The above figures are based upon determinations of carbonic 

 acid and hence include all carbonates present in the soil. 



In order to obtain some knowledge as to the condition in which 

 the carbonate was present in the soil, the several fractions separated 

 in the course of the mechanical analysis were examined. All the 

 similar fractions obtained from each of six E-W rows of bores were 

 mixed, each row separately. The carbonate was determined in each 

 fraction, the results are shown in Table II. 



TABLE II. 



The above figures refer to mixtures of all samples taken on the 

 E-W lines indicated, A being the most northerly (see Map). The 

 large amount of carbonate in the coarse sand of the lines M and P 

 is noteworthy. This deposit is probably the most ancient, but there is 

 no evidence that there is any relation between the age of a deposit 

 and the amount of carbonate. Moreover, on the average there is 

 less carbonate in the deep than in the surface samples (see Table I). 

 Much of this land is flooded yearly after the Nile flood, and only 

 becomes dry in early summer. Whether there is any great accumu- 

 lation of shells (of fresh water molluscs) during this inundation 

 I am not aware, but it is quite possible that something of this nature 

 might afford an explanation. Nile water contains a small amount 

 of carbonate of lime in solution, and it is probable that molluscs, 

 directly or indirectly, obtain the material for their shells from this 

 source. This would explain the greater amount of carbonate in the 

 southern portion which has been subjected to this annual flooding for 

 a long period. 



Nearly the whole of this area lies between the contours of 0-5 

 M and 1-0 M. There are a few small patches below the former and 

 some higher than the latter, but their total area only represents a 

 small proportion of the whole. 



A summary of the results of the mechanical analysis is given 

 in Table III. 



