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term, which long usage sanctions, of petrified wood, lithoxylon 
of ory otologists. This may be divided into dilferent classes, ac- 
cording to the predominance of the different earths with which it is 
impregnated : thus petrified wood may be subdivided into silicious 
wood, calcareous wood, aluminous wood, &c. 
The nature of these several fossil woods we shall now proceed 
to examine, pointing out the different kinds into which each may 
be again subdivided, and the several species and varieties which 
demand particular observation. Fossil wood, which has been mine- 
ralized by an impregnation with silex, holzstein of the Germans, 
and which we may term silicious fossil wood, may be divided 
into two kinds. The first is that, in which the wood had suffered 
no real change in its nature, during its existence in a subterranean 
situation, previous to that produced by the silicious impregnation. 
The second is that, in which bituminization had wrought its peculiar 
change on the wood, previous to its impregnation with silicious 
matter. Of the former kind I know but one instance, and that of 
rather rare occurrence ; which is, where the wood, previous to 
having been buried, had undergone that change, which we fre- 
quently see take place ; every part of the wood having been re- 
moved but the mere ligneous fibre ; the light mass which is left being 
in that state which is designated by the term rotten-wood. The wood 
having been impregnated, whilst in this state, with silex, yields an 
appearance exactly resembling that of rotten-wood ; but occasions 
no small surprise to any one who, taking such a specimen in his 
hand, expecting from its appearance to find it exceedingly light, dis- 
covers it to be possessed of considerable weight, from the great 
quantity of silex it contains. The specimen figured at Plate II. Fig. 1. 
is of this kind, it having the peculiar light appearance of rotten- 
wood, whilst its impregnation with silex has been to such a degree, 
as to have allowed it at one end to have assumed a very high polish, 
from the lapidary’s wheel. Since this specimen has been engraved, 
VOL, I. u u 
