T he geology of Abyssinia has been more or less examined by several eminent French and German travellers—Rüppell† Roth‡, D'Abbadie§ Rocher d'Héricourt‖, and especially Ferret and Galinier¶ but still there is very much left to be ascertained before the geological structure of the country can be said to be thoroughly known. The peculiar circumstances under which the late expedition was carried out limited the area of observation to the line of march from Annesley Bay to Mágdala; but along that line and, in some instances, in its immediate neighbourhood a very fair opportunity was afforded for judging of the general geological structure of the country, and of the relations of the most important rock-systems to each other. Roughly speaking, after passing the Posttertiary or late Tertiary volcanic rocks and alluvial deposits of the coast, the formations met with presented a regular ascending series as far as Mádala, where the rocks belong to the highest group, with the exception of recent alluvial deposits, met with on the highlands. After the departure of the expeditionary force, a few additional observations were made in Northern Abyssinia about Massowa, the Bogos country, and the Anseba valley. The following are the formations which have been noticed in Abyssinia, in descending order:— 7. Recent.—Soils of the highlands. Alluvial deposits near the coast. 6. Posttertiary?—Aden series of volcanic rocks. 5. Tertiary? or Cretaceous?—Bedded traps, basaltic and trachytic. Mágdala group. 4. Cretaceous? or Jurassic?—Bedded traps, chiefly basaltic. Ashángi group. 3. Jurassic.—Antalo limestones. 2. Infrajurassic (Triassic?).—Adigrat sandstones. 1. ?—Metamorphic It is unnecessary to dwell on the physical