THE SOIL. 23 



weathering agents are continually breaking off little par- 

 ticles from the hard rocks. Many of these lie where they 

 were dislodged and form the soil of the district : the rest 

 of these particles are washed by the rain into the river?, 

 and coming down the Nile in a state of suspension, are 

 ultimately deposited on the land and give a new supply 

 of soil. The quantity of matter carried in suspension 

 depends upon the velocity of the current and the size of 

 the individual particles. When the flood water is allowed 

 into the basins of Upper Egypt, the current practically 

 ceases, and the suspended particles are deposited on the 

 surface of the land. The clear water is run off and the 

 soil is left with a layer of new soil or Nile mud on its 

 surface. The coarser particles, largely sand, are first 

 deposited, whilst the fine clay is carried to the greatest 

 distance from the inlet of the basin and is deposited more 

 slowly. Hence we find that the soil near to the place of 

 entry of flood water into the basin is usually "lighter" 

 in character, and forms the "Erd Asfar"; whereas the soil 

 formed by the deposition of the fine clay gives us the 

 "heavy" "Erd Iswud." The same process goes on where 

 the land is under perennial irrigation, but much more 

 slowly, as the water contains less matter in suspension and 

 is not applied in such quantity. In addition to decomposed 

 rock material, the Nile brings down with it a supply of 

 organic matter derived from the dead bodies of animals 

 and plants which have lived in or near the river. 



Although practically all the land of the Nile valley has 

 been deposited by the river, yet the soil is not entirely 

 uniform in character. As already explained this arises 



