THE GASES IN ROCKS 547 
be the case with the gas which was excluded from growing crystals in 
deeper horizons, as in bathylithic intrusions, where final escape was 
difficult. In this problem of granularity, as in the matter of age, 
the quantities of gas evolved are probably determined by a combination 
of complex factors rather than by any single cause. 
RESULTS AT DIFFERENT TEMPERATURES 
The different gases are not all expelled from rock material at the 
same temperature, nor are they evolved at the same rate. In general, 
hydrogen sulphide and carbon dioxide are not only the first gases to 
appear, but they are more rapidly given off than the others. Carbon 
monoxide follows the dioxide as the temperature is raised, and gen- 
erally increases in relative importance, as the latter begins to subside, 
toward the end of the combustion. Hydrogen and marsh-gas are 
most conspicuous at high temperatures, and hence attain higher 
percentages in the last half of the gas than in the first half. Nitrogen 
appears to be disengaged with much difficulty, requiring considerable 
time at a high temperature. 
ABSORPTION 
Experiments to test the power of gas-absorption by rock material 
indicated that while a rock powder may take up certain gases while 
cooling from a high temperature under special conditions, absorption, 
if it goes on at all at ordinary temperatures, takes place very slowly. 
However, when rock powders which have apparently been deprived 
of all their gas were reheated after a sufficient interval of time, there 
was usually a second evolution of gas. An analysis of the gas from 
a drill core of Keweenawan diabase from Houghton, Mich., which 
was kindly furnished by Dr. A. C. Lane, showed 3.88 volumes of gas 
per volume of rock.' After the gas was extracted, the apparently 
exhausted powder was stored away in a paper bag. Six months later, 
when reheated, this material yielded 1.92 volumes of gas. From this 
and other similar experiments it was found that an interval of time 
partially restores the gas-producing properties of rock powders. For 
this phenomenon there are two possible explanations. Either, the 
first heating does not expel all the gas contained in the rock, which, 
by some sort of diffusion or molecular rearrangement, gradually pre- 
t Analysis No. 85. . 
