356 EFFECTS UPON ABYSSINIA. 



to the required depth, have been thus gradually 

 opened into, and as this is naturally aided by the 

 steep fall of the scarp, denudation goes on rapidly 

 when the first inclination towards the Hawash has 

 been given to the stream, that had previously 

 meandered upon a nearly level plain. In this 

 manner I contend, that the valley of the Airahra, 

 between the narrow ridges of Ankobar, and the 

 edge of the table-land at Tchakkah, has been 

 acted upon, and that the waters falling to the west 

 of Ankobar, and which now flow into the Hawash, 

 were formerly conducted to the Jumma, and so to 

 the Abi, when the two elevated points mentioned 

 were continuous, as they most certainly have been. 

 The geology of Abyssinia also favours these 

 strange alterations of its own face ; for it is 

 composed almost entirely of volcanic rocks, easily 

 decomposable, the operation, in fact, scarcely 

 requires the aid of water to occasion it ; for the 

 atmosphere alone crumbles the hardest rocks, in 

 the course of one year, into a stratum of loose earth ; 

 and water appears to be merely the carrying agent, 

 to remove the soft soil, and expose a fresh surface 

 to the action of the air. It is this which adds so 

 considerably to the fertility of the Argobbah 

 counties, situated on the scarp of the Abyssinian 

 table-land ; for every fresh year, virgin earth of the 

 most fertile capability, is offered spontaneously, 

 for the benefit of the cultivator, to whom, in this 

 situation, the use of manure is unknown. 



