THE NEW ZEALAND GAZETTE. 163

Hawke's Bay. I have thus obtained materials
which will enable me, on my return to Europe,
to construct a Topographical and Geological
Map of the central part of the Northern
Island.

My observations have, with the able
assistance of Mr. Drummond Hay, extended from
the East- to the West-Coast; and the numerous
peaks and ranges have afforded facilities for
fixing with satisfactory accuracy, by means of
magnetic bearings, on the basis of points pre-
viously fixed by the nautical survey of Capt.
Drury on the coast line, all the great natural
features of this portion of the country. A
great number of barometrical observations have
afforded me the means of ascertaining the
heights of mountains and plains in the interior,
which I shall be able to calculate with accuracy
by the aid of corresponding daily observations,
taken in Auckland by Colonel Mould, who has
kindly forwarded me a copy of his tables.

I have also obtained photographic and other
views of great interest, many of which were
taken by the gentlemen who accompanied me
on the expedition for this purpose; and a large
number of exceedingly valuable sketches have
been contributed by the talented pencil of our
president, Mr. C. Heaphy, for future publica-
tion in a geological atlas. Many of these are
decorating the walls and others are lying on the
table, and I shall be happy to show them to
any ladies and gentlemen who may feel an in-
terest in seeing them, at the conclusion of the
lecture.

My collections have been growing from
day to day, and include specimens of great
interest in most branches of Natural History.
I owe a great deal to the indefatigable zeal of
my friend and fellow-traveller, Mr. J. Haast,
who assisted me in collecting during our ex-
pedition. I am also much indebted to Mr.
J. Crawford at Wellington, Mr. A. S. Atkinson
of Taranaki, Mr. Triphook of Hawke's
Bay, Mr. H. T. Kemp of the Bay of Islands,
to the Missionaries, and to almost innume-
rable friends in Auckland.

Preliminary Remarks.

I cannot suppose that all my audience
are acquainted with the first principles of Geo-
logy. I shall therefore be under the necessity,
in order to make my report intelligible, of pre-
facing a few remarks upon the chief divisions
of the Geological formations.

The various rocks, soils, and minerals, which
occur upon the surface of the earth, or at vari-
ous depths beneath it—in one word, the ma-
terials of the "earth's crust"—are classified,
in the first place, with reference to their dif-
ferent origin, or, in other words, with reference
to the different circumstances and causes by
which they have been produced. They are
divided into four great classes—Plutonic, Meta-
morphic, Aqueous, and Volcanic rocks. Another
mode of classification is with reference to their
age—that is, to the comparative periods of their
formation. Those divisions will be easily
understood.

The Plutonic rocks comprehend all the
granites, syenites, porphyries, diorites—rocks
which agree in being highly crystalline, un-
stratified, and destitute of organic remains—
which are considered as of igneous origin,
formed in the earliest periods of the earth, in
great depths, and cooled and crystalized slowly
under great pressure.

The Metamorphic rocks are the crystalline
strata, or schists, called gneiss, mica-schist or
mica-slate, chlorite-schist, hornblende-schist—
also destitute of organic remains. According
to the most probable theory, these strata were
originally deposited from water in the usual form
of sediment, but were subsequently altered by
subterranean heat, so as to assume a new
texture.

The two first classes of rocks are usually found
in such a position that they form the founda-
tion on which the aqueous rocks were afterwards
superimposed. For instance, they compose
the central line of a range of mountains, on
both sides of which sedimentary rocks are de-
posited. Thus, in reference to their age, they
are considered as the oldest, and are therefore
called also Primitive.

There are exceptions to this rule in reference
to the age of certain plutonic rocks of eruptive
character. But I am now stating only gene-
ral principles, and therefore avoid all questions
leading to scientific discussions.

The next in order are the aqueous rocks—
the production of watery action. They are
also called sedimentary rocks, from the fact that
they are the hardened sediments accumulated at
the bottom of the sea or of fresh-water lakes.
They are stratified, or divided into distinct
layers or strata: as, for example, clay-slate,
marl, sandstone, limestone, and are divided
into three kinds, called arenaceous or siliceous,
argillaceous or clayey, and calcareous or
chalky—according to the respective predomi-
nance of Silica, Alumina, or Lime. Rocks of
this class cover a larger part of the earth's
surface than any others, and are of the greatest
interest on account of the organic remains
which are found imbedded in the different
strata.

There are two principal means of ascertain-
ing the relative age of aqueous rocks—derived,
the one from their position, the other from the
fossil remains they contain.

With reference to position—the bed which
lies uppermost, is of course the newest of all,
and that which lies at the bottom, the most
ancient.

With reference to the fossils it is not so easy
to give an explanation in few words; but some
idea may be formed from the well-ascertained
fact, that certain animals have existed for a
certain period, and then wholly disappeared and
been succeeded by other animals of different
species, which, in turn, have again given place
to others.

So, as Sir Charles Lyell truly says,
"a series of sedimentary formations is like
volumes of history, in which each writer has
recorded the annals of his own times, and then
laid down the book with the last written page