crystallized Bodies contaived in Lava. 305 



We know of no lava of ^tna, and I know of no others 

 which contain leucites; nor lavas of V^esuvius which contain 

 the whitish crystalline laminae so abundant in the lavas of 

 -^tna. This is a fact to which those naturalists who think 

 that these crystals are formed in lava ought to pay some at- 

 tention. If the leucites are in reality formed in them, Why 

 do not the lavas of ^tna contain them also ; while the latter 

 are filled with pyroxene schorls and chrysolites, which are 

 common to them with the lavas of Vesuvius? Is this diffe- 

 rence rather not more naturally explained bv the absence of 

 the leucite in the beds from which the lavas of ^Etna flow? 



We observe these same varieties in the lavas of different 

 volcanoes. Those of Hecla, some large specimens of which 

 I have, which were brought by Sir Joseph Banks, neither 

 contain pyroxene schorls, leucites, nor chrysolites, but plenty 

 of small white crvstalline bodies cleft into pieces, from the 

 size of a hemp.-seed to that of a pea, and of an irregular 

 form, which have the appearance and the hardness of quartz, 

 and which seem to be actually broken from it. 



The lavas of Mount d'Or, an antient volcano in Auvergne, 

 contain large crystals of amphihole, or hornblend and feld- 

 spar, which by their cracks and vitreous reflection show that 

 thev have experienced the action of the burning lava ; and 

 we find in other old volcanoes in Auvergne, pyroxene schorls 

 without leucites. 



The small gravel of the volcanic lake of Andernach is 

 filled with isolated pyroxene schorls, both whole and in 

 fragments. Do we find in this state the confused rays of 

 the cooled glass which form part of the mass of the glasa, 

 from which they cannot be separated, except in irregular 

 Iracturcs ? 



Among the facts which I opposed to the opinion of sir 

 . James Hall, quoted by M. Kleuriau dc Bellevue, an opinion 

 which is the same as his, I menlicmed a singular eruption of 

 Vesuvius which happened in 1734. An orifice was opened 

 Dear the level of the valley which separates the present cones 

 of Mount Somina. This orifice formed at the production 

 of the lava a grotto fringed by the si)ootiugs of melting lava; 

 it wiis a iius» of scoriae iu the form uf stalactites, the sprigs 

 Us gf 



