556 R. T. CHAMBERLIN 
The more restrictive phase of the problem of water will be discussed 
under the head of vulcanism. 
VULCANISM 
In the actual dynamics of vulcanism, provided the gases are original 
in the magmas, the state in which they occur is not of vital importance, 
except in so far as it determines the conditions under which the gases 
become free, from occluded or chemical bonds, to perform their part 
in the mobility of lavas, in the explosions which sometimes accompany 
eruptions, and in the phenomena of fumaroles and volcanic vents. 
The distinction between cavity, occluded, and chemically united gas, 
which is made in the case of solid igneous rocks, cannot be extended to 
the liquid lavas. In the liquid lava the gas may be supposed to be 
imprisoned mechanically, or else to form a part of the magmatic solu- 
tion. On the solidification of the mass, the gas, formerly existing 
in the free state, may enter chemical combinations at the lower tem- 
perature, may be occluded by the solid rock, or may become entrapped 
within the minerals last to crystallize. So, too, it is possible that 
some of the gas dissolved in the magma may, because of cooling and 
crystallization of adjacent portions of the solution, reach a super- 
saturated condition and appear in the solid rock also as gas inclusions. 
Otherwise, it would pass into the solid rock occluded or chemically 
combined. The condition of the gases examined in the laboratory 
need not, necessarily, correspond to a particular state of occurrence in 
the lava before crystallization. 
Gases mechanically distributed throughout the lava would always 
be an operative factor in vulcanism, while such gases as were chem- 
ically combined in the solution would, presumably, only become free, 
and hence fully operative, upon the lowering of the temperature and 
the relief of pressure, and probably but partially then. Since vapors 
and gases in the free state are the cause of volcanic explosions, they 
can be traced as far down in the conduits as explosions occur. From 
the nature of these explosions, which appear to be due to the accumu- 
lawrencite, and doubtfully schreibersite have been recognized. The occurrence of this 
terrestrial iron would indicate that material of this sort still occurs at points within the 
outer part of the earth. 
1 A falling temperature favors the liberation of hydrogen from water by ferrous 
compounds (see p. 553), while carbonates are most easily decomposed at low pressures. 
