128 GEOLOGICAL SURVEY OF THE TEREITORIES. 



EXTRACT FROM HOCHSTETTER'S " NEW ZEALAND." 



" Botli kinds of springs owe tlieir origin to the water permeating the 

 surface and sinliing through fissures into the bowels of the earth, where 

 it becomes heated by the still existing volcanic fires. High-pressure 

 steam is thus generated^ which, accompanied by volcanic gases, such 

 as muriatic acid, sulphurous acid, sulphureted hydrogen, and carbonic 

 acid, rises again toward the colder surface, and is there condensed into 

 hot water. The over-heated steam, however, and the gases decompose 

 the rock beneath, dissolve certain ingredients, and deposit them on the 

 surface. According to Bunsen's ingenious observations, a chronological 

 succession takes place in the co-operation of the gases. The sulphurous 

 acid acts first. It must be generated there where rising sulphur vapor 

 comes into contact with glowing masses of rock. Wherever vapors of 

 sulphurous acid are constantly formed, there acid springs, or solfataras, 

 arise. Incrustations of alum are very common in such places, arising 

 from the action of sulphuric acid on the alumina and alkali of the lavas ; 

 another product of the decomposition of the lavas is gypsum, or sulphate 

 of lime, the residuum being a more or less ferruginous fumarole clay, the 

 material of the mud-pools. To the sulphurous acid comes sulphureted 

 hydrogen, produced by the action of steam upon sulphides, and by the 

 mutual decomposition of the suli)hureted hydrogen and sulphurous 

 acid, sulphur is formed, which in all solfataras forms the characteristic 

 precipitate, while the decomposition of siliceous incrustations is either 

 entirely wanting or quite inconsiderable, and a smell of sulphureted 

 hydrogen is but rarely noticed. These acid springs have no periodical 

 outbursts of water. 



"In course of time, however, the source of sulphurous acid becomes 

 exhausted, and sulphureted hydrogen alone remains active. The acid 

 reaction of the soil disappears, yielding to an alkaline reaction by the 

 formation of sulphides. At the same time, the action of carbonic acid 

 begins upon the rocks, and the alkaline bicarbonates thus produced 

 dissolve the silica, which, on the evaporation of the water, deposits in 

 the form of opal, or quartz, or siliceous earth, and thus the shell of the 

 springs is formed, upon the structure of which the periodicity of the 

 outbursts depends. Professor Bunsen, rejecting the antiquated theory 

 of Makenzie, based upon the existence of subterraneous chambers, from 

 which the water, from time to time, is pressed up through the vapors 

 accumulating on its surface, according to the principle of the Hern 

 fountain, has proved in the case of the great geyser that the j)eriodical 

 eruptions or explosions essentially depend upon the existence of a frame 

 of siliceous deposits, with a deep, flue-shaped tube, and upon the sudden 

 development of larger masses of steam from the overheated water in 

 the lower portions of the tube. The deposition of silica in quantities suf- 

 ficient for the formation of this spring apparatus iu the course of years 

 takes place only in the alkaline springs. Their water is either entirely 

 neutral or has a slightly alkaline reaction. Silica, chloride of sodium, 

 carbonates, and sulphates are the chief ingredients dissolved in it. In 

 the place of sulphurous acid the odor of sulphureted hydrogen is some- 

 times observed in these springs. 



"Therocks, from which the siliceous hot-springs of New Zealand derive 

 their silica, are rhyolites, and rhyolithic tufas, containing seventy and more 

 per cent, of silica ; while we know that in Iceland palagonite, and pal- 

 agonitic tufas, with fifty per cent, of silica, are considered as the material 

 acted upon and lixiviated by the hot water. By the gradual cooling of 

 the volcanic rocks under the surface of the earth in the course of cen- 



