Language: French with 3-page English abstract
The area where the authors have studied the formations older than those presumed to be of the same age as the Katanga group comprises both Ruanda-Urundi and the mountaneous region of Belgian Congo bordered to the East by the Kivu-Ruzizi-Tanganyika line, to the North and the South by the parallels of 1°30' and 4°30' and to the West by the meridian of 28°30'. The study of previously published documents showed that the various formations distinguished by different authors had been unproperly correlated and that their stratigraphy was not known with sufficient accuracy. By detailed sections on 1/50O00 (or on a larger scale) interconnected by a guide horizon we have tried to establish the relationship between the rocks of Southern Urundi, of South-West Ankole and those of the Itombwe syncline.