286 University of California Publications in Geology [Vol- 13 



rather than elsewhere through the rock, where the pore spaces are 

 just as large and the impediments no greater? 



One school has argued that meteoric water would have great diffi- 

 culty in attaining any but a very weak concentration in metalliferous 

 minerals before reaching the vicinity of a freshly intruded igneous 

 mass, and that it would also have difficulty in approaching the latter 

 through the rock pores to absorb further quantities of mineral, on 

 account of the heat present. On the other hand the opposed school 

 has indicated that meteoric waters could pass through rock pores as 

 well as magmatic waters, that they could issue hot from fissures in 

 the walls and through the interior of an igneous mass on an equal 

 footing with juvenile waters ; and as pointed out by Lawson with par- 

 ticular strength in the paper above referred to, the idea that juvenile 

 mineral-bearing waters may issue in quantity from a marginally 

 crystallized magma is weak in that it assumes the restraint of the 

 magmatic waters from escaping until the last stage of segregation 

 when the pore spaces of the crystalline margins would offer a serious 

 barrier to its escape. 



R. A. Daly in his book, ' ' Igneous Rocks and Their Origin, ' ' makes 

 the strong point that the long preservation of the heat and life of 

 volcanoes is most easily interpreted as being due to the continual 

 migration to the vent, of masses of gas-rich magma from all parts of 

 the fluid reservoir beneath. These partial segregations of volatile con- 

 stituents of the mother-magma occur here and there through its mass, 

 or along its periphery, and by virtue of the lightness imparted to the 

 portions of magma in which they are occluded, these rise to the mar- 

 gins of the reservoir, drift along its roof to the extrance of the vent, 

 and thence rise to its crater where they escape by explosion or quiet 

 bubbling according to the concentrations of gas in them. On this basis 

 it can be easily understood that the great quantities of water given 

 off as steam at volcanic vents is misleading as to the proportion of 

 volatile material contained even in hydrous magmas. The flow of 

 lava from a vent might thus represent merely the escape of the masses 

 of convected magma which served as the vehicles for segregations of 

 magmatic gases. From other considerations advanced in Daly's book 

 it is also easy to understand that a magma which comes to rest beneath 

 the surface might be relatively deficient in volatile materials, since 

 if these were present magmatic "blow-piping" would have taken 

 place in a "cupola" above the mass, fluxing and stoping a passage 

 for the ascent of the magma to the surface. These considerations 



