crustation is recent, we observe the woody texture contained in a solid case, and without any remarkable alteration; but in proportion as the calcareous envelope increases, the wood becomes disorganized, and changes insensibly into a dry and black powder." From this state he supposes the centre gradually to increase in solidity till the whole mass becomes a mere sandstone, and nothing but an arborescent form indicates the ancient state of vegetation.

The incrustations near Simon's Town are of a similar nature to those found in New-Holland, because, says Dr. Abel, the descriptions of authors correspond with the appearances I have witnessed, and because I have compared a specimen brought from Bald Head in New-Holland, by Mr. Brown, with those I obtained at the Cape, and can trace no essential difference, either in the external characters or chemical composition. It follows from this statement, that Flinders and Vancouver have confounded vegetable incrustations with true corals; and hence the reasoning on their supposed submarine origin, and modern rising of the Bald Head, &c. above the level of the ocean, is incorrect.

Geology of the North and South, and East and West Ranges of Mountains.-The ranges of mountains which run northward from the Cape Peninsula to Orange or Gariep River, in the points where examined, exhibited granite and slate, with vast deposites of sandstone or quartz rock with numerous table-shaped summits, thus showing a similarity of composition in these mountains to those of the Cape Peninsula.

The three great ranges of mountains that run from east to west, according to the reports of travellers, are of the same general nature, and eminently characterized by the vast abundance of sandstone reposing in horizontal strata upon the granite and slate, forming the middle, and very often the higher parts of the chains.

Geology of the Table-land.-From the third range onwards to lat. 300 S., the prevailing rock in the plains and hills is sandstone. At Dwaal River, the frontier of the colony, there are rocks of augite-greenstone and basalt, probably in veins traversing the sandstone. Rocks of the same description, disposed in beautiful globular concretions (not boulders, as stated by Burchell), occur near to Kaabes Kraal, 29° S. lat., probably in veins traversing the horizontal sandstone of that district. The Karreebergen, or Dry

Mountains, beyond the limits of the colony, form a range from five to ten miles broad, and range through the country to an unknown distance, from N.E. to S.W. These mountains are principally composed of sandstone, in hori zontal strata, and every where exhibit beautiful tableshaped summits. According to Burchell, "The sandstone rock continues onward to lat. 30° S., to near Modde or Mud Gap, where true quartz strata and vesicular trap-rocks make their appearance. In lat. 29° 15' 32" S., mountains, called the Asbestos Mountains, of clay-slate, disposed in horizontal strata, occur; there layers of asbestos occur in the slate. This asbestos is blue and yellow, and the fibres sometimes nearly three inches in length." In the same mountain, according to Burchell, green opal and pitchstone also occur. A range of black craggy mountains extends from the Kloof, in the Asbestos Mountains; the rocks are very probably trap. Further to the north, at Klaarwater, are vast beds of horizontally stratified limestone, without organic remains.

Account of the Sibilo of the Africans.-At Sensavan, or Blenk-Klip, nearly in S. lat. 28°, there is a ridge of quartz rock impregnated with micaceous iron ore, which, in many places, is collected into nests of considerable magnitude. This ore of iron is known throughout Southern Africa by the name Sibilo. Hither all the surrounding nations repair for a supply of that ornamental and, in their eyes, valuable substance. It forms, in some degree, an article of barter with more distant tribes, and even among themselves; so that the use of it extends over at least 50 of latitude. It is of a reddish colour, soft and greasy to the feel, -its particles adhering to the skin, and staining it of a deep red colour. The skin, says Burchell, is not easily freed from these glossy particles, even by repeated washing. The mode of preparing and using it is, simply grinding it with grease, and smearing it generally over the body, but chiefly on the head; and the hair is often so much clotted and loaded with an accumulation of it, that the clots look like lumps of the ore.

From the north of Sensavan to Lattakoo, the rocks are limestone without petrifactions, granite, and slate. In conclusion, it may be remarked, that as far as is known at present, the whole of the table-land of Southern Africa, to the

north of the Orange or Gariep River, is composed of horizontal limestone without petrifactions, clay-slate, sandstone or quartz rock, granite, greenstone, serpentine, and potstone. The most remarkable geological feature of the country is the horizontality of the strata, thus intimating their undisturbed state.

Geological Survey of the Karroo Ground recommended.To geological travellers we recommend a particular examination of the compact clay-ground called Karroo, which, if a deposite from ancient lakes, may prove to be a tertiary formation. The surface only of the Karroo ground has been described; for, as far as our information goes, no accounts have been published of its internal structure and arrangement. It is by the study of the structure and arrangement of its layers, and the careful examination of the minerals, rocks, organic remains (if any) it contains, and its chemical composition, that we can acquire a distinct conception of its true nature.

RIVERS.

The rivers of Africa, as far as connected with those regions of this continent described in the present volume, have been already particularly considered. As much, however, still remains to be known in regard to them, we may add, that the attention of travellers, in investigating their natural history, should, besides their geographical distribution, be directed towards the various circumstances connected with their fall, velocity, quantity of water they contain, their eddies, freshes, and bore, if any such occur; also, the nature of their beds, inundations, occultations, temperature at the surface, or at different depths; their cascades and rapids; their water, as to colour, transparency, and chemical composition; and they should not omit descriptions of the river scenery considered by itself, and also in reference to the surrounding country; and, lastly, the climate, and effects of the climate, and of the scenery of the rivers, on man, ought also to form objects of inquiry.

SOUTH AFRICAN LAKES.

In Southern Africa, lakes are but seldom met with, and among these, some few are salt. The most considerable salt lake hitherto met with by travellers, is that near to

Algoa Bay. It is resorted to by the inhabitants from very distant parts of the colony, for the purpose of procuring salt for their own consumption or for sale. It is situated in a plain considerably elevated above the level of the sea, is of an oval form, and about three miles in circumference. It is named Zoutpan or Saltpan, an appropriate name, as the sun and wind do here what is effected in salt-works by artificial heat. When Mr. Barrow examined it, the greatest part of its bottom was covered with one continued body of salt, like a sheet of ice, the crystals of which were so united that they formed a solid mass as hard as rock. The dry south-easterly winds of summer, agitating the water of the lake, produce on the margin a fine, light, powdery salt, like flakes of snow. This is equally beautiful as the refined salt of England. Another salt lake, according to Lichtenstein, occurs on the western coast of the colony near to Elephant River, from which the inhabitants of the district supply themselves with this necessary of life. A salt lake of considerable extent is said to occur in about S. lat. 30°, in the upper part of the river-district of the Orange River. The most northern, of which I have been able to gain any intelligence, says Burchell, is one about the 27° S. lat., eastward of Lattakoo. The Karroo clay, as already mentioned, is probably a deposite from lake water, at a time when the tracts where it occurs were covered with water.

Particulars to be attended to in investigating the Natural History of Lakes.-Travellers, in examining and describing lakes, ought to ascertain their relations to rivers and springs, their magnitude, depth, temperature at the surface and at various depths, their colours, occultations, and agitations. The water of the lake ought to be submitted to chemical analysis, in order to ascertain whether it is fresh water, salt water, alkaline water, calcareous water, &c. Their mode of formation ought also to be considered, and the peculiar characters of lake scenery and climate should be attended to.

SOUTH AFRICAN SPRINGS.

The springs of Southern Africa may be divided into com mon, hot, and mineral.

Common Springs.-Although much rain falls in the Cape district, it affords but comparatively few springs.

This paucity of springs may be explained, as Mr. Barrow remarks, by attending to the nature of the rocks, and their mode of arrangement. Where two of the formations of the district occur together, as sandstone and granite for example, and the sandstone lies upon the granite, whose upper surface is above the level of the neighbouring country, springs will occur abundantly around the line of junction of the two formations. In this case the water percolates through the sandstone, which is a porous rock; but its farther progress downwards is arrested by the granite, which is a dense and compact rock, and therefore, when it reaches the surface of the granite, it accumulates there, and either remains stationary, or flows along its surface, until it finds an opening at the surface, where it issues forth in the form of springs. On the contrary, if the sandstone deposite rests upon granite, whose upper surface is below the level of the surrounding country, the percolating water, on reaching the granite, will accumulate there, and flow off by rents into the lower and distant parts of the country, but few springs will be observed issuing from the sandstone.

Hot Springs.-The only hot springs particularly described by travellers are those of Brand Valley and Zwarteberg.

Brand Valley. The hot spring here is larger than that at Zwarteberg. It forms a shallow pond of about fifty feet across, of the most transparent water, in the middle of which several strong springs bubble up through a bottom of loose white sand, and afterward flowing in a very copious stream, become a rivulet, which, for at least a mile and a half, continues so hot, that its course along the valley may, at any time of the day, but more particularly early in the morning, be traced by the steam which perpetually arises from it. The pond is sheltered by a small clump of white poplars, which thrive perfectly well, although growing at the very edge of the water, and bedewed with the hot steam, which ascends to their highest branches. No plant, it seems, can grow in the water itself; but the margins of the bank are thickly covered with sedge, particularly cyperus fascicularis. Royena glabra, a species of rhus, and a variety of plants, stand within the influence of its heat. The thermometer, when plunged into the pond, rose only to 144° Fahrenheit, but to the hand it felt nearly scalding hot; so that the