302 DYNAMICAL GEOLOGY. [Book II. __ 

regarded as a kind of mother-liquor out of which the silicates 
crystallize apart from relative fusibility. As 
But beside the effects from increase of temperature and pressure 
- we have to take into account the fact that water in a natural state is 
never chemically pure. In its descent through the air it absorbs in 
particular oxygen and carbon dioxide, and filtering through the soil it 
abstracts more of this oxide as well as other results of decomposing 
organic matter. It is thus enabled to effect numerous decom- 
positions of subterranean rocks even at ordinary temperatures and 
pressures. But as it continues its underground journey and obtains 
increased solvent power, the very solutions it takes up augment its 
capacity for effecting mineral transformations. The influence of 
dissolved alkaline carbonates in promoting the decomposition of 
many minerals was long ago pointed out by Bischof. In 1857 
Sterry Hunt showed by experiments that water impregnated with 
these carbonates would, at a temperature of not more than 212° Fahr., 
produce chemical reactions among the elements of many sedimentary 
rocks, dissolving silica and generating various silicates." Daubrée 
likewise proved that in presence of dissolved alkaline silicates at 
temperatures above 700° Fahr. various siliceous minerals, as quartz, 
felspar and pyroxene, could be crystallized, and that at this tempera- 
ture these silicates would combine with kaolin to form felspar.? 
The presence of fluorine has been proved experimentally to have 
a remarkable action in facilitating some precipitates, especially tin 
oxides, as well as in other parts of the mechanism of mineral veins.® 
Further illustrations of the important part probably played by this 
element in the crystallization of some minerals and rocks have been 
published by St. Claire Deville and Hautefeuille, who by the use of 
compounds of fluorine have obtained such minerals as rutile, brookite, 
anatase and corundum in crystalline forms K. de Beaumont in- 
ferred that the mineralizing influence of fluorine had been effective 
even in the crystallization of granite. He believed that “the 
volatile compound enclosed in granite, before its consolidation 
contained not only water, chlorine, and sulphur, like the substance 
disengaged from cooling lavas, but also fluorine, phosphorus and 
boron, whence it acquired much greater activity and a capacity for 
acting on many bodies on which the volatile matter contained in the 
lavas of Etna has but a comparatively insignificant action.’”° 
Application of experimental results to the theory of the 
metamorphism of rocks.—In a large number of instances it is 
doubtless quite impossible to say from which of the various sources 
of hypogene heat above enumerated, or from what combination of 
1 Phil. Mag. xv. p. 68. 
2 Bull. Soc. Géol. France, xv. p. 103. : 
* Virst suggested by Daubrée, Ann. des Mines (1811), 3me sér, xx. p. 65. 
* Comptes Rendus, x\vi. p. 764 (1858) ; xlvii. p. 89; Ivii. p. 648 (1865), 
® Sur les Lmanations Volcaniques et Métalliferes, Bull. Soc. Géol. France, iv. (1846), 
p. 1249. This admirable and exhaustive memoir, one of the greatest monuments of 
1. de Beaumont’s genius, should be consulted by the student. ‘ 
