404 Transactions, 



magma near the earth's surface. The magma eagerly absorbs the water, 

 and in consequence swells and becomes more fluid. The resulting pressure, 

 which is analogous to osmotic pressure, forces the magma outwards, and 

 thus volcanic eruption begins (4, p. 18). 



According to the assumptions made in this paper, a fusion magma has 

 little or no inclination to absorb water, and, if so, the hypothesis advocated 

 by Arrhenius fails to hold good. Moreover, it is not easily understandable 

 how large quantities of sea water could find their way into a magma against 

 enormous opposing pressure. 



An aqueo-igneous magma stoping its way upward during folding move- 

 ments of the earth's crust may find a plane of weakness leading to the 

 surface. In this case the probability is that water and other volatile sub- 

 stances will escape, whilst the magma, or those portions losing water, will 

 consolidate. 



It may happen that heat has accumulated in part of an originally aqueo- 

 igneous magma to such an extent that the temperature of this portion is 

 raised well above 1000° C, and all or nearly all its water is free from com- 

 bination. The opening of communication with the surface will relieve the 

 pressure that keeps the aqueous and other gases confined, or holds them in 

 solution. The result will be a series of violent explosions in the volcanic 

 vent, analogous to geyser eruptions, which will scatter volcanic ash, 

 pumice, &c., far and wide. When the gases have nearly exhausted them- 

 selves there may follow effusions of acidic lava. The cooling of the magma 

 as it rises in the volcanic conduit, together with the loss of water and the 

 extrusion of lava, promotes part crystallization and differentiation. If to 

 these changes we add the influence of magma drawn laterally to the volcanic 

 vent or vents from regions outside the original disturbance, we shall have 

 hypothetical data quite adequate to account for all the phenomena of 

 vulcanism. 



Volcanic action may originate through a fusion magma, nearly devoid 

 of water, finding its way to the surface. Such an occurrence is rare, or 

 perhaps impossible. 



Hot Springs and Geysers. 



Hot springs and geysers are usually attributed to expiring volcanic 

 action. Since the early stages of vulcanism may afford escape for all or 

 most of the water in a magma, a magmatic source for the heated waters of 

 the final stage can be postulated only with difficulty. If, however, an 

 aqueo-igneous or other magma containing water approach the surface it 

 may give rise to boiling springs, the water of which (in part at least) will 

 be of magmatic origin. Thus hot springs may indicate rise of magma, and 

 precede as well as follow a period of igneous activity. 



Summary and Conclusions. 



The physical or chemico-physical state of water in rock-magmas is not a 

 matter of indifference. By making assumptions that are consistent with 

 known facts, but have not as yet been experimentally proved or disproved, 

 the following conclusions may be reached : — 



1. It is possible for an aqueo-igneous magma to form at temperatures 

 not far above 365° C. In this magma there may be uncombined water 

 acting as a solvent and physically in the liquid state. At somewhat higher 

 temperatures uncombined water no longer acts as a solvent, and may be 

 regarded as physically a gas, held in solution only by pressure. At still 

 higher temperatures no combined water can exist in the maffma and all 



