THE GASES IN ROCKS 545 
Cambrian; they are included under the head of Total pre- 
Cambrian. 
TABLE VIII 
IGNEOUS Rocks 
No. of 
Order Age of Rocks Analy- | H.S CO, (@f0) CH; 1Bb, N2 Total 
ses 
I Neh eats cs eet, arenes 7 0.03] 7-44] 0.35] 0.07| 3.79] 0.21/11.89 
2 IBTOLETOZOGae ee naa ie 8 HOO! HOS) lla Ople 250i) mL 47 
Be dlebertianyy swe olen ona taat 18 POO| 1 ZO) oT ain) Os CBO OS 
4 INeGemte lavas ean: 5 .03| O7]| } JOE ©O))) 702 60 
es = | 
Total pre-Cambrian....| 28 O2|| 2'-70|5 723) OO 2e Lal = atoll 5 25 
Granditotalieee cee alee5 i ROE ||. 2) Os elO | cOG| lee 2 Ol OO sno 
The rapid and steady decline in the quantity of every gas, in passing 
down the columns from the Archean through the Proterozoic and 
Tertiary to Recent lavas, is very striking. ‘These differences may be 
due to a combination of causes. The older rocks may yield more 
gas than the recent, owing to metasomatic changes which have been 
slowly taking place within the rocks. If this be so, the analyses indi- 
cate that this process is progressing at an exceedingly slow rate. Or 
the early magmas may have been more highly charged with gas, some 
of which has escaped as they were worked over and over and brought 
to the surface in later times. Both of these processes have probably 
been operative. 
TABLE IX 
SEDIMENTARY AND META-SEDIMENTARY ROCKS 
No. of HLS 
Order Age of Rocks Analy- SO COz | "co GH H, Nz | Total 
ses : 
IBKOtELOZOIGHs saree 17 ORAS 0. 08| On Til Ono) T1312] O05) 277 
DaeisaleOzOlen irs ion fe cease IO SCO eRe AG oe SONS) auerlad re eee a), he) 
3 IMIEEOVACHS tne Se eine a oleh: I HOO|HCAT Ds | ame OA|lin Asie sOd!le 08 
Motalaraateasesc tones 28 H277]| OZ |5. s2O0ley Of 1x00|/\- sO) 22243 
Age appears to make less difference in the gas evolved from sedi- 
mentary or meta-sedimentary rocks than it does in the case of igneous 
rocks. All of the Proterozoic specimens were of metamorphic types 
while only one of the Paleozoic sediments had been metamorphosed. 
The Mesozoic representative was a Jurassic shale altered by an intru- 
