
parent opal is observed in the cavities of wood, in small undu- 
lated nests, or in stalactites. 
The colours which these , opalized woods present are extreme- 
ly numerous ; sometimes they are absolutely white, and some- 
times they assume very deep colours, yellow, red, brown, green, 
as well as all the intermediate tints, resulting from the mixture 
of these principal colours. The same piece of wood, if it be of 
considerable size, as sometimes happens, presents colours alto- 
gether different in their different parts, as well as more or less 
translucidity or opacity. In many cases the texture of the 
wood is completely preserved ; and when the colour is also re- 
tained in an equal degree, it is impossible to distinguish by 
mere inspection, the petrified specimens from those which 
are in their original unaltered state. It might be thought that 
this wood is capable of burning, and I have sometimes been 
obliged to make the experiment, in order to convince myself 
that it was not so. In some of the pieces, the tissue of the 
ash, in others that of the fir, are supposed to be seen ; but 
most commonly it is almost impossible to form any idea of their 
original nature. 
- There is also a particular modification.in which the wood, 
although it has passed into the opaline state, presents a fibrous 
tissue, the fibres in which have no coherence, separate easily from 
each other, and even preserve their flexibility : not unfrequently 
a specimen is in one part of this structure, while in another it is 
compact. It is difficult to say what may be the cause of this 
modification : I have often imagined that it originated from the 
circumstance of the wood being in part altered before it became 
petrified. In fact, I have often seen half petrified wood which 
presented this fibrous structure: this explanation, however, is 
only to be regarded as an opinion. 
