418 DOMAIN XII. VOLCANIC. 



HYPONOME I. HARD TUFO, 



This has often the appearance of a grey argil- 

 laceous stone, and is used for building in various 

 parts of Italy. It is generally grey and porous, 

 and sometimes contains small leucites, whence 

 this kind is called partridge-eyed tufo*. It may 

 also embrace fragments of granite; but when 

 these are numerous, and joined with fragments of 

 marble and other substances, it assumes the name 

 of peperino, which is a volcanic bricia, or glu- 

 tenite. 



Micronome 1. Of Clay, Sand, Powder, Pu- 

 mice, 8$c. 



This is the most usual form of tufo ; but the 

 clay seems to be chiefly inserted by the infiltra- 

 tion of the waters from superior soils and emi- 

 nences. 



Tufo, from Herculaneum, Pompeia, Iceland, 

 &c. &c. 



Hard tufo, from Mont Anis and Polignac, in 

 Auvergne, where it is used for building. 



* Patrin, v. 2Q8. The isle Ventotiene (Dol. Ponces, 41) con- 

 sists almost entirely of a volcanic tufo, a soft stone with an argil- 

 laceous base, including fragments of lava, slags, pumice, &c, 



