THE GEOLOGY OF ATJCKLAY1). 
37 
beside the boiling surf of the Ngahapu basin will always retain 
a vivid impression of its terrors. The terrace of siliceous 
deposit on the shores ol Rotomahana are unequalled in the 
world, nor is there anything that even bears any resemblance 
to them. 
9. On the Roturua lake the intermittent boiling springs ol 
Whcilcare ware wet are the most interesting. TVailcite , the prin¬ 
cipal u ngawha, ,; issues from the top ol a siliceous cone some JO 
feet high, and is surrounded by several smaller gevseis, boiling 
mud-pools, and solfataras. At intervals of considerable length, 
sometimes extending to many months, all these “ngawhas" begin 
to play together, and form a scene which must be most wondeilul 
and beautiful. 
The hot springs of Ohinemntu form agreeable bathing places, 
the fame of which is already established. 
10. The last in the line are the great solfataras on the pumice- 
stone plateau between .Rotorua and Rotoiti—such as Tikitere 
and Rnaliine. 
1 will now say a few words in explanation of these pheno¬ 
mena. 
All the waters of the Springs are derived from atmospheric 
moisture, which, falling on the high volcanic plateau, peimeates 
the surface and sinks into fissures. Taupo—the axis of which 
corresponds with the line of the Hot Springs may also be con 
sidered as a vast reservoir, from which the lower springs are 
. supplied. The water, sinking into the fissures, becomes heated 
by the still-existing volcanic fires. High-pressure steam is thus 
generated, which, together with the volcanic gases, decompose 
the trachytic rocks. The soluble substances are thus lemoved 
by the water, which is forced up, by the expansive force of the 
steam and by hydrostatic pressure, in the shape of boiling 
springs. The insoluble substances form a residuum of white or 
red fumarole clay, of which the hills at Terapa lound Roto ma¬ 
ll an a and the Pairoa consist. 
All the Hew Zealand hot springs, like those of Iceland, 
abound in Silica, and are to be divided into two distinct classes 
_the one alkaline , and the other acid. Io the lattei belong 
the solfataras characterised by deposits of sulphur, and nevei 
forming intermittent fountains. All the intermittent spiings 
i) 2 
i 
