DALY. — THE NATL'RE OF VOLCAXIC ACTIOX. 



87 



is so copiously exhaled during a volcanic eruption. At the same time 

 this process aocnunts for the widespread occurrence of magnetite in 

 igneous rocks." '* 



The abundant animal life of Cambrian and later time implies that 

 the earth's atmosphere has long had a very low cuntent of carlxtn diu-x- 

 ide. The amount of this o.xitle which has been locked up in the car- 

 bonate rocks since the beginning of the Cambrian period is so enormous 



Figure 7. Ideal longitudinal section of an abyssal injection, showing the 

 relation of vulcanism to the secular rise (arrow.s) of juvenile gas. The middle 

 vent is artive because it originates at the highest point (cupola) in the in- 

 jected body. The other vents are extinct because of this advantage of the 

 middle vent. Solid black represents the already crystallized material of the 

 injection. Cross-lined area is the countr>'-rock. Length of section about 100 

 kilometers. 



that mo.st of it, or all of it, mu.st be considered as of juvenile origin. 

 Yet more clearly than in the case of water, carbon dioxide must be 

 regarded as a ])rimary constituent of earth magma. Under the same 

 conditions as those described by Chamberlin, ferrous iron is oxidized to 

 magnetite by carbon dioxide, yielding carbon monoxide and G<H)(> cal- 

 ories ])er gram molecule. 



The list of the juvenile gases and vapors also includes nitrogen, 

 chlorine, sulphur, and hyilrocarbon.s. These and other volatile sub- 



" n. T. Chamberlin, The r,a.ses in Rocks, Publication No. IOC), Carnegie 

 Institution of Wiushington, 1908, p. 00. 



