ItECmT FORMATIONS. 197 



bouring hills, and probably formerly existed over the 

 plain, but have been removed by denudation. As no 

 thickness of soil is generally found upon the limestones, 

 that which covers the Buya plain can scarcely be derived 

 from them. 



This black soil of Abyssinia, moreover, appears to be 

 only derived from the disintegration of dolerites, not 

 from trachytes. The two are usually intermingled, so that 

 the soil upon the hills is derived from both : but on the 

 plateau of Dalanta and Wadela, between the Takkazzy^ 

 and Jitta rivers, the route from Santara to Gaso traverses 

 a region of trachytic rocks alone, and the soil is light- 

 coloured ; whilst from a little south-west of Gaso to the 

 Jitta, and again on the plateau between the Jitta and 

 Bashilo, the rock is basaltic and the soil black. Of course 

 it will be found that black soils are met with elsewhere ; 

 any soil which accumulates under marshy conditions is 

 usually dark-coloured : but the interesting circumstance 

 is the constant association of a peculiar soil, dark in 

 colour, and well suited for the cultivation of cereals and 

 cotton, with basalts and other doleritic rocks. 



Flakes of Obsidian. — In many places, small chips of 

 obsidian are found scattered about, frequently far from 

 any locality where the rock is met with in situ. From 

 their peculiar form, and the nature of the facets, there 

 can be little or no hesitation- in attributing these to 

 human manufacture. They are evidently the chips 

 struck off in the process of manufacturing stone imple- 

 ments, and are perfectly identical in shape with similar 

 chips found extensively in Europe and India. 



