Fkiedlaender. — On New Zealand Volcanoes. 505 



mentioned gap of the main crater-rim, is confluent with the 

 slope of the great cone of Ngauruhoe itself. This is correctly 

 represented on the above - mentioned survey-map. In the 

 south-west pai't of the crater there is a large hole, the details 

 and bottom of which are hidden by the large amount of steam 

 which is constantly coming out. By far the greater part of 

 the steam had its origin in that hole, though there were many 

 other places steaming. 



Two facts betrayed a very low degree of activity — the 

 presence of considerable masses of snow in different parts of 

 the crater and the smell of sulphuretted hydrogen (H2S). It 

 is to be hoped that the expression " sulphur-fumes," or similar 

 words, will go entirely out of use in descriptions of volcanoes, 

 for they convey three very different meanings — viz., pure 

 sulphur (S), sulphuretted hydrogen H.2S), or the dioxide of 

 sulphur (also called sulphurous acid) (SO.2). The latter two, 

 moreover, exclude each other, as they readily combine to form 

 water and sulphur. The first one — pure sulphur — is found 

 together with the second in many fumaroles. The last one — 

 SO.2 — is an indicator of a very much higher temperature and 

 volcanic activity. As everybody's nose easily distinguishes 

 between the irritating, cough-producing, and choking SO2, the 

 unpleasant smell of H2S, and the rather insignificant odour of 

 pure sublimating sulphur, I cannot see why the ambiguous 

 term " sulphur-fumes" plays such an important part in many 

 reports. Even the very bad smoke of Vesuvius, which to 

 noses not quite chemically untrained of course indicates the 

 prevalent presence of quite a different exhalation — viz., hydro- 

 chloric acid (HCl) — is very frequently libelled as "sulphur- 

 smoke." Ngauruhoe was working with the comparatively 

 harmless H^S, while in Te Mari there seemed to be SOo ; but, 

 as I was always on the lee side, I am not sure. 



As to the relation of the Tongariro system to Ngauruhoe, 

 it is scarcely necessary to say that the former cannot be 

 looked upon as the " somma" of Ngauruhoe. This is one of 

 the very few mistakes I found in Hochstetter's excellent book 

 "New Zealand," a mistake the more excusable as Hoch- 

 stetter, as he states himself, was not able to visit the vol- 

 canoes on account of the native tajJii. The only formation 

 that perhaps may be a " somma" of Ngauruhoe is a series of 

 hills in the south, between the cone and Nga-puna-a-tama ; 

 but, as I saw those only from a distance — from the slope and 

 north top of Euapehu — I could not express a certain opinion. 

 The reason why Tongariro cannot be styled a "somma" of 

 Ngauruhoe is double — first, it does not surround the cone of 

 Ngauruhoe ; and, second, it bears a number of craters on the 

 top. A " somma " is the rim of an old crater, and therefore, 

 as its prototype, has no vents on its top. 



