May 2, 1892.] 



KNOWLEDGE. 



97 



The group best known consists of about a hundred, but ' 

 so near together that they are all within an area of about 

 two square miles. This place is about tliirtv miles from 

 the active volcano Hecla, in the south-western part of 

 Iceland. Two of the geysers — which are so named from 

 the Icelandic word ;/fi/.«rt, to rage — are conspicuously 

 gi-eater and more important than the otliers, and the 

 larger of the two, called Great Geyser, has been carefully 

 observed and described, first by Mackenzie, and afterwards 

 by Bunsen, Descloiseaux, and others. 



This intermittent natural fountain of boiling water has 

 been found to have a shaft or tube descending to about 

 78 feet below the surface, with a diameter varying from 

 f> to 8 feet, which at the top expands into a funnel-shaped 

 mouth or basin, .50 feet by 46 feet, that is really the crater 

 of a mound sloping on all sides, from its margin to the 

 level of the adjoining land. With intervals of about six 

 hours between, a column of hot or boiling water is ejected 

 high into the air, 100 to 200 feet. After this, which 

 continues for five or six minutes, an explosion of steam 

 occurs, the tube is emptied, and there is no more ejection 

 of hot water for another period of six hours. During this 

 time the tube gradually refills, when there is another 

 ejection followed by a violent explosion of steam as before. 

 Thus, throughout the year, amid the ice and snows of 

 Iceland, this extraordinary periodical ejection of boOing 

 water and steam goes on. The throat, the crater, and all 

 around this aqueous volcano is coated with a deposit of 

 silicious sinter, and it is an accumulation of this hard white 

 material that has formed the mound and the sides of the 

 basin from the centre of which the tube descends. 



Although the great increase in recent years of our 

 knowledge of the physical features of the earth's surface 

 has made us acquainted with many other and greater 

 eruptive boiling springs, yet the geysers of Iceland retain 

 their place as types, and the hypotheses to explain geyser 

 action are founded on the phenomena they present. Of 

 these one of the first was that of Sir .J. Herschel, who 

 supposed a rock cavity holding water with a conduit from 

 it to the surface passing througli a stratum of very hot 

 rock which would so greatly heat the water in passing as 

 to cause the eruptive action. It was Bimsen, however, 

 who was the author of the now generally accepted 

 hypothesis — that the water as it collects from the 

 surroimding rocks, in the lower part of the shaft, is heated 

 by a hot zone to much over boiling point, as it was actually 

 found by Bunsen tobe 260" Fahrenheit within the tube, but 

 that the pressure of the column of water above prevented the 

 formation of steam. This goes on until the force generated 

 overcomes the pressure, when the column of water above 

 is ejected, and the lower water being relieved of the 

 i-estraining pressure is suddenly converted into steam, and 

 so produces the final explosion and emptying of the shaft. 

 This action has been imitated by an arrangement devised 

 by Professor Tyndall, who also illustrated the bringing 

 about of premature eruptions of the geyser called the 

 Strokkr by obstructing its tube with clods of earth. 



A much grander exhibition of thermo-hydraulic action 

 was displayed on the opposite side of the globe, when Von 

 Hochstetter, in 1859, explored the volcanic regions of the 

 North Island of New Zealand. From one point could be 

 seen on both sides of the valley of the Eiver \Yaikato 7G 

 clouds of steam arising from hot cascades, falling into the 

 river from white basins, some -srith rising and falling 

 fountains, some pausing, some playing simultaneously, and 

 so forming a wonderful system of grand natural water- 

 works. The steaming cascades fell over white, red, and 

 yellow terraces, while periodical eruptions occurred at 

 points between them. 



Still greater wonders were found to the north-west of 

 the valley of the Waikato, where was the now famous 

 lake of Eoto Mahana, a lake of warm water, amidst boil- 

 ing springs that were continually pouiing into it immense 

 volumes of hot water over marble-like terraces, on the hill 

 slopes around. On a small island in the lake, potatoes 

 and meat could be cooked by the steam given out when- 

 ever a little hole was dug in the ground. Te Tarata, 

 " the Tattooed Rock," rose on the east side of the lake to 

 a height of 80 feet in snow-white terraces, and on its 

 summit was an immense basin filled to the brim with 

 water boiling, but clear and of a brilliant blue tint. The 

 white terraces over which the water fell in cascades to the 

 lake, formed by the deposition of silica by the cooling 

 water, had on each level basins, with projecting semi- 

 ckcular margins, and holding bright blue water, from 

 which stalactites of pure silica depended, and added a 

 light and fairy-like beauty to this marvellous piece of 

 natural architectme. Other boiling springs, with descend- 

 ing terraces, were on this side of the lake, and they were 

 confronted on the west side by Otukapuarangi displaying 

 its pink terraces, which, with the blue waters surrounded 

 by red, white, and yellow walls of rock, added additional 

 colour to the wonderful scene. 



It has been necessary to write of these marvels of the 

 Eoto Mahana lake in the past tense, as they are things of 

 the past, for in -June, 1886, a great volcanic eruption com- 

 pletely destroyed the terraces, the springs, and even the 

 lake itself. Had, therefore, this part of New Zealand 

 not then been explored, mankind would not have known 

 of these magnificently beautiful wonders of Nature in the 

 Britain of the Southern Seas. 



To find a stOl more extensive display of Hot Springs we 

 must return to the northern hemisphere, and visit that 

 remarkable area in Wyoming, the Yellowstone National 

 Park, in which are congregated so many natural wonders, 

 and which has recently been described in these pages. 



The thermo-aquatic phenomena here seen are on a much 

 grander scale than anywhere else, but it is impossible now 

 to do more than very briefly state the general character of 

 these marvels. In addition to other parts of this region, 

 in which there are numerous Hot Springs, both tranquil 

 and eruptive, there is an area occupied by an imexampled 

 development of the one class, and a second in which are 

 concentrated extraordinary groups or collections of the 

 other class. The former of these areas is that of the 

 "Mammoth White Mountain Hot Springs." These in 

 their character and surroundings resemble those of the 

 destroyed White and Pink Terraces of New Zealand, but 

 instead of silicious they deposit calcareous matter, and 

 they are on a larger scale. The terraces are as brilliantly 

 white, the water is as clear and blue, and the other colours 

 are as varied and vivid as were those around the Eoto 

 Mahana lake. Stalactites, coral-like forms, and exquisite 

 bead-work ornament the terraced basins and the platforms 

 that cover the entire face of the mountam, rising from the 

 banks of Gardiner's River at 5845 feet above the level of 

 the sea to 6522 feet. An analysis of the travertine of 

 the terraces formed by these springs, given by Dr. Hayden, 

 is as follows : — 



10505 



