41

THE GEOLOGY OF AUCKLAND. 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 of 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 of
Whakarewarewa are the most interesting. Waikite, the prin-
cipal "ngawha," issues from the top of a siliceous cone some 20
feet high, and is surrounded by several smaller geysers, 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 wonderful
and beautiful.

The hot springs of Ohinemutu 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 Ruahine.

I 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, permeates
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 tracytic rocks. The soluble substances are thus removed
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 round Rotoma-
hana and the Pairoa consist.

All the New 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. To the latter belong
the solfataras characterised by deposits of sulphur, and never
forming intermittent fountains. All the intermittent springs
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