1885.] Agency of Water in Volcanic Eruptions. 255 



which after sixteen days ceased, but the flow of lava continued for 

 four months without farther explosions. In the eruption of Santorin 

 of 1866, the rock- emission proceeded for days in silence, the pro- 

 truded mass of lava forming a hill nearly 500 feet long by 200 feet 

 high, which a witness compared with the steady and uninterrupted 

 growth of a soap bubble. The eruptions of Mauna Loa are remark- 

 able for their magnitude and at the same time for their quiet. 

 Speaking of the eruptions of 1855, Dana says there was no earth- 

 quake, no internal thunderings, and no premonitions. A vent or 

 fissure was formed, from which a vast body of liquid lava flowed, 

 rapidly but quietly, and without steam explosions, for the space of 

 many months. 



On the other hand, paroxysmal eruptions are generally accompanied 

 by earthquakes, and begin with one powerful burst, followed rapidly 

 by a succession of explosions, and commonly with little extrusion of 

 lava, although it is to be observed that a large quantity must be 

 blown into scoriee and lost in the ejections. Such was the eruption 

 of Coseguina in 1835, and of Krakatoa in 1883. Sometimes in these 

 paroxysmal eruptions, there is absolutely no escape of lava, scoria? 

 alone being projected. A common feature in eruptions, and which 

 indicates the termination of the crisis, is the stopping of the lava, 

 though the gaseous explosions continue for some time with scarcely 

 diminished energy. 



There is, thus, no definite relation between the quantity of explo- 

 sive gases and vapours and the quantity of lava. If the eruption 

 of lava depended on the occluded vapour, it is not easy to see 

 how there could be great flows without a large escape of vapour, or 

 large volumes of vapour without lava. The extrusion of lava has 

 been compared to the boiling over of a viscid substance in a vessel, 

 but the cases are not analogous. 



The only logical way in which it would seem possible for water to- 

 be present, is on the hypothesis of Sterry Hunt, who supposes the 

 molten magma to be a re-melted mass of the earlier sedimentary strata, 

 which had been originally subject to surface and meteoric action. 

 But in the end the preceding objections apply equally to this- 

 view. 



There is the further general objection to the presence of water in 

 the molten magma, in that were the extrusion of lava due to this 

 cause, the extrusion of granite and other molten rocks (which do not 

 as a rule lie so deep as the lava magma) should have been the first to 

 feel its influence and to show its presence. Yet although water is- 

 present, it is in such small quantities, that these rocks never exhibit 

 the scoriaceous character which lava so commonly possesses. 



Nor is lava always scoriaceous, as it should be if the hypothesis 

 were correct. Many lavas are perfectly compact and free from vapour 



