402 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 23, 



to the west, that the descent in the former direction is abrupt, in the 

 latter gradual, and that from Senafe, where the force first reached 

 the highlands, lat. 14° 40' N., to south of Antalo (about 13° 10') the 

 country is comparatively entirely open, with but few ascents or 

 descents of importance, of an average height of nearly 8000 feet 

 above the sea, and composed principally of metamorphic rocks, 

 limestone, and sandstone ; whilst from a few miles south of Antalo 

 the road traverses a succession of passes from 9000 to 10,500 feet 

 above the sea, and the only rocks seen are volcanic, belonging to 

 two distinct groups of bedded traps. 



Metamorphic rocks. — These form the base of the greater portion 

 of the Abyssinian plateau, if not^^of the whole. As usual, they vary 

 to a very great extent in mineral character and degree of meta- 

 morphism, some being highly crystalline and even porphyritic 

 granites, others mere slaty schists still exbibiting the original 

 bedding. Wo reason was observed for dividing them into several 

 groups ; but it is possible and even probable that more extensive 

 study would justify such division. 



The direction of the foliation is very constant. Prom Af Abed in 

 Habab (lat. 16° 10' N.) to about 25 miles south of Adigrat in Tigre 

 (about 13° 50'), upwards of 150 miles, it rarely diverged more than 

 a few degrees from due north and south. The dip is not quite so 

 constant ; but it is usually nearly vertical, though exceptions, pro- 

 bably due to disturbance, occur, at the base of the outer ranges es- 

 pecially. In the Anseba valley and around Keren in Bogos the 

 strike of the foliation changes to north-east and south-west. 



This strike is clearly due to cleavage, and not to original bedding ; 

 for in some very slaty rocks near Senafe the original bedding was 

 observed crossing the foliation. The same might also have been 

 inferred from the regularity of strike and high dip. 



This strike corresponds with many important features of the 

 country, such as the north and south ravines which cut through the 

 outer ranges and tend to so great an extent to facilitate access to 

 the highlands. 



Adigrat Sandstone. — This is a massive sandstone, generally white 

 in colour, of considerable thickness, which caps many of the higher 

 ranges in Agame, and the steep white scarps of which are perhaps 

 the most striking natural feature in northern Tigre. It is in places 

 about 1000 feet in thickness, but usually less. No fossils have been 

 found in it, and its age is uncertain. Mpssrs. Eerret and Galinier 

 class it, though with doubt, as Tertiary ; but as I found it to all ap- 

 pearance distinctly passing beneath the oolitic limestone of Dongolo 

 south of Adigrat, it is evidently of older date. It is far from clear 

 whether the limestone rests conformably upon it ; probably it does 

 not do so, as otherwise it is difficult to understand the total absence 

 of the limestone about Adigrat and Senafe, where trap ^lone rests on 

 the sandstone. It is possible that the coal-bearing sandstones 

 known to exist west of Lake Dembea may belong to the same 

 series as the Adigrat sandstone. 



The Adigrat sandstone always rests on metamorphic rocks. It is 



