04 DOMAIN XII. VOLCANIC. 



lava, mingled with others of a violet colour, and 

 bits of white limestone*. Dolomieu describes 

 Bricias, a siliceous lava, which is a bricia of siliceous 

 substances and pumice. In another passage he 

 seems to doubt whether Etna ever had any erup- 

 tions of mud, so common in the continental vol- 

 canos of Italy, and which, according to him, 

 have formed stones of an argillaceous base called 

 peperino ; nor are there any bricias called tufo, 

 formed in the water by volcanic ejections f. He 

 however describes a glutenite of fragments of 

 compact lava, black clay rock, and spathose 

 iron ore, cemented by a clay with red and white 

 veins. What is called leucite lava is a glutenite 

 of those crystals, cemented by tufo or compact 

 lava. 



Tufo itself may be regarded as a glutenite or 

 volcanic sandstone; but in this instance forms 

 so important a feature of volcanic eruptions, 

 that it has been considered apart: so that the 

 present division must only be understood to com- 

 prise what are called large-grained glutenites, 

 though in some instances tufo may pass into 

 bricia. In his classification of volcanic sub- 

 stances Faujas has joined them together; but 

 his account shall be transcribed, as it presents 



* 1529. 



f Ponces, 108, Etna 354. But compare Ferrara, 



