Africa

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 of the } Igneous complex of

continental platform. } sheared igneous

} rocks;granites.

and Australia. At the close of the Karroo period there was a remarkable

manifestation of volcanic activity which again has its parallel in the

Deccan traps of India.

How far the Karroo formation extended beyond its present confines has not

been determined. To the east it reached India. In the south all that can be

said is that it extended to the south of Worcester in Cape Colony. The

Crystal Mountains of Angola may represent its western boundary; while the

absence of mesozoic strata beneath the Cretaceous rocks of the mid-Sahara

indicates that the system of Karroo lakeland had here reached its most

northerly extension. Towards the close of the Karroo period, possibly about

the middle, the southern rim of the great central depression became ridged

up to form the folded regions of the Zwaarteberg, Cedarberg and Langeberg

mountains in Cape Colony. This folded belt gives Africa its abrupt southern

termination, and may be regarded as an embryonic indication of its present

outline. The exact date of the maximum development of this folding is

unknown, but it had done its work and some 10,000 ft. of strata had been

removed before the commencement of the Cretaceous period. It appears to

approximate in time to the similar earth movement and denudation at the

close of the palaeozoic period in Europe. It was doubtless connected with

the disruption of Gondwana Land, since it is known that this great

alteration of geographical outline commenced in Jurassic times.

The breaking up of Gondwana Land is usually considered to have been

caused by a series of blocks of country being let down by faulting with the

consequent formation of the Indian Ocean. Other blocks, termed horsts,

remained unmoved, the island of Madagascar affording a striking example. In

the African portion Ruwenzori is regarded by some geologists to be a block

mountain or horst.

In Jurassic times 1he sea gained access to East Africa north of

Mozambique, but does not appear to have reached far beyond the foot-plateau

except in Abyssinia.

The Cretaceous seas appear to have extended into the central Saharan

regions, for fossils of this age have been discovered in the interior. On

the west coast Cretaceous rocks extend continuously from Mogador to Cape

Blanco. From here they are absent up to the Gabun river, where they

commence to form a narrow fringe as far as the Kunene river, though often

overlain by recent deposits. They are again absent up to the Sunday river

in Cape Colony, where Lower Cretaceous rocks (for long considered to be of

Oolitic age) of an inshore character are met with. Strata of Upper

Cretaceous age occur in Pondoland and Natal, and are of exceptional

interest since the fossils show an intermingling of Pacific types with

other forms having European affinities. In Mozambique and in German East

Africa, Cretaceous rocks extend from the coast to a distance inland of over

100 m.

Except in northern Africa, the Tertiary formations only occur in a few

isolated patches on the east and west coasts. In northern Africa they are

well developed and of much interest. They contain the well-known nummulitic

limestone of Eocene age, which has been traced from Egypt across Asia to

China. The Upper Eocene rocks of Egypt have also yielded primeval types of

the Proboscidea and other mammalia. Evidences for the greater extension of

the Eocene seas than was formerly considered to be the case have been

discovered around Sokoto. During Miocene times Passarge considers that the

region of the Zambezi underwent extreme desiccation.

The effect of the Glacial epoch in Europe is shown in northern Africa by

the moraines of the higher Atlas, and the wider extension of the glaciers

on Kilimanjaro, Kenya and Ruwenzori, and by the extensive accumulations of

gravel over the Sahara.

The earliest signs of igneous activity in Africa are to be found in the

granites, intrusive into the older rocks of the Cape peninsula, into those

of the Transvaal, and into the gneisses and schists of Central Africa. The

Ventersdorp boulder beds of the Transvaal may be of early palaeozoic age;

but as a whole the palaeozoic period in Africa was remarkably free from

volcanic and igneous disturbances. The close of the Stormberg period

(Rhaetic) was one of great volcanic activity in South Africa. Whilst the

later Secondary and Tertiary formations were being laid down in North

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