DALY. — THE NATURE OF VOLCANIC ACTION. 121 



actual volcanic pipe and, according to the law of mass-action, exother- 

 mic reactions on a large scale are to be expected. The possibility that 

 energy was potentialized in the primitive basaltic substratmn by the 

 formation of dissolved eudothermic compounds, like cyanogen, ozone, 

 hydrogen peroxide, etc., is indicated. In consequence of changes in 

 pressure and temperature, due to injection, the dissociation of those 

 compounds and the formation of new, stable compounds formed partly 

 or wholly from their elements, give a double source of heat in the mag- 

 matic column. The heats of formation for the probable reactions are so 

 great that small masses of juvenile gas might furnish a relatively large 

 supply of heat. Though it is at present impossible to estimate the 

 fraction of the total volcanic heat due to chemical reactions, a working 

 philosophy of vulcanism should give due regard to the hypothesis that 

 a central vent is a true furnace. 



Using Siegl's recent results from experiments, the writer has calcu- 

 lated the approximate rate of heat loss through radiation at an active 

 crater. The loss by radiation occurs, in general, at a much faster rate 

 than the heat loss by conduction into the walls of the vent for a depth 

 of many kilometers. The methods of the transfer of heat from the 

 depths are discussed. 



The principle of " two-phase convection " is concluded to be essential 

 to the maintenance of prolonged activity at central vents. This con- 

 ception is illustrated by the analogy of solid spheres moving, under 

 gravity, in viscous fluids. 



Explanation is offered for the dormancy and related periodicity of 

 certain vents ; for the typical shape of such a vent, and for its com- 

 paratively small size. These features, when coupled with long persis- 

 tence in activity, are chiefly dependent on two-phase convection. 

 Since the latter process is, in its turn, dependent on the rise of gases 

 in the magma chamber, this general conception of central eruptions is 

 called the gai^-fiuxlng hijjfotke!^'is. 



The petrographic variety of lavas is to be largely explained on prin- 

 ciples which have been demonstrated in plutonic geology. The lavas 

 emitted at central vents may be : primary basalt ; differentiates of pure 

 primary basalt ; syntectic magmas, i. e. those produced by the solution 

 of foreign rock in primary basalt ; or differentiates of syntectic mag- 

 mas. The petrographic diversity in the lavas of neighboring volcanoes 

 becomes better understood through the recognition of the two ("prin- 

 cipal " and "subordinate ") classes of central vents. 



The explosiveness of volcanoes is a necessary step in tiie march of 

 events following abyssal injection. The inciting cause is to be sought 

 in the tension of resurgent gas as well as of juvenile gas. Progress in 



