GEOLOGY OF COVyiRY JROUXI) SEXATE. 41 



This ridge joins the Seuafe rocks, the remarkable crags 

 already referred to (see Plate I.), which are immediately 

 west of the position occupied by the British camp during 

 the campaign. The rock composing these hills is softer 

 and more earthy than that of the other rises, and the 

 resemblance to an argdlaceous sandstone is most remark- 

 able. The form of these hills, and of those near Adowa, 

 which are visible in the distance, and may probably be 

 of the same rock, is so similar to the immense hummocks 

 which generally occur in granite and granitoid gneiss, 

 that they might easily be mistaken at a distance for the 

 latter formation, as they were at the first sight by Colonel 

 Phayre and the pioneers of the army. On a nearer 

 approach, their resemblance to sandstone is greatly in- 

 creased by their brown colour. Another point in which 

 they simulate sedimentary rocks is in being traversed by 

 dark ferruginous streaks and bands. 



The hill immediately east of Senafe is of a rather 

 different trachyte, greyer and more crystalline. It rests 

 upon a thin bed of sandstone, and the latter upon 

 metamorphics, so that the volcanic rock is in this case 

 evidently a flow. As will be seen presently, the same 

 is the case further south. This hill affords an excellent 

 example of the complete unconformity between the 

 trachyte, even when distinctly occurring as a flow, and 

 the sandstone ; for although tbe latter rock upon the sides 

 of this hill nowhere exceeds fifty feet in thickness, the 

 next lull to the north, one of the spurs of Sowera, only 

 separated by a valley not half a mile broad, is entirely 

 composed of sandstone, and is higher than the trachyte 



