44

40 THE GEOLOGY OF AUCKLAND.

remember several striking examples which I can mention - as
the Pupuki Lake on the North Shore; Orakei Bay in the
Waitemata; Geddes's Basin (Hopua) at Onehunga; and the
tidal Basin (Waimagoia) at Panmure; - Pupuki Lake, believed
to be bottomless, has been ascertained by Captain Burgess (who
kindly sounded it at my request) to be only 28 fathoms. I call
those basins and similar formations, tuff-craters or tuff-cones.
The excellence of the soil of Onehunga at Otahuhu is owing
to the abundance of such formations, decomposed strata of
which form the richest soil that can be met with. It is curious
to observe how the shrewder among the settlers, without any
geological knowledge, have picked out these tuff craters for
themselves, while those with less acute powers of observation
have quietly sat down upon the cold tertiary clays.

After the submarine formation of the tuff-craters, the volcanic
action continuing, the isthmus of Auckland was slowly raised
above the sea, and then the more recent eruptions took place,
by which the cones of scoria, like Mount Eden, Mount Wel-
lington, One tree Hill, Mount Smart, Mount Albert, and Ran-
gitoto, were formed and great out-flowings of lava took place.
Many peculiar circumstances, however, prove that those moun-
tains have not been burning all simultaneously. It can easily
be observed that some lava streams are of an older date than
others. In general the scoria cones rise from the centre of
the tuff-craters (Three Kings, Waitomokia, Pigeon Hill near
Howick.) Occasionally, as in the instance of Mount
Wellington, they break through the margin of the tuff-crater.

The Crater System of Mount Wellington is one of the most
interesting in this neighbourhood, as beautfully shown by the
large map which Mr Heaphy has kindly prepared for me from
actual survey. There are craters and cones of evidently dif-
ferent ages. The result of the earliest submarine eruptions is a
tuff-crater. The Panmure road passes through the tuff-crater,
and the cutting through its brim exhibits beautifully the
characteristic outward inclination of the beds of ashes, elevated fom
their fomer horizontal levels by the eruptions, which threw up
the two minor crater cones south of the road - one of which is
now cut into by a scoria quarry. After a comparatively long
period of quiescence, there arose from the margin of the first crater