184 M. C. Dcville on the origin of Granite. 



especially when we find that the predominant mineral in the 

 Vesuvian lavas is amphigene, a substance resembling quartz in 

 its infusibility. Can it be doubted that in such a case we 

 witness the more or less rapid transformation of a melted or 

 viscous magma (certainly, as M. Durocher remarks, more fusible 

 than the most refractory of the minerals which could be sepa- 

 rated from it) into a solid rock almost entirely composed of 

 crystalline elements ? Truly it is pre-eminently an eruptive act ; 

 for it is one by definition. But at the same that these streams 

 of liquefied earth, as M. Humboldt calls them, escape from the 

 volcano, bodies of quite a different nature are also disengaged, — 

 alkaline and metallic chlorides, a small quantity of sulphates and 

 phosphates, then at various intervals of time and place hydro- 

 chloric, sulphurous, hydrosulphurous, and carbonic acids, but 

 more especially aqueous vapour. The latter rises from the 

 lava many years after its eruption ; and any one who has fol- 

 lowed day by day, step by step, the chemical phenomena of 

 lava in motion, can have no doubt as to the origin of the water. 

 Like other substances, it forms an integral part of the magma ; 

 and like them it separates at a given moment, in proportion as 

 the internal reactions of the incandescent mass are affected*. 



As far as I know, M. Elie de Beaumont, in the memoir pre- 

 viously quoted, was the first to establish this kind of preliminary 

 solution of water and of salts in incandescent lavas. He rightly 

 refers it to certain phenomena which are readily reproduced in 

 the laboratory, such as the spitting of silver, the experiments 

 on the spheroidal state, of bodies, &c. It may be added, that 

 the properties of obsidian and its artificial transformation into 

 pumice furnish also an indisputable proof of this fact. 



But these gaseous exhalations which accompany lava do not 

 disappear without leaving some traces. The more or less com- 

 plicated reactions which are set up between their elements and 

 those of the rock or of the atmosphere produce the chlorides of 

 iron, of copper, of cobalt, of lead, specular iron, and protoxide of 

 iron, oxide of copper, alkaline sulphates, sal-ammoniac, apatite, 

 which, in varying quantities, doubtless impregnate all modern 

 lavas. 



If, starting from the eruptive phenomena which we may daily 

 witness, we pursue the analogy to the older rocks, to the 

 granites, is it possible not to admit, with M. Elie de Beaumont, 

 the existence of granitic fumaroles, which separating from the 



* I am strongly inclined to think that the powerful columns of aqueous 

 vapour which cause the explosions, which form, as it were, the first act of 

 all great eruptions, are only emanations from lavas below : they accumulate 

 until their expansive force bursts through the solid crust of the crat jr, and 

 projects it into the air. 



