PHYSICAL OEOORAPUY OF ABYSSINIA. 161 



with detritus. It is evident that tlie lake must be of 

 very small geological antiquity, or it would have been 

 filled up long since. At the same time basaltic rocks 

 disintegrate as a rule much more rapidly on the surface 

 than gneiss and granite, and would therefore retain traces 

 of glacier action for a less time. But though, if the 

 whole globe was at a much lower temperature during 

 the glacial epoch, there appears no improbability in the 

 existence of glaciers even in the tropics at a height of 

 eight thousand feet above the sea,^ still the ravines 

 around Ashangi are so unlike glacier valleys that it is 

 scarcely credible that the lake can owe its origin to the 

 action of ice. 



■^ Their traces have been found by Mr. H. B. Medlicott in the Wester-n 

 Himalayas, far below this, only a few degrees further north. 



M 



