﻿xlvi PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



quartz, he states that it is probable that water has played a part 

 in the formation of all of them*. 



The powerful action of water at a high temperature, under great 

 pressure, upon mineral substances has been recently most satis- 

 factorily proved by the synthetic experiments of M. Daubreef . In 

 stating the object of his researches, he observes — " No one is un- 

 acquainted with the results obtained long ago by Berthier and 

 Mitscherlich, and more recently by Ebelmen, regarding the forma- 

 tion of silicates at high temperatures by means of fusion. Thus, 

 while the dry process yielded by various methods crystallized anhy- 

 drous silicates, some of which are identical with those found in 

 metamorphic rocks, it had hitherto been found impossible to obtain 

 similar imitations by the humid process. Synthetic experiments, 

 guided by geological induction, could alone solve the question. Such 

 is the aim of those in which I have endeavoured to bring into play 

 affinities capable of producing like combinations." He enclosed the 

 minerals he operated upon in a glass tube partially filled with water, 

 which he inserted in a strong iron tube, between which and the glass 

 tube water was poured, to counterbalance the tension of the vapour 

 in the glass tube, which would have caused it to burst. The iron 

 tube being firmly closed by a screw, was placed in a bed of charcoal 

 powder, and exposed for several weeks to the heat of a gas-making 

 furnace, in which the heat could not be less than 850° Fahr., and 

 when taken out was allowed to cool gradually. "With all the precau- 

 tions he could take, so great was the tension of the vapour, that, of 

 the many experiments, two tubes out of three exploded. 



After being exposed to the heat of the furnace for a week, the 

 structure of the glass was no longer recognizable. It was entirely 

 changed into a white substance, perfectly opake, and adhering to the 

 tongue, exactly resembling kaolin. In some of the experiments the 

 form of the tube was preserved, but in others the glass was reduced 

 to a white powder. Entirely new combinations had been formed : 

 the water had become highly charged with an alkaline silicate ; and 

 the opake substance, which at first sight had appeared amorphous, was 

 found to be entirely composed of crystalline elements. They were 

 seen, even "without the aid of a magnifying glass, to consist of limpid 

 colourless crystals, having the ordinary bipyramidal form of quartz 

 and its usual appearance ; they were, in fact, no other than crystallized 



et plus constant des eruptions, dans toutes les regions du globe. La singuliere 

 propriety que possedent les silicates incandescents des laves de retenir pendant 

 fort longtemps, et jusqu'au moment de leur solidification, des quantites d'eau 

 considerables, demontre clairement que Taction de la chaleur n'exclut pas cede de 

 l'eau, et parait annoncer que cette derniere a, meme a ces bautes temperatures, 

 une certaine afiinite pour les sdicates. Nous ne connaissons des masses situees a 

 une certaine profondeur dans notre globe que ce qu'en apportent les volcans: or 

 ces dejections renferment toutes, sans exception, de l'eau, soit combinee, soit 

 melangee; nous sommes done en droit de penser que l'eau joue un role tout a 

 fait important dans les principaux phenomenes qui emanent des profondeurs."— 

 Daubree, Etudes et Experiences Synthetiques sur le Metamorphisme, p. 85. 



* Bulletin de la Societe Geologique de France, 2de serie, vol. iv. p. 1249. 



t Observations sur le metamorpbisme, et recbercbes experimentales sur quelques 

 uus des agents qui ont pu le produire. 



