540 R. T. CHAMBERLIN 
sive. The unusual amount of sulphur gas in the Proterozoic list is 
due to two weathered rocks which contained iron sulphate. However, 
even with these omitted, the hydrogen sulphide is abnormally high 
in the rocks of thisage. One of the Paleozoic shales was so calcareous 
as to yield g. 28 volumes of carbon dioxide, which accounts for the large 
quantity of this gas. The two bituminous shales (analyses 41 and 
42) are not included in these averages, since their excessive volume 
of gas from organic sources would so influence the figures as to disguise 
some of the characteristics of the other rocks. 
ANALYSES CLASSIFIED BY THE GRANULARITY OF THE ROCKS 
TABLE X 
IcNEouS Rocks 
| No. of | 
Order | Granularity | Analy- } HeSmincO: CO CH H, | N. | Total 
leases | 
| | i} 
| | = | 
I Mine-craine dice <cu ee 22 | 0.02| 2.75| 0.31| 0.06] 1.68] 0.12] 4. 
2 Medium-grained..... a its) | LOD) 227i) ely Ole VAs ees O| ay AReeTe 
3 Coarse-crained s,s tie II | .O1 40 LO|,).04] 1420)! 108) 383 
4 | Various porphyries (mostly | 
| AN Entlany) ever niee 5 OO} 4 07} .04 22 05 79 
From this table it would appear that the fine-grained rocks give off 
more gas than those of coarser granularity. One of the reasons for 
this difference probably lies in the fact that metasomatic changes are 
favored in fine-grained rocks, whose crystals, being smaller, afford 
more numerous junction-planes between the crystals, through which 
solutions more readily traverse the rock than in the coarse-grained 
varieties. Among other changes, hydration and carbonation should 
alter fine-grained rocks more effectively than coarse-grained ones. 
Fineness of grain in igneous rocks usually means that the lava 
cooled rapidly, and this would hinder the escape of the inclosed gas. 
But in the process of slow crystallization, such as produces large 
crystals and coarse texture, much more of the gas would be likely 
to be crowded out of the growing crystals. However, as a general 
rule, fine-grained igneous rocks are surface flows, while coarse-tex- 
ture types were formed at some depth below the surface, and hence 
a larger proportion of whatever gas was expelled from the rapidly 
cooling lavas would be more likely to escape altogether than would 
