Discussion.
Mr. Seeley remarked that in the base of the Oxford Clay, there was what he regarded as a peculiar form of Dakosaurus, with two serrated ridges close together on one side of the tooth, and one on the other. Vertebrae of similar character to those exhibited occurred in the Kimmeridge Clay at Ely, but the teeth were rarely perfect. The author's conclusions confirmed his own surmises.
4. On the GEOLOGY of a Portion of Abyssinia*. By W. T. Blanford, Esq., F.G.S., Assoc. Roy. School of Mines, &c., late Geologist Abyssinian Expeditionary Force.
The geology of Abyssinia has been more or less examined by several eminent French and German travellers — Ruppell†, Roth‡, D'Abbadie§, Rocher d'Hericourt ||, 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 Magdala ; 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 Magdala, 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. Magdala group.
4. Cretaceous? or Jurassic? — Bedded traps, chiefly basaltic. Ashangi group.
3. Jurassic. — Antalo limestones.
2. Infrajurassic (Triassic ?).— Adigrat sandstones.
1. ? — — Metamorphic rocks.
It is unnecessary to dwell on the physical geography, which has been already amply treated by numerous able observers. It is sufficient to remark that the portion of Abyssinia traversed is the dividing ridge between the salt plain to the eastward and the Nile valley
- The present is an abstract of the observations made, which will be published
at length elsewhere.
† Mus. Senckenberg. i. 286, p. 12.
‡ Munchn. gel. Anz. 1844, &c.
§ Bull, de la Soc. Geol. vol. x. p. 121.
|| Bull, de la Soc. Geol. 1846, p. 541 ; Compt. Rend. vol. xii. p. 732.
¶ Voy. en Abyss, vol. iii.
