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“* What is the cause of the disturbance?” They had seen that 
vast volumes of steam accompanied eruptions, and they might 
therefore look to water as a factor in the problem. Lava might 
be compared to the molten slag which issues from furnaces ; 
if they poured water upon it explosions resulted. Lava was 
mineral substances in a state of fusion, and if large volumes of 
water could get access to the depth of fusion then they could 
imagine the explosions which would take place and the volumes 
of steam and water-vapour which would be generated. Mr 
Wethered then explained the objections which had to be met 
in accounting for volcanic action as caused by water coming in 
contact with hot lava in the interior of the earth. He did not 
think that water found access by percolation. The most 
probable explanation was that it entered through fissures and 
faults which were formed by shrinkage of the earth’s crust. A 
possible cause of the New Zealand eruption was a movement 
along the great fault-line that traversed the north and south 
islands in a north-easterly direction, which may have allowed 
sea-water to enter to the depths of fusion. 
Earthquakes were next dealt with. He hadalready pointed 
out that earthquakes preceded volcanic eruptions. It would 
appear as though the volcanic forces were trying to break loose, 
and that their efforts caused an earthquake. Doubtless earth- 
quakes occurred without volcanic eruptions, that was, so far as 
they knew, but seeing that in the great majority of instances 
the shocks came from under the sea, it was impossible to say 
whether earthquakes had resulted ina submarine volcano or 
not. The shocks were propagated through the strata of the 
earth in a series of waves, which radiated from the centre 
of disturbance. The vibrations were in two directions: those 
usually first felt were in the direction in which the waves were 
travelling, and then a motion was felt at right angles to the 
former. These two movements were termed waves of compres- 
sion and distortion. Now what could produce these vibrations 
and oscillations which were termed earthquakes? It had been 
shown by Professor Milne that the majority of earthquakes are 
due to explosive effects at volcanic foci. It had been shown 
