59

EXPLANATION OF THE MAPS. 55

VOLCANIC FORMATION.

1. The north side of the Manukau Harbour is formed of a rugged
rocky coast wall composed of mighty layers of volcanic
stone masses, consisting of angular fragments of the
different volcanic basis of rocks - Trachy-Dolerite, Ande-
site, &c., which are transformed landwards into different
coloured conglomerate clays.

2. On the southern side of the Manukau Harbour, and on both
sides of the Waikato, thence to the Aotea Harbour,
extensive strata of basaltic conglomerate cover the ter-
tiary layers, and with these conglomerates are immediately
connected masses of eruptive basalt, without forming
distinct craters.

3. The volcanic zone which encloses the Middle Waikato
basin, and is situated between this and the Lake Taupo, is
principally formed by trachyte and pumice, with which
are connected a very long line of volcanos, such as Karioi,
Pirongia, Kakepuku, Maungatautari, Aroha, and many
others. These mountains consist of tracytic, andesitic,
and doleritic rocks; their summits are decayed and
destroyed, and their craters scarcely recognisable.

4. The volcanic formation of the Taupo zone consists of a
rhyolithic and tracytic lava. The volcanic eruption
which commenced in the tertiary period continued, and
gave to the Northern Island its present form only in the
qaternary period. The eruptive masses of the Taupo
zone consist of lava (the richest known) of silicious earth,
also of rhyolithic rocks of all kinds, with obsidian and
pumice. Near the centre of the Northern Island, on
the southern border of the great inland lake Taupo, the
water of which fills a large sunken crater, there rises on
a plateau of pumice of 2,000 feet above the level of
the sea the two giant volcanoes of New Zealand, Tongariro
and Ruapahu. The Tongariro volcano, which rises to an
elevation of 6,500 feet, is yet active as a Solfatara, with
two large and constantly steaming craters (Ngauruhoe
and Ketetahi). Ruapahu, which is 9,000 feet high, is
covered with everlasting snow, and its fires seem to be
extinct. These two mountains are accompanied on their
northern side by a number of smaller extinct volcanoes,