The African rift valley, one of the most outstanding topographic and geologic features of the earth's crust, is also accompanied with many peculiar geophysical phenomena, that is, anomalies of gravity, heat flow, and geomagnetism, which suggest the connection to the earth's interior. Based upon many studies hithertio made, the hypothesis of mantle convection can most adequately elucidate the peculiarities of the rift valley. As it is well known, unit cell of the convective current causes a horizontal tensional stress at the bottom of the crust situated on the lateral flow, and a compressional stress at that on the downward flow. Therefore, if it is permissible to consider that the rift valley has been torn away by the lateral tension attributed to the mantle convection, the genetical relationship to the compressional area should be clarified. Judging from the geohistorical studies, the African rift valley commenced with the gentle up-doming movement in the Mesozoic era. It followed the rifting with volcanic actions at the Tertiary period, which feebly continued up to the recent. Namely, it coincides with the Alpine orogenic cycle in age. The problem is thus focused on the point that although the Alpine orogenic belt, which is undoubted compressional zone at that time, is oriented in E-W direction from the Mediterranean coast to the Himalayan undulation, the tensional zone of the African rift valley has N-S trend on the whole. Judged by the geotectonic studies, the crustal framework of the Africa is composed of three continental cores implying the oldest Precambrian rock in the world, such as west Africa, Congo, anb Kalahari cratons, which are joined with the latest Precambrian—earliest Palaeozoic Mozambique belt. All of them consist of metamorphic rocks, however, the rocks of continental cores may be harder and stiffer than those of the Mozambique belt. Furthermore, the extention of the belt is trending nearly N-S direction in East Africa, and the interior structure of the belt also takes the same direction in general. It is of the present writer's opinion that these factors, tectonic elongation, interior structure, and less hardness of rocks of the Mozambique belt controlled the disharmonic trend and location of the African rift valley against the Alpine orogenic belt.
More than six hundred African languages (mostly tribal languages) have been hitherto reported and examined by Europeans, some of whom tried the classification of those tribal languages based on either regional or linguistic similarities. But any classification presented by them does not prove to be final, partly because regional similarities can not be wholly depended upon particularly in Africa where various tribes have been constantly moving and mixing without having influence on each other and without forming local colour, and partly because linguistic similarities can not be also wholly depended upon in case that those similarities are not justified by means of tracing the movement in the past of the related tribes and thus lined with historical facts. It is possible that the two tribal languages located side by side and regarded similar in respect of syntax or grammar never belong in reality to the same language family, and so those classifications based on either legional or linguistic similarities can not be more than hypothetic. Though this sort of hypothesis is useful, I agree, not only to the linguistic but also to the historical research, I am afraid it can not be duly adapted to the present-day African languages now having the role as the languages in the societies: in the past time when the tribes were isolated from each other the tribal languages were used only in the limit of separate tribes, but now when the tribes are incorporated into society —either rural or urban, local or national—, they are used in the society composed of several tribes. To clarify the structure of such a complex language society, the above-mentioned traditional classification seems unsatisfactory, and some new method of grouping, maybe sociological and phenomenal, is required. The present language society in Africa has three coexisting attributes, that is tribal, local, and national. By those three qualifiers I mean tribal language, lingua franca developed from some tribal language, and European language once used by colonial governor, and ofthose three regions —tribe residence, local society and nation— the secondseems to be the most important, as this region has a unity guaranteed by the former kingdom so proudly reminded by the natives and it is not so artificial as the nation. For the most part the present nations in Africa lack the unity and they are rather federal from the cultural point of view. Though the regions covered by such lingua franca as Swahili, Hausa, Lingala, etc. have, to a certain degree, the unity not solely linguistic but geographical, historical, economical, the importance of the component tribal languages in those regions can not be negligible. A lingua franca and a tribal language have their roles separately, and these roles correspond to the structure of such local region determined by the whole history of the component tribes. This structure or the layers due to those tribal activities is just the research object of linguistic sociology, which I am going to apply to the region around Stanley Pool in Bas Congo. This method of grouping African languages may be too phenomenal, but I believe it is more efficient to understand present-day Africa as it is. Moreover I never deny a contribution the traditional classification will make to such a grouping of African languages.
The aim of this investigation is to make clear differences between the oil palm production of West Africa and that of South-East Asia. In the most case, the oil palm is cultivated in West Africa by the peasant-type cultivation, while in South-East Asia, by the plantation system. From this fact, it may be considered that the quality of oil and kernel produced in South-East Asia is better than that of West Africa. Nevertheless, the oil palm trees cultivated in South-East Asia being older than those of West Africa, they must be replaced by new ones and fertilized efficiently.
This paper is based on partial materials which were collected by myself during my anthropological research from 1964 to 1966 at Ujiji; an African town in the western region of Tanzania. It aims to analyse the social stratification and the occupational differentiation of this town Ujiji. I. Presently we can observe clearly the existence of the following six stratified groups. (1) Swahili people: Islamic Africans. (2) WAHA-tribes men: Manual workers from the north-western region of Tanzania. (3) WAGENI: Wageni means the guests in the Swahili language. Mostly they are sent here as government employees from other regions of Tanzania. (4) Arabians: At the beginning, they had arrived here in 19th century as traders of tusks and slaves. Now most of them are merchants. (5) Indians: They had arrived here in the beginning of 20th century as traders or employees of Germans. Now most of them are merchants. (6) Europeans: Some European officers had stayed here during the era of colony. After independence, a few missionaries live in the suburban area. II. Swahili people function as a core group at Ujiji. Originally they are from many tribes of Congo (Kinshasa) and Tanzania, but now form a transtribal group as Islamic Africans. Since the beginning of 20th century, they had made WAHA-tribesmen subordinate as a lower caste like that under the influence of the Arabian slavery. III. Through the social development for one hundred years in Ujiji, we can recognize the fact of occupational differentiation among African inhabitants. In the case of modern city, this differentiation works as a socio-economic factor which causes social stratification. But at Ujiji, other socio-cultural factors dominate over it, namely, religious, racial, tribal and cultural traits from the above-mentioned six groups as social strata of this folktown. This phenomenon is a social characteristic feature of Ujiji, a town, originated from the multitribal regional society.