NOME IV. TUFO. 421 



Micronome 1. White Tufo. 



This consists, as already mentioned, of commi- 

 nuted pumice, and often presents larger fragments 

 of that stone. It may, from the various influence 

 of the waters, be indurated in some parts, and in- 

 coherent in others. 



Micronome 2. Black and red Tufo. 



Tufo, of comminuted black dross, from the 

 mountains of Iceland. 



The same, from Etna, and its filial hills. 



Tufo of small red scoriae, from Monte Rosso. 

 This mountain, chiefly formed of volcanic sand, is 

 1000 feet in height 



Micronome 3. Tarras or Puzzolana. 



This is chiefly a ferruginous clay, as already Tarras, 

 explained ; but ferruginous tufos in general may 

 be applied to the same purposes. The tarras 

 found near the Rhine is of the same nature and 

 quality ; and is supposed, by impartial authors, to 

 be of volcanic origin. A more candid and equita- 

 ble judge cannot be invoked than the patient and 

 experimental Saussure, who not only allows the 

 mountain of Chenevari, and some others in the 

 south of France, to be of volcanic origin ; but 

 has also published an interesting account of his 



