340 Transactions. — Geology. 



plateau is bounded by a range of mountains which passes 

 northwards into the main range west of Taupo Lake. On the 

 north the plateau is separated from Lake Taupo by the vol- 

 canic mountains Pihanga and Kakaramea (4,266ft.) and the 

 ridge of volcanic rock which connects them. The Waikato 

 Eiver (called in this part of its course by the natives the 

 Tongariro) rises in Ruapehu and flows northwards towards 

 Lake Taupo, receiving many tributaries from the eastern side 

 of the Euapehu-Tongariro chain and from the western slopes 

 of the Kaimanawa Range, and passes to the east of Pihanga 

 as a broad, shallow, swiftly-flowing river. It enters Lake 

 Taupo at the southern end, about two miles from Tokaanu, and 

 has formed a very considerable delta, composed of the debris 

 of volcanic rock from the western sides of the various cones, 

 and of the slate found in the Kaimanawas. These two mate- 

 rials, of such different origin, are present in approximately 

 equal proportions. 



Ruapehu is the highest of the great volcanic cones, rising 

 to 8,878ft. Many observers seem to have suspected that the 

 vapour hanging about the summit on certain occasions, even 

 in fine dry weather, was due to volcanic energy in the moun- 

 tain ; but it was not till April, 1886, when Mr. Cussen 

 ascended the mountain, that the matter was placed beyond 

 doubt.* He found a lake of warm and steaming water occu- 

 pying a basin about 300ft. below the two chief peaks of the 

 mountain. No steam was rising from the mountain during 

 my visit to the district in 1888 ; but I was informed that it 

 had been seen a few weeks earlier. 



The summits of Ruapehu and Ngauruhoe are distant from 

 one another a little more than eight miles, but they are con- 

 nected by a ridge of volcanic rock, on top of which lie two 

 lakes known by the name of Nga Puna-a-tama. These lakes 

 appear to lie in craters which mark the sites of former centres 

 of activity along the volcanic line. 



Tongariro lies close to and abutting on the north-east side 

 of Ngauruhoe, and the latter mountain is often miscalled 

 Tongariro. The two mountains, though so close together, are 

 sufficiently distmct in form and position to call for separate 

 recognition. 



Ngauruhoe. — Ngauruhoe is considerably higher than To- 

 ngariro. It forms a beautifully regular steep-sided cone, which 

 rises to the height of 7,481ft. The height is greatest to the 

 east, so that viewed from the north the mountain has an 

 obliquely-truncated appearance. From the crater on the top 

 steam constantly issues in considerable volumes, and, driven 



"Thermal Activity in the Ruapehu Crater," by L. Cussen, "Trans. 

 N.Z. Inst.," vol. xix., p. 374. 



