394 
their primitive form ; in others, appearances offer themselves dissi- 
milar to those of any known recent tree. The specimen at PI. II. 
Fig. 3, has been supposed, by some, to be of this .kind; whilst 
others have supposed it, from its large pores,, to have belonged to 
some tree allied to the cabbage-tree. The petrified wood of the 
linden-tree (Philyrites^, is said to possess generally a clear white 
hue. Mr. Walch describes a white petrified wood found in Hungary, 
which he supposes may have been of this tree ; but he says that it 
contains a stony substance, resembling a resin ; but which it cannot, 
however, have been, since this tree yields no resin ; nor does resin, 
although it hardens very readily, ever petrify. Besides, he remarks, 
that it exceeds in quantity the remaining ligneous substance, and 
manifests no mark of its being of a resinous nature, even when 
exposed to the fire. He therefore concludes this matter must be of 
the nature of spar, approaching to horn-stone ; but which, like all 
spar, does not give sparks with the steel. The substance here 
described, was doubtless similar to that which has been before 
noticed, as having been described by Mr. Walch, and as most 
probably being a variety of the pitch-stone or semi-opal ; and, 
perhaps, a combination of clear bitumen and silex. In a most beau- 
tiful specimen of fossil wood of this kind, lately obtained from the 
collection of Mr. Forster, and which is more than a foot in length, 
and a foot and a half in circumference, almost the whole of its 
substance is formed of a semi-opaline substance, possessing the clear 
white hue mentioned by Mr. Walch, mingled with a dark brown 
semi-pellucid pitch- stone : the surface only presenting the real ap- 
pearance of wood, and that in a withered shivery state, but yet 
impregnated with silex. 
Those substances which, though now in a petrified state, are sup- 
posed to have derived their forms from the art of man, previous to 
their undergoing the change from wood to stone, will be examined 
with propriety, in this place, whilst considering the varieties which 
