NOME IV. TUFO. 419 



The same, with bitumen and chalcedony, from 

 Clermont. 



Micronome 2. Of Dross, and pulverised Lava. 



This, in the course of ages, assumes consider- 

 able hardness, while it shews its origin by its 

 black colour, arising from the drosses or scoria ; 

 the latter are sometimes red from calcination, 

 whence seems to arise the name of Monte Rosso, 

 ejected by Etna in the terrible eruption of 1669 ; 

 but the surface at least is chiefly incoherent. This 

 tufo in particular sometimes affects the magnetic 

 needle. Black tufo sometimes resembles wacken. 



A tufo of fragments of lava, drosses, sand, 

 augite, and conchitic limestone, in a paste of 

 marl. Ferrara, p. 67. 



Micronome 3. With fragments o/Granite t or 

 other substances. 



When these are numerous and closely set, the 

 stone becomes a volcanic glutenite ; but they are 

 sometimes rare and remote. 



A tufo of lava and limestone, from Cape Pas- 

 saro and the rocks of the Cyclops, Sicily*. 



* Ferr. 181. 



2 E 



