118 Frederick Guthrie on Salt-Solutions 



If the earth were a sphere of liquid having a density of 5, 

 the pressure at its centre would he over three million atmo- 

 spheres — a pressure competent to preserve the density of 

 water at a temperature sufficient to fuse perhaps the most 

 refractory known rocks. But at this high temperature the 

 water would, judging by analogy, mix freely with the rock 

 and relieve itself — one cannot yet say how much (compare, 

 however, my next memoir, IX.), but certainly very greatly 

 from its tension. 



That there are true sedimentary formations of course no 

 one can deny ; but to attribute to marine influence the 

 formation of rocks because water is found within them, or 

 because w T ater is liberated when melted rock-masses are 

 ejected, is a contention no longer supportable. Obsidian 

 melted and under pressure will, I presume, mix freely with 

 water. When this pressure is gradually removed, water- 

 vapour escapes, and although it takes with it a large amount of 

 heat, the temperature of the obsidian may still remain above 

 its point of anhydrous fusion, or it may be maintained fused 

 by heat from other sources. Finally cooled, it is the familiar 

 glassy amorphous mineral. A quick release of pressure 

 entails a quick vaporization of water and a quick loss of heat. 

 The obsidian mass, during and because of the loss of water 

 and the loss of heat, becomes pasty and " rises " like dough 

 during fermentation, and becomes pumice, which is often 

 found overlying obsidian. A quicker release of pressure 

 from above causes the vesicular and vesiculating masses to be 

 projected, and if the vesiculation is carried far and fast 

 volcanic dust is produced. That water is one of the ac- 

 companiments of volcanic activity is well known. The 

 presence of hydrochloric acid in the ejecta, and the almost 

 universal neighbourhood of the sea to active volcanoes, has 

 favoured the view that the material for the motive power is 

 supplied by the marine irruption. Without entering upon 

 the question as to whether sea-water is essential to volcanoes, 

 and whether hydrochloric acid is a product of the action of 

 acid silicates or silicic acid upon the chlorides in that liquid, 

 I contend that the evidence is conclusive that at one period 

 the melting masses contain water. They are in the same 

 predicament as the nitre liquified along with water at a high 

 temperature and under corresponding great pressure. 



This subject has been so fully discussed by Daubree in his 

 various memoirs, and is so ably treated in his Geologie 

 Expdrimentale, that, as far as their geological bearing is 

 concerned, my experiments may be considered as merely 

 adding another chapter to his work. 



