164 GORGES AND RAVINES. 



as previously stated, inland perpendicular cliffs, 

 especially in friable rocks, are inclined to remain 

 perpendicular even in our temperate climate, as 

 the denudants that principally act on them are the 

 wind and heat; and if wind can act so effectively in 

 this country, what would it not be able to perform 

 in those countries where the heat is excessive and 

 hurricanes common. 



It has previously been pointed out that some of 

 the ravines in larconnaught seem due nearly solely 

 to the contraction of the rocks, and greater effects 

 might be expected in a country like Abyssinia, 

 where the rocks are exposed to a tropical heat ; and 

 if at the first these deep narrow gorges were thus 

 opened, rain and rivers would deepen them, while 

 the nearly perpendicular character of their sides 

 would be preserved principally by the action of the 

 wind, denudation from above being prevented by 

 the luxuriant growth of tropical vegetation, or by 

 the capping of igneous rocks. Of debris to be 

 carried away by the streams there ought to be very 

 little in addition to that abraded off the bottom of 

 the gorges, as nearly all of what was denuded by the 

 winds would be borne away upwards to be scattered 

 over the high lands. 



The contraction of the rocks would account not 

 only for the formation of the ravines, but also for 

 lake-basins like that of Lake Ashangi, without the 



