MAGMATIC ACTION OF HOT SPRINGS. 255 



thus went on on a large scale in primeval times, it is argued, still go on when- 

 ever a body of magma consolidates; a large part of the water of this fluid material 

 is separated and expelled and most of it escapes to the surface as hot springs, 

 adding to the surface waters already originated by similar separations. 



Of these two explanations, the former may seem more familiar and probable, 

 because of our acquaintance with ordinary surface waters and our lack of intimacy 

 with newborn magmatic waters. Yet the magmatic explanation is the only one 

 of whose possibility we have ocular demonstration. We have no such demon- 

 stration that surface waters can penetrate downward till they are heated far 

 above the boiling point and then rise again and emerge, and we can reach such an 

 idea only by a process of speculation which is not even logical reasoning. On the 

 other hand, the vast quantities of water vapor given off by lavas at many volcanic 

 centers afford proof that water is present in these unconsolidated magmas and 

 separates on cooling. Furthermore, the phenomena of contact metamorphism, 

 especially that connected with siliceous rocks, show, as has often been pointed out, 

 that in depth similar water vapor is expelled from cooling rock, even under great 

 pressure. 



Volcanic activity has sometimes been ascribed to the infiltration of surface 

 water, which, on coming into contact with heated rocks below, causes explosions 

 and extravasations of lava; and the water given off from the cooling lavas is thus 

 thought to have a surface origin. Many facts, however, which can not be gone into 

 here are against this hypothesis. Concerning the steam given off at Vesuvius, 

 Prof. E. Suess remarks: a 



u* * * j j s a (. j eas t; certain that the quantities of steam issuing from the 

 parasitic crater must have come from a zone in which the temperature equals or 

 exceeds the melting point of most rocks, and in which there can be no question of 

 porous or f ragmen tal rocks, and therefore no question of infiltration of vadose* 

 water." 



That is, the principle of capillarity above referred to can not apply to rocks at 

 these great temperatures and can not explain the water in lavas. 



When the upward movements in the lava bodies have ceased and a crust of 

 cooled and solid rock has congealed at the surface, consolidation will progress 

 downward. The aqueous vapor given off from this lower cooling lava will become 

 condensed to water on its passage through the cooled crust and will so emerge. 

 It seems, therefore, impossible to escape the conclusion that at least some hot 

 springs, the after-phenomena of volcanic activity, have the origin above described, 

 and contain newborn water separated from the magma. 6 ' 



aeog. Jour., vol. 20, p. 519. 



6 Surface. 



eSuch water has been called juvenile or primitive by Professor Suess, and hifpofjene by one of his translators, to 

 distinguish it from the shallow underground water derived irom the surface, or radose water, the latter term having 

 been proposed by Posepny in his essay on ore deposits. 



