68 THE GASES IN ROCKS. 



earth was probably not quite analogous, in all respects, to the formation 

 of the meteorites. Whether we take the meteoritic material to repre- 

 sent the heavier part of the original matter of the solar system, or the 

 stellar system, as a whole, matters little in the geologic problem. If, in 

 truth, the unoxidized, heterogeneously aggregated material of meteorites 

 be typical of the original heavy material of the earth, it becomes evident 

 that, in the case of our planet, other factors have been at work which are 

 not operative in the bodies of which the meteorites are supposed to be 

 fragments. These visitors from space are characterized by such minerals 

 as cohenite, (Fe,Ni,Co) 3 C, lawrencite, FeCl 2 , oldhamite, CaS 2 , and schreib- 

 ersite, (Fe,Ni,Co) 3 P, which, next to nickel-iron, is the most widely distributed 

 constituent of iron meteorites, 1 though of less importance in the stony 

 specimens. Such compounds imply an absence of both free oxygen and 

 water in notable quantities. Of like import is the absence of hydrated 

 minerals, such as micas and amphiboles. Water and an oxygenated atmo- 

 sphere appear to be the agents which are lacking in the bodies from which 

 the meteorites were derived, but which have been the operative factors in 

 working over the outer portion of the earth. 



But the original source of the earth's atmosphere and hydrosphere 

 is taken to be gas occluded, or absorbed, in the primitive meteoritic material. 

 These original gases, escaping, furnished both atmosphere and hydrosphere 

 when the earth became of sufficient size to retain them. A self-regulating 

 system was inaugurated. In the early stages of the hydrosphere, when 

 growth by infalling planetesimals was rapid, much water was buried 

 within the fragmental crust. This material, worked over by volcanic 

 activity, brought to the surface and subjected to weathering and erosion, 

 and buried beneath more material, has undergone assortment and altera- 

 tion until the accessible rocks at the present time are very different from 

 the meteoritic matter. Since the earth attained its growth and the infall 

 of planetesimals slackened, much less water has penetrated to great depths 

 below the surface. Post-Archean sedimentaries have not yet reached 

 thicknesses sufficient to carry inclosed water down to the depths from 

 which the lavas arise. Deep mines indicate that fractures and fissures 

 do not convey water down to very great depths at the present time. If 

 water does not penetrate so rapidly now, and hydration and carbonation 

 are less effective, it is also probably true that subsiding vulcanism brings 

 less gas to the surface. 



It is essentially a system of balance. At the same time that water is 

 being buried with sediment, its elements, hydrogen and oxygen, the latter 

 in the form of the oxides of carbon, are exhaled from the earth's interior 

 through volcanic outlets. But the system here suggested is very different 

 from the postulated limited cycle of underground water which, following 

 Daubree's famous experiment, 2 has crept into geologic literature as the 

 origin of volcanic vapors and the modus operandi of vulcanism. Instead 

 of surface-waters following cracks and fissures down to the hot lavas there 

 to be absorbed, the water already is present, and is a part of the rocks and 



1 Farrington, Jour, of Geol., vol. 9, pp. 405-407 and 525-526. 



2 Daubre, Etudes Synthe'tiques de G6ologie Exp6rimentale, t. 1, pp. 236-246. 



