196 GEYSERS OF AUCKLAND. 



Geysers of New Zealand. The geysers of New Zealand are in 

 some respects much less interesting. They extend over a line of 

 fracture in the Northern Island, which lies between the crater of 

 Tongariro and the crater of White Island in the Bay of Plenty. 

 Here geysers rise over a distance of about 17 miles, associated with 

 hot springs, which come up through rhyolitic rocks, formed of horn- 

 blende and sanidine felspar. Most of the waters are alkaline, owing 

 to the quantity of soda which they contain, and there can be no 

 doubt that the silica in them has been dissolved from out of the 

 volcanic rocks. The temperature of these waters varies from 80 to 

 200. Many of the smaller geyser springs throw up water to a height 

 of 30 or 40 feet. Some of the basins fill in ten minutes, and are in 

 eruption every two hours. The best-known geysers are on the lake 

 Rotomahana. One forms a hill above the lake, with a basin 100 

 feet in diameter and 1 5 feet deep, terminating in a pipe which is 8 

 feet wide. Its waters are of an intense sapphire blue, and as they 

 descend, form successive milk-white or pinkish terraces of silica, in 

 which the water gradually loses its intensity, and passes through a 

 turquoise colour in the middle terraces, to a faint blue tinge at the 

 base, where the overflow passes into the warm lake. When the silica 

 is deposited, according to Von Hochstetter, it is at first as soft as 

 gelatine, and gradually hardens into a mass which has a sandy texture 

 and chalky aspect, but is frequently infiltrated so as to resemble 

 chalcedony or opal. Fumeroles abound all over the geyser region, 

 and there are occasional minute mud volcanoes 3 to 4 feet high. So 

 near to the surface are the heated springs that they can often be 

 tapped at will by pushing a walking-stick into the ground. 1 Extinct 

 geysers occur in the Azores ; and the sinter deposits there have pre- 

 served leaves of trees perfectly. 



The Boracic Acid Jets of Tuscany. About 15 miles S.W. of 

 Volterra many jets of vapour, charged with boracic acid, rise from a 

 narrow valley in the secondary limestone. . Mr. Hamilton 2 describes' 

 large fissures which have in this way been filled up by deposits of 

 calcareous sinter. By passing the vapour through water the boracic 

 acid is collected, and the water is then evaporated. Similar discharges 

 of vapour occur in the neighbourhood at Sarrezano, Castelnuove, and 

 Monte Rotondo. The vapour escapes from hundreds of vents often 

 with the noise of a steam boiler blowing off its steam. 



Hot Springs. Hot springs are by no means limited to volcanic 

 regions, but they are most numerous where igneous rocks have been 

 intruded. 3 Therefore we regard them as indicating that surface 

 waters have penetrated to a depth where the rocks are still heated, and 

 thus warmed, have risen again to the surface by different channels. 

 Among the best-known examples in Europe are the sulphurous springs 

 of Aix-la-Chapelle (171 F.), the springs of Ems (131), Wiesbaden 



1 Hochstetter, " New Zealand : its Physical Geography, Geology, and Natural 

 History." 



Hamilton, P. Geol. Soc., 1844, p. 477. 



3 See Daubeny's "Volcanoes," 2(1 ed., p. 544. 1848. 



