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bery varied with groves and grottos, in which the sporting fish display their infinite
variety of vivid and resplendent colouring.
L is t o f Specimens,
Amygdaloidai trap, containing crystallized zeolite, chabasie, mesotype, analcime
o liv in e s o a p - s to n e mica ;—c h a lc e d o n y ja s p e r , and carbonate of lime.—C,
T A H I T I . ( O T A H E I T E . )
-VV. Tabiti, like those of Gambier, is formed of volcanic rocks and corals.
Th e chief body and centre of the island is composed o fth e former, while its base is surrounded
by a flat zone o fth e latter, extending iu some places from the sea beach to the
mountain foot, a distance of three miles, or even more ; whilst at others it is interrupted
by the ridge of the sloping mountain ju tting out into the sea.
The declivities of the mountains are diversified by numerous knolls rising above
each other, and variegated with the long grass of the saccharum fatuum, the scanty
covering of the polypodium pedatum, a few shrubs of the metrosideros spectabilis and
the dodonea viscosa, interrupted by bare and brick-coloured tufa. Their tops are frequently
rounded, m a few places uneven and precipitous, but seldom peaked, and are
covered w.th a deeply verdant vegetation. Tbe mountain streams flow rapidly down
the deep ravines, receiving accession to their waters from numerous cascades on each
side, and carry along with them the lighter volcanic matters to be strewed on the surface
of the coral plain, or blacken with their sand the whole lino of the beach. On this
nnxtnre of lava and coral may in some measure depend the richness of the bordering
plain, abounding with cocoa nuts, bread-fruit, sugar-cane, &c. varying from 200 yards
to a quarter of a mile. ^
A t unequal distances from the beach a coral reef is raised round the greater part of
the island almost, and in some places altogether, to a level with the surface of the sea
In several places this line of circumvallation has not yet been raised to within several
fathoms of the surface, affording at these points an entrance to vessels ; whilst there Is
room and perfect safety for more than all the navies of Europe to ride in calm water
within the reef. These entrances or breaks in the wall are observed to be generally
situated opposite the mouth of some river, and have been attributed lo the influence of
the fresh water preventing the usual growth of the corals. To me it appears more
probably dependent upon the original inequality of the bottom, on which these natural
artificers bave raised their structure.
The island is chiefly made up of basaltic lava of different degrees of porosity
The most solid, formerly used for hatchets or adzes, is frequently met with in nearW
horizontal strata, and contains very few imbedded minerals. Tbe more porous lavas
are full of basaltic hornblende, olivine and zeolites. In numerous excursions np the
ravines I met with columnar basalt, in one place only, about nine miles up Matavai
nver, the columns being about twelve inches in diameter, here it forms a perpendicnlar
and picturesque cliff, diversifying its front with natural bendings of the pillars at the
G E O L O G Y . 167
lower part, and a kind of projecting gallery of curved pillars near the top. I t is surrounded
on all sides by a luxuriant vegetation. This basalt contains nodules of olivine,
but wants the basaltic hornblende so universally diffused over the island. In no other
place indeed did I find it absent. Olivine and zeolite, although common, are in smaller
quantities, and steatite rather rare.
Specimens from this island are varieties of tufa, lava, and basalt;—olivine, meso-
typ©» analcime, basaltic hornblende, steatite.—C.
A V A T S C H A B A Y , K A M T S C H A T K A .
An extended view of the country around the Bay of Avatscha ranges over swelling
plains, thinly covered with wood, and in the summer with a deep green vegetation, till
i t comes to the lower mountains disposed in long barren ridges, among which some lofty
and isolated mountains rise abruptly to 8,000 or 12,000 feet. On the 1st day of July,
1826, the lower range had their sides thinly furrowed with white snow, whilst the more
lofty had their tops entirely veiled in it. From one of the highest of these (Avatshin-
skaia), to the north-east of the bay, we could distinctly perceive volumes of white smoke
issuing at more than one opening, and the surface of the snow on its sides blackened, as
if by a recent fail of volcanic ashes.
The isthmus that forms the western side of the small harbour of Petropaulski is
composed of clay-slate, containing various coloured jaspers, and dipping at an angle
varying from 30« to 45° to the south. Between the village and Rakowena harbour the
clay-slate ceases and is succeeded by serpentine containing amianthus.
On the left hand of the entrance of the harbour of Rakowena, all around its shores,
the cliffs are high and perpendicular, and composed of trap, quartz and serpentine.
Columnar basalt shews itself in several places. The second perpendicular promontory
on the right side of the entrance to the harbour of Rakowena is composed of a
porous basalt, in perpendicular pentagonal and hexagonal columns of moderate size,
reposing upon horizontal strata of slate-clay, apparently hardened by the action of heat.
Columnar basalt is seen in the face of the cliff under the north-east signal station, reposing
upon an extensive bed of porphyritic green-stone. This rises up from under
the basalt towards the south-west, but the cliffs outside this again assume somewhat of
the columnar appearance for a short distance, when the tufa seems to preponderate, and
is continued to the outer boundary of the bay on tbe north-eastern side.
On the western side of the bay basalt is disposed in horizontal columns, forming,
as it were, a thick wall, standing out from the cliff, and having its base washed by the
sea. In the face of the tufaceous cliff behind, there are curved columns of the same
nature.
The western part of the bay, towards the entrance, and the coast facing the open
sea, appear to be chiefly tufaceous, and frequently of a brick colour. A t Paralunka
there are thermal springs which are probably in a volcanic formation.
The clay-slate that forms the high isthmus on the north-west of the harbour of
Petropaulski is continued into the higher hill, between it and the lake on the road to
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