The process by which a delta, extending eighty or one hundred miles from the sea, has been formed may be seen going on at the present day--the coarser particles of sand are driven out into the ocean, just in the same way as we 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.
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