BY PROFESSOR STEPHENS, M.A., F.G.S., (fee. 521 



the subterranean pressures — whatever their origin may be — are 

 likely to repeat their previous action, the fiery liquid will again 

 rise through the water-bearing strata, and the same series of 

 explosions recommence. While lava is free from water, either 

 involved in its mass or in contact with it, its flow will be regular 

 and its cooling gradual ; it will produce streams or hills or cones 

 of lava, and will therefore tend to accumulate to some extent 

 about its vent. When, however, the reverse is the case — and 

 steam is generated at a white heat and under enormous pressure, 

 the resulting explosions, as at Krakatoa, scatter into space not 

 only the aforesaid accumulation, but also the new and active lava 

 itself. (I leave out of consideration the ordinary process of cone 

 formation with tuff, fragmentary lavas and pumice, as beside the 

 present question, since neither Tarawera nor any of the other 

 volcanic eminences about these lakes seem to have been so 

 constructed). Such a rise in the temperature of the lower 

 portions of the siphons of these springs as would be produced by 

 a movement of molten rock towards the surface would certainly 

 stimulate their action in the highest degree, while the more 

 intense heat in the rocks in immediate contact with the lava 

 would, as certainly, result in the rapid formation of intensely 

 expansive steam under intensejpressure, which, even if we put out 

 of the question the steam which is originally or at least actually 

 engaged in the lava itself, is sufficient to account for the tuff and 

 pumice (if not lava) eruptions at Tarawera. Nor can one readily 

 imagine any other cause which would readily bring about so 

 sudden an access of violence in the ordinary action of hot springs, 

 together with simultaneous volcanic discharges of very com 

 siderable intensity. 



Geysers are but little dependent upon waters derived from a 

 distance. They are not phenomena of the same kind as con- 

 tinuously flowing hot springs or artesian wells A very small 

 quantity of water is sufficient to keep a large geyser in work, 

 the outflow in many instances being inconsiderable. A heated 

 stratum of rock, at no very considerable depth from the surface, 

 perforated by a funnel or vertical pipe with orifice above, open to. 



