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 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 Africa and around the margins
of the rest of the continent, Africa received its last great
accumulation of strata and at the same time underwent a
consecutive series of earth-movements. The additional strata
consist of the immense quantities of volcanic material on
the plateau of East Africa, the basalt flows of West Africa
and possibly those of the Zambezi basin. The exact period
of the commencement of volcanic activity is unknown. In
Abyssinia the Ashangi traps are certainly post-Oolitic. In
East Africa the fissure eruptions are considered to belong
to the Cretaceous. These early eruptions were followed by
those of Kenya, Mawenzi, Elgon, Chibcharagnani, and these
by the eruptions of Kibo, Longonot, Suswa and the Kyulu
Mountains. The last phase of vulcanicity took place along
the great meridional rifts of East Africa, and though feebly
manifested has not entirely passed away. In northern Africa
a continuous sequence of volcanic events has taken place from
Eocene times to latest Tertiary; but in South Africa it is
doubtful if there have been any intrusions later then Cretaceous.
During this long continuance of vulcanicity, earth-movements
were in progress. In the north the chief movements gave
rise to the system of latitudinal folding and faulting of the
Moroccan and Algerian Atlas, the last stages being represented
by the formation of the Algerian and Moroccan coast-outline
and the sundering of Europe from Africa at the Straits of
Gibraltar. Whilst northern Africa was being folded, the East
African plateau was broken up by a series of longitudinal
rifts extending from Nyasaland to Egypt. The depressed areas
contain the long, narrow, precipitously walled lakes of East
Africa. The Red Sea also occupies a meridional trough.
Lastly there are the recent elevations of the northern coastal
regions, the Barbary coast and along the east coast. (W. G.*)
III. ETHNOLOGY In attempting a review of the races and
tribes which inhabit Africa, their distribution, movements
and culture, it is advisable that three points be borne in
mind. The first of these is the comparative absence of natural
barriers in the interior, owing to which intercommunication
between tribes, the dissemination of culture and tribal
migration have been considerably facilitated. Hence the
student must be prepared to find that, for the most part,
there are no sharp divisions to mark the extent of the
various races composing the population, but that the number
of what may be termed ``transitional'' peoples is unusually
large. The second point is that Africa, with the exception
of the lower Nile valley and what is known as Roman Africa
