Реферат: Africa

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; }