394 



their primitive form ; in others, appearances offer themselves dissi- 

 milar to those of any known recent tree. The specimen at PL 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 ex- 

 posed 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 de- 

 scribed, 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 serni-opal ; and, perhaps, a 

 combination of clear bitumen and silex. In a most beautiful spe- 

 cimen of fossil wood, of this kind, lately obtained from the collec- 

 tion 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 appear- 

 ance of wood, and that in a withered shivery state, but yet impreg- 

 nated 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 



