According to topschoolsintheusa, the geological formations that make up the soil of Ethiopia are the following:
1. The basement of archaic crystalline rocks (granites, syenites, gneisses and phyllites) which are considerably folded and emerge in a strip on the eastern slopes of the Tigrè plateau, of the ‘Amhara (Amḥārā, Amārā), of the Goggiam up to the borders of the Scioa. More widely these rocks extend on the western slope, especially in the Walleggà (Wållaggā) (where they contain considerable concentrations of auriferous quartz) from the plains going up into the valleys that furrow the plateau, such as those of Setit-Takkazè and Abai. Other extensive outcrops are observed in the extreme south of Ethiopia, in S. del Lago Margherita, between the mouth of the Omo and the upper Daua.
2. The “sandstones of Adigrat”, so called by the city of the same name, in Tigrè. They are coastal or continental deposits, formed at the expense of the underlying crystalline base and represented by red, yellow, brown or variegated quartz sandstones, which due to their position are considered equivalent to the Triassic and perhaps in part to the Liassic. They rest horizontally on crystalline schists both in Adigrat and in the upper Takkazè basin, both in the Abai valley and (apparently) in the Hawash valley (Ḥawāsh).
3. The “limestones of Antalo (Ḥenṭālo)”, containing a rich Jurassic marine fauna, rest in their turn on the sandstones in a large slab near Macallè (Maqalē, in Tigrè), and come back to surface in the same position on both sides opposites of the Abai valley, on the northern side of the plateau of Harar and then broadly in the bottom of the valleys that descend from this towards Uebi Scebeli and Juba in Ethiopian Somalia.
4. The “upper sandstones” of Antalo and Abai, little known, perhaps, represent the Lower Cretaceous: certain Cretaceous sandstones emerge in the Arussi plateau, where they are associated with marine limestone deposits in the Gillett mountains and near Abunas (Abunās).
5. The Cretaceous limestones with marine fossils of the Aptian, perhaps also of the Barremiano, emerge on the Arussi plateau in Abunas and also in the valley of the middle Uebi Scebeli, between Faf and Barri and in the Sciaveli.
6. The Tertiary sector is not represented by marine deposits within the borders of Ethiopia, except perhaps in the Ethiopian part of the Somali plateau (seeogaden), where it is possible to extend the Eocene deposits emerging in the finite British Somalia. The deposits of gypsum and salt, which internally border the Danakil depression, exploited in Dallol also for their potassium salt content, as well as certain lake deposits around the Galla lakes, in southern Ethiopia, must be ascribed to the recent Tertiary and Quaternary sectors. Also at N. del Lago Rodolfo and in the Omo valley were found layers with remains of mammals attributable to the Pliocene: Elephas and Dinotherium, associated with Hippos and Crocodiles. Pliocene and Quaternary are likewise, at least in part, the lateritic continental deposits, etc. that cover the plateau for large stretches, and the travertines of the springs.
7. The volcanic formations are widely extended in Ethiopia and are generally divided into two series: the Trappica series, consisting of dolerites and basalts with liparitic dikes and intercalations of tuffs and breccias, probably goes back to the Cretaceous and the ancient Tertiary, and forms the great Abyssinian plateau, both in Tigrè (Adua) and in Amhara, where it reaches the highest heights of the whole region in Semien, both in Scioa, and finally in south-western Ethiopia (Caffa) and in the highlands of Harar, of the Galamo, Sidama, M. di Laggio, etc. The “Aden series” it is made up of basalts and trachytes of the Pliocene and Pleistocene ages, interspersed with the sedimentary rocks of the Eritrean lowland, and connected with numerous well-preserved volcanic systems, and in part still active or barely quiescent. Among the most notable are the Afdera nel Birù, apparently active in 1907, the Dofane, the Erta-alè, the Dabita and the Aielù in the middle Hawash valley, the Fantallè in Ethiopia and the Zuqualà (Zequalā; m. 2920) to S. di Addis Abeba, with crater-lake, and many others. These recent or very recent volcanic formations almost entirely occupy southern Danakil, the Hawash valley, the area of the Galla lakes, thus rejoining the volcanic regions of Lake Rudolf and those of the great trench of the Kenyan Colony.
This volcanic activity, even recent and very recent, is to be placed in relation with the tectonics of the country, which would mainly result from systems of fractures: one of these, with a N.-S. direction, would have determined the formation of the eastern slope of the plateau and the great danakil pit; the other, directed ENE.-OSO., that of the Harar escarpment: from the point of convergence of the two systems, which coincides with the Hawash groove, the fractures proceed parallel with a NE.-SO. direction, generating closed depressions of the Galla lakes, up to the extreme N. of the Rodolfo Lake, where the great sinking trench of East Africa begins (see Africa: Geology).