270 O'N THE FORMATION OF ROCKS. (June, 



Compact Lava, Mud Lava, 



Porous Lava, Obsidian or Volcanic GlasSy 



Porphyritic Lava, Pumice Sione, 



Scoria, Cinders, &,c. 



Second Order, Eesembling the first order in struc- 

 ture, position, and component parts, having the remains 

 of craters, with currents of lava diverging from them: 

 though the fire, which may have formed them, is now 

 extinct; the evidence of their origin resting on direct and 

 positive analogy: 



Basalt, Pearlstone, 



Trap formation, called by Porphyry attending" the 



Werner the newest Fleets Trap as above. 



Trap formation, Clinkstone ditto, &c. 



Pitchstone, 



Third Order. Where the rocks resemble the second 

 hi texture and component parts, but where all the craters, 

 cinders, scorise, and most of the porous rocks, have been 

 washed away, leaving only the solid parts, such as 



Basalt, Pitchstone, 



Trap, called by Werner the Porphyrj^, 



newest Fleets Trap forma- Clinkstone, &c, 



tion, 



These rocks resemble the volcanic in relative posi- 

 tion, covering indifferently all the other classes of rocks, 

 and in detached pieces, without any extensive continuity 

 or stratification, bat divided by vertical fissures, the proof 

 of tli-'ir origin resting on a more distant analogy than or- 

 der second. 



