544 COAST OF THE NETHERLANDS. 
vise means of extracting from rivers at flood, the whole volume 
of their suspended material and of depositing it at the same 
time on their banks, the system of cross-dikes and colmatage 
must be limited to torrential streams transporting large propor- 
tions of sediment, and to the rivers of hot countries, like the 
Nile, where the saturation of the soil with water, and the secur- 
ing of a supply for irrigation afterwards, are the main objects, 
while raising the level of the banks is a secondary consider- 
ation. 
