IV. 



SOIL-CARRIERS 



WE have now seen by what means the rocks are 

 crumbled down ; but in many cases much besides 

 crumbling is necessary to convert rock into good soil. 

 On a bleak hill-top the crumbled materials will be of 

 little use owing to the climate, though they may be 

 most valuable when brought down to the lowlands. 

 But, more than this, nearly all the soils which we look 

 upon as especially fertile have been made so by being 

 mixed. We have now to see how this mixing has been 

 effected, and how the crumbled matter of the rocks has 

 been transferred from one place to another. 



When we consider which are the best corn-producing 

 regions of the earth, our thoughts naturally turn first to 

 Egypt, once the granary of the world. 



And what is Egypt ? ' The gift of the Nile,' as the 

 ancient historian says. The soil which produces such 

 wonderful crops has not been produced by the decay 

 of the rocks upon which it rests, but is a mixture of 

 soils brought in great part from the lofty mountains of 

 Abyssinia, hundreds of miles away. The only fertile 

 tracts in Abyssinia itself are due to the sediment 

 washed down from these mountains, which are rich in 

 the minerals most desired by plants, but, like the 



