V. 



SOIL-BINDERS 



The materials being ground up, mixed, and in some 

 cases transported, there are still two important matters 

 to be attended to before anything strictly to be called 

 ' soil ' can be formed. 



First, these materials have to be bound to the 

 spot where they have been deposited ; and, secondly, 

 before they can grow any but poor crops they in 

 many cases need the addition of animal or vegetable 

 matter. 



Nile-mud, and river-mud in general, already con- 

 tains some proportion of this, and does not consist of 

 mineral matter only. 



But the first thing is to make the future soil 

 settle down, since nothing of value can grow in a 

 wandering sand-drift. The deposits, whatever they 

 be, need protection against the washing of the rain 

 and the drying of the wind, which will not only dry 

 the surface, but blow it away in clouds if it is left 

 exposed. 



Even to this day the plains of Hungary suffer from 

 dust-storms, though they have long been covered with 

 vegetation ; and we may easily imagine how much 



