Week 15

You all know the history of the Nile; how, when the rains fall
very heavily in March and April in the mountains of Abyssinia,
the river comes rushing down and brings with it a load of mud
which it spreads out over the Nile valley in Egypt. This annual
layer of mud is so thin that it takes a thousand years for it to
become 2 or 3 feet thick; but besides that which falls in the
valley a great deal is taken to the mouth of the river and there
forms new land, making what is called the "Delta" of the Nile.
Alexandria, Rosetta, and Damietta, are towns which are all built
on land made of Nile mud which was carried down ages and ages ago,
and which has now become firm and hard like the rest of the
country. You will easily remember other deltas mentioned in books,
and all these are made of the mud carried down from the land to
the sea. The delta of the Ganges and Brahmapootra in India, is
actually as large as the whole of England and Wales, (58,311
square miles.) and the River Mississippi in America drains such a
large tract of country that its delta grows, Mr. Geikie tells us,
at the rate of 86 yards in year.

All this new land laid down in Egypt, in India, in America, and
in other places, is the work of water. Even on the Thames you
may see mud-banks, as at Gravesend, which are made of earth
brought from the interior of England. But at the mouth of the
Thames the sea washes up very strongly every tide, and so it
carries most of the mud away and prevents a delta growing up
there. If you will look about when you are at the seaside, and
notice wherever a stream flows down into the sea, you may even