28 



THE GASES IN ROCKS. 



TABLE 15. Meteorites. 



A comparison of the two types of meteorites indicates that carbon 

 dioxide is much more important in the gas from stony specimens than in 

 that from the metallic bodies, but that iron meteorites yield several times 

 as much carbon monoxide and hydrogen as do the stones. Sufficient data 

 are not at hand to permit a comparison of the amount of marsh-gas from 

 these two types; nitrogen, however, appears to come in greater volume from 

 the iron meteorites. 



ANALYSES CLASSIFIED BY THE AGE OF THE ROCKS. 1 

 TABLE 16. Igneous rocks. 



In addition to those rocks which could be classed either as Archean or 

 Proterozoic, there were others which could only be called Pre-Cambrian; 

 they are included under the head of Total Pre-Cambrian. 



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 com- 

 bination 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 indicate that this process is progress- 

 ing 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 17. Sedimentary and meta-sedimentary rocks. 



1 In this classification of analyses by the age of the rocks, and in the following one 

 based on granularity, only my own analyses have been used. 



