Tertiary Lands of Tigrinyaland and Semien

This is the thirteenth part of the geological description of Tigrinyaland¹ and Semien,² which has been adapted from Messrs. Ferret and Galinier’s work published in 1847.³ In this installment, the tertiary lands of Tigrinyaland and Semien will be reviewed.

We include in Tertiary terrains:

1. A set of deposits of sandstone, tripolis, clays, porcellanites, limonites, etc.
2. A set of volcanic rocks, trachytes, retinites, basalts, wackes, amygdaloids, etc.

We cannot establish divisions in these Tertiary terrains, as is usually the case. All we can say is that the whole of the sedimentary rocks probably belong to a single geological epoch, and that the volcanic rocks came to light at different successive epochs. If we were permitted to assign an age to the sedimentary terrains, we would relate them to the Miocene terrains.

All the rocks of the Tertiary terrain play a very large role in the geological constitution of Abyssinia;⁴ because from the southern limit of the Tarenta mountains⁵, they form almost the entire plateaus of the provinces of Tigray⁶, Shiré, Agamé, as well as Semien. They also crown the highest mountains of these provinces. Tertiary rocks are rarely found in deep valleys. As the ravines deepen, we see rocks of the other terrains reappear, which proves that the thickness of the tertiary terrains is not considerable, relative to that of the others.

We may divide the tertiary lands of Abyssinia into two categories:

1. Those which are formed of sedimentary deposits; and
2. Those which are formed of volcanic flows.

Reference Notes

1. Tigrinyaland was a collective name of the Midri-Bahri (modern-day state of Eritrea) and Tigray (the northernmost region of modern-day Ethiopia). The term employed for Tigrinyaland by Messrs. Ferret and Galinier in their book is “Tigré”, which had been the designation used by the Amhara rulers of Abyssinia to refer both to the Tigrinya people and the Tigrinyaland. ↩︎
2. Semien was historically the frontier province of the Tigrinya with the Amhara. However, since the reign of Emperor Susenyos, the province of Semien had been governed by members of the Amhara royalty and nobility. Following the death of Dejazmatch Sabagadis in 1831, Semien under its Amhara ruler Dejazmatch Wubbe turned from the frontier province of the Tigrinyaland to the power-center of the Tigrinyaland. This continued until the rise of Emperor Tewodros in 1855. ↩︎
3. Ferret, Pierre Victor Adolphe et Galinier, Joseph Germain (1847) Description Géologique du Tigré et du Samen. Voyage en Abyssinie dans les provinces du tigre, du samen et de L’amhara. Tome troisième. Paulin: Paris. ↩︎
4. Abyssinia is a reference to the region which encompasses the modern-day states of Ethiopia, Eritrea, Djibouti, parts of Sudan and parts of Somalia. ↩︎
5. The Tarenta mountain chain forms the eastern escarpement of modern-day eritrea, and looks down on the Eritrean eastern lowlands which are close to the Red Sea. ↩︎
6. The Tigray Province was bounded on the east by the province of Agame, on the west by the province of Shire, on the south by the River Wari, and on the north by the River Mereb. ↩︎