368 THE FERTILITY OF SOILS IN THE TROPICS 



land is about 0^3 per cent., of medium land about 0*5 per 

 cent., and of poor land about 0*8 per cent. The barren 

 land may contain any amount of salt up to 25 per cent. 

 The Biala Colony of 500 feddans contained before wash- 

 ing an average of 10 per cent, of salt. 



In the more northern parts of the Delta all the samples 

 were also examined for sodium carbonate and bicarbonate 

 which in certain areas are present in considerable quan- 

 tities. The sodium carbonate is of great importance as 

 its presence adds very greatly to the cost of land re- 

 clamation, a small quantity rendering the land impervious 

 to water. A detailed survey of certain carbonate areas 

 of Government land was made with a view to watching 

 the effect of treatment with gypsum. 



The field-sheets when they come in are reduced to the 

 scale of i : 50,000 to obtain a more convenient map for 

 ready reference. The original sheets will, of course, be 

 stored and will be available in years to come for com- 

 parison with the improved condition of the land which 

 it is hoped will be the outcome of the drainage works. 



A reference to the fertility map of the Central Delta 1 

 shows the gradual transition from good land in the 

 south, through medium land to bad land, with large areas 

 of barren land in the north, and it will t>e seen what a 

 large amount of improvement has to be effected before 

 the whole area becomes good or medium land. It is 

 also interesting to note the close dependence of the fer- 

 tility on the altitude above sea-level, or, in other words, 

 on the natural drainage. 



The contoured map 1 on the same scale as the fertility 

 map shows that the general division between good and 

 medium land follows roughly the 6-metre contour, whilst 

 the division between bad and barren lies somewhere near 

 the 5-metre contour. This is true in general and also 

 in particular. The area of the good land to the north 

 of Belqas is an example. Reference to the contoured 

 map shows that there is here a hog's back with an 

 altitude of less than one metre with the Bahr Belqas 



1 Not reproduced. 



