be formed in 

 the crater. 



]g5 ON THE CRYSTALS IN LAVAS, 



from derom- large number of these very leucites, from the smallest size 

 posed lava. ^^ ^y^^^ ^^ ^ ^-^^l^ cherry. They must have come from 

 spongy lava at no great distance, that has been decomposed. 

 I have seen some of the same nature near Civita Castel- 

 Similar ones lana ; the whole surface of which was spotted with a multi- 

 c'^t U '^ tude of white grains. Unfortunately, and to my great re- 

 gret, it rained very hard at the time, which prevented my 

 alighting from my carriage. How can we conceive, that 

 the multitude of loose leucites at Frescati were formed 

 from the substance of the lava that included them ? They 

 are a little transparent, and of a slightly yellow colour : is 

 there in this any analogy with the colour or raa.tter of lava ? 

 Indeed we might as well maintain, that the garnets in- 

 cluded in a rock have been formed of the substance of that 

 rock. 

 Cryjtalssaid to Mr. Fl. de Bellevue imagines, that the crystals thrown 

 out separately by the crater *' are new products, formed ia 

 the crater itself by a first cooling." 

 None bin by Nothing is formed in the crater, or to speak more accu- 

 sublimatiou. lately on its sides, but crystals of salts and sulphur by sub- 

 limation; and never any crystal of solid matter like those 

 contained in lava. 

 The lava said To support this opinion he fixes two epochs : the first of 

 to cool in the which, according to him, takes place in the crater itself. A 

 its eruption, fii'st cooling in the crater I But let us admit this supposi- 

 .tion. Thvis we have a lava cooled and hardened : but from 

 a lava come to this state none of the substances contained 

 in it could be separated so as to appear loose : for this it 

 miist be plunged again into the fire of the volcano; and 

 would it not there enter again into fusion ? 

 The crystals '^ ^^^ crystals that are found detached on the cone of a 



jnerely thrown crater have been separated in the crucible of the volcano 

 TjJc'sions. ^ itself by the ebullition of the melted lava, and the jets of 

 Crater on Etna its explosions. The crater that opened on Etna in 1669 

 flf 1C69. exhibits a very instructive example. The very large cone 



raised by this opening is covered with an innumerable mulr 

 titude of pyroxene &choerls, all without exception covered 

 by a slight crust of th-e lava that contained them, mixed 

 among the small scorise in which some are included. This 

 lava cannot have been cooled for a moment from the first 



instant 



