'216 meunier: formation of magmatic gases 



silicates (anorthite and other feldspars). It is to be noted that 

 the formation of these products, while sufficient to elucidate the 

 origin of volcanic minerals, and often carried out at the expense 

 of sedimentary strata which have undergone the orogenic over- 

 blanketing by an intruded sheet, as described above, is neverthe- 

 less incomplete from our point of view, because of the free com- 

 munication of the subterranean laboratory with the atmosphere. 

 That communication is in fact incompatible with the retention 

 of those gaseous substances that represent the generative force, 

 and henoe incompatible with the conditions that enable the erup- 

 tion to take place. That situation, however, will vanish of itself, 

 if in place of the burning coal mine we consider the case of a 

 natural over-blanketing with its accompanying conditions. 



Among the results of the heating of sedimentary layers impreg- 

 nated with the products that would escape from them if subjected 

 to distillation, two require special mention: (1) The mobility 

 imparted to the molecules, enabling them to enter the crystal- 

 line state through a veritable refusion which we may call aqueous; 

 (2) the incorporation, by occlusion, of these vapors themselves 

 within the liquid produced. The resulting substance is a com- 

 pound which, despite the enormous difference in composition 

 and surroundings, suggests a comparison with aqueous liquids at 

 ordinary temperature in which soluble gases have been impris- 

 oned by pressure. The typical case is that of Seltzer water (soda- 

 water), that is to say, the solution, under the necessary pressure, 

 of carbonic acid gas in water, which constitutes a sort of aqueous 

 magma. 



The characteristic property of this magma is its tension; it 

 persists without change of constitution so long as the surrounding 

 pressure does not diminish ; but if by any process the reservoir con- 

 taining this magma is put in communication with a region of 

 less pressure, the equilibrium which tends to establish itself 

 between the two regions causes the disengagement of all or part 

 of the dissolved gas. Thus by merely pressing on the lever of a 

 soda water siphon, a veritable eruption may be produced. The 

 dissolved gas, tending to reach a state of equilibrium with the 

 adjoining atmosphere, separates from its solvent, but carries that 



