602 DAY AND SHEPHERD WATER AND VOLCANIC ACTIVITY 



and rational significance. In all the experience of the Geophysical Labo- 

 ratory with the thermal study of silicates, we have found no natural rocks 

 or minerals which did not set free gases in considerable quantity when 

 heated in the laboratory to a temperature high enough to melt their chief 

 constituents. Chamberlin, 22 in his elaborate series of analyses of the 

 gases contained in rocks, seems to have had the same experience. If these 

 studies together represent sufficient breadth of experience to justify a 

 sweeping conclusion, then there are no "dead" rocks, meaning thereby 

 igneous rocks, which no longer release original volatile ingredients when, 

 heated to melting. On the other hand, if we admit the nearly or quite 

 universal distribution of gaseous ingredients in igneous rocks, but sup-, 

 pose these gases were in equilibrium with each other throughout the solidi- 

 fication period, then reheating in the laboratory could discover no "explo- 

 sive'*' rocks. The distinction "dead" rocks and "live" or "explosive" rocks 

 loses all significance so long as it applies merely to rocks containing gases 

 in virtual equilibrium with each other, which merely release the gas when 

 heated. But immediately we understand that in lavas carrying gases in 

 solution or mechanical imprisonment the gases shut up therein may react 

 together, with release of heat, the moment they are free to do so, "explo- 

 sive" lava has a definite meaning, and Brum's experience (loc. cit., p. 55), 

 that "once the expansion has commenced nothing [for example, with- 

 drawal of the source of heat] can stop it," becomes a most illuminating 

 one. Rapid expansion of the reacting gases, together with the weakening 

 of the inclosing walls through the accession of heat thus supplied from 

 within may very well produce explosive phenomena, in the sense in which 

 Brun used the term, either in nature or in the laboratory. It is otherwise 

 somewhat difficult to see how simple adiabatic expansion of a gas inclosed 

 in walls of obsidian, which are very viscous even at very high tempera- 

 tures, can produce "explosions" in the manner postulated by Brim. 



WATER AND THE BASIC MINERALS 



There is another conclusion which has been freely offered by those who 

 hold to the view that H 2 can not be present as such in the emanations 

 from active volcanoes, of which a statement may be found in the quota- 

 tion from Green in the opening paragraph of this paper. It states that 

 "the basic minerals themselves give no indications, in the main eruptions, 

 of having been in contact with water, highly susceptible as they are to 

 such an influence/' 



28 R. T. Chamberlin : The gases in rocks. Publications of the Carnegie Institution of 

 Washington, No. 106. 



