Soil-Carriers 



35 



rocks, scooping out for itself a wide, deep bed. The solid 

 mass of rock thus removed, grain by grain, has also con- 

 tributed 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 contain 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, con- 

 tains 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 are 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 sea. Fresh water being hghter 

 than salt, flows over the latter at first, before the two 

 mingle; and as sea water abounds in these minute forms 

 of life to a much greater extent than river water does, and 

 as fresh water is as deadly to the one as salt to the other, 

 the destruction wherever the two come in contact must be 

 wholesale. 



But where rivers are affected by the tide, there the salt 

 water flows up under the fresh, for many a mile above 

 their mouths, carrying with it a living freight, which must, 

 to a large extent, perish and be left behind; while the 

 microscopic inhabitants of the river water are destroyed 

 with equal certainty wherever they come in contact with 

 that which is salt, or even brackish; that is, partially salt. 



The whole of southern Louisiana, with its extensive 

 cotton and rice fields, was made in hke manner by the 



