~ 
4 
306 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
than others and these, on the Blue Nile, for example, already show 
through their difference of habits, compared to their congeners of the’ 
upper Dinder, an adaptation to the changing conditions. 
The entire country up to the Abyssinian border is monotonously 
flat, and covered largely with an open forest of thorn trees among 
which the red-barked gum-arabic tree is conspicuous. A very few 
(aa resp 
SE1 Mesharat ‘ahs 
Rei Abad / 
UZ Oru, ‘& “s ‘ 
Yomi; 4; g, 
Fig. 1.— Sketch map of the Blue Nile Valley. 
small and isolated hills or ‘gebels’ project here and there abruptly. 
from the plain, and alone break its monotony. The Blue Nile has cut, 
a channel through this broad plain, but so steep are its banks for many | 
miles in succession, that access to the water is difficult, and hardly P| 
be obtained except where gullies, cut down during the torrential rains _ 
r 6URhee 
