ON THE FOKMATION OF CRYSTALLINE ROCKS. 279 



easily reducible to vapor, become sufficient for their explanation? 

 This is the first idea which naturally presents itself to our minds; for 

 nature shows us an abundance of vapors of energetic affinities in the 

 exhalations from the craters of volcanoes or their still incandescent 

 lavas. These vapors and gases are combinations in which electro- 

 negative bodies predominate, which the former mineralogists called, 

 as if by instinct, the miner aliseo^s, as chlorine, sulphur, carbon, more 

 rarely fluorine and boron. The recent observations of Boussingault, 

 Bunsen, and Charles Deville, have contributed to make known the 

 nature of these gaseous or volatile ejections. 



Carbonic, sulphydric, and even sulphuric acid might foi'merly have 

 acted on some rocks in a manner similar to what we now see in some 

 formations of gypsum and of alunite, or in the rocks near the volca- 

 noes of the Andes and of Java, which are reduced under their action 

 to mere mud. The decomposition of vapors containing chlorine forms 

 under our eyes specular iron, and might have heretofore given rise 

 in many formations to oxide of tin and of titanium, as both observa- 

 tion and synthetical experiment have taught us. It is in a similar 

 manner that crystallized magnesia or periclase contained in the lime- 

 stones thrown out of Mount Somma, might have been produced from 

 the decomposition of chloride of magnesium by carbonate of lime. 

 This supposition, which the abundance of chloruretted vapors of the 

 active volcano rendered probable, has been corroborated by an ex- 

 periment in which I artificially imitated that mineral.* It is remark- 

 able to see the same substances which have produced periclase at 

 the ex[>ense of the limestone form, when in solution and at a lower 

 temperature, dolomite. The part which these chlorures at high tem- 

 peratures have borne in producing the crj'stallization of minerals is 

 clearly shown from the very recent experiments of Manross, Forch- 

 hammer, and Henry Deville. 



Other experiments have shown that the chlorides of silicium and 

 of aluminum by reacting, in a state of vapor, on the bases which 

 enter into the composition of rocks, form simple or multiple silicates 

 which are identical with natural products.f But if mica subjected to 

 heat still gives off the fluorides of silicium, boron, and lithium, shall 

 we venture to affirm that granitic pastes did not also originally con- 

 tain the chlorides of silicium, boron, and lithium, although we do not 

 now find them in the neighborhood of volcanic orifices ? for they could 

 not be otherwise than decomposed and precipitated by the vapor of 

 water before arriving in the atmosphere. Do we not still see chlorine 

 fixed in considerable quantities in crystalline masses, as in the syenite 

 containing zircon, of Norway, and in the rock of llmen, (raiascite,) 

 where it is principally combined with eleolite, and where it appears 

 in the train of zirconium, tantalium, and other rare elements, which 

 are almost exclusively peculiar to those rocks? With regard to fluo- 



° Researches on the artificial production of minerals belonging to the families of the 

 silicates and the aluminutes by the action of vapors on rocks. — [C^mptts Rendusdel Acadtmie, 

 vol. xxxix, p. 135 ) 



•j- Coniptes Rendm dc I'Academie, vol. xxxix, p. 135. 



