DOMAIN XII. VOLCANIC. 



journey to the extinct volcanoes in the Brisgaw, 

 being in the Black Forest adjacent to the Rhine*. 

 Puzzolana forms a remarkable feature of several 

 extinct volcanoes; but Mr. Kirwan, who has an 

 inconceivable aversion for those grand phenomena, 

 often passes in silence the most cogent authorities 

 against his system, and argues that tarras is of a 

 pseudo-volcanic origin. Yet his accounts of these 

 two substances, so useful to the arts, and espe^ 

 cially to a maritime people, are more carefully 

 composed than those of any other writer, and de^ 

 serve transcription. 



Kirwan's " PUZZOLANA. 



account. 



" Reddish, or reddish brown; grey, or greyish 

 black. That of Naples is generally grey ; that of 

 Civita Vecchia more generally reddish, or reddish 

 brown. Dolomieu's notes, 32. 



" Its surface rough, uneven, and of a baked 

 appearance. It comes to us in pieces of from the 

 size of a nut to that of an egg. 



" Its internal lustre, 0. Its transparency, 0. 



" Its fracture uneven, or earthy, and porous ; 

 commonly filled with particles of pumice, quartz; 

 scoriae, &c. 



" Hardness, 3. Very brittle. Sp. gr. from 



* Journal de Physique. New Series, vol. i. 



' 



