Intelligence and Miscellaneous Articles. 317 



By the reaction of perchloride of iron upon lime I have ohtained 

 haematite, either in very distinct specular crystals like those of Saint 

 Crothard.or in transparent hexagonal laminae, presenting by refraction 

 a ruby-red colour. Perchloride of iron mixed with chloride of zinc, 

 furnishes, under the same conditions, a crystalline compound analo-' 

 gous to franklinite. 



Lastly, crystallized magnesia, or the perichse of La Somma, may 

 easily be obtained by the reaction of lime upon chloride of magne- 

 sium which is found amongst the abundant chlorinated vapours of 

 the fumaroles of Vesuvius. The same chloride, decomposed by 

 aqueous vapour, also furnishes periclase, and chloride of zinc gives 

 crystalline oxide of zinc. 



The results just described lead to geological consequences to which 

 1 can only refer very briefly in this place. I do not pretend to 

 say that all the silicates composing the mass of the crystalline rocks 

 are formed by vapours. But even in the midst of the fused rocks of 

 Vesuvius, a certain number of minerals, to which M. Scacchi has 

 recently directed attention, are met with which appear to be pro- 

 ducts of sublimation. 



Amongst the minerals of the oldest formation, there are many also 

 which could not by fusion have lined the fissures in which they are 

 now found so well isolated ; such are the diopside pyroxene, with 

 garnet of Piedmont and the Ural, the adular feldspaths and theperi- 

 chne of the Alps, the epidotea and axinites of l'Oisans, and manv 

 others. : 



The great richness of the crystalline limestones in minerals often 

 foreign to the neighbouring rocks, cannot result entirely from the 

 fact that the lime, by reacting upon the silica, has served for the 

 formation of peculiar silicates. Whatever might have been the 

 original impurities of the limestones, corundum, spinel, periclase, or 

 chondrodite could not have been produced in them without the sub- 

 sequent introduction of foreign chemical agents. 



All these various products of transport,— silicates, alumiiiates, 

 oxides, and other combinations, formed either in fissures or in the 

 midst of rocks now become very compact, are explained, it appears 

 to me, in the most satisfactory manner by the intervention of chlo- 

 rinated or fluorated emanations. Besides, in the case of such vola- 

 tile and penetrating compounds, there is nothing to oppose the idea 

 that their action may have extended itself over spaces of considerable 

 thickness from their centre of disengagement, as in the crystalline 

 schistose rocks of the Alps or of Brazil. Sometimes the substitution 

 of the silicates thus formed has only been partial, as in many of the 

 crystalline limestones, which remain as perpetual witnesses of the 

 ancient exhalations which have escaped from the neighbouring erup- 

 tive rocks. Sometimes the attack has been more complete, and the 

 primitive mass has even disappeared in the state of solute chloride, 

 just like the water which has formed the specular iron ore of the 

 volcanos. 



If we turn to the crystalline limestones and dolomites most largely 



