wider by the action of the atmosphere and running water. The inclined plain, or space between the most southern range of mountains and the seacoast, varies from 20 to 60 miles in breadth, and, reckoning from the interior of the country, forms the third terrace of Southern Africa. The flat tract enclosed between the southern chain and the Zwarteberg forms the second terrace. The vast tract, or the Great Karroo, contained between the Zwarteberg and the Nieuweveld Gebirgte, is the first terrace. The second and first terraces, which contain so much Karroo ground, may formerly have been inland seas or lakes. The great bank of gravel, sand, and clay, which ranges along the coast and under the sea, from the Cape of Good Hope to Natal, and to South lat. 37°, may be considered as another terrace.

Description of the Karroo Plains.-The Karroo ground, which forms so striking a feature in the external aspect of the Cape district, is loam or sandy clay, mixed with particles of ochre of iron. Lichtenstein says it is not more than a foot in thickness. This may apply to some, but by no means to the greater number of localities. From the nature of the soil, and other concomitant causes, the vegetation must at all times be very meagre; and in summer, when the sun has dried the soil to the hardness of brick, it ceases almost entirely. The mesembryanthemum, and some other succulent plants; some kinds of gorteria, of bergia, and of asters, whose roots, like the bulbs of lilacious plants, nature has fortified with a tenfold net of fibres under the upper rind, to protect them against the hardened clay: such plants alone resist the destructive nature of this inhospitable soil.

As soon as, in the cooler season, the rains begin

to fall, and penetrate into the hard layer of loam, these fibres imbibe the moisture, and, pushing aside the clay, the germ of the plant, under their protection, begins to shoot, and in a few days the arid waste is covered with a delicate green covering. Soon after, myriads of flowers ornament the whole surface. "The mild mid-day sun," says Lichtenstein, "expands the radiated crowns of the mesembryanthemums and gorteriæ, and the young green of the plants is almost hidden by the glowing colours of their full-blown flowers, while the whole air is perfumed with the most fragrant odour. The odour is more particularly delightful, when, after a calm day, the sun declines, and the warm breath of the flowers rests quietly on the plain. At this time the whole dreary desert is transformed into one continued garden of flowers. The colonist, with his herds and his flocks, leaves the Snowy Mountains, and, descending into the plain, there finds a plentiful and wholesome supply of food for the animals; while troops of the tall ostrich and the wandering antelope, driven also from the heights, share the repast, and enliven the scene. But how soon is the country again deprived of all its glory! It scarcely continues more than one month, unless late rains, which must not often be expected, call forth the plants again into new life. As the days begin to lengthen, the increasing power of the mid-day ray checks once more the lately-awakened powers of vegetation. The flowers soon fade and fall, the stems and leaves dry, and the hard coat of soil locks up the germs until the rains return; the succulent plants alone still furnish food for the herds and flocks. The streams soon begin to dry, the springs almost cease to flow, till at length the universal

drought compels the colonists to return to the mountains; yet even then they quit the plain with reluctance, and the flocks, accustomed to endure thirst, still linger behind, feeding on the succulent plants, which afford at once food and drink, and are particularly salutary to those that bear wool. Every day, however, the Karroo becomes more and more solitary, and by the end of September it is wholly deserted. The hardened clay bursts into a thousand cracks, which evince to the traveller the great power of an African sun. Every trace of verdure

is vanished, and the hard red soil is covered over with a brown dust, formed from the ashes of the dried and withered plants. Yet amongst these ashes is the seed nourished that is to produce future generations, and the relics of one year's vegetation furnishes manure that is to cherish the germs till the next year's rain again brings them forth."

Lichtenstein thus describes his first view of the Great Karroo:-"The space between the mountainranges is the Great Karroo, as it is called, a parched and arid plain, stretching out to such an extent that the vast hills by which it is terminated are almost lost in the distance. The beds of numberless little rivers cross, like veins, in a thousand directions, this enormous space; the course of them might in some places be clearly distinguished by the darkgreen of the mimosas which spread along their banks. Excepting these, nowhere, as far as the eye could reach, was a tree to be seen, nor even a shrub, or any signs whatever of life."

As the geology of the country in the vicinity of Cape Town is that best known to us of any part of

Southern Africa, we shall first describe the arrangements observed in that quarter, and afterwards notice what is known of the rocks of other parts of this division of Africa.

At

Geognosy of the Peninsula of the Cape of Good Hope. The peninsula of the Cape of Good Hope is a mountainous ridge, stretching nearly north and south for forty or fifty miles, and connected on the east side, and near its northern extremity, with the main body of Africa, by a flat sandy isthmus, about ten miles broad, having Table Bay on the north of it, and False Bay on the south. The southern extremity of this peninsula, extending into the sea, with False Bay on the east, and the ocean on the south and west, is properly the Cape of Good Hope, and is nearly the most southern point of Africa. this point the chain of mountains which forms the peninsula, though rugged, is lower than at the north end, where it is terminated by Table Mountain and two others, which form an amphitheatre overlooking Table Bay, and opening to the north. The mountains of the ridges extending from the Cape to the termination of the peninsula in the north, vary in shape; but the most frequent forms incline more or less to sharp conical. The three mountains that terminate the peninsula on the north, are the Table Mountain in the middle; the Lion's Head, sometimes called the Sugar Loaf, on the west side; and the Devil's Peak on the east. The Lion's Head, which is about 2160 feet above the level of the sea, is separated from the Table Mountain by a valley that descends to the depth of 1500 or 2000 feet below the summit of the Table Mountain, which

is itself 3582 above the level of the sea. On the west of the Lion's Head there is a lower eminence, named the Lion's Rump, 1142 feet high, from which the ground declines gradually to the sea. The amphitheatre formed by these three mountains is about five or six miles in diameter, in the centre of which is placed Cape Town.

The rocks of which this peninsula is composed are few in number, and of simple structure. They are granite, gneiss, clay-slate, greywacke, quartz rock, sandstone, and augite-greenstone, or dolerite. Of these the most abundant are granite and sandstone; the next in frequency are clay-slate and greywacke; and the least frequent are gneiss and dolerite. In some parts, as at the Steinberg, the sandstone is traversed by veins of red iron ore. Abel mentions a vein six feet wide, and extending for upwards of one hundred feet.

The strata of the Neptunian rocks, or those whose formation is connected with the operation of water, generally range from west to east, that is, across the peninsula. The southern and middle parts of the peninsula have been but imperfectly examined. Captain Hall remarks, that the same general structure and relations seem to occur all over the peninsula as in the mountains around Cape Town. The late Dr Clarke Abel, in the account of his voyage to China, gives the following description of a fine display of stratification in a mountain that faces the sea, in the neighbourhood of Simon's Bay, which was pointed out to him by one of our pupils, an active and intelligent officer, Captain Wauchope, R. N." The sandstone, forming the upper part of