ON THE CRYSTALS IN LAVAS. 



18^ 



the most part even on their surface. Is not this a farther 



proof, that these crystals were preexistent to the lava ? 



Mr. Fl. de Believue does not admit this conclusion : yet, 



if we attend to the fact, it will be found very convincing. 



The surface of the jets of this singular stalactite, and that Sublimed iron 



of the interior of the blebs, are covered with a multitude of" '"'""t*;?*^- 

 . . ' . tides on these 



shmmg points, which are perceptible only by the reflection jets. 



of the light. When viewed by a lens with a high magni- 

 fying power, they appear to be very slender bundles of sub- 

 limed iron, 



I will mention another remarkable fact, the discovery of 

 which required all the attention, with which I have exa- 

 mined volcanic phenomena. 



The branches that separate from a stream of lava, or the When lava 



lava itself when it is not abundant, break into fracjments ^''^^^^ *"*°^ 



1 . . 1 • 1 • 1 • I ■ iragments, be- 



at their extremity, which in this case have no progressive fore it is cooled 

 motion, but by the flowing of these fragments pushed for- below redness, 

 ward or to the sides by an impulse from the interior. These seentn it. 

 fragments heaped up retain their heat a long time. This 

 is seen when they are viewed by night ; and felt in the day 

 . by the heat they diffuse, as well as by the sulphurous and 

 mephitic gasses they exhale. These fragments broken off 

 from the lava itself, which have not ceased for a moment 

 to be red hot, exhibit at their surface pyroxene schoerls. 

 I possess two such fragments, which I took from the spot 

 myself, and which have several. What can reasonably be 

 objected to so many facts ? Yet I abridge the enumeration 

 of them, 



" Mr. Salmon and Mr. de Buch," says Mr. Fl. de Bel- Opinion of 

 levue, " have demonstrated, to all those who are acquainted j^'d °'\^'^'^ 

 with existing volcanoes, that the crystals of leucite could 

 only have been formed during the slow refngeration of the 

 lava." 



I am acquainted with existing volcanoes, of which I Contradicted. 

 have just given proofs ; yet from my observations I draw a 

 quite opposite conclusion. The facts I have cited, which 

 are true and exact, decide the question. 



With regard to the opinion of these two naturalists T Why should 

 will add, that it sins in an essential point. What ground l^rmedtn laTC 

 is there for distinguishing the kucites from the pyroxene more than th« 



schoerls •'^^^ "y^^^'* 



