MBTAMOliPHICS. 165 



In the region around Senafd and Adigrat no very 

 granitoid tract was observed ; the beds for the most part 

 do not appear to be highly crystalline. Probably in 

 Hamazen, north of Agam^, the same is the case, as the 

 country is said to be remarkably level. But at Keren, in 

 Bogos, and again about forty miles further to the north- 

 east, near Af Abed and Eairo, in Habab, the rocks are 

 highly granitoid, and even porphyritic, containing large 

 crystals of felspar. For the most part all traces of folia- 

 tion have disappeared, as is usual in such formations, and 

 the only structure, apart from the crystallization, which 

 can be detected, is the general direction of the bands of 

 rock, often rising into hills. The strike of these corre- 

 sponds approximately with that of the foliation in the 

 gneiss of the neighbourhood, and every here and there, 

 throughout the area composed of granitoid rocks, the 

 gneissic structure may be traced by searching for it.^ 



^ But a few years ago such granites as that above described were looked 

 upon as intrusive rocks, and it was even supposed that the alteration of the 

 metamorphic formations in their neighbourhood was due to them. This view 

 is scarcely yet completely exploded amongst geologists, partly, perhaps, be- 

 cause so few have opportunities for seeing large areas of metamorphic rocks. 

 It is, therefore, well to point out every instance which can be adduced tending 

 to prove the complete similarity in origin of the crystalline non-foliated rooks 

 and of the laminated mica-schist and gneiss. The appearance of the grani- 

 toid tracts in Abyssinia is precisely the same as in India, where metamorphic 

 rooks are developed on the most extensive scale, and cover nearly half the 

 peninsula south of the Gangetic plains. With their great opportunities for 

 observation, I believe there is not a single geologist on the Indian Survey 

 who questions the identity in origin of the foliated and non-foliated rocks. 

 The two pass into each other everywhere. The granitoid masses evidently 

 owe their more crystalline condition either to a difference of chemical consti- 

 tution, original or produced subsequently to their deposition, which rendered 

 them better adapted to the development of the minerals constituting granite 



