On the Agency of Water in Volcanic Eruptions. 157 



rainfall stand higher, which they must do whenever the land is even 

 only a few feet above the sea level, so long will those waters dam 

 back and keep ont the sea- water, but whenever their level is brought 

 below that of the sea level, then inevitably will the sea-water flow 

 inland until the level is restored. Thus fresh- water remains accumu- 

 lated during a period of repose, may be ejected during the early 

 stages of the eruption, and may be succeeded by marine ejections when 

 the exhaustion of the fresh-water springs leads to the influx of the sea. 



There are difficulties in adapting this hypothesis to volcanoes in a 

 state of permanent action such as Stromboli and Kilauea, but they are 

 not more formidable than those presented on other hypotheses. 



In both those volcanoes there is a maintained state of slight unstable 

 equilibrium — a constant oscillation of the lava in the volcanic duct 

 coupled with a small loss, whether in the form of ejected scoria3 or of 

 slight occasional overflows of lava. As these conditions are per- 

 manent, they would induce in the manner before described a per- 

 manent influx of water either through permeable strata at depths, or 

 by soakage of surface or sea water through the loose volcanic matter 

 above ; and as owing to this incessant drain, the underground reser- 

 voirs would not have time to fill to their full extent, so it is probable 

 that the influx of water would always be small, but sufficient to main- 

 tain the slight and constant disengagement of vapour bubbles that 

 goes on. Mallet says that there is a perennial spring on Stromboli at 

 a higher" level than the crater. 



The independence of neighbouring volcanoes also presents another 

 difficulty. If, however, the volcanoes of Southern Italy or- those of 

 Hawaii are, as suggested by Dana, on separate lines of fissure, it is 

 possible that on the assumption of excessive viscidity of the lava, 

 friction may oppose greater resistance along the horizontal planes 

 which separate them at depths, than along the vertical column of 

 ascent in which the increasing fluidity, as the pressure lessens, 

 diminishes the friction. This is merely a suggestion. Although seem- 

 ingly independent, there is occasionally both in the Italian and in the 

 Hawaian volcanoes, symptoms of sympathetic action. 



On the hypothesis advanced in these pages, a reason is also afforded 

 why a greater volcanic activity should be maintained along coast lines 

 than inland, in the circumstance that when the inland waters which 

 feed for a time the explosive action are exhausted, they are succeeded 

 through their now deserted channels, by an influx of sea water that 

 serves to keep up for a longer period the state of volcanic activity, 

 and maintain passages open for the extrusion of the lava. It is thus 

 that the great inland volcanic areas of Auvergne, the Eifel, Hungary, 

 and Central Asia have, on the withdrawal of the surrounding waters, 

 become gradually extinct, and that the great volcanoes of the present 

 day have settled in ocean centres, or along coast lines. 



