, . III. DIST. CHAR. Substance. 143 



Woodstone. Jam. 'p. 661. F. Veg. that of 



wood only f . 

 Flint. Kirw. p. 301. F. Animal, frequently 



of Echini. 

 Calcedony. 



Common. Kirw. p. 297. F. An. and Veg. The 

 animal, that of shells, the vegetal, that of 

 wood. 

 Opal. 



Semi-opal. Kirw. p. 290. F. Veg. and An. 

 Semi-opal sometimes constitutes petrified 

 wood, and, in this state, is called ligniform, 

 or -wood opal. Bones of quadrupeds have 

 heen found penetrated with a variety of semi 

 opal. 



Pitclistone. Kirw. p. 292. F. Veg. of wood. 

 Jasper. Kirw. p 309. F. An ? f f. 



t This stone is ranked by Karsten, Kirwan, &c. as a species 

 distinct from any of the foregoing siliceous stones. Werner and 

 Jameson consider it as a subspecies of Hornstone. Other minera- 

 logists have supposed it to be merely a modification of quartz or 

 flint. It certainly does not appear that the substance, which the Ger- 

 mans denominate Woodstone, has, as yet, been subjected to any 

 particular analysis, in order to determine its specific difference from 

 the stones just mentioned. External characters will hece scarcely 

 suffice as a ground of distinction, as they evidently depend, in a 

 great measure, on the substance of the original body and, if such 

 structure be admitted as a distinction in this instance,why not in others? 



ft According to Bergman (Med. de Syst. Foss. p. 78.) shells 

 sometimes occur filled with jasper. In another treatise (Phys. 

 Geo. p. 304.) be seems to doubt it, although he quotes his friend 



