622 GEOLOGY. 



globe has been much neglected in current conceptions of early condi- 

 tions. If the lavas of the supposed molten globe absorbed propor- 

 tionately as much water- vapor as the volcanic lavas often contain, it 

 would probably take forty or fifty times the present ocean and atmos- 

 phere to supply them. Any remnants of these original lavas might 

 well be supposed to hold gases. Even rocks derived from them by 

 deep-seated solidification might retain much gas. (2) The other phase 

 of the view assumes that the gases were entrapped when the globe was 

 built up of meteoroidal or plane tesimal matter, as assumed in the accre- 

 tion hypothesis. 



Under either of the last two views the gases may be said to be pri- 

 mary, and genetically connected with the origin of the lavas themselves. 

 Such gases would be a contribution to the atmosphere and the hydro- 

 sphere. This view does not exclude the idea that as the lava rises 

 through the surface- rocks, other gases are formed by contact, and that 

 they may be absorbed into the rising column. On the contrary, the 

 view recognizes the possibility that a tongue of lava rising into the 

 upper formations may encounter bodies of water, or masses of thor- 

 oughly water-soaked rock, from which great quantities of steam may 

 be generated, and that this accessory steam may be a large factor in 

 the initial explosion which often accompanies the development of a 

 new volcano, or the new eruption of an old one after a long period of 

 quiescence. 



A decision on the vital question whether the volcanic gases are largely 

 primary, or are essentially secondary, has not yet been reached; but 

 it will doubtless be reached when a sufficient number of really repre- 

 sentative analyses of volcanic gases have been made, and when the 

 phenomena of the gases occluded in igneous rocks have been thoroughly 

 investigated. 



The peculiar proportions of the rock-gases, in which hydrogen and 

 carbon dioxide so greatly preponderate, seem to imply that they are 

 not derived from the atmosphere; at least if they were so derived, 

 there must have been a selective absorption of a most remarkable kind, 

 because hydrogen is present in the atmosphere in exceedingly small 

 quantities, while carbon dioxide is a very minor constituent. At the 

 same time, as already remarked, no free oxygen is usually found in 

 these absorbed gases. 



The question as to whether the larger part of the volcanic gases is 



