THE NEW ZEALAND GAZETTE. 269

cemented together by the feldspathic mud which
usually accompanies such eruptions.
Trachytic breccia of similar character is of frequent
occurrence in other parts of New Zealand, encircling
the districts where energetic volcanic action once
prevailed, either as rudely stratified masses of im-
mense thickness, which overlie the deposits that
were forming in the sea at the time of their eruption,
or as massive dykes that have pierced through and
consolidated among these same strata.

When the nature and origin of this rock is taken
into consideration, it is evident that the petroleum
it contains can only be accidentally present and
must have been originally derived from some other
source, and indeed it is probable that this rock has
only acted as a condenser and absorber of gaseous
vapour produced by the natural distillation of deep-
seated strata of carboniferous matter.

It should be remarked that among the recent
superficial deposits along the same coast, there are
found considerable beds of lignite and decomposing
vegetable matter, and though such deposits cannot
account for the dissemination of the oil in the rock
to a depth of 115 feet (at which depth I understand
decided indications of its presence have been
obtained), still it is well to bear in mind the
existence of such superficial deposits, as it is quite
possible that they may give rise to small quantities
of bituminous oil, and to other indications that might
tend to mislead explorers in searching for true oil
wells.

The real source of the oil is most probably to be
looked for in the coal seams that belong to the
Brown Coal Formation, that is believed to form the
base of the series of tertiary strata that extends
under Mount Egmont, and the valleys of the Wan-
ganui and other rivers which enter the sea along the
coast between Mokau and Otaki.

This coal formation, which is probably not a con-
tinuous sheet but occupies issolated depressions in
the Paleozoic rocks, is overlaid by marine strata of
various kinds, comprising clay shales, sandstones, and
limestones that were accumulated during a gradual
depression of the land beneath the sea.

The volcanic eruptions seemed to have commenced
at the period of the greatest depression, most pro-
bably with the eruption of volcanic rock, like that
which forms the trachytic breccia that now yields the
petroleum.

The volcanic action, at first submarine, was con-
tinued with the re-emergence of the land, becoming
gradually more feeble and more localized, until the
great cone of Mount Egmont was piled up in the
atmosphere.

The total thickness of the submarine strata which
in the deepest part of the basin overlie the brown
coal formation, cannot be less than 2,000 feet, and to
this must be added at least an equal thickness of
submarine volcanic formations, above which rises the
true volcanic cone of Mount Egmont to a height of
8,270 feet, composed principally of lavas and scoria
beds of recent date.

Under this immense accumulation any brown coal
beds that exist in the deeper part of the basin must
have been subject throughout a lengthened period of
time to the combined action of heat from the frequent
injection of igneous dykes, and moisture from the
percolation of water to supply that which was carried
off in the form of steam during the volcanic eruptions;
and one of the most probable results of the chemical
action produced would be the formation of bituminous
vapours that would ascend through the strata along
lines occupied by dykes and fissures until they reached
rocks sufficiently cool to cause their condensation into
the form of oil.

In the foregoing endeavour to account for the
remarkable fact of the presence of petroleum in the
volcanic rock at Taranaki, it has been necessary to
rely greatly on the analogy of geological structure
which may reasonably be expected to exist between
the district in question and other parts of New
Zealand where similar superficial features prevail, as
the information which has been derived from actual
observation of the district is yet very limited.

It must be distinctly understood that there is no
similarity between the mode of occurrence of the rock
oil, so far as it has yet been found at Taranaki, to
that which prevails in the oil-bearing districts in the
United States of America and Canada; for although
it is held by some geologists that in these countries
the oil has also been produced by destructive distil-
lation of coal seams, which are now represented by
seams of anthracite coal, or have been wholly removed
by denudation; still the nature and arrangement of
the condensing rock has been very different, and this,
of course, will completely alter the case so far as the
practical search for petroleum is concerned.

In the United States the wells are sunk principally
in very ancient strata—older, perhaps, than many of
the slate rocks of New Zealand, but lying in an
undisturbed and nearly horizontal manner over
immense areas.

In Oil Creek Valley, according to Professor Draper,
these strata consist of clay shale in beds of about
one hundred feet in thickness, separated by layers
of sandstone of twenty to thirty feet.

The borings are carried through alternate beds of
this description to a depth of 400 feet before the oil
is obtained plentifully, although it also exists in the
upper strata in small quantity.

In this case it undoubtedly percolates through the
more porous layers of sand rock, so that the process
for obtaining it is like ordinary well-sinking, and a
continued supply can be calculated on with consider-
able certainty.

In Canada the oil is also obtained much in the
same way by piercing horizontal beds of limestone
and shale of Silurian and Devonian age, the oil being
found in the cracks and fissures of the former rock.

In that district there are also surface wells sunk
in the superficial gravel and clays that have been'
saturated with the oil rising to the surface by natural
springs.

The steady supply of rock oil from the American
wells is no doubt due to the great extent and
regularity of the porous strata in which it has been
accumulated, and through which it percolates in the
same manner as water supplying artesian wells.

The petroleum wells of Italy, Asia Minor, and the
Crimea, have more resemblance to what may be ex-
pected in New Zealand, in so far that the oil escapes
from strata of tertiary age and is always more or less
distinctly connected with active or extinct volcanic
agency.

Professor Ansted in a recent article on this
subject, describes the petroleum in the Crimea as
springing from blue clay shales that underlie a crust
of marine limestone of recent tertiary formation.

The petroleum wells up in the bottom of valleys
that have been eroded through the limestone and so
exposed the shales, and evidence of deep-seated
chemical action is indicated by mud volcanos from
which liquid mud accompanied with an escape of gas,
slowly oozes and forms conical mounds and hillocks.

In these tertiary strata we have a marked resem-
blance to the older tertiary rocks of New Zealand
which overlie the brown coal formation, and as I have
already described, underlie the eruptive rocks of such
volcanic centres as Mount Egmont; and I am in-
clined to think that the proper place to expect
petroleum to occur in large quantities may be in con-
nection with lines of dislocation at some distance