90 Transactions. 



Physiography of the District. 



So many writers have already discussed this aspect of the 

 subject that little need be added here. There are, however, a 

 few matters that seem to have, in part, escaped attention 

 previously, and others which allow of very different interpreta- 

 tions. 



The actual craters of the large volcanoes have often been 

 described. It will, perhaps, be interesting to make a few remarks 

 on the crater of Ngauruhoe, which I have visited six times since 

 1891. 



The two earliest accounts, by Dyson and Bidwill, represent 

 the crater as a profound abyss which could not be descended 

 on any side, nor could the bottom be seen. 



In December, 1890, it was possible to walk all over the 

 bottom of the main crater, though steam- jets of some size were 

 to be found in many places. Round each steam-jet there was a 

 small cone of sulphur. The small scoria cone on the north rim 

 of the main crater was then much more active than the main 

 crater itself. 



A year later the crater had completely changed, and there 

 was a large pit near the centre of the main crater. This pit 

 was the scene of rather violent activity, and it was impossible 

 to see to the bottom of it. 



But little change has taken place since that time, though 

 the pit has become larger, and has changed its position rather 

 to the west, so that in December, 1906, its western side coincided 

 with the western flank of the mountain. At this time the moun- 

 tain was rather inactive, and it was possible to see to the bottom 

 of the pit. It was about 250 ft. in depth, with nearly vertical 

 sides, which were encrusted with sulphur, and from which steam 

 issued in clouds. At the bottom of the crater was a pond of 

 water of a bluish-green colour. There was a scum, apparently 

 of sulphur, and the water was in ebullition. Sulphuretted 

 hydrogen was being emitted in small quantity, but sulphur- 

 dioxide was in far larger amount. The small-rim crater to 

 the north was nearly quiescent. 



In February, 1907, the mountain became rather violent, 

 and emitted large quantities of dust, which fell over the country 

 to leeward. The mountain was ascended in March, during the 

 continuance of the active phase. The crater appeared to have 

 undergone no material change, but the shower of acid rain 

 and mud prevented me from making more exact observations. 

 The mud was six inches deep on the rim of the crater, and 

 ■extended 2000 feet down the side of the cone. 



The craters on Ruapehu and Tongariro have undergone 



