302 AXXUAL OF SCIENTIFIC DISCOVERY. 



Schcerer, in his inquiry into the origin of granite, has appealed to the evi- 

 dence afforded us by the structure of this rock, that the more fusible feld- 

 spars and mica crystallized before the almost infusible quartz. He also 

 points to the existence in granite of what he has called pyrognomic miner- 

 als, such as allanitc and gadolinite, which, when heated to low redness, un- 

 dergo a peculiar and permanent molecular change, accompanied by an 

 augmentation in density, and a change in chemical properties, a phenom- 

 enon completely analogous to that offered by titanic acid and chromic oxide 

 in their change by ignition from a soluble to an insoluble condition. These 

 facts seem to exclude the idea of an igneous fusion, and point to some other 

 cause of liquidity. The presence of natrolite, as an integral part of the zir- 

 con-syenites of Xorway, and of talc and chlorite, and other hydrous min- 

 erals in many granites, shows that water was not excluded from the original 

 granitic paste. 



Scheerer appeals to the influence of small portions of carbon and sulphur 

 in greatly reducing the fusing-point of iron. He alludes to the experiments 

 of Schaf hautl and "\Vohler, which show that quartz and apophylite may be 

 dissolved by heated water under pressure and rccrystallized 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 discussion with 

 Durocher, is strongly confirmed by the late experiments of Daubre'e. 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 crystal- 

 lizing in the form of quartz. When the glass contained oxide 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 these experiments upon vitreous alkaliferous matters, the 

 process of nature in the metamorphosis of sediments is reversed; but Dau- 

 bre'e found still further that kaolin, when exposed to a heat of 400 C. in 

 the presence of a soluble alkaline silicate, is converted into crystalline feld- 

 spar, 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 al- 

 kaline solutions. These beautiful results were communicated to the French 

 Academy of Sciences in November, 18-37, and 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 

 1SCG, 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, in the presence of a solution of alkaline carbonate. 

 I there also suggested that the silicates of alumina in sedimentary rocks 

 may combine with alkaline silicates to form feldspars and mica, and that it 

 would be possible to crystallize these minerals from hot alkaline solutions 



