322 
TRAVELS IN AFRICA. 
Chap. XXXI. 
of the presence of the watery element, and which 
seemed indeed to be the only thing which was at 
present to be seen here. 
How different was this appearance of the country 
from that which it exhibited in the winter from 1854 
to 1855, when more than half of the town of Ng6rnu 
was destroyed by the water, and a deep open sea 
was formed to the south of this place, in which the 
fertile plain as far as the village of Kiikiya lay buried. 
This great change seems to have happened in con- 
sequence of the lower strata of the ground, which 
consisted of limestone, having given way in the 
preceding year, and the whole shore on this side 
having sunk several feet; but even without such a 
remarkable accident, the character of the Tsad is 
evidently that of an immense lagoon, changing its 
border every month, and therefore incapable of being 
mapped with accuracy. Indeed, when I saw to-day 
the nature of these swampy lowlands surrounding 
the lake, or rather lagoon, I immediately became 
aware that it would be quite impossible to survey its 
shores, even if the state of the countries around should 
allow us to enter upon such an undertaking. The 
only thing possible would be on one side to fix the 
farthest limit reached at times by the inundation of 
the lagoon, and on the other to determine the extent 
of the navigable waters. 
Having returned to the town, I related to the 
vizier my unsuccessful excursion in search of the 
Tsad, and he obligingly promised to send some horse- 
