1869.] blanford abyssinia. 401 



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. Yertebrse 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 GrEOLOGY of a Poetion of Abyssinia*. By "W. T. Blan- 

 FORD, Esq., F.G.S., Assoc. Eoy. 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 — Riippellf, Roth J, D'Ab- 

 badie§, Rocher d'Hericourt ||, and especially Ferret and Galinier^ ; 

 but still there is very much left to be ascertained before the geo- 

 logical 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. Eoughly 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 ex- 

 ception 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. Mag- 

 dala 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 sufii- 

 cient to remark that the portion of Abyssinia traversed is the divi- 

 ding ridge between the salt plain to the eastward and the Nile valley 



* The present is an abstract of the observations made, which will be pub- 

 lished at length elsewhere. t Mus. Senckenberg. i. 286, p. 12. 



\ Miinchn. gel. Anz. 1844, &c. § Bull, de la Soc. G-eol. vol. x. p. 121. 



II Bull, de la Soc. Geol. 1846, p. 541 ; Compt. Eend. vol. xii. p. 732. 

 ^ Voy. en Abyss, vol. iii. 



