VOYAGE TO THE
having daylight enough to get in with the coast, it became
necessary to anchor for the night, though in deep water.
3d of September .-^Having reached nearly lat. 36 5 N.
and long. 126 E. we sailed this morning amongst a range
of islands extending as far as the eye could reach, both to
the southward and northward, at the distance of six or
seven leagues from the main land. By two o clock we
were close to the outer cluster of the islands, and the passages
appearing clear between them, we sailed through
and anchored inside. While passing one of these islands
in the ships, a t no great distance, it looked so curiously
formed, that, on anchoring, we went in the boats to examine
its structure more minutely *. While we were thus engaged,
* We found the north-east end composed of a fine-grained granite; the
middle of the island of a brittle micaceous schistus of a deep blue colour ; the
strata are nearly horizontal, but dip a little to the S. W. This body of strata
is cut across by a granite dyke, at some places forty feet wide, at others not
above ten ; the strata in the vicinity of the dyke are broken and bent in a remarkable
manner; this dislocation and contortion does not extend far from the
walls of the dyke, but veins of granite branch out from it to a great distance,
varying in width from three feet to the hundredth part of an inch: the dyke is
viable from the top of the cliff to the water’s edge, but does not re-appear on
the -.'-^p o n d in g cliff of an island opposite to it, though distant only thirty
yards. This island is composed of the same schistus, and is cut in a vertical
direction by a whin dyke, four feet wide, the planes of whose sides lie N. E.
and S. W., being at right angles to those of the great granite dyke in the neighbourhood,
which run S. E . and N. W. The strata contiguous to the whin
dyke are a good deal twisted and broken, but not in the same degree as at their
contact with the granite dyke.
the natives had assembled in a crowd on the edge of the
cliff above u s ; they did not seem pleased with our occupation
of breaking their rocks, for, from the moment we
The whin dyke is formed of five layers or sets of prisms laid across in the
usual way. Beyond the small island cut by the whin dyke, at the distance of
only forty or fifty feet, we came to an island rising abruptly out of the sea, and
presenting a high rugged cliff of breccia, fronting that on which the granite dyke
is so conspicuous: the junction of this rock with the schistus cut by the granite
and the whin would have been interesting; but although we must have been at
times within a few yards of it, the actual contact was every where hid by the sea.
The whole of the S. W. end of this island is formed of breccia, being an assemblage
of angular and water-worn pieces of schistus, quartz, and some other
rocks, the whole having the appearance of a great shingle beach. The fragments
of the schistus in this rock are similar to that which forms the cliff first spoken of.
The theory which presented itself to us on the spot was, that the great mass
of strata which forms the centre of the island was formerly at the bottom of the
o c e a n a n d that the western part, which is now a firm breccia, had been a beach
shingle produced by the action of the waves on the strata: the granite which
forms the eastern end of the island had been forced into its present situation
from beneath the strata, with sufficient violence to dislocate and contort the beds
nearest to it, and to inject the liquid granite into the rents formed by the heaving
action of the strata as they were raised up. I t is natural to suppose that the ragged
edges of the strata forming the sides of these cracks would be subjected to a
grinding action, from which the strata more remote might be exempted; and in
this way we may account for the extraordinary twisting, and separation of masses
along the whole course of the granite dyke. In the dyke, as well as in the veins
which branch from it, there are numerous islands of schistus. That this last
was softened, seems to follow from the frequent instances which occur of its
being bent back upon itself without producing cracks. The same heat, propagated
by the melted granite in the neighbourhood, may also be supposed to
have reduced the shingle beach to a state of semifusion by the aid of some flux
contained in the sand scattered amongst it. We could not discover any circumstance
by which the relative antiquity of the two dykes mentioned above, could
be ascertained.
C