THE GASES IN ROCKS 543 
AVERAGES OF THE GROUPS 
“WAG ey: 
e= IGNEOUS ROCKS 
l | | 
No. MyperorRock | eee 5| HaS | CO. | Co / CH, | 12h; | N, | Total 
| 
ie RASC Gelovisis: sas onion ocedet 2 | 0.00] 4.06] 0.19] 0.05] 3.44] 0.13] 7.87 
2 |Diabases and basalts....... LAG leo] 3OO| a 44 T2254. TTT 3 6 
Bal Gabbrosyandediorites a. .3| ol ss \eeenO2| 2.531) = v.13) 21-07) 2100 Hath | Alig / 
4 |Granites and gneisses......| 19 KOO| 1547 9. 22|| “05/1. 36|— 00!) 3). 
Caliinclesitestsnir: icant) as 7 | 20] 1.86) -18} .06)  .20)  .09) 2-3 
OBI Syenitess asses se sc fie || cle) eats 07 05) .QI| .O4] 1.25 
7]. Oh OVUSS.: cooee seals 5 oe oo 4 fore) 69 05 02) .06] .05 87 
8 |Miscellaneous porphyries 2 GO Sep eCllt | eevee O4|ne7/0 
| 
The general averages bring out the fact that, while rocks of each 
group may vary considerably among themselves, each group as a 
whole fits into a logical place in relation to the other groups. The 
established order appears to be, most gas from those rocks which 
contain the greatest proportion of ferromagnesian minerals. ‘Though 
much influenced by other conditions, such as relative age and nature 
of the igneous mass, the general deduction may be made that the 
volume of gas obtained from rocks varies, in a rough way, in propor- 
tion to the percentage of ferromagnesian minerals present. Dia- 
bases, basalts, and basic schists take first rank in the quantity of 
gas evolved. Next to them appear diorites and gabbros which are 
also near the basic end, but formed under different conditions. 
Andesites are out of their place in this list, as they take precedence over 
granites in the proportion of ferromagnesian minerals, but these ande- 
sites were all either of Tertiary or Recent age, whereas most of the 
granites came from pre-Cambrian formations, and, as the next table 
will show, ancient igneous rocks yield more gas than modern’ ones. 
The rhyolites, which combine a scarcity of basic minerals with Ter- 
tiary age, foot the list. 
It is to be noted that the rank of a type of rock on the basis of an 
individual gas does not in all cases correspond to its rank for some 
other gas, or in respect to total volumes. The andesites tested gave 
more carbon dioxide than either the granites or the syenites, though 
both of these types greatly surpassed the andesites in the matter 
of hydrogen. But this involves another factor: in deep-seated rocks, 
