Chap. LIV. THE NATRON LAKE OR A'bGE. 
67 
eminence, with its snow-white surface girt all round 
by a green border of luxuriant vegetation. The sky- 
was far from clear, as is very often the case at this 
season ; and a high wind raised clouds of dust upon 
the surface of the lake. 
The border of vegetation was formed by well-kept 
cotton-grounds, which were just in flower, and by 
kitchen-gardens, where deraba or Corchorus olitorius 
was grown, the cultivated ground being broken by 
dum bush and rank grass. Crossing this verdant and 
fertile strip, we reached the real natron lake, when we 
hesitated some time whether or not we should venture 
upon its surface ; for the crust of natron was scarcely 
an inch thick, the whole of the ground underneath 
consisting of black boggy soil, from which the sub- 
stance separates continually afresh. However, I learned 
that, while the efflorescence at present consisted of 
only small bits or crumbled masses, during the time 
of the biggela, that is to say, at the end of the rainy 
season, larger pieces are obtained here, though not to 
be compared with those found in Lake Tsad, — the 
kind of natron which is procured here being called 
" boktor," while the other quality is called " kilbu 
tsarafu." A large provision of natron, consisting of 
from twenty to twenty-five piles about ten yards 
in diameter, and four in height, protected by a layer 
of reeds, was stored up at the northern end of the 
lake. The whole circumference of the basin, which 
is called " abge " by the inhabitants, was one mile 
and a half. 
