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Updated: July 17, 2025
Nor does their almost universally volcanic composition favour the admission that they are the wrecks of sunken continents; if they had originally existed as mountain-ranges on the land, some at least of the islands would have been formed, like other mountain-summits, of granite, metamorphic schists, old fossiliferous or other such rocks, instead of consisting of mere piles of volcanic matter.
I should have liked to have worked out the exact relative positions of the quartz-conglomerate and the contorted schists, for I have no doubt that a day or two's search amongst the ravines would have shown many natural sections that would have thrown great light upon the subject; but I had no time to devote to it.
About a mile from the first-named town, the contorted schists cropped up again, and were followed, as before, by beds of soft decomposing trap, and these again by thick beds of quartz-conglomerate. This succession was repeated two or three times during the day's journey. The trap beds formed, by decomposition, a dark fertile soil. Wherever maize was planted on it, it was thriving greatly.
The laminae of the clay-slate are straight; and it was interesting to observe, that as they assumed the character of gneiss, they became undulatory with some of the smaller flexures angular, like the laminae of many true metamorphic schists. This formation makes the most imposing feature in the geology of Southern Africa.
This is the usual geological condition on the right bank of the Cataracts. On the other side we pass over masses of porphyritic trap, in contact with the same mica schists, and these probably give to the soil the great fertility we observed. The great body of the mountains is syenite.
"It is impossible to avoid associating such a formation with the fine, smooth, homogeneous clays and schists, poor in fossils, but showing worm- tubes and tracks, and bunches of doubtful branching things, such as Oldhamia, silicious sponges, and thin-shelled peculiar shrimps.
We have seen that the shores of the Pacific, for a space of 1,200 miles from Tres Montes to Copiapo, and I believe for a very much greater distance, are composed, with the exception of the tertiary basins, of metamorphic schists, plutonic rocks, and more or less altered clay-slate.
To his first fauna, which was older than any then known in this country, he gave the name of Etage C; his two first stages A and B consisting of crystalline and metamorphic rocks and unfossiliferous schists.
I may add that wherever I met with the gneiss, mica, schists, and slates, in Sikkim, very near one another, I invariably found that their cleavage and foliation were conformable. This, for example, may be seen in the bed of the great Rungeet, below Dorjiling, where the slates overlie mica schists, and where the latter contain beds of conglomerate.
But the colors of those gray-blue granites, mingling with the black and tawny schists, must have been seen in order to understand how vividly a spectral image was suggested by the empty and gloomy carcass of the building.
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