A Comparison of the ecological characteristics and social structure among three species of African great apes have been discussed. T. Kano brought the first ecological data of pygmy chimpanzees (Pan paniscus) last year. He indicated several specific features in the food habit, behaviour and grouping of this species. General remarks on this species seem to be more similar to chimpanzees (P. troglodytes) than to gorillas (P. gorilla). However, the data are not enough in comparing the social structure of pygmy chimpanzees with that of chimpanzees and gorillas. In this paper, I tried to contrast chimpanzees with gorillas especially in the habitat, food habit, spacing of unit-groups and social structure. In spite of the long-termed studies of chimpanzees, the sustaining mechanism of their social structure remains unexplained. I presumed four possible types of the structure on the basis of the data which have been collected so far. Clarifying the life history of male chimpanzees and the functions of male-bonding in unit-group of chimpanzees should be very important problems for the future studies. Recently Dian Fossey has made it clear that the society of gorilla rotates by means of kidnapping of young females by a male. Although the two societies have a common feature that they are neither matrilineal nor patrilineal, the social structure of both species is conspicuously different. If they were derived from a common ancestor, more detailed comparative studies of the ecology, behaviour and social structure should solve riddles of speciation process of both species, chimpanzees and gorillas.
The Mesozoics near Mombasa are composed chiefly of Triassic non-marine arkosic sandstone and Jurassic marine shale dipping gently southeastwards. In the latter shale facies, rhythmically interbedded sandstone (feldspathic quartz arenite) and shale are locally developed. A swarm of sole markings, mostly flute casts, are well preserved on the base of feldspathic quartz arenite, suggesting that the sandstone was deposited by turbidity currents. Detrital fragments of ortho-quartzite sandstone are commonly embraced in feldspathic quartz arenite. The paleocurrent direction indicates that the clastic material came from the northwest provenance and that the dispersal system was controlled exclusively by a lateral supply. The lateral transportation of elastics as well as the progressive change of sedimentary facies from the Triassic to the Jurassic may be interpreted as a result of the rifting of the Gondwanaland.
The active East African Rift System traverses the east African plateau over 4500km from the Afar depression to the Zambezi river. It is divisible into the eastern and western rifts. The rift system consists of some graben structures arranged en echelon: each graben also consists of en echelon normal faults. Geological phenomena in the areas of rift valleys suggest that the fracturing of the African continent had occurred under the stress field of tensional tectonics: the rifting area is apparently confined in the narrow belt along the rift valleys. We can consider the belt as a fractured region occurred between two rigid plates. The geometrical analysis of a strain ellipse had led to a conclusion that the geometrical interrelationship of en echelon fracturing depends on the angle θ between the trend of the fractured zone and the direction of horizontal extention. We can find the latter direction by using a formula α=45°-θ/2, where α is the angle between an element of en echelon fractures and its row or array: α is defined as RE-angle. The method was applied to the determination of the direction of the horizontal extension along the rift valley area (Fig. 1). The eastern rift as well as the western one is considered as an element of en echelon structure and the region which involves both their elements is regarded as the first-order structural unit in Africa. It is supposed that some deep lineament in the lower part of the lithosphere might have controlled the trend and space of the structural unit since 2000m.y.
In this short paper on Indians in East Africa, their historical contributions to the development of the East African countries; the social, economical and political implications of the Indian immigration during the Colonial Period and the resulting problems of conflicting demands of an emerging plural society are dealt with very briefly, touching only a few relavent features which have a direct bearing upon a better understanding of this controversial and much misunderstood minority.