NOME I. COMPACT LAVA. 323 



sents very small lineaments of black mica; 

 scratches glass, and melts under the blow-pipe 

 into a greyish white amel. 



" Felsite lava, grey, and sometimes of a whitish 

 grey, analogous to the foregoing, with the differ- 

 ence that, in this, the paste, which also encloses 

 some lineaments of black mica, is looser and less 

 adherent, and that the spherical globules are much 

 larger, and of a felspar a little vitreous, but very 

 compact. They cannot be better compared than 

 to large peas. Some specimens are found, where 

 the base which contains them being in part de- 

 stroyed, the globules have resisted, and offer saliant 

 protuberances which have a false appearance of 

 orbicular crystals. These contain in their interior, 

 as well as on their surface, linear portions of fel- 

 spar, whiter than the globular paste which contains 

 them ; there are also some specks of black mica. 

 It is probable that these globules may pass into a 

 kind of obsidian called lucks saphir, when a violent 

 heat produces vitrification." 



As the base of this lava consists of felspar or 

 felsite, it is often very compact. In describing 

 an immense current, which descends from the an- 

 cient crater of Etna towards Mascali, Dolomieu 

 says that it lies under vesicular lava, and is of a 

 very fine grain, and conchoidal fracture, like petro- 



