The natural vegetation of Ethiopia has been classified into 12 types by Dr. Mooney. The author collected some plants of five types of this area and described the vegetation in details based on his own observations Especially, explanations call attention in regard with such important drugs produced in this country as gum arabic, frankincense, kosso and khat, concerning the following aspects: botanical origin, habitat, quality, commercial form, uses, etc.
I. Geological and geophysical characteristics of the African Rift Valley are summarized in this article. The African Rift Valley forms a part of a world-wide fracture zone, extending from the Red Sea and the Gulf of Aden to the Indian Ocean to link up with the midoceanic ridges, whose medial part are often occupied by the rift structure. Various independent evidences suggest the tensional origin of the rift valleys. The pattern of alkaline igneous activity shows a remarkable correspondence to the rift pattern, and these are probably ascribed to the same major process. The occurrence of the carbonatites is the most striking petrological feature found in the region of the Rift System, and the active volcano Oldoinyo Lengai near the Kenya-Tanzania border, one of the outstanding examples of this activity, yielded lavas of high alkali carbonatite in its last eruption. Emphasis was given especially on petrological and geochemical properties of carbonatite and other volcanic rocks in the African Rift Valley. II. The Olduvai Gorge, located at the transitional area between the eastern Rift Valley and the central African peneplane, became famous for the discoveries of the oldest human bones named zinjanthropus boisei by Leakey. At the Gorge the Pleistocene sedimentaries, divided into the Beds I-V in ascending, consist of the alternation of lake deposits and eolian ones, which suggest the repetitions of wet and dry climates during the Pleistocene. The Balbal depression at the eastern extremity of the Gorge and several faults cutting the Beds I-IV are oriented in NE-SW direction and reveal a movement of the Rift Valley at that time. Recently, K-Ar age of the Bed I is determined and the problems on the correlation to the international standard and the Pleistocene chronology of east Africa are debated. After the re-examination of the stratigraphy and the paleontology of the Beds I-IV, and the Pluvial-Glacial correlation, we come to the conclusion given in Table 5.
Each of these religious beliefs shares in the same functions as follows: explanation of various misfortunes; moral sanction; and maintenance of a social structure. Besides each of them stands in a complementary relationship with one another in its functions indicated above. In many societies sudden death or serious diseases are thought to be caused by witches. Whereas ancestores give misfortunes of less severity, for ancestors do harms only when their descendants fail to observe their traditional way of living or their duties towards their kinsmen or ancestors, so that the descendants may correct their misbehaviors. Witches are generally associated with such character that tends to bring troubles into human relations. In this way people succeed in rejecting and banishing the persons of too much envious, competitive or uncompromising character from their society. Consequently witch-craft belief regulates the relationship between co-wives, neighbors and co-workers. Ancestor worship, on the contrary, gives sanction upon the relationship between a senior and a junior member of a kin group. Unless a son obeys his father's command, misfortunes fall upon the son, for the irritated father would not sacrifice to the ancestor in favor of his son. Witchcraft belief contributes to the maintenance of the solidarity of a group in two ways: it gives a safe way of dissolving frustrated feelings of the members which are created by conflicts that institutions and systems of the society might inevitably produce; and it prohibits the accusation of a witch within an intimate, cooperative kin group in which a collaborate relationship should be retained lest the fundamentally required stability of the society as a whole should not be broken. On the other hand ancestor worship considerably reinforces the authority of heads of kin groups of various size. The right of giving sacrifices to the ancestor is ascribed only to the heads, and thus the rest of the members must depend upon the heads in order to secure their ancestor's favor. In these ways the solidarity of the cooperative relationship among the members of a society is effectively strengthened and maintained by witchcraft belief and ancestor worship.
This report is based upon the data collected by a social anthropological field work at the village of Mangola in the Mbulu District of the north-central part of Tanzania. The field work was carried out from May, 1963 to April, 1964 when the author was enrolled as a member of anthropological team of Kyoto University Africa Scientific Expedition. The village of Mangola is a “compound society, ” consisting of agricultural Bantu, agrico-pastoral Mbulu, pastoral Mangati, and hunting-gathering Tindiga. The author tries to illustrate the social functions of “tribe” by investigating marriage systems, political systems, life histories of migrating individuals (the migration is called tembea in Swahili), and so on. He found out that “tribe” in this area is not isolated society but rather fluid and open.