deposited on the land. Owing to various circumstances, 

 as for example, the position of the basin itself, whether 

 at the beginning or end of a section, the position of the 

 land in the basin, the nature of the flood, the figures given 

 can only be regarded as an approximation, but at the 

 same time they are sufficiently accurate for ordinary 

 purposes. Again it is difficult to estimate the quantity 

 of water which, on an average, enters the various basins, 

 as, owing to the fact that it is continually passing through 

 them even though they are full, the actual capacity of a 

 l);i si n does not accurate!)' represent the quantity of water 

 which has had the opportunity of depositing its mud. 



As a general rule, we may state that the basins receive 

 about 5.000 cubic metres of water per feddan, and on the 

 assumption that 130 parts per 100.000 are deposited, 

 each feddan receives about 6|- tons of sediment. The 

 weight of an ordinary clay soil to a depth of 22 or 23 centi- 

 metres is from 3,000,000 to 3,500,000 rott per feddan, 

 thus 6 J tons are equivalent to a little over 1 millimetre 

 in depth. It would thus require 10 years to add a depth 

 of 1 centimetre to the soil. As regards the composition 

 of the deposit, as already mentioned, great differences are 

 observable in the analyses at our disposal. The most 

 reliable are probably those which have been made at the 

 School of Agriculture, Ghizeh, and in which the composi- 

 tion of the suspended matter during flood is stated to be. 

 as follows : 



Insoluble matter and silica ... 57*54 per cent. 



Potash -53 



Soda .. '")! 



