1 78 GEOLOGY. 



no great height in general, along the sides of the valleys, 

 all of which contain streams, and have a striking cha- 

 racter, due to the nearly perpendicular sides and the 

 narrow flats covered with grass and bushes at the 

 bottom. Except in the valleys, the soil is poor, and 

 only low scattered scrub occurs on the hills. The latter 

 are a rolling upland, very distinct from the plateaux of 

 sandstone or the terraced ridges and rounded hummocks 

 of the trap. 



Where the Antalo group rests upon the Adigrat 

 sandstones at Mai Dongolo, the two formations are 

 apparently conformable. Whether they are so through- 

 out it is impossible to say ; there was not time for 

 sufficient exploration of the country to determine the 

 question. The non-occurrence of any limestone upon 

 the sandstones of Adigrat and Senafd is opposed to the 

 idea of the two being conformable. A similar doubt 

 rests upon the relations of the lower series of traps with 

 the limestone, as will be seen in treating of the volcanic 

 rocks in the next section. 



This want of opportunity for determining precisely 

 the relations of the limestone to the rocks above and 

 below is the more to be regretted, as the present is the 

 only group which has yielded fossils. Organic remains 

 abound in it, as so frequently occurs amongst limestone ; 

 but in general they consist only of oysters, half-defaced 

 casts of bivalves, and spines of Echinodermata, none 

 of which are of much value for affording determinations 

 of age. For a long time it seemed to me as if similar 

 ill-preserved specimens were the only fossils to be found, 



