198 Igneous Hocks and Volcanos. 



that quartz and apophylite may be dissolved by beated water 

 under pressure and recrystallized on cooling. He recalls the 

 aqueous fusion of many hydrated salts, and finally suggests that 

 the presence of a small amount of water, perhaps five or ten per 

 cent., may suffice at a temperature which may approach that of 

 redness, to give to a granitic mass a liquidity, partaking at once 

 of the characters of an igneous and an aqueous fusion. 



This ingenious hypothesis, sustained by Scheerer in his discus- 

 sion with Durocher, * is strongly confirmed by thelate experiments 

 of Daubree. He found that common glass, a silicate of lime and 

 alkali, when exposed to a temperature of 400° C, in presence of 

 its own volume of water, swelled up and was transformed into an 

 aggregate of crystals of wollastonite, the alkali with the excess 

 of silica separating, and a great part of the latter crystallizing in 

 the form of quartz. When the glass contained oxyd of iron, the 

 wollastonite was replaced by crystals of diopside. Obsidian in 

 the same manner yielded crystals of feldspar, and was converted 

 into a mass like trachyte. In the experiments upon vitreous alka- 

 liferous matters, the process of nature in the metamorphosis of 

 sediments is reversed, but Daubree found still farther that kaolin, 

 when exposed to a heat of 400° C. in the presence of a soluble 

 alkaline silicate, is converted into crystalline feldspar, while the 

 excess of silica separates in the form of quartz. He found natural 

 feldspar and diopside to be extremely stable in the presence of 

 alkaline solutions. These beautiful results were communicated to 

 the French Academy of Sciences on the 16th of November last, 

 and as the author well remarked, enable us to understand the 

 part which water may play in giving origin to crystalline minerals 

 in lavas and intrusive rocks. The swelling-up of the glass also 

 shows that water gives a mobility to the particles of the glass at 

 a temperature far below that of its igneous fusion. 



I had already shown in the Report of the Geological Survey of 

 Canada for 1856, p. 479, that the reaction between alkaline silicates 

 and the carbonates of lime, magnesia and iron at a temperature 

 of 100° C. gives rise to silicates of these bases, and enables us to 

 explain their production from a mixture of carbonates and quartz, 



* Note. — See for the arguments on the two sides, Bulletin of the Geo 

 Soc. of France, Second series, vol. iv., p.p. 468, 1018 ; vi. 644 ; vii., 2?6 

 viii., 500 ; also, Elie de Beaumont, Ibid, vol, iv., p. 1312. See also the 

 recent microscopical observations of Mr. Sorby, confirming the theory of 

 the aqueous-igneous origin of granitie. — L.E. fy D.Phil. Mag., Feb. 1858. 



