374 PROCEEDINGS OF SECTION C. 



On the west the rhyolite rocks extend to Taumaranui. On the south 

 to the Kaimanawa Range. In general, there are huge nearly horizontal 

 lava flows resting upon Upper Miocene rock. The rock is generally 

 white, with phenocrysts of felspar rather abundant. In section the 

 base is very glassy, yet with a structu.re related to a flow structure 

 producing a pattern not unlike the damascened appearance of a gun 

 barrel. The felspar is usually andesine. Hypersthene is usually com- 

 mon, but other minerals rare. Everywhere the rocks are covered with 

 a thick mantle of pumice. The pumice has been distributed in some 

 measure by water, and is often hundreds of feet thick. It is mingled 

 with charred wood, evidently carried down in the flood with the pumice. 

 In places several old soils can be distinguished between successive layers 

 of pumice. The pumice contains the same minerals as the rhyolite,. 

 and on the shores of Lake Taupo, where it has been triturated by the 

 waves, crystals of hypersthene can be gathered in large numbers, as. 

 noted long ago by Hutton. These crystals in some cases give a good 

 interference figure. The dispersion and opticaxial angle are those 

 characteristic of hypersthene. 



Throughout this district there are no cones from which it can be 

 said that the flows of rhyolite proceeded. There are several rhyolitic 

 mountains, e.g., Tarawera Ngongotaha, but in them, as elsewhere, the 

 rhyolitic lavas appear but little inclined. It is probable that the 

 tremendous emissions of pumice have levelled up the contours of the 

 country and obscured the cones. 



Through the rhyolite plateau there are several projecting cones, 

 often of large dimensions — -Ruapehu, Ngauruhoe, Tongoriro, Kakepuke, 

 and many others. In nearly all cases where these have been examined 

 they have been found to consist of andesitic rock. The fact that their 

 more recent lavas have a surface free from pumice shows that their 

 emission was subsequent to the eruption of pumice. On the other hand, 

 the fact that their older lavas are covered by pumice does not prove that 

 any eruptions of pumice succeeded their emission. It must always be 

 borne in mind that the light pumice is always being redistributed by 

 running waters, and at the eruption of Tarawera there was a striking 

 illustration of the manner in which pumice might be scattered far and 

 wide by an andesitic eruption, for augite andesite was, so far as known, 

 the only fused rock matter that accompanied that eruption. 



All the rocks of these cones that I have seen are hypersthene 

 andesites. [d) Seeing that Hill has mentioned phonolites as occurring on 

 Ruapehu, and Hutton has mentioned hornblende andesites, and Thomas 

 augite andesites from Ngauruhoe and Tongariro, I revisited these 

 mountains to find out whether my previous collections had been repre- 

 sentative. On the south, south-west, and east sides of Ruapehu I 

 found nothing but hypersthene augite andesites, and the same is true 

 of the other mountains. I also carefully examined the gravels of the 



(d) Specimens recently sent to me by the Rev. W. Fletcher, of Taupo, show 

 that Tauhara is an exception to this statement. The rocks of which it is composed 

 are different textural forms of dacite, with large quartz and reddish-brown horn- 

 blende. 



