420 DOMAIN XII. VOLCANIC. 



HYPONOME II. SOFT TUFO. 



This is either found in an incoherent form, or 

 easily crumbles into small fragments. When it 

 chiefly consists of comminuted pumice it is called, 

 Lapiiio. in its recent state, lapillo or rapillo; and some- 

 times, though improperly, 'white puzzolana; for 

 the absence of iron must render it unfit to be used 

 as a cement, which is the chief quality of puzzo- 

 lana. It sometimes consists of minute scoria?, or 

 dross, in which case it is called black puzzolana; 

 and at Naples a rapillo; now constituting, ac- 

 cording to Dolomieu, almost all the mountains 

 around Etna, with nine-tenths of that mountain 

 itself* 



The proper puzzolana, also called Trass or 

 Tarras, which is used to consolidate buildings 

 under water, is a ferruginous clay, of a grey, 

 brown, or reddish colour ; and is more likely than 

 any of the others to be a muddy ejection from the 

 volcanoes. 



* Dolomieu, Etna, 323, 328. Volcanic scoriae, like those of a 

 smithy, or more porous, form all the conic mountains around Etna, 

 and perhaps nine-tenths of its mass. At Naples they are called ' 

 rapillo. (Dol. Etna, p. 328.) They are of the nature of lava ; , 

 while puzzolana is burnt clay. Ferrara, a superior judge, denies 

 the extent of the tufos, and says they do not form one half of Etna : 

 p. 336. 



