404 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 23, 



Ashdngi group of traps. — The lower subdivision consists entirely 

 of doleritic rocks. 



Amygdaloidal basalts prevail, associated with volcanic ash or 

 breccia. The beds are usually disturbed, and frequently inclined at 

 considerable angles. 



The only place where the traps of this group were seen resting on the 

 lower rocks was in the Mishek valley, where they are based upon the 

 upper sandstones and conglomerates of the Antalo limestone. The 

 section is obscure ; but there appears to be unconformity. 



In mineral character there is a marked resemblance between the 

 rocks of this group and those of the great trappean formation of 

 "Western India. 



Mdgdala group of traps. — These consist partly of doleritic, partly 

 of trachytic flows and ash breccias, the former predominating in 

 general, but the latter very largely developed, especially in the 

 higher portions of the group, and frequently occurring in beds of 

 great thickness, weathering into immense vertical scarps, to which 

 the peculiar profile of the higher peaks is largely due. To these 

 thick beds the Abyssinian chieftains are indebted generally for the 

 almost impregnable hiU forts which form so remarkable a feature of 

 the country. Agreatproportionof the beds are brecciated; and many, 

 both brecciated and non-brecciated, are highly columnar. Some sedi- 

 mentary rocks were found interstratified in the gorge of the Jidda 

 river and near Magdala, but no fossils were detected in them. 



These beds in Waag and Lasta differ from the subjacent group in 

 being almost perfectly horizontal. To them I am disposed to refer 

 the horizontal beds of the Harat range, west of Adigrat ; and pro- 

 bably the lofty ridges of Simen (or Samen), west of the Takkazzye, 

 are, in part at least, of the same age. If this be the case, this group 

 of beds must once have covered the greater portion, if not the whole 

 of Northern Abyssinia, and have been removed by denudation, 

 which in all probability was entirely subaerial. Their detritus, 

 spread over the valley of the Nile, doubtless accounts in a great 

 measure for the fertib'ty of Egypt. 



It is difficult to say whether the singular trachytes of Senafe, 

 which are probably identical in origin with the well-known pecu- 

 liarly formed ranges around Adowa, belong to the same group. 

 They may be accumulations around the ancient volcanic nuclei. 



Nothing positive can be asserted as to the exact geological age of 

 either group of traps. The great outbursts which have covered 

 Western India are Upper Cretaceous* (prenummulitic) ; and the 

 volcanic rocks so largely developed on the south coast of Arabia f 

 are very possibly, in part at least, of the same age. There may be a 

 general connexion between all these enormously developed series of 

 lava-flows, without their being absolutely contemporaneous. Their 

 enormous mass and their persistent horizontality, in many instances 

 over large areas, entitle them to greater attention than they have 

 over received. 



* See Memoirs of the Geological Survey of India, vol. vi., Art. 3. 

 t Carter, Journal Bombay Br. Eoy. As. Soc. vol. iv. pp. 28, 91, &c. 



