VOLCANIC PHENOMENA 251 



nebulous condition of the globe, the molten nucleus could obtain a 

 grasp on its occluded gases. 



The new hypothesis simplifies the problem not only by making the 

 volcanic water and the accompanying vapors indigenous to the earth's 

 mass, but by giving a plausible explanation of how they came to be a 

 part of the magma. Volcanoes are at once the outlets for relief of accu- 

 mulated vapor pressure and a source of ocean and atmospheric suppty. 

 With the reduction in volume of steam and the lighter gases, the heavier 

 and non-explosive gases become more evident, and then occur the later 

 phenomena known as fumaroles, solfataras, soffioni, and mofettes. It 

 may be that in the volcanic reservoirs the several vapors are arranged, 

 as in the atmosphere, according to their specific gravity. 



The existence of carbon dioxide springs (mofettes), such as the " Dog 

 Grotto " near Naples and the "Valley of Death " in Java, are well ex- 

 plained under the new l^pothesis. Under the old view the mofettes were 

 compelled to derive their carbon supply from limestones and carbona- 

 ceous shales. The Dog Grotto, with its strong and continuous flow for 

 some thousands of }^ears, probably, would imply a subterranean limekiln 

 of immense extent. Shales could not furnish the supply, as they are not 

 sufficiently permeable. This topic will come up again in discussion of 

 the hydrocarbons. 



The chlorides and other haloid salts in volcanic emanations have been 

 assumed to come from sea water or from marine sediments, where the sea 

 had left them. The variety of gases in volcanic eruptions can not all be 

 derived from meteoric water, and some of them are not contained in sea 

 water. The abundant sulphur compounds have not been accounted for 

 at all. The resemblance of the mineral contents of the sea to the vol- 

 canic products lies in the fact that the ocean is itself the product of 

 volcanism. The old view has put the effect for the cause. 



The existence of volcanoes remote from any water body, and in arid 

 regions, is not a difficulty under the new hypothesis. The compara- 

 tively nonhydrous condition of the molten rock in many outpourings is 

 not entirely clear, but it is less a difficulty under the new hypothesis, 

 since this does not favor homogeneity in the earth's mass nor uniform 

 distribution of the volatile matter. The possible comparative dehydra- 

 tion of the deep interior of the earth has already been noted. Moreover, 

 there is, so it would seem, greater opportunity for localization or concen- 

 tration of the volatile matter under the new than under the old hypoth- 

 esis, because of greater porosity of the earth's mass. 



The theory of primogenial water-substance and other vapors under the 

 new hypothesis does not at once sweep away all the difficulties and mys- 

 teries of volcanism, but it gives a more rational philosophy of the matter 



XXXIII— Bur,i. Geol. Soc. Am., Vol. 15, 1903 



