THE BLUE NILE. 49 



in fish, cliiefly cyprides of a different species from those of the Nile. A kind of 

 bivalve also occurs, resembling the oyster in appearance and flavour. 



Issuing from the lake at an altitude of 6,200 feet, the Abai flows at first towards 

 the south-east, forming a first fall near Woreb, 5 miles below the outlet. Expanding 

 lower down to a width of about 650 feet, it winds along through shad}^ fields to the 

 Tis-Esat, or Alata Falls, where it is suddenly precipitated from a height of over 80 

 feet into a j^awning chasm shrouded in vapour. In the centre of the cascade stands 

 a pyramidal rock surmounted by a solitary tree constantly agitated by the breeze. 

 Immediately below this spot the Abai plunges into a winding gorge, at one point 

 scarcely 8 or 10 feet wide, crossed by a bridge of Portuguese construction. Some 

 30 miles farther on it is crossed by another bridge, the central arch of which has 

 given way, its broken fragments forming a reef amid the tumultuous waters under- 

 neath. The whole distance between these two bridges is little more than a succes- 

 sion of falls and rapids, with a total descent of at least 2,000 feet. Alpine masses 

 tower to the right and left above the gorge, which seems to have no outlet. But 

 after describing a complete semicircle round the Abyssinian plateau, the Abai 

 emerges on the plain in a north-westerly direction. The fall in this vast circuit is 

 altogether over 4,000 feet, while throughout its lower course, terminating at the 

 Khartum confluence, the incline is scarcely perceptible. Here it winds in gentle 

 meanders between its alluvial banks, which are constantly yielding to the erosive 

 action of the stream. 



During the dry season the Bahr-el-Azraq diminishes in volume downwards, and 

 in many places may be easily forded. For more than half the year the Yabus and 

 Tumat, its chief tributaries from the south, are apparently merely dried-up wadies, 

 although the water still percolates beneath the sands. The Rahad, or Abu-Ahraz, 

 also one of its large eastern affluents, which rises on the west slope of the Abyssinian 

 border range, is completely exhausted for a long way above the confluence before 

 the wet season. But from June to the middle of September, when the rain falls in 

 torrents on the mountain slopes, its vast bed overflows its banks, supplying abundant 

 water to the cultivated riverain tracts. The Bender, however, another river rising 

 in Abyssinia, appears to be perennial. Nowhere else would it be more useful or 

 more easy to construct reservoirs and control the discharge than in this hydro- 

 graphic basin, which at the confluence of the two great arteries at Khartum 

 stands at an altitude variously estimated at from 1,250 to 1,450 feet above sea- 

 level. 



The northern as well as the southern section of the Abyssinian plateau is also 

 comprised in the Nile basin. But here the affluents of the great river rise, not on 

 the western slope, but in the very heart of the highlands, close to the range forming 

 the water-parting between the Mediterranean and the Bed Sea. The Takkaze, 

 main headstream of the whole Atbara hydrographie system, has its source at an 

 elevation of nearly 7,000 feet, and flows at first westwards, as if to fall into Lake 

 Tsana. But the gorge through which it descends between its crystalline schist 

 walls rapidly attains a level far lower than that of the Ethiopian uplands. At the 

 point where the river trends northwards it has already fallen to an altitude of con- 



4 — AF. 



