Africa

Mediterranean. Among the birds most characteristic of Africa are the ostrich and the secretary-bird. The ostrich is widely dispersed, but is found chiefly in the desert and steppe regions. The secretary-bird is common in the south. The weaver birds and their allies, including the long-tailed whydahs, are abundant, as are, among game-birds, the francolin and guinea-fowl. Nany of the smaller birds, such as the sun-birds, bee-eaters, the parrots and halcyons, as well as the larger plantain-eaters, are noted for the brilliance of their plumage. Of reptiles the lizard and chameleon are common, and there are a number of venomous serpents, though these are not so numerous as in other tropical countries. The scorpion is abundant. Of insects Africa has many thousand different kinds; of these the locust is the proverbial scourge of the continent, and the ravages of the termites or white ants are almost incredible. The spread of malaria by means of mosquitoes has already been mentioned. The tsetse fly, whose bite is fatal to all domestic animals, is common in many districts of South and East Africa. Fortunately it is found nowhere outside Africa. (E. HE.; F. R. C.)

1 With the islands, 11,498,000 sq. m.

2 Estimated.

3 See the calculations of Capt. T. T. Behrens, Geog. Journal, vol. xxix. (1907).

4 The estimate of Capt. H. G. Lyons in 1905 was 1,107,227 sq. mi.

5 including waterless tracts naturally belonging to the river-basin.

II. GEOLOGY

In shape and general geological structure Africa bears a close resemblance to India. Both possess a meridional extension with a broad east and west folded region in the north. In both a successive series of continental deposits, ranging from the Carboniferous to the Rhaetic, rests on an older base of crystalline rocks. In the words of Professor Suess, ``India and Africa are true plateau countries.''

Of the primitive axes of Africa few traces remain. Both on the east and west a broad zone of crystalline rochs extends parallel with the coast-line to form the margin of the elevated plateau of the interior. Occasionally the crystalline belt comes to the coast, but it is usually reached by two steps known as the coastal belt and foot-plateau. On the flanks of the primitive western axis certain ancient sedimentary strata are thrown into folds which were completed before the commencement of the mesozoic period. In the south, the later palaeozoic rocks are also thrown into acute folds by a movement acting from the south, and which ceased towards the close of the mesozoic period. In northern Africa the folded region of the Atlas belongs to the comparatively recent date of the Alpine system. None of these earth movements affected the interior, for here the continental mesozoic deposits rest, undisturbed by folding, on the primary sedimentary and crystalline rocks. The crystalline massif, therefore, presents a solid block which has remained elevated since early palaeozoic times, and against which earth waves of several geological periods have broken.

The formations older than the mesozoic are remarkably unfossiliferous, so that the determination of their age is frequently a matter of speculation, and in the following table the European equivalents of the pre-Karroo formations in many regions must be regarded as subject to considerable revision.

Rocks of Archean age cover wide areas in the interior, in West and East Africa and across the Sahara. Along the coastal margins they underlie the newer formations and appear in the deep valleys and kloofs wherever denudation has laid them bare. The prevailing types are granites, gneisses and schists. In the central regions the predominant strike of the fohae is north and south. The rocks, for convenience classed as pre-Cambrian, occur as several unconformable groups, chiefly developed in the south where alone their stratigraphy has been determined. They are unfossiliferous, and in the absence of undoubted Cambrian, Ordovician and Silurian strata in Africa they may be regarded as of older date than any of these formations. The general occurrence of jasper-bearing rocks is of interest, as these are always present in the ancient pressure-altered sedimentary formations of America and Europe. Some unfossiliferous conglomerates, sandstones and dolomites in South Africa and on the west coast are considered to belong to the Cambrian, Ordovician and Silurian formations, but merely from their occurrence beneath strata yielding Devonian fossils. In Cape Colony the Silurian age of the Table Mountain Sandstone is based on such evidence.

The Devonian and Carboniferous formations are well represented in the north and south and in northern Angola.

Up to the close of the palaeozoic period the relative positions of the ancient land masses and oceans remain unsolved; but the absence of marine strata of early palaeozoic age from Central Africa points to there being land in this direction. In late Carboniferous times Africa and India were undoubtedly united to form a large continent, called by Suess Gondwana Land. In each country the same succession of the rocks is met with; over both the same specialized orders of reptiles roamed and were entombed.

The interior of the African portion of Gondwana Land was occupied by several large lakes in which an immense thickness—amounting to over 18,000 ft. in South Africa—-of sandstones and marls, forming the Karroo system, was laid down. This is par excellence the African formation, and covers immense areas in South Africa and the Congo basin, with detached portions in East Africa. During the whole of the time—-Carboniferous to Rhaetic—that this great accumulation of freshwater beds was taking place, the interior of the continent must have been undergoing depression. The commencement of the period was marked by one of the most wonderful episodes in the geological history of Africa. Preserved in the formation known as the Dwyka Conglomerate, are evidences that at this time the greater portion of South Africa was undergoing extreme glaciation, while the same conditions appear to have prevailed in India

TABLE OF FORMATIONS

Sedimentary. Igneous.

Recent Alluvium; travertine;

coral; sand dunes; continental } Some volcanic islands;

dunes. Generally distributed } rift-valley volcanoes.

Pleistocene. Ancient alluviums and }

gravels; travertine. }

Generally distributed. } A long-continued

Pliocene. N. Africa; Madagascar. } succession in the

} central and northern

Miocene. N. Africa. } regions and among

} the island groups.

Oligocene. N. Africa. } Doubtfully represented

} south of the Zambezi.

Eocene. N. Africa, along east and }

west coasts; Madagascar. }

Cretaceous Extensively developed in } Diamond pipes of S.

N. Africa; along coast } Africa; Kaptian

and foot-plateaus in east } fissure eruptions;

and west; Madagascar. } Ashangi traps of

} Abyssinia

{Jurassic N. Africa; E. Africa;

K{ Madagascar; Stormberg } Chief volcanic period

a{ period (Rhaeric) in S. } in S. Africa

r{ Africa }

r{Trias. Beaufort Series in S. }

o{ Africa; Congo basin; }

o{ Central Africa; Algeria; }

{ Tunis. }

{Permian. Ecca Series in S. Africa. } Feebly, if anywhere

} developed.

Carboniferous. N. Africa; Sabaki Shales }

in E. Africa; Dwyka }

and Wittebery Series in }

South Africa }

Devonian. N. Africa; Angola; Bokkeveld } Not recorded.

Series in S. Africa }

Silurian. {Table Mountain Sandstone }

{ in S. Africa, Silurian(?). }

Ordovician. { Doubtfully represented } Klipriversberg and

{ in N. Africa, French } and Ventersdorp Series

Cambrian { Congo, Angola. and by } of the Transvaal (?).

{ Vaal River and Waterberg }

{ Series in S. Africa }

Pre-Cambrian. Quartzites, conglomerates }

phyllites, jasper-bearing } S. Africa and generally.

rocks and schists. }

Generally distributed. }

Archeaan. Gneisses and schists