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Updated: May 5, 2025
This whole pile resembles, but not very closely, some of the less brecciated parts of the great porphyritic conglomerate formation of Chile; but it does not probably belong to the same age, as the porphyries here rest unconformably on the altered feldspathic clay-slate, whereas the porphyritic conglomerate formation alternates with and rests conformably on it.
Again, I incidentally noticed in North Wales, where glaciers had passed over the truncated edges of the highly inclined laminae of clay-slate, that the surface, though smooth, was worn into small parallel undulations, caused by the competent laminae being of slightly different degrees of hardness.
The clay-slate is in many parts capped by a thick mass of fragments of the same rock, firmly recemented; and both together have been injected and broken up by very numerous hillocks, ranging north and south, of lilac, white, dark and salmon- coloured porphyries: one steep, now denuded, hillock of porphyry had its face as distinctly impressed with the angles of a fragmentary mass of the slate, with some of the points still remaining embedded, as sealing-wax could be by a seal.
Either it or the sea-breeze generally sets in between seven and eight a.m., when the stony, sandy world has been thoroughly sunned. The short divide beyond the far bank of the Sirr is strewn with glittering mica-schist that takes the forms of tree-trunks and rotten wood; and with dark purple-blue fragments of clay-slate looking as if they had been worked.
The only thing which reminded us of the gale outside, was every now and then a puff from the mountains, which made the ship surge at her anchors. December 25th. Close by the Cove, a pointed hill, called Kater's Peak, rises to the height of 1700 feet. The surrounding islands all consist of conical masses of greenstone, associated sometimes with less regular hills of baked and altered clay-slate.
The rock which appeared here and there on the riverbank was an indurated clay-slate, sometimes crystalline, and thrown up almost vertically. Right and left of us rose isolated limestone mountains, their white precipices glistening in the sun and contrasting beautifully with the luxuriant vegetation that elsewhere clothed them.
Whether Mr Wells be right in his conclusions, remains to be proved; geologists will not fail to examine into his proofs. They may, however, remember, that Agassiz has remarked, that saw-dust through which water has been filtered, will 'assume a regular stratified appearance; and that, in beds of clay and clay-slate, the deposits are such as to justify these conclusions.
The fourth and last great division of rocks are the crystalline strata and slates, or schists, called gneiss, mica-schist, clay-slate, chlorite-schist, marble, and the like, the origin of which is more doubtful than that of the other three classes.
The clay-slate, dark, soft, and laminated, appeared everywhere. Lower down, on the same slope, Mr. Grant had dug a second shaft, somewhat smaller than the upper: both were full of rain-water. Mr. Walker mentions a large native pit near the centre, whence rich stone had been taken.
Further north, however, to the west of this great range, there is no clay-slate, but only gneiss, mica, and hornblendic slates, resting on great barren hills of true granite, and forming a tract about sixty miles in width. Fitton in "Geological Proceedings" volume 1 page 29; also some observations by Captain Fitzroy "Voyages" volume 1 page 375. I am indebted also to Mr.
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