464 Transactions. — Geology. 



ward of the lake : it is everywhere. Northward, westward, and 

 southward similar deposits occur, but the quantity is much less 

 to the southward, and volcanic grits and stones are absent. It 

 is evident that the pumice-deposit is the most recent up to the 

 time of the Tarawera eruption, as it is continuous over such a 

 large extent of country, and shows that the distribution must 

 have been from the same general centre. It would be difficult, 

 if not impossible, to give even an estimate of the quantity of 

 pumice that is distributed over the volcanic belt of this Island ; 

 but it seems certain that the ejection took place, as in the case 

 of Rotomahana and Tarawera, suddenly, and as an attendant of 

 hvdrothermal activity. Volcanic outbursts do not send out the 

 same kind of products, and it is doubtful whether any of the 

 volcanoes to the south of Roto-aira have ever ejected pumice 

 in quantity. Had the pumice been ejected from Ruapehu. 

 Ngauruhoe, or Tongariro, much larger quantities might have 

 been expected to the south and east of these mountains. Their 

 growth and that of Mount Egmont is similar. Pumice is dis- 

 tributed by explosive means, lava by flows ; the former is 

 ejected, the latter wells and spreads as a plastic mass. In these 

 mountains the traces of lava-flows are common, but not so in 

 the case of pumice. A scoriaceous kind of pumice and clinker is 

 spread lightly over the Rangipo Desert, but nowhere in the direc- 

 tion of the mountains ; hence the probability is that the great 

 rift extending from Pihanga through the present Lake Taupo and 

 down the Waikato in the direction of Wai-o-tapu was brought 

 about by explosions that spread pumice and varieties of lavas 

 over such a large extent of country, just as the Rotomahana 

 explosion spread blue mud. scoria, and varieties of shattered 

 lavas. 



What Rotomahana is becoming by the inflow of water, 

 Taupo became perhaps hundreds of years ago. Volcanic action 

 and volcanic phenomena are yet active in the North Island. 

 and there is evidence of continuous activity from the Secondary 

 period. Nor is there any reason to suppose that the volcanic- 

 district will not again be subject to lava-flows and explosions 

 due to hvdrothermal causes : both may be expected, and in the 

 coming years science may be able to determine even the times 

 of their coming. 



