having the appearance of a great shingle beach and cliffs.
The fragments of the schistus in this rock are similar to that
which forms the cliff first spoken of, (Specimen 8.)
The theory which presented itself to us on the spot was,
tha t the lower part of the great mass of strata which now
forms the centre of the island was formerly at the bottom
of the ocean ; and that the western part, now a firm breccia,
had been a beach of shingle produced by the action of the
waves on the upper strata, which may have formed a coast
above the sea : the granite of 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 thé hèaving 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 remotë 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 insulated portions 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, generated by the melted granite
in the neighbourhood, and which appears to have been just
sufficient to soften the schistus, may 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
the fragments. We could not discover any circumstance
by which the, relative antiquity of the two dykes mentioned
above could be inferred.
The junction of the granite and schistus above described,
resembles very much the well known .junction a t the Lowrin
mountain, in Galloway, described by my father, Sir James
Hall, in the 7th vol. of the Edinburgh Transactions. I t is
also very like the junctions a t the Cape of Good Hope,
described in the same volume. The same theory has been
found to explain them, all.
Specimen 7. Fine-grained granite, composed of white
quartz, white feldspar, .and olive-green mica. This rock (7)
forms the .eastern, end of the island; the schistus .next
described (8). the „centre, and the breccia mentioned immediately
afterwards (9) the western end.
8. Fine-grained compact micaceous schistus: some of
the specimens appear to contain plumbago. The strata
lie northTwest , and, south-east, dipping, only a few degrees
from, the horizontal fine.
9. Breccia,, composed of, angular and contorted fragments
of micaceous schistus, and angular pieces of feldspar
and quartz. This rook forms the western end of Hutton’s
Island * ;, it, rises- in high rugged cliffs. The angular pieces
of schistus are of a similar rock, to that described above (8).
10. Dyke, porphy ritic granite, composed of white quartz,
\yhite feldspar, and bronze-coloured, mica. This dyke cuts
across the schistus last mentioned,, in a direction north-east
* The island above.described, was.sovnained by Captain Maxwell, in.compliment
to the memory of the distinguished philosopher whose theory has been
used to explain the curious phenomena which it exhibits.