There is no salt in fresh rain-water. River water tastes fresh, sea water salty. Yet the oceans are fed by the rivers that flow into them. Then where does the salt in the sea come from?
When rain falls on the ground it soaks into the earth. In the earth are all sorts of minerals—salt, lime, magnesia, potash, sulphur, iron and many others. These are dissolved or melted and carried along by the water. Of all the minerals in the earth salt is most easily dissolved by water. So very often, we have salt springs. Rivers are fed by springs, and all of the minerals are in river water, but not enough so you can taste them. All the time this salt and other minerals are poured into the ocean by the rivers. When the sun takes vapor up into the rain clouds it takes only the water, leaving the minerals behind, just as lime is left in a teakettle. In this way the minerals in the sea, salt and everything else, slowly becomes greater in quantity as the centuries go by. About three and a half per cent of sea water is minerals, today. That is, if you put one hundred quarts of sea water in a tank and boil until the water is all boiled away, you will have three and a half quarts of dry salt, magnesia, lime, potash and other minerals. The greater part would be salt.
What would you think, then,, of water in which there are from fifteen to twenty quarts of salt and other minerals in every hundred quarts of water? The water of our Great Salt Lake and of the Dead Sea is four or five times as salt as the ocean. Like the ocean, they have no outlets in rivers. So they keep all the minerals that come into them. After ages and ages they will lose all their water, dry up and leave great salt beds behind. Do you think that could ever happen to the big oceans?
Source: http://chestofbooks.com/reference/The-New-Student-s-Reference-Work-Vol5/Why-Is-The-Water-Of-The-Ocean-Salt.html#.ViIKU_krLIU#ixzz3ooTIG3AH
