God Arises
The Challenge of The Qur’an
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and flow of the sea, have large quantities of salt-
water gush upstream at high tide but, again the
waters do not mix. The salt water forms an upper
layer, the fresh water remaining below it. At ebb
tide, the salt water recedes, leaving the fresh water,
as it was before.
Man had observed such natural phenomena from
ancient times, but he did not know the laws of
nature which governed them. It has recently been
discovered by modern research that the way liquids
flow is governed by a difference in salinity and thus
density because saline water is denser than fresh
water; when two water bodies converge, the more
saline of the two flows beneath the less saline. Thus,
a river flowing into the sea flows on the surface,
sometimes for great distances; the Mississippi, for
example, appears as a brown, fresh-water stream in
the blue waters of the Gulf of Mexico. Salinity
variations in the oceans and seas are partially
responsible for large-scale seawater circulation.
A well-known example is the flow to the
Mediterranean Sea, which is separated from the
North Atlantic by a sill, 320 metres (1,050 feet) deep,
