t*OND and Smith. — On the Eruption of Mt. Tdrnwera. 343 



classes of rocks are ejected from volcanoes — tbe acidic, or 

 trachytic, denoting tbe earlier ; the basic, or basaltic, tbe later 

 stages of volcanic life. There are well-known exceptions to this 

 general rule, but, taken as a whole, tbe evidence tends to show 

 that such is tbe life history of most volcanic districts. 



It may be that some volcanoes commence their career by 

 tbe ejection of acidic matter, and continue throughout tbe whole 

 course up to their final extinction, terminating in the ejection 

 of basaltic matter, without material interruption of their activity 

 — whilst others, after making a commencement, are quiescent, 

 or only partially active, for ages, remaining in the acidic stages 

 for such lengthened periods, that volcanoes which can be shown 

 to be far younger in actual age have bad their day and become 

 extinct. 



Such seems to be tbe case with tbe Taupo, or central zone. 

 It is still in tbe acidic stage, whilst tbe younger volcanoes of 

 this isthmus appear to have run their full course, and have 

 become extinct. 



In connection with this subject and tbe recent eruptions, 

 (which may happen to mark the beginning of a period of greater 

 activity,) it is a matter of very great interest to ascertain 

 whether they show by their action any change in tbe character 

 of the ejected matter — whether, in fact, the ejecta are still 

 acidic or trachytic, or whether, on the other hand, any basaltic 

 or basic matter has also accompanied tbe outburst. We shall 

 have something to say on this point further on. 



The central volcanic district of this island is of immense 

 extent, far larger, indeed, than is generally known, if we include 

 in it the areas covered by volcanic matter, which spreads over 

 a vast extent of country. Commencing in tbe far south, tbe 

 noble mountain of Kuapebu, 8,878 feet high, which until quite 

 recently was believed to be extinct, marks by its lava and 

 consolidated mud streams tbe most southerly edge of the district. 

 A line drawn thence in a north-east direction will pass along 

 a belt of country celebrated all over the world for its extra- 

 ordinary development of volcanic and thermal action, until it 

 terminates in the active volcano of White Island. In this belt 

 of country we have types of all the known forms of volcanic 

 action. The active crater on Ngauruboe has, within quite a 

 recent period, (1869, and possibly 1881,) ejected hot lavas, which 

 were seen rolling down its symmetrical cone ; whilst it still con- 

 stantly emits clouds of steam from tbe solfataras at tbe bottom. 

 Tougariro, a few miles north, is still active, but in tbe solfatara 

 or fumarole stage. This fine mountain, 6,400 feet high, is now 

 but the ruin of what it must have been in former times. Its 

 seven craters, two of which have lakelets within them, and one 

 with steam issumg from a fissure in its side, the powerful 

 emission of steam from Ketetahi and Te Maari — points on its 



