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164 GEOLOGY.
composed of large and detached blocks heaped upon one another, and rising to the
greatest height towards the middle of the island; the whole has the appearance of an
ancient volcanic production.—C.
E A S T E R i s l a n d
Has its surface diversified by hills and valleys. Many of the hills have round and
hollowed tops (the remains of extinct volcanos). The valleys are of gradual ascent, and
covered with bare grey stones and a scanty vei'dure. The high and perpendicular shore
of the eastern end is formed of distinct horizontal strata of volcanic rocks, resembling
some parts of the Giant’s Causeway; but I saw none that assume the regular columnar
form.
The rocks upon which we landed in Cook’s Bay were a hard vesicular lava of an ash
grey colour, and the missiles discharged a t us by tbe natives from behind these rocks
were lava of different degrees of hardness, some so soft and decayed as to break with
the fall.—C.
P IT C A IR N ISLA N D .
Rises bold, precipitous and irregular, out of the sea to the height of about 700 feet,
with a circumference of nearly four miles. On the north side the slope is gradual, and
indented with valleys. To the westward is a steep mountain ridge, excavated in some
places into caverns, whicli afford shelter to the goats. This forms one end of the high
and broken ridge, which extends round by the south to the eastern extremity of the
island, where it terminates in the lofty cliff that looks down upon the north-east landing
place called Bounty Bay. The ascent from the beach everywhere, except on the northern
side, is so steep as in many places to be almost impracticable. The whole of the
island is of ancient volcanic formation, and in most places is composed of a conglomerated
tufa, so loose that it is easily converted into a dry gravelly soil, producing yams,
taro, fee, yappe, sweet potatoes, &c. There is a reddish colouring over the greater part
of the island, excepting the precipices which terminate each extremity of the high ridge.
The western extremity is a black and easily disintegrated tufa, with imbedded masses of
compact lava. The north-eastern end is a grey arenaceous tufa, varying in hardness,
and has been unequally worn into grooves and projections, smoothed as if by art. Tbe
rocks near the sea in Bounty Bay, and along the northern shore, are chiefly formed of a
porous lava inclosing crystals of felspar.
The sea around tbe island is deep close to the shore. Pieces of recent coral are
thrown upon the rocky beach.
Specimens from Pitca irn Island.
Vesicular lava, containing large crystals of glassy fe lsp a r;—Volcanic tufa, composed
of small angular portions of porous and of compact lava, with a yellowish green
earth imbedded, and traces of zeolites;—Basaltic lava, with imbedded olivine;—
Obsidian.—C.
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165
GAMBIER IS LA N D S .
The nine largest and most elevated of this group are of volcanic origin. There are
also two small and low islands which are the production of corals. One of these has
not yet given root to any vegetable. Corals abound to a great extent beneath the
surface of the water, and are gradually rising in the whole space between the volcanic
islands. They are also surrounding the group with a wall of circumvallation several
yards in breadth.
The general character of tbe rock composing these islands is a porous basaltic lava,
in one place passing into argillaceous tufa, in another into solid and angular columns of
compact basalt.
The imbedded minerals are zeolites, soap-stone, chalcedony, olivine and calcareous
spar, as in the north of Ireland ; there are different coloured jaspers which are peculiar
to these islands. They contain also numerous dykes, traversing the strata in a direction
generally from east to west, and differing from the strata they intersect in greater
solidity and durability, and in containing a greater quantity of olivine ; they often proje
c t in walls from one to four feet high, and are from one to three feet wide. These
veins or dykes are separated by a well-defined line from the general rock which they
pass through; some dip slightly to the south, others are perpendicular. They appear to
traverse all the islands, occasionally bifurcating, as upon the eastern side of the small
island next to Marsh Island. They are sometimes porous, and sometimes, when compact,
contain a few particles of olivine ; but they almost always, whatever be their individual
structure, rise prominent from the surrounding rock.
These islands preserve the general form of igneous productions in other parts of
the world, rising out of the ocean by black perpendicular cliffs, and terminating at a
considerable height in conical peaks. Two of them are particularly remarkable, being
solitary, and when seen from a considerable distance at sea, with a thin cloud hovering
over them, have the appearance of smoking volcanos. Small patches of productive soil
have been formed at tbe bottom of the bills, by the rain washing down the disintegrated
particles from the declivities, and the waves of the sea washing up sand and fragments
of coral. These spaces (with a very few spots on the slopes) are the parts that produce
vegetable food or timber, e. g. the cocoa-nut, bread-fruit tree, banana, tbe yappe, the
sweet potato, the amai or miro, the clotli-tree, the doodoe, the hibiscus, rosa sinensis,
and some others.
The extensive basin within the vast wall of coral that encircles this group of islands
is more or less filled up, mostly so along the shores, where the numerous crowds of coral
animals have raised their labours to the surface at low water, or even up to half-tide.
In the intervening space the bottom is very uneven, at one place twenty fathoms, at
another only of three or four from the surface. The corals which most abound are the
explaiiaria, astrea, madrepora cervicornis, meandrina, aud pocillipora damicornis.
The transparent limpidity of the water permits the eye clearly to see these different
zoophytes at from five to seven fathoms’ depth, forming, as it were, a submarine shrub-
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