NOME I. COMPACT LAVA. 317 



" It is seldom that they are homogenous ; they 

 are, on the contrary, almost always interspersed 

 with different minerals; those which have been 

 most remarked are felspar, augite, hornblende, 

 garnet, leucite, olivine, and mica."* 



Recently Breislak, certainly an intelligent writer, 

 mentions many kinds of compact lava, without 

 any notice concerning their rarity or singularity^. 

 Ferber, an unprejudiced judge, likewise gives a Ferber's ideas, 

 catalogue of compact lavas, amounting to fifteen 

 kinds. He especially says that the common black 

 lava, which covers Vesuvius on every side, is 

 porous on the surface, spongy, and light, and 

 therefore employed in vaulted roofs; but at a 

 greater depth it is extremely compact, and then 

 used in foundations, and in paving the streets^. 

 Yet he compares it with slags ; and speaks of its 

 being mixed with a reddish iron ochre, like the 

 rocks under the basaltin in the north of Ireland, 

 and in the Faroe isles. But Ferber possibly 

 means only porous lava, which he styles compact, 

 in comparison with the common vesicular lava: 

 and it is possible that the latter may abound in 

 cabinets, because it is easily detached from the 



* Brochant, ii. 626. 



f Voyage dans la Campanie, Paris, 1801, 8vo. 



J Letters on Italy, p. 154. 



