Imatges de pÓgina

the mountain, is of a reddish colour, very crystalline in its structure, and approaching, in some specimens, to quartz rock. Immediately beneath the sandstone is a bed of compact dark-red argillaceous sandstone, passing, in many places, into slate of the same colour. This bed rests upon another of very coarse loosely-combined sandstone resembling gravel. Under this is another layer of dark-red sandstone, terminating in a conglomerate, consisting of decomposed crystals of felspar, and of rounded and angular fragments of quartz, from the size of a milletseed to that of a plover's egg, imbedded in a red sandstone base. Beneath the conglomerate commences a bed, which I at first took for granite, and which is composed of the constituents of granite in a decomposed state, intermixed with green steatite, and a sufficient quantity of the red sandstone to give it a reddish hue. The felspar of the bed is decomposed, and exactly resembles that of the conglomerate above it. The mica seems, in a good measure, to have passed into steatite. The quartz is in small crystals, frequently having their angles rounded. This bed is several feet in thickness, and gradually terminates in the granite; but the precise line of junction I was unable to trace. The appearances thus were in the following order:—

1. Horizontally-stratified sandstone.

2. Bed of compact dark-red sandstone, passing into slate.

3. A bed of coarse sandstone resembling gravel. 4. A second layer of compact dark-red sandstone, passing

5. Into a conglomerate, consisting of decomposed crystals of felspar, and fragments of quartz in a sandstone basis.

6. A bed composed of the decomposed constituents of granite and red sandstone, passing

7. Into granite."

The above is the only spot to the southward of the range of mountains near Cape Town which has been particularly described in a geognostical view. To the northward of Cape Town, it is said that the mountains are principally composed of the same rocks as those which occur throughout the peninsula, and whose characters and position have been exaImined with considerable attention in the Lion's Rump, Lion's Head, Table Mountain, and Devil's Peak, by our pupils the late Dr Clarke Abel, Dr Adam, now of Calcutta, the late Captain Carmichael, and also by Captain Basil Hall. From the observations furnished to us by these naturalists, and also from accounts published by them, we have drawn up the following description:

Lion's Rump.-The Lion's Rump rises by an easy ascent, and, excepting at one or two points, is covered to the summit with a thin soil, bearing a scanty vegetation. Dr Adam informs us that vegetables appeared to be most luxuriant over the sandstone of the peninsula, but less so on the soil formed by the decomposition of the granite, and, least of all, over clay-slate, as on the Lion's Rump, where clay-slate is the predominating rock. Although this latter hill has been cultivated in some places, yet it presents a stunted vegetation; while the upper part of Lion's Head and Table Mountain, though

much more elevated, display rich and more vigorous shrubs.* It is composed of clay-slate, greywacke, and sandstone. The clay-slate and greywacke appear to alternate, and the sandstone rests upon the slate. The slate is distinctly stratified; the strata on one side of the hill dip to the north, on the opposite to the south, and in the middle or centre of the hill they are nearly perpendicular. Numerous veins of compact quartz traverse the strata in all directions. A quarry, which has been wrought to a considerable extent on the east side of the hill, exhibits a fine view of the structure of the clay-slate, and in one place there is a bed of sandstone in the slate. The sandstone, which is of a yellowish-gray colour, is composed of grains of quartz, with disseminated felspar and scales of mica.

Lion's Head-The strata of clay-slate continue to the base of the Lion's Head. Here they are succeeded by strata of compact gneiss, composed of gray felspar and quartz, with much dark-brown mica in small scales. It much resembles the gneiss interposed between granite and clay-slate in the

* Constantia, so celebrated for its wine, is situated at the bottom of the range leading from Cape Town to Simon's Bay, where sandstone is the predominating rock; and the soil of the farms of the neighbouring ground appears to be composed of it, in a state of decomposition, and of vegetable mould. That it is the sandstone which essentially contributes to the excellence of the soil Dr Adam is inclined to believe, from having observed several spots at the foot of the same range, nearer Cape Town, with a soil richer in vegetable mould, but whose produce was held much inferior. The principal rock there was granite, and its superincumbent sandstone has suffered less decomposition than that adjoining to Constantia.

transition mountains in the south of Scotland; as at Criffel, and near New Galloway in Kirkcudbrightshire. The gneiss is distinctly stratified, and the strata in some places dip under the next rock, which is granite; in others, they dip from it. Numerous transitions are observed from the granite into the gneiss; and, in the same bed of compact gneiss, one part will be gneiss, while another will be granite. Beds of granite, in some places, appear to alternate with the gneiss. Veins of granite, from a few inches in width to several feet, traverse the gneiss and clayslate, and are observed projecting from the body of the granite, and shooting among the neighbouring slaty strata. Granite forms a considerable portion of the Lion's Head. It is composed of pale-red felspar, gray quartz, and brownish-black mica. It is more frequently coarse granular than fine granular, and is often porphyritic. It is occasionally traversed by veins of quartz, or of felspar, or of granite. In some parts the granite is traversed by veins of dolerite or augite-greenstone, and one of these veins, as described by Dr Abel, appears divided and shifted. This appearance is represented in No 3 of Dr Abel's Geological Views at the Cape of Good Hope. As we ascend the mountain, we find the granite succeeded first by a reddish sandstone, and this, in its turn, is covered by a brown sandstone that reaches to the summit. These sandstones are principally composed of granular concretions of quartz, with a few disseminated grains of felspar and scales of mica. The sandstone is distinctly stratified, and the strata dip at a small angle all around the Lion's Head and the north-west side of the Table Mountain. On the opposite side of the latter, however,

from the seabeach, we may see it, beyond the gorges, making an angle with the horizon of not less than 45°. Dr Adam says, "During a ride to Constantia one day, I observed this high inclination more particularly on the ridge extending from the Devil's Peak by Simon's Bay; and, having afterwards visited the spot on purpose, found the sandstone very much elevated in its position above the common level of the strata, and, at one place, nearly perpendicular to the horizon, running from north-east to south-west."

Table Mountain.-The next and highest mountain, the Table Mountain, presents many interesting appearances. The lowest part of the mountain, on one side, is red sandstone; higher up, and apparently rising from under it, are clay-slate, greywacke, and gneiss. These rocks are disposed in strata, arranged nearly in a vertical position, with an east and west direction. They are intermingled with granite, which is the next rock on the ascent of the mountain. The granite, at its line of junction with the slate, both gneiss and clay-slate, is often much intermixed with them; and numerous veins of granite shoot from the mass of the granite rock itself into the bounding strata. At a higher level than the granite, sandstone makes its appearance, and continues upwards to the summit of the mountain. The lowest of the summit sandstone is of a reddish colour; the next above it is of a yellowish colour; and the upper part, or that on the summit, is of a gray, or beautifully white colour, and sometimes so coarsely granular as to appear in the state of conglomerate. In many places, the sandstone passes into quartz rock, and is very highly crystalline. The

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