552 R. T. CHAMBERLIN 
SIGNIFICANCE OF THE THREEFOLD STATE 
While chemical reactions and the phenomena of occlusion imply 
that gas exists in the interior of the earth, the presence of gas inclosed 
in cavities, under great pressure, adds the further implication that 
the gas often exceeded the point of saturation of the magma, at least 
at the stage of solidification. Cavity gases are most abundant in 
minerals of poorly developed cleavage, pointing perhaps toward a 
strong tendency to escape along cleavage planes during, or after, 
crystallization. While most commonly observed in non-cleavable 
quartz, the gas inclusions in that mineral may owe their abundance 
to the fact that quartz is generally the last mineral to crystallize out 
of a magma, and hence such absorbed gases as did not enter into the 
other crystals would become concentrated in the siliceous residue, 
and might supersaturate it. It is probably this freely moving gas 
above the point of saturation which contributes most to the mobility 
of lavas. Dissolved gases and vapors, while favoring fluidity, would 
seem to be relatively less effective. However, gases mechanically 
entrapped in crystalline rocks are quantitatively not very prominent, 
suggesting that perhaps the theory of liquidity due to gas is overworked. 
But, on the other hand, it is true that as a lava cooled down to the 
point where the last mineral crystallized, its gas-solvent powers would 
be increasing, allowing some of the gas to pass into solution. At the 
same time, free gas would be occluded by the growing crystals. 
Experiments upon the re-absorption of gas by exhausted rock powder 
indicate that a portion of the gas unites chemically as the heat dimin- 
ishes. Because of these processes, liquid lavas may be supplied with 
free gas, though the solidified rocks retain but little gas in this condition. 
WATER AND HYDROGEN 
The reversible reactions involving hydrogen, water, and iron 
compounds, which cause uncertainties in the extraction of gases by 
heat, are also operative within the earth. In the laboratory, when 
either ferrous salts and water, or ferric compounds and hydrogen, 
are heated in tubes without the removal of the products, reversible 
reactions set in until a condition of equilibrium is established. Hydro- 
gen and water, ferrous and ferric salts, are all present in a state of 
balance. In the interior of the earth, the heated, though solid rocks 
