Soil-Carriers 43 



equal no doubt to the old one in richness, and capable 

 of bearing crops as abundant, should it ever rise above 

 the waters. A delta is possible only where there is 

 little or no tide, or current, to carry the sediment 

 away. 



But it must not be forgotton that something more 

 has been done than merely to transport this wonderful 

 soil. It has also undergone much mixing, and con- 

 sists not only of mud washed from the Abyssinian 

 mountains but of sand, which is blown into the river 

 in vast clouds from the desert. The Nile itself, too, 

 has done a great deal of grinding, and sand- and mud- 

 making, as well as its tributaries. Sand, driven by 

 water, will wear away the hardest rock by degrees ; 

 and by means of the sand which the wind blows into 

 it, the river has cut its way through the rocks, scoop- 

 ing out for itself a wide deep bed. The solid mass of 

 rock thus removed, grain by grain, has also contributed 

 in no small degree towards the formation of the Great 

 Delta. 



But even this is not all. No soil can be really 

 fertile, however rich in mineral matter, unless it con- 

 tain some amount of animal or vegetable matter. 

 And this, too, has been supplied to the Delta in an 

 interesting and remarkable way. 



Nile-water, like that of all rivers more or less, 

 contains a vast number of microscopic animals and 

 vegetables, the lowest and simplest forms of life, which 

 are not only left behind with the mud, but arc killed 

 in myriads where they come in contact with salt water. 

 The Mediterranean being a tideless sea, this wholesale 

 destruction cannot take place except at the mouth of 

 the river, and for a certain distance beyond it in the 



