A species of white porpoise is common in the seas about these islands. It is of a clear white colour, with a very slight tinge of pink. I estimated its length to be about eight or nine feet.
Of birds we procured a fine species of black Pelican, a blue-coloured Heron, several specimens of Columba litoralis, and a variety of the same bird of a bluish cast; another handsome species of Columba, of an iron-brown colour, a green-coloured species of the same bird; a species of Falco of a white colour, and a few others, together with some curious fish, of which, as well as of the former, figures have been taken. Amongst the more curious objects, will be found a very beautiful species of Lacerta, and several large species of Cancer, found by the people at the watering-place. Descriptions of these will be found in the catalogues.
In the examination of the rocky shores and bare cliffs of Sechang, the geological student will find an ample field for speculation. We have visited few islands whose structure has interested us more.
For an account of the mineral masses, see the Catalogue, and the accompanying specimens. I shall here attempt, what these, in their insulated state, are not well calculated to convey, some information respecting their relative position, &c.
At various distant points on several of the islands, are to be seen, chiefly at the time of low water, extensive masses of a coarse-grained granite, abounding in plates of gray and black mica, and possessing a considerable degree of slaty structure, the mica being disposed chiefly in parallel laminæ. There is reason to suppose that this rock constitutes the base of the islands, as well as of the bay formed by them. On its horizontal surface, it terminates abruptly, without ascending into elevated or peaked masses, having a rough, horizontal surface, rarely rising above high-water mark. It is not to be seen at any distance from the sea-shore, being there concealed by the superincumbent rocks.
On this horizontal surface of the granite are placed two principal superincumbent rocks, quartz-rock, and granular limestone. These seem to rest alike upon the granite of their base, their relative position being lateral with regard to each other. They are much intermixed, and often alternate with each other. The quartz-rock rises into the highest peaks; the limestone often laps over it, so as to appear to have it for its base.
The quartz-rock varies in appearance. The grey and the white are the principal varieties; in both there is a considerable proportion of calcareous matter, and they effervesce briskly. Some parts are compact, with a fracture nearly conchoidal; such are often traversed by small seams of pure white quartz. Other parts are distinctly slaty, and here the strata are displaced, contorted, and curved; such parts are soft; penetrated by caves of considerable extent.
Masses of pure quartz abound in some parts of this rock.
The granular limestone is also of various appearance. It is intermixed with small veniform portions of dolomite, finely crystallized. Both the dolomite and granular varieties are completely soluble in sulphuric acid.
On the smaller islands, the quartz-rock is intersected by retiform veins of iron ore.