WEST COAST OF COREA.
From an Island in Latitude 37º 45' North.
1. Compact stratified pale-pink lime-stone; variegated in colour; strata highly inclined.
2. Very compact slaty light-grey rock; strata inclined at an angle of 75º, dipping towards the north-east.
3. Dark olive steatitic rock, containing fragments of granular marble.
4. Very fine-grained greenish hornblend rock.
5. Vine-grained purplish slate; the strata highly inclined.
6. Greenish-grey slate, containing crystals of white feldspar and specks of hornblend: strata highly inclined, dipping towards the north-east.
SPECIMENS FROM HUTTON'S ISLAND, COAST OF COREA.
Latitude 36º 10' north, longitude 126º 13' east.
The following note is taken from the narrative at page 8.
We found the north-east end composed of a fine-grained granite[19]; the middle of the island of a brittle micaceous schistus of a deep blue colour[20]; the strata are nearly horizontal, but dip a little to the south-west. This body of strata is cut across by a granite dyke[21], 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, though 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 visible from the top of the cliff to the water's edge, but does not re-appear on the corresponding 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[22], four feet wide, the planes of whose sides lie north-east and south-west, being at right angles to those of the great granite dyke in the neighbourhood, which run south-east and north-west. 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 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[23], 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 south-west 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 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, that 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 the heaving action of the strata as they were raised up. It 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 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 semi fusion 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 at the Lowrin mountain, in Galloway, described by my father, Sir James Hall, in the 7th vol. of the Edinburgh Transactions. It is also very like the junctions at 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 north-west and south-east, dipping only a few degrees from the horizontal line.
9. Breccia, composed of angular and contorted fragments of micaceous schistus, and angular pieces of feldspar and quartz. This rock forms the western end of Hutton's Island[24]: it rises in high rugged cliffs. The angular pieces of schistus are of a similar rock to that described above (8).
10. Dyke, porphyritic granite, composed of white quartz, white feldspar, and bronze-coloured mica. This dyke cuts across the schistus last mentioned, in a direction north-east and south-west. It is nearly vertical, and varies in breadth from nine to forty feet, with numerous ramifications.
11. Dyke of compact whin stone. This dyke is composed of five layers of prisms, whose length is at right angles to the walls of the dyke. It is nearly vertical. Its direction north and south, and is about five feet thick.
MAIN LAND OF COREA.
12. Lead-coloured, fine-grained, micaceous schistus. From the main land of Corea, latitude 36º 10' north, longitude 126º 48' east. The strata lie north-west and south-east, and are nearly vertical; the natives objected to our examining the cliffs, though distant less than a quarter of a mile from the beach.
ANOTHER ISLAND OFF THE COAST OF COREA.
Latitude 34º 23' north, longitude 126º east.
13. Decomposing fine-grained rock; composed of flesh-coloured feldspar, white quartz, and porcelain clay.
ANOTHER ISLAND NEAR THE ABOVE.
14. Rock composed of white feldspar and quartz. The strata of this rock were very much contorted.
This rock is the most general of any in this range of islands, at least as far as we had opportunities of examining them. The islands on this coast are very numerous; they lie in great clusters along a line of three degrees and a half of latitude. The islands vary in length from five or six miles to as many yards, and are of all forms. We saw none that were remarkably high, and none which seemed volcanic. As our stay on the coast was only nine days, and as the ships were almost always under weigh except at night, it was quite impossible to make any careful or valuable geological observations. It offers a splendid field to future voyagers.
GREAT LOO-CHOO ISLAND.
1. Grey stratified lime-stone without shells. This specimen was taken from the north end of the island, where the ranges of hills were mostly composed of it: the strata being highly inclined. The hills rise to the height of four or five hundred feet, and present nothing interesting.
2. Fawn-coloured, cellular, granular lime-stone. The cliffs at Napakiang are composed of this rock; it also appears to stretch along the whole of the south-west and south parts of the coast. In the narrative, this rock has been erroneously called coral. These cliffs are curiously hollowed out into horizontal caves, which have all the appearance of having been worn by the dashing of the waves; but as it is obvious, that in their present situation the sea can never have reached the face of the cliffs, it seems probable that the whole coast may have been raised up, by a gentle movement, without dislocating the strata, or disturbing the horizontal position, in which it seems probable that these caves were formed.
The variety of coralines which girt the shores of this island was very great, and large collections were made, as well of these as of the numerous zoophites which filled up every part of the reefs below high-water mark. This collection, of which unfortunately no duplicates were kept, was afterwards lost.
SULPHUR ISLAND
Lies in latitude 27º 5' north, and longitude 128º 25' east. An accurate representation of it is given as a frontispiece.
We attempted to land, but the surf broke every where so high against the rock that this was impossible. There is a crater on the left side with white smoke issuing from it; this has a strong sulphuric smell. The sides of the crater are stratified. The south end of the island is about four or five hundred feet high, and is formed of a dark dingy red rock distinctly stratified; at several places it is cut vertically by great dykes, which being more durable than the strata which they intersect, stand out from the face of the cliffs to a considerable distance.
FOOTNOTES:
[Footnote 19: Specimen 7, infra.]
[Footnote 20: Specimen 8.]
[Footnote 21: Specimen 10.]
[Footnote 22: Specimen 11, infra.]
[Footnote 23: Specimen 9.]
[Footnote 24: The island above described was so named 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.]