Chap. XXVIII. ISLANDS IN THE ZAMBESI. 577 



going on at the present day — the coarser particles of sand are 

 driven out into the ocean, just in the same way as Ave see they 

 are over banks in the beds of torrents. The finer portions are 

 caught by the returning tide, and, accumulating by successive 

 ebbs and flows, become, with the decaying vegetation, arrested 

 by the mangrove roots. The influence of the tide in bringing 

 back the finer particles gives the sea near the mouth of the 

 Zambesi a clean and sandy bottom. This process has been 

 going on for ages, and, as the delta has enlarged eastwards, the 

 river has always kept a channel for itself behind. Wherever 

 we see an island all sand, or with only one layer of mud in it, 

 we know it is one of recent formation, and that it may be swept 

 away at any time by a flood ; while those islands which are 

 all of mud are the more ancient, having in fact existed ever since 

 the time when the ebbing and flowing tides originally formed 

 them as parts of the delta. This mud resists the action of 

 the river wonderfully. It is a kind of clay on which the 

 eroding power of water has little effect. Were maps made, 

 showing which banks and which islands are liable to erosion, 

 it would go far to settle where the annual change of the 

 channel would take place ; and, were a few stakes driven 

 in year by year to guide the water in its course, the river 

 might be made of considerable commercial value in the 

 hands of any energetic European nation. No • canal or 

 railway would ever be thought of for this part of Africa. 

 A few improvements would make the Zambesi a ready means 

 of transit for all the trade that, with a population thinned by 

 Portuguese slaving, will ever be developed in our day. Here 

 there is no instance on record of the natives flocking in 

 thousands to the colony, as they did at Natal, and even to the 

 Arabs on Lake Nyassa. This keeping aloof renders it un- 

 likely that in Portuguese hands the Zambesi will ever be 

 of any more value to the world than it has been. 



2 p 



