43

THE GEOLOGY OF AUCKLAND. 39

observation of the Natives, who have thus indicated the true line
of the chief volcanic action in the island.

Having now described the older and more extensive volcanic
phenomena of the interior, I proceed to notice the later pheno-
mena of volcanic action in the immediate neighbourhood of Auck-
land.

The Auckland Volcanic District.

The isthmus of Auckland is completely perforated by volcanic
action, and presents a large number of true volcanic hills, which,
although extinct and of small size, are perfect models of volcanic
mountains. These hills - once the funnels out of which torrents of
burning lava were vomited forth, and afterwards the strongholds of
savage cannibals - are now the ornaments of a happy land, the
home of peaceful settlers, whose fruitful gardens and and smiling
fields derive their fertility from the substances long ago thrown
up from the fiery bowels of the earth.

My Geological Map of the Auckland District contains no
less than sixty points of volcanic eruption within a radius of
ten miles - the variety of which, together with the regularity of
their formations, gives very great interest to this neighbourood.
The newer volcanic hills around Auckland are distinguished
from the older ones in the interior, not only by their age, but
by the different character of their lava - the older being trachytic,
while the Auckland are all basaltic. I have not yet mentioned
the difference between Trachyte and Basalt. I will therefore
say a few words in explanation. The difference consists in the
minerals of which the rocks are composed. Trachyte is com-
posed of a mixture of glassy feldspar (sanidin) and hornblende:
obsidian and pumice-stone are the usual concomitants of
trachytic lava. Basalt consists of a minutely-crystalline mass
of feldspar mixed with augit; an admixture of greenish grains
of Olivin is characteristic of basalt.

In order to gain a clear idea of the history of the Auckland
volcanoes, we must suppose that before the period in which the
Auckland isthmus was slowly raised above the level of the
sea, a submarine volcanic action was already going on. The
products of this submarine action are regular beds of volcanic
ashes, which form highly interesting circular basins with strata
always inclining from within, outwards. You will at once